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PROBLEM ASSESSMENT REPORT <br /> 14600 West Frontage Road Manteca California <br /> 6.0 CONCEPTUAL SCHEDULE <br /> Actual selection of a viable option for treatment and/or disposal of hydrocarbon-bearing <br /> soil at the site, from those outlined above, depends on a number of variables requiring <br /> further definition These variables include <br /> • determination of the hydraulic conductivity of the impacted soils, and, <br /> • determination of the soil's permeability to air and the potential rate(s) of <br /> Ivapor extraction that may be expected under in-situ vapor extraction <br /> A conceptual schedule of events to help determine the above variables should include <br /> a) refinement of soil and hydrocarbon volume calculations based on analytical results <br /> obtained to date and determination of the intended fate of the remaining aboveground <br /> tanks, b) additional soil sampling and analysis for hydraulic conductivity, and c) vapor <br /> extraction testing of selected wells, possibly to include installation of vapor extraction wells <br /> within the vadose zone, to determine soil air permeability and expected vapor extraction <br /> rates <br /> Once determination of the above variables is complete, selection of a remediation option <br /> will be documented in a final remedial plan to be submitted to the involved regulatory <br /> agencies <br /> The presence of free-phase and dissolved hydrocarbons in groundwater necessitates the <br /> need to address groundwater remediation alternatives Because of the variable nature <br /> of the hydraulic gradient and the lack of data on possible contributing sources on nearby <br /> properties, conclusions about the distribution of petroleum hydrocarbons in groundwater <br /> at this time would be premature Therefore, the selection or design of a groundwater <br /> remediation system, based on the currently available data, would also be premature To <br /> address groundwater quality beneath the site, the following is proposed <br /> • Continued groundwater monitoring to assess the effect of interim floating liquid <br /> hydrocarbon removal on groundwater quality and to define chemical and <br /> hydrogeologic-trends with respect to groundwater, <br /> I Formulate a contingency to add an automated floating liquid hydrocarbon recovery <br /> system to the wells, to be determined on the basis of evaluation of data collected <br /> during and after soil remediation, and, <br /> IFormulate a contingency to provide gradient control by extraction and treatment <br /> of groundwater as indicated by data collected during future monitoring events <br /> I <br /> I90-097A PAR 17 <br />