ARCHIVED REPORTS XR0000203 - Laserfiche WebLink

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EXECUTIVE SUMMARY In accordance with Caltrans Contract No 53W202 and Task Order No 10-5171000-05, Geocon Environmental Consultants, Inc (Geocon) is submitting the enclosed Problem Assessment Report and Corrective Action Plan (PAR/CAP) for the Caltrans Shop 10 facility located at 1603 B Street in ' Stockton, California This PAR/CAP presents the cumulative results of environmental site assessment work and vapor extraction pilot testing performed at the subject site The work described herein was performed to delineate the vertical and lateral extent of petroleum hydrocarbons impacts to soil and ' groundwater, to evaluate interim soil remediation options, and to present preliminary soil vapor extraction design criteria ' In February and March 1989, four gasoline/diesel fuel underground storage tanks (USTs) and one waste-oil UST were removed from the site Initial subsurface investigations were performed at the site between 1987 and 1994 by Woodward Clyde Consultants, Alton Geoscience, and Nmyo and Moore These investigations included the installation and monitoring of eighteen groundwater monitoring wells and the chemical analysis of soil and groundwater samples The results of these studies indicated the presence of total petroleum hydrocarbons as gasoline(TPHg) impacts to soil and groundwater resulting ' from the former fuel UST systems Between September 1995 and August 1996, Geocon restored eight temporarily abandoned wells, and installed three vapor extraction test wells and two additional groundwater monitoring wells, performed quarterly groundwater monitoring and a vapor extraction pilot test(VET) The VET was performed to ' collect site specific data and evaluate the feasibility of using vapor extraction as a soil remediation alternative ' Based on Geocon's review of the cumulative soil and groundwater data obtained at the site, the majority of the residual TPHg currently remaining in soil is located beneath the gasoline and diesel UST excavation to a depth of approximately 50 feet below the ground surface (bgs) The vertical and lateral limits of residual TPHg in on-site vadose zone and capillary fringe soil have been established as described in the PAR/CAP The volume of TPHg-impacted soil in the vadose and capillary fringe ' zones is estimated at 2,000 and 3,000 cubic yards, respectively ' The soil analytical data obtained from this investigation provided the ability to reasonably estimate the distribution of petroleum hydrocarbons in soil beneath the site and initiate corrective action ' planning Evaluation of the site conditions and data obtained from the vapor extraction pilot test indicated that soil vapor extraction is feasible and the most cost effective remediation technology for the impacted soil The results of the VET performed at the site indicate an initial start-up vapor extraction system (VES) TPHg mass extraction rate of approximately 300 pounds per day Based upon an extraction flowrate of 100 standard cubic feet per minute (scfm), an effective ROI in excess of 80 feet could be established to capture petroleum hydrocarbons existing in on-site vadose zone and capillary fringe soil It is estimated that a 100 scfm therm-ox based VES operated for a 12 to 18 Project No S8100-06-18A -1- December 9, 1996