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4 SUMMARY OF FINDINGS Philip has continued to monitor subsurface conditions and the plume of gasoline- Impacted groundwater at the Earthgrain's facility Philip's data from this current monitoring event, and from previous assessments Indicates that the plume of impacted groundwater is approximately 80 to 180 feet wide, and some 550 feet long, elongated in the same east-northeast direction as groundwater flow The highest concentrations of petroleum hydrocarbon compounds are centered near the former gasoline USTs ' The lateral extent to the north, south, and west had been delineated by historic, non- detectable, petroleum concentrations measured in groundwater samples collected from wells in those directions However, some relatively low petroleum concentrations were measured, during this current event, in samples collected from wells MW-4, MW-9, MW-10, and MW-13 Petroleum concentrations in recent samples from these wells had generally been non-detectable Philip will continue to monitor these wells to assess conditions along the boundaries of the plume The most downgradient well, MW-08, had no detectable concentrations of TPH-G, BTEX, or oxygenates A TPH-G concentration of 100 µg/1 was measured in a groundwater sample collected from CPT-3 during the May 1999 site Investigation This same sample did not contain benzene and Acculabs had characterized the TPH- G analysis as being uncharacteristic of a typical gasoline, suggesting that the Impact was more characteristic of degraded gasoline Philip will continue to monitor results of MW-08 and MW-12 to assess this downgradient extent The highest concentrations of petroleum impact in groundwater had historically been detected in groundwater samples collected from well MW-1 Data from this round of monitoring indicates that higher petroleum concentrations are more closely centered in the vicinity of sparge well SP-1 and piezometer PZ-1, which are located about 20 feet northeast and northwest (respectively) from MW-1, in the vicinity of the former gasoline USTs The highest TPH-G concentrations were measured in samples collected from PZ-1 (21,000 µg/l), SP-1 (20,000 pg/1), PZ-2 (16,000 µg/1), and MW-1 (15,000 µg/1) The highest benzene concentrations were measured in samples collected from PZ-1 (3,700 µg/1), SP-1 (3,300 pg/1), MW-1 (630 µg/I), and PZ-2 (230 µg/l) i ' Oxygenate compounds have been monitored for at this site since 1997 There has never been any oxygenate compound, other than DIPE, detected in any groundwater sample DIPE was measured at a concentration of 26 lig/l in the current sample collected from well MW-12, which is more than the previously highest measured value of 16 µg/l (1/29/98 sample from MW-7) However, that increase is relatively slight Philip will continue to monitor the oxygenate levels to assess movement of the groundwater plume August 1999 Groundwater Monitoring Report Prepared for 1'HL CARTHGRAINS COMPANY Prepared by P11111p St,rvlces Corp P\62400132\121382LG16240014'\0899MON DOC October 9 1999