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June 1996 -3 - 953-7001002 2. SUMMARY OF SITE INVESTIGATIONS AND REMEDIAL ACTIVITIES The following sections outline chronologically the investigations and remediation performed at the site December 198 -Four underground tanks were removed from this facility in December 1988 (Figure 2) Soil samples collected following tank removal indicated that one or more of the tanks had leaked The maximum concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene,and xylenes reported in soil samples collected during tank removal were 145 mg/kg, 1 1 mg/kg,5 7 mg/kg and 19 mg/kg respectively Ethylbenzene 1 was not detected in any of the soil samples TPH in the diesel range was also reported at a maximum concentration of 560 mg/kg but was reported by the laboratory to be a "very weathered hydrocarbon" Results of soil samples from the tank removal are summarized in Table A-1 in Appendix A Groundwater was encountered in the base of the tank excavation and gasoline approximately four to six inches thick was observed floating on groundwater encountered in the bottom of the excavation The amount of gasoline that leaked is unknown (URS, 1989) August 1989 -Three monitoring wells MWAD, MW-1S and MW-6S were completed by URS in August 1989 to assess the potential impacts of the gasoline release on the groundwater quality Wells MW-11) and MW-6S were installed in the uppermost water-bearing zone and MW1-D was installed in the second water bearing zone Figure 2 illustrates the location of monitoring wells at the site March 1990- In March 1990, six additional monitoring wells, MW-2S,3S,4S,4D, 5S and 7S were installed by WHF Appendix A contains the results of the soil sampling conducted during the construction of these wells TPHg was detected in soil samples from borings for MW-4S and MW-417 at a concentrations of 30 mg/kg and 61 mg/kg,respectively Xylenes were also detected at 0 0079 mg/kg in the soil sample from MW-413 Both samples were from a depth of 15 feet No TPHg or BTEX were detected in soil samples from borings for monitoring wells MW-2S,3S, 5S and 7S July 19900 -WHF conducted a 31 point soil vapor survey in July 1990 to determine the extent of soil and groundwater hydrocarbon contamination at the site (WHF, 1990) The vapor survey results indicated that petroleum hydrocarbons extended east and southeast of the former tank excavation February 1991 -WHF excavated approximat1 2,000 cub ards of soil from the area of the former tank excavation in order to remove the source of petroleum hydrocarbons Twenty- four confirmation soil samples were collected from the excavation and were analyzed for TPHg and BTEX With the exception of one sample (S-13 with 10 6 mg/kg), TPHg was not detected Low concentrations of BTEX were reported in 6 of the 24 confirmation soil samples The maximum concentrations of BTEX concentrations were 0 40 mg/kg benzene and 0 19 mg/kg toluene in confirmation soil sample S-3 along the southeast side, , 0 57 mg/kg ethyl benzene in soil sample S-13 and 0 32 mg/kg xylenes in soil sample S-10 both from the southern end of the excavation During this phase of the investigation monitoring wells MW-8S and MW-9S were installed 9537001 R01(7l3M) Golder Associates