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KLEINFELDER 6 CONCLUSIONS N AND RECOMMENDATIONS ' 6.1 SOIL In January and March of 1991, the three underground storage tanks and contaminated soil ' were excavated and removed from the site. Elevated TPH concentrations remain in the soil at the bottom of the tank excavation as indicated by 2 of the 14 samples collected. ' Results of the remaining 12 samples indicate that the bulk of petroleum hydrocarbon contaminated soil has been removed from the excavation area. Based on the analytical results, Kleinfelder does not recommend additional assessment of the vertical extent of petroleum hydrocarbon migration at the bottom of the excavation. ' The source of contamination has apparently been removed with the excavation of the tanks and the bulk of the contaminated soil. Although elevated TPH concentrations were ' detected at two locations and remain in the soil at depths of 16 and 21 feet, there does not appear to be a significant vertical component of petroleum hydrocarbon migration based on the results from borings B-1 and B-2. The lateral extent of hydrocarbons, if any, beyond the excavation is not known. However, boring B-1 was drilled at an angle 201 from vertical. ' The 20, 25 and 40 auger foot samples were collected approximately 6, 8 and 13 feet west of the property fence. Based on the results of these three samples from boring B-1, there does not appear to have been significant lateral migration of petroleum hydrocarbons beneath a depth of 20 feet. Additionally, ground water was encountered at a depth of 69 feet, approximately 50 feet below the detected concentrations remaining in the ' excavation. The TPH concentrations remaining at the bottom of the excavation should degrade naturally over time. Furthermore, the site is covered with an asphalt cap which ' will reduce the potential for surface water infiltration and vertical migration of the remaining petroleum hydrocarbon concentrations. ' 6.2 GROUND WATER ' Based on the location of monitoring well MW-1 through the excavation, and the lack of detectable concentrations during the latest sampling event, Kleinfelder does not recommend the installation of additional monitoring wells at this time. Ground water was 69 feet below the ground surface, and significant petroleum hydrocarbon concentrations have not been detected in the soil below a depth of 22 feet. Since monitoring well MW-1 FR1-92-15 Page 18 of 21 ' Copyright 1992 Kleinfclder,Inc.