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Mr. Kyle Christie May 14, 1990 Page 3 closed ice chest from the time of collection through delivery to the laboratory. All purging and 4 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. Groundwater Flow ' Water-level elevations 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 December 1989 was approximately east, under a hydraulic 1 gradient of 10 feet per mile or 0.2 percent. Table 1 and Figure 2 present water-level data collected since 1987. The water levels have increased 0.5 to 2.5 inches since September 1989. December 1989Analytical 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 December 1989 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 I [less than 6 micrograms per liter (µg/!)]. The June and September 1989 data indicated significant increases in BETX (up to 7,100 µg/1). In December 1989, the BETX concentrations decreased to levels seen in 1987 through early 1989. Only the benzene concentration is currently above the Department of Health Services (DHS) Maximum Contaminant Level (MCL). These fluctuations are thought to be caused by changes in groundwater flow direction. During June and September 1989, the groundwater flow direction was to the north, resulting in the transport of contaminants toward ATR-1. In December 1989, the groundwater flow direction shifted to the { east, and the decreased BETX levels in ATR-1 are likely the result of, the influx of uncontaminated water from the west. Similar fluctuations are seen in well ATR-2, although the degree of fluctuation is much less. Benzene is above MCL in ATR-2. The benzene, ethylbenzene, and xylene concentrations in ATR-3 are above the DHS MCLs; the benzene concentration decreased by approximately 15 percent since the September 1989 sampling, but the ethylbenzene and xylene concentrations increased by up to 100 percent. Because of the proximity of ATR-3 to the likely source of the contaminants (the UST complex and associated piping), it is not thought to be affected greatly by changes in groundwater flow direction. The decreasing trend noted in the September 1989 data from ATR-4 was not continued in December 1989, with BETX concentrations returning to approximately the same levels as in June 1989. Benzene is the only BETX constituent above the DHS MCL in ATR-4. I Brown and Caldwell Ccr.sur!tar,,s