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• Quarterly Groundwater Monitoring Report, September - November, 1992 January 22, 1993 Manna Pro, 4004 South EI Dorado, Stockton, CA 3 Groundwater Quality Data The six monitoring wells were sampled on October 29, 1992, after groundwater level monitoring The wells were purged to collect samples representative of aquifer conditions The pH, temperature, and conductivity were measured with a YS1 3650 meter during purging Wells MW-1, MW-2, MW-4, and MW-5 bailed dry after purging less than 4 well volumes of groundwater Four well volumes of groundwater were removed from wells MW-3 and MW-6 The wells were allowed to recharge to approximately 80 percent of static water level before samples were collected Samples were collected using a Teflon® bailer and placed into sample containers supplied by the laboratory performing the analyses Equipment was cleaned between samples using an Alconoe and water solution and rinsed with de-ionized water A field blank and rinsate sample were collected in the field for Quality Assurance/Quality Control (QA/QC) measures Samples were labeled and placed in an ice-chilled cooler for transport to GTEL Environmental Laboratories, Inc in Concord, California, and were accompanied at all times by a chain-of-custody record Samples from the October 29, 1992, sampling event were analyzed by the lab 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, Total dissolved lead using EPA Method 7421 The results of laboratory analyses are included in Attachment 2, Table 2 The laboratory analytical reports are included in Attachment 3 As shown in Table 2, pH ranged from 6 6 to 71 Specific conductance ranged from 890 to 2,000 micro-mhos per centimeter (umho/cm) at 25° Celsius The specific conductance reading for well MW-4 was 20,30014mho/cm (This number is much higher than previous measurements and may be the result of an error in field measurement or data recording ) The results of pH and specific conductance analyses in the samples collected were generally similar, suggesting that the water is from the same hydrologic zone Aromatic volatile organics analyzed for and detected included benzene, toluene, ethylbenzene, and xylenes (BTEX) Total benzene ranged from 3 micrograms per liter (µg/l), or parts per billion (ppb) in the sample from well MW-4 to 29,000 u g/I in the sample from well MW-1 Concentrations of TPH- G ranged from 170µg/I in well MW-4 to 81,000,ug/I in well MW-1 Total dissolved lead was not detected in the samples collected this quarter In general, TPH-G and BTEX concentrations have decreased since the July 1992 sampling event Figure 2 illustrates the TPH-G plume as constructed using the October 29, 1992, analytical results The extent of petroleum hydrocarbon dissolved in the shallow groundwater is similar to that indicated by previous interpretations R2919A2 DH rT_101 GROUNDWATER TECHNOLOGY, INC