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Corrective Action Plan Ia.,/ '4," Page 2 Cutter/Western Lift Site GPE Project No. 102.3 December 12,2003 Remedial Action Pilot Test & Feasibility Study, and dated August 1, 2003 and a directive of the San Joaquin County Environmental Health Department dated September 29, 2003. 1.2 Proposed Scope of Work The goal of the work described herein is to complete the engineered remedial work for this site. This work will be based on the vapor extraction method of contaminant removal and will be aided by air sparging. To accomplish this goal, new vapor extraction and air sparge wells will be constructed in the vicinity of the release and surface equipment will be installed to operate the wells and to monitor the performance. The following two sub-sections discuss the guiding concepts of the tasks being proposed by this CAP, and introduce the major elements of the work that will be needed to accomplish the stated goals. 1.2.1 Conceptual Basis In recent years, groundwater has been at relatively high levels; generally in the vicinity of 30 feet below grade. The surface of groundwater in recent years has, however, been as high as 22 feet bgs, but as late as 1994 was as low as 40 feet bgs. Currently, the level is about 33 bgs. The highest concentrations of gasoline are known to lie from about 35 to 45 bgs, well below the surface of groundwater. Based on information in the Pilot and Feasibility Study and other related reports, and due to the soil characteristics as well as the height of the water column over the contaminated interval, it was determined that remedial measures based solely on vapor extraction would not be sufficient to materially reduce the contaminant mass below groundwater in a reasonable period of time. Air sparging was introduced as a method to mobilize the hydrocarbon plume located underneath the groundwater surface. Air sparging is a process in which air is injected into the saturated subsurface. This, in-turn, introduces oxygen, thus helping to facilitate the growth of aerobic bacteria, while also mobilizing contaminants and bringing them to the groundwater surface thus enhancing the effectiveness ti of vapor extraction. As these mobilized hydrocarbons move through, and up the water column, adjacent vapor extraction wells may be used to extract the mobilized petroleum hydrocarbons. The pilot test conducted in the summer of 2003 suggested that sparging would be effective in mobilizing hydrocarbons from the saturated zone in this manner. The method of sparging air into the saturated zone with the partial purpose of mobilizing hydrocarbons toward vapor extraction points is essentially a petroleum displacement technique. One way to use the displacement technique efficiently is to establish a regular pattern or grid of vapor extraction wells in conjunction with a similar pattern of sparge wells. We propose to employ the "4-spot" pattern in which a "triangle" of three approximately equally spaced vapor extraction wells with a sparge well in the center of each pattern. (See the site map for a graphical representation and specific well locations.) A total of four such 4- spot patterns are called for. The spacing of this grid pattern was determined based upon on the radius of influence of the sparge wells. In the pilot test of 2003, it was concluded that the V 2937 Veneman Ave.,#13240 Geo-Phase Environmental Inc. Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295