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KLEiNfELDER 5 CONCLUSIONS AND RECOMMENDATIONS Soil and ground water.adjacent to the excavation was found to be affected by petroleum hydrocarbons. The lateral extent of impact appears to be limited to the area within 10 to 15 feet north, west, and south of the excavation. The area east of the excavation could not be investigated because of the presence of the warehouse, and the conditions in this area are not known. The ground water gradient was found to be to the southwest,opposite the regional ground water gradient. A monitoring well was not installed directly downgradient from the excavation,however, soil-gas survey samples downgradient of the excavation did not reveal __. the presence of petroleum hydrocarbons in the ground water. .Analysis of ground water samples indicate that ground water does not appear to be affected by petroleum hydrocarbon constituents 30 feet west of the tank excavation. Ground water from MW-1 did appear to be affected by coliform,possibly due to the nearby sewer Iine. The iow permeability of the soil, the shallow ground water gradient, and probable gradient fluctuations due to tides and/or seasonal variations would affect the migration of -- contaminants in ground water. Therefore, it is possible that ground water samples from MW-1, a monitoring well located 30 feet west of the tank excavation, and soil gas sample w locations K and F would be affected if contaminants migrated from the tank excavation. A well southwest of the tank excavation does not appear to be necessary at this time. Kleinfelder recommends continued monitoring of the ground water quality and gradient to assess the effects of seasonal variations and to provide reproducibility of the date for statistical validity-. The need for another monitoring well southwest of the excavation also should be evaluated if a sufficient level of reproducibility is reached and the initial data is validated. Meanwhile, Kleinfelder recommends that the affected soil and ground water around the excavation be remediated. Because of the shallow nature of the ground water, soil remediation options should consider options for combining the treatment of the first -- W As,required,.a copy of this report should be submitted to San Joaquin County,Public Health Services. F15-90-101 $ Copyright 1990 Kleinfeider, Inc.