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C3enCvgrcaC?eckn�es Inc Page 6 Soil Groundwater Investigation Report George s Service Project No 425 2 August 5 1997 In summary, elevated levels of BTEX and TPH-Gas continued to be present in MW-1 and MW-2 MTBE was detected and confirmed in MW-I MW-3 was again non-detect for all analytes MW-4, MW-5 and MW-102 showed elevated levels of BTEX and TPH-Gas The highest levels of TPH-Gas detected during this monitoring was in MW-102 MW-6, MW-7, MW-8 and the three domestic wells were non-detect for all analytes 3.2 Site Hydrology On May 9, 1997 the top of casings were surveyed into a common elevation The elevation of MW-2, determined during a previous surveying event, was used as the benchmark elevation A site specific groundwater gradient and bearing was calculated from the depth to water measurements taken during the groundwater monitoring The gradient was 0 0024 ft/ft flowing N20°W The average elevation of groundwater under the site was 91 33 feet above mean sea level Monitoring well 3, 4 and S were used to determine gradient They were chosen because they reflect the gradient over the largest area of the site and surrounding properties The groundwater elevation for MW-5 was considerably higher then the rest of the wells, 0 63 feet higher then the average groundwater elevation at the site There are several possible explanations for this 1 Incorrect surveying of top of casing elevation 2 Incorrect depth to water measurement 3 Local recharge in the area of the well Before the next monitoring event the top of casing will be resurveyed to eliminate the possibility that was the problem Table 3 in Appendix A is a summary of water level elevations, gradient slopes and bearings Figure 4 is a groundwater gradient map for the site 3.3 Geology aodl YiOd Obseirvattions The following section discusses the subjective field observations and geology documented during this investigation based on the interpretations of the field geologist o The shallow geology of the site is predominately silt, sandy silt and silty sand Soil samples from the shallow wells were non-detect for all analytes However, during the drilling of MW-4 and MW-5 both staining and odor were noted in the shallow samples. five and ten foot respectively The five foot sample from MW-4 did not contain enough material in the spoon for analysis The five and ten foot samples from MW-5 also did not contain enough material for analysis 0 A sandy clay to very plastic clay layer was encountered in MW-102 from 37 5 to 42 feet below ground surface 0 A clayey sandy gravel layer was encountered in MW-102 at 45 feet below ground ' surface This layer also had the highest levels of Toluene, Ethyl Benzene, Total Xylenes and TPH-Gas This is also the layer in which MW-102 is screened Water samples from this well showed the highest concentrations of TPH-Gas and high concentrations of BTEX compounds i 1