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Mr. KyIc ChrStie September 24, 1990 Page 5 t' Table 1 presents the chemical analytical results from the groundwater samples collected over the past 2 years. BETX constituents in the June 1990 groundwater samples from well PR-I are below detection limits. From the remaining wells that were sampled in June 1990, BETX constituents are detectable in wells BHD-1, E-2, E-5, E-8, E-10, E-11,and E-12. The benzene concentration exceeds California Department of Health Services (DHS)Maximum Contami-cant Levels (MCLs) of I microgram per liter(gg/l)in all of these samples. Benzene concei:trations have varied in each well over time. The groundwater samples from wells E-5, E-8, E-10, E-1 t,and E-12 showed increases since they were last sampled(in March 1990). Decreases in benzene concentration were observed in the samples from wells BHD-1 and E-2. (These wells were last sampled irk either August or Decenibe: 1989.) A map of the benzene concentrations in the June 1990 groundwater samples is shown on Figure 1. The benzene concentrations are not contoured because not all of the wells were sampled. For comparison, Figure 2 is a contour map of the March 1990 concentrations when all of the wells were sampled. The concentration of ethylbenzene is above the DHS MCL of 680 pg/l in wells E-10 and BHD-1. The concentration of toluene is above the DHS Drinking Water Action Level of 100 µg/1 in monitoring wells E-10 and BHD-1. The concentration of xylene is above the DHS ?ICL of 1,750 gg/l in monitoring well,E-10 and BHD-1. Groundwater Flow Groundwater levels at the site are being measured in each well on a biweekly basis using an electronic water level indicator. The levels are measured relative to top-cf-casing elevations in order to determine groundwater elevations and monitor possible changes in flow direction. Table 2 shows the water-level measurements collected since January 1990. Beginning in late April 1988, the groundwater flow direction was influenced by the recovery system. Sometime in April 1989, the recovery pump stopped operating, The malfunction was detected in June 1989. Repair of the recovery system is almost complete. However,the recovery system is currently being hampered by unexplained fluctuations in the lower explosive level meter, which is located in the recovery well. Brown and Caldwell personnel are attempting to identify the cause of these fluctuations. As a result, the recovery pump is being operated on a manual basis for testing purposes. On June 18, 1990, Brown and Caldwell personnel measured water levels at the site. The recovery system was being treated at the time, and had been pumping at a rate of 5.3 to 5.9 gallons per minute for 4 days, prior to the measurements being taken. Figure 3 is a water-level contour map for June 18, 1990. The figure shows unsteady state conditions and that water levels at that time were affected by the pumping. During static conditions, groundwater flows to the northeast. As shown on Figure 3, the area of influence from the recovery system extends off site, to each side of the station. Brown and Caldwell �.0�1511!t�IRiS