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l I 1, Page 4 Ms. Vicki McCartney, REHS February 20, 2004 V concentrations of petroleum hydrocarbons. However, this Plan proposes additional investigation to supplement that information. L Six soil borings (B -I through B-6) will be driven with a CPT rig at the locations shown in Figure L 3 and soil samples will be collected as illustrated in Gregg Drilling Company's flyer (Attachment A). Five soil samples will be collected from each boring (except B-2) at depths of 15, 20, 25, 30 and 35 feet (approximate depth of groundwater table is 40 feet as shown in Table 3). Samples from boring B-2, located in the vicinity of the former dispenser, will be collected at depths of 10, 15, 20, 30 and 35 feet. Soil samples will be noted for physical characteristics by the site geologist and screened for volatile organic compounds using a photoionization detector (PID). At least two samples from each boring will be selected for subsequent chemical analysis based on PID measurements (those having the highest values). Additional samples may be selected for analysis if further profiling would be beneficial for site characterization. ti Selected soil samples will be capped, labeled, stored in an iced chest, and subsequently delivered under chain of custody to an analytical laboratory for chemical testing. Soil samples will be L analyzed for BTEX, TPH-G, MTBE, TBA, DIPE, ETBA, TAME, 1,2 -DCA and EDB. Analytical data will be used to estimate the mass of residual petroleum hydrocarbon impact in the vadose zone. j.. Groundwater Assessment Borings B-1 and B-6 will be driven deeper beneath the groundwater table. Boring B-1 is located near the source of the release and B-6 is hydraulically downgradient from it. Discrete 4 groundwater samples will be collected in the manner described in Gregg's groundwater sampling ILr flyer contained in Attachment A. Samples will be collected from each boring at depths of 60, 70 and 80 feet to assess the vertical extent of petroleum hydrocarbon impacted groundwater. PSC's L. April 14, 2003 report contained soil sample data suggesting that the vertical extent of impact was 55 feet at the source. EHD information indicates that the groundwater table may have been at a • depth of 80 feet in 1978. L If access is granted by the adjacent property owner, a groundwater sample will be collected from 1 the irrigation well located about 400 feet south of the former leaking UST. Groundwater samples L from the irrigation well and the two CPT borings will be capped, labeled, stored in an iced chest, and subsequently delivered under chain of custody to an analytical laboratory for chemical testing. Groundwater samples would be analyzed for BTEX, TPH-G, MTBE, TBA, DIPE, ETBA, TAME, 1,2 -DCA and EDB. r j„ Quarterly Groundwater Monitoring b KLEINFELDER 3077 Fite Circle, Sacramento, CA 95827-1815 (916) 366-1701 (916) 366-7013 fax a..