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�y Mr Harlin Knoll N San Joaquin County Environmental Health Division • 7 July 2000 Page 4 !, 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 Purging and sampling logs are provided in Attachment 6 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 balers were equipped with a bottom- release device The waste disposal form and manifest for the sampling wastewater are provided in Attachment 7 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 rso 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 for analysis In January and May 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 9 µg/I during the first round of sampling and 4 0 µg/l during the second round Upgradient well MW-2 contained lie TPHg concentrations of 91 µg/1 during the first round of sampling and 440 µg/I from the second round, MTBE was not detected in either round of sampling The samples from cross-gradient well MW-3 did not contain detectable concentrations of TPHg, BTEX, and MTBE after both rounds of groundwater sampling Analytical results from the groundwater sampling are summarized in Table 2 ' In EPA's Drinking Water Advisory Consumer Acceptability Advice and Health Effects Analysis on MTBE (EPA-822-F-97-009 December 1997), they state regarding MTBE "that keeping concentrations in the range of 20 to 40 micrograms per liter (µg/1) of water or below will likely avert unpleasant taste and odor effects" Additionally, the State of California has proposed primary drinking water standards as a public health goal for MTBE of 13 µg/I Although these values are proposed as goals and considered low by the industry, the concentrations of MTBE found in the shallow, unused groundwater at the site are below these aggressive objectives Groundwater Flow Characteristics Groundwater was encountered during drilling activities at a depth of 25 feet below grade During groundwater sampling, the depth to groundwater was measured in MW-1 at 17 78 feet below grade, MW-2 at 17 27 feet below grade, and MW-3 at 17 86 feet below grade Currently, groundwater flow direction is to the northeast based on depth to groundwater and conversations with City of Stockton water department personnel In a S\BFS\STOCKTON\LTR\LTR004 DOC 717100