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Atlantic Richfield Company 12 <br /> ARCO 4932, t5 E HardmS Way,Stockton,CA June 7 2002 <br /> ' groundwater monitoring events from September 2000 through April 2002, and an - <br /> average T of 0 34 fe/min, capture zones of approximately 31 feet and 48 feet were <br /> calculated in the downgradient and cross-gradient directions, respectively Calculations <br /> are included in Attachment J <br /> ' VARIANCES TO THE JANUARY 15, 2002 AND MARCH 11, 2002 WORK <br /> PLAN SUBMITTALS,AND FEBRUARY 14, 2002 SJCEHD LETTER- <br /> ' AQUIFER TESTING <br /> • Observation wells. According to SECOR's January 15, 2002 work plan and the <br /> ' February 14, 2002 SJCEHD letter, the wells proposed for use as observation <br /> wells consisted of wells MW-1, MW-3, MW-4, MW-5, MW-6, MW-7 <br /> However during aquifer testing, wells MW-1, MW-4, MW-6, and MW-7 were Z <br /> used as observation wells These wells were chosen a retraction poen s based_.-,- <br /> on their variable proximities from pumping well EW-1, and because these wells <br /> are target area wells, which contain the highest concentrations of petroleum <br /> hydrocarbons and MtBE in groundwater Though monitoring water levels <br /> within MW-3 and MW-5, would assist in observing the radius of influence, <br /> these wells were omitted as observation points based on the absence of <br /> petroleum hydrocarbons and minor concentrations of MtBE in the wells and <br /> because the selected observation wells would provide adequate data for <br /> ,* evaluating the radius of influence as a result of continuous GWE during aquifer <br /> testing <br /> • Groundwater Sampling. Contrary to what was proposed in past work plan <br /> submittals and within the February 14, 2002 SJCEHD letter and due to an <br /> oversight, groundwater samples were not collected prior to and during aquifer <br /> testing However, quarterly monitoring and sampling of site groundwater <br /> monitoring wells, including the newly installed wells, was conducted on April <br /> 11, 2002, approximately one week following termination of aquifer testing <br /> 1 Decreases in MtBE were observed in wells MW-1 and MW-2, with the lowest <br /> concentration of MtBE (530 ug/l)reported in MW-2 since monitoring for the <br /> ' presence of TPHg, BTEX, and MtBE began in 2000 <br /> Since the beginning of the quarterly groundwater monitoring program in 2000, <br /> ' site wells have not been monitored for the presence of total petroleum <br /> hydrocarbons as diesel (TPHd) This analyte was proposed for analysis in the <br /> past work plan submittals Since diesel has never been dispensed at the site, <br /> SECOR will continue to implement the current sampling program without <br /> conducting sampling for the presence of TPHd Currently, groundwater <br /> samples are collected and analyzed for the presence of TPHg and BTEX by the <br /> 1 DHS/LUFT Method and fuel oxygenates by EPA Method 8260B <br /> i <br /> 1 <br /> 1 I IARCO149321Reports\Asmt&AgfiTstRpt doc <br />