Final Feasibility Study Report.pdf

FINAL

FEASIBILITY STUDY RESULTS REPORT

D-Q UNIVERSITY, YOLO COUNTY, CALIFORNIA

Prepared fo r

U .S. Army Corps o f Eng ineers

1325 J S t reet

Sacramento, CA 95814

June 12 , 2012

FUDS Project No.: J09CA1180 Contract Number: W1912BV-10-D-2012

ECS Inc.

1571 Parkway Loop, Ste B

Tust in, CA 92780-6523

Brown and Caldwel l 10540 White Rock Road, Suite 180 Rancho Cordova, Cal i fornia 95670

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D-Q UNIVERSITY, YOLO COUNTY, CALIFORNIA

SIGNATURE PAGE

Signatures of pr inc ipal personnel responsible for review and development of th is report .

Reviewed by:

Dhananjay Rawal, REM #11266 ECS/ECSBC JV Quality Control Systems Manager

Approved by:

Wendy Linck, P.G. # 6934 Brown and Caldwell/ECSBC JV Project Manager

Guy Graening, P.E. # M29796 Brown and Caldwell/ECSBC JV Project Engineer

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D-Q UNIVERSITY, YOLO COUNTY, CALIFORNIA

DISTRIBUTION LIST

ADDRESS NUMBER OF COPIES

Mr. Tim Crummett ............................................................................... 5 electronic (PDF and Native) and 5 hard copies

U.S. ARMY CORPS OF ENGINEERS

1325 J Street Sacramento, CA 95814-2922

Mr. Mark Clardy .......................................................................................................... 1 electronic PDF and 1 hard copy

CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD

11020 Sun Center Drive, Suite #200 Rancho Cordova, CA 95670

Mr. Dhananjay Rawal, ECSBC JV Quality Control Systems Manager ........................ 1 electronic PDF and 1 hard copy ECS, Inc.

1571 Parkway Loop, Suite B Tustin, CA 92780

Ms. Wendy Linck, ECSBC JV Project Manager Mr. Guy Graening, ECSBC JV Project Engineer Mr. Greg Menna, ECSBC JV Field Team Leader File ........................................................................................................ 1 electronic (PDF and Native) and 1 hard copy

BROWN AND CALDWELL

10540 White Rock Road, Suite 180 Rancho Cordova, CA 95670

Table of Contents D-Q Univ. Feasibility Study Results Report i

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TABLE OF CONTENTS

1. INTRODUCTION ..................................................................................................................................................... 1-1

1.1 Purpose and Objective ................................................................................................................................. 1-1

1.2 FUDS Program and Site Eligibility ................................................................................................................ 1-1

1.3 Feasibility Study Approach ........................................................................................................................... 1-2

2. REMEDIAL INVESTIGATION SUMMARY .............................................................................................................. 2-1

2.1 Site Description and Operational History ...................................................................................................... 2-1

2.2 Summary of Previous Investigations ............................................................................................................. 2-1

2.2.1 Groundwater Pilot Test Summary ..................................................................................................... 2-2

2.3 Geologic and Hydrogeologic Summary ........................................................................................................ 2-3

2.4 Summary of Nature and Extent of Contamination in Shallow Groundwater ................................................. 2-5

2.4.1 TCE Groundwater Plume (AOC-4) ................................................................................................... 2-5

2.4.2 TPH-DRO Groundwater Plume (AOC-5) .......................................................................................... 2-5

2.5 Site Conceptual Model Summary ................................................................................................................. 2-5

2.6 Risk Assessment Summary .......................................................................................................................... 2-6

2.7 Volume and Mass Estimates for Remediation .............................................................................................. 2-7

3. IDENTIFICATION AND SCREENING OF TECHNOLOGIES ................................................................................. 3-1

3.1 ARARs .......................................................................................................................................................... 3-1

3.1.1 Chemical-Specific ARARs ................................................................................................................ 3-1

3.1.2 Location-Specific ARARs .................................................................................................................. 3-1

3.1.3 Action-Specific ARARs ..................................................................................................................... 3-2

3.1.4 Remedial Action Objectives .............................................................................................................. 3-2

3.2 General Response Actions ........................................................................................................................... 3-3

3.3 Identification and Screening of Technology Types and Process Options ..................................................... 3-3

3.3.1 Screening Approach for Process Options ......................................................................................... 3-4

3.3.2 Selected Process Options ................................................................................................................. 3-4

3.4 Identification of Remedial Alternatives .......................................................................................................... 3-5

4. DEVELOPMENT OF ALTERNATIVES AND DETAILED ANALYSIS ...................................................................... 4-1

4.1 Alternative 1 – No Action .............................................................................................................................. 4-3

4.2 Alternative 2 – Monitored Natural Attenuation .............................................................................................. 4-3

4.3 Alternative 3 – Enhanced Biodegradation and Groundwater Recirculation .................................................. 4-5

4.4 Alternative 4 – Permeable Reactive Barriers ................................................................................................ 4-6

4.5 Alternative 5 – ISCO Direct Groundwater Injection ....................................................................................... 4-7

5. COMPARATIVE ANALYSIS OF ALTERNATIVES .................................................................................................. 5-1

5.1 Overall Protection of Human Health and the Environment ........................................................................... 5-1

5.2 Compliance with ARARs ............................................................................................................................... 5-1

5.3 Long-Term Effectiveness and Performance ................................................................................................. 5-2

5.4 Reduction of Toxicity, Mobility or Volume through Treatment ....................................................................... 5-2

5.5 Short-Term Effectiveness ............................................................................................................................. 5-2 ii

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5.6 Implementability ............................................................................................................................................ 5-3

5.7 Cost .............................................................................................................................................................. 5-3

5.8 Regulatory Agency and Community Acceptance .......................................................................................... 5-4

6. SUMMARY AND CONCLUSIONS .......................................................................................................................... 6-1

7. LIMITATIONS ......................................................................................................................................................... 7-1

8. REFERENCES ....................................................................................................................................................... 8-1

APPENDIX A: PRELIMINARY ANALYSIS OF POTENTIAL ARARS............................................................................ A

APPENDIX B: DETAILED COSTS OF ALTERNATIVES .............................................................................................. B

APPENDIX C: COSTING BACK-UP (CD) ..................................................................................................................... C

LIST OF FIGURES

Figure 1-1. Site Location Map .............................................................................................................................. 1-4 Figure 1-2. D-Q University Layout ........................................................................................................................ 1-5 Figure 2-1. Potentiometric Surface Map, 2/11/11 Pilot Test in Operation ............................................................ 2-9 Figure 2-2. TCE Concentrations in Shallow Groundwater .................................................................................. 2-10 Figure 2-3. Diesel Range Hydrocarbon Concentrations in Shallow Groundwater .............................................. 2-11 Figure 4-1. Alternative 2 - Monitored Natural Attenuation .................................................................................... 4-9 Figure 4-2. Alternative 3 - Enhanced Bioremediation and Groundwater Recirculation....................................... 4-10 Figure 4-3. Alternative 4 - Permeable Reactive Barriers .................................................................................... 4-11 Figure 4-4. Alternative 5 - In Situ Chemical Oxidation ........................................................................................ 4-12

LIST OF TABLES

Table 1-1. National Contingency Plan Criteria ..................................................................................................... 1-3 Table 2-1. Historical Groundwater Flow Directions and Gradient ......................................................................... 2-4 Table 2-2. Groundwater Risk Screening Evaluation for Vapor Intrusion .............................................................. 2-7 Table 2-3. Comparison of Groundwater Maximum Detected Concentrations to MCLs ........................................ 2-7 Table 2-4. Comparison of Groundwater Concentration from D-Q-GWM-5 to MCLs ............................................ 2-7 Table 2-5. TCE Mass and Volume Estimates in Shallow Groundwater ................................................................. 2-8 Table 2-6. TPH-DRO Mass and Volume Estimates in Shallow Groundwater ....................................................... 2-8 Table 3-1. Screening of Remedial Technologies and Process Options for Groundwater ..................................... 3-6 Table 5-1. Comparative Analysis of Short-Term Effectiveness ............................................................................ 5-3 Table 5-2. Comparative Analysis of Costs ........................................................................................................... 5-4 Table 6-1. Summary of Comparative Analysis of Alternatives .............................................................................. 6-1 iii

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LIST OF ACRONYMS

AOC Area of Concern ARARs applicable or relevant and appropriate requirements AST above ground storage tank bgs below ground surface BC Brown and Caldwell

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act cis-1,2-DCE cis-1,2-dichoroethylene COC chemical of concern COPCs contaminants of potential concern CPT cone penetrometer test

Data Gap RI Data Gap Investigation and Treatability Study Report DCE dichloroethylene DERP Defense Environmental Restoration Program DERP-FUDS Defense Environmental Restoration Program - Formerly Used Defense Site DoD Department of Defense

ECS Enviro Compliance Solutions ESL Environmental Screening Level

FS Feasibility Study FUDS Formerly Used Defense Site gpm gallons per minute GSA General Services Administration

ILCR Incremental Lifetime Cancer Risk ISCO in situ chemical oxidation IUR inhalation unit risk factor

MCL maximum contaminant level mg/L milligrams per liter MNA monitored natural attenuation

NCP National Contingency Plan NPDES National Pollutant Discharge Elimination System iv

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O&M operation and maintenance

PRB permeable reactive barrier PRP potentially responsible party

RAO remedial action objective RI Remedial Investigation RI/FS remeidial investigation/feasibility study RWQCB California Regional Water Quality Control Board

SARA Superfund Amendments and Reauthorization Act SI Site Inspection SWRCB State Water Resources Control Board

TBC To-Be-Considered TCE trichloroethylene TDS total dissolved solids TOC tolal organic carbon TPH-DRO total petroleum hydrocarbons - diesel range organics trans-1,2-DCE trans-1,2-dichloroethylene µg/L micrograms per liter USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency UST underground storage tank

VOCs volatile organic compounds

WDRs Waste Discharge Requirements

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D - Q U N I V . F E A S I B I L I T Y S T U D Y R E S U L T S R E P O R T

1 . I N T R O D U C T I O N

This report presents the final Feasibility Study (FS) to evaluate alternatives for the remediation of groundwater impacted with volatile organic compounds (VOCs), primarily trichloroethylene (TCE) for the D-Q University Formerly Used Defense Site (FUDS) located in Yolo County, California (Site). This document was prepared by Brown and Caldwell (BC) for the U.S. Army Corps of Engineers (USACE), Sacramento District under Enviro Compliance Solutions Inc., (ECS); ECSBC Joint Venture, Contract # W1912BV-10-D-2012. D-Q University is a FUDS located in Yolo County on the north side of County Road 31 (Covell Road) and approximately 9 miles west of Davis, California. The town of Davis is located approximately 14 miles west of Sacramento, California. The location of D-Q University is provided on Figure 1-1 and the Site layout is provided on Figure 1-2.

This report is written to accommodate the public, as well as the regulatory community. Since readers will have a wide range of technical knowledge, the text is designed for the non-technical reader, while summary tables and appendices accommodate the more technically oriented reader.

1.1 Purpose and Objective

The remedial investigation/feasibility study (RI/FS) of the former D-Q University has been performed under the FUDS program. In accordance with FUDS guidance, the overall project is being conducted consistent with the National Contingency Plan (NCP) and the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA or Superfund). The purpose of the FUDS program is to reduce, in a timely and cost effective manner, the risk to human health, safety, and the environment from contamination resulting from past Department of Defense (DoD) activities. CERCLA provides the framework to address and clean up releases of hazardous substances. The objective of the FS is to support a decision between the responsible party and the regulatory agency regarding the most appropriate remedy for the Site.

1.2 FUDS Program and Site Eligibility

The land on which D-Q University currently lies was owned and occupied by the U.S. Army from 1952 to 1969 and was most commonly called the former West Coast Relay and Radio Transmitting Station. All real properties formerly owned by, leased by, possessed by, or otherwise under the jurisdiction of the Secretary of Defense or elements of the U.S. military are managed within the FUDS program. Policy and guidance for the FUDS program is provided in USACE Engineering Regulation 200-3-1 (USACE, 2004). The Remedial Investigation (RI) identified Areas of Concern (AOCs) where past DoD activities at the former station may have impacted the environment. FUDS program funding can only be used to assess and remediate DoD liability at an eligible property, which is defined as real property. Under the FUDS program, land that was previously utilized by DoD and that has no “beneficial use” history will be characterized and, if necessary, remediated to an appropriate standard.

Under the FUDS program, one of the parameters to be considered during the initiation of a project is whether the property (or specific item/site) has been beneficially used by any owner, operator, or other party that may be considered a potentially responsible party (PRP). If USACE determines the contamination was caused solely by DoD, it will be mitigated by USACE through the FUDS program. If an investigation is

1: Introduction D-Q Univ. Feasibility Study Results Report

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\\bcsac01\projects\39000\139564 - USACE DQ Univ Remediation\Feasibility Study Report\Final FS\Final Feasibility Study Report.doc initiated (by any party) and DoD is determined to be only partially responsible, USACE will investigate to the extent necessary to determine DoD liability.

Consideration must also be given to the ability to identify DoD-generated contaminants from contaminants introduced by other PRPs, on or off the FUDS property. If identification of separate contaminant streams cannot be achieved, or if separate remediation of DoD-generated contaminants cannot be realized, the project may be ineligible for remediation under the FUDS program. If commingled contamination exists, a PRP project must be initiated and the Department of Justice will negotiate a contribution settlement with the current landowner/responsible party based on a liability analysis.

Further, the Defense Environmental Restoration Program – FUDS (DERP-FUDS) policy does not allow the USACE to provide cost recovery to property owners nor does it allow USACE to recover costs from property owners for remedial work. However, the property owner may initiate an investigation and/or clean-up action and subsequently seek cost reimbursement from the Department of Justice by filing a tort claim.

The former West Coast Relay and Radio Transmitting Station is a FUDS as defined by the DERP. The DERP-FUDS statute [10 USC 2701 (a) (2)] requires that projects addressing hazardous substances, pollutants, and contaminants be conducted consistent with the CERCLA and the Superfund Amendments and Reauthorization Act of 1986 (SARA). The FUDS identification number for D-Q University is J09CA1180.

1.3 Feasibility Study Approach

This FS follows the procedures presented by the United States Environmental Protection Agency (USEPA) in the Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (USEPA/540/G- 89/004) (USEPA, 1988). This approach includes the following tasks:

Describe the background information for the Site, including the Site history, nature and extent of groundwater contamination, contaminant fate and transport, and risks to human health and the environment;

Estimate the volumes of waste in groundwater beneath the Site to a level sufficient to cost and compare different remedial alternatives;

Identify remedial action objectives (RAOs) and potential applicable or relevant and appropriate requirements (ARARs) that will determine the necessary extent of cleanup for the Site;

Develop a series of general response actions, technology types, and process options that are potentially applicable to the Site;

Screen the process options to eliminate those that can not be implemented technically at the Site;

Assemble the process options into remedial alternatives;

Conduct a detailed analysis of the selected process options based on the nine NCP criteria; and

Perform a comparative analysis of the alternatives to identify the best remedial options for the Site.

Table 1-1 presents the nine NCP Criteria. The threshold criteria are statutory requirements of the NCP.

Thus, they must be met by the selected remedy. The primary balancing factors are the criteria upon which the FS analysis is based. The modifying considerations are typically not addressed in the FS, but rather are determined on comments from regulatory agencies and the public on the Proposed Plan.

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Table 1-1. National Contingency Plan Criteria

Criterion Threshold

Criteria Primary Balancing

Factors Modifying

Considerations

Overall Protection of Human Health & Environment X

Compliance with ARARs X

Long-Term Effectiveness & Permanence X

Reduction of Toxicity, Mobility & Volume Through Treatment X

Short-Term Effectiveness X

Implementability X

Cost X

State or Support Agency Acceptance X

Community Acceptance X

This report specifically presents alternatives to remediate groundwater impacted with VOCs at the Site. The VOCs evaluated and identified in the Human Health and Ecological Risk Assessment (USACE, 2011) were the same as those considered for the preliminary analysis of potential chemical-specific ARARS presented in this FS report.

The remainder of this report summarizes the remedial investigations at the Site, describes the nature and extent of contamination, analyzes the effectiveness of the enhanced biodegradation and groundwater recirculation pilot test, identifies potential ARARs, and develops the RAOs. General response actions, technology types, and process options are identified and screened. Remedial alternatives that meet the RAOs are developed and analyzed in detail. Finally, the remedial alternatives are compared and conclusions are presented.

Figure 1-2

D-Q University Layout

D-Q University, Yolo County, California139564

March 2011

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D - Q U N I V . F E A S I B I L I T Y S T U D Y R E S U L T S R E P O R T

2 . R E M E D I A L I N V E S T I G A T I O N S U M M A R Y

This section provides a description of the Site, summarizes historical and current Site uses, and describes previous environmental investigations relevant to the FS. A more detailed description of Site background information can be found in the Data Gap Remedial Investigation and Treatability Study Report (Data Gap RI) (Brown and Caldwell, 2010).

2.1 Site Description and Operational History

In 1952, 651.55 acres of agricultural land were acquired by the U.S. Army for the Sacramento Valley Radio Transmitter Station to support the Signal Corps Radio Station (call letters: WVY) (Hoover et al., 1990;

Dynamac, 1992). The 651.55 acres is referred to as the Site. The former West Coast Relay and Radio Transmitting Station is referred to as the Station and the current D-Q University as the Campus. Essentially, the Site includes the surrounding agricultural fields and the former Station or the current Campus. In 1969, the property was designated as surplus and turned over to the General Services Administration (GSA).

Permanent ownership of the land was acquired by D-Q University in 2001.

Improvements to the Site during U.S. Army occupation included the construction of a transmitter building (Building 100), a power generation building (Building 101), a relay building (Building 102), barracks (Building 103), storage buildings, two incinerators, utilities, six Underground Storage Tanks (USTs), four above ground storage tanks (ASTs) inside Building 100, twenty-two transformers, two waste oxidation lagoons, two cooling water injection (disposal) wells, and one cooling water supply well (Dynamac, 1992).

At the time of the acquisition by D-Q University, the Station contained all of the original buildings, most of the generating and pumping machinery, two waste oxidation lagoons, two cooling water injection wells, six USTs, six ASTs, two incinerators, and 13 of the transformers. The other nine transformers were removed prior to the property transfer. All USTs, one AST not in use within Building 101, the incinerator located west of Building 103, and 10 of the 13 transformers have been removed by USACE from the Station. The incinerator east of Building 102 and three of the four ASTs inside Building 101 had been removed prior to USACE involvement (USACE, 1997). The facilities, three remaining transformers, and two other ASTs are still being used by D-Q University.

There are no structures within a 1-mile radius other than those associated with the Campus or farming activities. Surrounding the Campus are agricultural lands that are currently leased to farmers that plant and harvest alfalfa. The Yolo County Airport is approximately 1.75 miles northeast from D-Q University (Figure 1-1). The layout and current use of the facilities and locations of groundwater wells, waste oxidation lagoons, and other pertinent structures are identified in Figure 1-2.

2.2 Summary of Previous Investigations

As part of the FUDS process, an RI, inclusive of a Data Gap RI (Brown and Caldwell, 2010) was conducted by Brown and Caldwell for the USACE Sacramento District that defined potential source areas, nature and extent of contamination, subsurface characteristics, transport mechanisms, contaminant fate, and a conceptual site model (Brown and Caldwell, 2008). It eliminated from further consideration those AOCs that pose little or no threat to public health or the environment, determined if there is any potential need for removal action, set priorities for site inspections, and gathered existing data to facilitate later evaluation of the

2: Remedial Investigation Summary D-Q Univ. Feasibility Study Results Report

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\\bcsac01\projects\39000\139564 - USACE DQ Univ Remediation\Feasibility Study Report\Final FS\Final Feasibility Study Report.doc release pursuant to the Hazard Ranking System conducted by the USEPA. The RI identified that the primary chemicals of concern (COC) are VOCs, primarily TCE in groundwater and diesel range organics (TPH- DRO) in soil and groundwater. The groundwater AOCs and the focus of this FS are:

AOC-4: TCE groundwater plume

AOC-5: diesel groundwater plume at the former location of USTs #1-4

A summary of these AOCs are:

TCE Groundwater Plume (AOC-4) - The horizontal and vertical extent of TCE-impacted groundwater is defined and is primarily found within a sand/gravel unit at 25 feet to 40 feet below ground surface (bgs).

Reported detections of TCE were found in deeper groundwater (between 80 feet and 145 feet bgs) within thin discontinuous lenses of fine sand. TCE in deeper groundwater appeared isolated near GW-601 and the former Cooling Water Supply Well. TCE degradation via reductive dechlorination is minimal based on data collected to date which indicate minor concentrations of TCE degradation (or breakdown) products in Site groundwater samples.

TPH-DRO Groundwater Plume (AOC-5) - The extent of TPH-DRO in shallow groundwater was defined in the area of former fuel oil USTs #1-4. As reported for TCE, TPH-DRO was also found in deeper groundwater (between 80 feet and 145 feet bgs). TPH-DRO was found in multiple deeper groundwater samples and likely originated from leaking lubricating oil from the pump shaft when it broke at depth during abandonment of the former Cooling Water Supply Well. In addition, the deeper TPH-DRO impacts at 84 and 94 feet bgs are unassociated with the impacted shallow groundwater resulting from the former USTs #1-4. The highest concentrations are at the deeper depths, not beneath the former USTs, and the stratigraphy indicates few discontinuous thin lenses of fine sand beneath the preferred water-bearing zone at 25 to 40 feet bgs. A profile of TPH-DRO indicates that the well may be the vertical conduit through which the TPH-DRO was able to get deeper.

2.2.1 Groundwater Pilot Test Summary

The purpose of the groundwater pilot test was to evaluate if enhanced biodegradation and groundwater recirculation can remediate TCE in the apparent TCE source area. A total of 10 groundwater wells, a treatment system, and conveyance network were installed from August 2009 to November 2009 to support the pilot test: three extraction wells (D-Q-GEW-1 through -3), five injection wells (D-Q-GIW-1 through -5), and two monitoring wells (D-Q-GMW-7 and -7A). The treatment system operated for 1 month in 2009 (November/December) and then 6 months from August 2010 to February 2011. Performance monitoring results indicate a clear reduction in TCE during the pilot test operational timeframe of 2009 to 2011 and that reducing conditions have been established in the saturated zone and that biodegradation has occurred. More details about the pilot test system operation, maintenance and conclusions are provided in the Groundwater Pilot Test Results Report (Brown and Caldwell, 2011). The following specific conclusions were drawn from the pilot test:

The treatment system was maintained with greater than 90% operational uptime;

TCE has decreased from 86 to 4.1 µg/L in the treatment zone;

DO has decreased to below 0.5 milligrams per liter (mg/L) and ORP has decreased to below 50 mV which are conditions typically required for reducing conditions and anaerobic bacteria to function;

Nitrate and sulfate have decreased to 1.39 mg/L and 53 mg/L, respectively, but may still be at concentrations that compete with reductive dechlorination (i.e., sulfate reducing bacteria may be active);

A system flow rate of 10 gallons per minute (gpm) and amendment dose of 200 lbs per week appear to be the optimal treatment settings to achieve the target dose of amendment in the treatment zone;

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Total organic carbon (TOC) increased to near or exceeding the 30 mg/L target for the carbon-based amendment. Operation of the system created a gradient for Site groundwater, in the direction of Site extraction wells. These patterns suggest that the amendment was distributed thoroughly by recirculating groundwater through the treatment zone;

Concentrations of biodegradation products (ethene, ethane, chloride) have remained constant while methane concentrations have increased significantly indicating that methanogenic microorganism activity has likely increased;

Changes to secondary water quality parameters included a temporary increase of arsenic, manganese and iron. Other secondary water quality parameters (i.e., pH and total dissolved solids [TDS]) remain unchanged; and

The lack of TCE daughter products prevents a definitive conclusion that biodegradation rates have increased and an assessment of whether bioaugmentation is needed. However, it appears that the combined technologies of groundwater recirculation and enhanced biodegradation have been effective at reducing TCE concentrations.

2.3 Geologic and Hydrogeologic Summary

This section provides the setting for site-specific geology and hydrogeology.

There have been focused efforts in the region to determine the stratigraphy of the area. Those efforts are summarized below.

As summarized in the RI (Brown and Caldwell, 2008) and the Data Gap RI (Brown and Caldwell, 2010), subsurface stratigraphy for the Site is interpreted from cone penetrometer test (CPT) logs and geologic boring and well logs.

The maximum depth penetrated is 165 feet bgs. The stratigraphy (depicted in the graphic to the right), is comprised of fine-grained units of silt and clay interlayered with a predominant shallow layer of coarse-grained sand and gravel. CW-2 is the former Cooling Water Supply well (Figure 1-2). The nearest CPT log to CW-2 is CPT-601, approximately 45 feet away. Small discrete sand lenses were found at depths greater than 40 feet bgs but are discontinuous. The shallow sand/gravel layer is a relatively continuous and generally encountered at 25 feet bgs to 40 feet bgs with a thickness of approximately 15 feet underlying the Site to approximately 8 feet on the south side of County Road 31.

Based on the data collected to date, there appears to be three hydrostratigraphic zones. They are outlined below in order of appearance from ground surface to the maximum depth logged (165 feet bgs):

Low permeability silts and clays (0 to 25 feet bgs1), Permeable relatively continuous sand/gravel unit (generally at 25 feet bgs to 40 feet bgs), and

Low permeability silts and clays and discontinuous sand/gravel units (generally 40 feet bgs to 165 feet bgs).

1 Maybe as deep as 30 feet bgs south of County Road 31.

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Groundwater was first encountered at the top elevation of the sand/gravel unit generally at 25 feet bgs beneath the Station. During the RI in all phases of water level monitoring, static water levels rose to depths above the top of the screened interval for all Site wells. This information suggests confined or semi-confined conditions within the shallow units.

There is connection between the wells screened within the 25 to 40 foot sand/gravel unit. Evaluations performed under an aquifer test (Brown and Caldwell, 2010) showed that wells screened within these zones generally respond consistently with each other indicating that they are hydraulically connected. The maximum fluctuation of groundwater elevations in the wells during the period of monitoring is approximately 6 feet.

Greater than average winter rainfall resulted in higher groundwater elevations across the Site in 2010. On average, 2010 elevations were 10 feet higher than measured in 2009. A potentiometric surface map for February 11, 2011 is presented as Figure 2-1 for those wells that nearly to fully screen the shallow water bearing zone (i.e., D-Q-GMW-7, D-Q-GEW-1, D-Q-GEW-2, D-Q-GEW-3, D-Q-GIW-1, and D- Q-GIW-5/GEW-5). The groundwater elevations shown on Figure 2-1 represent depth to water measurements collected when the pilot test system was in operation. Due to subtle differences in the shallow water bearing zone lithology and well pumping rates, the resulting groundwater elevation map shows a groundwater depression at extraction well D-Q-GEW-3 and a groundwater mound in the area of groundwater extraction well D-Q-GEW-2. The pilot test system operates with injections wells cycling on and off and extraction wells operating nearly continuously. During the cycle, extraction water fills a holding tank while the injection wells are cycling on and off. There is a period where the extraction wells can be off and groundwater is recovering when the tank has filled to the high float level but the injection wells are still cycling on. On Figure 2-1, a depression appears around D-Q-GEW-3 but there is a mound of groundwater around D-Q-GEW-2 suggesting that this condition occurred. Based on historical groundwater level data, groundwater flows towards the south-southeast, the same direction as the long axis of the TCE plume (Table 2-1).

Table 2-1. Historical Groundwater Flow Directions and Gradient

Date Generalized Flow Direction Gradient (feet/feet) Data Source

Jan 2001** Southeast* 0.0009* (A)

4/11/02** East to southeast 0.0008 to 0.001 (B)

8/8/02** Northeast to east to southeast 0.001 to 0.003 (B)

3/24/03** Northeast to southeast 0.001 to 0.003 (B)

9/10/03** Northeast to southeast 0.001 to 0.004 (B)

12/15/03** Northeast to southeast 0.0009 to 0.008 (B)

4/8/04** East to southeast 0.001 --

5/30/06** East to southeast 0.001 --

6/21/07** East to northeast 0.003 (C)

6/9/2008** East to northeast 0.005 (D)

11/9/09*** South-southeast 0.009

2/11/2011*** Variable due to operation of pilot test system

Not calculated because of the variable gradient induced during pumping

* Based on wells D-Q-GMW-1 thru D-Q-GMW-3 ** An assumed datum of 100 feet was used as the reference point (finish floor of Building #100) to determine the measuring point for each well and from those points and the depth to water measurement, a groundwater elevation was calculated.

*** Based on a resurvey of all wells to State Plane Coordinate System, Zone 2, NAD83 (horizontal datum) and N. American Vertical Datum

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Table 2-1. Historical Groundwater Flow Directions and Gradient

Date Generalized Flow Direction Gradient (feet/feet) Data Source

1988 (Vertical datum).

Data Sources:

(A) SCA. 2001. Final Report – Groundwater Site Investigation and Supplemental Groundwater Site Investigation, D-Q University, Yolo

County, California. October.

(B) USACE. 2004b. Annual Groundwater Monitoring Report, D-Q University, Yolo County, California. September.

(C) USACE. 2008. Annual 2007 Groundwater Monitoring Report, D-Q University, Yolo County, California. May.

(D) USACE 2009. Annual 2008 Groundwater Monitoring Report, D-Q University, Yolo County, California. July.

2.4 Summary of Nature and Extent of Contamination in

Shallow Groundwater

The following summary describes the nature and extent of impacts to shallow groundwater from the two groundwater AOCs, TCE (AOC-4) and TPH-DRO (AOC-5). Supporting information can be found in the RI (Brown and Caldwell, 2008) and the Data Gap RI (Brown and Caldwell, 2010).

2.4.1 TCE Groundwater Plume (AOC-4)

The horizontal and vertical extent of TCE-impacted groundwater is defined and is primarily found within a sand/gravel unit at 25 feet to 40 feet bgs. The residual source area of TCE in shallow groundwater is located approximately 20 feet east of Building #100 based on 1998 boring SS-7 (1,700 µg/L) and 2006 CPT boring GW-601 (1,100 µg/L) (Figure 2-2).

TCE does not appear to be degrading via reductive dechlorination. There are essentially no degradation (or breakdown) products found in soil or groundwater. Cis-1,2-dichoroethylene (cis-1,2-DCE) has been reported in groundwater but only three times since 1997. Other natural attenuation mechanisms, such as dilution or dispersion, do not appear to be significantly affecting the plume. This fact is also supported by no decrease or increase in TCE concentration trends for the permanent groundwater monitoring wells.

2.4.2 TPH-DRO Groundwater Plume (AOC-5)

The size of TPH-DRO in the shallow groundwater is defined as the small area southeast of and resulting from the former USTs #1-4 (Figure 2-3). RI data indicate that TPH-DRO concentrations range from 250 to 480 µg/L in the area of the former tanks. The TPH-DRO shallow groundwater plume is completely contained within the TCE shallow groundwater plume (Figure 2-3).

2.5 Site Conceptual Model Summary

Hydrostratigraphic cross sections indicate alluvial sediments at the Site were deposited as part of the Tehama Formation and consist primarily of silts and clays with coarse-grained sediments. There is a relatively continuous sand/gravel unit generally at 25 to 40 feet bgs that extends beneath the Site.

Data Gap RI groundwater samples collected at multiple depths suggest that there is only one water-bearing unit with paths of preferential groundwater flow within the shallow sand/gravel at 25 to 40 feet bgs. Beneath this sand/gravel unit is a fine-grained unit consisting of silt and clay that extends to depths of at least 165 feet bgs based on Data Gap RI drilling. Discontinuous thin lenses of fine sand were observed during Data Gap RI drilling. A connection between the primary shallow water-bearing unit and the deeper sand formation could not be established.

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Based on groundwater elevations measured in permanent groundwater monitoring wells screened within the shallow sand/gravel unit and the depth to first encountered groundwater, groundwater conditions are confined or semi-confined. Additional groundwater elevation data collected within deeper discontinuous sand lenses supports the same conditions to the maximum depth penetrated where groundwater was encountered (150 feet bgs).

Groundwater flow is south-southeast, the same direction as the long axis of the TCE and TPH-DRO plume, and under a flat gradient of 0.001 to 0.009. On February 11, 2011, groundwater elevations reflected extraction and the rebound of water levels while the pilot test system was in operation. The extent of the TCE and TPH-DRO is laterally defined and contained within this shallow water-bearing zone at 25 to 40 feet bgs. The TCE plume extends nearly 2,800 feet to County Road 31; however, the TPH-DRO plume is much smaller and contained within the area of the former Station.

2.6 Risk Assessment Summary

A quantitative risk screening evaluation was conducted by USACE using the most recent groundwater data to identify the potential hazards and evaluate the potential risks they pose through vapor intrusion into existing (e.g. Building 100) or potential future buildings at D-Q University. Groundwater concentration data were collected following in-situ treatment. The treatment is being conducted to enhance biodegradation of chlorinated volatiles in the suspected source area. Groundwater sample analytes included cis-1,2-DCE, trans-1,2-trichloroethylene (trans-1,2-DCE), TCE, naphthalene and vinyl chloride. Naphthalene and vinyl chloride were not detected. Previous investigations indicated that chlorinated volatile organic compounds were below detection limits in the suspected soil source area. The soil area from which the samples were collected was subsequently designated “no further action”. Groundwater data were used in the risk screening evaluation rather than soil gas data because Site soils did not allow for collection of active soil gas samples (SCA Environmental, 2001). According to USACE, passive soil gas samplers were installed near the source area and around the perimeter of Building 100 for the purpose of determining if and where additional sampling might be informative, with low levels of TCE in eight of 32 samples, none of which were located around the perimeter of the closest building to the source area, Building 100. The results of the passive soil gas sampling are semi-quantitative and not suitable for use in a risk screening evaluation as there are no comparison criteria. Groundwater concentrations were also evaluated against drinking water standards to evaluate potential offsite risks if groundwater is used as drinking water.

The maximum detected concentrations for each compound evaluated are presented in Table 2-2. The maximum detected concentrations were compared to the California Regional Water Quality Control Board (RWQCB) Environmental Screening Levels (ESLs) for potential vapor intrusion concerns from groundwater (ESL Table E-1; http://www.swrcb.ca.gov/rwqcb2/water_issues/available_documents/ESL_May_2008.pdf). These values are a conservative estimate of risk since:

ESLs were derived assuming a high permeability soil (92% sand, 5% silt, 3 % clay) over a moist clayey loam (33% sand, 34% silt, 33% clay). As shown by the soil boring logs (Brown and Caldwell, 2010) and by an inability to pull a vacuum to collect soil gas samples, D-Q Site soils have a higher percentage of fine grained materials.

The assumed depth to groundwater used to derive the ESLs was nine feet. The shallow groundwater aquifer at D-Q University is below nine feet.

Although the TCE cancer slope factors have been updated since 2008, the inhalation pathway is still valid since the inhalation unit risk factor (IUR, 2E-06) is still current as the same value proposed by California

EPA.

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Results show an incremental lifetime cancer risk of 8.89E-08 and a hazard index of 0.0018 from vapor intrusion into indoor air. Both of these values are well below the USEPA action limits of 1E-06 and 1, respectively, indicating that further action or evaluation with regards to vapor intrusion is not necessary.

Table 2-3 shows the comparison of the maximum detected concentrations to current federal and California maximum contaminant levels (MCLs). All compounds exceed the state MCLs, while only TCE exceeds both criteria. However, these values are within the source area and do not represent a current exposure to an offsite receptor. The most recent data from the furthest down-gradient source area well (D-Q-GWM-5) show that only concentrations of TCE exceed the federal and/or state MCLs (Table 2-4).

Table 2-2. Groundwater Risk Screening Evaluation for Vapor Intrusion

Location Analyte Maximum Detected Concentration (µg/l)

ESLa (µg/l)

ILCR

(unitless)

Hazard Quotient (unitless)

D-Q-GEW-3 cis-1,2-dichloroethylene 12 17,000 - 0.0007 D-Q-GEW-3 trans-1,2-dichloroethylene 21 19,000 - 0.0011 D-Q-GMW-4 trichloroethylene 160 1,800 8.89E-08 -

Hazard Index 0.0018 a ESL = Environmental Screening Level, Table E-1 for Commercial/Industrial Land Use (RWQCB, 2008) ILCR = Incremental Lifetime Cancer Risk µg/l = micrograms per liter

Table 2-3. Comparison of Groundwater Maximum Detected Concentrations to MCLs

Maximum Detected Concentration (µg/l)

Federal MCLa (µg/l)

California MCLb (µg/l)

D-Q-GEW-3 cis-1,2-dichloroethylene 12 70 6 D-Q-GEW-3 trans-1,2-dichloroethylene 21 100 10 D-Q-GMW-4 trichloroethylene 160 5 5 a Federal Maximum Contaminant Level, http://water.epa.gov/drink/contaminants/index.cfm as of 3/28/11 b California Maximum Contaminant Level, http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chemicalcontaminants.aspx as of 3/28/11 µg/l = micrograms per liter Bolded values indicate an exceedance of an MCL.

Table 2-4. Comparison of Groundwater Concentration from D-Q-GWM-5 to MCLs

Maximum Detected Concentration (µg/l)

Federal MCLa (µg/l)

California MCLb (µg/l)

D-Q-GMW-5 cis-1,2-dichloroethylene <0.2 70 6 D-Q-GMW-5 trans-1,2-dichloroethylene <0.2 100 10 D-Q-GMW-5 trichloroethylene 160 5 5 a Federal Maximum Contaminant Level, http://water.epa.gov/drink/contaminants/index.cfm as of 3/28/11 b California Maximum Contaminant Level, http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chemicalcontaminants.aspx as of 3/28/11 µg/l = micrograms per liter Bolded values indicate an exceedance of an MCL.

2.7 Volume and Mass Estimates for Remediation

An initial determination can be made of volumes and masses of contaminated media to which general response actions may be applied. As described in previous sections, contamination at the Site is generally limited to VOCs (primarily TCE) and TPH-DRO in shallow groundwater. Table 2-5 provides volume and mass estimates for TCE in shallow groundwater. The estimates assume that TCE concentrations greater than 5 µg/L will be addressed by the remedial alternatives. The total volume was calculated from the lateral extent and thickness of the saturated interval and the porosity of the aquifer material. Lateral extent was estimated

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The effective porosity was based on published values for sandy soil to gravelly soil (Fetter, 1994). For each concentration contour, the TCE concentration used in the mass calculation was set at the average of all detections in the contour range (e.g., ≥ 50 µg/L and < 100 µg/L) reported during the February 2011 monitoring event. Based on these estimates, approximately 5.5 pounds of TCE is remaining in shallow groundwater that extends approximately 26 acres to County Road 31. For the more concentrated portion of the plume (i.e., TCE greater than 50 µg/L), approximately 2.6 pounds (or nearly 50 percent of the total TCE mass) extends approximately 2 acres located in the central portion of the Site.

Table 2-5. TCE Mass and Volume Estimates in Shallow Groundwater

Contour Interval (µg/L)

Feb. 2011 Avg. TCE

Concentration

Lateral Extent of Impacted

Water

Saturated Thickness

Saturated Soil Volume

Effective Porosity

Volume of Impacted Water

Estimated Mass of

TCE

≥ 5 µg/L and < 50 µg/L 12 µg/L

1,037,500 ft2 (23.8 acres)

15 ft 15,562,500 ft3 0.25 29,101,900 gal

2.9 lbs (1.3 kg)

≥ 50 µg/L and < 100 µg/L

81 µg/L 52,000 ft2 (1.2 acres)

15 ft 780,000 ft3 0.25 1,458,600 gal

1.0 lbs

(0.45 kg)

≥ 100 µg/L 195 µg/L 34,500 ft2

(0.79 acre) 15 ft 517,500 ft3 0.25 967,700 gal

1.6 lbs (0.72 kg)

Totals 1,124,000 ft2 (25.8 acres)

31,528,200 gal

5.5 lbs (2.5 kg)

Table 2-6 provides volume and mass estimates for TPH-DRO in shallow groundwater. The estimates assume that TPH-DRO concentrations greater than 100 µg/L will be addressed by the remedial alternatives.

These estimates were created in a similar manner to the TCE estimates.