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i 1 <br /> 0. 0098 ft/ft directed N 110 E. The slope is consistent with the <br /> previous calculation of 0. 008 ft/ft. The gradient direction shows <br /> a 52 degree change to the east, but is consistent with regional <br /> trends. <br /> ' 4. 5 Groundwater Laboratory Results <br /> TPH as gasoline and benzene were detected in monitoring well MW-1 <br /> at levels of 99 µg/L and 9 . 9 ug/L (ppb, parts per billion) <br /> respectively. Benzene was also detected in monitoring well MW-4 at <br /> a level of 0. 9 Ag/L. No other constituents were detected in any of <br /> the samples. The water sample analyses are summarized in Table 4 . <br /> The laboratory results and chain of custody are attached in <br /> ' Appendix B. <br /> 5.0 CONCLUSIONS & RECOMMENDATIONS <br /> No contamination was detected in soil samples collected from the <br /> ' two monitoring wells drilled during this phase of investigation. <br /> There is no evidence of vadose zone contamination in the vicinity <br /> of these borings. <br /> TPH as gasoline was detected in monitoring well MW-1 at a level of <br /> 99 ppb. This is less than 50 % of the concentration measured in <br /> November 1992 . The level of benzene has decreased in this well from <br /> 15 ppb to 9 . 9 ppb and no diesel or toluene were detected in this <br /> sampling event. <br /> ' GeoAudit recommends that the quarterly monitoring program for the <br /> site be continues. Monitoring wells MW-1, MW--4 and MW-5 should be <br /> monitored quarterly, with the next event scheduled by September 21, <br /> 1993 . Because no contamination has been detected in monitoring <br /> ' wells MW-2 and MW-3 in previous events, we recommend that these <br /> wells be sampled on a yearly basis until site closure. However, the <br /> depth to groundwater should be measured in these wells to assist in <br /> determining groundwater gradient information. <br /> 6.0 LIMITATIONS <br /> 1 <br /> our professional services were performed using that degree of care <br /> and skill ordinarily exercised by environmental consultants <br /> practicing in this or similar localities. The findings were mainly <br /> based upon analytical results provided by an independent <br /> laboratory. Evaluations of the geologic conditions at the site have <br /> ' been made from a limited number of available data points (i.e. soil <br /> samples) , and subsurface conditions may vary away from these data <br /> points. No other warranty, expressed or implied, is made as to the <br /> professional recommendations contained in this report. <br /> 5 <br /> I <br />