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r <br /> n � � <br /> S E C 0 <br /> i <br /> • Mr Harlin Knoll <br /> October 24, 2005 <br /> Page 2 <br /> Number of Detections Minimum Detected Maximum Detected <br /> Constituents above the MDL of the 10 Concentration in pg/L(Well ID) Concentration In Vg1L(Well ID) <br /> Total Samples <br /> TPHg 3 100(MW-3) 3,200(MW-2) <br /> Benzene 2 1 (MW-4D) 88(MW-2) <br /> MtBE 2 6(MW-3) 44(MW-2) <br /> TBA 0 ND ND <br /> Explanation <br /> MDL=Method detection limit <br /> pg/L= Micrograms per liter <br /> ND = Constituent reported below the laboratory reporting limits <br /> CONCLUSIONS <br /> Historical groundwater monitoring data show that concentrations of tertiary amyl methyl <br /> ether (TAME) has been below Its respective method detection limit (MDL) In wells MW-1, <br /> MW-2, and MW-3 from 1998 to present Ethanol, dl-Isopropyl ether (DIPE), and ethyl <br /> tertiary butyl ether (EtBE) have never been detected in any site monitoring wells at or above <br /> the MDL since sampling began in 1998 In groundwater monitoring wells MW-1, MW-2, <br /> MW-4, MW-5, MW-5D, MW-6, MW-6D, and MW-7, concentrations of TAME have been at <br /> or above MDL since sampling began In 1998 TAME was detected In MW-3 at 2 6 mg/L in <br /> February 2001 and in MW-4D during three consecutive monitoring events May, June and <br /> October 2003 with concentration of 11 mg/L, 5 mg/L and 3 mg/L respectively However, <br /> prior to and following detections, TAME concentrations have been below the MDL from <br /> 2002 to present <br /> Hydrographs of the analytes TPHg and benzene show that, despite fluctuating <br /> concentrations, there is an overall trend that Indicates a gradual decrease In the analytes <br /> over time (Figures 1-4) <br /> RECOMMENDATIONS <br /> In light of the above observations, with the San Joaquin County Environmental Health <br /> Department (EHD) approval, SECOR recommends removing the analytes ethanol, DIPE, <br /> EtBE, and TAME from the sampling protocol beginning in the fourth quarter 2005 SECOR <br /> would also like to meet with the EHD to discuss future activities at the site <br /> N IFileslProtects\Chevron\RetaiN#9-32321Periodic Monitonng1200513005 QMR doc <br /> i <br /> ,r <br />