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f <br /> v S E C 0 R <br /> Ms. Lori Duncan <br /> San Joaquin County EHD <br /> May 24, 2005 <br /> Page 3 of 4 <br /> completed during the first quarter and annually on samples from seven wells which best <br /> represent a cross-section of the plume to investigate the effects of the SVEIAS system <br /> operation on natural attenuation processes. <br /> SECOR proposes to change the monitoring frequency of testing for methyl tertiary butyl <br /> ether (MtBE), fuel oxygenates, 1,1-dichloroethane (1,1—DCA), and ethyl dibromide (EDB) to <br /> an annual basis based on non-detectable concentrations in groundwater since May 1992, <br /> when 53 micrograms per liter (Ng/L) tertiary amyl methyl ether (TAME) and 230 pg/L TAME <br /> were reported in monitoring wells MW-14 and VM-2, respectively. <br /> Analytical test methods will conform to the tables below: <br /> Table 1: Vapor Analyses <br /> Analyte Method <br /> BTEX EPA Method TO-3 <br /> TPH/g EPA Method TO-3 <br /> TPH/d NIOSH Method 1550 <br /> Monthly data from Table 1 analyses will be used to assess the effects of the AS/SVETS <br /> on soil and groundwater contamination. The data will be used to estimate the duration of <br /> system operation. In addition, vapor sampling at each of the SVE wellheads will be <br /> completed semi-annually and samples analyzed for the above constituents. Wellhead <br /> sampling will include field measurement of oxygen and CO2. <br /> Table 2: Groundwater Analyses <br /> Analyte Method <br /> BTEX EPA Method 8260 <br /> MtBE EPA Method 8260 <br /> TPH/g EPA Method 8015M <br /> TPH/d EPA Method 8015M <br /> Fuel Oxygenates, EPA Method 8260 <br /> 1,1-DCA, EDB <br /> Quarterly data from Table 2 analyses will be used to evaluate the effect of air sparging and <br /> soil vapor extraction on groundwater contaminant concentrations. The data will also be <br /> used to estimate the duration of system operation. <br /> I:ICALTRANS1Stockton-Shop 101GW Monitoring\Letter to SJ County_Final.doc May 24,2005 <br /> Project No.940T.43148.00 SECOR International Incorporated <br />