20180927_DQ Decision Document_Final.pdf

DECISION DOCUMENT

TCE GROUNDWATER PLUME (AOC-4)

TPH-DRO GROUNDWATER PLUME (AOC-5)

D-Q UNIVERSITY

YOLO COUNTY, CALIFORNIA

FORMERLY USED DEFENSE SITE PROPERTY

NUMBER – J09CA1180

U.S. Army Corps of Engineers

Sacramento District

1325 J Street

Sacramento, California 95814

September 2018

Decision Document - D-Q University FUDS AOC-4-TCE Groundwater Plume AOC-5-TPH-DRO Groundwater Plume Final Yolo County, California September 2018 i

TABLE OF CONTENTS

PART 1: DECLARATION

1.1 SITE NAME AND LOCATION

1.2 STATEMENT OF BASIS AND PURPOSE

1.3 ASSESSMENT OF D-Q UNIVERSITY AOCs-4 AND 5

1.4 DESCRIPTION OF SELECTED REMEDY

1.5 STATUTORY DETERMINATIONS

1.6 DATA CERTIFICATION CHECKLIST

1.7 AUTHORIZING SIGNATURE

PART 2: DECISION SUMMARY

2.1 NAME, LOCATION, AND BRIEF DESCRIPTION

2.2 D-Q UNIVERSITY FUDS HISTORY

2.3 SITE INVESTIGATION HISTORY

2.3.1 TCE Groundwater Plume (AOC-4)

2.3.2 TPH-DRO Groundwater Plume (AOC-5)

2.3.3 Groundwater Pilot Test

2.3.4 Long-Term Monitoring

2.4 COMMUNITY PARTICIPATION

2.5 SCOPE AND ROLE OF RESPONSE ACTION

2.6 D-Q UNIVERSITY FUDS RESPONSE SITE CHARACTERISTICS

2.6.1 Site Geologic and Hydrogeologic Summary

2.6.2 Site Conceptual Model Summary

2.7 CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE USES

2.8 SUMMARY OF SITE POTENTIAL RISKS / HAZARDS

2.8.1 Soil Vapor Intrusion Pathway

2.8.2 Groundwater Ingestion Pathway

2.9 REMEDIAL ACTION OBJECTIVES

2.10 DESCRIPTION OF ALTERNATIVES

2.10.1 Alternative 1 – No Action

2.10.2 Alternative 2 – Monitored Natural Attenuation

2.10.3 Alternative 3 – Enhanced Biodegradation and Groundwater Recirculation ii

2.10.4 Alternative 4 – Permeable Reactive Barriers

2.10.5 Alternative 5 – In Situ Chemical Oxidation

2.11 COMPARATIVE ANALYSIS OF ALTERNATIVES

2.11.1 Threshold Criteria

2.11.2 Balancing Criteria

2.11.3 Modifying Criteria

2.12 SELECTED REMEDY

2.13 STATUTORY DETERMINATIONS

2.14 DOCUMENTATION OF SIGNIFICANT CHANGES

PART 3: RESPONSIVENESS SUMMARY

3.1 STAKEHOLDER COMMENTS AND LEAD AGENCY RESPONSES

3.2 TECHNICAL AND LEGAL ISSUES

REFERENCES

iii

LIST OF TABLES

Table 1 – D-Q University FUDS Selected Remedy

Table 2 – Screening-Level Risk Evaluation of Soil Vapor Intrusion Pathway

Table 3 – Screening-Level Risk Evaluation of Groundwater Ingestion Pathway

Table 4 –Maximum Contaminant Levels

Table 5 – Applicable or Relevant and Appropriate Requirements

Table 6 – Comparative Analysis of Remedial Timeframe and Costs

Table 7 – Summary of Comparative Analysis of Alternatives

LIST OF FIGURES

Figure 1 – D-Q University Location

Figure 2 – D-Q University Layout

Figure 3 – Well Locations and TCE and TPH-DRO Plume Boundaries

Figure 4 – TCE Reduction in Source Area

Figure 5 – Alternative 3 – Enhanced Biodegradation and Groundwater Recirculation

Figure 6 – Alternative 4 – Permeable Reaction Barriers

Figure 7 – Alternative 5 – In Situ Chemical Oxidation

LIST OF ATTACHMENTS

Documentation of Central Valley Regional Water Quality Control Board Concurrence on D-Q University FUDS Selected Remedy

Administrative Record Index

Public Meeting Announcement and Presentation iv

LIST OF ACRONYMS AND ABBREVIATIONS

AOCs Areas of Concern ARARs Applicable or Relevant and Appropriate Requirements ASTs above ground storage tanks bgs below ground surface BTEX benzene, toluene, ethylbenzene, and xylenes CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CFR Code of Federal Regulations COC chemical of concern CPT cone penetrometer test DCE dichloroethylene DERP Defense Environmental Restoration Program DoD Department of Defense FS Feasibility Study FUDS Formerly Used Defense Site ISCO In situ chemical oxidation MCL maximum contaminant level µg/L micrograms per liter mg/kg milligrams per kilogram mg/L milligrams per liter NCP National Oil and Hazardous Substances Pollution Contingency Plan PRB permeable reactive barrier RAOs remedial action objectives RI Remedial Investigation RWQCB Regional Water Quality Control Board SARA Superfund Amendment and Reauthorization Act SI Site Inspection TCE trichloroethylene TPH-DRO Total Petroleum Hydrocarbon-Diesel Range Organics USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency USTs underground storage tanks UU/UE unlimited use / unrestricted exposure VOCs volatile organic compounds WOLs wastewater oxidation lagoons

PART 1: DECLARATION

1.1 SITE NAME AND LOCATION

Site Name: D-Q University, Yolo County, California

Formerly Used Defense Site (FUDS) Project Number: J09CA1180, TCE Groundwater Plume (AOC-4), TPH-DRO Groundwater Plume (AOC-5)

Federal Facility Identifier: CA99799F600300

This Decision Document covers two Areas of Concern (AOCs): AOC-4 – Trichloroethylene (TCE) Groundwater Plume and AOC-5 – Total Petroleum Hydrocarbon-Diesel Range Organics (TPH- DRO) Plume. D-Q University is located in Yolo County on the north side of County Road 31 (Covell Road). The location of D-Q University is provided on Figure 1. D-Q University comprises approximately 652 acres in a rural setting in Yolo County, California, approximately 5 miles east of Winters and 2 miles west of Davis. There are a number of former Department of Defense (DoD) buildings remaining on the site that have been repurposed for uses associated with the university.

Surrounding D-Q University is agricultural land that is currently leased to farmers that plant and harvest alfalfa and other crops. This Decision Document summarizes information that can be found in greater detail in the Remedial Investigation Report (RI) (Ref. 1) and Feasibility Study Results Report (FS) (Ref. 2) as well as other documents contained in the Administrative Record.

1.2 STATEMENT OF BASIS AND PURPOSE

This Decision Document presents the Selected Remedy for D-Q University AOC-4 and AOC-5 in Yolo County, California, as documented in the Proposed Plan for Groundwater Remedial Action, D-Q University FUDS, Yolo County, California (Proposed Plan) (Ref. 3). The Selected Remedy was chosen in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Ref. 4), as amended by the Superfund Amendment and Reauthorization Act (SARA) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) (Ref. 5). This decision is based on the Administrative Record for this site.

The Central Valley Regional Water Quality Control Board (RWQCB) concurs with the Selected Remedy. Documentation of RWQCB’s concurrence is included as an attachment to this Decision Document (Ref. 6).

1.3 ASSESSMENT OF D-Q UNIVERSITY AOCs-4 AND 5

The Selected Remedy in this Decision Document is necessary to protect the public health, welfare or the environment from potential exposures to chemicals, primarily TCE, remaining in groundwater at the D-Q University FUDS.

1.4 DESCRIPTION OF SELECTED REMEDY

Five remedial alternatives were evaluated for D-Q University FUDS. The Selected Remedy is presented in Table 1.

TABLE 1 – D-Q UNIVERSITY FUDS SELECTED REMEDY

Site

Evaluated Alternatives for D-Q University

Alternative 1 No Action

Alternative 2 Monitored

Natural Attenuation

Alternative 3 Enhanced

Biodegradation

Alternative 4

Permeable Reactive Barriers

Alternative 5 In Situ Chemical

Oxidation

AOC-4

AOC-5 2 1

1 In the source area of the TCE plume.

2 For the remaining diffuse portion of the TCE plume.

From August 2009 to February 2011, the U.S. Army Corps of Engineers (USACE) implemented Alternative 3 in the source area as part of the pilot test, and enhanced biodegradation and groundwater recirculation was effective in reducing TCE concentration from 390 micrograms per liter (µg/L) to 15 µg/L. The remaining maximum TCE concentration in groundwater is 120 µg/L (as of March 2017) and deed restrictions on groundwater use will be recorded to protect human health.

Groundwater samples will be routinely collected and analyzed for site contaminants, degradation products, bioparameters, and general groundwater parameters. Alternative 2 is the most cost effective, but has the longest remedial timeframe. Natural processes most likely were responsible for the initial decrease of TCE concentration from the historical maximum of 1,700 µg/L in 1998 to 390 µg/L in 2009. Specific details regarding implementation of the remedy will be developed during the remedial design phase. Because this remedy will not allow for unlimited use / unrestricted exposure (UU/UE) within the first five years, Five-Year Reviews will be implemented until UU/UE is reached.

1.5 STATUTORY DETERMINATIONS

The Selected Remedy for the D-Q University FUDS is Alternative 3 in the source area of the TCE plume, and Alternative 2 for the remaining portion of the TCE plume. Based on the information currently available, the selected remedy is protective of human health and the environment, complies with Federal and State requirements that are applicable or relevant and appropriate to the remedial action (unless justified by a waiver), is cost-effective when evaluated against the nine criteria described in the NCP, 40 Code of Federal Regulations (CFR) Section 300.430(e)(9)(iii), and utilizes permanent solutions to the maximum extent practicable. The selected remedy provides the best balance of trade offs when compared to the other evaluated alternatives with respect to the balancing and modifying criteria specified in the NCP by providing the best overall and long term effectiveness and the highest reduction of groundwater contamination.

The NCP establishes the expectation that treatment will be used to address the principal threats posed by a site whenever practicable (40CFR 300.430[a] [1] [iii] [A]). The selected remedy satisfies the statutory preference for treatment as a principal element of the remedy through enhanced biodegradation and groundwater recirculation in the source area of the TCE plume. Although the selected remedy does not strictly satisfy the statutory preference for treatment for the remaining portion of the TCE plume, the immediate need for further active remediation is not warranted.

Because restrictions would be placed on the deed for the property for use of groundwater for drinking or bathing, UU/UE will not be initially met and therefore, statutory reviews will be conducted every five years after initiation of the remedial actions selected in this Decision Document to ensure that the remedies are protective of human health and the environment. Use of groundwater for agricultural irrigation may be allowed. The deed restrictions and statutory reviews would be implemented until remedial action objectives (RAOs) are achieved.

1.6 DATA CERTIFICATION CHECKLIST

The following information is included in the Decision Summary (Part 2) of this Decision Document. Additional information can be found in the Administrative Record file. The index for the Administrative Record file is provided as an attachment to this Decision Document.

• Summary of characterization of nature and extent of contaminants in groundwater (Section 2.3)

• Potential risk represented by contaminants (Section 2.8)

• RAOs established for the site and the basis for these objectives (Section 2.9)

• How contaminants in groundwater will be addressed (Section 2.12)

• Current and reasonably anticipated future land use assumptions (Section 2.7)

• Estimated Remedial Action costs (Section 2.11.2)

• Key factors that led to selecting the remedy (describing how the Selected Remedy provides the best balance of tradeoffs with respect to the balancing and modifying criteria, highlighting criteria key to the decision) (Section 2.10).

1.7 AUTHORIZING SIGNATURE

This Decision Document, prepared by USACE, Sacramento District, presents the Selected Remedy for D-Q University FUDS. The U.S. Army is the lead agency under the Defense Environmental Restoration Program (DERP) at D-Q University FUDS and has developed this Decision Document in compliance with CERCLA, as amended by SARA and the NCP. This Decision Document will be incorporated into the larger Administrative Record file for D-Q University FUDS, located at the public library in Winters, California. This document, presenting the Selected Remedy for D-Q

University FUDS with a total cost estimate of $2,952,000, is approved by the undersigned, pursuant to Memorandum, CESPD-PDM, August 16, 2016, subject: Redelegation of Assignment of Mission Execution Functions Associated with Department of Defense Lead Agent Responsibilities for the Formerly Used Defense Sites Program, and to Engineer Regulation 200-3-1, FUDS Program Policy.

APPROVED:

Cheree D. Peterson, SES Date Signed Director, Programs South Pacific Division

PART 2: DECISION SUMMARY

The Decision Summary identifies the Selected Remedy, explains that remedial action is necessary to ensure protection of human health and the environment, and provides a substantive summary of the Administrative Record file that supports the remedy selection decision.

2.1 NAME, LOCATION, AND BRIEF DESCRIPTION

D-Q University is 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. The closest water supply well is located 0.4 mile north of the site. This well is used for agricultural water supply and is located up-gradient of the campus property. Surrounding the Campus are agricultural lands that are currently leased to farmers that plant and harvest agricultural crops including alfalfa and other crops.

Based on fifteen monitoring wells, five injection wells and three extraction wells, the site stratigraphic model was developed. The site stratigraphy is comprised of fine-grained units of silt and clay with a predominant shallow unit of coarse-grained sand and gravel. Small discrete sand lenses were found at depths greater than 40 feet below ground surface (bgs) but are discontinuous.

The shallow sand/gravel unit is relatively continuous and generally encountered between 25 feet bgs and 40 feet bgs underlying the site, thinning significantly toward the south and County Road 31.

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

• low permeable silts and clays (0 to 25 feet bgs to 32 feet bgs),

• a permeable relatively continuous sand/gravel unit (generally at 25 feet bgs to 40 feet bgs),

• low permeable silts and clays (generally 40 feet bgs to 130+ feet bgs), and,

• a discontinuous sand/gravel unit (generally 65 feet bgs to 80 feet bgs).

2.2 D-Q UNIVERSITY FUDS HISTORY

The land currently occupied by D-Q University was originally part of the Rancho Rio de los Putos land grant. The area was divided and sold to individual landowners and used primarily for dry farming. In 1952, 651.55 acres of agricultural land were purchased by the United States Department of the Army for the Sacramento Valley Radio Transmitter Station to support the Signal Corps Radio Station (Ref. 1). Of the few drawings that exist of the facility, it was also commonly known as the West Coast Relay & Radio Transmitting Station.

Improvements to the site during 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 wastewater oxidation lagoons (WOLs), two cooling water injection (disposal) wells, and one cooling water supply well (Ref. 1). The site layout is provided on Figure 2.

In 1969, the property was designated as surplus and turned over to the General Services Admin-istration. In January 1971, the Department of Transportation conveyed 4.85 acres by quitclaim deed to the county of Yolo for right of way purposes and in April of the same year, the Department of Health, Education, and Welfare conveyed by quitclaim deed 643.05 fee acres and 3.65 easement acres to D-Q University, with the stipulation that the property must be used continuously for educational purposes during the following 30 years. Permanent ownership of the land was acquired by D-Q University in 2001.

At the time of quitclaim, the Station contained all of the original buildings, most of the generating and pumping machinery, two WOLs, two cooling water injection wells, six USTs, six ASTs, two incinerators, and 13 transformers. Nine other 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 site. The incinerator east of Building #102 and three of the four ASTs inside Building #101 had been removed prior to USACE involvement (Ref. 1). The facilities, three remaining transformers, and two other ASTs were still being used by D-Q University.

Although the source of the TCE is unknown, Building #l00 was potentially used as a radio repair shop, a cooling room, an operations room, a transformer yard, a storage room, and maintenance storage. Therefore, a possible source of TCE is the floor drains in Building #l00. Building #100 was used as a cultural arts center by D-Q University.

2.3 SITE INVESTIGATION HISTORY

In 1986, Congress established the DERP for cleanup of active and former military sites. Based on its past use by the Department of the Army, Signal Corps, to support the Signal Corps Radio Station WVY, the D-Q University site was designated as a FUDS property on 5 August 1992, and became eligible for cleanup funding under this program. Previous investigations at the D-Q University FUDS are summarized below.

2.3.1 TCE Groundwater Plume (AOC-4)

1997: TCE contamination was first discovered during a site investigation conducted in the spring of 1997. Two groundwater samples were collected from the shallow groundwater, south of the irrigation ditch, and east of Building #100 (the exact location of these samples is unknown). In one sample, TCE was detected at 11 μg/L, and in the other sample, cis-1,2-dichloroethylene (DCE) was detected at 19 μg/L.

1998-1999: An active soil gas survey was performed in May 1998; however, due to the clayey/silt consistency of the subsurface soils, it was not possible to retrieve a sufficient volume of soil vapor to conduct the analysis. A groundwater investigation of both the shallow groundwater (10 feet bgs to 15 feet bgs) and deep groundwater (~ 90 feet bgs) was also conducted during this time. Of 15 groundwater samples collected, five of the samples contained TCE ranging from 1.3 μg/L to

1,700 μg/L; all other samples were non-detect at less than 5 μg/L. One sample was collected in the deep groundwater, at approximately 90 feet bgs to 100 feet bgs, and was tested for volatile organic compounds (VOCs) using U.S. Environmental Protection Agency (USEPA) Method 8260; the results of the sample were non-detect (< 5 μg/L) for TCE and its daughter products (cis-1,2-DCE, trans-1,2-DCE, and vinyl chloride).

2000: A supplemental groundwater investigation was conducted in November 2000. Of the four samples collected, only one sample contained TCE at concentrations higher than the maximum contaminant level (MCL) of 5 μg/L at 5.2 μg/L. After this investigation, six permanent monitoring wells were installed in the spring of 2001 to monitor both diesel and TCE contamination.

2002: During quarterly monitoring events of the permanent monitoring wells that USACE conducted from April 2002 through April 2004, TCE has been discovered to be consistently above the MCL of 5 μg/L in four of the six monitoring wells. The wells are east of Buildings #100 and #101 and can be seen on Figure 3.

2004 Site Inspection: Extent of the TCE plume was explored during a Site Inspection (SI) that occurred in April 2004. The objective of this event was to define the horizontal extent of TCE in the shallow groundwater, and to determine if TCE breakdown products were present. TCE sample results ranged from non-detect (< 1.0 μg/L) to 990 μg/L; there were no breakdown products detected above the established comparison criteria of 5 μg/L. Due to unexpected sample results, and time and financial constraints, the goal of defining the horizontal extent of the TCE plume was not fully realized. During the execution of the SI, USACE collected 36 samples primarily southeast from Building 100, and the plume boundaries were identified in every direction except the southeast (Figure 3). Based on the data, the outline of the plume boundary suggested that there were two plumes, one originating east of Building #100 and a second plume appearing in the agricultural field east of Building #102. The RI in 2006 was used to update the conceptual site model. Details about the RI are provided below. In summary, the RI data indicates that there is only one plume but appeared to be two plumes in 2004 because the lack of connecting data.

2007 RI: Seventy-six groundwater samples were collected from 34 locations and six permanent groundwater monitoring wells (not including duplicate samples). All samples were analyzed by USEPA Method 8260B. Other than TCE and a detection of cis-1,2-DCE, no other VOCs were reported in any groundwater samples collected during the RI. This fact is consistent with previous investigation results. Cis-1,2-DCE (6.2 μg/L) was reported in the groundwater sample collected at 22 feet bgs from a cone penetrometer test (CPT) boring. Only two other occurrences of cis-1,2-DCE have been reported in groundwater since 1997 and are located within the same area. Additionally, no other degradation products of TCE have been reported in any samples collected at the site.

Within shallow groundwater and within the shallow sand/gravel unit, the horizontal extent of TCE-impacted groundwater extends from Building #100 in a southeasterly direction to south of County Road 31, a total distance of approximately 2,800 feet (Figure 3). The width of the plume is approximately 500 feet.

TCE was reported unexpectedly in a deep groundwater sample. The sample was collected at a depth of 102 feet bgs to 108 feet bgs, much deeper than the shallower sand/gravel unit and within the presumed less permeable silt. TCE was reported at 63 μg/L. Once the delineation of the shallower TCE and TPH-DRO plumes was completed, another boring was pushed on the last day of the RI to determine the vertical extent of the TCE found in deep groundwater. The groundwater sample was collected from an interval of 141 feet bgs to 145 feet bgs. TCE was reported at a concentration of

6.0 μg/L, just above the MCL of 5 μg/L.

2.3.2 TPH-DRO Groundwater Plume (AOC-5)

1995: In August 1995, two 10,000-gallon and two 25,000-gallon diesel/fuel oil USTs and associated piping were removed from the area just north of Building #101 (Figure 3). Several soil samples were collected at the bottom or on the sidewalls of the UST excavation (approximately 11 feet bgs to 20 feet bgs). Groundwater was present in the UST #1-4 tank excavations at approximately 20 feet bgs. One groundwater sample was collected from the UST #3-4 excavation.

Soil samples contained TPH-DRO and benzene, toluene, ethylbenzene, and xylenes (BTEX). TPH- DRO soil concentrations ranged from non-detect to 15,000 milligrams per kilogram (mg/kg).

Highest concentrations were reported in soil samples collected beneath the east end of UST#3 (15,000 mg/kg) and UST#4 (7,400 mg/kg). The groundwater sample contained 1.7 μg/L of diesel range hydrocarbons. After sampling, groundwater was removed from the excavation using a vacuum truck because a sheen of floating fuel product was observed. No over-excavation of soil was performed. Following sampling activities, all excavations were backfilled with imported pea gravel and aggregate.

1998: In the spring of 1998, groundwater and soil samples were collected to define diesel contaminant boundaries. Ten boring locations were analyzed outside of the limits of the former UST excavation. Both soil and groundwater samples were analyzed for TPH-DRO and BTEX. Soil sample TPH-DRO results ranged from non-detect (< 1.2 mg/kg) to 1,200 mg/kg (collected at 12 feet bgs); groundwater TPH-DRO results ranged from non-detect (< 50 μg/L) to 1,200 milligrams per liter (mg/L). In all of the soil and groundwater samples, results for BTEX were non-detect (< 0.0055 mg/kg for benzene, toluene and ethylbenzene, and < 0.03 mg/kg for total xylenes).

1998-2000: Supplemental groundwater investigations to delineate diesel-impacted shallow ground-water were executed in May 1998, February 1999, and November 2000. A sample from deeper groundwater (at 90 feet bgs) was also collected southeast of the abandoned Cooling Water Supply Well. Of fifteen groundwater samples analyzed from the shallow groundwater, nine samples contained TPH-DRO ranging from 48 μg/L to 1,200 μg/L; all others were non-detect (< 100 μg/L).

In the suspected source area at USTs #1-4, diesel-impacted groundwater ranged in concentrations from 48 μg/L to 950 μg/L. Three other samples, including the highest detection of 1,200 μg/L, appeared geographically separate from the UST plume (Figure 3). Therefore, the source of these samples was suggested to be from another source other than the USTs. Both deep aquifer (approx-imately 90 feet bgs to 100 feet bgs) samples had TPH-DRO results less than 50 μg/L. The samples were also tested for motor oil-range hydrocarbons, and the results were non-detect (< 300 μg/L).

The goal of the supplemental investigation conducted in November 2000 was to determine whether the diesel-impacted shallow groundwater plume was one continuous plume caused from one source (USTs #1-4), or separate plumes caused by a different source. Seven groundwater samples were collected to further assess areas impacted by TPH-DRO and identified the presence of two separate diesel plumes. Only one sample contained diesel range hydrocarbons above the reporting limit at 51 μg/L. The supplemental site investigation results further confirmed two separate diesel plumes. The source of one small plume in the agricultural field to the east of D-Q University was suggested to be the result of agricultural farming activities and not associated with former USTs #1-4.

2004 SI: In April 2004, USACE conducted a SI during which groundwater samples were collected from five locations west of the former location of the USTs, and were analyzed for TPH-DRO and natural attenuation parameters. During this event, USACE was not able to define the plume horizontally to the comparison criteria of 50 μg/L due to time and financial restraints. During the execution of the SI, detections ranged from non-detect to 200 μg/L.

2007 RI: Forty five groundwater samples were collected from 21 locations and six permanent groundwater monitoring wells (not including duplicate samples). All samples were analyzed by USEPA Method 8015B. The extent of TPH-DRO in shallow groundwater has been 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 originates from lubricating oil associated with the former Cooling Water Supply Well. The horizontal extent of this deeper impact of TPH-DRO is bigger in size, appears to originate at the former well, and appears unassociated with the impacted shallow groundwater resulting from the former USTs #1-4. A profile of TPH-DRO indicates that the well may be the vertical conduit through which the TPH-DRO was able to get into deeper groundwater.

2.3.3 Groundwater Pilot Test

As part of the FS (Ref. 2) conducted by USACE, a pilot test was conducted to evaluate if enhanced biodegradation combined with groundwater recirculation could remediate the TCE source area.

From August 2009 to November 2009, USACE conducted an aquifer test to determine hydro-geologic characteristics of the shallow water-bearing zone and installed monitoring wells, a mobile treatment system, and conveyance pipe network to support the pilot test. During the aquifer test, over 200,000 gallons of impacted groundwater were extracted, treated and disposed, and key aquifer parameters were evaluated for use in the pilot test. The treatment system was constructed/installed in October 2009 and operated from November to December 2009 to distribute nutrients throughout the TCE source area. The system was operated by extracting impacted groundwater from three wells, treating the water with activated carbon, amending the extracted water with nutrients, and returning the water to the subsurface through five wells. Two new performance monitoring wells were installed and sampled periodically to determine if natural microorganisms were biodegrading the TCE. From December 2009 to August 2010, the system was turned off and the plume was allowed to equilibrate or rebound. After this “rebound period”, the system was operated from August 2010 to February 2011. Monitoring indicated that conditions conducive to biodegradation had been established in groundwater and TCE concentrations in the source area were reduced from 390 µg/L to 15 µg/L. The introduction of nutrients resulted in some temporary increases of arsenic, manganese and iron concentrations in groundwater; however, the overall success of the pilot test indicated that the combined technologies of groundwater recirculation and enhanced biodegradation are an effective remedial alternative. See the resulting graph below (Figure 4) that illustrates the reduction in TCE concentrations in the source area from 1998 to 2011.

2.3.4 Long-Term Monitoring

In August 2012, eight shallow groundwater monitoring wells were installed to supplement the existing monitoring well network by adding wells cross gradient and downgradient of the former TCE source area. Annual monitoring was recommended in order to measure seasonal variations in water levels and groundwater quality that will influence data interpretation. Thirteen monitoring wells were selected for sampling to meet the project objectives. The monitoring wells selected for long-term monitoring provide sufficient groundwater data needed to determine changes in concentrations within the dissolved phase plume and to determine biodegradation rates. The selected monitoring wells are located at the plume boundaries, the plume core, and at background locations. The objectives of the long-term monitoring for the site are listed below:

• To monitor natural processes as they attenuate concentrations of VOCs and TPH-DRO detected in groundwater;

• To verify that the plumes remain stable; and

• To document progress towards and eventual attainment of remedial action objectives.

The results of the long-term monitoring are incorporated into annual groundwater monitoring reports for the site.

2.4 COMMUNITY PARTICIPATION

In accordance with CERCLA, DoD, and U.S. Army regulations, USACE, Sacramento District, has conducted public involvement activities and provided the public opportunities to participate throughout the RI/FS, Proposed Plan, and Decision Document processes by hosting a public meeting during the remedial alternative selection process, and establishing and maintaining a publicly accessible Administrative Record file for the site. While coordinating with property owners to obtain Rights of Entry for field investigations, USACE, Sacramento District, also requested input regarding future land use at the D-Q University FUDS. Community involvement is also facilitated through fact sheets, media interviews, site visits, and public notices published in local newspapers and at public meetings during the remedy selection process when community members were invited to provide comments and recommendations. USACE considered the public comments in determining which proposed remedial alternative would be most appropriate for D-Q University

FUDS.

The Proposed Plan (Ref. 3) was presented during a public meeting. USACE, Sacramento District, held the public meeting on August 8, 2018 to present the remedial alternatives for D-Q University FUDS and to answer questions from the community related to the remedial alternatives and the proposed Selected Remedies. Comments to the Proposed Plan (Ref. 3) were accepted during a public comment period that ended on August 31, 2018. The announcement of the public meeting in the newspapers and the public meeting presentation are provided as attachments to this Decision Document. Responses to stakeholder (e.g., state regulators) comments received regarding the proposed remedy presented in the Proposed Plan are presented in the Responsiveness Summary provided as Part 3 of this Decision Document.

The RI and FS reports (Refs. 1 and 2) and the Proposed Plan (Ref. 3) documents were made available to the public prior to the comment period through the Administrative Record file located at:

Winters Community Library 708 Railroad Avenue Winters, CA 95694

All stakeholder comments included in the Responsiveness Summary (Part 3) were reviewed and considered in preparing this Decision Document.

2.5 SCOPE AND ROLE OF RESPONSE ACTION

Based on the findings presented in the RI and FS reports, 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.

This Decision Document presents the final response action for D-Q University FUDS and addresses the groundwater contamination through the Selected Remedy. The Selected Remedy presented in this Decision Document complements USACE’s overall strategy, following the USEPA guidance, to address DoD contamination at the property and allow for the current use of the land to continue and allow for reasonably anticipated future land use (Ref. 7).

2.6 D-Q UNIVERSITY FUDS RESPONSE SITE CHARACTERISTICS

This section provides an overview of D-Q University FUDS characteristics, including: site geology and hydrogeology, as well as the site conceptual model.

2.6.1 Site Geologic and Hydrogeologic Summary

As summarized in the RI (Ref. 1), subsurface stratigraphy for the site is interpreted from CPT logs and geologic boring and well logs. The maximum depth penetrated is 165 feet bgs. The stratigraphy is comprised of fine-grained units of silt and clay interlayered with a predominant shallow layer of coarse-grained sand and gravel. 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, and as noted in Section 2.1, there appears to be four hydrostratigraphic zones: low permeable silts and clays (0 to 25 feet bgs to 32 feet bgs), a permeable relatively continuous sand/gravel unit (generally at 25 feet bgs to 40 feet bgs), low permeable silts and clays (generally 40 feet bgs to 130+ feet bgs), and, a discontinuous sand/gravel unit (generally 65 feet bgs to 80 feet bgs).

Groundwater was first encountered at the top elevation of the sand/gravel unit generally at 25 feet bgs beneath the site. 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 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 six feet.

2.6.2 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 feet bgs to 40 feet bgs that extends beneath the site.

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. Discontinuous thin lenses of fine sand were observed during drilling. A connection between the primary shallow water-bearing unit and the deeper sand formation could not be established.

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 low to moderate gradient of 0.001 to 0.009. 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.

2.7 CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE

USES

Permanent ownership of the land was acquired by D-Q University in 2001. All areas of the D-Q University FUDS are accessible to the public. Surrounding the Campus is agricultural land that is currently leased to farmers that plant and harvest various crops. The most recent crop data (2017) indicate that crops planted and harvested were alfalfa, oat, orchardgrass, and wheat. The land south of County Road 31 is owned by other parties and also used for agriculture. The property is zoned for public/quasipublic which is applied to lands that are occupied or used for public and governmental offices, places of worship, schools, libraries, and civic uses, which includes activities conducted in privately-owned facilities such as schools, museums, and fraternal organizations.

Residential use is not allowed. Land use is not anticipated to change in the foreseeable future.

Groundwater at the site is of generally good quality and is considered as suitable or potentially suitable, at a minimum, for municipal and domestic water supply, agricultural supply, industrial service supply, and industrial process supply. Implementing deed restrictions on groundwater use will prevent its use for domestic purposes.

2.8 SUMMARY OF SITE POTENTIAL RISKS / HAZARDS

The chemical of concern (COC) that is the focus of this Decision Document is TCE in groundwater.

Although TCE concentrations within the source area were reduced to 15 µg/L, a maximum TCE concentration of 120 µg/L was recently detected slightly upgradient from the area treated by the pilot study (March 2017). Given the land use and groundwater only exposures, potential risks to ecological receptors were not evaluated. The potential human health risks were evaluated based on the most recent site maximum TCE concentration of 120 µg/L. USACE conducted a quantitative screening-level risk evaluation posed by two exposure scenarios: 1) VOC vapor intrusion into indoor air of existing buildings (e.g., Building 100) or potential future buildings at D-Q University; and 2) ingestion of VOC-impacted groundwater extracted from a potential future drinking water well.

2.8.1 Soil Vapor Intrusion Pathway

Previous investigations indicated that VOCs in site soil were near analytical detection limits and the tight, clayey site soils did not allow for collection of active soil vapor samples; therefore, site soil was subsequently deemed to require no further evaluation or remedial action. Consequently, groundwater data were used to evaluate this exposure pathway. Results in Table 2 show that the incremental lifetime cancer risk and non-cancer hazard index, based on a residential exposure scenario and the current maximum TCE concentration in groundwater, are well below USEPA risk management ranges. This demonstrates that further remedial action to address potential vapor intrusion from VOCs in groundwater is not required.

TABLE 2 – SCREENING-LEVEL RISK EVALUATION OF

SOIL VAPOR INTRUSION PATHWAY

Well Name Site Chemical Maximum Groundwater Concentration

USEPA Incremental Lifetime Cancer Risk

USEPA Hazard Quotient (non-cancer risk)

D-Q-GMW-6 TCE 120 µg/L 3 x 10-7 0.1 Acceptable Level 10-6 to 10-4 < 1.0

2.8.2 Groundwater Ingestion Pathway

At the time of the RI a human health risk assessment was not conducted for the drinking water exposure pathway. Subsequently, a screening level risk calculation was conducted since groundwater ingestion is considered a potentially complete pathway (based on a drinking water beneficial use for groundwater in the region). Using the maximum detected groundwater concentration for TCE results in an incremental lifetime cancer risk of 2 × 10-4, which exceeds the EPA acceptable risk range; and a non-cancer hazard index of 40, which exceeds the target hazard index of 1. This unacceptable risk associated with the groundwater ingestion pathway is the basis for taking a remedial action at the site. Groundwater data were also compared to drinking water standards. Results in Table 3 show that the maximum concentration of TCE in groundwater exceeds the MCLs (an MCL has not been established for TPH-DRO).

TABLE 3 – SCREENING-LEVEL RISK EVALUATION OF

GROUNDWATER INGESTION PATHWAY

Well Name Site Chemical Maximum Groundwater

Concentration, Feb. 2011 CA Maximum

Contaminant Level USEPA Maximum

Contaminant Level

D-Q-GMW-6 TCE 120 µg/L 5 µg/L 5 µg/L

2.9 REMEDIAL ACTION OBJECTIVES

RAOs are site-specific, initial cleanup objectives that are established on the basis of the nature and extent of the contamination, Applicable or Relevant and Appropriate Requirements (ARARs), and the potential for human and environmental exposure. The RAOs generally address the contaminants of potential concern, exposure routes and receptors, acceptable contaminant level, and restoration time frame. USACE established the following RAOs on the basis of the nature and extent of contamination, potential human health risks, and ARARs.

1. Prevent ingestion of groundwater containing TCE and daughter degradation byproducts above MCLs (see Table 4 for current MCLs) and restore groundwater to levels of less than or equal to MCLs.

TABLE 4 – MAXIMUM CONTAMINANT LEVELS

COC CA Maximum Contaminant Level USEPA Maximum Contaminant Level

TCE 5 µg/L 5 µg/L

Daughter Products CA Maximum Contaminant Level USEPA Maximum Contaminant Level cis-DCE 6 µg/L 70 µg/L trans-DCE 10 µg/L 100 µg/L

Vinyl Chloride 0.5 µg/L 2 µg/L

Modifications to the remedy components, RAOs, and/or methodology used to determine attainment, may be necessary in the future in the event findings from future five-year reviews determine that these types of technical practicability limitations are impacting the ability to meet the RAOs in what may be considered a reasonable timeframe (see Section 2.12).

2.10 DESCRIPTION OF ALTERNATIVES

Based on a review of D-Q University FUDS characterization and ARARs, response action alternatives were identified, evaluated, and recommended for implementation at the site. Five remedial alternatives were developed from the selected process options and are described below.

Note that alternatives two through five all include the recommendation of institutional controls (in the form of groundwater use restrictions) and groundwater monitoring process options.

• Alternative 1 – No Action. This alternative involves no response actions of any kind and the status of the TCE groundwater plume is not monitored. CERCLA requires its inclusion for comparison purposes.

• Alternative 2 – Monitored Natural Attenuation. This alternative involves monitoring the natural attenuation of the contaminant plume and implementing deed restrictions on groundwater use.

• Alternative 3 – Enhanced Biodegradation and Groundwater Recirculation. This alternative involves enhancing natural biodegradation of the contaminant plume by adding nutrients in situ and inducing groundwater flow through the treatment area. This alternative also includes two additional process options: groundwater monitoring to assess treatment performance; and groundwater use restrictions until the plume is remediated.

• Alternative 4 – Permeable Reactive Barriers. This alternative would use a series of permeable trenches that would treat contaminated groundwater as it passes through a reactive material in the trench. This alternative also includes the groundwater monitoring and water use restrictions process options.

• Alternative 5 – In Situ Chemical Oxidation. This alternative involves the injection of an oxidizing agent into groundwater to destroy contaminants in situ. This alternative also includes the groundwater monitoring and water use restrictions process options.

Although not part of the remedy, five-year reviews would be required for any alternative under which hazardous substances, pollutants, or contaminants remain above levels that allow UU/UE following remedy implementation. Five-year reviews would be conducted to monitor the effectiveness of the remedy and determine if the response action continues to minimize human health risks and be protective of human health and safety and of the environment.

2.10.1 Alternative 1 – No Action

This alternative involves no remedial actions of any kind and the status of the TCE groundwater plume is not monitored. CERCLA requires its inclusion for comparison purposes.

2.10.2 Alternative 2 – Monitored Natural Attenuation

This alternative consists of monitoring plume stability and the ability of natural groundwater processes to attenuate the TCE and TPH-DRO plumes. The plume appears to be stable due to several factors: aggressive remediation of the source area during the pilot test, relatively flat groundwater gradients, and natural attenuation of the diffuse portion of the plume. Natural attenuation is commonly associated with natural (or enhanced) biodegradation from naturally occurring organisms; however, it is also noted that abiotic degradation (i.e., degradation that is not related to biologic/organism) of TCE by reactive minerals has been recognized in the industry in the past 5 to 10 years. Prior to the pilot test, there was a significant decrease in TCE concentration most likely attributable to natural attenuation processes; however, recent monitoring indicates TCE biodegradation is minimal without enhancement (i.e., addition of nutrients and recirculating groundwater). Monitoring wells are within the plume itself, and cross- and down-gradient of the plume (Figure 3).

As discussed previously, 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. TCE does not appear to be degrading via naturally occurring bioremediation. There are essentially no degradation (or breakdown) products found in soil or groundwater. Other natural attenuation processes, such as diffusion and dispersion, though active at the site, are not diminishing the concentrations at a noticeable rate. This fact is also supported by no decrease or increase in TCE concentration trends for the permanent groundwater monitoring wells. This option can be effective in reducing contamination, but can require an extended remedial timeframe. However, there is an extent of contamination still remaining that warrants treatment to expedite natural attenuation. Plateau conditions typically occur around 30-70 µg/L where it is not cost effective to perform active treatment. There are multiple wells representing a plume area with current TCE concentrations above 100 µg/L that justify active treatment.

Under this alternative, additional monitoring wells would be installed and groundwater samples routinely collected and analyzed for site contaminants, degradation products, bioparameters, and general groundwater parameters. In addition, deed restrictions on groundwater use would be recorded to protect human health (deed restrictions are acceptable to the land owner). This alternative would eventually meet the RAOs.

2.10.3 Alternative 3 – Enhanced Biodegradation and Groundwater Recirculation

This alternative applies the two remediation technologies successfully demonstrated in the pilot test to the concentrated portion of the plume. Treatment would occur in 13 treatment “cells” that would be operated sequentially (Figure 5). Each treatment cell would require nine new groundwater wells to be installed: three extraction wells, four injection wells, and two performance monitoring wells.

The existing mobile treatment system used in the pilot test would be connected to the new wells and treatment would be conducted for about six months before the system is moved to the next cell.

Enhancing biodegradation is expected to reduce the timeframe required for remediation from over

30 years (in Alternative 2) to 15 years: about seven years for active treatment (i.e., 6-months per cell) in the concentrated portion of the plume, and eight years for natural attenuation processes to address the diffuse portion of the plume. Similar to Alternative 2, this alternative includes installing new groundwater wells relative to the plume, routine sampling and analysis, and groundwater use restrictions until the plume is remediated.

2.10.4 Alternative 4 – Permeable Reactive Barriers

This alternative uses a series of permeable trenches that would treat contaminated groundwater as it passes through a reactive material (e.g., zero…