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Mr Knoll February 19, 1999 Page 4 site during drithng consisted of dark brown clay from the surface to approximately 20 to 25 feet bgs A silty sand was encountered from approximately 25 to 30 feet bgs in Boring EFS-1 and 20 to 22 feet bgs in Boring BFS-2 The soil types observed are described on the boring logs which are attached in Appendix B Groundwater was encountered during drilling activities at 25 feet bgs in BFS-I and 20 feet bgs in BFS-2 TPH and BTEX were not detected above method reporting limits in the soil samples submitted from depths ' of 13 5 and 20 feet bgs in BFS-I and 15 5 and 18 5 feet bgs in BFS-2 Analytical results for the soil and groundwater samples are summarized in Table 2 The laboratory reports and chain-of-custody documents are found in Attachment C ' Groundwater analysis reported TPH as gasoline in BFS-I at 4,200 nucrograms per Inter (ug/L) BTEX was also detected in the groundwater samples from BFS-I Three oxygenates MTBE, DIPE, and Ethanol were ' also detected at concentrations of 0 78, 6 1 and 6 4 ug/L in water from BFS-1 BFS-2 had total:xylene at a concentration of 0 55 ug/L as the only gasoline constituent reported above Method Detection Limits Analytical results of groundwater are summarized in Table 2 ' CLOSURE ANALYSIS ' Based on additional local research, the groundwater quality in the vicinity of the site is poor due to overdraft of the groundwater basin There are two inactive water supply wells within a 1 mile radius of the site However, these supply wells have been inactive for the last 20 years due to the poor quality of groundwater The three gasoline tanks (Tank Nos 1 through 3) under investigation were cleaned and filled with sand in 1967 Therefore, no further release to soil in the vadose zone or additional impact to groundwater is possible Based on the previous investigation conducted by Foothill Engineering in 1997, impacted soil was present beneath Tanks 2 and 3 at a depth of approximately 25 feet The impacted soil is hunted to the area beneath these tanks verified by slant Borings P113 and PB4 which are down gradient and towards the north Foothill Engineering concluded that the impacted soil was aged gasoline ' In December 1998, QST drilled two borings BFS-1 and BFS-2 Boring BFS-1 was drilled approximately 7 feet to the east of Tank 2 and Boring BFS-2 was drilled approximately 13 feet to the south of Tank 3 Petroleum hydrocarbons were not detected in soil samples analyzed from Borings BFS-1 and BFS-2 indicating that impacted soil is residual and limited to the area beneath the tanks Soil samples from this investigation were also analyzed for MTBE and other oxygenates and these constituents were not detected in the soil samples Thus confirming Foothill's conclusion that the impacted soil detected is likely from an aged release of gasoline Analytical results from groundwater samples collected during the QST investigation showed the presence of TPH, BTEX and oxygenates in groundwater sample BFS-1 TPH, BTEX and MTBE were not detected in the groundwater sample collected from Boring BFS-2 Therefore, the data indicates that the impact to groundwater is limited However, MTBE was not detected in the soil samples like the other petroleum hydrocarbons so the source of the MTBE is questionable Given the absence of a known MTBE source onsite and the presence of MTBE in groundwater, the cause of the petroleum hydrocarbon impact to groundwater