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Mr. Kyle Christie October 9, 1990 Page 3 Groundwater from each well was sampled using a disposable polyethylene bailer equipped with a bottom-emptying valve. For each well, the samples were drained directly from the bottom valve into seven 40-milliliter glass bottles with Teflon-lined septa and inspected to ensure that no air bubbles remained within the bottles. The samples were stored on ice in a closed ice chest from the time of collection through delivery to the laboratory. All purging and sampling equipment was washed with laboratory-grade detergent and tap water then rinsed with deionized water before each use. All groundwater generated during the purging and sampling process was removed from the site by Armour Petroleum Service under a bill of landing and disposed of at a fire-training center in Fairfield, California. Groundwater Flow Water-level elevations at the site are measured in each well on a quarterly basis. Elevations are based on an arbitrary 100-foot on-site bench mark (an X in top of concrete retaining wall on west side of Site 1). The water levels are measured relative to the top of well casing with an electronic water/oil interface probe. The groundwater flow direction has shifted from east in December 1989 to approximately northeast in April 1990, under a hydraulic gradient of 7 feet per mile or 0.001 (0.13 percent). Table 1 and Figure 2 present water-level data collected since 1987. The water levels in the wells have decreased between 1 and 1.5 inches since December 1989. April 1990 Analytical Results All of the samples were analyzed for BETX and TPH by U.S. Environmental Protection Agency (EPA) Method 8015 using Method 5030 as the sample introduction method, and purgeable halocarbons by EPA Method 8010. The analytical results of the groundwater samples collected in the previous quarters and April 1990 are summarized in Table 2. Complete laboratory results for the December groundwater sample analyses are included in this report as Appendix A. BETX Results. The BETX levels in well ATR-1 have fluctuated significantly over the past 3 years. The 1987, 1988, and early 1989 data indicated relatively low concentrations of BETX [less than 6 micrograms per liter (µg11) benzene]. The June and September 1989 data indicated significant increases in BETX (up to 7,100 µg/1 xylene). In December 1989, the BETX concentrations decreased to levels seen in 1987 through early 1989. The April 1990 data indicate a slight increase over the December data nevertheless only the benzene concentration is currently above the Department of Health Services (DHS) Maximum Contaminant Level (MCL). The shift in groundwater flow direction may account for the slight increase in BETX concentrations in ATR-1. Brown and Caldwell Consultants