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V � A S S O C I A T E S I N C current AST location contained elevated concentrations of total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), and methyl tertiary butyl ether (MTBE) The extent of impacted soil was defined and generally extended along the backside of the levee, west of the store The Anel extent was approximately 200 feet in length and 65 feet in width and was limited to depths between 5 and 15 feet bgs Additionally, MTBE impacted soil extended eastward, between the store and office building The groundwater plume generally extended along the backside of the levee, west of the store, and was approximately 225 feet long and 70 feet wide Concentrations were highest in the boring adjacent to the former and current product lines The extent of TPHg in groundwater was not fully defined to the west and south but samples indicated that the borings in those directions were near the edge of the plume Additionally, TPHd and MTBE have migrated eastward GROUNDWATER MONITORING AND SAMPLING On December 4, 2003, ATC personnel conducted the fourth quarterly groundwater monitoring and sampling of monitoring wells MW 1 through MW7 Water level measurements were collected from the monitoring wells prior to purging and sampling Well locations are shown on Figure 2 Subsequent to monitoring, each well was purged by extracting a minimum of three well casing volumes of groundwater While purging, groundwater parameters (temperature, conductivity, and pH) were monitored and allowed to stabilize before water samples were collected Samples were collected using dedicated, disposable bailers with bottom emptying devices to reduce volatilization All purged groundwater was contained in 55-gallon drums approved for hazardous liquid storage on-site pending appropriate disposal Groundwater well purge and sample logs are contained in Attachment 1 The groundwater samples collected from each well were placed on ice and transported under chain-of-custody documentation to Argon Laboratories (FLAP #2359) in Ceres, California The groundwater samples were analyzed for TPHd, TPHg, benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA methods 8015/8021B and total lead utilizing EPA method 200 9 Fuel oxygenate additives including MTBE were analyzed by EPA method 8260B RESULTS Water levels have increased an average of 0 35 feet since the last monitoring event on September 30, 2003 (Table 1) Depth to groundwater levels ranged from 2 25 to 10 98 feet below ground surface (bgs) A groundwater gradient map was created using the data collected on December 4, 2003 (Figure 3) Groundwater generally flows to the east, away from the slough, with a gradient of approximately 0 07 feet/foot or 374 feet per mile • TPHd was not analyzed in groundwater samples collected from wells MW1 through MW7 TPHg was detected in the groundwater sample collected from well MW7 at a concentration of 310 ppb s 1625141quart1yl4gr-2003 doc 3