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1 <br /> Groundwater samples were collected from the five wells using a Teflon sampling bailer, packed in <br /> 16 an iced cooler, and transported under Chain-of-Custody manifest to Sparger Technologies, Inc , <br /> ' a California-certified analytical laboratory located in Sacramento, California The laboratory <br /> analyzed each field sample for benzene, toluene, ethylbenzene, xylenes (BTEX) and Total <br /> ' Petroleum Hydrocarbons as gasoline (TPH-gasoline) using EPA Method 8015/8020 The <br /> laboratory reports and chain-of-custody documents are included as Attachment 2 <br /> Analytical results of the second quarter 1996 sampling event indicate that petroleum hydrocarbons <br /> ' are not present in groundwater above their detection limits The current and historical laboratory <br /> results and their detection limits are summarized in Table 2 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> This report documents the fourth of four consecutive quarters of groundwater monitoring and <br /> sampling performed by IT Corporation As summarized in Table 1, since July 25, 1995, the <br /> groundwater surface elevation has risen an average of 8 61 feet Since May 1992, the <br /> PP groundwater surface elevation has risen an average of 19 06 feet This extreme rise in the <br /> groundwater table has likely resulted in groundwater elevations above the screened interval of the <br /> wells This condition can lead to inconsistent groundwater flow direction and gradient <br /> interpretations and unrepresentative groundwater sample collection and analytical results <br /> As summarized in Table 2, groundwater samples have been collected and analyzed from on-site <br /> ' wells since August 1990 The highest concentrations of gasoline hydrocarbons were recorded <br /> between May 1992 and January 1993 in MW-3 at 1,100 parts per billion (ppb) TPH-gasoline and <br /> ' 160 ppb benzene Since that time, gasoline hydrocarbon concentrations in the wells have declined <br /> steadily The last sampling event in April 1996 resulted in non-detected concentrations for all <br /> ' parameters analyzed for the first time <br /> This steady decline in gasoline hydrocarbon concentrations is likely due to natural biological <br /> ' degradation but may also be indicative of groundwater elevations above the well screen intervals <br /> Natural degradation will continue to reduce the concentration of any remaining gasoline <br /> hydrocarbons in the groundwater and overlying soil <br /> 2 <br />