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f: petroleum hydrocarbons were present in the on-site soils in a small area centering around borehole #3. Dissolved petroleum hydrocarbon residues were also found in the shallow groundwater at two of the three wells. No floating product was observed. a The shallow groundwater aquifer at the site consists of a very thin lens of silt, sand, gravel and clay. While limited informa- tion is available regarding the specific s._te lithology, it is expected that this water bearing zone possesses low transmissiv- ity and a relatively slow velocity. However, interconnections, if any, between the shallow aquifer and deeper water bearing zones remain unknown. Additionally, due to the site's proxirity F" to the Port of Stockton, the groundwater flow direction may jf fluctuate due to tidal effects. Based on the known site conditions, the lack of beneficial usages of the shallow aquifer and the high cost of groundwater treat- ment, the Problem Assessment Report did not recommend that groundwater remediation be attempted at the site. However, it a.., was recommended that a limited pump test of one well be conducted to determine if the sustainable yield capacity of the aquifer system is less than 200 gallons per day. This information will v. assist the regulatory agencies to assess the usability of the aquifer in question. In response to the findings of the soil and groundwater sampling program, WESTON was directed by the County of San Joaquin to evaluate alternatives for remediating the site and to two final remedial plan. prepare a 2.0 REMEDIAL PROJECT ALTERNATIVES As detailed in the Problem Assessment Report, the soil and j groundwater sampling program identified the lateral and vertical, extent of the petroleum hydrocarbon presence within the soil at the site. As the concentration levels detected were sufficient to require remediation, a limited feasibility evaluation was conducted to assess alternative approaches to remediate the area. Three approaches were considered as follows: A. Excavation to remove soils containing TPH concentrations in E excess of 100 mg/kg down to first groundwater. ' B. In-situ , volatilization (ISV) to remediate the soils in '�. place. r ' C. In-situ flushing of the soils to remediate the soils in }, place. Summarized below are the principle factors considered during the evaluation of three alternatives. A. Excavation of Soils in Excess of 100 mg/kg TPH - 2 -