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of groundwater samples in Table 2,and copies of laboratory analytical results are included as Appendix E. Field observation forms of well purging and sampling are included as Appendix F. The next quarterly sampling wrts on 2 May 1991. 'Io compensate for the dry monitoring wells, piezometers P and 1112,vapor recovery wells V 1,V3,and V4,and the new groundwater monitor- ing well MW1 I were included. Well MW8, which this time had enough water in its casing,was also sampled. Besides regular TPM and 13TEX analyses, upgradient wells MWS and IW 1 and recovery wells RW1,RW2,and RW4 were sampled,and the samples were analyzed for volatile and semi-vola- tile organics,TPH-diesel, priority pollutant metals,general Minerals,anions,and BOD. These analyses were needed to adequately design a treatment system and to characterize groundwater chemistry, at which point it would be possible to evaluate Elie future effects of the extraction/treatment system on groundwater and to determine if groundwater had already been affected by chemicals or other activity,such as agriculture,not related to Exxon's use of the site. The highest concentrations of petroleum hydrocarbons were found in samples collected from well V4;the highest concentration was 200,000 gg/L of TPH. Three other wells, RW4,V 1,and V3, had TPH concentrations above 100,000 pg/L (Table 2). Petroleum hydrocarbon concentra- tions were lower in samples collected from the upgradient wells (IW1, P1,and P2), but the concentration of TPH in samples collected from well MW8,located across Pershing Avenue and downgradier-t from a Shell service station, was 57,000 pg/L. The highest concentration of benzene was also found in samples collected from well V4 (31,000 itg/L). In well V4, LPPH 0.05 feet thick was monitored prior to purging on 2 May 1991. Chemical analysis of groundwater samples from wells RW 1, RW2, RW4, and IW 1 by EPA Method 8240 for volatile organics did not find any components besides BTEX at concentrations greater than detection limits. Groundwater samples from these wells were also analyzed for semi-volatile compounds by EPA Method 8270. Only 2-methylnaphthalene(ranging from 80 to 200 pg/L)and naphthalene(ranging from 22 to 690 pg/L)were found in groundwater samples. Of the priority pollutant metals,arsenic was found in concentrations exceeding drinking water standards of 0.05 mg/L in wells RW 1 and RW2 at concentrations of 0.080 and 0.058 mg/L, respectively. Manganese was also found in groundwater samples above the acceptable level for drinking water of 0.05 mg/L. Summaries of analytical results for general minerals,major anions,and priority pollutant metals are in Table 6,and copies of laboratory reports are included in Appendix E. Figures 6 and 7 show isocontours of TPH and benzene concentrations in groundwater under the investigated area on 30 January 1991, and the concentrations in samples collected on 2 May are shown in Figures 8 and 9. �L7!-.h'n7a�i,n91M 1