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[ I I� . Ground water samples were analyzed for total petroleum hydrocarbons as gasoline (TPH-G) , totalpetroleum hydrocarbons as diesel (TPH-D) , and BTEXconstituents at Sequoia Analytical of Concord, California. The official laboratory reports and chain of custody record are included in Appendix D. DISCUSSION OF RESULTS r The laboratory results for this and previous quarterly around water monitoring and sampling events are summarized in Table 1. A ground water elevation contour map, based on the depth to ground water measurements collected on November 26, 1991, is presented in Figure 3 . Concentrations of petroleum hydrocarbon constituents detected in ground water samples are presented in Figure 4. Results of this ground water monitoring and sampling event and laboratory analysis indicate the following: o The average depth to ground water is 11. 0 feet with an average hydraulic gradient of 0.013 foot/foot to the northeast. o Detectable concentrations of TPH-G and xylenes were present only in the ground water samples collected from AW-3 (610 parts per billion (ppb) TPH--G and 0.48 ppb xylenes) . o The laboratory reported the presence of TPH-D concentrations in all ground water samples collected; as quantified against a diesel standard. These results are anomalous; all prior analysis for TPH-D (with the exception of the samples collected from AW-3) showed that detectable concentrations of TPH-D were not present in any of the ground water samples collected. Furthermore, review of chromatograms and discussion with the laboratory indicates that (with the exception of AW-3) the constituents quantified as TPH-D in the ground water samples were "definitely not a fuel" (personal communication, Sequoia Analytical, March 4, 1992) . o The distribution of diesel-ranee petroleum hydrocarbons is apparently limited to the vicinity of AW-3 . o The historical absence of BTEX constituents (except for the October 2, 1990 data for AW-3) in the ground 2