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Mr Harlin KnollN San Joaquin County Environmental Health Division (DR I �_� 20 February 2001 . Page 4 Third Quarter 2000 Groundwater Analytical Results In August 2000, groundwater samples from well MW-1 (installed near the former source area) contained no detectable amounts of TPHg or BTEX A small amount of MTBE was detected in MW-1 at a concentration of 7 7 pg/I Upgradient well MW-2 contained TPHg concentrations of 430 pg/I I The samples from cross-gradient well MW-3 did not contain detectable concentrations of TPHg, BTEX, and MTBE 1,2-Dichloroethane (DCA) and 1,2-dibromoethane (EDB) were not detected in the groundwater samples from each well Analytical results from Ithis round of groundwater sampling are summarized in Table 1 Fourth Round of Groundwater Sampling and Analytical Results At the request of the SJCEHD, the monitoring wells were sampled again in January 2001 The groundwater sampling and analytical procedures were conducted in accordance with Orion's work plan Depth to groundwater was measured before sampling using a Solinst water level meter Approximately 3 casing volumes were purged from the wells . before sampling Throughout purging and lust before sampling the wells, pH, specific conductivity, temperature, and turbidity of the evacuated groundwater were measured and recorded These measurements were made to confirm that the well was purged sufficiently Water samples were collected after the measurements stabilized to within 10 percent of the previous readings or a baseline was established Purging and sampling logs are provided in Attachment 1 Purging and sampling was performed using a 2-inch- diameter Teflon and disposable polyethylene bailers suspended from a nylon line The Teflon bailer was decontaminated between each well use The bailers were equipped with a bottom-release device Water samples were collected from the wells in new 40-milliliter glass bottles with Teflon-lined caps provided by the analytical laboratory These samples were collected so that no headspace was present in the bottle A field blank was not collected because the wells were sampled using disposable bailers The samples were delivered to Positive Lab Service of Los Angeles, California, a State—certified laboratory n The samples were analyzed for TPHg using modified EPA Method 8015 and for BTEX and MTBE using EPA Method 8260 Analytical laboratory reports and chain-of-custody forms for the January 2001 sampling activities are included in Attachment 2 r In January 2001, groundwater samples from well MW-1 (installed Just north of the 1 former source area) contained no detectable amounts of TPHg or BTEX MTBE was . detected in MW-1 at a concentration of 42 pg/l Upgradient well MW-2 contained TPHg concentrations of 170 pg/I The samples from cross-gradient well MW-3 did not E5\BF5\ST0CKTON\LTR\LTR007 DOC 2/20/01