Technical Memorandum No. 2

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TECHNICAL MEMORANDUM No. 2

Date: February 21, 2013

To: Salinas Valley Water Coalition

From: Timothy Durbin

Subject: California-American Water Company Response to comments by Geoscience on

technical memorandum by Timothy Durbin dated December 3, 2012 regarding

proposed pumping.

Introduction

I prepared the technical memorandum California-American Water Company Comments on proposal to pump groundwater from the Salinas Valley groundwater basin dated

December 3, 2012 (Memorandum), which is attached. The Memorandum addresses the

groundwater pumping that California-American Water Company (CalAm) proposes for

delivering feedstock to a desalinization plant. The proposed groundwater pumping is part of the

Monterey Peninsula Water Supply Project (MPWSP). The Memorandum reviews previous

hydrologic studies and analyses by Geoscience and others. The Memorandum makes

recommendations regarding the additional work that needs to be done to understand adequately

the potential groundwater impacts associated with the use of groundwater as feedstock to the

desalinization plant. In response to my Memorandum, Geoscience Support Services, Inc.

(Geoscience) prepared a 35-page document titled Review and Comments to December 3, 2012,Technical Memorandum Prepared by Mr. Timothy Durbin(Comments). This Technical

Memorandum No. 2 responds to the Geoscience Comments.

Geosciences Comments actually underscore the fundamental point of my Memorandum

-- that site-specific information is needed for the proposed project site. My Memorandum

describes data collection and analyses that are needed to fill the data gaps. To provide

background for my recommendations, my memorandum described the groundwater system and

how that system might respond to the proposed pumping. While taking exception to some of my

descriptions, calling them outdated and incorrect, Geoscience nevertheless relies on the very

same data from my 1978 report to describe the extent of the Salinas Valley Aquitard (SVA).

Further, Geoscience emphasizes that it is updating its model to respond to the concerns

expressed in my Memorandum and that it will be further refining its model to meet those

concerns (Comments, p. 3).

Exhibit SV-3


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My Memorandum was intended to make constructive recommendations, and the intent of

this memorandum is the same. The objective of the Salinas Valley Water Coalition is not to

oppose the project but to express concern that the project be designed to avoid adverse impacts

on the Salinas Valley groundwater basin, and particularly on the 180-foot aquifer. My advice to

the Coalition has been that the proposed project could be operated without adverse impacts to the

Salinas Valley groundwater basin were it to be sited and designed properly, which is expressed

in my original memorandum.

My principal conclusion is that site-specific data and analyses are needed, On this issue,

Geosciences and I are in complete agreement. Geosciences states in its Comments:

the distribution and thickness of the SVA in the project area is

important since the flow regimes in the underlying Dune Sand

Aquifer and 180-Foot Aq1uifer in which project pumping may

take place will be directly impacted by the extent and thickness of

an aquitard, if present.

Although alluding to more recent work of others, Geoscience does not present citations

to such work, and apparently concurs that further study is needed. Geoscience states in its

Comments:

Additional proposed project studies include exploratory test

drilling, test wells, geophysical surveying and long-term aquifer

testing. Results from these studies and testing will be evaluated

and used to further refine the project details, such as the final well

locations and well construction details for the current proposedMPWSP.

A continuum of possibilities exists, which range from the complete absence of clayey sediments

in the subsurface to the occurrence of a thick low-permeability aquitard. Recent hydrogeologic

assessments done for the Monterey County Water Resources Agency (MCWRA, 2001 and 2004)

suggests the likely occurrence within the project area of an aquitard that separates the dune

deposits from the underlying 180-foot aquifer. While Geoscience may consider the work done

for the MCWRA outdated, it forms a significant basis for the characterization of the

hydrogeologic setting within the project area. The collection of site-specific data very well could

lead to a different characterization, but Geoscience defends the position that an aquitard ofhydrologic significance is absent without the benefit of site-specific information. The actual

subsurface conditions must be resolved by field studies and data analyses, but the field studies

will need to be more extensive than just constructing and operating a test well.


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The remainder of this memorandum addresses specific comments by Geoscience,

including their comments on the project description, hydrogeologic setting, groundwater

modeling, and recommendations.

Changing Project Description

Geoscience offers the criticism that my Memorandum is based on an outdated project

description. The project description has changed over time. I relied on the original MPWSP

application to the California Public Utilities Commission and Appendix H to that application. I

additionally relied on the updated CEQA project description (CPUC, 2009), which is included

within Appendix H and specifically references the Geosciences modeling report (Geosciences,

2008). The project has subsequently changed as indicated by California-American Water

Company (2012a and 2012b), CPUC (2012), and Geoscience (2013). At one time the project

consisted of wells within the 180-foot aquifer that were alternatively located north and south of

the Salinas River. Then wells within the dune deposits were identified as a contingency. Thelatest iteration is wells in the dune deposits as the preferred project, with wells in the 180-foot

aquifer as a contingency.

Nevertheless, my recommendations would be the same for any project site along the

Monterey Bay shore. The hydrogeologic setting and hydrodynamic response of the groundwater

system must be characterized for whatever project configuration and site finally are selected.

That will require constructing exploratory wells, perhaps conducting geophysical surveys,

collecting chemical and isotopic data, collecting groundwater-level data, and appropriately

analyzing the compiled data. The data necessary for an adequate evaluation generally do not

exist for potential project sites along Monterey Bay, and an extensive data collection programwill be required for any selected site. The successful design and operation of the project requires

site-specific field work and data analyses.

Hydrogeologic Setting

Geoscience is mostly critical of my description of the hydrogeologic setting and how that

setting might affect the hydrodynamic response of the groundwater system to the proposed

project. Both Geoscience and I use geographic extrapolations of existing data to assess what

might be the actual hydrogeologic conditions at a project site. For the most recently proposed

site, the existing hydrogeologic data appears to consist of three wells that are about a mile distant

from the project site (Geoscience, 2013, Figure 8). Site-specific data appear to be absent within

the one-mile radius of the proposed project, and they are very limited at further distances

(Geoscience, 2013, Figure 8).


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The critical hydrogeologic issue is whether an aquitard separates the 180-foot aquifer

from the overlying dune deposits within the proposed project area. Geoscience states seemingly

unequivocally that such an aquitard does not exist. They extrapolate geographically from various

previous studies to make that contention; such extrapolations are necessary because site-specific

data are not available. I believe that an aquitard of hydrologic importance probably exists, but I

also believe that any uncertainty can be removed by undertaking an appropriate site-specific field

investigation. The significance of an aquitard to the project depends on its thickness and vertical

hydraulic conductivity, but it depends also on whether the project consists of wells in the dune

deposits or the 180-foot aquifer. For wells within the dune deposits, the occurrence of an

aquitard or other low-permeability materials would tend to prevent impacts to the 180-foot

aquifer. For wells within the 180-foot aquifer, the absence of an aquitard could increase the

proportion of seawater drawn into the feedstock wells. However, the actual importance of the

existence or absence of an aquitard can be assessed only by conducting appropriate field

investigations, data analyses, and groundwater-flow and salinity-transport modeling.

Geoscience, in its Comments, acknowledges that the investigations and modeling as I

describe are necessary, and are in fact planned. Nevertheless, it persists in the defense of a

particular conceptual model of the hydrogeologic setting. It makes particular reference to a map

of the aquitard overlying the 180-foot aquifer that appears within my 1978 USGS report on the

Salinas Valley groundwater basin (Durbin and others, 1978). Geoscience makes several

comments regarding that map. The map shows the extent of the aquitard that was significant to

the development of a Salinas Valley basin-wide groundwater model. However, that valley-wide

mapping scale is not suitable for assessing the hydrogeologic setting with respect to small-scale

features of significance to the hydrodynamics of the proposed project. Correspondingly, in

developing my Memorandum, I used hydrogeologic information developed recently for theMCWRA (2001 and 2004). Geoscience commented that the cross-section in my memorandum

does not match the map in my 1978 report. That is the case precisely because the cross section I

relied on was developed from the more recent and applicable MCWRA investigations.

MCWRA (2004) developed a number of hydrogeologic cross sections through the

northern Salinas Valley. The most relevant are cross sections A-A' and B-B'. Section A-A'

extends southeastward from Monterey Bay along the cross-section line that appears on Figure 2

in my Memorandum. Section A-A' begins at Monterey Bay about one-mile north of the Salinas

River mouth. Section B-B' is generally parallel to Monterey Bay. At the currently proposed

project site, the cross-section line is about one-half mile landward of Monterey Bay. MCWRA

(2004) indicates that the aquitard overlying the 180-foot aquifer is more than 100 feet in

thickness where section A-A' intersects Monterey Bay near the Salinas River mouth. Perhaps

more germane to the Geoscience Comments, MCWRA (2004) indicates that the aquitard is more

than 50 feet in thickness where section B-B' is opposite the proposed project site. MCWRA


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(2001) shows a geographical delineation of the southward extent of the aquitard overlying the

180-foot aquifer that suggests the proposed project site is underlain by the aquitard.

The cross section include within my Memorandum is derived from the MCWRA (2004)

cross section A-A'. The landward part of that cross-section was intended as a simplification of

the MCWRA cross section. The seaward part of the section was constructed by connecting the

180-foot and 400-foot aquifers as depicted on the MCWRA cross-section with the outcrops of

those aquifers beneath Monterey Bay as depicted by Greene (1970). Geoscience suggests that my

cross section in total has no basis. That certainly would be the case if the work by MCWRA and

Greene is faulty. If no basis exists for defining the hydrogeologic setting seaward from the

proposed project area, additional field data are necessary to define that setting.

Groundwater Modeling

My principal criticisms of the Geoscience model (Geoscience, 2008) are (1) thedirectness of the connection between the groundwater system and Monterey Bay as represented

in the model, (2) the use of the Salinas Valley Water Project Phase II as a baseline condition, and

(3) and the absence of simulating post-project conditions.

Much of the Geoscience commentary on my Technical Memorandum is consumed with

the question of what is the hydrogeologic setting at the project site. As I noted above, a

continuum of possibilities exists, which range from a complete absence of clayey sediments in

the subsurface to the occurrence of a thick low-permeability aquitard. The more important

question that follows is how the groundwater system is connected to Monterey Bay, including

the dune deposits, 180-foot aquifer, and deeper parts of the groundwater system. The Geosciencemodel is based on the one end of the continuum. Their hydrogeologic and hydraulic conceptual

model assumes that the groundwater system within the dune deposits and 180-foot aquifer is

intimately connected to Monterey Bay. That conceptual model leads axiomatically to the

conclusion that the groundwater extracted from wells within the 180-foot aquifer will consist

almost entirely seawater drawn from Monterey Bay. However, that conclusion is nothing but a

derivative of the assumption that within the project site the 180-foot aquifer in not overlain by an

aquitard, which is not a site-specific fact but an extrapolation that appears to contradict the recent

hydrogeologic work for MCWRA (2001 and 2004). The appropriate approach is to consider the

possibility that some degree of separation might exist between the 180-foot aquifer and

Monterey Bay.

Were the Salinas Valley Water Project (SVWP) Phase II to be implemented, groundwater

levels within northern Salinas Valley would be higher than presently occur. The general present

condition is that groundwater levels decline geographically eastward from Monterey Bay, and

seawater intrusion correspondingly occurs. The implemented elements of the Salinas Valley


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Water Project have retarded the advance of the seawater front within the groundwater system,

and eventually may stop the advance. That has been achieved by delivering surface water to

coastal agricultural producers and their corresponding reduction in groundwater pumping. The

SVWP Phase II involves further reduction in coastal groundwater pumping, which most likely

would produce groundwater flows toward Monterey Bay and expulsions of seawater from the

groundwater system. The possibility of adverse groundwater impacts from the proposed project

are reduced when evaluated under the assumption that the SVWP Phase II will be implemented.

The Geoscience modeling of the project assumes that advantageous condition, even though the

SVWP Phase II may never be implemented. Accordingly, as I suggested, Geoscience apparently

will evaluate the project with and without the implementation of SVWD Phase II.

In my memorandum I suggest that adverse groundwater impacts could occur at the

cessation of groundwater pumping for the project. I indicate that the modeling of the project

pumping should include the simulation of a post-project period. While Geoscience appears to

believe that the possibility of post-project impacts is infinitesimally small, nevertheless, the bestapproach is to test that possibility with the simulation of a post-project period.

Recommendations

As I said in my Memorandum, pumping from the dune deposits with shallow wells or

Ranney collectors probably will not adversely impact the Salinas Valley groundwater basin, but

field work and data analyses are needed to substantiate that conclusion. As I also said in my

Memorandum, pumping from the 180-foot aquifer is much more likely to result in unacceptable

impacts. For either case, the uncertainty must be reduced by conducting a thorough hydrologic

investigation. Such an investigation would consist of five parts.

1. The understanding of the hydrologic setting along Monterey Bay must be refined.Previous investigations have established the general hydrologic setting, but additionalsite-specific work is needed to define the thickness and extent of the 180-foot aquifer,overlying aquitard, and dune deposits. Especially important are identifying the onshoreand offshore extent, thickness, and continuity of the aquitard overlying the 180-footaquifer, and defining the hydraulic connections among the 180-foot aquifer, overlyingaquitard, and dune deposits. The hydrogeologic investigation will require the compilationand analysis of existing hydrogeologic information, the construction of new boreholes,and perhaps conducting geophysical surveys. The number of boreholes must be sufficient

to construct at least three hydrogeologic cross section perpendicular to the Monterey Bayshore: through the project site, immediately north of the site, and immediately south ofthe site. At least nine boreholes into the 180-foot aquifer would be required. Whether theproposed pumping from the 180-foot aquifer or the dune deposits will have adverseimpacts will depend largely on the details of the actual hydrogeologic setting.

2. An understanding of the seawater-intrusion mechanisms must be developed. Historicalseawater intrusion has occurred by some combination of the mobilization of naturally


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occurring seawater within the groundwater system, pumping-induced vertical leakagefrom Monterey Bay into the groundwater system, extrusion of naturally occurringseawater within the aquitards deposited as lagoonal sediments, and other mechanisms.The collection and analysis of geochemical and other information will be required toidentify details of the seawater-intrusion processes. Whether the proposed pumping from

the 180-foot aquifer or the dune deposits will have adverse impacts may dependsignificantly on the actual processes that will be activated by the proposed pumping.

3. Large-scale aquifer tests will be needed to supplement the hydrogeologic and seawater-intrusion investigations. As long as wells in both the dune deposits and 180-foot aquiferare considered as primary or contingency water supplies, separate tests must beconducted with pumping from the 180-foot aquifer and the dune deposits. The tests needto include monitoring wells within the 180-foot aquifer, the overlying aquitard, and thedune deposits. The pumping rates and test durations must be sufficient to identifyprocesses that will be activated by the full implementation of the proposed water-supplypumping. This could involve pumping for a year or more. However, a shorter duration

might be sufficient for pumping from the dune deposits. The tests should be designedwith respect to pumping rates, observation-well placement, and test duration using agroundwater model to predict the expected response of the groundwater system duringthe test and to evaluate the identifiability of critical hydraulic characteristics of thegroundwater system.

4. A local groundwater model must be developed that represents the essential elements ofthe groundwater system onshore and offshore along Monterey Bay. The model mustsimulate both groundwater flow and solute transport. The model must represent thehydrologic setting, including the thickness and extents of the dune deposits, 180-footaquifer, 400-foot aquifer, and deep aquifer, and the intervening aquitards. The modelmust represent the hydraulic characteristics of the groundwater system, and it mustrepresent the seawater-intrusion process active within the groundwater system. Thedevelopment of an adequate model may require simulating the effects of water density onthe hydrodynamics of the groundwater system. The boundary and initial conditions forthe local model should be derived from SVIGSM. However, the simulation run on theSVIGSM must represent a realistic representation of baseline conditions. The appropriatebaseline condition is for the continued operation of the CSIP project without additionalacreage. An expansion of CSIP is not in place or envisioned at this time, and it is not anappropriate or realistic depiction of baseline conditions for analyzing the potentialimpacts of the CalAm proposal. The proposed CalAm pumping must be simulated for afinite period, and an extended post-project period must be simulated.

5. The modeling results for both the primary and contingency proposal must be subjected toa thorough sensitivity analysis. The modeling results will unavoidably always containuncertainty, even though the objective of the modeling exercise and supportinginvestigations described above will be to minimize the uncertainty. The sensitivityanalysis will quantify how the modeling results might change with different assumptionsabout the hydrogeologic setting, seawater intrusion processes, and the hydrauliccharacterization of groundwater system.


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I believe the best interest of CalAm and the community would be served by conducting

thorough field investigations, data analyses, and modeling evaluations. An unfortunate outcome

would be to have the project fail after implementation because the information used in the design

was inadequate. I continue to believe that my recommendations represent good advice.

References

California-American Water Company, 2012a, Application of the California-American WaterCompany for approval of the Monterey Peninsula water supply project and authorizationto recover all present and future costs in rates: Before the California Public UtilitiesCommission.

California-American Water Company, 2012b, Application of the California-American WaterCompany for approval of the Monterey Peninsula water supply project and authorization

to recover all present and future costs in rates, California-American Water Companycontingency plan compliance filing: Before the California Public Utilities Commission.

California Public Utilities Commission, 2012, CalAm Monterey Peninsula Water Supply Project

Notice of Preparation.

California Public Utilities Commission, 2009, California American Water Company Coastal

Water Project, Final Environmental Impact Statement.

Durbin, T. J ., Kapple, G. W., and Freckleton, J . R., 1978, Two-dimensional and three-

dimensional digital models for the Salinas Valley groundwater basin, California: U. S.Geological Survey Water Resources Investigations 78-113.

Geosciences Support Systems, Inc., 2008, North Marina groundwater model evaluation ofpotential project, 2008: Report prepared for California American Water.

Geoscience Support Systems, Inc., 2013, Review and comments to December 3, 2012, Technical

Memorandum prepared by Mr. Timothy Durbin California-American water Company

Comments on proposal to pump groundwater from the Salinas Valley groundwater

basin.

Greene, H. G., 1970, Geology of southern Monterey Bay and its relationship to the ground water

basin and salt water intrusion: U. S. Geological Survey Open-File Report 70-141.

Monterey County Water Resources Agency, 2001, Final report on hydrogeologic investigation of

the Salinas Valley basin in the vicinity of Fort Ord and Marina, Salinas Valley,

California: Report prepared by Harding Lawson.


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Monterey County Water Resources Agency, 2004, Hydrostratigraphic analysis of the northernSalinas Valley: Report prepared by Kennedy/Jenks Consultants.

Documents

Technical Memorandum No. 2