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4 <br /> 2905 West Benjamin Holt Drive, Stockton, California March 16, 1994 <br /> Chevron U.S.A. Products Company Page 9 <br /> � g <br /> 4.0 CORRECTIVE ACTION ALTERNATIVES <br /> 4.1 Overview <br /> Based on the results of previous site assessment, four alternatives for corrective action at the site are <br /> proposed as follows: <br /> N Source removal, isolation, and groundwater monitoring and sampling <br /> ■ Bio-Sparging <br /> 0 Soil vapor extraction <br /> ■ Air sparging,with soil vapor extraction <br /> An alternative for groundwater extraction and treatment is intentionally avoided since no immediate <br /> threat exists to the local water supply. The use of a hydrocarbon mass removal aeration technology, <br /> such as vapor extraction, air sparging or bio-sparging, targeted at the source of hydrocarbons (former <br /> UST pit), will induce shrinkage of the dissolved hydrocarbon plume. In-situ remediation technologies are <br /> preferred to avoid disruption of operations at this newly remodeled service station existing on site. A <br /> brief description of the implementation, objectives and effectiveness of each alternative are summarized <br /> below. <br /> 4.2 Source Removal, Isolation, and Groundwater Monitoring and Sampling <br /> The objectives of this alternative are to remove the active sources of groundwater contamination, <br /> delineate all hydrocarbon-impacted soil and groundwater, and to establish an effective groundwater <br /> monitoring program that demonstrates containment of the contaminant plume. Implementation of this <br /> alternative began with the removal of the former UST's, associated piping, and hydrocarbon-impacted <br /> soil in 1989. <br /> Periodic groundwater monitoring and sampling would continue at the site to monitor site conditions. All <br /> monitoring wells would be gauged for depth to water to determine the magnitude and direction of <br /> groundwater flow beneath the site, and sampled to determine the concentration of dissolved BTEX and <br /> TPH-G. The objectives of the monitoring and sampling program would be to monitor the effects of <br /> natural attenuation of hydrocarbons in groundwater and to assure that the dissolved phase <br /> �✓ 5073PAR.RPr g r <br /> GROUNDWATER <br /> �I! TECHNOLOGY <br />