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' Report—Remedial Action Feasibility Page 3 Cutter Lumber—Western Lift Site GPE Project No 102 3 . August 1,2003 ' the site Subsequent soil borings confirmed that the release had impacted the vadose zone soil and the groundwater In March of 1998, seven groundwater monitoring wells were installed to monitor the groundwater plume Two wells, MW-1 and MW-4 still remain ' from the initial Western Lift investigation near the south end of the Property Field work and groundwater monitoring completed at the site since 1997 show that a former leaking underground gasoline storage tank impacted the soil and groundwater with gasoline range ' petroleum hydrocarbons 1.2 Corrective Strategy ' The goal of the work described herein is to develop new engineering data, as the basis of a Feasibility Study to identify which of several alternatives is the most feasible and cost effective method to adequately mitigate the residual soil and groundwater contamination This work was augmented by information from the remedial investigation at the adjacent site, the Former Manna Pro Property - 4004 S El Dorado Street The work, described in the following sections was completed pursuant to a directive of the San Joaquin County EHD dated September 7, 2001 The following two sub-sections discuss the guiding concepts of pilot test and the mayor elements accomplished by the work performed 1.2.1 Conceptual Basis of Pilot Test Past work performed at an adjacent Property (4004 S El Dorado) documented pilot-level field testing and a Feasibility Study of a remedial concept involving simultaneous vapor extraction and groundwater pumping This work provides some of the basis for possible future corrective action at the Cutter Lumber / Western Lift site These two sites bear many similarities due to the common geologic and hydrologic features and to similar characteristics of the contaminant plumes Since the early 1990's groundwater levels in this part of Stockton have risen at least 10 feet This fact in conjunction with the known distribution of gasoline means that much of ' contaminant mass lies well below the groundwater surface Unfortunately, this deeper groundwater contamination is not likely to be efficiently mitigated by the simple vapor extraction We have suggested that vapor extraction can be an important part of a remedial action plan, but will not be effective in mitigating hydrocarbon contamination situated more than a short distance beneath the groundwater surface Air sparging to introduce oxygen into the subsurface and mobilize contaminants may address the deep contamination plume Infected air will encourage the growth of aerobic bacteria and should also help to mobilize light hydrocarbons As these mobilized hydrocarbons move through and up the water column, down-gradient vapor extraction wells may be used to Iextract the mobilized hydrocarbons • 2937 Veneman Ave ,#B240 Geo-Phase Environmental Inc, Phone(209)569-0293 Modesto, CA 95356 Fax(209)569-0295