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.Y d-4 Groundwater Results This section presents the field and analytical results of groundwater samples collected from the ten monitoring wells and one extraction wcil at the site. On October 16, 1990, all ten of the monitoring wells were sampled {ATR-9. ATR-10, and ATR-1? were developed prior to sampling). The developing and sampling of the weils was performed in accordance with Brown and Caldwell's July 11, 1990 work plan, The groundwater samples were analyzed for BETX and petroleum hydrocarbons using EPA Modified Method 8015 with extraction by EPA Method 5030, and purgeable halocarbons,specifically 1,2-Dictrloroethane using EPA Method 601. In addition, the groundwater from ATR-9, ATR-10,and ATR-12 was analyzed for fecal coliform and nitrates as required by the County for wells located within 50 feet of a sanitary sewer line. The results of these samples and samples collected in previous sampling events, from wells MW-1 through ATR-7, are presented in Table 4-3. The analytical laboratory reports for all of the groundwater :samples are included in this report as Appendix E. As each well was purged, field measurements of pH..Electrical cJnductivAv, and volume of water were recorded. Table 4-4 presents these recorded measurements. These parameters are monitored to ensure that representative samples are collected from each well. Groundwater BETX Results. The groundwater samples from four of the ten monitoring wells at the site contain detectible concentrations of at least one of the BETX constituents and none of the off site wells contained any BETX constituents based on a laboratory detection limit of 0.5 micrograms per liter(pg/l). BETX concentrations occur in groundwater at ATR-r_,ATR-3, ATR-4, and ATR-5 with the highest concentration at A!R-3. Only'o-ior BETX concentrations 1 occur at ATR-l. Benzene concentrations are at or above the Califortia State Department of Health Services(State) action level of 1 pg/1 in all wells with detectible benzene concentrations. Ethylbenzene,toluene, and xylene concentrations exceeded the state action level only in ATR-3. ' Figure 4-1 presents benzene concentrations for each well. Groundwater TPH Results. Petroleum hydrocarbons were identified in three of the ten wells based on a laboratory detection limit of 50 pg/1. As with BET.C, the highest petroleum hydrocarbon conczatration occurs at ATR-3(14,000 pg/1)• Groundwater from ATR-4 and ATR-5 also contained petroleum hydrocarbons. Groundwater Purgeable Halocarbon Results. Only one of the groundwater samples (ATR-2)contained a detectible concentration of 1,2-dichior concentration of6. �n This is based on a laboratory detection limit of 0.5 pg/1. to the highTPH concentration ATR-3, it was necessary to dilute the sample before analyzing thus making the detection limit higher. A concena-v lon of 1.3 pg/1 tetrachloroethene was identified in the groundwater sample from A`1R-6. The source of these constituents is unknown. Fecal Coliform Results. Of the.three wonitoring wells tested for this bacteria, only one (ATR-9)showed positive at 2 most probable number per 100 milliliters (MPNol O0mQ based on forn and would a detection limit of 2 MPN/100mi This is most likely naturally occurring not be associated with a sewer line leak. 'IRIIMrR7!'tl,�llnrmll�IIRS�Q�4�910m�