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Quarterly Groundwater Monitoring Report, July-August 1995 2 Manna Pro,4004 South El Dorado, Stockton, California October 17, 1995 Groundwater Monitoring Data On July 31, 1995, 10 existing groundwater monitoring wells were gauged for depth to water (DTW) DTW measurements were also taken from the groundwater extraction well (EW-1) and the three observation wells (OB-1, OB-2, and 013-3) 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) The groundwater elevations this quarter decreased an average of 2 00 feet since the April 1995 elevations were measured A potentiometric surface map is presented In attachment 1, figure 1, as interpreted from the data in attachment 2, table 1 The results of groundwater monitoring are Included in attachment 2, table 1 The groundwater elevation data collected from MWA and MW-3 were not used in the preparation of the potentiometric 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 varies 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 July 31, 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 with 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 Concord, California, 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 July 31, 1995, sampling event were analyzed by the laboratory for aromatic volatile organics and total petroleum hydrocarbons as gasoline (rPH-g) using Environmental Protection Agency (EPA) Method 8020 and gas chromatography/flame-Ionization detector (GC/FID), respectively ■ total dissolved lead using EPA Method 7421 42020090 GWM ❑❑0 GROUNDWATER ❑❑❑ TECHNOLOGY