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1 11 Chevron U S A , Inc February 20, 1992 02320 2338 Page 5 TPH-G in groundwater over time If no significant changes in concentration occur over a period of one year then a closure plan for the site will be submitted for approval by SJCPHS 4 3 Excavation of Impacted Sod To implement this alternative, further assessment would be required to identify the presence of impacted soil Sod borings would be drilled in the vicinity of the tank pit and fuel delivery lines and sampled every five feet Samples would be field screened with a portable organic vapor meter to determine which samples would be submitted for laboratory analysis Upon receipt and analysis of the soil analytical data, a work plan could be prepared to identify the areas to be excavated and to evaluate disposalltreatment alternatives for the excavated soil 4 4 Soil Vapor Extraction As mentioned in the above paragraph, further assessment would be required to identify the presence of impacted soil Assessment would require a soil vapor extraction pilot test to determine the concentrations of BTEX and TPH-G in the vapor phase and to evaluate the radius of influence attainable through vapor extraction at the site The test would be conducted by using one of the 0 existing monitoring wells as an extraction point and measuring the induced vacuum at the surrounding monitoring wells Air samples would be collected to determine the concentration of BTEX and TPH-G in the vapor phase Emissions produced during the pilot test would be controlled by an appropriate method Upon analysis of pilot test results, a work plan detailing the steps required to implement the soil vapor extraction system would be submitted to SJCPHS for approval 4 5 Cost Benefit Analysis of Corrective Action Alternatives Monitoring wells are already in place at the site, therefore the costs associated with continuation of quarterly monitoring and sampling would be the labor, materials, transportation, and laboratory analyses fees of monitoring and sampling By maintaining the monitoring/sampling program for one year, seasonal trends in concentrations of BTEX and TPH-G could be analyzed in conjunction with monitoring data to further evaluate the effects, if any, of residual contamination on the quality potential of immediate local water supplies Implementation of both excavation and/or soil vapor extraction would require additional assessment to identify the presence of impacted soil at the site An assessment phase of work must be completed before the corrective action can be implemented Costs associated with assessment, 233SCAP RPT -W�P GROUNDWATER TECHNOLOGY