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Quarterly Groundwater Monitonng Report, October-December 1994 2 Manna Pro,4004 South EI Dorado, Stockton, CA January 19, 1995 Groundwater Monitoring Data On October 12, 1994, 10 existing groundwater monitoring wells were monitored 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 0131-3) 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 1 36 feet since the April 1994 elevations were measured The results of groundwater monitoring are Included in attachment 2, table 1 A potentiometric surface map, as interpreted from the data In table 1, is presented In attachment 1, figure 1 The groundwater elevation data collected from MW-1 was not used in the construction of the potentiometric surface map since it is believed not representative of the water level elevation conditions in the area As shown in figure 1, the average groundwater gradient in the site vicinity is approximately 0 002 foot per foot radiating from the area of former excavation The groundwater flow direction radiates from the former excavation area in a north- northwesterly direction The current groundwater flow has returned to the historic direction following the previous quarter's flow which was to the south-southeast Groundwater Quality Data The 10 monitoring wells were sampled on October 12, 1994 Before sampling, the static water in the 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 Three well-casing volumes of groundwater were purged from the wells or the wells were purged until dry The wells were allowed to recharge to approximately 80 percent of the static water level before samples were collected Samples were collected using 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 from October 12, 1994, 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 00968015 202 EE9GROUNDWATER TEaiNoLocy, INC