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The Q 20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 1 THE Q 20 CONCEPT: SUSTAINABLE WELL YIELD AND SUSTAINABLE AQUIFER YIELD H. Maathuis 1 , G. van der Kamp 2 1 Saskatchewan Research Council, Saskatoon Environment and Forestry Division 2 National Water Research Institute, Saskatoon Prepared for: Alberta Environment Saskatchewan Watershed Authority Prairie Farm Rehabilitation Administration Prairie Provinces Water Board SRC Publication No. 10417-4E06 July 2006

THE Q CONCEPT: SUSTAINABLE WELL YIELD AND SUSTAINABLE ... Q20 Concept... · The Q 20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield i EXECUTIVE SUMMARY The Q20 concept

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Page 1: THE Q CONCEPT: SUSTAINABLE WELL YIELD AND SUSTAINABLE ... Q20 Concept... · The Q 20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield i EXECUTIVE SUMMARY The Q20 concept

The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 1

THE Q20 CONCEPT: SUSTAINABLE WELL YIELD

AND SUSTAINABLE AQUIFER YIELD

H. Maathuis1, G. van der Kamp2

1Saskatchewan Research Council, Saskatoon Environment and Forestry Division

2National Water Research Institute, Saskatoon

Prepared for: Alberta Environment

Saskatchewan Watershed Authority Prairie Farm Rehabilitation Administration

Prairie Provinces Water Board

SRC Publication No. 10417-4E06

July 2006

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THE Q20 CONCEPT: SUSTAINABLE WELL YIELD

AND SUSTAINABLE AQUIFER YIELD

By H. Maathuis1, G. van der Kamp2

1 Saskatchewan Research Council, Saskatoon Environment and Forestry Division

2 National Water Research Institute, Saskatoon

Prepared for: Alberta Environment

Saskatchewan Watershed Authority Prairie Farm Rehabilitation Administration

Prairie Provinces Water Board

SRC Publication No. 104717-4E06

July 2006

Saskatchewan Research Council 125 – 15 Innovation Blvd. Saskatoon, SK S7N 2X8

Tel: 306-933-5400 Fax: 306-933-7299

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield i

EXECUTIVE SUMMARY

The Q20 concept for estimating the maximum long-term yield of a well was introduced by Farvolden in 1959 in Alberta. It is based on estimates of water level drawdown in the pumping well after 20 years of pumping. The application of this method for groundwater permitting is limited to Alberta. This report examines the origin and validity of the Q20 concept. The Farvolden Q20 concept has proved useful over the years by providing an objective and quantitative estimate of maximum well yield. However, the method is based on a simplistic theoretical aquifer model, that of a fully confined infinite aquifer, and therefore it may result in faulty estimates of long-term well yield, particularly for buried valley aquifers. More sophisticated aquifer models are now available which can provide better estimates of long-term well yields and of interference between wells. It is recommended that the use of the Farvolden Q20 method be discontinued and instead that a modified Moell equation based on applying the appropriate aquifer model be used. Such a change would not imply a radical departure from the existing procedures, but merely involves use of more flexible and reliable methods for predicting the drawdown in the pumping well after 20 years of pumping In analogy to the Q20 concept, this report introduces the R20 concept. R20 is defined as the distance from the pumping well where the drawdown after 20 years of pumping equals a pre-set drawdown limit SR20. It is recommended that R20 be based on the annual average pumping rate and not on the maximum daily rate and the estimate of R20 should use the same aquifer model as the one used for estimating Q20. R20 provides an estimate of the distance over which significant well interference or impacts on surface water may occur after 20 years of pumping. It is this R20 that should be used in determining to which distance a field survey of wells and surface water should be conducted, and to decide whether or not an aquifer management plan may need to be developed.

As pressures on groundwater resources are increasing throughout the Prairie Provinces, the issue of sustainable yield of an aquifer or aquifer system is becoming more important. A review of the concept of sustainable yield is also included in this report.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield ii

TABLE OF CONTENTS LIST OF TABLES......................................................................................................................... iv LIST OF FIGURES ........................................................................................................................ v LIST OF APPENDICES................................................................................................................ vi LIST OF SYMBOLS .................................................................................................................... vii ACKNOWLEDGEMENTS.........................................................................................................viii

1.0 INTRODUCTION .............................................................................................................. 1

2.0 HYDROGEOLOGICAL SETTING OF THE PRAIRIES ................................................. 3

3.0 DEFINITIONS.................................................................................................................... 4

3.1 Aquifer and Aquitard .............................................................................................. 4 3.2 Unconfined and Semi-confined Aquifer................................................................. 4 3.3 Recharge, Replenishment and Discharge ............................................................... 4

4.0 PROCESS AND REQUIREMENTS OF ALLOCATING GROUNDWATER WITHDRAWALS .............................................................................................................. 5

4.1 INTRODUCTION .................................................................................................. 5 4.2 Alberta..................................................................................................................... 6 4.3 Saskatchewan.......................................................................................................... 8 4.4 Manitoba ................................................................................................................. 9 4.5 British Columbia..................................................................................................... 9 4.6 Nova Scotia........................................................................................................... 10 4.7 Ontario .................................................................................................................. 11 4.8 North Dakota......................................................................................................... 12 4.9 Discussion............................................................................................................. 13

5.0 THE Q20 METHOD .......................................................................................................... 15

5.1 Introduction........................................................................................................... 15 5.2 Development of the Theis equation for drawdown due to pumping from a

confined aquifer .................................................................................................... 15 5.3 History of the Q20 Method .................................................................................... 17

5.3.1 Farvolden Q20............................................................................................ 17 5.3.2 Apparent Q20 ............................................................................................. 19 5.3.3 History of Moell Method .......................................................................... 20 5.3.4 Bibby’s Approach ..................................................................................... 20

5.4 Q20 versus Q200, Q10 and Q5 ................................................................................. 21

6.0 PROPOSED MODIFICATION OF THE Q20 METHOD ................................................ 22

6.1 Comparison of Q20 versus Analytical Aquifer Models......................................... 22

7.0 R20 CONCEPT.................................................................................................................. 24

7.1 Introduction of R20 Concept.................................................................................. 24 7.2 Comparison of Farvolden Q20, Theoretical Q20 and R20 ....................................... 25 7.3 Well interference and criteria for going to aquifer management plan .................. 28

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield iii

8.0 CASE HISTORIES........................................................................................................... 30

8.1 Introduction........................................................................................................... 30 8.2 Alberta................................................................................................................... 30

8.2.1 Grande Prairie ........................................................................................... 30 8.2.2 Town of Sexsmith ..................................................................................... 31 8.2.3 Innisfail and Olds, Alberta........................................................................ 31 8.2.4 Grand Rapids (Lower Mannville Formation) Aquifer.............................. 32 8.2.5 Calgary Valley Aquifer............................................................................. 33 8.2.6 Multiple Wells in a Subdivision ............................................................... 34

8.3 Saskatchewan........................................................................................................ 34 8.3.1 Estevan Valley Aquifer............................................................................. 34

8.3.1.1 Introduction 34 8.3.1.2 Pumping Tests .........................................................................................35 8.3.1.3 Sustainable Pumping Yield of the Estevan Valley Aquifer System....36 8.3.1.4 Discussion .............................................................................................37

8.3.2 Senlac Area, Saskatchewan ...................................................................... 38

9.0 SUSTAINABLE YIELDS OF AQUIFERS ..................................................................... 41

9.1 Introduction........................................................................................................... 41 9.2 History of Terminology ........................................................................................ 41 9.3 Sustainable Pumping Rate .................................................................................... 42 9.4 Watershed-based Water Resource Management .................................................. 44 9.5 Aquifer Management Plans................................................................................... 45

10.0 CONCLUSIONS AND RECOMMENDATIONS ........................................................... 47

11.0 REFERENCES ................................................................................................................. 49

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield iv

LIST OF TABLES Table 1 Groundwater licenses and annual groundwater allocations in the Prairie Provinces ....5 Table 2 Length of pumping test and information required for the anticipated maximum

water diversion/drainage (Alberta Environment, 2003) ................................................7 Table 3 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (case 1: = 10-5 m/day) .....................................................26 Table 4 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (case 2: = 10-4 m/day) .....................................................26 Table 5 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (case 3: = 10-3 m/day) .....................................................27 Table 6 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (T =100 and 500 m2/day) ................................................27 Table 7 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (T =10 and 5 m2/day) ......................................................27 Table 8 “Regional” transmissivities and resulting Q20 for 1984 Estevan Valley aquifer

pumping test data, for assumed durations of the pumping test....................................36 Table 9 Estimated sustainable pumping rate of the Estevan Valley aquifer.............................36 Table 10 Farvolden Q20 for Senlac production wells, based on top of Judith River Formation.38 Table 11 Farvolden Q20 for Senlac production wells, based on depth to top of screen..............39 Table 12 Comparison of allocated, actual, Farvolden Q20 and estimated pumping rates for the

Senlac production wells ...............................................................................................39

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield v

LIST OF FIGURES Figure 1 Schematic illustration of the classification of aquifers in the Prairie Provinces................................................................................................. in back Figure 2 Simplified maps of freshwater yielding bedrock aquifers in the Prairie Provinces................................................................................................. in back Figure 3 Thickness of drift in the Prairie Provinces ......................................................... in back Figure 4 Location of major buried valley aquifers in the Prairie Provinces..................... in back Figure 5 Locations of groundwater allocations in the Prairie Provinces .......................... in back Figure 6 Schematic illustration of Farvolden’s apparent transmissivity concept ............. in back Figure 7 Definition of local and regional transmissivity .................................................. in back Figure 8 Comparison of Q20 versus Q10, Q5 and Q200 ....................................................... in back Figure 9 Estevan Valley aquifer system in southeastern Saskatchewan .......................... in back Figure 10 Location of production well and observation wells 1965 Estevan Valley aquifer pump test ............................................................................................... in back Figure 11 Results of the March 4 – 12, 1965 Estevan Valley aquifer pumping test .......... in back Figure 12 Semi-log plot of drawdown versus time for the 1965 Estevan Valley aquifer

pumping test ....................................................................................................... in back Figure 13 Semi-log plot of drawdown versus time for production well and selected monitor wells, 1984 Estevan Valley aquifer pumping test ................................ in back Figure 14 Location of production and monitor wells in the Senlac area ............................ in back Figure 15 Cross section through the Senlac area................................................................ in back Figure 16 Hydrographs for observation wells Senlac area and monthly volumes pumped from production wells........................................................................... in back Figure 17 Drawdown in observation wells in the Senlac area and monthly total withdrawals………………………………………………………………….....in back Figure 18 Semi-log plot of drawdowns observed in Senlac observation wells OW-5 and OW-6, average drawdown in the production wells and modelled drawdown in OW6……………..…………………………………………………………..in back

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield vi

LIST OF APPENDICES Appendix A Saskatchewan – Groundwater Allocation Process and Guidelines for Groundwater Investigation Report............................................................................................ A-1 Appendix B Review of Pumping Test Analyses ......................................................................B-1 Appendix C Farvolden (1959) - Groundwater Supply in Alberta............................................C-1

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LIST OF SYMBOLS a Annum = year

'vK Vertical hydraulic conductivity of aquitard (m/day)

D Thickness of aquifer (m) T = KD Transmissivity of aquifer (m2/day) TW = TW Cross-sectional transmissivity of a buried valley/strip aquifer (m3/day) W Width of buried valley/strip aquifer (m) Ta Apparent transmissivity (m2/day) b’, b’’ thickness overlying and underlying aquitard (m) Qt Pumping rate of pumping test (m3/day) Q20 20-year safe well yield (m3/day) Q20a Apparent 20-year safe well yield (m3/day) Qr Requested pumping rate t Time since pumping started (days) L = (Tc)½ Leakage length (m)

c = ( '

'

bKv ) Vertical hydraulic resistance (days)

S Storativity of aquifer (dimensionless) Sy Specific yield of an unconfined aquifer (dimensionless) Sw =SW Cross-sectional storativity of buried valley/ strip aquifer (m) S’, S” Storativity of overlying and underlying aquitards (dimensionless) Ss Specific storage coefficient (m-1) Sf Safety factor (dimensionless) stime Drawdown (m) at a particular time, as indicated in text ∆sp Drawdown per unit log cycle R20 Distance from pumping well where drawdown after 20 years of pumping equals

SR20 (km) SR20 Pre-set amount of drawdown (m) HA Available drawdown (m) rw Radius well screen (m) rc Radius of well casing (m) dam3 Cubic decameters (1 dam3 = 1,000 m3)

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield viii

ACKNOWLEDGEMENTS The project has been prepared for and was funded by: Alberta Environment (AE), Saskatchewan Watershed Authority (SWA), the Prairie Farm Rehabilitation Administration (PFRA), Prairie Provinces Water Board (PPWB) and the Saskatchewan Research Council (SRC). The preparation of this report greatly benefited from the input and comments by: Nga de la Cruz, and Robert George, Alberta Environment; Nolan Shaheen and Cas Rogal, Saskatchewan Watershed Authority; John Drage, Nova Scotia Environment and Labour; Rob Matthews and Bob Betcher, Manitoba Water Stewardship; Dr. Alfonso Rivera, Chief Hydrogeologist, Geological Survey of Canada; Dr. Diana Allen, Department of Earth Sciences, Simon Fraser University; Mike Wei, Water Stewardship Division, Ministry of Environment, British Columbia and Mr. Ken Hugo, Sabatini Earth Technologies Inc., Calgary; Dr. David Rudolph, Department of Earth Sciences, University of Waterloo.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 1

1.0 INTRODUCTION Water is essential to life and basic to quality of life, economy, culture and ecosystems. Both surface water and groundwater are a renewable resource but are not unlimited. Surface water occurrences in the Plains of northern North America (Alberta, Saskatchewan, Manitoba, Montana, and North Dakota) are limited. Surface water supplies are susceptible to climatic variability, subject to water quality issues and, to a variable but often significant degree, have been allocated. In contrast, groundwater occurs virtually everywhere beneath the ground surface. Consequently, groundwater historically has played, and continues to play, an important role as a source of water for domestic, municipal, agricultural and industrial use. However, groundwater resources are limited due to the geological setting and climatic conditions. Recharge to surficial and shallow aquifers is limited due to the semi-arid climate. Replenishment to the deeper aquifers is limited because of the low vertical hydraulic conductivity of the till and bedrock aquitards that lie above them. The Constitution Act indirectly designates the Provinces as the owner of both groundwater and surface waters and having the responsibility for the development, management and protection of these resources. In western Canada, the first legislation dealing with surface water allocation and licensing was in 1894 under the Northwest Irrigation Act, which was administrated by the federal government. Administration of surface water was transferred to the provinces in 1931. In the early 1960s, Saskatchewan amended the existing Water Resources Acts and included a requirement for a permit for withdrawal of groundwater for non-domestic uses. In 1971, the Alberta Water Resources Act was amended specifically to include the diversion and use of groundwater. In Manitoba, groundwater licensing was introduced in 1972. The first part of this report (section 4) examines the processes and requirements used in the Prairie Provinces, and selected other jurisdictions, for allocating groundwater withdrawal permits. In Alberta, the Q20 method has been used to evaluate safe well yields. The origin, assumptions and applicability of the Q20 method, and variations on this method, are discussed in section 5. This report proposes a new approach to calculating a Q20 which is based on the hydrogeology of the aquifer, assumed or determined hydraulic properties and the selection of the appropriate aquifer model (section 6). A basic requirement in applications for a permit for groundwater withdrawals is to conduct a field survey of wells within a specific radius of the proposed well. In analogy to Q20, the R20 concept is introduced (section 7). The R20 provides an indication of the distance from a proposed well to which such a well inventory should extend. The R20 is the distance from the pumping well where the drawdown after 20 years at the average annual rate of withdrawal equals a pre-set drawdown. A number of cases histories are discussed in section 8. Considering that water resources are not unlimited, the increasing demands for reliable supply of clean water and the conflicting demands for the limited water resources, governments all over the world have moved towards watershed based integrated surface water – groundwater resource management. In recent years, Saskatchewan issued its “Water Management Framework”

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 2

(Saskatchewan, 1999), Alberta its “Water for life. Alberta’s strategy for sustainability” (Alberta, 2003), and Manitoba “The Manitoba Water Strategy” (Manitoba, 2003). The cumulative impact of groundwater withdrawals can result in a major impact on aquifer systems as a whole, may impact surface waters, and therefore raises the issue of sustainability. Issues related to the sustainability of groundwater resources are briefly discussed in section 9.

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2.0 HYDROGEOLOGICAL SETTING OF THE PRAIRIES The focus of this report is on potable groundwater resources of the Prairie region, roughly the area of the Western Canada Sedimentary Basin in the Prairie Provinces. The groundwater resources in the Canadian Shield area and the Rocky Mountain area are not considered, although the methods that are described may be applicable there as well. The term “non-saline” groundwater refers to water with a TDS (or sum of ions) less than 4,000 mg/L. From a hydrostratigraphic point of view, two main types of aquifers and aquitards can be distinguished: bedrock and Quaternary or “drift” aquifers/aquitards. Furthermore, aquifers can be unconfined or semi-confined. The term bedrock applies to all sediments below the bottom of the Quaternary sequence. Drift is defined as the deposits between the top of bedrock and the present ground surface. A schematic illustration of the various types of aquifers in the Prairie Provinces is shown in Figure 1. It is beyond the scope of this report to provide a detailed description of the geological and hydrogeological setting of the Prairies. Generalized descriptions of the hydrogeological settings can be found in Lennox et al. (1988), Pupp et al. (1989; 1991), Betcher et al. (1995) and Maathuis and Thorleifson (2000). More detailed information can be obtained from the provincial agencies in charge of mapping groundwater resources. Figure 2 shows a simplified map of freshwater yielding bedrock aquifers. These aquifers occur at varying depths, and range from outcropping at the ground surface to being buried by up to hundreds of meters of bedrock and Quaternary sediments. Bedrock aquitards are formed by bedrock silts and clays. The thickness of drift in the Prairies ranges from zero meters in unglaciated areas (e.g. Cypress Hill area in southwestern Saskatchewan and in southeastern Alberta), to over 300 m (Figure 3). Quaternary aquifers can be classified into; (preglacial) buried valley, intertill and surficial aquifers. The preglacial buried valley aquifers (Figure 4) are long, narrow features which form an important groundwater supply source. However, the longitudinal extent of these aquifers is interrupted by barriers. It is noted that aquifers of the buried valley type are not limited to the (preglacial) buried valleys but can also occur within bedrock formations and within glacial deposits. Aquifers within the drift are formed by pro- and post-glacial stratified deposits. Drift aquitards are formed by tills and silts and clays within stratified units, and surficial silts and clays. Within the Prairies, only in Saskatchewan have Quaternary aquifers and aquitards been mapped systematically at a regional scale.

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3.0 DEFINITIONS 3.1 Aquifer and Aquitard An aquifer is a saturated geologic unit that is permeable enough to transmit significant quantities of water under ordinary hydraulic gradients, or as the term is commonly used in the water-well industry: an aquifer is a saturated geologic unit that is permeable enough to yield economic quantities of water to wells (e.g. Freeze and Cherry, 1979; Kruseman and de Ridder, 1990). Aquifers can be part of a geological formation, the entire formation or group of formations. An aquitard is a saturated geologic unit which is permeable enough to transmit water in significant quantities when viewed over large areas and long periods, but does not yield economic quantities of water to wells (Kruseman and de Ridder, 1990). 3.2 Unconfined and Semi-confined Aquifer An unconfined aquifer, or water-table aquifer, is an aquifer bounded at the bottom by an aquitard and at the top by the water table. A semi-confined, or leaky aquifer, is an aquifer bounded at the top and bottom by aquitards. Typically, semi-confined aquifers occur at depth, whereas unconfined aquifers are near the ground surface. However, near discharge areas semi-confined aquifer may become unconfined, i.e. the water table can occur within the permeable formation below the overlying aquitard. 3.3 Recharge, Replenishment and Discharge In this report the terms recharge and replenishment are introduced to avoid confusion between recharge to the groundwater system as represented by the water table and flow into semi-confined aquifers, which often is also referred to as recharge. The term recharge refers solely to water that originates directly from precipitation, or surface water bodies, infiltrates into the ground surface and moves downward to become part of the saturated groundwater system. Groundwater discharge is the amount or rate of water that leaves the groundwater system, either by flow to surface water, discharge onto the ground surface in the form of springs or seeps, or by (evapo)transpiration. The term replenishment, as used in this report refers to the amount or rate of flow into semi-confined aquifers, through under or overlying aquitards. Outflow from a semi-confined aquifer is the amount or rate of vertical flow out of a semi-confined aquifer, through underlying or overlying aquitards, or in some cases, by lateral flow into a surface water body. In the semi-arid Prairies, recharge to the water table and replenishment of shallow semi-confined aquifers is limited by the amount of precipitation. The low hydraulic conductivity of thick aquitards is the factor limiting replenishment of deep semi-confined aquifers (Maathuis and van der Kamp, 1986; van der Kamp and Maathuis, 1991).

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 5

4.0 PROCESS AND REQUIREMENTS OF ALLOCATING GROUNDWATER WITHDRAWALS

4.1 INTRODUCTION

Groundwater is important in the Prairie Provinces as a source of water supply. While in total volume groundwater use may be small compared to surface water use, groundwater plays a critical role, particularly in rural areas. The most current numbers of groundwater licenses and annual groundwater allocations in the Prairie Provinces are listed in Table 1. The locations are shown in Figure 5. Table 1 Groundwater licenses and annual groundwater allocations in the Prairie

Provinces

Province Number of licenses

Annual Allocation (dam3/a)4

Alberta 40,2101

2,6992

261,610

220,160

Saskatchewan3 3,087 153,660

Manitoba4 689 81,310 Source: 1. Alberta Environment, all allocations 2. Alberta Environment, allocations greater than 6,250m3/a 3. Saskatchewan Watershed Authority. 4. Manitoba Water Stewardship. Values rounded off to nearest 10 dam3/a (1 dam3 = 1,000 m3)

The volumes of allocated groundwater withdrawals are an estimate only of the actual volumes used. The databases for Saskatchewan show 833 wells, which are still in the application stage with no volumes allocated. The Manitoba database lists 154 wells for which allocations (volume 17,850 dam3) have expired. Many of these wells still may be in use. The Saskatchewan and Manitoba databases can not be directly compared with the Alberta database because the Alberta database also includes estimates of small-scale water use by traditional agriculture users for spraying crops and watering livestock (up to a maximum allocation of 6,250 m3/a). These allocations were recorded through an intensive 3-year registration program, which was conducted to protect the legal water use priority of traditional agricultural practices. When only considering wells with an allocation greater than 6,250 m3/a, the number of licensed wells is significantly lower. It must be noted that the volumes allocated commonly are much higher than the actual volumes withdrawn. Also, in a number of cases allocated volumes were for a Asingle@ pumping event and/or wells that are currently not used for production. In the following sections the process of allocating groundwater withdrawals in various jurisdictions is examined. A review of groundwater allocation law has also been conducted by Nowlan (2005).

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4.2 Alberta In Alberta, the Water Resources Act was amended in 1971 to include diversion and use of groundwater. In 1999, the Water Resources Act was replaced by the Water Act (http://www.qp.gov.ab.ca/Documents/acts/W03.CFM). Associated with the Water Act are the Water (Ministerial) Regulations (http://www.canlii.org/ab/laws/regu/1998r.205/20040623/whole.html). Since the inclusion of groundwater into the Water Resources Act significant effort has been made to license existing production wells. Old and new production wells have been licensed and assigned a priority number (date). The priority date follows the doctrine of “first-in time, first-in right”, which assigns available water to the most senior license holders first, in the event of a drought or other water shortage. The Water Act distinguishes between an approval, a license and a temporary diversion license, and also provides a statutory right for water diversion to supply household use (up to 1,250 m3/a, 3,425 L/day) and traditional agricultural use (up to 6,250 m3/a, 17,100 L/day). Household users and traditional agricultural users can divert water without obtaining prior authorization. A registration program was conducted to assign priority dates to traditional agricultural operations. The main types of authorization for groundwater diversions are listed below:

• An approval is needed for withdrawal of groundwater for dewatering for coal or bitumen mining, construction, and groundwater remediation (water not needed for any use). Approvals are also required for construction activities within waterbodies or permanent disturbances to waterbodies (i.e. stream bed alterations).

• A temporary diversion license is required for short-term diversion (up to one year) and is

not assigned a priority number.

• A groundwater withdrawal license is required for longer-term uses. Most agricultural, industrial, commercial and municipal water uses are granted licenses with 10 year to 25 year terms under the Water Act. Licenses are renewable at the term expiry, subject to specified review provisions in the Water Act.

• The diversion and use of groundwater can be exempt from licensing requirements under

specific circumstances, which are identified in schedule 3 of the Water (Ministerial) Regulation. Saline groundwater can be diverted for any purpose without a license under the Water Act.

In granting new allocations of water, a number of considerations are taken into account, such as; protecting the aquifer from over development, protecting water supplies of households and prior license holders, and protecting the environment. The applicant for a groundwater withdrawal license has to conduct a groundwater evaluation and submit the results in support of the application. Guidelines for conducting such an evaluation and the information that needs to be submitted have been detailed by Alberta Environment (2003). The information required is summarized below:

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(1) Description of geology and hydrogeology of the proposed site (2) Field-verified survey of existing wells within expected area of impact (minimum 1.6

km) (3) Conduct pumping/recovery test to determine aquifer properties, extent of aquifer and

sustainable yield. The minimum requirements for the length of the pumping and recovery test are a function of anticipated maximum pumping rate (see Table 2)

(4) Interpretation of pumping test data (5) Determination of theoretical long-term yield (Q20) of a proposed production well

using either the Farvolden or Moell method (6) Determine the impact of pumping on the aquifer, other users, surface water bodies

and the aquatic environment Table 2 Length of pumping test and information required for the anticipated

maximum water diversion/drainage (Alberta Environment, 2003)

Anticipated Daily Pumping Rate

Number of Days

Anticipated Maximum

Yearly Water Requirement

Length of Pumping & Recovery test at Anticipated

Maximum Pumping Rate

Observation/Monitoring

Site

up to 10 m3/d (2200 Igpd) (1.5 Igpm)

365 3650 m3 (803,000 Ig)

2 + 2 hours* (or longer) and at least 90%

recovery 0

10 to 35 m3/d (2200 to 7700 Igpd)

(1.5 to 5.3 Igpm) applicant to enter applicant to enter

24 + 24 hours (or longer) and at least 90%

recovery 0 – 1

35 to 65 m3/d (7700 to 14,300 Igpd)

(5.3 to 10.0 Igpm) applicant to enter applicant to enter

24 + 24 hours (or longer) and at least 90%

recovery 1

65 to 265 m3/d 14,300 to 60,500 Igpd)

(10.0 to 40.0 Igpm) applicant to enter applicant to enter

48 + 48 hours (or longer) and at least

90% recovery 1 – 2

greater than 265 m3/d applicant to enter applicant to enter 72 + 72 hours

(or longer) and at least 90% recovery

1 – 2

* In some cases, more information or longer pumping tests may be required. Legend: d = day, g = gallons, I = Imperial, m = minute, m3 = cubic metre = 220 Ig

It is noted that the guidelines allow the proponent to use the most appropriate method for analyzing the pumping test data, but the long-term yield must be estimated using the Q20 method which is based on the assumption that the aquifer is fully confined (see section 5). It is estimated by regional offices of Alberta Environment that 90% of the licenses are based on pumping test data for only the production well; for 10% of the licenses pumping test data may include one or more observation wells. Conditions attached to most large-scale groundwater licenses require annual reporting to Alberta Environment. Small-scale operations usually do not have any information collection or reporting requirements. Currently the available knowledge about location and volume of groundwater diversions is variable in quality and difficult to access or compile, because the data are collected and stored in various formats over several decades of record. Alberta Environment is currently

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 8

preparing digital reporting and database methods to provide better access to the groundwater data that are submitted by license holders.

4.3 Saskatchewan The Saskatchewan Ground Water Conservation Act and the Ground Water Regulations (http://www.publications.gov.sk.ca/details.cfm?p=544 ) state that a license to withdraw groundwater is required for all uses except for domestic purposes. Domestic purposes are defined as: “household and sanitary purposes, the watering of stock, the spraying of crops, the watering of noncommercial lawns and gardens adjoining private residences, but does not include the sale or barter of water for such purposes” (Regulations, Interpretation, section 2(c)). Although not specifically stated, and fitting within the definition of domestic, it is policy to consider 5,000 m3/a as the maximum for domestic use. For example, a livestock operation with more than 300 cattle or a landowner who has more than 300 head of cattle watered from a single well for an extended period of time would require a groundwater license. The first Water Rights License dates back to 1962. The process of approving the development of a groundwater sources has three (3) components;

(a) a permit to conduct a Groundwater Investigation (b) approval to Construct and Operate Works (c) a Water Rights License to use Groundwater

A Groundwater Investigation Report has to be submitted, which includes the information outlined in the Groundwater Approvals Fact Sheet (Saskatchewan Watershed Authority, 1999). The fact sheet is included in Appendix A. The summarized basic requirements are:

(1) Base map and minimum of two cross sections (2) Field verified inventory of all wells within expected area of influence (minimum

within radius of 3.2 km from proposed production well) (3) Minimum of two observation wells, completed in same aquifer as the production well (4) Minimum 24 hr pumping and 24 hr recovery test (5) An evaluation of pump/recovery test results, with estimates of well yield, aquifer

yield and basin yield (6) An evaluation of the impact of project on surrounding users.

The method(s) used to analyze the pumping test/recovery data, and to determine yields and potential impact are subject to the judgment of the hydrogeologist involved in the project. An approval to Construct and Operate Works and Water Right License might be issued with any terms and conditions considered appropriate by the Saskatchewan Watershed Authority. For example, taking mitigative measures, and requiring monitoring of withdrawals, water levels and water quality. Water Rights Licenses in Saskatchewan do not have an expiry date stipulated in the Act or Regulations. However, as part of the conditions, Water Rights Licenses for industrial withdrawals generally have an expiry term of 5 years to allow for a review of the water use and monitoring data (personal communication; Cas Rogal, 2005).

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 9

4.4 Manitoba The Manitoba Water Rights Act (1988) (http://web2.gov.mb.ca/laws/statutes/ccsm/w080e.php) establishes a priority of the purposes for withdrawing of groundwater:

1. domestic purposes (no license required, up to 25,000 liters per day) 2. municipal purposes (license required - no lower limit) 3. agricultural purposes (license required if more than 25,000 liters per day) 4. industrial purposes (license required – no lower limit) 5. irrigation purposes (license required if more than 25,000 liters per day) 6. other purposes (license required).

The process of developing a groundwater supply involves:

1. Submission of an application for a Groundwater Exploration Permit. 2. Permit issued with conditions including, a requirement that the proponent engages

the services of a consulting hydrogeologist registered with the APEGM. 3. Submission of a Groundwater Assessment Report by the proponent’s consultant. 4. Upon review of the report by Water Licensing staff, issuance of a Water Rights

License. Depending on the volume of water to be withdrawn and potential third party impact, the Groundwater Exploration Permit may require the proponent to conduct a pumping test (usually a minimum 24-hour test for a confined aquifer and up to a 72-hour test for water table aquifer), with one or more observation wells. Domestic wells may be included as an observation well if they are expected to be impacted by the proposed withdrawal. Staff of the Water Licensing Branch reviews reports submitted by consulting hydrogeologists to ensure the long-term sustainability of the proposed water taking. In addition, the potential for impacts on other groundwater users, surface water bodies and the natural environment are all taken into consideration before a license is issued. The Manitoba Water Rights Regulation 126/87 (http://www.canlii.org/mb/laws/regu/1987r.126/20040616/whole.html) states that the term of a license shall not exceed 20 years. Permits are no longer issued for several sub-basins of the Assiniboine Delta Aquifer, as these sub-basins are fully allocated. Similar situations exist for the Winkler Aquifer. The assessment that these basins are fully allocated is based on a conservative estimate. The regulations require that every holder of a license under the Act shall keep records of water use on a form approved by the Minister. These records have to be reported by February 1st of the following calendar year. In addition, the licensee may be required report water levels in either the pumping well or in a nearby observation well on a periodic basis. 4.5 British Columbia The Water Act (http://www.qp.gov.bc.ca/statreg/stat/W/96483_01.htm) in British Columbia Requires that a license be obtained to divert and use surface water, but does not require a license for groundwater withdrawals. The Act does, however, establish that the licensing requirement

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 10

can be made to apply (by regulation) to groundwater province-wide or in specific areas in the future. However, under the Water Utility Act (http://www.qp.gov.bc.ca/statreg/stat/W/96485_01.htm) and Utilities Commission Act (http://www.qp.gov.bc.ca/statreg/stat/U/96473_01.htm), private water utilities using groundwater as a water supply source require a certificate of Public Convenience and Necessity (CPCN). Guidelines for groundwater information required in support of a CPCN are outlined in Land and Water British Columbia Inc. (2004) and British Columbia Ministry of Environment, Lands and Parks (1999). The guidelines suggest conducting a step-drawdown test to determine an optimum pumping rate, followed by the longer-term pumping test. The long-term capacity of the well is based on extrapolating the drawdown at the end of the test to 100 days, and using the drawdown at 100 days to determine the long-term specific capacity of the well. Extrapolation to 100 days was selected as recharge is assumed to occur annually after 100 days. A safety factor of 30% is applied and factors such as well interference, surface water – groundwater interactions water quality and seawater encroachment may impact the long-term capacity. Most estimates of well capacity are made based on drawdown measured from the production well. In British Columbia there is no requirement to report groundwater withdrawals. The impact of groundwater withdrawals is monitored by British Columbia’s network of groundwater level observation wells. 4.6 Nova Scotia The Activities Designation Regulations (Division I) of the Environment Act of Nova Scotia requires that a water withdrawal approval is needed if a groundwater withdrawal exceeds 23,000 liters per day (http://www.gov.ns.ca/just/regulations/regs/env4795.htm). In allocating groundwater withdrawals, the following guidelines are used:

● Withdrawals from the aquifer must be sustainable (sustainable is defined as not causing unacceptable environmental, economic or social consequences)

● New groundwater withdrawals should not cause any significant adverse effects to existing groundwater users

● Groundwater allocations are based on a “first-come, first-served basis”, with priority given to drinking water applications

● Groundwater allocations are based on the applicant’s projected water needs within a 10 year period (note: under the Approvals Procedures Regulations, groundwater withdrawal approvals are valid for 10 years)

An application to withdraw groundwater requires the submission of a hydrogeological report prepared by, or under the direction of, a qualified hydrogeologist. The Nova Scotia Environment and Labour guide to groundwater withdrawal applications and hydrogeological study requirements can be found at http://www.gov.ns.ca/enla/water/withdrawalApproval.asp. The hydrogeological study requirements are summarized below:

(1) Site description (well field) description, intended water use, pumping rate, inventory of wells within a minimum radius of 500 m)

(2) Description of local and regional geology and hydrogeology (3) Pumping test information (typically a 72-hr pumping test is required and/or 95%

recovery)

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 11

(4) Evaluation of potential impacts (including assessment of sustainable yield, well interference, water quality, seawater intrusion and groundwater-surface water inter action)

(5) Development of monitoring and mitigation plans (at a minimum, a permit holder is required to monitor and record withdrawals)

The current (2004) guidelines do not indicate a specific method for analysis of the pumping test data; however, a detailed analysis/interpretation of the pumping test data is required. This analysis should include, but is not limited to: graphical analysis of the data, calculations for aquifer characteristics, such as transmissivity and storativity/specific yield, identification of boundary conditions, assessment of the potential drawdown at various times and selected distances from the pumping well, predicted drawdown in the pumping well compared to the amount of available head and to the pump intake depth. The rational for selecting a specific analytical method(s) along with assumptions and limitations, must be clearly stated. Groundwater withdrawal approvals have terms and conditions attached which may include, but are not limited to: a requirement for the approval holder to measure and record the daily water volume withdraws; and, a requirement for the approval holder to measure and record groundwater levels. Approval holders are required to provide these withdrawal and water level monitoring records to the Department upon request. In the past, the Q20 method has been used, in combination with other considerations, to calculate a long-term well yield (personal communication; John Drage). The fact that it was used in Nova Scotia was likely due to relocation of a staff member of Alberta Environment to Nova Scotia. 4.7 Ontario The Ontario Water Resources Act (http://www.canlii.org/on/laws/sta/o-40/20050627/whole.html, section 34) requires that a permit for groundwater withdrawals greater than 50,000 L/day except for domestic and traditional agricultural use, i.e. cattle watering (irrigation of market crops using groundwater requires a permit to take water). Municipal and non-municipal drinking-water systems using groundwater as raw water also require approvals under the Safe Drinking Water Act (http://www.e-laws.gov.on.ca/DBLaws/Statutes/English/02s32_e.htm, part V and VI). Permits are categorized as Category 1, 2 and 3 (MOE, 2005a,b). Category 1 typically applies to renewal of an existing permit. Provided no past interference/impacts, no scientific study is required as part of the renewal process. Category 2 pertains to short-term, non-recurring, withdrawals for less than 7 days (e.g. pumping tests) or less than 30 days and less than 400,000 L/day (e.g. construction related dewatering). Category 3 includes groundwater takings that do not meet Category 1 or category 2 criteria. General guidelines for the information to be submitted in support of a Category 2 and 3 application for a permit to take water have been outlined by the Ontario Ministry of the Environment (MOE, 2005a,b). Information to be submitted includes:

● Map showing the location of proposed well(s) and nearby wells and relevant surface water features

● Use and volume of groundwater

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 12

● A determination of the potential interference with existing groundwater users (including a statement of how it was determined)

● Results of a hydrogeological investigation. In addition to standard hydrogeological information, such a report must include a prediction of possible undesirable effects and, if significant concerns remain as a result of the prediction, plans to monitor and mitigate the impact and to implement water conservations measures where possible.

Established practice is that pumping tests conducted as part of hydrogeological investigations should be 24 hours minimum and for large takings up to 72 hours. Recovery should be monitored until at least 85% recovery has been achieved. All permits have a condition attached which requires the permit holder to measure and report daily water volume taken. Permits may also have additional conditions attached to it such as water level and water quality monitoring, continuous analysis and prediction of effects, supplementation of water supply to surface water bodies and wetlands, temporary provision or permanent replacement of affected well water supplies and reporting requirements. In reviewing an application the following is taken into account: potential for impacts on other groundwater users and protection of the natural function of ground-water dependant surface features such as streams and wetlands and associated ecosystems (Regulation 387/04, http://www.e-laws.gov.on.ca/DBLaws/Source/Regs/English/2004/R04387_e.htm). Concepts of “sustainability” are applied on a local basis where potential impacts on groundwater availability have been deemed significant. The areas of the province where significant pressures on availability develop are often the areas where the alternative of a piped surface water supply – i.e. from the Great Lakes – presents itself. While it is a policy rather than a regulation, the following priority of uses is applied if needed (Ministry of Environment and Energy, 1994, p. 13): “established” uses, whether established by prior Permit or, where a Permit is not required, by prior use; where additional issues arise, private domestic and farm purposes take precedence, followed by municipal water supply, industry, commercial and irrigation. Current practice is to issue permits for a maximum period of 10 years. Permits for golf course irrigation are for 5 years and water bottlers 2 years. Currently under development is a broad-based “Source Water Protection Plan” designed to address risks to water availability and quality. 4.8 North Dakota The North Dakota Century code, Chapter 61-04 (http://www.swc.state.nd.us/waterlaws/rules/ 8903WatApp.pdf ) requires that a permit be obtained for groundwater withdrawals unless the water is for domestic or stock use. Other types of use (industrial/commercial, municipal, rural water, and irrigation) therefore require a permit. Watering of less than 1.2 dam3/a (one acre-foot per year) is considered domestic rather than irrigation use. Regardless of the proposed type of use, a permit is required for pumping of more than 15.4 dam3/a (12.5 acre-feet/year). A cattle feedlot or a dairy operation using more than 12.5 acre-feet of water per year would therefore require a permit.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 13

To obtain a conditional permit, the applicant must submit the following information to the state engineer: quantity of water requested per year, maximum pumping rate, location of well, use of water, method of irrigation and location of land to be irrigated (if applicable), and a location map prepared by a registered land surveyor. The applicant is also required to notify landowners within a 1.6 km (1 mi) radius from the area within which the proposed well is to be installed and municipalities and water associations within a 19 km (12 mi) radius, including a notification in the county newspaper published for two consecutive weeks. After completion of the well, the pumping rate from the well may be measured by the State Water Commission. Subject to inspection, the conditional permit will be perfected after the water has been put to beneficial use (beneficial use means use of water for a purpose consistent with the best interests of the people of North Dakota). In the case of competing applications, the following priority is used: (1) domestic use, (2) municipal use, (3) livestock use, (4) irrigation use, (5) industrial use and (6) fish, wildlife and outdoor recreational uses. In the water permit application process the applicant is not required to submit well completion and pumping test data. However, it is required that the production well be installed by a certified water well contractor, who, in turn, is required to submit a well driller's report including the well construction details. When aquifer property information is deemed necessary for groundwater management, aquifer tests will be performed by the State Water Commission staff, commonly using permitted production wells. The state engineer may add any conditions to a water permit deemed necessary for the proper management of the water resource. While permit holders are required to submit annual water use data, water levels in areas of significant withdrawals are monitored in wells constructed by the State Water Commission. 4.9 Discussion Within the jurisdictions selected for review there are many similarities in the process and requirements for allocating groundwater withdrawals. However, there are some notable exceptions:

● The Water Act of British Columbia currently does not include regulations for the withdrawals of groundwater. However, the Act specifies that licensing requirements can be made to apply to groundwater in all or part of British Columbia a date specified by regulation.

● The Saskatchewan Groundwater Conservation Act and Groundwater Regulations does not recognize the “first come – first serve” principle, but in granting a license existing users are taken into account. Contrary to other jurisdictions, the Saskatchewan Act and Regulations also do not specifically define a rate above which a license is required nor do they specifically define a license expiry date. However, by policy the maximum domestic use is set as 5,000 m3/a and industrial projects are approved for a period of 5 years.

In most jurisdictions a withdrawal rate (ranging from 3,400 to 50,000 L/day) is used above which a license/permit is required. It is unclear why a specific rate was selected, but it does not appear to be based on hydrogeological or factual considerations.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 14

It is common that monitoring (water level, water quality and actual volumes pumped) requirements are attached to a license/permit. While the need for such data is essential (for example, Rivera et al., 2004) in assessing the performance of aquifers under stress, collecting and processing of this information by the provinces is generally inadequate. The reason for this typically is lack of manpower and funding. The Q20 concept deals with the long-term sustainable yield of a well. Determination of the long-term sustainable well yield is never specifically mentioned as being required in the application for withdrawal permit in the other jurisdictions reviewed. All jurisdictions include an assessment of potential impacts on other users and on surface water as part of the licensing procedure. However, the criteria for evaluating such impacts vary widely from one jurisdiction to the other, and are, at best, only vaguely defined. It is also not clear how cumulative impacts of many groundwater users are addressed or whether they are addressed at all. With the exception of Nova Scotia, which has used the Alberta Q20 concept in the past (apparently in relation to the relocation of an Alberta Environment staff member); the Q20 concept has not been used anywhere else. The reason for the limited application of the Q20 concept outside Alberta is not known. Most jurisdictions require renewal of an allocation permit after a certain period of time. This time period is variable, ranging from 5 to 20 years, and typically no justification is provided for the adopted renewal period.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 15

5.0 THE Q20 METHOD 5.1 Introduction The Q20 concept (Farvolden, 1959) is based on a theoretical model that was developed in the 1930’s and 1940’s for the flow of groundwater to a well (Theis, 1935; Jacob, 1940). This model is based on assumptions that strongly limit its application. Numerous more general models for the analyses and pumping tests have been developed since the first introduction of the Q20 method in 1959. The evaluation of the Q20 method which is the subject of this report will be strongly based on theoretical models for the analysis and prediction of drawdown of groundwater levels due to pumping. As the Farvolden Q20 method is based in the Theis equation, a brief review of the Theis equation is provided in section 5.2. A more extensive review of pumping test theory is provided in Appendix B of this report. 5.2 Development of the Theis equation for drawdown due to pumping from a confined

aquifer Theis (1935) developed the following equation, referred to as the nonequilibrium equation, for calculation of the drawdown in an aquifer subject to pumping at a constant rate:

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛+−+−−=== ∫

∞ −

!3.3!2.2ln5772.0

444

22 uuuuKD

QuW

KDQ

udue

KDQ

s tt

u

ut

πππ [1]

where:

s = drawdown (m) in a well at a distance r from the production well Qt = constant pumping rate (m3/day) KD = transmissivity (T) of the aquifer (m2/day) (T = KD) r = distance of observation well from production well (m) S = storativity of the aquifer (dimensionless) t = time since pumping started (days) W(u) = well function

u = KDt

Sr4

2

[2]

It is of interest to note that Theis (1935, page 521) states that, theoretically, equation [1] is “applicable only to unconfined water bodies”. At the time that Theis published his equation, few data were available on confined aquifers and there was no rigorous concept of the storage coefficient for confined aquifers. Based on a rigorous definition of specific storage for confined aquifers, Jacob (1940) re-derived the Theis equation. Consequently, it was not until after Jacob’s 1940 publication that the 1935 Theis equation became “established” as the equation for the analysis of pumping test data from confined aquifers. Cooper and Jacob (1946) showed that for small values of u (u<0.01), i.e. large values of time or small values of r, the drawdown s in equation [1] can be approximated by:

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 16

SrKDt

KDQ

KDtSr

KDQ

s tt2

2 25.2log4

30.24

ln5772.04 ππ

=⎟⎟⎠

⎞⎜⎜⎝

⎛−−= [3]

Equation [3] is sometimes referred to as the “modified nonequilibrium equation” and is known as Jacob’s straight line method. Kruseman and de Ridder (1990, page 67) suggest that the condition u<0.01 is rather rigid and that for all practical purposes the condition u<0.1 can be used. Equation [3] can also be written in the form:

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

TtSr

TQ

s t

25.2log

430.2 2

π [4]

Equation [4] shows that drawdown is a linear function of log(r), except for very large r or small time. Drawdown at various distances from the pumping well and for large times can thus also be easily calculated. This is particularly useful for assessments of well interference. When the drawdown and time data are plotted on semi-logarithmic paper (t on logarithmic scale) a straight line can be drawn through the data. Defining ∆sp as the difference in drawdown per log cycle of time, the transmissivity T (T = KD) is obtained from:

p

t

sQ

=π43.2

[5]

and

2025.2

rTt

S = [6]

where; t0 is the time where the straight line intercepts the time axis at the point s=0 The Theis equation and Cooper and Jacob approximation are based on the following assumptions (e.g. Kruseman and de Ridder, 1990):

1) the aquifer is confined 2) water is released instantaneously with the decline of head in the aquifer 3) the aquifer has an infinite aerial extent 4) the aquifer is homogeneous, isotropic and of uniform thickness over the area

influenced by the test 5) prior to pumping, the piezometric surface is horizontal (or nearly so) over the area

that will be influenced by the test 6) the aquifer is pumped at a constant discharge rate 7) the well penetrates the entire thickness of the aquifer 8) the pump well has an infinitesimal diameter (i.e. negligible storage in the well).

The assumption that the aquifer is confined strongly limits the applicability of the Theis equation, because it requires that there is no significant flow into the aquifer from the overlying and underlying aquitards. Strictly speaking this condition is rarely valid, especially after long duration of pumping. The assumption of a uniform aquifer of infinite extent is also rarely satisfied, especially as the drawdown “cone” extends father out after a long pumping duration. In

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 17

practice pumping test analyses based on the Theis equation tend to produce reasonably good estimates of transmissivity and storage coefficient near the pumping well provided there are two or more observation wells. However, it cannot be relied upon for prediction of long-term behavior under pumping for water supply. As we shall see, this limitation has important implications for the “Q20” method. 5.3 History of the Q20 Method 5.3.1 Farvolden Q20 Farvolden (1959, see appendix C) prepared a seminal report on groundwater supply in Alberta. In his discussion of methods for determining the safe yield of wells, he identified two possible cases. The first case is one where “a stable pumping level is established – this indicates that the recharge balances the discharge”. For this case he recommended that the specific capacity of the well be calculated by:

DrawdownStablelwaspumpedRatethewelCspacitySpecificCa =)( [7]

The capacity of the well can then be calculated by: )7.0()( factorsafetyxdrawdownavailableHxCswellofCapacity = [8] where the available drawdown is the distance from the static level in the well to the top of the aquifer. Here it is clear that “capacity of the well” represents the long-term sustainable yield since the pumping level is no longer decreasing. It is of interest to note that the current version of the Alberta Groundwater Evaluation Guideline (2003) does not include this method. The second case discussed by Farvolden is the one where “the water level continues to decline – this indicates that the well is drawing water from storage”. For this case, Farvolden introduced the concept of estimating the drawdown in the pumping well after 20 years of pumping to determine the sustainable yield of a well, commonly referred to as “the Q20 method”. He suggested (p. C6) “If the well is to last 20 years (about 10 million minutes), the drawdown curve, when projected, must not have a greater drawdown than we have available where it intersects the 10 million minute line on the time scale”. Farvolden assumed that the long-term drawdown would follow the line predicted by the Theis theory for fully confined aquifer, i.e. a straight line on a Cooper-Jacob semi-logarithmic plot: “Since at a given rate the well draws down equal amounts for each log cycle or time division, then from 1/10 of a minute to 10 x 106 there are 8 cycles. Therefore, if the well is pumped at such a rate that for each time division on our scale it will draw down ⅛ of total H (available drawdown), then in 20 years the well should be exhausted” (Farvolden, 1959, page 7). Based on equation [5], Farvolden thus defined a “safe rate” of a well as:

fAfA STHS

HTQ 683.0

30.2)8/(4

20 ==π [9]

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 18

where: HA= available drawdown = (depth to top of aquifer – depth to static water level). S f is a safety factor for which Farvolden used 0.70, and Q20 is the “safe rate”. It is noted that Farvolden used a constant pumping rate, which is assumed here to be the maximum daily pumping rate. Because pumping is seldom continuous, the actual long-term drawdown in the production well will be less than the drawdown (available head x safety factor) used to determine the Q20 for a maximum daily pumping rate. Note that Farvolden did not use the Q20 symbol and terminology, but we use it here for the sake of easier comparison with modifications that where introduced later. Farvolden simply uses the notation Q (without subscript) to designate the safe yield of a well for a twenty year period. It was Tóth (1966, page 74) who introduced the notation Qs20 (safe yield supplied from storage for twenty years). Over the years, the notation was simplified to Q20. Here, and in the following discussion, the original units and various symbols used by the original authors have been translated to consistent metric units and symbols. Moell (1975, page 7) appears to have introduced the definition for available head in an unconfined aquifer: “The available head in an unconfined aquifer is arbitrarily chosen as ⅔ of the elevation difference between the base of the aquifer and the static water level”. Farvolden (1959) uses a safety factor of 0.7, but does not indicate how he derived at this value and what it is for. The number appears to be arbitrary and the opinions as to what it represents vary. For example, Moell (1975, page 7) states: “The safety factor is used to offset over-estimates of sustained yield which result from assuming the aquifer to be of infinite extent, of constant thickness and homogeneous and isotropic”. Parks and Bentley (1996, page 467-468) state: “Geologic heterogeneities and recharge boundaries are not explicitly considered. Well inefficiency may be accounted for by multiplying the available drawdown by a safety factor less than one before calculating the Q20, e.g. a safety factor of 0.70 allows 30% of available drawdown for well losses”. It is well known in the water well industry that well losses may increase over time due to incrustrations and bio-fouling but this has not been specifically mentioned in discussion of the safety factor. It should be noted that the calculation of the value of transmissivity T in the method suggested by Farvolden (equation [9]) is an intermediate step that is not strictly necessary for the calculation of Q20. This fact was also noted by Bibby (1979) who further states: “that if the drawdown curve is presumed known for 20 years for any constant pumping rate, then the 20-year sustainable yield can be obtained by a linear shift of this curve”. In equation form:

fp

At S

sHQQ ⎟

⎟⎠

⎞⎜⎜⎝

Δ=

820 [10]

Equation [10] is the Farvolden expression for Q20 (equation [9]) written in terms of the drawdown per unit log cycle of time (Δsp).

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 19

5.3.2 Apparent Q20 In 1961, when Farvolden published the results of a study on the groundwater resources of the Paskapoo Formation in the Pembina area, there were no pumping test data available but a large number of drawdown or production test data. Typically, these drawdown or production tests were of short duration and only an initial or static water level and the water level at the end of the test was recorded. Farvolden (1961) introduced the concept of “apparent transmissivity”. The “apparent transmissivity” is calculated from equation [5], using only the initial or static water level and the water level at the end of the test (Figure 6). Farvolden (1961, page 9) was well aware of the shortcomings of this method as he states: “The validity of this method of determining transmissibility is open to serious doubt because a number of factors that may have significant influence on the results are not considered”. Ozoray (1970, see Ozoray, 1977) prepared a nomogram for the calculation of the apparent transmissivity. Ozoray (1972, page 7) appears to be the first one to have used the term “apparent” 20-year safe yield. Ozoray (1972) states that, provided that they are available in adequate numbers, apparent transmissivities and safe yields values give “a valuable indication of regional variations in relevant rock properties”. In their evaluation of the groundwater availability in the Onaway map area, Moell and Schnurr (1976) also used the concept of apparent transmissivity (TA) and apparent safe yield (Q20A). However, they were well aware that the apparent transmissivity and therefore, the apparent safe yield were only gross estimates. The concept of apparent transmissivity (Ta) and apparent safe yield (Q20a) was used by Hydrogeological Consultants Ltd. in their evaluation of the groundwater potential in counties in Alberta (http://www.agr.gc.ca/pfra/water/groundw_e.htm (also available at http://www.hcl.ca/ reports.asp). For short-term pumping tests (typically 2 hr tests), and with information available for the pumping rate, length of test, drawdown at end of test and radius of well casing, Hydrogeological Consultants Ltd. used the following approach in calculating the apparent transmissivity and apparent Q20 (Hydrogeological Consultants Ltd, 1998, page 12 and 13):

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛+−+−−=

!3.3!2.2ln5772.0

4

22 uuuus

QT t

a π [11]

tTSr

ua

c

4

2

= [12]

where: Qt = pumping rate (m3/day), Ta = apparent transmissivity (m2/day), s = drawdown at end of pumping test (m), =2

cr radius of casing (m), S = storativity (taken as 10-4) and t = duration of pumping test (days). Since Ta occurs in both equations [11] and [12], Ta is determined by iteration. The apparent safe yield Q20a is then calculated from:

7.0***78.020 Aa HTaQ = [13]

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 20

Equation [13] is similar to equation [9] except that (HA/7) rather than (HA/8) was used as the starting time was taken as 1 min. It is noted that any analysis of short-term 2+2 hrs of pumping test data required for water supplies of up to 10 m3/day (see Table 2) may not yield meaningful long-term well yield information. The transmissivity determined from such a test may not be reliable and consequently, the Farvolden Q20 based on this transmissivity is questionable. It is further noted that the modified Moell equation (equation [15] in the next section) can not be applied to calculate a Q20 as ∆s beyond 100 minutes can not be determined. While the results of these types of test should continue to be reported, in practice, these tests are merely used by drillers to determine the pump setting. 5.3.3 History of Moell Method Moell (1975, page 7) introduced a variation of Farvolden’s “safe rate” calculation for the case when well losses need to be considered:

p

At

ssHQ

QΔ+

=610

20 [14]

where: s10 = drawdown at time = 10 min This equation was developed by staff of Alberta Environment (Moell, 2004; personal communication). In the AE Groundwater Evaluation Guideline (2003, page 14), a slightly modified version of Moell’s equation is being used:

fp

At Sxss

HQQ

Δ+=

510020 [15]

where: s100 = drawdown at time = 100 min and ∆sp = “drawdown per log cycle of time’ (implying straight line behavior on a semi-logarithmic plot). Equation [15] is similar to equation [10] for determining the Farvolden Q20 except that it eliminates Farvolden’s assumption of zero drawdown in the pumping well after 0.1 minutes of pumping. 5.3.4 Bibby’s Approach Bibby (1979) introduced the concepts of “local’ and “regional” transmissivity. The concepts of “local’ and “regional” transmissivity are based on the fact that drawdown curves often show “limbs” (Figure 7). Bibby (1979) argued that the initial straight line and the transmissivity derived from it represent “local” transmissivity. He further states that “the values of transmissivities of all tests of a few hours of duration may be considered to be “local” transmissivity” (Figure 7). The transmissivity of the final straight line then would represent average or effective transmissivity, referred to as “regional”. Based on extending the final straight line to 1 x 107 min, and using the principle of proportionality, Bibby (1979) used the following equation to calculate the 20-year sustainable pumping rate:

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 21

Q

At S

HQQ,20

20 = [16]

where: Q20 = 20-year sustainable pumping rate, HA = available drawdown, S20,Q = extrapolated drawdown after 20 years at the pumping rate Qt. Extrapolation of the straight line to 1 x 107 is not necessary since:

pQ ssS Δ+= 41000,20 [17] therefore, equation [16] becomes:

p

At ss

HQQΔ+

=41000

20 [18]

In a more general form equation [18] becomes:

)log7(20

pLpt

At tss

HQQ−Δ+

= [19]

where: L

tL T

Qs

π43.2

TL = long-term transmissive capacity (m2/day) tp = duration of pumping test (days)

pts = drawdown at time tp (m) ΔsL = slope per log cycle of drawdown curve, corresponding to long-term transmissive capacity (m)

s1000 = drawdown in pumping well after 1000 minutes 5.4 Q20 versus Q200, Q10 and Q5 Farvolden (1959) does not specifically mentions why he selected t = 107 min (≈20 years) as end point. Perhaps his reasoning was that if a well yield would last for 20 years it would last in perpetuity. For a specified length of time n (years), and 0.1 min as starting point, equation [9] can also be written as (personal communication: J. Toth):

)log1(47.5

nH

TQ An += [20]

For any given T and HA, and setting the yield of a well at 20 years to 100%, Figure 8 shows Qn (in percentage relative to Q20), for times ranging from 0.5 to 200 years. This Figure shows that Q200 would be 89% of a calculated Q20, justifying the reasoning that a Q20 yield would last in perpetuity. Q10 and Q5 would be 4% and 10% higher than the long-term yield Q20, estimate. The use of a Q5 or Q10 could lead to overestimation of the sustainable well yield since most wells will be in operation for longer than 5 or 10 years.

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6.0 PROPOSED MODIFICATION OF THE Q20 METHOD 6.1 Comparison of Q20 versus Analytical Aquifer Models The methods for determining Q20 discussed in chapter 5 are essentially based on the assumption that drawdown measured in a pumping well can be extrapolated to the long term (20 year) behavior on the basis of the Theis equation for a fully confined aquifer. Aquifer heterogeneities, boundaries, etc. are dealt with by introducing safety factors or “local transmissivities” or other corrections. As we have seen, and as was recognized by Farvolden (1961), Parks and Bentley (1996) and others, there are very few, if any, aquifers that satisfy the Theis assumptions of large extent and no recharge into the aquifer. Hence it is not surprising that the “straight-line extrapolation” method gives rise to numerous problems. Since it is well established that most aquifers have different behaviors (e.g. semi-confined aquifers going to steady-state) and since proven mathematical models for such behaviors are available, it seems reasonable to suggest that the Q20 method can be brought up to date by adapting it to different aquifer types as appropriate. Essentially this means going back to Farvolden’s original reasoning: “If the well is to last 20 years (about 10 million minutes), the drawdown curve, when projected, must not have a greater drawdown than we have available where it intersects the 10 million minute line on time scale”. But instead of always using only the Cooper-Jacob (i.e. Theis) drawdown curve, even for aquifers where we know it is not applicable, we can use whichever drawdown curve is most appropriate for the aquifer that is being evaluated. Incorporating a safety factor of 0.7 as proposed by Farvolden, the calculation would be:

tQ

tA s

QHQ

,2020 **70.0= [21]

Where HA is the available drawdown, Qt is the rate of pumping of the pumping test, and tQS ,20 is the estimated drawdown after 20 years at the pumping rate Qt, calculated on the basis of the most appropriate aquifer model. Equation [21] is similar to equation [16], which was used by Bibby (1976). Typically the drawdown in the pumping well is influenced by details of the well construction and placement (e.g. partial penetration, well losses, development of the formation, etc.). Therefore, the drawdown in the pumping well cannot be predicted solely on the basis of a theoretical aquifer model, but must be evaluated by means of a pumping test. This local drawdown at the pumping well is established early on during a pumping test and can be determined from the early-time drawdown data, typically the first 100 minutes of pumping. The further long-term decline of the water level in the pumping well can be predicted on the basis of the appropriate aquifer model, tested by means of the later-time portion of the pumping test. The local drawdown may depend in a complex manner on the pumping rate, and this dependence is commonly evaluated by means of step drawdown tests, conducted prior to carrying out an extended pumping test. The current recommendations of the Alberta Groundwater Evaluation guidelines deal with the problem of local drawdown at the pumping well by suggesting that the long-term drawdown be estimated as the sum of the measured drawdown after 100 minutes plus the predicted further drawdown from 100 minutes to 20 years (using the Moell model, equation [15]). This approach can be easily adapted to more general aquifer models by taking:

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 23

( )

theoryrsyrs ssss min10020min10020 −+= [22] And then equation [15] becomes:

( )[ ]theoryrstAf sssQHSQ min10020min10020 /** −+= [23]

This new approach to calculating Q20 requires that an appropriate set of theoretical equations and aquifer parameters must be selected, based on the hydrogeology of the aquifer, and if possible, on the pumping test results. In fact, the pumping test should be designed to obtain the requisite aquifer parameters if possible. Such an approach to the design and analysis of pumping tests is common practice nowadays and it is a logical extension of this practice to apply it also for the calculation of Q20. It is important to note that for application of equation [23] it is not necessary to identify some more or less realistic “drawdown per log cycle of time” on the basis of straight-line segments in a semi-logarithmic plot of drawdown. For complex aquifer settings the calculation of theoretical drawdown at 20 years may include consideration of aquifer boundaries using image well theory. Numerical models could also be used where such applications are justified by the scope of the project and the availability of hydrogeologic information. The proposed method for calculating Q20 is applicable to types of aquifers typically found in the Prairies and can be applied elsewhere to similar aquifers. However, other aquifer types such as those formed by karstic limestones or fractured rock, or located in a very humid or very arid area, may require specialized models to determine Q20. The drawdown in the well as measured after 100 minutes of pumping, s100min may be influenced by well losses. The value of s100min may therefore need to be adjusted for pumping rate if well losses are significant. From a practical point of view application of equation [23] may, therefore, require that a step-drawdown test be conducted prior to the pumping test in order to be able to estimate well losses for different pumping rates.

Where there is uncertainty about the nature and extent of the aquifer that is being tested it is recommended that the most conservative model be applied that is consistent with what is known of the aquifer. For example, if the aquifer is known to be strongly bounded and perhaps channel-like, then it would be appropriate to use the channel aquifer model for estimating Q20. The pumping test should then be carried out with the object of verifying whether the aquifer is indeed strongly bounded and exhibits channel-like behavior. Although these requirements for arriving at a value of Q20 may seem difficult to follow and overly onerous, this is not in fact the case. In many provinces the guidelines for groundwater evaluation already expect that the nature and extent of the aquifer should be identified and that the analysis of the pumping test data should use the appropriate aquifer model.

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7.0 R20 CONCEPT 7.1 Introduction of R20 Concept One of the major concerns with groundwater evaluation is the problem of evaluating the impact of additional withdrawals on existing or future wells and on surface waters such as wetlands, springs or streams. Provincial guidelines for Alberta require that all other users and/or surface water bodies that might be affected should be evaluated over a distance of 1.6 km from the well site or for even larger distances, if necessary. Saskatchewan makes a similar stipulation for a distance of 3 km. These specified distances are helpful, but may be too onerous in some cases and too lax in others. Drawdowns can extend anywhere from a few meters to tens of kilometers from the pumping well, depending on the type of aquifer and the rate of pumping. The extent of the drawdown for any well can always be estimated on the basis of the same aquifer model as is used to determine Q20. Any of the equations that are used to calculate the drawdown after 20 years, at the pumping well, can also be used to calculate the drawdown at any distance from the pumping well after 20 years. This possibility suggests that the radius of influence of the well can be defined as R20, where R20 is the distance from the pumping well where the drawdown SR20 after 20 years of pumping at the requested rate, Qr equals some given limit, which might typically be set as about equal to the natural fluctuation of the water level in the aquifer, say 0.5 m for prairie aquifers. (Qr should of course always be less than or equal to the maximum safe well yield Q20) In a general form, the drawdown in an aquifer due to pumping at a steady rate Qt from a single well is given by:

( ) ( ),....,,43.2

, LtrWTQs t

tr π= [24]

where ( ),...,, LtrW is a theoretical well function: for example, for a confined aquifer ( ),...,, LtrW is the Theis well function ( )uW .

R20 is defined as the distance from the pumping well, where the drawdown after 20 years of pumping at rate Qt equals a pre-set limit SR20:

( ),....,20,43.2

2020 LyearstRWTQS t

R ==π

[25]

As an example, consider the case of a perfectly confined aquifer [equation 3], for which the Cooper-Jacob semi-log plot can be applied. The drawdown after 20 years (7,305 days) is given by;

Sr

KDKDQs t

22025.16436log

43.2π

= [26]

Defining R20 as the distance from the pumping well where the drawdown after 20 years of pumping at requested rate Qr equals a pre-set limit SR20, equation [26] leads to:

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 25

Qr

KDSRSKDR

2046.520

10

1128= [27]

For steady-state flow in a semi-confined and buried-valley aquifer equation, the same reasoning can be followed to calculate a R20 value. Equations for R20 have been provided in Appendix B. For many situations there will be no simple closed-form equations for calculating R20. However, the generally available type curves can be used to calculate drawdown at various distances after 20 years and thus a value for R20 can be estimated. The function ( ),...,, LtrW can in principle also be developed by means of a numerical model that takes into account the complexity of real-world aquifers and aquitards. In such a case R20 would define an irregular boundary outside of which the predicted drawdown does not exceed the defined limit such as 0.5 m. 7.2 Comparison of Farvolden Q20, Theoretical Q20 and R20 It is instructive to carry out some sample calculations of Q20 and R20 for a typical range of aquifer transmissivity and other hydrogeologic parameters as well as for different types of aquifer settings (water table, semi-confined, etc.) Following the Alberta Environment Guidelines (2003), let’s assume that pumping tests were carried out on wells completed in various types of aquifers, that the results were analyzed with the most appropriate method for the hydrogeological setting, and the resulting aquifer/aquitard characteristics were determined as follows (see list of symbols): transmissivity T = 100 m2/day, Tw=105 m3/day (W=1,000 m), D=10 m, b’=30 m,

'vK =10-5 to 10-3 m/day (≈ 10-10 to 10-8 m/s), S=10-4, Sy=0.25, SA=SW=0.1, Ss=10-6 m-1

(aquitard), rc=0.075 m, HA=20 m (= 14 m when safety factor is included) and L=17,300 m. In Tables 3 to 7 values for Q20 are shown based on the Farvolden method (equation [9]), and the aquifer/aquitard parameters listed above. These tables also show the actual Q20 values based on the modified Moell equation proposed in this report (equation [23]). In applying equation [23] the aquifer/aquitard properties above were applied to rigorous theory, assuming that well losses are negligible and the well is fully penetrating. The program Aqtesolv™ was used to determine the actual Q20 for the available drawdown specified above. According to the Alberta guidelines, after determination of the aquifer/aquitard properties, the Farvolden (equation [9]) or Moell method (equation [15]) must be used to calculate the Q20. As shown in Tables 3 to 6, application of the Farvolden method yields a value of 956 m3/day of the Q20 for the various aquifer types considered, except for the water table aquifer. The lower Q20 value of 320 m3/day for the water table aquifer is due to the fact that the available drawdown is ⅔ times the saturated thickness of the aquifer. Including a safety factor of 0.7, the HA for the water table aquifer thus equals 4.7 m. For the water table and fully confined aquifers, the original Moell (equation [15]) and modified Moell (equation [23]) methods will yield exactly the same results because the Moell equations are based on the same aquifer model. However, for the other types of aquifers the Moell methods are ambiguous because they depends on a determination of the drawdown per log cycle of time,

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 26

a parameter that is only definable for the ideal confined or ideal water table aquifers. It is for this reason that the original Moell method is not shown in Tables 3 to 7. For the other aquifer types the drawdown is not a function of the logarithm of time and the drawdown per log cycle of time is not defined (see case history of the Estevan channel aquifer). The value of R20 in Tables 3 to 7 is calculated for a pumping rate equal to the actual Q20, the maximum safe well yield, and thus, the values of R20 shown in the tables are the maximum values. In most cases the requested pumping rates are smaller than Q20 and the values of R20 will be correspondingly smaller. However, there is no simple relationship between the pumping rate and the value of R20 – each case must be determined individually. Table 3 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (case 1: 'vK = 10-5 m/day)

Aquifer setting

Type curve Q20 Farvolden(m3/day)

Q20 Modified

Moell (m3/day)

R20 (SR20= 0.5 m)

(m)

b’ (m)

Water table Theis (1935) 320 237 700 0 Semi-confined Jacob and Hantush (1955) 956 708 16,700 30 Semi-confined (buried-valley)

Vandenberg (1977) 956 132 54,200 30

Leaky Hantush (1960) 956 662 35,200 >>30 Confined Theis (1955) 956 613 86,000 N/A Table 4 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (case 2: 'vK = 10-4 m/day)

Aquifer setting

Type curve Q20 Farvolden(m3/day)

Q20 Modified

Moell (m3/day)

R20 (SR20= 0.5 m)

(m)

b’ (m)

Water table Theis (1935) 320 237 700 0 Semi-confined Jacob and Hantush (1955) 956 777 5,600 30 Semi-confined (buried-valley)

Vandenberg (1977) 956 309 15,500 30

Leaky Hantush (1960) 956 711 15,400 >>30 Confined Theis (1955) 956 613 86,000 N/A

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Table 5 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical aquifer/aquitard parameters (case 3: = 10-3 m/day)

Aquifer setting

Type curve Q20 Farvolden (m3/day)

Q20 Modified

Moell (m3/day)

R20 (SR20= 0.5 m)

(m)

b’ (m)

Water table Theis (1935) 320 237 700 0 Semi-confined Jacob and Hantush (1955) 956 865 1,925 30 Semi-confined (buried-valley)

Vandenberg (1977) 956 564 3,950 30

Leaky Hantush (1960) 956 784 5,200 >>30 Confined Theis (1955) 956 613 86,000 N/A Table 6 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (T =100 and 500 m2/day) Aquifer setting

'vK

(m/day)

Q20 Farvolden (m3/day)

Q20 Actual (m3/day)

R20 (m)

Q20 Farvolden (m3/day)

Q20 Actual (m3/day)

R20 (m)

T = 100 m2/day T = 500 m2/day Water table N/A 320 237 700 1,605 1100 1,400 Semi-confined 10-5 956 708 16,700 4,781 3,315 35,500 10-4 956 777 5,600 4,781 3,630 12,000 10-3 956 865 1,925 4,781 4,010 4,050 Buried-valley 10-5 956 132 54,200 4,781 347 127,000 10-4 956 309 15,500 4,781 953 38,500 10-3 956 564 3,950 4,781 2,220 11,000 Leaky 10-5 956 662 35,200 4,781 3,120 75,500 10-4 956 711 15,400 4,781 3,338 32,500 10-3 956 784 5,200 4,781 3,655 11,250 Confined N/A 956 613 86,600 4,781 2,905 186,000 Table 7 Comparison of Farvolden Q20, modified Moell Q20 and R20 for hypothetical

aquifer/aquitard parameters (T =10 and 5 m2/day) Aquifer setting

'vK

(m/day)

Q20 Farvolden (m3/day)

Q20 Actual (m3/day)

R20 (m)

Q20 Farvolden (m3/day)

Q20 Actual (m3/day)

R20 (m)

T = 10 m2/day T = 5 m2/day Water table N/A 32 26.5 255 16 13.8 190 Semi-confined 10-5 95.6 78 5650 47.8 40 4050 10-4 95.6 87 1925 47.8 45 1390 10-3 95.6 97 655 47.8 51 475 Buried-valley 10-5 95.6 31 15500 47.8 22 11000 10-4 95.6 56.5 3950 47.8 38 3735 10-3 95.6 94.5 655 47.8 50 525 Confined N/A 95.6 67 29000 47.8 34 20750

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It is evident from Tables 3 to 7 that for a water table, semi-confined and even a truly confined aquifer, the Farvolden Q20 as compared to the modified Moell Q20 does not provide a conservative estimate of the long-term (20 year) yield of a well as often is assumed. In fact, for these types of aquifers the Farvolden Q20 overestimates the long-term yield. The reason for this is evident when equation [6] is considered. Farvolden (1959) assumes a starting point of 0.1 minutes. For a transmissivity of 100 m2/day, rc=0.075m, for example, equation [6] yields a storage coefficient of 2.78, which obviously is erroneous. As is evident from the large differences in the Farvolden Q20 and modified Moell Q20 for buried valley aquifers (see Tables 3 to 7), the Farvolden method can not be used to estimate the long-term yield of a well completed in a buried valley aquifer. This is not only due to the reason mentioned above, but is due in particular to the geometry of such aquifers (long, narrow and bounded on all sides). As is shown in Table 6, higher transmissivity values lead to higher yields and larger R20 values. Similarly (Table 7), lower transmissivities would lead to smaller yields and R20 values. The significance of Tables 3 – 7 is that R20 values may range from several hundreds of meters to tens of kilometers. It is argued that guidelines for groundwater evaluations should be flexible with respect to the distance of field-verified surveys from the proposed groundwater development. Evaluation of interference effects with other groundwater users or with surface waters could be required to be carried out to a distance equal to R20 from the well site. For some wells this may prove very onerous, for other cases this may greatly reduce the amount of effort involved. Wells will seldom be pumped continuously at the requested rate and a requested volume may be withdrawn in a period much less than a year. Therefore, the R20 should be based on the annual average pumping rate and not on the maximum daily rate. The R20 calculated for an average annual pumping rate may be much smaller than the R20 based on the daily maximum rate. For “infinite” water table, semi-confined and confined aquifers the R20 distance will be in the form of the radial distance from a well. For buried valley aquifers it should be the distance along the aquifer, in both directions away from the well. In any case, this criterion for determining the radius of influence of the well is based on a realistic assessment of the aquifer properties, the same assessment on which the estimate of modified Moell Q20 is based, i.e. the expansion of the drawdown “cone” in space as well as in time. 7.3 Well interference and criteria for going to aquifer management plan Well interference is the drawdown in one well due to pumping from other wells. The 20-year drawdown in neighbouring wells due to pumping from the proposed well can be calculated in a straightforward manner using the appropriate aquifer model (equation [25]). A graph of drawdown versus distance from the proposed well may suffice to evaluate the potential impacts, and identify any mitigative actions (e.g. setting a pump deeper) that might be necessary. The reverse is also true. The drawdown in the proposed well due to pumping from other wells can be calculated in a similar manner. The reciprocity principle (Appendix B: section B9) can be a useful tool for such analyses.

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For most cases of relatively low proposed pumping rates and low aquifer transmissivity, the impacts of pumping from one additional well are not likely to extend more than a few km from the proposed well site. However, cases that involve high pumping rates and large drawdowns in confined high-permeability aquifers may require extensive mitigative actions, particularly if the aquifer is a buried channel aquifer. As illustrated by the calculations summarized in Tables 3 to 7, the zone of well interference may extend many km away from the proposed well site for such cases. In practice, the influence of aquifer heterogeneity and aquifer boundaries cannot be easily taken into account with this simple method, and where such complications are likely to be important sound judgment must be used, or a numerical model may necessary. The more troublesome question, however, involves the identification and prediction of regional lowering of groundwater levels due to the cumulative impacts of many small groundwater users. Such impacts can be difficult to identify with certainty unless reliable long-term observation well records are available and the withdrawal rates by all significant groundwater users are known or can be estimated. Clearly aquifers with high values of R20 are particularly at risk because the drawdown at any point in the aquifer is likely to be due to many users at distance of up to tens of kilometers away. The summation for cumulative drawdown should be carried out for all wells that potentially make a significant contribution to the drawdown at any particular location. This is where the standard Q20 practice of using the Theis/Cooper-Jacob model (i.e. assuming a fully confined aquifer) to make predictions of drawdown is questionable. As shown in Tables 3 to 7, the Cooper/Jacob equations lead to very large values for the radius of influence of a pumping well after 20 years. Most groundwater evaluations would therefore have to involve well surveys extending over very large areas. And indeed, if this fully confined aquifer model were realistic it would imply that over large areas of Alberta and Saskatchewan cumulative drawdown in the deeper aquifers should be very large after a century of groundwater pumping. In areas where groundwater is being increasingly exploited the risk exists that numerous small withdrawals from individual wells, each of which appears to have little impact, can add up to major impacts on the aquifer system as a whole. Such impacts will eventually become apparent, as for the well-known case of the High Plains aquifer in the United States. It is preferable to identify such problems beforehand and develop an aquifer management plan for the aquifer which takes all the groundwater uses into consideration. The above suggestion for using R20 to estimate the radius of influence of wells can serve to identify the need for an aquifer management plan. If the radius of influence of the well includes many other users or extends to surface waters that are likely to be impacted, then the need for an aquifer management plan is indicated. Further criteria might include a limit on the total withdrawals from the aquifer, the average rate of abstraction on an aerial basis compared with the estimated rate of groundwater recharge or of baseflow in streams, or a limit on the maximum drawdown at any point of the aquifer.

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8.0 CASE HISTORIES 8.1 Introduction Various reviews and summaries of groundwater developments in the prairie region have been published over the years in journals and reports. These published case histories provide a convenient and easily-accessible source of information with regard to the approaches that were used, the results of the initial investigation and, in some cases, the longer-term responses of the groundwater system to pumping. These case histories may not necessarily represent the best examples of aquifer management. The drawback to these published case histories is that usually only selected portions of the original data are presented. One sees the case history through the eyes of the authors, and an in-depth review of the case is not feasible. 8.2 Alberta 8.2.1 Grande Prairie Two relatively small groundwater developments near Grande Prairie AB, Sexsmith and Silver Pointe Village, were described by George et al. (2003). The paper addresses the technical aspects of the developments as well as the regulatory and conflict resolution aspects. The Silver Pointe Village development concerns a 90 m deep well in a 24 m thick sandstone aquifer of the Wapiti Formation confined by about 66 m of shale and clay till. The sandstone is described as consisting of lenticular beds that are not laterally extensive. The piezometric head in the aquifer was 39 m below ground level and available drawdown above the top of the aquifer (not quoted in the paper) appears to be about 30 m. The deeply incised valley of the Wapiti River, about 8 km south of the site is a prominent groundwater discharge feature which controls the regional groundwater flow. A 48 hour pumping test with an observation well showed almost ideal confined aquifer behavior. It gave a transmissivity of 15.5 m2/day and storativity of 3.3x10-4. A theoretical Q20 value of 255 m3/day was calculated, apparently using the Farvolden method as outlined in the Alberta Guidelines. The well was licensed for the requested use of up to 218 m3/day. Seven (7) domestic and commercial wells were identified within 1.6 km of the new well and analysis indicated that the available drawdown in these wells would be reduced by a maximum of 35%. Local concerns were addressed through a proactive communications strategy and public controversy was avoided. The hydrogeologic information given by George et al. (2003) allows a further evaluation of the Q20 method as applied in this case. The main concerns here are with the connectedness of the aquifer, and the extent and magnitude of the drawdown cone. The considerable depth of the piezometric surface below the ground level (39 m) strongly suggests that the sandstones are regionally extensive and connected, so that the confined aquifer in which the well and neighbouring wells are completed is drained very effectively to the Wapiti valley 8 km away. The Farvolden Q20 calculation of safe well yield, which assumes an infinite aquifer, is therefore reasonable but would not be applicable if the sandstone beds are indeed not laterally extensive. However, the confined nature of the aquifer and its extent mean that after 20 years the drawdown cone of the new well at a pumping rate of 218 m3/day will extend far beyond the 1.6 km of the field-verified well survey. A quick calculation shows that, after 20 years of pumping, drawdown

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of more than 0.5 m could occur out to a distance of 27 km from the well site (R20 as defined in this report). The large regional extent of the drawdown cone indicates that numerous wells may all impact each other to the point where the yield of each individual well could be seriously compromised. Evaluation of the impact of the new well on other wells, and vice versa, should therefore be carried out far beyond the distance of at least 1.6 km as required by the Alberta Guideline. Assessment of the safe well yield based on the Q20 method is therefore not appropriate and the need for a regional aquifer management plan is clearly indicated. 8.2.2 Town of Sexsmith George et al. (2003) also describe a groundwater allocation issue for the Town of Sexsmith, about 20 km north of Grand Prairie. Fewer details are provided, but the general hydrogeologic situation is similar to that of Silver Pointe Village, with perhaps more heterogeneous aquifer units. There are numerous wells in the area (104 water wells within 4 km of the well field in question) and conflicts arose over perceived risks to the future availability of groundwater resources. There was unusual sensitivity to such risks, in part because water levels in some of the wells were above or near ground surface so that drawdown would be very apparent and would involve a need for installing deep well pumps. Considering the possibility of extensive well interference in the similar hydrogeologic setting of Silver Pointe Village, the apprehension of risk to groundwater resources in the Sexsmith area may not be altogether misplaced. Here again reliance on single-well Q20 methods for determining safe well yield is questionable, and development of a regional aquifer management plan is advisable. 8.2.3 Innisfail and Olds, Alberta Bibby (1979) proposed a groundwater evaluation method for dealing with the highly heterogeneous nature of the Paskapoo Formation in southern Alberta. His report includes details of pumping tests and long-term pumping and water level histories for wells near Innisfail and Olds, Alberta. The case history of the Innisfail well is especially detailed, to the point that Bibby termed it the best-documented case history in Alberta. The Innisfail well was completed immediately beside the Red Deer River, with a screened section extending from 27 to 44 m depth (90 to 145 feet) in sandstone beds of the Paskapoo Formation. Bibby reproduced the 24-hour pumping test results for 41 wells completed in the Paskapoo Formation within 20 km of the Innisfail well, including the test on the Innisfail well itself. The 24-hour drawdown histories for all these tests show a wide variety of behaviors, very few of which correspond to any of the standard aquifer models. The local transmissivities, estimated on the basis of selected segments of “semilog straight line” behavior, vary from 0.07 to 790 m2/day (5 to 53,000 Igpd). Out of all the 41 wells that were tested the Innisfail well itself gave the highest transmissivity (790 m2/day). The average rate at which the Innisfail well was pumped increased gradually from 490 to 870 m3/day. Bibby (1979) provided an eight year history of pumping from the Innisfail well and water level records from a nearby observation well. The rate of pumping increased by about 75 % over the eight years, but the drawdown in the observation well increased from about 4 to about 12 m over the same time and showed no sign of coming to equilibrium. Bibby’s approximate analysis of the long-term drawdown near the well, assuming a fully confined aquifer, gave a transmissivity of 24 m2/day, smaller than the pumping test result by a factor of 30. The Q20 of the

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well, based on the 8 year record, is therefore correspondingly smaller by a factor of 30 than the value of about 10,000 m3/day that can be calculated by the Farvolden method from the original pumping test. Bibby (1979) also presented the pumping test results and subsequent pumping and water level histories for three production wells completed in the Paskapoo formation near Olds Alberta. The data for these wells are less complete and detailed, but the general pattern appears to be the same as for the Innisfail well, i.e. much smaller long-term transmissivity and no obvious sign of aquifer replenishment even after years of pumping and water level drawdown. These case histories illustrate very clearly that for heterogeneous aquifers, such as are common within the Paskapoo formation, Q20 estimates that are based on short-term pumping tests cannot be relied upon to reflect the long-term response of the well-aquifer system to pumping. This is particularly likely to be the case when high well yields are sought because the wells are then likely to be completed in the most permeable aquifer zones, often after considerable test drilling of less permeable low-yield locations. For such cases it is very likely that short-term testing will over-estimate the long-term safe yields of the wells. For such heterogeneous formations there will always be a high level of uncertainty in the estimates of safe well yields based on short-term pumping tests. However, the uncertainty can be reduced by extending the duration of pumping tests where large yields are sought. Recovery of the water levels after pumping ceases should be monitored for a very long time afterwards, preferably until the residual drawdown can no longer be distinguished from the background fluctuations of the water level (see section B8). In this manner the effects of the nearest boundaries of the permeable aquifer zone can be identified and incorporated in the evaluation of well yield. The lack of obvious aquifer replenishment, even after up to 8 years of pumping, is also a notable feature of these case histories, particularly for the Innisfail well, seeing that it is situated adjacent to the Red Deer River with a casing depth of only 27 m. The implication is that, in some places at least, there may be very poor vertical hydraulic connections within the Paskapoo Formation and very little induced replenishment due to the pumping. Thus evaluation of the long-term well yields should be done on the assumption of zero aquifer replenishment unless the data and hydrogeological setting clearly show the contrary. 8.2.4 Grand Rapids (Lower Mannville Formation) Aquifer Freeman and Pockar (2003) provide a thoughtful and valuable discussion of groundwater management and regulations in Alberta, dealing with cumulative effects of multiple wells, surface-groundwater interactions and water conservation. As an example, they describe the case of the Lower Mannville Grand Rapids Aquifer near Fort McMurray AB. This is an extensive regional aquifer, confined over much of the area in question by thick shale and glacial till. Several high yield groundwater extractions are envisioned so that cumulative impacts on the wells and on regional surface water bodies are all of concern. As implied by the authors, a Q20 approach to intensive groundwater development in such a regional aquifer is not appropriate. Instead a detailed regional three-dimensional hydrogeological model was developed to evaluate the impacts of the proposed withdrawals. One of the results of this model is that significant drawdown can be expected to extend up to tens of kilometers from the production wells.

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This case of the Grand Rapids aquifer serves to emphasize the point that in confined aquifers drawdown “cones” can indeed extend to many kilometers distance from production wells, and that single-well Q20 methods are not adequate for such cases once high-rate groundwater pumping is proposed. Cumulative impacts can be dealt with fairly readily when only a few high-rate industrial wells are proposed, as for the example described by Freeman and Pockar (2003). The case becomes much more problematic when numerous low-rate wells are involved, many of which have been in existence for years and with very little reliable information on pumping rates and long-term water level trends. Q20 methods are no longer appropriate if estimates of drawdown show that many wells are likely to be interfering with each other. However, development of a useful aquifer management plan will be greatly hampered if historic water level records are not available. A high priority should therefore be given to installing observation wells in such aquifers, in locations where the long-term water-level trends will not be obscured by highly transient drawdown due to pumping from one or two nearby wells. 8.2.5 Calgary Valley Aquifer Parks and Bentley (1996) describe the application of derivative methods for the evaluation of groundwater yields and estimates of Q20. They provide several examples of pumping tests carried out at various locations in the Calgary Valley Aquifer, a channel aquifer, incised into bedrock shale and confined by thick clay-rich glacial deposits. Such aquifers are common in the prairie region of Alberta and Saskatchewan. The interest of the examples given by Parks and Bentley resides in their detailed analysis of the rate of change of drawdown with time (the derivative) during pumping tests in the complex setting of the Calgary Valley Aquifer. The essence of this method is based on the Cooper and Jacob (1946) method of determining the transmissivity of confined aquifers from the slope of the drawdown curve on a plot of drawdown versus the logarithm of time (the semilog plot). Parks and Bentley suggest that late-time linear segments on the semilog plot can be used to estimate regional transmissivity and Q20 by the method of Farvolden. The actual pumping test data presented by Parks and Bentley show complex drawdown responses that are roughly consistent with the expected behavior for heterogeneous channel aquifers. The drawdown responses deviate from the simple straight-line behavior expected on the Cooper-Jacob model for confined aquifers of infinite extent. Instead the slope of the semilog drawdown plots tends to increase with time, and correspondingly the resulting values of Q20 tend to be smaller for later-time data. For most of the results it is not obvious that the late-time data of the pumping test show convergence to linear segments (i.e. a constant semilog derivative), which raises the question whether the values of Q20, calculated on the basis of linear segments, can be used with confidence to predict the long-term response of the aquifer to pumping. The use of “linear segments” of a complex semilog drawdown plot is subject to two major problems: firstly the fundamental Cooper-Jacob assumption of an extensive aquifer is violated for any complex aquifer with boundaries near the pumping well and secondly, the identification of “linear” segments tends to be a subjective matter with little or no theoretical or statistical backing. The examples shown by Parks and Bentley illustrate these concerns quite well as do the

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pumping test analyses for the heterogeneous Paskapoo Formation presented by Bibby (1979). Values of “local” or “regional” transmissivity” can be calculated by the “linear segment” approach but it usually not clear what these numbers mean. The corresponding numbers for Q20 are of dubious value and it is not surprising if they sometimes lead to major overestimates or underestimates of the long-term safe well yield. For such complex aquifer settings a simple “cookbook” Q20 approach is not appropriate and a cautious approach to groundwater allocations is indicated, based on professional hydrogeological judgment. 8.2.6 Multiple Wells in a Subdivision Hugo (2001) discussed the problem of groundwater allocations based on the Q20 approach where numerous closely spaced wells are envisioned, as might be the case for new subdivision. Their proposed method is based on the principle of superposition and is generally valid and useful because the principle of superposition is widely applicable for groundwater flow problems, irrespective of aquifer heterogeneity. The theoretical example that is presented by Hugo (2001) is instructive with regard to the extent of the drawdown “cone”. The authors evaluate the interference between eight (8) wells all located within 1 km of each other and show that the available drawdown for each well is not reduced to the extent that the safe yield of each well is unacceptably reduced. However, a rough estimate of the extent of the cumulative drawdown cone, based on the numbers given by the authors, shows that a drawdown of up to 0.5 m could be expected at a distance of 8 kilometers It is to be expected that in areas where new subdivisions are being developed there may be a very large number of wells within an 8 km radius. The cumulative drawdown due to all such wells may very well be large enough to reduce the yields of many of the wells beyond acceptable limits, apart from the likely impacts on surface water bodies. The authors do not discuss this concern, which falls outside the scope of their paper, but their example can be taken as another illustration of the need to deal with cumulative drawdown often well beyond the usual limits of 1 to 3 km suggested in the Alberta Groundwater guidelines. 8.3 Saskatchewan 8.3.1 Estevan Valley Aquifer 8.3.1.1 Introduction The Estevan Valley aquifer system in southeastern Saskatchewan is a major aquifer of the buried valley type and is one of the major preglacial buried valley aquifers in Saskatchewan. The aquifer system is unique in that it has been the subject of groundwater resources evaluations since the early 1960s. Because of these studies and the large amount of data collected, this system has become the reference system with regard to the peculiar behaviour of buried valley aquifers (e.g. van der Kamp and Maathuis, 2002; Maathuis and van der Kamp, 2003) The Estevan Valley aquifer system consists of the Yellowstone, Missouri, Estevan and “Northern” channel aquifers (Figure 9). These valleys were incised into the low-permeable silts and sands formed by the Eastend to Ravenscrag formations. The valleys were filled with predominantly coarse-grained sediment of the Empress Group, up to 80 m thick. However, over most of its extent the aquifer consists of an upper and lower unit, separated by a silt and clay

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layer. The aquifer is overlain by a 60 – 80 m thick aquitard which is composed mainly of clay-rich till but locally includes stratified sediments. Within Saskatchewan the aquifer is at least 70 km long and up to 4 km wide. 8.3.1.2 Pumping Tests In the period of March 4 – 12, 1965 an eight (8) day pumping test (11,520 min) was carried out at the “Macoun” site, about 21 km northwest of Estevan to determine the hydraulic properties of the Estevan valley aquifer at this location (Figure 9). The layout of the production and observation wells is shown in Figure 10. The pumping rate was about 3,010 m3/day (460 Igpm). The drawdown data were originally analyzed by Walton (1965) and were published by Walton (1970, page 258). Because the drawdown was affected by boundaries within the first 20 minutes of the test and due to the short distances between the pumping well and observation wells #1 and #2, only the data for observation well #3 were analyzed by Walton (Figure 11). Using the Theis type curve analysis, the drawdown data for observation well #3 showed a transmissivity of about 2,800 m2/day (180,000 Igpm/ft) and a storage coefficient of 2.2 x 10-4. Based on an available drawdown of 73 m and using the Farvolden method, the transmissivity calculated by Walton would yield a Q20 of 97,720 m3/day. Using the approach commonly used to calculate the Q20 (i.e. determination of the “regional” transmissivity), Figure 12 shows the drawdown versus time and the straight lines fitted through the latter part of the drawdown data. The average ∆sp equals 2.04 m, translating to a “regional” transmissivity T of about 270 m2/day and a corresponding Farvolden Q20 of 9,425 m3/day. The original Moell method (equation [15]), with s100 = 2.46 m (8.08 ft), gives a Q20 of 12,150 m3/day. In 1984, a 29 day (September 17 – October 15) pumping test was conducted at a rate of 6,537 m3/day on well PW2UL (renamed later PW4UL), followed by recovery measurements till August 2, 1985. The locations of the production well and selected observation wells are shown in Figure 9. Figure 13 shows a semi-log plot of the drawdown versus time for the production well as well as for selected observation wells. The drawdown data were extended to 317 days using the recovery data, using the method described in Appendix B, section B.8. The static water level in PW4UL was about 5.4 m below ground level (bgl) and the top of the Estevan Valley aquifer is at 61.3 m bgl, giving an available drawdown of about 56 m. Based on the drawdown data for the production well, and using the approach commonly used to calculate Q20, Table 8 shows the calculated “regional” transmissivity and resulting Farvolden Q20 and original Moell Q20, for various assumed durations of the pumping test.

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Table 8 “Regional” transmissivities and resulting Q20 for 1984 Estevan Valley aquifer pumping test data, for assumed durations of the pumping test

Duration

of test ∆s (m)

“Regional”

Transmissivity (m2/day)

Q20 Farvolden (m3/day)

1 day 1.65 725 19,425 5 days 3.1 385 10,340 29 days 5.35 225 5,990 317 days 11.93 100 2,690

This Table 8 further illustrates that the use of “linear segments” of a complex semilog drawdown plot to determine values of “regional” transmissivity” and corresponding Q20’s, leads to dubious answers. The Table indicates in particular that short tern pumping tests may lead to gross overestimates of the long-term yield. Using the modified Vandenberg type curves (see Appendix B, section B.6), van der Kamp and Maathuis (2002) calculated a transmissivity of the aquifer of about 1,380 m2/day and a L value of 37 kilometers. According to the Alberta Environment Guidelines this transmissivity value, which was obtained using the appropriate aquifer model, has then to be applied to either the Farvolden or Moell method for calculation of the Q20. Using the Farvolden method, the resulting Q20 would be 30,250 m3/day. The corresponding R20 would be 202 kilometers (assuming an infinite length of the aquifer). 8.3.1.3 Sustainable Pumping Yield of the Estevan Valley Aquifer System Over the past four (4) decades several attempts have been made to estimate the yield of the aquifer (Table 9). Table 9 Estimated sustainable pumping rate of the Estevan Valley aquifer

Estimated yield (dam3/a)

Reference Method

16,000 Walton (1965, 1970) electrical analog model 11,000 Meneley (1972) image well theory 20,000 Puodziunas (1977) image well theory applied to a rectangular strip

aquifer 5,250 Beckie and Pasloske, 1985 calculated by assuming recharge equal to 5%

of precipitation 2,900 - 5,300 van der Kamp, 1985 numerical model

4,500 Maathuis and van der Kamp, 1989 172 days of pumping data and channel aquifer type curves

4,000 Van Stempvoort and Simpson, 1994 performance of aquifer

2,400 - 2,800 Maathuis and van der Kamp, 1998 actual performance of aquifer, after 6 years of pumping and 3 yrs of recovery

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An analysis of the drawdown/recovery (Maathuis and van der Kamp, 1998) showed that at the end of the pumping period steady-state conditions were not reached and that water levels would have continued to drop if pumping would have continued at the average rate of 10,270 m3/day. Based on water levels not dropping below the top of the aquifer in the well field area, they revised the long-term sustainable yield of the aquifer down to 6,575 – 7,670 m3/day (2,400 – 2,800 dam3/a). 8.3.1.4 Discussion Buried valley aquifers are common in the glaciated terrain of North America (e.g. Maathuis and Thorleifson, 2000; Shaver and Pusc, 1992; van der Kamp, 1986). However, increasing evidence is found that these types of aquifers, while longitudinally extensive, are not continuous and that the continuity is interrupted by low transmissivity barriers (Shaver and Pusc, 1992; Meneley, 1970). What causes these barriers remains a matter of speculation. If monitor wells have been installed throughout a buried valley aquifer prior to significant withdrawals, the presence of a barrier can be identified if there is a large hydraulic head difference between monitor wells (e.g. the Estevan valley aquifer case). In other cases, a barrier or barriers only become apparent when the aquifer is stressed by pumping (e.g. Maathuis, 2005). Rarely have barriers been found by exploratory testhole drilling. The Estevan case history allows for the following observations:

● Buried valley aquifers are of finite extent and are bounded on all sides by low-permeable units and can be considered a “bucket’ type of aquifer.

● Because of their hydrogeological setting (long, narrow, highly transmissive and bounded on all sides), pumping-induced drawdowns in buried valley aquifers may extend over tens of kilometers on each side of a production well or well field.

● In a “bucket” type of aquifer, a drawdown cone initially will be created within the well field area but as pumping continues the water levels will drop throughout the entire area by about the same amount. Additional recharge to the aquifer is induced by the drawdown of the water levels in the aquifer. The drawdown will continue until pumping balances the lateral and vertical recharge, or in the case that the pumping rate exceeds the maximum possible recharge, will continue to drop indefinitely until pumping becomes unpractical.

● After pumping has ceased there will be a rapid infilling of the drawdown cone in the well field area, by lateral flow toward the pumping centre. A general flattening of the water levels will occur and throughout the entire aquifer there will be similar amounts of residual drawdown.

● As with any type of semi-confined aquifer, the rate of recovery will decrease with time and depending on the hydrogeological setting, complete recovery may take a long time.

● As with any type of aquifer, reliable estimates of the maximum sustainable pumping rate can only be made if long-term pumping and water level data are available.

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8.3.2 Senlac Area, Saskatchewan In the Senlac area, a groundwater supply was needed as a water source to generate steam for recovery of heavy oil. An initial production and observation well was constructed in 1984 (EBA, 1984). In 1995, five (5) additional production wells and four (4) observation wells were drilled (Golder Associates, 1995). The locations of these production and observation wells are shown in Figure 14. This Figure also shows the location of wells survey (3 km radius) and cross section lines. To illustrate the geological setting cross section A – A’ is shown in Figure 15 (see Figure 14 for location of the cross section line). The site is characterized by drift (30 m) overlying sediments of the Judith River Formation (Oldman Formation in Alberta). The Judith River Formation is a heterogeneous formation composed of sand and silt, and silt and clay units, forming the Judith River aquifer system. At the well field site the aquifer system was subdivided into an upper and lower aquifer unit separated by a silt and clay unit (see Figure 15). All the production wells were completed in the lower Judith River aquifer unit. A step-drawdown test (5 steps each lasting 10 min) was carried out on each production well and subsequently, a 24 + 24 hr pumping/recovery test was conducted. Transmissivity and, if applicable storativity, values were determined using the Cooper and Jacob method (Golder Associates, 1995). Based on the reported calculated transmissivities, and using the common definition of available drawdown (depth to top of aquifer – depth to static water level), Table 10 shows the corresponding Farvolden Q20 (equation [9]). Table 10 Farvolden Q20 for Senlac production wells, based on top of Judith River

Formation

Production well

Depth to top Judith River Fm

(m)

Static water level

(m)

Available drawdown to top of aquifer

(m)

T

(m2/day)

Farvolden Q20

Top aquifer

(m3/day)

WSW-1 45.7 15.7 30 16 229 WSW-2 52.4 20.4 32 29 444 WSW-3 48.2 18.1 30.1 12.5 185 WSW-4 32.3 6.3 26 20 248 WSW-5 51.8 9.4 42.4 31 628 WSW-6 46.3 8.9 37.4 34 608

Available drawdown: depth to top aquifer – static water level Considering that the production wells were completed in the lower Judith River aquifer, a different approach was used in assessing the long-term yield of the production wells (Golder, 1995). The available drawdown was taken as: depth to top of screen – static water level – 4 m. The 4 m is arbitrary safety factor to assure that the water level will remain above the top of the screen. Based on this definition of available drawdown Table 11 shows the associated Farvolden Q20’s.

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Table 11 Farvolden Q20 for Senlac production wells, based on depth to top of screen

Production well

Depth to top Screen

(m)

Static water level

(m)

Available drawdown To top of

screen (m)

T (m2/day)

Farvolden Q20

Top of screen

(m3/day) WSW-1 90.5 15.7 70.8 16 542 WSW-2 99.4 20.4 75 29 1040 WSW-3 92.1 18.1 70.1 12.5 419 WSW-4 85.4 6.3 75.1 20 718 WSW-5 87.2 9.4 73.8 31 1094 WSW-6 103.9 8.9 90 34 1463

Available drawdown: depth to top of screen – static water level – 4 m The approach taken by Golder (1995) results in much higher Farvolden Q20’s because of the larger available heads when the top of the screen rather than the top of the aquifer is taken as base for calculation of the available head. In Table 12, a comparison is provided of the allocated and actual, production, the measured drawdown during the final year of production, Farvolden Q20’s based on top of screen and top of aquifer and the estimated long-term pumping rates based on a numerical model which included well interference (Golder, 1985). The numerical model did not include the impact of pumping from WSW-6 as this well was considered the back-up well. Table 12 Comparison of allocated, actual, Farvolden Q20 and estimated pumping rates

for the Senlac production wells

Allocated volume

Actual production

Available drawdown

x 0.7

Estimated actual drawdown

Farvolden Q20

top of aquifer

Farvolden Q20

top of screen

Estimated Q (Golder, 1995) Interference included

Production well name

m3/day m3/day m m m3/day m3/day m3/day WSW-1 521 488 50 46 229 542 524 WSW-2 589 528 53 35 444 1040 590 WSW-3 389 240 49 28 185 419 393 WSW-4 400 293 53 23 248 718 400 WSW-5 400 263 52 34 628 1094 400 WSW-6 389 64 63 16 608 1463 not available Total 2688 1876 1713note 3813note 2307note

Note: Total does not include WSW-6 as this production wells is a standby well This Table shows that the actual volumes produced were less than the allocated and estimated volumes and significantly less than the Farvolden Q20

(top of screen). The actual pumping was about 70% of the allocated volume. The actual drawdowns in the production wells after 7 years of pumping averaged about 60 % of the available drawdowns, indicating that estimated sustainable rates including well interference (Golder, 1995) and the allocated rates were at best marginally sustainable for longer pumping. The Farvolden Q20 rates based on the top of the well screens would not have been sustainable, even for 7 years of pumping.

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In Figure 16, the hydrographs are shown for the observation wells in the Senlac area, together with the combined monthly pumping volumes. Figure 17 shows the drawdown in the distant observation wells and the average drawdown in the production wells, plotted against time on a semi-log scale. The data suggest that even after 7 years of pumping the there was still no indication of equilibrium. The drawdown in the distant observation well OW6 (about 4,000 m from the centre of the well field) can be matched fairly well assuming a fully confined aquifer with transmissivity T of 110 m2/day and a storativity S of 0.0012 (Figure 17). This value of T is about 5 times larger than the average T at the pumping wells, perhaps because at this distance from the well field the upper portion of the aquifer effectively contributes to the overall flow to the wells. Assuming that the aquifer is infinite and fully confined a value of R20, the radius of influence of the well field, can be calculated using the values of T and S determined from observation well OW6. The calculation shows that for the actual total monthly production rates, a drawdown of 0.5 m would be observed at a distance 24.9 km after 7 years of pumping. If pumping would have continued after 7 years at a rate of 2.052 m3/day (average rate between November 1998 and March 2003), a drawdown of 0.5 m after 20 years of pumping would have been observed at a distance of about 45 km. The monitoring data for this case therefore indicate that the influence of the pumping may have extended to a very large distance. This case history illustrates the value of long-term monitoring of the aquifer under pumping stress in order to obtain reliable evaluation of the sustainable yield. It is also clear that a simple Q20 approach is not appropriate for such complex cases of multiple wells in a real aquifer. The zone of influence of the pumping may have been very large, extending outward to tens of km from the well field. It is unlikely therefore that all possible impacts on other groundwater users and on surface water were fully identified.

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9.0 SUSTAINABLE YIELDS OF AQUIFERS 9.1 Introduction In the previous sections the long-term yield of a single well discussed. In addition to providing a long-term well yield, both the Alberta groundwater evaluation guidelines (Alberta Environment, 2003, p.13) and the Saskatchewan Watershed Authority guidelines appear to imply that a proponent of a groundwater development provides information on the long-term (“safe”) yield of the aquifer. The concept of defining the desirable development of groundwater resources remains as relevant today as it was 100 years ago. Over time, however, the focus has shifted from “pure” groundwater resource development to integrated water resources management, typically meaning watershed-based groundwater – surface water management. This, in turn, is closely related to the transition of the concept of safe yield to the concept of sustainability (e.g. Alley and Leake, 2004). 9.2 History of Terminology A brief history of the development of the yield concepts has been provided by Alley and Leake (2004). A comprehensive listing of concepts and definitions recently was provided by Kalf and Woolley (2005). A brief summary is provided below. The term ‘safe yield’ was introduced by Lee (1915) who defined annual safe yield as “the quantity of water that can be pumped regularly and permanently without dangerous depletion of the storage reservoir”. Meinzer (1923, p 55) defines the safe yield of an aquifer as “the rate at which water can be withdrawn from an aquifer for human use without depleting the supply to such an extent that withdrawal at this rate is no longer economically feasible”. As documented by Mann (1963), the definition of safe yield was expanded to include considerations, such as not to induce undesirable water quality changes (Conkling, 1946), and not to interfere with prior rights (Banks, 1953). Todd (1959, p. 200) defines the safe yield of a groundwater basin as “the amount of water which can be withdrawn from it annually without producing an undesired result”. He discusses four categories of undesirable results: water supply availability (i.e. safe yield can not exceed long-time mean annual water supply to the basin as otherwise there would be mining of groundwater), economics (i.e. excessive cost of pumping), water quality (i.e. pumping-induced changes in water quality such as induced seawater intrusion) and water rights (i.e. interference with prior water right within or in adjacent basins). He also mentions that other factors such as pumping-induced land subsidence could limit the safe yield. Todd (1959, page 212) further states that “any determination of safe yield is based on specified conditions, either existing or assumed, and any changes in these conditions will change the safe yield”. The term safe yield of an aquifer simply is the amount of water that can be withdrawn from the aquifer (or aquifer system) based on the hydraulic characteristics of the aquifer (or aquifer

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system), subject to specified conditions. Other terms used for safe yield are “perennial yield”, “sustained yield” (Mann, 1963), and more recently, “sustainable pumping” (Devlin and Sophocleous, 2005). The Brundtland Commission report (World Commission on Environment and Development, 1987) defines sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. While it is obvious that with respect to groundwater resources the concepts of safe yield and sustainability of a groundwater resource are closely related, sustainability is a much more encompassing concept. Sustainability of groundwater resources is linked to the biosphere, bio-diversity of ecosystems, human activities and welfare (e.g. Alley et al., 1999; Alley and Leake, 2004; Devlin and Sophocleous, 2005). Although the concepts of safe yield (sustainable pumping) and sustainability (sustainable development) have a number of constraining factors in common, because of the broader definition of sustainability, a safe yield may not be sustainable (Sophocleous, 1997; Devlin and Sophocleous, 2005). Both the development of a safe or sustainable yield can not be done without explicitly stating the assumptions on which it is based, and may have to include a time component. Neither a safe or sustainable yield can have a fixed value as physical parameters may change over time. For example: changes in land use activities, climate variability and climate change will over time impact the hydrologic cycle (Alley and Leake, 2004; Sophocleous, 2004). Furthermore, the way society views and values water and the environment are subject to change over time. 9.3 Sustainable Pumping Rate It has been a common misconception that the development of a groundwater resource is safe if the average annual rate of groundwater withdrawals does not exceed the average annual rate of natural recharge. In the literature this safe yield concept is referred to as the Water Budget Myth (Bredehoeft et al., 1982; Bredehoeft, 1997; Bredehoeft, 2002). Theis (1940, p. 227) stated: “Under natural conditions, previous to development by wells, aquifers are in a state of approximate dynamic equilibrium. Discharge by wells is thus a new discharge superimposed upon a stable system, and it must be balanced by an increase in recharge of the aquifer, or by a decrease in the old discharge, or by loss of storage in the aquifer, or by a combination of these”. Based on Theis (1940), Bredehoeft and Young (1970), Bredehoeft et al. (1982), Bredehoeft (2002), and Devlin and Sophocleous (2005) have repeatedly demonstrated that the Water Budget Myth is an invalid concept. Prior to any development, steady-state conditions prevail in most groundwater flow systems and natural recharge will balance the natural discharge:

000 =− DR [28] where: R0 is the mean “virgin” recharge and D0 the mean “virgin’ discharge.

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To have a groundwater development, some disturbance of the system is necessary. At some time, t, after the start of a groundwater development, equation [28] becomes:

( ) ( ) 00000 =+−Δ+−Δ+ dtdvQDDRR K [29]

where; ∆R0 = the change in mean recharge rate, ∆D0 the change in the mean discharge, QK withdrawal rate and dt

dv the rate of change in storage of the groundwater system.

The objective of arriving at a sustainable aquifer pumping rate is establishing a new equilibrium (steady-state condition) at some point in time after pumping started. In other words, dt

dv = 0.

Since R0 = D0, equation [29] simplifies to:

00 DRQK Δ−Δ= [30] In the literature the term (∆R0 - ∆D0) is referred to as “capture”. The significance of equation [30] is that the virgin recharge and discharge do not need to be known to estimate the sustainable pumping (Bredehoeft et. al., 1982; Bredehoeft, 2002; Devlin and Sophocleous, 2005). Equation [30] states that the sustainable pumping from an aquifer, or aquifer system, must result in establishment of a new, and acceptable, steady-state condition and that under these circumstances the yield comes from an increase in recharge and/or decrease in discharge. As pointed out by Devlin and Sophocleous (2005), the natural discharge from the aquifer is reduced by pumping; therefore, ∆D0 is actually a negative number. In other words, the sustainable pumping rate can be larger than the changes in either recharge or discharge rates alone (Devlin and Sophocleous, 2005). With regard to pumping water from a surficial aquifer (water table aquifer) for irrigation purposes, Devlin and Sophocleous (2005), based on a discussion by Kendy (2003), suggested that the term “net” pumping rate would be more appropriate as a portion of the water pumped may return to the aquifer as recharge. Sophocleous and Delvin (2004) argued that although sustainable pumping rates depend on changes in recharge and discharge rates, determination of sustainability requires knowledge about recharge rates. The sustainable pumping rate of a well or well field depends on the geometry of the aquifer and on the location of the well(s) relative to the recharge and discharge zones. In addition, it must be realized that it will take time for a new equilibrium to establish itself. It is difficult to envision how pumping from surficial aquifers in the Prairies will result in an actual increase in the mean annual recharge (∆R0). Consequently, with respect to surficial aquifers, much, if not all, of the capture will have to come from a reduction in discharge (∆D0). This could be in the form of a reduction in the volume of discharge to a surface water body or as a reduction in evatranspiration, With respect to semi-confined aquifers in the Prairie Provinces a sustainable pumping rate might be achieved by a combination of increase in recharge and decrease in discharge. In his calculation of yield of major aquifers in Saskatchewan, Meneley (1972) only considered the term ∆R0 (increase in vertical replenishment) and referred to that as the net groundwater

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yield. He argued that with respect to groundwater resources in a basin the decrease ∆D0 can not be credited as a net increase in water resources in a basin as the decrease merely reduces the amount of surface outflow. Since all the major high yield aquifers in Saskatchewan are semi-confined aquifers, the net groundwater yield was calculated from:

Ab

KHA

cHARQ vAA

net '

'

=Δ= [31]

where: Qnet is the net groundwater yield (m3/day), ∆HA (m) the average change in hydraulic head in the aquifer and A the surface area of the aquifer (m2) and c is the vertical hydraulic resistance (days). As used by Meneley (1970), equation [32] states that the net groundwater yield of a semi-confined aquifer is dependent on pumping-induced increase in the vertical replenishment to the semi-confined aquifer, by an increase in the vertical hydraulic gradient. The Qnet is a function of the actual available drawdown and an upper limit for ∆R0. The maximum amount of vertical replenishment, assuming that the water table is not affected, is achieved when ∆HA=b’ (unit gradient). Then, per unit area (A=1), equation [31] becomes:

'vnet KQ = [32]

In general, it may not be practical to lower the water level throughout an entire aquifer to the top of the aquifer because of the large number of wells required. However, for most semi-confined aquifers there will be sufficient available drawdown to induce ∆R0 to the limit set. The yield of aquifers with a good hydraulic connection to a surface water body (i.e. alluvial aquifer, buried valley aquifers underlying rivers with a significant amount of alluvial fill, aquifers in hydraulic connection to reservoirs etc.) can be significant. However, water from such aquifers is derived from induced recharge/replenishment from surface waters. In such cases aquifers merely perform a transfer function and their yield can not be considered an addition to the water resources of a basin. 9.4 Watershed-based Water Resource Management Throughout the world water resources managers have come to the realization that surface water and groundwater should be managed as an integrated resource rather than as separate resources. In recent years, Saskatchewan issued its “Water Management Framework” (Saskatchewan, 1999), Alberta its “Water for life. Alberta’s strategy for sustainability” (Alberta, 2003), and Manitoba “The Manitoba Water Strategy” (Manitoba Water Stewardship, 2003). Elsewhere, the European Union issued its European Water Framework Directive (European Parliament and of the Council, 2000). This directive, focused on both water quality and quantity protection, will have a profound impact on watershed-based integrated management of the water resources in Europe. In Saskatchewan, planning for watershed-based water resource management is underway in six watersheds (North Saskatchewan River, South Saskatchewan River, Upper Qu'Appelle River, Moose Jaw River, Upper Assiniboine River, and Lower Souris). The primary focus of the watershed and aquifer management planning process will be to protect and secure source water

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to ensure present and future safe drinking water needs are met. However, activities designed to address these issues are expected to have a positive impact on other water-related and ecological issues within the planning area http://www.swa.ca/Stewardship/WatershedPlanning/Default.asp). While in one case, the Upper Assiniboine River basin, groundwater resources have been included in the planning process, this still needs to be done for the other 5 watersheds. Because groundwater constitutes only a small percentages of the allocated water resources in Alberta, watershed-based water resource management plans tends to focus solely on surface water aspects and on the well being of ecologic systems. Even major watershed based plans, such as the one developed for the South Saskatchewan River basin, neglect the groundwater resources and groundwater - surface water interactions. 9.5 Aquifer Management Plans Aquifer management plans are not new nor is the general approach to establishing an aquifer management plan. The technical components of an aquifer management plan typically are (e.g. Banga et al., 1994): ● establishment of comprehensive geological and hydrogeological databases ● establishment of the geological and hydrogeological settings ● comprehensive evaluation of the groundwater resources ● evaluation of past groundwater use and prediction of future use ● development of a groundwater allocation plan ● development of a groundwater protection plan ● development of monitoring programs ● education plan From an organisational point of view, the development of an aquifer management plan is based on consensus building, with a stakeholders group being the central and most critical unit. For the technical aspects the stakeholder group is supported by, and in part provide guidance to, a technical support group. Although more and more driven by governmental policies, in particular those related to source water protection and groundwater supply sustainability, there are other reasons for starting aquifer management plans. Another important reason is highlighted in this report and is related to the R20 concept. The development of an aquifer management plan for the Regina area in Saskatchewan was started in the mid 1980s, and probably was the first aquifer management plan to be started in the Prairie Provinces. The development of the plan was driven by the fact that at the time groundwater, obtained from several well fields, constituted 30% of the total municipal water supply for the City of Regina, but no Water Rights Licenses were issued for the production wells. Because these well fields were in operation for decades there were no quantity issues as such, but little was known about the aquifers in which the production wells were completed and their long-term yield. The Saskatchewan Southeast aquifer management plan was initiated in the later 1980s in response to a plan to withdraw large amounts of water from the Estevan Valley and the Tableland aquifer systems. At that time little was know about the water resources in these

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aquifers and the potential impact of the proposed withdrawals on these aquifers, adjacent and overlying aquifers and surface waters. The City Of Yorkton is totally dependent on groundwater for its municipal water supply (Maathuis, 1991). The City obtains its water from several aquifers systems. As was the case for the City of Regina, the absence of Water Rights licences for the City of Yorkton production wells formed the impetus for the starting the development of an aquifer management plan. The plan was started in the early 1990s and, after a decade of collecting additional information, it is now being finalized. The Town of Edson, Alberta, and its surrounding area, depends on groundwater for its water supply. Continuous development of the Town and area and concerns about the sustainability of these groundwater resources formed the impetus for the development of an aquifer management plan (Komex International Ltd., 2001). Water quantity was the major concern driving the development of the Milk River aquifer reclamation and conservation plan (Printz, 2004). Community-based concern regarding the wise use of groundwater and the protection of this resources lead to the development of management strategies for the Grimshaw aquifer (Agriculture and Agri-Food Canada, 1998). In Manitoba, aquifer management plans have been developed for a numbers of aquifers, including the Winkler and Oak Lake aquifers. The aquifer plans were developed in response to local concerns regarding groundwater supplies. The Assiniboine Delta Aquifer is the focus of the province’s aquifer management planning.

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10.0 CONCLUSIONS AND RECOMMENDATIONS

● The Farvolden Q20 concept is a flawed concept and, as is demonstrated in this report, may result in estimates of long-term well yields which are not conservative as commonly is assumed. Rather, the Q20 gives estimates that are considerably higher than Q20’s based on actual aquifer models. This statement is valid for water table, semi-confined and confined aquifers and, in particular, for buried valley aquifers. Farvolden Q20 estimates for wells completed in a buried valley aquifer significantly overestimate the long-term well yield, due to a large degree to the geometry of such aquifers.

● The use of the Farvolden Q20 should be discontinued and instead the following

modified Moell equation (Alberta Environment, 2003, page 13) should be used: ( )[ ]

theoryrstAf sssQHSQ min10020min10020 /** −+=

The estimate of s20yrs should preferably be based on applying the appropriate aquifer model, rather than on determining a ∆sp (drawdown per log cycle).

● To allow for obtaining actual drawdown data at 100 min, the following revision to

the suggested water level monitoring frequency (Alberta Environment, 2003, page 12) is proposed:

From 0 to 10 minutes* every minute From 10 to 30 minutes* every 5 minutes From 30 minutes to 2 hours* every 10 minutes From 2 to 4 hours every 30 minutes From 4 to 12 hours every hour From 12 to 24 hours every 2 hours From 24 to 36 hours every 4 hours From 36 to 48 hours every 6 hours After 48 hours every 8 to 12 hours

* suggested revision

● In analogy to the Q20 concept, this report introduces the R20 concept. R20 is defined as the distance from the pumping well where the drawdown after 20 years of pumping at a rate of Q20 equals a pre-set drawdown limit SR20. In practice, requested withdrawals (Qr) will be less than Q20. Therefore, the R20 (R20r) based on Qr will be less than the R20 based on Q20. It is recommended that R20r be based on the annual average pumping rate and not on the maximum daily rate. It is the R20r that should be used in determining to which distance a field survey of well should be conducted, and to decide whether or not an aquifer management plan should be developed.

● Apparent transmissivities and associated apparent Q20’s, as calculated from short-

term pumping tests (the typical 2+2 hr) have little meaning. In approving requested groundwater allocations for pumping rates less than 10 m3/day, the specific capacity of the well should be used as a guide to estimate the safe pumping yield of a well.

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● For all pumping tests of 24 hrs or longer, recovery measurements should be continued until near full (95%) recovery.

● In all cases, the estimate of the long-term yield of a well should be based on the

results of pumping tests, using appropriate aquifer models, and in combination with the professional judgments of the hydrogeologist. Long-term yield estimates should never be solely based on prescribed procedures for calculation of Q20’s.

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11.0 REFERENCES Agriculture and Agri-Food Canada, 1998. Proposed Community-focused Management Strategy

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Saskatchewan experience. In Proceedings 47th Canadian Water Resources Association Conference, Winnipeg, June 14-17, pp.273 – 282.

Beckie, V.G., and Pasloske, G.R. 1985. Estevan Valley Aquifer System. Exploration and pump

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Bredehoeft, J.D. 2002. The water budget myth revisited: why hydrogeologists model. Ground Water, Vol. 40, No. 4, pp 345-340. Bredehoeft, J.D., and Young, R.A. 1970. The temporal allocation of ground water; a simulation

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surrounding areas. Komex International Ltd., Calgary Kruseman, G.P., and N.A. de Ridder. 1990. Analysis and evaluation of pumping test data

(second edition). International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands, ILRI Publication 47, 377 p.

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Maathuis, H. and Thorleifson, L.H., 2000. Potential impact of climate change on prairie groundwater supplies: review of current knowledge. Saskatchewan Research Council, Publication No. 11304-2E00, 43 p.

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Valley aquifer in southeastern Saskatchewan; a 40-year historical perspective. Proceedings 4th Joint IAH/CNC-CGS Conference, Winnipeg, Volume I, pp. 293 – 296. (CD-rom)

Maathuis, H., and van der Kamp, G. 1989. Preliminary evaluation of the Estevan Valley and

Tableland Aquifers. Saskatchewan Research Council Report R-1220-2-E-89, 69 pp. Maathuis, H. and van der Kamp, G. 1998. Evaluation of pumping and recovery data for the

Estevan and tableland aquifers. Saskatchewan Research Council, Publication No. 10421-1C98, 28 p.

Maathuis, H., 1991. Evaluation of the groundwater resources in the Yorkton area. Interim report.

Saskatchewan Research Council, Publication No. R-1220-7-B-91, 165 p. Maathuis, H., and van der Kamp, G. 1986. Groundwater observation well network in

Saskatchewan, Canada. Proceedings of Canadian Hydrology Symposium No. 16, National Research Council Canada, NRCC No. 25514, pp. 565-581.

Manitoba Water Stewardship. 2003. The Manitoba water strategy. Manitoba Water Stewardship,

27 p. (http://www.gov.mb.ca/waterstewardship/waterstrategy/pdf/water-strategy.pdf) Mann, J.F. 1963. Factors affecting the safe yield of ground-water basins. Transactions American Society of Civil Engineers, Volume 128, pp. 180 – 190. Meinzer, O.E. 1923. Outline of groundwater hydrology, with definitions. US Geological Survey, Water Supply Paper 494. Meneley, W.A. 1972. Saskatchewan. In Water Supply for the Saskatchewan-Nelson Basin,

Appendix 7: Environmental Considerations, Section F: Groundwater, pp. 673-723. Saskatchewan-Nelson Basin Board.

Ministry of Environment and Energy, 1994. Water management. Policies. Guidelines. Provincial

water quality objectives. Ontario Ministry of Environment and Energy, Queens’ printer for Ontario, PIBS 3303e, 67 p. (http://www.ene.gov.on.ca/envision/gp/3303e.pdf)

MOE (Ontario Ministry of the Environment). 2005a. Permit to take water (PTTW). Manual.

Ministry of the Environment, Queens Printer for Ontario, PIBS 4932e (http://www.ene.gov.on.ca/envision/gp/4932e.pdf)

MOE (Ontario Ministry of the Environment). 2005b. Guide to permit to take water application

form. Ministry of the Environment, Queens Printer for Ontario, PIBS 5046e http://www.ene.gov.on.ca/envision/gp/5046e.pdf

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 53

Moell, C.E. 1975. Guidelines – groundwater supply evaluations, for residential subdivisions – single family wells. Alberta Environment, Earth Sciences and Licensing Division, Report No. 1617, 8 p.

Moell, C.E. and Schnurr, P. 1976. Groundwater availability in the Onoway map area, Alberta.

Alberta Environment, Earth Sciences and Licensing Division, Report No. 1514, 8 p. Nova Scotia Environment and Labour. 2004. Guide to groundwater withdrawal approvals.

Nova Scotia Environment and Labour, Water and waste Water, 16 p. (http://www.gov.ns.ca/enla/water/pdf/guideToGroundwaterWithdrawalApprovals.pdf) Nowlan, L. 2005 Buried Treasure - Groundwater permitting and pricing in Canada. Walter and Duncan Gordon Foundation (http://www.gordonfn.org/) Ozoray, G.F. 1970. Nomogram for determination of apparent transmissivity. Alberta research

Council, Internal report, 4p. Ozoray, G.F. 1972. Hydrogeology of the Wabamun Lake area, Alberta. Alberta Research

Council, Report 72-8, 19 p. Ozoray, G.F. 1977. Apparent transmissivity and its determination by nomogram. In

Contributions to the hydrogeology of Alberta, Alberta Research Council, Bulletin 35, p.13 – 17.

Ozoray, G.F. 1977. Apparent transmissivity and its determination by nomogram. In

Contributions to the hydrogeology of Alberta, Alberta Research Council, Bulletin 35, pp13 -17.

Parks, K.P. and Bentley, L.R. 1996. Derivative-assisted evaluation of well yields in a

heterogeneous aquifer. Canadian Geotechnical Journal, Vol. 33, No. 3, pp 458-469. Printz, J. 2004 Milk River aquifer reclamation and conservation program. 1999-2004

Summary report. Agriculture and Agri-Food Canada, PFRA, online report, http://www.agr.gc.ca/pfra/water/reports/aquifer_e.pdf

Pupp, Ch., Stein, R., and Grove, G. 1989. Groundwater quality in Alberta: hydrogeology,

quality concerns, management. Environment Canada, NHRI Contribution No. 89051, 113 p.

Pupp, Ch., Maathuis, H., and Grove, G. 1991. Groundwater quality in Saskatchewan:

hydrogeology, quality concerns, management. Environment Canada, NHRI Contribution CS91028, 66p.

Rivera, A., Allen, D.M, and Maathuis, H. 2004. Climate variability and change – groundwater

resources. In Threats to water availability in Canada, Environment Canada, NWRI Scientific Assessment Report Series No. 3 and ACSD Science Assessment Series No.1, Chapter 10, pp. 77 – 83.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 54

Saskatchewan. 1999. Water management framework. Government of Saskatchewan, 36 p. (http://www.se.gov.sk.ca/ecosystem/water/framework/)

Saskatchewan Watershed Authority, 1999. Fact sheet: groundwater relating to the construction

and or operation of groundwater works and rights to use groundwater. Saskatchewan Watershed Authority, Moose Jaw.

Shaver, R.B. and S. W. Pusc, 1992. Hydraulic barriers in Pleistocene buried-valley aquifers.

Ground Water, Vol. 30, No. 1, 21-28. Sophocleous, M. 1997. Managing water resources systems; why “safe” yield is not sustainable.

Ground Water, Vol. 35, No.4, p. 561. Sophocleous, M. 2004. Climate change: why should water professionals care? Ground Water, Volume 42, No. 5, p. 637. Sophocleous, M., and Delvin, J.F. Discussion “The water budget myth revisited: why

hydrogeologists model”, Bredehoeft, J.D. 2002. Ground Water, Volume 42, No. 4, p. 618.

Theis, C.V. 1935. The relation between the lowering of the piezometric surface and the rate and

duration of discharge of a well using ground-water storage. Transactions American Geophysical Union, Vol. 16, pp. 519-524.

Theis, C.V. 1940. The source of water derived from wells; essential factors controlling the

response of an aquifer to development. Civil Engineer, 10, pp 277-280. Todd, D.K. 1959. Ground water hydrology. John Wiley & Sons, New York, 336 p. Tóth, J. 1966. Groundwater geology, movement, chemistry, and resources near Olds, Alberta.

Alberta Research Council, Bulletin 17, 126 p. van der Kamp, 1985. Yield estimates for the Estevan Valley Aquifer system using a finite-

element model. Saskatchewan Research Council, Publication No. R-844-4-C-85. 49 p. van der Kamp, G. 1986. The groundwater resources of Saskatchewan’s deep buried-valley

aquifers. Proceedings of Canadian Hydrology Symposium No. 16, Regina, June 3-6, 1986, Ed. J.M. Wigham, national Research Council, Canada Associate Committee on Hydrology, pp. 529 – 543.

van der Kamp, G., and Maathuis, H. 1991. Annual fluctuations of groundwater levels as a result

of loading by surface moisture. Journal of Hydrology, Volume 127, Nos. 1-4, pp. 137 - 152.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield 55

van der Kamp, G., and Maathuis, H. 2002. The peculiar groundwater hydraulics of buried valley aquifers. In Stolle, D., Piggott, A.R. and Crowder, J.J., Proceedings 55th Canadian Geotechnical and 3rd joint IAH-CNC Conference, Southern Ontario Section of the Canadian Geotechnical Society, pp. 695 -698.

Van Stempvoort, D.R., and Simpson, M. 1994. Hydrogeology of the southeast aquifer

management plan. Volume I; text. Saskatchewan Research Council, Publication R1220-9-E-94, 223 p. (revised 1995)

Walton, W.C. 1970. Groundwater resource evaluation. McGraw-Hill, New York, 664 pp. Walton, W.C. 1965. Potential yield of a sand and gravel aquifer in a buried valley near Estevan,

Saskatchewan. Results of aquifer and well production tests and evaluation of groundwater potential. Report prepared for Saskatchewan Research Council, 54 pp.

World Commission on Environment and Development. 1987. Our common future. Oxford

University press, New York

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield

Appendix A

Saskatchewan – Groundwater Allocation Process and Guidelines for Groundwater Investigation Report

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield A-1

FACT SHEET GROUNDWATER RELATING TO THE CONSTRUCTION AND OR OPERATION OF GROUNDWATER WORKS AND RIGHT TO USE GROUNDWATER

The Saskatchewan Watershed Authority (Corporation) is a provincial Crown corporation that has been established to manage, administer, develop, control and protect the water, watersheds and related land resources for the economic, social and environmental benefit of Saskatchewan. Included in this mandate, The Corporation has the responsibility for administering the regulatory approval process for construction and operation of wells and other groundwater works. This authority is derived from The Saskatchewan Watershed Authority Act and The Ground Water Conservation Act and Regulations. Use of Groundwater requires an Approval Under the Act, all groundwater use except domestic requires an approval. Examples of works which require approval are: municipal, industrial (including groundwater de-watering), intensive livestock operations, commercial, public institutions and irrigation. The intent of the Corporation=s approval process for groundwater projects is to ensure the sustainable and environmentally sound development of the province=s groundwater resources. Approval Process The Corporation=s regulatory approval process for development of a groundwater source project has two parts. The proponent of a proposed groundwater development is required to obtain:

1) Groundwater Investigation Permit; 2) Approval to Construct and Operate Works and Water Rights License to use

Groundwater.

Part I -- GROUNDWATER INVESTIGATION PERMIT The purpose of a groundwater investigation is to ensure that the groundwater source can sustain the proposed development, without any adverse impacts on the source or existing groundwater users and it is the primary source of information on which the Approval To Operate and Water Rights License is based. The following outlines the requirements and procedures of the Groundwater Investigation Permit process.

$ Application for Permit to Conduct Groundwater Investigation is to be submitted on a prescribed form along with a $10.00 fee. The applicant must identify the land location of proposed investigation, the intended use of the water, the estimated annual quantity required and the estimated pumping rate.

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$ The Corporation will review the application and if no potential conflicts are

apparent, a Permit To Conduct Groundwater Investigation will be issued. Included with the permit will be any hydrogeological information we have on file, together with general guidelines covering the detail and type of information which should be collected during the investigation. A qualified hydrogeologist is required to supervise/conduct the investigation.

$ At the conclusion of the groundwater investigation, regardless if the investigation

was successful in identifying/developing a suitable groundwater source, the consultant/proponent is required to submit two copies of the Groundwater Investigation Report to the Corporation. Groundwater Regulations require the report be filed within 60 days of the completion of the investigation.

$ The Groundwater Investigation Report should contain the following information:

General requirements

- A map or plan showing the extent and location of the project including ancillary

works (pumping wells, observation wells, pipelines, test holes, all surveyed from legal boundaries), and surrounding well users in the same aquifer.

- A field verified inventory of all wells within a 3.2 km. radius of the project, the

inventory should include: a) owners name; b) land location; c) type of well and depth; and d) depth to the non-pumping water level.

If the anticipated draw down in the aquifer is expected to exceed the 3.2 km. radius, the inventory shall be expanded to cover the expected area of influence.

- At least two geological cross-sections defining the target aquifer. All test drilling

and evaluation should be supervised by a qualified hydrogeologist.

- Copies of any surface lease, easement or purchase agreements for the access or use of the land affected by the project, the easements should also include any pipeline routes.

- At least two permanent observation wells (piezometer) completed and sealed in

the target aquifer.

- An estimate of the maximum pumping rate and annual quantity required.

- Construction dates of works if in place already.

Well information

- Original borehole geophysical logs and descriptive logs of all test holes.

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- Copies of well and observation well completion records.

- A minimum 24 hour pump test showing:

a) casing elevation of pumping well and observation wells; b) depth to static water level in pumping and observation wells; c) draw downs in pumping and observation wells; d) time and pumping rate; and e) recovery measurements in pumping and observation wells after

pumping has stopped, the recovery period shall be of the same duration as the pump test or until the aquifer has recovered to pre-pumping level.

Aquifer information

- An evaluation of the pump test and recovery data with estimates of the well yield,

aquifer yield and basin yield stating the method of analysis and assumptions used.

- A water chemistry analysis, detailing the major ions, for municipal projects and analysis for metals will also be required.

- An evaluation of the affects of the project on surrounding users. - When groundwater models (computer) are used for aquifer evaluation, the

following information shall be supplied: a) the name and type of model used; b) the input data; c) the boundary conditions;

d) a sensitivity analysis; e) all assumptions made; f) the results; and g) a discussion of the validity of the results.

Part II - APPROVAL TO CONSTRUCT AND OPERATE WORKS and WATER

RIGHT LICENCE TO USE GROUNDWATER If the groundwater investigation was successful, the project proponent is required to file an Application for Water Rights License & Approval To Construct and Operate Works under The Watershed Authority Act. The following outlines the requirements and procedures of the Water Rights License & Approval To Construct And Operate Works process.

$ Application for Water Rights License and Approval To Construct And Operate Works shall be submitted on prescribed form along with the appropriate fee (see application instructions) and a general plan showing the proposed works and location relative to legal boundaries.

$ The Groundwater Investigation Report is used as base documentation to support

the Application for Water Rights License & Approval To Construct and Operate

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Works. The report should identify any potential adverse impacts and present mitigation measures for the impacts, if required.

$ The Corporation will review the application and conduct a technical evaluation of

the Investigation Report to ensure its= completeness and adherence to accepted scientific practice. The Corporation will then advise of any other requirements such as land control from other land owners or consents from rural municipalities, Department of Highways and others should they be affected by your works.

$ If there is a potential for conflicts with other water users, or it is determined that

effects will be significant, the Corporation may require public consultation (advertisement or a public meeting). The Corporation will deal with and discuss with you any concerns or objection as a result of the public consultation which may result in additional investigation, special terms or conditions added to the Approval, development of mitigative plans or denial of Approval.

$ Once all regulatory and procedural requirements have been met, the Corporation

may issue an Approval To Construct Works if appropriate; or

$ When the construction of the works is complete, the Corporation may inspect the works and if all is in order issue a Water Right License and an Approval to Operate works subject to any terms and conditions required.

$ Immediately after the issuance of an Approval, the Corporation will register a

Notice against the appropriate Land Title which will tie the Approval to the land.

$ It should be noted, that the Water Rights License is not a guarantee that the quantity and quality of groundwater allocated will be constant. The License only grants the proponent access to the groundwater should it be available.

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield

Appendix B

Review of Pumping Test Analyses

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield B-1

REVIEW OF PUMPING TEST ANALYSES B.1 Introduction The introduction of the Theis equation gave a huge stimulus to the development of quantitative hydrogeology. Its limiting conditions have led to development of a large number of more complex mathematical models for analyzing pumping tests and for predicting the response of aquifers to pumping. This extensive literature has been summarized in review papers (e.g. Weeks, 1980; Moench, 1985; van der Kamp, 1985; several recent handbooks (e.g. Kruseman and de Ridder, 1990) and has been incorporated in various commercial computer packages (e.g. AQTESOLV from HydroSolve Inc., and Aquifertest(pro) from Waterloo Hydrogeologic Inc.). For the purpose of placing the Q20 method in the context of real-world aquifers, which are generally semi-confined or unconfined and bounded, the principal models are discussed in this Appendix. With respect to semi-confined aquifers, the hydraulic properties of the overlying and underlying aquitard are of importance. Provided a pumping test is properly designed the pumping test results will provide this information. Additional methods for determining the in situ hydraulic properties of aquitards have been provided by van der Kamp (2001). B.2 Development of the Theis equation for drawdown due to pumping from a confined

aquifer Based on an analogy with the conduction of heat, Theis (1935) developed the following equation, referred to as the nonequilibrium equation, for calculation of the drawdown in an aquifer:

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛+−+−−=== ∫

∞ −

!3.3!2.2ln5772.0

444

22 uuuuKD

QuW

KDQ

udue

KDQ

s tt

u

ut

πππ [1]

where:

s = drawdown (m) in a well at a distance r from the production well Qt = pumping rate (m3/day) KD = transmissivity (T) of the aquifer (m2/day) (T = KD) r = distance of observation well from production well (m) S = storativity of the aquifer (dimensionless) t = time since pumping started (days) W(u) = well function

u = KDt

Sr4

2

[2]

It is of interest to note that Theis (1935, page 521) states that, theoretically, equation [4] is “applicable only to unconfined water bodies”. At the time that Theis published his equation few data were available on confined aquifers and there was no rigorous concept of the storage coefficient for confined aquifers. Based on a rigorous definition of specific storage for confined aquifers, Jacob (1940) re-derived the Theis equation. Consequently, it was not until after Jacob’s

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The Q20 Concept and Sustainable Well Yield B-2

1940 publication that the 1935 Theis equation became “established” as the equation for the analysis of pumping test data from confined aquifers. Cooper and Jacob (1946) showed that for small values of u (u<0.01), i.e. large values of time or small values of r, the drawdown s in equation [4] can be approximated by:

SrKDt

KDQ

KDtSr

KDQ

s tt2

2 25.2log4

30.24

ln5772.04 ππ

=⎟⎟⎠

⎞⎜⎜⎝

⎛−−= [3]

Equation [3] is sometimes referred to as the “modified nonequilibrium equation” and is known as Jacob’s straight line method. Kruseman and de Ridder (1990, page 67) suggest that the condition u<0.01 is rather rigid and that for all practical purposes the condition u<0.1 can be used. Equation [3] can also be written in the form:

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

TtSr

TQ

s t

25.2log

430.2 2

π [4]

Equation [4] shows that drawdown is a linear function of log(r), except for very large r or small time. Drawdown at various distances from the pumping well and for large times can thus also be easily calculated. This is particularly useful for assessments of well interference. When the drawdown and time data are plotted on semi-logarithmic paper (t on logarithmic scale) a straight line can be drawn through the data. Defining ∆sp as the difference in drawdown per log cycle of time, the transmissivity T (T = KD) is obtained from:

p

t

sQ

=π43.2

[5]

and

2025.2

rTt

S = [6]

where; t0 is the time where the straight line intercepts the time axis at the point s=0 The Theis equation and Cooper and Jacob approximation are based on the following assumptions (e.g. Kruseman and de Ridder, 1990):

1) the aquifer is confined 2) water is released instantaneously with the decline of head in the aquifer 3) the aquifer has an infinite aerial extent 4) the aquifer is homogeneous, isotropic and of uniform thickness over the area influenced

by the test 5) prior to pumping, the piezometric surface is horizontal (or nearly so) over the area that

will be influenced by the test 6) the aquifer is pumped at a constant discharge rate 7) the well penetrates the entire thickness of the aquifer 8) the pump well has an infinitesimal diameter (i.e. negligible storage in the well).

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The Q20 Concept and Sustainable Well Yield B-3

The assumption that the aquifer is confined strongly limits the applicability of the Theis equation, because it requires that there is no significant flow into the aquifer from the overlying and underlying aquitards. Strictly speaking this condition is rarely valid, especially after long duration of pumping. The assumption of a uniform aquifer of infinite extent is also rarely satisfied, especially as the drawdown “cone” extends father out after a long pumping duration. In practice pumping test analyses based on the Theis equation tend to produce reasonably good estimates of transmissivity and storage coefficient near the pumping well provided there are two or more observation wells. However, it cannot be relied upon for prediction of long-term behavior under pumping for water supply. In most cases pumping tests are conducted on production wells only. When using a single well and provided that the discharge is kept constant, the Jacob straight line method can be applied to estimate the aquifer transmissivity. However, additional assumptions have to be met. For single-well pumping tests in confined aquifers the following condition has to be satisfied (Kruseman and de Ridder, 1990):

KDr

t c225

> [7]

where rc is the radius of the casing (m). If the time condition is met, the effect of storage in the well can be neglected. For single-well tests conducted in leaky aquifer the influence of leakage is negligible if (Kruseman and de Ridder, 1990):

)20

(20

25 22

KDSLcSt

KDr c =<< [8]

Based on equation [3], the drawdown after 20 years (7,305 days) is given by;

Sr

KDKDQs 220

25.16436log4

3.2π

= [9]

Defining R20 as the distance from the pumping well where the drawdown after 20 years of pumping at rate Qr equals a pre-set limit SR20, equation [9] leads to:

Qr

KDSRSKDR

2046.520

10

1128= [10]

B.3 Unconfined Aquifers The analytical model developed by Neuman (1975) for unconfined (or water table) aquifers is generally useful, but it neglects the reduction of aquifer transmissivity near the pumping well due to dewatering of the aquifer. Drawdown in the pumping well is therefore underestimated. Neuman’s model shows that at large times and at distances more than an aquifer thickness away from the pumping well, the drawdown follows the Theis equation, with the storage coefficient equal to the specific yield of the aquifer material, which for sands typically takes values of about 0.2 to 0.3. Thus, equations [5] and [6] can be used to predict the long-term drawdown of the

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The Q20 Concept and Sustainable Well Yield B-4

water table due to pumping. Nwankor et al. (1992) showed that the low values of specific yield that are typically obtained from pumping tests in unconfined aquifers are not useful for long-term predictions because they are obtained by neglecting short-term vertical gradients in the saturated zone including the saturated capillary fringe above the water table. B.4 Semi-confined Aquifers Hantush and Jacob (1955) extended the pumping test models to include aquifers that receive recharge through an overlying aquitard, but without significant storage within the aquitard. Their results for drawdown due to pumping from a semi-confined aquifer are:

( )LruW

KDQ

s t ,4π

= [11]

where L is the leakage length, u is defined by equation [2] and:

( ) ∫∞

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

u uLru

uLruW 2

2

4exp1, du [12]

The extension of aquifer theory to semi-confined aquifers removes the Theis assumption of a fully confined aquifer, but is still dependent on all the other assumptions listed in section B2. For this case it is also assumed that drawdown above the aquitard (i.e. at the water table, or in an overlying aquifer) is negligible and, therefore, the system eventually comes to a steady-state condition where the flow through the aquitard is equal to the rate of pumping. The leakage factor L (length) is a measure for the spatial distribution of the leakage through an aquitard into a leaky aquifer and vice versa. It is defined as (Kruseman and de Ridder, 1990):

TcKbKDL

v

== '

' [13]

where: L = leakage length (m), K= hydraulic conductivity of aquifer (m/day), D = thickness of aquifer (m), b’ = thickness of overlying aquitard (m), Kv

' = vertical hydraulic conductivity of

overlying aquitard (m/day), vK

bc''

= = vertical hydraulic resistance (days), T = transmissivity of

aquifer (m2/day). The leakage factor is often denoted by the symbol “B” (e.g. Hantush and Jacob, 1955). In typical prairie settings the leakage factor L may range in value from a few hundred meters to hundreds of kilometers. The hydraulic resistance c characterizes the resistance of an aquitard to vertical flow, either upward or downward. The vertical hydraulic resistance of aquitards in the Prairies may range from hundreds of days to thousands of years. Note that the unit of time used here and in subsequent equations is “days”, but “seconds” (1 day = 86,400 seconds) are also commonly used.

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The Q20 Concept and Sustainable Well Yield B-5

The leakage length is a useful parameter in estimating the impact of pumping from, or injection into, an infinite semi-confined aquifer. For steady-state radial flow to a well, the drawdown in such an aquifer is given by (de Glee, 1930; Hantush and Jacob, 1955):

⎟⎠⎞

⎜⎝⎛=

LrK

KDQs t

02π [14]

Where Ko is the modified Bessel function of second kind and zero order. For example, if the steady-state drawdown in a 0.15 m (6 inch) diameter well is 1.0 m , then the drawdown at distances r=L, 2L, 3L is 0.034 m, 0.009 m and 0.003 m, respectively. It is evident from this example that for radial flow the major drawdown occurs within a radius L from the production well and that at a distance r=3L the impact is negligible. It can also be shown (Hantush, 1960; van der Kamp, 1985) that the drawdowns will be near steady state for time of pumping greater than c’S:

SKbSct v )'/'(' => [15] For typical prairie aquifers the values of c’S may range from a few hours to several years. Although steady-state behavior may not be attained or even approached during the pumping test, it is very likely to be attained during subsequent production over the next 20 years. Assuming that after 20 years of pumping the drawdown cone has come to a steady-state condition, the drawdown is given by:

( ) ( )LrK

KDQrS r

020 2π= [16]

or, rewritten

r

R

QKDS

LRK 2020

02π

=⎟⎠⎞⎜

⎝⎛ [17]

where, L = (Tc)1/2 and K0 the modified Bessel function of second kind and order zero. There are no simple limiting approximations for K0 in the range of values of r/L that are likely to be relevant for calculating R20. In this case, therefore, the value of R20 must be determined by calculating the drawdown after 20 years at various distances and interpolating to estimate the value of r that gives the limiting drawdown SR20. Values of K0 are tabulated in handbooks and are also available through various common software packages. B.5 Leaky Confined Aquifers Hantush (1960) extended the theory for confined aquifers to the case of a confined aquifer between very thick aquitards with flow coming from the aquitards. For typical prairie hydrogeological settings, such aquifers are encountered greater depths, usually within the bedrock His results are:

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The Q20 Concept and Sustainable Well Yield B-6

),(4

βπ

uWKD

Qs t= [18]

where u is defined by equation [5] and:

⎥⎥⎦

⎢⎢⎣

⎡+=

KDSbSK

KDSbSKr

''

''''

'

''

4β [19]

∫∞ −

−=

u

u

dyuyy

uerfu

euW)(

),( ββ [20]

If the aquitards have relatively high permeability the behavior described by equation [18] can vary markedly from that described by the Theis equation for a fully confined aquifer. However, for most cases the drawdown behavior of such leaky confined aquifers is difficult to distinguish from that for a fully confined non-leaky aquifer. The influence of leakage flow from adjoining aquitards can best be assessed by plotting drawdown data for at least two observation wells on one composite log-log plot of drawdown versus t/r2 (Weeks, 1980). If the aquifer is fully confined (i.e. Theis-like behavior) the plots for the different observation wells will coincide, whereas they will be separated if there is significant “leaky” behavior. B.6 Buried Valley aquifers Many prairie aquifer formations where deposited under deltaic, fluvial or glaciofluvial conditions. It is not surprising therefore that many aquifers in the region appear in the form of buried channels within low-permeability units. The drawdown behavior of such narrow bounded aquifers can differ markedly from that of the extensive “sheet” aquifers for which the previously reviewed theory was developed. Vandenberg (1976, 1977) developed theory for a semi-confined channel aquifer incised into impermeable deposits and overlain by an aquitard:

( )LxuF

TWxQ

s t ,2

⎟⎠⎞

⎜⎝⎛= [21]

where:

⎟⎟⎠

⎞⎜⎜⎝

⎛=

TtSxu

4

2

and ( ) dyyLxyyL

xuFu

⎟⎠⎞

⎜⎝⎛ −−⎟

⎠⎞⎜

⎝⎛= ∫

∞−

22232

1

4exp2/1, π [22]

in which: s = drawdown x = distance between pump well and observation well (x ≥W) W = width of aquifer t = time since pumping started Qt = constant pumping rate S = storativity of the aquifer T = transmissivity of the aquifer

L = leakage length = ( ) 21'/' vKTb

b’ = thickness of the aquitard '

vK = vertical hydraulic conductivity of aquitard

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Y = dummy variable of integration Vandenberg (1977) provided detailed tables of values for the type curves of dimensionless drawdown F(u, x/L). The Vandenberg type curves were re-formulated by van der Kamp (1985) and van der Kamp and Maathuis (2002) to a form that is more closely related to the standard (Hantush and Jacob, 1955) type curves for an extensive semi-confined aquifer. The modified type curves represent plots of dimensionless drawdown V as a function of dimensionless time t' and dimensionless distance x/L, and the equation for the drawdown in a channel aquifer can then be written in the form:

( ) ( )LxtV

TLQ

txsW

t ,2

, '⎟⎟⎠

⎞⎜⎜⎝

⎛= [23]

⎟⎠⎞

⎜⎝⎛= 2' LS

TttW

W [24]

where x is the distance along the strip aquifer, s(x, t) is the drawdown, t is the time since the start of pumping and Q is the pumping rate. V and t' are related to Vandenberg's F(u, x/L) and u by V = (x/L)F and t' = (x2/L2) (1/4u). Values for the function F (u, x/L) can be found in Vandenberg (1976) and Kruseman and De Ridder (1990). The modified type curves are identical to the type curves presented by Zhang (1992) with the proviso that here the cross-sectional transmissivity TW and storage SW are used rather than T and S.

The type curve parameters are expressed in terms of TW, the cross sectional transmissivity of the aquifer; SA, the cross-sectional storage coefficient of the aquifer; and L, the leakage factor, defined by:

'WTTW = [25]

'WSSW = [26]

2

1

'''⎟⎟⎠

⎞⎜⎜⎝

⎛=

v

W

KWbT

L [27]

where T and S are the average values of transmissivity and storage coefficient of the aquifer, averaged over the full width of the aquifer, W' is the width of the top of the aquifer, b’ is the thickness of the overlying aquitard, and KV’ is the vertical hydraulic conductivity of the aquitard. Use of the cross-sectional parameters TW and SW is appropriate for a buried-valley aquifer because it is usually the total water transmitting and water storing capacity of the aquifer that counts. For instance, the total rate of flow of water along the aquifer is simply the product of TW and the hydraulic gradient along the aquifer. If a representative value of TW for a buried-valley aquifer can be determined, then there is no need to worry about the complex details of the variations of hydraulic conductivity over the cross-section. Thus the use of these cross-sectional parameters obviates the need to define the exact width of the aquifer - a parameter that is likely

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to be difficult to determine in many cases because the aquifers tend to have poorly defined uppermost edges. The analytical solution shows that the behavior of a leaky strip aquifer is governed by the three aquifer parameters TW, SW and L. The drawdown approaches steady state for times exceeding c’S as for the Hantush and Jacob (1955) case. At steady state the drawdown at distances more than one aquifer width away from the pumping well is given by (Vandenberg, 1977):

( )Lx

W

t eT

LQs /

0 2−

⎟⎟⎠

⎞⎜⎜⎝

⎛= [28]

At distances of more than one aquifer width away from the pumping well, the flow is essentially linear, parallel to the valley. Due to the bounded nature of such aquifers the drawdowns are much greater and extend much farther than for a semi-confined “sheet” aquifer with similar transmissivity and similar hydraulic resistance of the overlying aquitard. It is not uncommon for significant drawdown and well interference to be encountered at distance of tens of kilometers from the pumping well. An example of this different behavior is summarized in Table B1, which shows that the drawdown in a channel aquifer can easily be ten times as great as in a corresponding sheet aquifer. Table B1 Comparison of steady-state drawdown in an infinite strip aquifer and an infinite

sheet aquifer (after van der Kamp and Maathuis, 2002)

Distance (m)

Drawdown (m)

Strip aquifer Sheet aquifer 0.127 >23.3 2.68

30 >23.3 1.52

500 >23.01 0.93

1000 22.7 0.78

7000 19.1 0.37

35,000 8.58 0.09

70,000 3.16 0.02 Based on: L = 35 km, T = 0.03 m2/s, W = 1,000 m rw= 0.127 m and Qt = 40 L/s During a typical short-term pumping test for a channel aquifer, lasting at most a few days, the drawdown shows characteristic behavior, starting out for the first few minutes or hours as a standard sheet aquifer, and then increasing at a much greater rate as the influence of the nearby boundaries is felt. It seems likely that many pumping test results that appear to defy analysis in fact reflect channel aquifer-like behavior. A further indication of such a case would be that

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nearby test holes did not encounter the aquifer. As we shall see, the occurrence of such aquifers has marked implications for the determinations of sustainable well yields by the Q20 method. For an infinite buried-valley aquifer, again assuming that the drawdown has reached a steady-state condition, R20 can be calculated from equation [28]:

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

LQTS

LRr

WR2020

2ln [29]

B.7 Heterogeneous aquifers The above models all assume that the aquifer is homogeneous and of constant thickness and transmissivity. Most real-world aquifers are more complex, some so much so that use of the standard models to predict their behavior is open to question. Bibby (1979) proposed the application of statistical methods to short-term transmissive capacity data in order to arrive at an estimate of the long-term transmissive capacity for heterogeneous aquifers. Based on a concentric ring model, Bibby (1979) uses the estimated geometric median as the estimate of the expected value of long-term transmissive capacity. The estimate then could be used to predict 20-year safe yields of wells and, based on the superposition principle, the drawdown at a production well for arbitrary long-term production programs. The method is limited to “infinite” aquifers as it can not be used to evaluate settings where distinct boundaries exist (Bibby, 1979, page 41). The method also requires a sufficient number of transmissivity data derived from short-term pumping tests to form a good random sample. The method proposed by Bibby appears to only to have been applied to the two sites (Innesfail and Olds) described in his report. B.8 Use of Recovery Data For determining the best value of Q20 the long-term behavior of the aquifer must be estimated. It is important therefore to extract as much information as possible on long-term drawdown behavior from the pumping test. One obvious but expensive way to do this is to lengthen the duration of the pumping test and this may be essential if a critical groundwater supply is to be proven. However, the recovery of the water levels in wells after pumping ceases can effectively lengthen the duration of the test and provide valuable additional information on the properties of the aquifer. Theis (1935) described a method of analyzing recovery data for confined aquifers based on the Theis equation and using the ratio t/t’ of the time t’ since pumping ceased divided by the time (t) since pumping started. This method is still widely used for the analysis of recovery data although it is only applicable for fully confined aquifer and therefore has limited usefulness. Van der Kamp (1989) described a general method for the analysis of recovery data which assumes only that the superposition principle is applicable, but is not dependent on an assumption as to the type of aquifer model that is applicable. With this method the recovery

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phase of the pumping test can be used to determine how the drawdown would have evolved if the pumping had carried on. For a constant rate pumping test the constant rate drawdown s0(t) can be calculated from the drawdowns s(t) measured during the pumping and recovery periods of the test. In equation form:

( )∑=

−=p

kkttsts

010 )( [30]

where: t1 is the duration of the pumping test. For the typical 24 – 24 hour pumping and recovery test equation [30] becomes: ( ) ( )tsts =0 for 0≤t<t1 [31] and ( ) ( ) ( )10 ttststs −+= for t1≤t<2t1 [32] where: ( )ts = observed residual drawdown at time t and ( )1tts − =observed drawdown at time t – t1. For long recovery periods in particular the measured recovery will be subject to errors due to measurement error and natural changes in the static water level. Including an error term, equation [30] becomes (van der Kamp, 1989):

( ) ( )tEkttstsp

k±−= ∑

=010 )( [33]

where: ( ) ( )∑=

−=p

kttetE

01

For confined and semi-confined aquifers van der Kamp’s approach may allow the effective duration of the pumping test to exceed the duration of pumping by a factor of ten or more. The information obtained by means of a pumping test of standard duration (typically one to five days) can thus be greatly increased if the subsequent recovery after pumping ceases is observed until full recovery has been achieved. With modern stand-alone pressure-transducer technology this can be done with little added expense. Essentially the drawdown and recovery phases of the aquifer test can be and should be considered as one single aquifer test and treated as such. Observation of recovery is particularly valuable for cases where it is expected that the aquifer is semi-confined and may go to steady state within a reasonable duration of aquifer testing. If indeed it is observed that the recovery is complete at some given time after the start of pumping, this means that if pumping had continued the drawdown would have attained steady state at this time. B.9 Reciprocity Principle A simple quantitative approach for calculating cumulative impacts can be based on the appropriate aquifer model, making use of the “principle of reciprocity” (van der Kamp, 1989; McKinley et al., 1968). This principle states that the drawdown at any well due to pumping from another well is exactly equal to the drawdown that would occur at the pumping well if the other

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well were pumped at the same rate instead. The principle is valid for any subsurface flow problem for which the flow laws are linear, i.e. virtually all groundwater applications that do not involve dewatering of the aquifer or changes of the hydraulic properties of the formations. For a uniform infinite aquifer, once a 20-year distance-drawdown curve is calculated for a pumping at rate Qp from any point “p” in the aquifer, then the drawdown at that point due to pumping at rate Qi from any other point “i” at distance ri is given by:

( ) ( )p

iyrstryrstip Q

Qss

i*20,20, == = [34]

where: )20(1, yrstps = is the drawdown at p due to pumping at rate Qi at i. )20,(, yrstrpi i

s = is the drawdown at distance ri due to pumping at rate Qp at p. With this relationship the total drawdown at point “p” due to pumping from other wells can be calculated through a simple summing up. For example, the impact of cumulative pumping on a flowing well can be evaluated: if the total drawdown exceeds the static head above ground level at the flowing well, then the well will cease to flow.

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B.10 References Bibby, R. 1979. Estimating sustainable yield to a well in heterogeneous strata. Alberta

Research Council, Bulletin 37, 60 p. Cooper, H.H., and Jacob, C.E. 1946. A generalized graphical method for evaluating formation

constants and summarizing well field history. Transactions American Geophysical Union, Vol. 27, pp. 526-534.

De Glee, G.J. 1930. Over grondwaterstromingen bij onttrekking door middel van putten. Thesis. J. Waltman, Delft, 175 pp. Hantush, M.S. 1960. Modification of the theory of leaky aquifers. Journal Geophysical

Research, Volume 65, pp. 3713 – 3725. Hantush, M.S., and Jacob, C.E. 1955. Non-steady radial flow in an infinite leaky aquifer.

Transactions American Geophysical Union, Volume 36, pp. 95-100.

Jacob, C.E. 1940. On the flow in an elastic artesian aquifer. Transactions American Geophysical Union, Volume. 21, pp. 574-586.

Kruseman, G.P., and N.A. de Ridder. 1990. Analysis and evaluation of pumping test data

(second edition). International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands, ILRI Publication 47, 377 p.

McKinley, R.M.,S. Vela, and L.A.Carlton, 1968. A field application of pulse testing for detailed

reservoir description, J. Pet. Technology, V 20, 313-321. Moench, A.F., 1985. Transient flow to a large-diameter well in an aquifer with storative

confining layers. Water Resources Research, Vol. 21, 1121-1131. Neuman, S.P. 1975. Analysis of pumping test data from anisotropic unconfined aquifers

considering delayed gravity response. Water Resources Research, Volume 12, pp. 329 – 342

Nwankor, G.I., Gillham, R.W., van der Kamp, G. and Akindunni, F.F. 1992. Unsaturated and

saturated flow in response to pumping of an unconfined aquifer: field evidence of delayed drainage. Ground Water, 30, 690-700.

Theis, C.V. 1935. The relation between the lowering of the piezometric surface and the rate and

duration of discharge of a well using ground-water storage. Transactions American Geophysical Union, Vol. 16, pp. 519-524.

Vandenberg, A. 1976. Tables and type curves for analysis of pump tests in leaky parallel-

channel aquifers. Environment Canada, Inland Waters Directorate, Technical Bulletin 96, 28 p.

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The Q20 Concept and Sustainable Well Yield B-13

Vandenberg, A., 1977, “Type Curves for Analysis of Pump Tests in Leaky Strip Aquifers; J. of Hydrology Vol. 33, 15-26.

van der Kamp, G. 1985. Brief quantitative guidelines for the design and analysis of pumping

tests. In Hydrogeology in the Service of Man, Memoires 18th Congress of the International Association of Hydrogeologists, Part 4, pp. 197-206.

van der Kamp, G, 1989. Calculation of constant-rate drawdowns from stepped-rate pumping

tests. Ground Water, Volume 27, No.2, pp 175 - 183 van der Kamp, G. 2001. Methods for determining the in situ hydraulic conductivity of aquitards -

an overview. Hydrogeology Journal, 9, 5-16. van der Kamp, G. and Maathuis, H. 2002. The perculiar groundwater hydraulics of buried-

channel aquifers. In Stolle, D., Piggott, A.R., and Crowder, Proceedings of the 55th Canadian Geotechnical and 3rd Joint IAH-CNC groundwater Speciality Conference, Niagara Falls. Southern Section of the Canadian geotechnical Society, pp.695 – 698.

Weeks, E.P. 1980. Aquifer tests. In National handbook of recommended methods for water-

data acquisition, Chapter 2, Groundwater. U.S Department of the Interior, Reston, Virginia.

Zhang, W.Z. 1992. Transient groundwater flow in an aquifer-aquitard system in response to

water level changes in rivers or canals. Journal of Hydrology, 133 (1992) 233-257 Elsevier Science Publishers B.V., Amsterdam

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Appendix C

Farvolden (1959) - Groundwater Supply in Alberta

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GROUNDWATER SUPPLY IN ALBERTA

By R.N. Farvolden, 1959

Alberta Research Council, unpublished report Most groundwater problems can be divided into three general classes: 1) Geological problems, 2) Hydrological problems, 3) Engineering problems. 1) The geology of an area should be the first factor to be considered in any groundwater

problem. A study of the geology may indicate depth, thickness, extent, and general hydrologic properties of the formations that will be encountered in drilling.

2) The hydrology of the formations in the area must be studied to determine whether or not

sufficient water occurs in the aquifers to make them worth developing. 3) The engineering problem is the problem of getting the water from the aquifer to the

surface at an economic rate and this is the problem most familiar to drillers. This paper deals with only the first two types of problems. General Geology of the Alberta Plains For the proper understanding of the geology of an area one must have an idea of the processes involved in creating the conditions that we see today. Therefore, I will present a very sketchy outline of the history of the deposits encountered here in shallow drilling. For millions of years before the Rocky Mountains were built, the Alberta plains region was more or less covered by a shallow sea. Rivers emptying into the sea brought in clay, silt and some sand and this mixture of mud settled to the bottom and eventually became hundreds of feet thick. In some places where the wave action was strong, the bottom muds were agitated by the waves and the clay was washed out and removed leaving sand bars and beaches. The same thing happens in present-day lakes and seas. The sea was surrounded by low swampy ground, inhabited by dinosaurs and supporting a heavy growth of vegetation. Sometimes the sea retreated exposing long stretches of mud flats. Where the waves worked this mud the winnowing action formed wide sand beaches. Sometimes the sea advanced and flooded the swamps and lowland areas. The swamps and their thick deposits of peaty material became buried in mud. This process was repeated many times until after millions of years, hundreds of feet of sediments had accumulated. The mud eventually hardened into shale, the sand became cemented to form sandstone, and the organic deposits of the swamps altered to coal. About twenty-five million years ago the land to the west began to rise, driving the sea off this part of the continent. This was the birth of the Rocky Mountains and marked the end of the dinosaurs. As the land rose, rivers began to flow from the new highlands, across the plains, and on to the ocean.

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The rivers, of course, flowed over the bedrock surface of the shales, sandstones and coal seams which had been previously deposited. Valleys were carved in this surface and sand and gravel deposits accumulated along the valley bottom. It is likely a fairly well-developed drainage system had been formed before the next major geological event changed the face of the land once more. About one million years ago ice began to accumulate in the Rocky Mountains and in the Northwest Territories. The ice thicknesses became so great that the ice flowed out in all directions to cover all of Western Canada. This was the great Glacial Age or Pleistocene Epoch. As the ice scraped across the ground it picked up a huge load of clay, sand, boulders, soil, and chunks of the bedrock. Several times the ice front was melted back and then re-advanced but finally the glaciers retreated completely from our part of the world. As the glaciers melted the material they had picked up in their journey from the north (most of our glaciers came from the north rather than from the mountains) was left as a blanket over the whole area, covering the bedrock and in places filling up the preglacial valleys that had been carved by the preglacial river system. The most common glacial deposit in an unsorted mixture of clay, silt, and sand with boulders and rock fragments, which is called till. Most of Alberta is covered by a mantle of till from 20 to 70 feet thick and in places over 250 feet thick. Where the great quantities of meltwaters from the ice formed large streams the deposits were sorted and sand and gravel beds were laid down while the silt and clay was carried away. This fine material was deposited in lakes, and drillers often find thick layers of soft clay and silt which originated this way. About this time our present drainage system began to form. Rivers gradually cut valleys into the new drift until today they are established in deep, well-developed valleys again. In many places the rivers have cut down right through the drift cover and the bedrock is exposed in the valley walls. The valleys in the Peace, Athabasca, North Saskatchewan, Battle, Red Deer, Bow, Belly, Oldman, St. Mary, and South Saskatchewan all show this feature. Of course, the sands and gravels along our present rivers form a very important source of groundwater. Thus, as far as groundwater development is concerned we see there are two major types of deposits: the unconsolidated deposits and the bedrock formations. The unconsolidated deposits are also known as the drift, Pleistocene deposits, glacial deposits, the mantle, the soil, recent alluvium, etc. The bedrock may be referred to as the consolidated formations, or by the terms used to describe the rock, such as shale, sandstone, and coal. Ground Hydrology and Related Characteristics Unconsolidated deposits The most important aquifers in the unconsolidated deposits are: 1) the sands and gravels that occur in the preglacial valley, 2) the sands and gravels that occur associated with glacial meltwater channels, and 3) the sands and gravels along present-day rivers.

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There are several points which must be kept in mind when planning a water supply in these deposits. 1. Except for one or two places, the gravels of the unconsolidated deposits are the only

possible source for large groundwater supplies (say 200 gpm or more) on the Plains. 2. When prospecting in these deposits there is no point in drilling below the drift - bedrock

contact because, as you can see, these deposits can’t occur below the bedrock. 3. The aquifer may be very limited in extent. 4. The limits of the aquifer may be determined by a study of the airphotos of the area,

especially if some control is available from test holes. This is possible because the sands and gravels are usually near the surface and thus show up on the airphotos. (This is not so where preglacial gravels have been buried by thick till).

5. In many cases the aquifers are close to the surface and so are readily recharged by local

precipitation. 6. The water in these deposits is usually hard and contains iron. 7. It is almost always necessary to install a screen if the well is to be fully developed and

efficient. The bedrock formations The most important aquifers in the bedrock formations are: 1) the sandstone horizons which are free of clay and silt and are not made impermeable by “cement” of some sort closing all the pore spaces; 2) coal seams which carry water in fractures; 3) fractured sandstone beds which are too well cemented to carry water in their pore spaces but which carry water in the fractures. Points to Keep in Mind when Planning a Water Supply from the Bedrock 1. In most places in Alberta capacities of over 20 gpm require careful testing and

completion methods. 2. Because of the manner of their origin the aquifers can be expected some lateral

continuity. 3. There is likely no indication on the surface that the aquifer exists at depth. 4. Since the aquifers are buried, recharge is more difficult and the water may come from

greater distances than in the case of unconsolidated deposits. 5. The water is generally soft, and salinity increased with depth as a rule. Soda may be a

problem and as it can’t be tasted (with certainty) the water should be analysed.

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6. The hole may stand open and this is a good completion method provided no

complications arise. Both the bedrock and the unconsolidated deposits often contain strata of very fine, loose sand which carries water under pressure, and caves and heaves easily. Drillers call this material quicksand and case it off. This sand can be developed into a good source of water under certain conditions. The Capacity of the Well Let us assume that a well has been drilled and it is to be tested for capacity. The amount of water a well will “make” depends upon two things: 1) the amount of water the aquifer can transmit, and 2) the efficiency of the well in producing this water. Testing a Well for Capacity Pump test 1. Prepare to take depth-to-water readings to either the near 1/10 foot of 1 inch while the

well is pumping, either by: 1. wetted tape 2. electric tape 3. air line,

and be prepared to record the readings. 2. Measure depth to water (DW) several times at intervals before the test starts to establish

the static level. 3. Be prepared to measure the rate of pumping. There should be some previous test to

determine the best rate. It is no use pumping a well at 30 gpm if at this rate the well pumps off in 10 minutes. Similarly, there is little gained in test pumping of 50 gpm well at 3 gpm.

4. Record the time the pump starts - all times are referred to this time. 5. Record readings for drawdown (dd) and time (t) at: every minute from 1 to 10 minutes every 5 minutes from 10 to 30 minutes every 10 minutes from 30 to 100 minutes every 50 to 100 minutes from 100 to 1000 minutes. 6. Take regular measurements of the rate of pumping.

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7. Record the time the pump is turned off and take recovery measurements like drawdown measurements.

The Drawdown Curve Two curves are possible: 1. A stable pumping level is established - this indicates that the recharge balances the

discharge; 2. Water level continues to decline - this indicates that the well is drawing water from

storage. To calculate the capacity of the well: Case One: (1) Calculate the specific capacity.

(dd)Drawdown

(Q) pumpted was well theRate (Cs)Capacity Specific =

This will determine the amount of water the well will produce per minutes for each foot of dd.

(2) Calculate the total available drawdown (dd), that is, the pressure (H) of the water in the

formation. H (available drawdown) = depth to top of aquifer - (depth to) static level. (3) Capacity of well = Cs (specific capacity) x H (available drawdown) x safety factor (0.7). Case Two: (1) Plot the drawdown (dd) on the vertical axis and the time on the horizontal axis, as before,

but notice that the scale on the horizontal axis is logarithmic, that is, its divisions increase by a power of 10 (100, 101, 102, 103) rather than by simple arithmetic addition. These plots should form a straight line.

(2) Project this line into the future. (3) If the well is to last 20 years (about 10 million minutes), the drawdown curve, when

projected, must not have a greater drawdown than we have available where it intersects the 10 million minute line on time scale. Since at a given rate the well draws down equal amounts for each log cycle or time division, then from 1/10 of a minute to 10 million

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield C-6

minutes there are 8 cycles. Therefore, if the well is pumped at such a rate that for each time division on our scale it will draw down 1/8 of the total H (available drawdown), then in 20 years the well should be exhausted.

To find this value then, divide the total H by 8 (H/8). (4) From the drawdown curve calculate the Transmissibility (T) - a formation factor:

time)of cycle logeach for dd (the dd Δ

pumping) of (rate Q x 264 T =

(5) The safe rate (Q) for the well is that rate at which ∆ dd (the drawdown for each log cycle

of time) will be 1/8 of H (total available drawdown), so

2110drawdown) available (total Hibility x (transmiss T (Q) rate Safe =

Multiply answer by a safety factor of 0.7.

Bail Testing Each driller has his own approach to bail testing. We must have the following information in order to work with bail test results: i) take measurements at intervals before bail test to determine static level; ii) bail at a steady rate for at least 30 minutes; iii) take the recovery each minute for 10 minutes, and then each 5 minutes for as long as the

bail test lasted. The information can be plotted to determine T (transmissibility) and when T is known the capacity of the well can be calculated (see (5) of Case Two). Testing the Aquifer The foregoing notes apply to the testing of an individual well. In order to test the capacity of an aquifer, the effect of the pumping well on other wells in the same aquifer must be tested. Definitions Water-table - Horizon below which all pore space is filled with water. Zone of saturation - zone below the water-table. Groundwater - water in the zone of saturation. Aquifer - geologic formation or zone which transmits enough water to supply a well or spring. (What is an aquifer in one area (desert) might not be considered an aquifer in another area.)

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The Q20 Concept: Sustainable Well Yield and Sustainable Aquifer Yield C-7

Two types of aquifer - artesian and water-table or confined and unconfined. Drawdown - the lowering of the water level in a well due to pumping. Water-table Well - a well in an unconfined or water-table aquifer - the water level represents the elevation of the water table. When such a well is pumped the aquifer is actually dewatered to provide water to the well. Artesian Well - a well in which the water in the aquifer is “confined” by an overlying impervious bed and the water in the well rises up the hole when the aquifer is struck. The distance the water rises above the aquifer represents the pressure of the water in the aquifer. If the water rises above land surface, the well will flow. Porosity - the percentage of pore space in a rock - the property of a rock that enables it to hold water. Permeability - the property of a rock that enables water to move through it, e.g. if the pore spaces are connected to a rock will be permeable. Transmissibility - a term used to indicate the ability of the aquifer to transmit water. Really, P x m = T. Drawdown - the fall in water level in a well when it is pumped. Cone of Depression - cone of pressure relief or drawdown caused by a pumping well. Specific Capacity - number of gallons per minute the well will produce with one foot of drawdown. Capacity - number of gallons per minute the well can produce.

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0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200Time, in years

130

120

110

100

90

80

Wel

l yie

ld, p

erce

ntag

e (%

)

130

120

110

100

90

80

Figure 8 Comparision of Q20 versus Q10, Q5 and Q200

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70

60

50

40

30

20

10

0D

epth

to w

ater

, in

met

res

0

100000

200000

300000

Mon

thly

pro

duct

ion,

m3

OW1OW2OW3OW4OW5OW6

1996 1997 1998 1999 2000 2001 2002 2003

Figure 16 Hydrographs for observation wells in the Senlac area and monthly volumes pumped from production wells

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35

30

25

20

15

10

5

0D

raw

dow

n, in

met

res

0

100000

200000

300000

Mon

thly

tota

l with

draw

als,

m3

OW-1OW-2OW-3 -Upper aquiferOW-4OW-5OW-6

Figure 16 Drawdown in observation wells in the Senlac area and monthly total withdrawals

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10 100 1000 10000Time since start of pumping, days

35

30

25

20

15

10

5

0D

raw

dow

n, m

etre

s

OW-5 - distance: 1800 mOW-6 distance: 4000 mTheis model: T=110 m2/day, S=0.0012Avereage drawdown in production wells

15

10

5

0

Figure 18 Semi-log plot of drawdowns observed in Senlac observation wells OW-5 and OW-6, average drawdown in the production wells and modelled drawdown in OW6

Note: assumed starting date of pumping February 15, 1996