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ATC Associates Inc. 1117 Lone Palm Avenue,Suite 201 Modesto,California 95351 C. 209-579-2221 Fax:209-579-2225 ASS OC'-1. AYES INC boreholes associated with M W 5 and M W6 at a depth of approximately 56.5 feet bgs. Petroleum hydrocarbons were not detected in these samples. i Two additional soil samples were collected from above the recent elevation of the groundwater table, but close enough to be considered to be within a smear zone. One soil sample was collected from the borehole associated with MW2 at a depth of approximately 50.5 feet bgs and one soil sample was collected from the borehole of MW7 at a depth of approximately 51.5 .feet bgs. Petroleum hydrocarbons were not detected in,the soil sample collected from.MW7. Total petroleum hydrocarbons quantified as kerosene (TPHk) and total petroleum hydrocarbons quantified as diesel (TPHd) were reported in the sample collected from MW2 at concentrations of 3.00 milligrams per kilogram (mg/kg) and 3.40 mg/kg, respectively. It should be noted, that the chromatograms associated with these results did not resemble typicalg chromatograms for kerosene and diesel. Based on the fact that the soil sample associated with MW2 was collectedfrom a depth that is approximately three feet above the most recently documented groundwater table elevation, coupled with the questionable laboratory results and 4he lack of positive detection in other samples collected from the saturated zone, calculations regarding contaminant mass in 1 saturated zone soil were not performed. Additionally, MW2 was used as the extraction well during i operation of the SVE system and consequently, calculations using the reported concentrations associated with the soil sample collected from 50.5 feet bgs would not be representative of current conditions in saturated zone soils. i 4.4 Groundwater Groundwater monitoring was initiated at the site in September of 1998,following the installation of MW I and has generally been conducted on a quarterly basis through January of 2009. The most recent ` groundwater sampling event was conducted on February 26,2010. MW2 through MW4 were added to the groundwater monitoring network in December of 1999, and MW5 through MW7 were added in December of 2001. TPHg,TPHk, TPHd,BTEX,and methyl tertiary butyl ether(MTBE)have historically been detected in groundwater samples collected from MWI and MW2. Sporadic detections of some of the analytes of interest.have been detected in samples collected from MW3. Petroleum hydrocarbons have never been detected.in groundwater samples collected from MW4 through MW7, with the exception of a j sole reported detection of TPHd in the groundwater sample collected from MW4 on June 22, 2000. Historical groundwater analytical data are included in Table 2. The following is a summary of the dissolved analytical results over the last 12 years: ' MW 1 is.installed in the approximate location of the former 'UST. TPHg, TPHk, TPHd, BTEX, and MTBE were initially detected in groundwater samples collected from this well when monitoring and sampling was initiated in September of 1998.TPHg, TPHk, and TPHd were last s detected in samples collected from this well in October of 2004, December of 2000, and January of 2008, at concentrations of 55 micrograms per liter (µg/L), 932 µg/L, and 130 µg/L, respectively. Benzene was last detected in samples collected from this well in July of 2003 at a ` concentration of 1.2 µg/L.. Toluene,ethylbenzene,and total xylenes were last detected in samples collected from this well in January of 2008 at concentrations of 0.86 µg/L, 0.55 µg/L, and 4.0 Vg/L, respectively. MTBE is typically present in samples collected from this well at concentrations below the primary maximum contaminant level (MCL) of 13 pg/L. An obvious f{ F S:Environmenta11625771Repons12010 closure summary.doc 6 I