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L Ms. Laurie Cotulla JiTt'llAugust 28, 1989 4 ` Page 3 June 1989 Analytical Results ENV iRNT SELJH < jN1HS All of the samples were analyzed for BETX and TPH using U.S. Environmental Protection Agency (EPA) Method 8015, modified. The analytical results of the groundwater samples collected in the previous quarters and June 1989 are summarized in Table 1. Complete laboratory results for the June groundwater sample analysis are included in this report as Appendix A. BETX Results. In well ATR-1, BETX concentrations have increased and the benzene concentration in this well exceeds the action level for drinking water as established by the California Department of Health Services (DHS). BETX concentrations in well ATR-2 have remained relatively constant for the past two quarters. The benzene concentration in well ATR-2 exceeds the DHS action level by only a slight margin. In well ATR-3, BETX concentrations have steadily declined since September 1988. However, benzene and toluene concentrations remain above action levels in well ATR-3. The benzene concentration has significantly decreased in well ATR-4 since September 1988. Also, in well ATR-4 the toluene concentration has decreased and the ethylbenzene and xylene concentrations have slightly increased. The benzene concentration in well ATR-5 has decreased but remains above the action level. Ethylbenzene, toluene, and xylene concentrations remain below DHS action levels in well ATR-5. BETX concentrations in ATR-6 remain below laboratory detection limits. Only trace concentrations of BETX have been identified in well ATR-7. TPH Results. Groundwater from the seven wells was analyzed for low boiling point hydrocarbons (C4-C12) and was not characterized as gas, diesel, or motor oil. Petroleum hydrocarbon concentrations were below detection limits in ATR-2, ATR-6, and ATR-7. Only trace amounts of petroleum hydrocarbons were identified in well ATR-1. ATR-3, ATR-4, and ATR-5 (nearest the underground tank complex) contained 4.5 parts per million (ppm), 1.3 ppm, and 2.2 ppm petroleum hydrocarbons, respectively. This is a decrease over the previous quarterly sampling interval. Groundwater Flow Groundwater levels at the site are measured in each well on a quarterly basis. The water levels are measured relative to the top of well casing with an electronic water/oil interface probe. The groundwater flow direction in June and September 1988 was to the north, under a hydraulic gradient of 12 feet per mile or 0.2 percent. In February 1989, the groundwater flow direction shifted to the northeast under a hydraulic gradient of 0.2 percent and has remained in this condition through June 1989. Conclusions Based on field observations and analytical results, the following conclusions are presented. Analytical results of groundwater samples collected during June 1989 show that benzene has decreased or remained nondetectable in four (ATR-3 through ATR-6) of the seven wells at the site. Of the other three wells, the benzene concentration has slightly increased in two of the BROWN AND CALDWELL 723 S STREET SACRAMENTO,CALIFORNIA 95814-7092•(916)444-0123