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Mr Harlin Knoll R IO N San Joaquin County Environmental Health Division • 20 February 2001 Page 2 removed from the site along with eleven other USTs located at the site The remaining tanks at the site are shown on Figure 2 and include Tanks #1 and #3 (7,500-gallon Icapacity each) and Tank #2 (550-gallon capacity) From February to May 1995, BFS conducted a soil remediation operation slightly north of the present site using a soil vapor extraction (SVE) treatment system The SVE location corresponds to the former location of Tanks #4 and #5, where impacted soils were detected during their removal in 1991 Hydrocarbons were rapidly removed to low asymptotic levels, below 30 parts per million by volume (ppmv) for total petroleum hydrocarbons as gasoline (TPHg) and non-detect for benzene A subsequent closure request was granted to BFS by the San Joaquin County Department of Health Services on 30 November 1995 Regional Groundwater Issues In a QST Environmental (QST) report dated 23 June 1999, a database search from a Vista report showed several sites within 0 16 miles with known gasoline releases including MTBE This report also noted that the groundwater flow direction for two neighboring sites is to the north-northeast One particular site of interest is an Arco station located 0 11 miles southwest at 205 N Center Street, which is directly upgradient from this property The station has a Code 3 MTBE release with concentrations greater than 35 micrograms per liter (µg/l) in the groundwater plume Orion also accessed "Geotracker", a new California Water Resources Control Board (CWRCB) tool for additional regional mapping of leaking underground fuel tank (LUFT) sites near this site Geotracker is a geographical information program maintained by the Lawrence Livermore National Laboratory to locate releases to the groundwater and identify vulnerable receptors Figure 3 is reproduced from the program's output to locate nearby LUFT sites to this property fSummary of Previous Investigations In May 1997, Foothill Engineering (FE) drilled four slant borings for the collection of 16 soil samples in the vicinity of the three remaining USTs TPHg concentrations were detected in the 20 to 25 feet below grade soil samples from PB1 and PB2 beneath Tank #3 at concentrations from 3 to 16,200 milligrams per kilogram (mg/kg) Benzene was not found above the specific EPA Method 8020 detection limits No groundwater samples were collected during this investigation FE concluded that the release was aged gasoline Subsequent local soil sampling results performed by BFS contractors have shown this release to be limited in extent to the area beneath the tank t S\BFS\STOCKT0N\LTR\LTR007 DOC 2/20/01