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Focused Groundwater Investigation Work Plan
<br /> Deuel Vocational Institution(DVI), Tracy, California Introduction
<br /> In December 2017,before the start of injection activities,the fourth quarter of 2017 (4Q17)quarterly GW
<br /> samples were collected from the scheduled wells. The wells sampled were MW-2-BP and MW-5-BP
<br /> (compliance wells),MW-6-BP and MW-26-BP (treatment zone wells),MW-24-BP and MW-25-BP
<br /> (transition zone wells), and MW-7-BP(background well). VOC concentrations in 4Q17 (before EHC-L
<br /> injections began) generally were less than those reported in previous quarters, specifically at MW-9-BP
<br /> (TCE at 34 µg/L,PCE at 180 gg/L, cis-1,2-DCE at 11 gg/L), and MW-26-BP(TCE at 9.7 gg/L,PCE at
<br /> 49 µg/L, and cis-1,2-DCE at 82 gg/L),but still exceeded the MCLs in the burn pit area(URS 2017).
<br /> Between December 6 and December 12,2017, in situ remediation was implemented at the project site.
<br /> The remediation involved advancing 21 borings, spaced at 20 feet on center,using a Direct-Push(DP)
<br /> drill rig to inject amendment in the areas around MW-26-BP and MW-6-BP, and immediately northwest
<br /> of MW-24-13P. The amendment was injected from the water table(approximately 10 feet bgs)to 25 feet
<br /> bgs, encompassing the screened interval of MW-26-BP. This well, located in the burn pit area,
<br /> historically had the highest VOC concentrations. The injection fluid consisted of EHC-L components
<br /> (EHC-L,ELS emulsion,DHC inoculum,and potassium bicarbonate as a buffer). In recent GW
<br /> monitoring events since this effort, GW at MW-9-BP has remained above the MCL for PCE and TCE,
<br /> prompting further investigation(URS 2020).
<br /> Between August 17 and August 31, 2020, a passive SG survey was conducted to characterize the
<br /> contaminants of concern(COCs)west of the burn pit area near MW-9-BP and to characterize the
<br /> potential risk of vapor intrusion into site facilities. The investigation used approximately three sampling
<br /> probes implemented near MW-9-13P, four sampling probes near the Grease Trap,two probes southeast of
<br /> the Grease Trap and along a utility,two probes placed outside of the Laundry/Print Shop,three probes
<br /> placed in the space beneath the former Laundry and Print Shop, and one probe to the southeast near the
<br /> administration area. Passive SG samplers were emplaced using a 3.5-inch-diameter hand auger. Each
<br /> borehole was advanced to 2 feet bgs. The samplers were retrieved on August 31, 2020, approximately 2
<br /> weeks after installation.
<br /> The investigation detected 14 analytes, including PCE, TCE, and cis-1,2-DCE,with maximum
<br /> concentrations of 4,470 micrograms per cubic meter(gg/m), 521 gg/m3, and 170 µg/m3,respectively.
<br /> These maximum concentrations were detected at SG-02. This investigation found at least one commercial
<br /> exceedance of PCE and TCE,prompting an SG investigation around SG-04 and SG-08; an IA/CS
<br /> evaluation near SG-2 (Laundry/Print Shop), and additional SG sampling around SG-12 (Grease Pit),
<br /> which were conducted in January 2022.Analytical results are of SG samples are depicted on Figures 2
<br /> through 4.
<br /> The site investigation SG sampling conducted in January 2022 detected several analytes,with
<br /> maximum concentrations of PCE(6,100 µg/m),TCE(7,200 gg/m3), cis-1,2-DCE(1,100 gg/m3), and
<br /> benzene(38 gg/m3)detected at vapor well(VW)VW-9,which is located about 10 feet northeast of MW-
<br /> 9-BP. PCE and TCE were detected above residential and commercial soil vapor screening limits in all
<br /> wells,with a few exceptions. PCE concentrations exceeded residential screening levels(SLs)in only
<br /> VW-5, and TCE concentrations exceeded residential SLs in only VW-1,VW-2,VW-5, and VW-7.All
<br /> benzene detections exceeded the residential soil vapor SLs,with only one exceedance(VW-9)above the
<br /> commercial soil vapor SL. Of the other detected analytes, cis-1,2-DCE and chloroform also exceeded
<br /> their respective residential soil vapor SLs with chloroform exceedances in two wells(VW-3 and VW-10).
<br /> The analytical results are shown in Figure 5. This investigation indicated that the project site may pose
<br /> unacceptable vapor intrusion risk to future indoor occupants.
<br /> Between May 2022 and May 2023,three semi-annual GW monitoring events were conducted which
<br /> found the area surrounding MW-9-BP has had concentrations of TCE and PCE exceeding their respective
<br /> 1-4
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