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1 ' 4.0 CONCLUSIONS 4.1 Mass Balance Quantities ' The mass quantity of TPH gasoline in the water was calculated using the inferred water contamination levels and plume size as indicated in figure four. Based on varying ' concentration levels with distance and estimated volumes of impacted water, a total gasoline mass of 0.045 kg or 45 grams was calculated in the water, assuming an average soil porosity of 30%. ' In December of 1994, the impacted soil was removed. However, there may have been some minor remaining soil contamination. Also, as the contaminated groundwater levels fluctuate, ' contamination can adhere to the soil and will remain adsorbed to the soil particles and not be released back into the groundwater. The volume of the soil that is impacted is inferred from the aerial extent of the groundwater contamination and data from the installation of monitor ' well MW-5 in September, 1999. Average contamination levels in the soil are based on the analytical results from soil samples taken while MW-5 was installed. This is the only resent soil analytical data that we have. Assuming a soil density of 100 pounds per cubic foot, the ' estimated volume of impacted soil is estimated to contain 19 kg of gasoline. The above mass balance quantities reflect approximate location and time-dependent contaminant quantities. They are best used empirically to make general assessments ' regarding contaminant diffusion and degradation, and should not be construed as defining actual mass quantities. 4.2 Groundwater Contamination Groundwater contamination was detected in monitoring well MW-2 and the newly installed MW-5. The groundwater contamination consisted of total petroleum hydrocarbons as gasoline, and associated aromatic volatile fuel components (BTEX). No contamination was detected in the other three wells. ' The groundwater contaminant plume in the vicinity of well MW-2 and adjacent MW-5 is inferred to extend down-gradient of well MW-2 approximately 60 feet. The plume is inferred to extend ' up-gradient and cross-gradient approximately 15 and 20 feet, respectively. Figure 4 illustrates the inferred limits of groundwater contamination for the December 1999 sampling event. ' 4.3 Groundwater Flow Direction and Gradient JJW prepared a groundwater potentiometric surface map based on the static groundwater ' elevations measured on December 17, 1999. The shallow groundwater was calculated to flow toward the north-northeast (N 4 E) at a gradient of approximately 0.0033 ft/ft. Figure 3 illustrates the ground-water potentiometric contour surface and flow direction. 4.4 ORC Effectiveness t A full scale ORCO emplacement has not been done since it has not yet been determined by the San Joaquin County Environmental Health Division that additional remediation is needed. A pilot test was accomplished by installing an ORCO sock in MW-2 in March, 1999. The .� Heterotrophic Plate Count increased from 680 CFU/mI on March 25, 1999 just prior to ORC® ' sock emplacement to 3,900,000 CFU/ml on September 13, 1999. 1 3 JJW GEOSCIENCES Inc.