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f P CLEARWATER G R O U P, I N C. Environmr tn!services test results can be found in Clearwater's Problem Assessment Report, Feasibility Study, and Remedial Action Plan, dated February 21, 1996, Air Sparging and Soil Vapor Extraction at a High Water Table During periods of a high table (i.e. <12 feet bgs), Clearwater proposes to extract soil vapors from proposed horizontal vapor well PHVW-1, which will be installed at a depth of approximately 6 feet bgs along the length of the utility trench from approximately MW-1 to VW-1 (Figures 2 and 5). Based on feasibility testing data, it is estimated that achievable flow from PHVW-1 will exceed the sum of that from the vertical wells (i.e. >160 cfm at a vacuum of 30" w.c.). Thus, vapor recovery from this well will be limited by the blower/hydrocarbon destruction equipment sized for the vertical wells. Conceptual soil vapor extraction air-flow pathways for the horizontal well are shown on Figure 5. It should be noted, that Clearwater believes it is more important to design the system around the vertical vapor extraction wells, which are screened in the contaminated zone, as it is anticipated that these wells will be used the majority of the time during remediation. Also, during high water, much of the soil contamination will be submerged, limiting vapor extraction effectiveness to the contamination in the vicinity of the air/water interface. Although greater vapor flow will be achievable from the horizontal well, it is anticipated that the zone of influence from this well will be somewhat less than the sum from the vertical wells (Figure 2). However, vapor recovery from the horizontal well should still control air resulting from air sparging. Air will continue to be sparged through SW-1 during periods of high water and vapor extraction from PHVW-1. Emissions Control and Equipment As note above, it is expected that initial hydrocarbon recovery rate will be approximately 338 - 600 pounds per day. Thus, in order to meet San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) emissions limit of 2 lbs/day of volatile hydrocarbons, emissions control will be required. Based on anticipated concentrations and flow rates, Clearwater recommends using a thermal oxidizer capable of treating high hydrocarbon concentrations at a flow rate of 200 cfm at a vacuum of at least 60" w.c. Clearwater recommends using a thermal oxidizer unit that converts to a catalytic oxidizer, as it is expected that influent hydrocarbon concentrations will diminish with time. The conversion should occur when it becomes more cost effective to operate a catalytic oxidizer than a thermal oxidizer, without jeopardizing the rate of site clean-up. Air will be supplied to the sparge wells by a air compressor. Although soil will likely be remediated before groundwater, air sparging should continue in order to remediate saturated zone contamination. However, the soil vapor extraction flow rate can be reduced so that it just captures sparged air. A soil Ruiz.4491 W.Durham Ferry.Tracy.CA 3 November 12,1996