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rrfl�rcx+lfsxER Mr. Charles Leubner 10 October 1991 Page 6 reasonable to infer that the lateral extent of the petroleum hydrocarbons in the soil in the direction of the proposed boring site is similar to the lateral extent in the directions of Borings B-2 and B-3. The lateral extent of the petroleum hydrocarbons in the soil in the southeast direction is thus estimated to be no greater than 10 feet to the west and 8 feet to the east of boring B-1. This estimate is based the distance that is half-way between the two borings in which hydrocarbons were not detected and boring B-1. Vertically, the extent of petroleum hydrocarbons as gasoline appears to be limited to the interval between the surface and a depth of 15 to 20 feet below the existing ground surface. Although the petroleum hydrocarbon constituents benzene, toluene, ethylbenzene and xylenes are present at depths below 20-feet, their concentrations are significantly lower than in the shallower soils. Although lead was detected in all of the samples analyzed, total lead concentrations did not exceed in any of the samples the Total Threshold Limit Concentration of 50 mg/Kg used for defining a hazardous waste The soil sample with the highest concentration of total lead was selected for determining the soluble lead concentration as defined by the WET method Soluble lead was not detected in the WET extract thus the lead present in the soil does not appear to be in a leachable form. If soil above the 20-foot depth is remediated, the highest concentrations of benzene, toluene, ethylbenzene, and xylenes remaining in the ground would be 27 ug/Kg, 96 ug/Kg, 10 ug/Kg and 68 ug/Kg, respectively. Since there are no action levels for these constituents in soil, proposed soil threshold levels for these chemicals were based on DOHS Maximum Contaminant Levels for benzene, ethylbenzene, and xylenes, and Applied Action Levels for toluene. A factor of 100 times the DOHS MCLs and Applied Action Levels, expressed as ug/Kg in soil, was used to develop the proposed threshold level shown on Table 1. The concentrations of benzene, toluene, ethylbenzene, and xylenes found in samples from 20 feet and below are all below the proposed threshold levels. Thus, remediating soil above the 20-foot depth would provide an adequate level of protection to groundwater quality. REMEDIAL ALTERNATIVES ANALYSES It is recommended that the soil containing the highest concentrations of petroleum hydrocarbons beneath the former tank site be remediated, i.e., from the ground surface to a depth of 15 to 20 feet below the ground surface. For estimating purposes, the area requiring remediation is 18 feet by 18 feet, which is based on one-half the distance between the boring over the tank where hydrocarbons were detected and the surrounding borings where no hydrocarbons were detected.