Applications to Stormwater Management

Presented by:

Mr. Brian Oram, PG, PASEOWilkes University

GeoEnvironmental Sciences and Environmental Engineering

DepartmentWilkes - Barre, PA 18766

570-408-4619

http://www.water-research.net

Nearly 50% of Soil is Space or Space Filled with Water

• Water – 25+ %

• Air – 25 + %

• Pore Space Makes Up 35 to 55 % of the total Soil Volume

• This Space is called Pore Space

Therefore, soil can be used as a storagesystem, treatment system, and transport media.

Soil Properties Critical To Stormwater Management

• Soil Texture

• Porosity and Pore Size

• Water Holding Capacity

• Bulk Density

• Aggregate Stability

• Infiltration Capacity

• Hydraulic Conductivity!!! Just to Name a Few Properties !!!!

Types of Pores

Micropores (< 10 microns)- Small

Mesopores (10 to 1,000 microns)- Medium

Macropores (> 1,000 microns)-Large

Source: http://www2.ville.montreal.qc.ca

Key Points on Soil PoresUnder gravity, water drains from macropores, where as, water is retained in mesopores and micropores, via matrix forces.

Coarse-textured horizons (e.g., sandy loam) tend to have a greater proportion of macropores than micropores- but they may not have more macropores than finer textured soils.

Soils with water stable aggregates tend to have a higher percentage of macropores than micropores.

Proportion of micropores tends to increase with soil depth,resulting in greater retention of water and slower flow of water with depth.

Water Holding Capacity

Textural Class

Available Water Capacity

(Inches/Foot of Depth)

Coarse sand 0.25–0.75

Fine sand 0.75–1.00

Loamy sand 1.10–1.20

Sandy loam 1.25–1.40

Fine sandy loam 1.50–2.00

Silt loam 2.00–2.50

Silty clay loam 1.80–2.00

Silty clay 1.50–1.70

Clay 1.20–1.50

Please Do Not Use Sand in a Bio-Retention System !

Bulk Density, Porosity, and Texture

Textural Class Bulk Density (Mg/m³)Porosity

(%)

Sand 1.55 42

Sandy loam 1.4 48

Fine sandy loam 1.3 51

Loam 1.2 55

Silt loam 1.15 56

Clay loam 1.1 59

Clay 1.05 60

Aggregated clay 1 62

Sands – Tend to have higher bulk density and lower permeabilityPlease do not use sands in Bio-Retention systems!

Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990).

How can a silt loam have moremacroporesthan sand? Answer: More Water Stable Structures

Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990).

Better Structural

Development More

Macropores

Water Stable Aggregates I

Aggregates on left are more water stable, i.e., aggregate stays together and do not separate into the its components, i.e., three soil separates.

Water Stable Aggregates

Water Stable Aggregates – IIThe Classic Photo

Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990)Great Desk Reference Text !!!!

PermeabilityClass Ksat Class

Inchesper hour Material

Impermeable Very Low <0.001417Massive, Rock,

Fragipan

Very Slow Low

0.001417to

<0.0147

Massive, Rock, Fragipan, clayey

Very Slow to Moderately

SlowModerately

Low

0.01417to

<0.1417clay, silty clay,

clay loams

Moderately Slow to Moderate

Moderately High

0.1417 to

< 1.417

silt, silt loam, loam, fine sandy loam

Moderate to Rapid High

1.417 to < 14.17

loamy sand to medium sand

Rapid Very High > 14.17coarse sand,

gravel

General Guide – To Ksat and Material

Hydrologic Soil Terms

Horton Equation, Philip Equation, Green- Ampt Equation

•Infiltration - The downward entry of water into the immediate surface of soil or other materials.

•Infiltration Capacity (fc)- The amount of water per unit area of time that water can enter a soil under a given set of conditions at steady state.

•Infiltration Flux (or Rate)- The volume of water that penetrates the surface of the soil and expressed in cm/hr, mm/hr, or inches/hr. The rate of infiltration is limited by the capacity of the soil and rate at whichwater is applied to the surface. It is a volume flux of water flowinginto the profile per unit of soil surface area (expressed as velocity).

•Cumulative infiltration: Total volume of water infiltrated per unit area of soil surface during a specified time period.

Infiltration Rate

Infiltration Rate (Time Dependent)

Infiltration with Time Initially High Because of a Combination of

Capillary and Gravity Forcesf = fc +(fo-fc) e^-ktfc does not equal K

Final Infiltration Capacity(Equilibrium)- Infiltration

Approaches q - Flux Density

Steady Gravity Induced Rate

Infiltration RateDecreases with Time

1) Changes in Surface and Subsurface Conditions

2) Change in Matrix Potential and Increase in Soil Water Content and Decrease in Hydraulic Gradient

3) Overtime - Matrix Potential Decreases and Gravity ForcesDominate - Causing a Reduction in the Infiltration Rate

4) Reaches a steady-state conditionfc – final infiltration rate

Infiltration Rate Function of Slope & Texture

Source: Rainbird Corporation, derived from USDA Data (Oram,2004)

Infiltration Rate Function of Vegetation

Source: Gray, D., “Principles of Hydrology”, 1973.

Infiltration Rate Function of Horizon A, B, Btx, Bt, C, R

C/R Testing - Areas Fractured Rock

Source: On-site Infiltration Testing - Mr. Brian Oram, PG (2003) and FX. Browne, Inc. (Lansdale, PA)

Infiltration (Compaction/ Moisture Level)

Site Compaction – Can Significantly Reduce Surface Infiltration Rate

Rain Drop Impact Bare Soil

Destroys Soil AggregatesDisperses Soil SeparatesSeals Pore SpaceAids in Loss of Organic MaterialCreates a Surface Crust

Source: (D. PAYNE, unpublished)http://www.geographie.uni-muenchen.de

Percolation Rate

Percolation Rate

Percolation -Downward Movement of Waterthrough the soil by gravity. (minutes per inch) at ahydraulic gradient of 1 or less.

Used and Developed for Sizing Small Flow On-lotWastewater Disposal Systems.

On-lot Disposal Regulations (Act 537) has preliminary Loading equations, but for large systems regulationstypically require permeability testing.

Also none as the Perc Test, Soak-Away Test (UK)

Not Directly Correlated to or a Component of Unsaturated or Saturated Flow Equations

Comparison Infiltration to Percolation Testing

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1 2 3 4 5 6 7 8 9 10Trail

Rat

e (i

n/h

r)

Infiltraton Test

Percolation Test

Percolation Testing Over

Estimated Infiltration

Rate by 40% to over 1000% *

Source: On-site Soils Testing Data, (Oram, B., 2003)

Hydraulic Conductivity

Darcys Law- Saturated FlowVertical or Horizontal

Volume of discharge rate Q is proportional to the head difference dH and to the cross-sectional area A of the column, but it is inversely proportional to the distance dL of the flow path andcoefficient K is called the hydraulic conductivity of the soil.

The average flux can be obtained by dividing Q with A. This flux is often called Darcy flux qw .

Flux Density or Hydraulic Conductivity (Ksp)

Side by Side (Pagoda, J, 2004)

Hydraulic Conductivity (Ksp) quantitative measureof a saturated soil's ability to transmit water when subjected to a hydraulic gradient. It can be thought of as the ease with which pores of a saturated soil permit water movement .

It has units of length per unit time such as mm/sec,mm/hour, or inches/ day (q = -K(ΔH/L ))Actually the term is volume/area/time= q = Q/At

Flux Density (q): The volume of water passing through the soil per unit cross-sectional area per unit of time.

Testing Methods

Goals of the Field Method

• Field Measurement of the Flux Density (qw) and calculate hydraulic conductivity – qw = Ksp (dh/dl)

• Field Measurement of Hydraulic Conductivity (Ksp)

Infiltrometer

Single Rings Infiltrometers

Cylinder - 30 cm in Diameter- Smaller Rings Available.

Drive 5 cm or more into Soil Surface or Horizon.

Water is Ponded Above the Surface- Typically < 6 inches.

Record Volume of Water Added with Time to Maintain a Constant Head.

Measures a Combination of Horizontal and Vertical Flow

ASTM Double Rings Infiltrometers

Outer Rings are 6 to 24 inches in Diameter (ASTM - 12 to 24 inches)Mariotte Bottles Can be Used to Maintain Constant HeadRings Driven - 5 cm to 6 inches in the Soil and if necessary sealed

Very Difficult to Install and Seal – ASTM Double Rings in NEPA

Significant Effort is Needed to Install and Seal Units

ASTM requires documentation of the Depth of the Wetting Front

Potential Leaking Areas

Other Double Rings Small Diameter

6” and 12” Double Ring 3” and 5” Double Ring in Flooded Pit

Infiltration Data- Double Ring Test

Note: Ring Diameter – 26 cm (Oram 2005)

Fc = Ultimate Infiltration Capacity (approx.0.47 cm/hr)

Infiltration Rate –cm/hrCumulative Infiltration(cm)

Steady-State Rate (slope)0.403 cm/hr

Estimated Methods- Based on Grain Size

Hazen MethodApplicability: sandy sediments• K = Cd10 2

• d10 is the grain diameter for which 10% of distribution is finer, "effective grain size" - where D10 is between 0.1 and 0.3 cm

• C is a factor that depends on grain size and sorting

Very Fine Sand, poorly

Sorted

40 - 80

Fine Sand withfines

40 - 80

Medium Sand,

Well Sorted

80 - 120

Coarse Sand,

Poorly Sorted

80 - 120

Coarse sand, well

Sorted, clean

120 - 150

C- Factor

Guelph and Amoozegar Borehole Permeameters

Photo Source:http://www.usyd.edu.auField Testing (Oram, 2000)

$ 1500 each

Measuring Hydraulic Conductivity

Constant or Falling Head Permeameter- Homemade - $ 15.00

12-inch/ 6-inch Double Ring

Side by Side Testing Mr. Brian Oram and Mr. Chris Watkins, 2003.

Constant Head Borehole Permeameters

Talsma Permeameter-Could be Homemade$ 50.00 Retail ($ 300.00)

Modified Amoozegar- Could be Homemade – $30.00- Retail ($ 200.00)

Side by Side Testing by Mr. Brian Oram and Mr. John Pagoda, 2004

Measuring Infiltration Rateto Estimate / Calculate the Flux Density

• Infiltrometers- Yes ! – Single ring- May Not Be Advisable – Multiple tests required– Double ring- Yes ! - May be difficult in rocky and stony areas(i.e., Most of the Poconos !) – Smaller Double Ring in Flood Pit – Yes !

• Flooded Infiltrometers – Yes !

• Adoption of a Strict Double Ring ASTM Method – Likely not appropriate, but method should be used as a guide by professionals.

• Cased Borehole Permeability Test – ASTM Method– Yes ! (Minimum diameter casing 4 inches) with bentonite packing of annular space – Maximum Pipe Height is a function of soil conditions.

My Recommendation and Opinion !Please Do NOT Use a

Conventional Percolation Rate or Percolation Test for Developing

Engineering Design !

Percolation Testing

• Does not directly measure permeability or a flux velocity.

• Has been used to successfully design small flow on-lot wastewater disposal systems, but equations and designs have a number of safe factors.

• Results may need to be adjusted to take out an estimate of the amount of horizontal intake area.

• Without Correction Percolation Data over-estimated infiltration rate data by 40 to over 1000 % with an adjustment for intake area error could be reduced to 10 to 200% (Oram, 2003) , but infiltration rate can overestimate saturated permeability by a factor of 10 or more (Oram, 2005).

• May need to consider the use of larger safety factors and equations similar to sizing equations used for on-lot disposal systems. Safety factors of 50% reduction may not be enough !!

• Borehole Permeability Testing can be a Suitable Method.

• Falling Head , Constant Head, and Quasi Constant Head Methods would be suitable.

• Permeability Data for Specific Site should be calculated using Geometric Average.

• Equations and Methods Based on Darcy’s Law and the result is a value for Ksp or qw.

• Do not recommend estimating permeability based on particle size distribution – Ok for preliminary desktop evaluations if data is available – Not for Final Design !

• Laboratory permeability testing is possible, but it may be difficult to get a representative sample and account for induced changes. May be Ok for Preliminary Evaluations.

SUMMARY

What NOW ?

The Hydrologic Cycle

Where is the Project Site ?

Discharge Zone Recharge Zone

Save Your Client – MoneyNone Structural Development Practices

• Maintain Soil Quality and Maximize the Use of Current Grading to Minimize Loss of O, A, and upper B horizons.

• Minimize Compaction, Maximize Native Vegetation, and Use Good Construction Practices

• Consider Hydrological Setting and Existing Hydrological Features in Site Design and Layout

Answer: New Development/ Construction Practices and New and Updated Ordinances and Planning Documents !

Infiltration System ApproachIndividual Infiltration BMP Units

Soil: Tunkhannock SeriesSoil had stratified sandand gravel lensesWater Table > 8 feetOpen Voids (Gravel and Cobbles)3 to 6 feetKsp Field Measured1 to 10+ inches per hourReported Permeability > 6 inches per hour

Design Used a Ksp of 0.5 inch per hour (50% reduction)

Note- A few sections of the site had permeability of 0.1 inch per hour

Infiltration Unit Configuration

Conceptual Design by:Malcolm Pirnie (Scranton, PA) and Brian Oram(October 2004), Anticipated Installation 2007.

Installed:

Sump and Grass Swale Prior to Unit and Geotextile within unit to capture large organic material

Concrete – Open bottom perforated tank not filled with gravel for storage.

Sizing Calculations- Areas 0.5 in/hr• Impervious Area Roof and Driveway– 3500 ft2• Design Storm – 1.3 inch• Volume of Water to Recharge- 2840 gallons (379 ft3)

• Design Loading- Based on Field Measured Soil Permeability- 0.5 inch per hour or 0.5 in3/in2.hour = 7.481 gpd/ft2

• Minimum Recharge Period – 72 hours (PADEP Recommended)

• Recharge Volume per day – 945 gpd

• Minimum Recharge Area- (945 / 7.481) =126 ft2

• Internal Tank Storage – 3 ft * 8 ft perforated Concrete Tank, plus 3+ foot perimeter and subsurface aggregate storage to generate a minimum surface area of 150 ft2.

• Additional Gravel Layer was added to Meet System Storage Requirement.

Primary Limiting Factor is Not Recharge Capacity but Providing Detention Storage or Storage in the System !

Sizing Calculations- Areas 0.1 in/hr• Impervious Area Roof and Driveway– 3500 ft2• Design Storm – 1.3 inch• Volume of Water to Recharge- 2840 gallons (379 ft3)

• Design Loading- Based on Field Measured Soil Permeability- 0.1 inch per hour or 0.1 in3/in2.hour =1.49 gpd/ft2

• Minimum Recharge Period – 72 hours (PADEP Recommended)

• Recharge Volume per day –945 gpd

• Minimum Recharge Area- (945 / 1.49) =634 ft2 (over 18 % of impervious)

• Recommended Changing the Recharge Period to 7 days to Reduce Infiltration Area to 270 ft2, but providing a system with 100 % detention storage. (7 % of impervious)

• This could not be approved and the project implemented a bioretention/ recharge design

Primary Limiting Factor is Area Requirement Caused by Recharge Period and not Recharge Capacity or Storage in the System !

Bio-Retention Systems

Image Source: http://www.co.monroe.in.us

Bio-Retention Concept

Sump and Grass Swale Prior to Unit and a By-pass Berm Structure for large runoff events.

System has a controlled discharge that maintains a discharge elevation that this consistent with natural water table conditions. Vegetation – Native Seed MixSoil Media – Native Soil from Site Modified to either a loam texture with 2 to 5 % organic material; covered with compost/mulch layer (on-site source).Washed Stone at the Base of the Unit.Sizing based on detention storage requirements and flowrouting.

Conceptual Design by: Malcolm Pirnie (Scranton, PA) and Brian Oram (2004)

Evaluating Recharge Capacity

•Step 1: Desktop Assessment - GIS

Review Published Data Related to Soils, Geology, Hydrology

•Step 2: Characterize the Hydrological Setting

•Where are the Discharge and Recharge Zones?•What forms of Natural Infiltration or Depression Storage Occurs?•How does the site currently manage runoff ?•What are the existing conditions or existing problems?

Evaluation Recharge Capacity

•Step 3: On-Site AssessmentDeep Soil Testing Throughout Site Based on Soils and Geological Data

Double Ring Infiltration Testing or Permeability Testing to calculate qw and provide estimate of loading rates?

How does the water move through the site ?

•Step 4: Engineering Review and Evaluation (meet with local reviewers and PADEP)

•Step 5: Additional On-site Testing

•Step 6: Final Design and Final BMP Selection

How Can We Use Site

Conditons ?

3 feet SurfaceBoulders

Surface Boulders CreatedNatural Depression StorageAreas that appeared to rangein width from 5 to 25 feet.Natural Depression Storage System – New Potential BMP !

Use Of Manufactured SoilsManufactured soils are loosely defined as soil amendment products comprised of treated residuals and various industrial by-products, such as foundry sand and coal ash.

•Use of Organic By-Products – Compost – Organic Soil and Mulch• Recycling of Industrial By-Products and Wood Products•Improving Quality Structural Stability and Nutrient Content ofUnconsolidated Materials with Poor Soil Quality• Use of Fly Ash, Incineration Ash, Recycling Remediated Soil/Unconsolidated Material, Spent Foundry Sands • Use of Soil Conditioners • Use of Dredge Materials and Sediment

I did not say these were off the shelf or easy options !

Artificial Soil Quality ImprovementAggregate Stability- Using a Polymer

No Soil Conditioner Less Soil Conditioner

Source: Brady, N. C., 1990

Interested – Get Involved and Stay Informed?

• Stormwater Manual Oversight Committee Website – Keywords in Google: (stormwater committee PA- 1st Site)

• Meets at the Rachel Carson Building – First Floor Conference Room

• Next Meetings April 25, 2006, May 23, 2006, and June 27, 2006.

• Download- Current Manuals, Discussions, and Meeting Minutes

Soils, Groundwater Recharge, and On-site Testing

Presented by:

Mr. Brian Oram, PG, PASEOWilkes University

GeoEnvironmental Sciences and Environmental Engineering Department

Wilkes - Barre, PA 18766

570-408-4619

http://www.water-research.net

PADEP in the Field

Darcy Equation- What is Delta H?