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POW- FIELD PROCEDURES Alton Geoscience monitored and sampled ground water Monitoring Wells AW-1 through AW-9 on January 22, 1993. Alton Geoscience ground water monitoring and sampling protocol is presented in Appendix A. Ground water field survey forms including field measurements and observations are presented in Appendix B. Ground water samples were analyzed for total petroleum hydrocarbons as diesel and gasoline (TPH-D and TPH-G), BTEX, and semi-volatile organics at Sequoia Analytical Laboratory, Concord, California. Official laboratory reports and chain of custody records are included in Appendix C. DISCUSSION OF RESULTS Laboratory results for this and previous ground water monitoring and sampling events are summarized in Table I. A ground water elevation contour map for the January 1993 event is shown in Figure 3. Results of this event are summarized as follows: • Average depth to ground water was 10.22 feet (corresponding to an increase in ground water elevations of 0.75 feet from the October 1992 sampling event), with an average hydraulic gradient of 0.01 foot per foot. The ground water gradient magnitude and 0 direction to the northeast is consistent with previous sampling events. • TPH-G and BTEX were not detected at or above reported detection limits in any of the wells except benzene in AW-9 (0.70 parts per billion (ppb)). This concentration of benzene is the lowest since sampling of AW-9 was initiated in April 1992, and appears to follow a trend of decreasing concentrations through time (see Table 1). f • TPH-D was present only in AW-3 (320 ppb). Ground water samples from AW-3 have typically been found to contain detectable concentrations of TPH-D, however, concentrations appear to have been decreasing over the last four quarterly sampling events (see Table 1). • Observed in this sampling event is an increase in ground water elevations across the site and a decrease in contaminant concentrations. It appears that a corresponding desorption of adsorbed-phase hydrocarbons is not occurring, which may be indicative of the effectiveness of the historical excavation in removing the hydrocarbon source. • Semi-volatile organics were present only in AW-4 (3.6 ppb phenol), AW-6 (14 ppb diethyl phthalate), and AW-8 (37 ppb 2-hexen-1-ol). The presence of these compounds are not consistent with the former use of the subject site and therefore do not appear related to the former bulk plant. 2