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v A <br /> O <br /> A S S O C I A T E S I N C <br /> current AST location contained elevated concentrations of total petroleum hydrocarbons as <br /> gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), and methyl tertiary butyl ether <br /> (MTBE) The extent of impacted soil was defined and generally extended along the backside of <br /> the levee, west of the store The Anel extent was approximately 200 feet in length and 65 feet in <br /> width and was limited to depths between 5 and 15 feet bgs Additionally, MTBE impacted soil <br /> extended eastward, between the store and office building <br /> The groundwater plume generally extended along the backside of the levee, west of the store, and <br /> was approximately 225 feet long and 70 feet wide Concentrations were highest in the boring <br /> adjacent to the former and current product lines The extent of TPHg in groundwater was not <br /> fully defined to the west and south but samples indicated that the borings in those directions were <br /> near the edge of the plume Additionally, TPHd and MTBE have migrated eastward <br /> GROUNDWATER MONITORING <br /> i <br /> The third quarter groundwater monitoring and sampling of monitoring wells MW1 through MW7 was <br /> conducted by ATC Associates Inc personnel on August 1, 2002 Water level measurements were <br /> collected from all monitoring wells prior to purging and sampling Well locations are shown on Figure <br /> 2 <br /> Subsequent to monitoring, each well was purged by extracting a minimum of three well casing volumes <br /> of groundwater While purging, groundwater parameters (temperature, conductivity, and pH) were <br /> momtored and allowed to stabilize before water samples were collected Samples were collected using <br /> dedicated, disposable bailers with bottom emptying devices to reduce volatilization All purged <br /> groundwater was contained in 55-gallon drums approved for hazardous liquid storage on-site pending <br /> appropriate disposal Groundwater well purge and sample logs are contained in Attachment 1 <br /> The groundwater samples collected from each well were placed on ice and transported under <br /> chain-of-custody documentation to Argon Laboratories (ELAP #2359) in Ceres, California The <br /> groundwater samples were analyzed for TPHd, TPHg, benzene, toluene, ethylbenzene, and xylenes <br /> (BTEX) and MTBE utilizing EPA methods 8015/8020 If MTBE was detected by EPA method <br /> 8020 then the sample was analyzed by EPA method 8260 to confirm the presence of MTBE <br /> RESULTS <br /> Water levels have decreased an average of 0 99 feet since the last monitoring event on May 5, 2002 <br /> (Table 1) A groundwater gradient map was created using the data collected on August 1, 2002 <br /> (Figure 3) Groundwater primarily flows east, away from the slough, with a gradient of approximately <br /> 0 08 feet/foot or 427 feet per mule <br /> TPHg and TPHd were not detected in any of the groundwater samples collected from wells MW1 <br /> through MW7, although the detection limit for TPHg in the sample from well MW7 was elevated due <br /> to dilution factors BTEX were not detected in the groundwater samples collected from wells MW1 <br /> w lw0rdpro1625141quart1yl2gr-2002 doe 3 <br />