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V 4AT C A S S O C I A T E S I N C BP-SB2-45 5 and BP-SB2-55 5, collected from SB2 at 45 5 feet and 55 5 feet bgs, respectively TPHg (1,700 mg/1), toluene (21 mg/l), ethylbenzene (6 2 mg/l), and xylenes (91 mg/kg) were detected at 45 5 feet however none were detected at 55 5 feet bgs 4 Of the 28 soil samples analyzed to date, no sample was reported to contain benzene above the laboratory method detection limit (MDL) 5 Soil samples collected were analyzed for MTBE by EPA Methods 8020 and/or 8260 MTBE was not detected in any of the soil samples above the laboratory MDLs ' 6 In April 1999, at the request of PHS/EHD, ATC completed a receptor survey for the subject property ATC reviewed PHS/EHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction logs, and conducted a site walk ' in the vicinity of the site to identify any groundwater wells located within a 2,000-foot radius of the site This survey revealed fifteen wells located within approximately 2,000 feet of the site The closest of these wells is an on-site domestic well located ' approximately 125 feet downgradient of the former USTs This well has been sampled twice by ATC and no petroleum hydrocarbons were detected during either sampling event 7.0 DEVALUATION OF LOW RISK CRITERIA � ' 7.1 ]Low Risk Groundwater Case Evaluation Using the criteria listed in CRWQCB's No Further Action (NFA) requirements, as outlined by ' CRWQCB (Appendix B of the Tri-Regional Recommendations), conditions at the subject site were evaluated to determine if NFA as a "low risk, groundwater case site" is appropriate for this site Criterion 1: Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass reduction rate of groundwater pollutants discussed in Criterion #4 below. ' As previously noted, laboratory analytical data indicate the majority of petroleum hydrocarbon-affected soils are present at depths from approximately 15 to 45 feet bgs However, trace levels toluene and/or xylenes were observed at depths of 65 5 1 feet and 85 5 feet bgs in borings SBI and SB2, respectively One might expect maximum groundwater degradation to occur when the water table rises and desorbs hydrocarbons from the soil matrix Between June 1999 and March 2000, a total of three quarterly groundwater monitoring events have been performed at the site Groundwater level measurements indicate that during this period, the water table was highest in March 2000 and lowest in December 1999 with a maximum fluctuation in any one w\I 48851reporU\NFA-RequesGdoc 12