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Quarterly Groundwater Monitoring Report, January-March 1993 2 Manna Pro, 4004 South EI Dorado, Stockton, CA July 11, 1994 Groundwater Monitoring Data On April 14, 1994, 10 existing groundwater monitoring wells were monitored for depth to water (DTW) DTW measurements were also taken from the groundwater extraction well (EW-1) and the three observation wells (08-1, 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) The groundwater elevations this quarter increased an average of 0 80 feet since the January 1994 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 was not used in the construction of the potentiometric surface map since it is believed that it is not representative of the elevation conditions in the area As shown in attachment 2, figure 1, the average groundwater gradient in the site vicinity is approximately 0 001 foot/foot radiating from the area of the former tank pit Groundwater Quality Data The 10 monitoring wells were sampled on April 14, 1994 Before sampling, the static water in the wells were purged to collect samples representative of aquifer conditions The pH, temperature, and conductivity were measured with a YSI 3650 meter during purging Three well-casing volumes of groundwater were purged from the 10 wells Equipment was cleaned after each sample was collected, using an Alconox and water solution and rinsed with deionized water The wells were allowed to recharge to approximately 80 percent of static water level before samples were collected Samples were collected using, 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 cooler, 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/quality control (QA/QC) Samples from the April 14, 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) Methods 5030 and 8020 and modified EPA Method 8015, and ■ total dissolved lead using EPA Method 7421 Analytical results indicated detectable concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) Benzene concentrations ranged from below method detection limit (MDL) in the samples 2879aa24 opo EMGROUNDWATER TECHNOLOGY, INC