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1v s V � • A S S O C I A T E S I N C 69 34 feet below the tops of the well casing elevations, representing an average decrease in the water table elevation of approximately 0 57 feet since September 2002 AS1(s), PZla(s), and PZlb(s) were dry during the December monitoring event The water level data were used to develop the groundwater elevation contour map (Figure Assuming horizontal isotropic conditions, groundwater in the uppermost aquifer varied across the site, but in general, flowed to the southeast The average hydraulic gradient on December 4, 2002 was calculated to be 0 003 ft/ft or approximately 13 ft/mile A summary of groundwater monitoring data is presented in Table 1 FREE PRODUCT REMOVAL Floating petroleum product has previously been observed in well MW2 On January 18, 2002, ATC installed a passive skimmer system in well MW2 in accordance with ATC's Workplan for Drinking Water Well Replacement, Temporary Water Source, and Free Product Skimmer Installation at Pacific Coast Recreation, 3755 Munford Avenue, Stockton, California, dated October 11, 2001 This workplan was approved by SJCEHD with minor modifications Approximately 0 36 gallons of free product has been recovered from the skimmer in well MW2 On December 4, 2002, an immeasurable trace amount of free product was observed in . well MW2 Table 3 summarizes the product thickness measurements and volume of product removed through the end of the fourth quarter of 2002 i FILTRATION SYSTEM In May 2002, a carbon filtration system was installed to remove petroleum hydrocarbons from the water in domestic well DW A water sample was collected from the first effluent port, identified as 1 CC Effluent contained no detectable concentrations of TPHg, BTEX, or fuel oxygenates Influent water samples collected from DW on December 4, 2002 contained 21,000 ppb of TPHg and 1,600 ppb of benzene Fuel oxygenates including MTBE were not detected in water samples collected from well DW TPHg, BTEX, and fuel oxygenates were not detected in water samples from the first and second effluent ports identified as 1 CC Effluent and 2CC Effluent in the filtration system It appears the filtration system is effective in removing petroleum products from water from well DW Analytical results are summarized in Table 2 CONCLUSIONS Concentrations from wells MW I through MW6 and MW9 remain consistent with the results from the previous sampling event Concentrations 1n wells MW7, MWS, and MW10 have increased since September 2002, but are within the range of concentrations measured during previous monitoring events Concentrations in wells AS 1(d), PZ 1 a(d), and PZ 1 b(d) have increased since the last monitoring event The direction and magnitude of groundwater flow was w 1163931quart1yl4gr-2002 doc 4