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Nf t�1�(-�-lENNEI Mr. Roy Knight 13 November 1997 Page 6 Even though stained and odorous soil is noted only to extend 3 to 5 feet below the bottom of DI- 2 and DI-4, laboratory results indicate that hydrocarbons are present to a depth of approximately 10 feet below these inlets. Lateral Extent Soil borings located around the drain inlets, except for SB-2 and SB-11 which were located two feet from the center of DI-1 and DI4 respectively, contained no detectable concentrations of petroleum hydrocarbons. SB-2 contained detectable levels of Total Oil and Grease and SB-11 contained detectable concentrations of TPH-D. Summary of Field Investigation Results Petroleum hydrocarbons detected in soil samples collected from borings in and around the four drain inlets appear to be limited to soil directly beneath each inlet. Based on this finding, it is recommended to remove soil down to a depth of approximately 8 feet below the base of DI-1, DI-2, and DI-3. Because diesel contamination was detected 7 to 8 feet below the bottom of DI- 4, it is recommended to excavate to approximately 10 feet beneath the bottom this drain inlet. Petroleum hydrocarbons in the samples collected around the drain inlets were only detected at DI-1 and DI-4. Total Oil and Grease was found 2 feet from DI-1 at a concentration of 76 mg/Kg and TPH-D found 2 feet from DI-4 at a concentration of 6.7 mg/Kg. Because the fine grained silt and clay appears to have prevented the migration of petroleum hydrocarbons and the compounds associated with the Total Oil and Grease analysis are relatively immobile, removal of soil from around the drain inlet does not appear warranted. Although the extent soil around the drain inlets that contains petroleum hydrocarbons is generally limited to within 1.5 feet of the edge of the drain inlet, a much larger amount of soil would have to be excavated to remove soil to the proposed depths. CONCLUSIONS AND RECOMMENDATIONS Petroleum hydrocarbons in soil appear to be limited to soil directly beneath the drain inlets. Excavation of soil around the drain inlets is not recommended because it would entail the removal of concrete and asphalt pavement from around the drain inlets as well as a large amount of clean soil. Because of the low concentrations of Total Oil and Grease and TPH-D detected in the lateral soil borings drilled at each drain inlet, we recommend limiting the removal to that soil which lies directly beneath the four drain inlets.