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concentrations were detected at this boring location from approximately 6 to 11 feet bgs Figure 5-1 delineates the area where TPH in soil appears to exceed 100 mg/kg The majority of the area is located under the warehouse ' building The southern extent of the area of elevated TPH soil concentrations is located between boring S2-B3 and monitoring well MW-4A This conclusion was based on soil chemical quality data collected during drilling of MW-4A in March 1992 which indicated that soil samples collected at 10 ft and 15 ft below the warehouse slab did not contain detectable TPH concentrations In addition, field observations made during drilling of MW-4A did not indicate that hydrocarbon compounds were present in soils at the MW-4A location Assuming that the soil interval containing elevated TPH concentrations is approximately 5 feet thick throughout the area delineated on Figure 5-1, the total estimated volume of TPH-impacted soil is approximately ' 210 cubic yards Review of ground water monitoring data for the vicinity of the TPH- impacted soil suggests that ground water has not been significantly impacted by TPH. As described in Section 4, TPH and BTEX detections in ground water samples are generally limited to samples collected from monitoring wells MW-1A. and MW-2A, which are located in the immediate vicinity of the former UST The concentrations of TPH and BTEX in samples collected from monitoring well MW-1A have decreased significantly since quarterly monitoring was initiated in April 1992, water samples collected after the soil removal activities are notably lower than those associated with early monitoring events No ' clear trends have been established for ground water samples collected from MW-2A If the residual TPH-affected soils were significantly degrading ground water quality, TPH and/or BTEX would likely be ' detected in monitoring well MW-4A, which is located immediately downgradient of the former UST location and the estimated area of residual TPH-impacted soil Only one sample collected from this well ' contained detectable concentrations of petroleum products The sample, collected in November 1994, contained 0 072 mg/1 of TPH and 0 001 mg/l of total xylenes and has not been confirmed by prior or subsequent ground water sampling The data collected regarding the bacteria community in soil underlying ' the excavation are inconclusive as to whether the population would be sufficient to rapidly degrade petroleum hydrocarbons 5-3