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i i 12 December 1995 i AGE-NC Project No 95-0134 Page 3 of 6 inot indicate the detection of petroleum hydrocarbons and benzene Ground water monitoring was conducted on five occasions between June 1994 and May 1995 by iGeoAudlt and AGE The depth-water was measured in MW-8, MW-9 and EW-1 The wells were purged and sampled on ouf 0"CAMons The ground water gradient ranged from 0 00048 ft/ft to 0 0040 ft/ft The flow direction ranged from N 84° E to N 56e E on four occasions An anomalous iflow direction of due south was observed in October 1994 Toluene and xylenes were detected in the sample from MW-9 at concentrations of 0 52 ppb and 2 9 ppb, respectively in June 1994 No other i petroleum hydrocarbons were detected in any of the samples during the four quarterly monitoring events i3.0. PROCEDURES i3 1 MONITORING WELL PURGE PROCEDURES On 27 September 1995, a Solinst water level meter was used to measure the depth to ground water in monitoring wells MW-8, MW-9 and EW-1 relative to the top of the casing The relative ground water elevations and hydraulic gradient were determined from these data (Table 1) iMonitoring wells MW-8, MW-9 and EW-1 were then purged using precleaned PVC bailers Approximately 8 to 9 gallons (nummum of three well volumes) of water were removed from monitoring wells MW-8, MW-9 and EW-1 Temperature, pH and conductivity were measured at one- gallon intervals using an ICM water analyzer The purged water was stored in 55-gallon DOT- approved drums and stored on-site Stabilization data and field logs are included in Appendix A i 3 2 GROUND WATER SAMPLE COLLECTION AND ANALYSES iWater samples were collected from MW-8, MW-9 and EW-1 using new disposable bailers Immediately upon retrieval, the samples were transferred into 40-m1 VOA vials preserved with i hydrochloric acid The samples were transported in a chilled container to Alpha Analytical Laboratories in Ukiah Each sample was analyzed for total petroleum hydrocarbons as gasoline (TPH- g) and volatile aromatics(benzene, toluene, ethylbenzene and xylenes BTE&X) in accordance with iEPA methods GCFID/5030 and 602, respectively i33 SESOIL MODELING PROGRAM • The American Petroleum Institute's (API) Risk/Exposure Assessment Decision Support System i (DSS) is a modeling program developed to estimate human exposure and risk from contaminated I