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• Quarterly Groundwater Monitoring Report,October -December 1995 2 Manna Pro 4004 South EI Dorado Stockton CA January 16 19% Groundwater Monitoring Data On October 18, 1995, 10 existing groundwater monitoring wells were gauged for depth to water(OTW) DTW measurements were also taken from the groundwater extraction well (EW-1) and the three observation wells(OB-1,OB-2,and OB-3) The DTW measurements were taken from surveyed points at the top of each well casing,which are referenced to an arbitrary datum (designated as 15 feet above mean sea levet) The groundwater elevations this quarter decreased an average of 2 33 feet since the July 1995 elevations were measured The results of groundwater monitoring are Included in attachment 1,table 1 A potentiometric surface map, as Interpreted from the data In table 1, is presented In attachment 2,figure 1 The groundwater elevation data collected from MWA were not used in the preparation of the potentlometric surface map since It is believed to not be representative of the water level elevation conditions In the area As shown in figure 1,the groundwater gradient vanes across the site, however,the highest elevations appear to be in the area north of the former excavation Groundwater Quality Data The 10 monitoring wells at the site were sampled on October 18, 1995 Before sampling,the static water In each well was purged to collect samples representative of aquifer conditions The pH, temperature, and conductivity were measured with a YSI 3650 meter during purging Equipment was cleaned after each sample was collected, using an Alconox and water solution and rinsed wdh de-Ionized water A minimum of three well-casing volumes of groundwater was purged from the wells or they were purged until the well became dry The wells were allowed to recharge to approximately 80 percent of static water level before samples were collected Samples were collected using Individual well dedicated, polyurethane,disposable bailers and placed Into sample containers supplied by the laboratory performing the analyses Samples were labeled, placed In an Ice-chilled Insulated chest and transported to GTEL Environmental Laboratories, Inc , In Wichita, Kansas, a California-certified laboratory, accompanied at all times by a chain-of-custody record A trip blank was also collected and accompanied the samples for quality assurance and control Samples collected during the October 18, 1995,sampling event were analyzed by the laboratory for ■ aromatic volatile organics and total petroleum hydrocarbons as gasoline (TPH-g) using Environmental Protection Agency(EPA) Method 8020 and gas chromatography/flame-Ionization detector(GC-FID), respectively ■ total dissolved lead using EPA Method 7421 Analytical results reported detectable concentrations of TPH-g as well as benzene,toluene, ethylbenzene,and total xylenes(BTEX) Benzene concentrations were below method detection limits 42020M os4 GROUNDWATER BE9TECHNOLOGY, INC Y��