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UPDATE 30 11--11-94 gallon and one 85 gallon activated carbon vapor scrub units The vapor scrub units are serviced by Exceltran and Cameron Yakima for change-out and re]uvenation. Prior to turning the system off on December 30 , 1993 the system had operated 12847 hours and recovered an estimated 18, 191 pounds of gasoline range hydrocarbons Since turning the system back on on February 16, 1994 until the last sampling of the system on November 7, 1994 an additional 248 pounds of gasoline range hydrocarbons has been recovered for at total of 18, 439 pounds . TPHg recoveries have been reduced to approximately 0 97 pounds per day, which is approximately 52% of the production rate prior to the turning the system off on December 30, 1993 (1 . 85 pounds per day) MODELING SOIL CONTAMINATION USING SOIL SAMPLE BORING CHEMICAL RESULTS OBTAINED FEBRUARY 2 , 1994 AND MOST RECENT VAPOR RECOVERY MONITORING ANALYSIS On February 2 , 1994 , three soil borings were drilled to obtain soil samples to document the effectiveness of the vapor extraction and to verify the removal of gasoline range hydrocarbons from the soil beneath this site On July 22 , 1992 , two areas remained with hydrocarbon impacted soils . Area A (beneath the western pump island) and Area B (east-southeast of the underground storage tank area) , see Figure 3B Estimates at that time indicated approximately 3436 pounds of gasoline range hydrocarbons remained in the soil and capillary fringe, see Update Status Report #15, page 33 The analytical results from the latest sampling (February 2 , 1994) show a reduction in the amounts of degraded gasoline range hydrocarbons, leaving an estimated 531 pounds remaining beneath the site This indicates a reduction of approximately 8Sk in two years Since that time through November 7, 1994 an additional 248 pounds of degraded gasoline range hydrocarbons have been removed by the VES, leaving an estimated 283 pounds of degraded gasoline range hydrocarbons beneath the site between the ten and forty foot depth below the surface- This latest removal total indicates a reduction of approximately 91. 81 in two and a half years The EPA models "VLEACH" and "BIOPLUME, TWO-DIMENSIONAL CONTAMINANT TRANSPORT UNDER THE INFLUENCE OF OXYGEN LIMITED BIODEGRADATION IN GROUND WATER" were utilized to predict the amount of hydrocarbons that may impact ground water and if/when ground water is impacted, the amount that would migrate off site, see SITE CLOSURE REQUEST, dated June 1, 1994 . VLEACH simulates the following process : advection, adsorption, vapor-phase diffusion and three-phase equilibrium. BIOPLUME simulates contaminant transport and solves the transport equation for dissolved oxygen (oxidation) These models assumed a somewhat "worst case" by considering no natural degradation or dilution occurring in the vadose zone, a dissolved oxygen of 8 mg/L in the background ground and surface waters (saturated conditions would be 9 1 mg/L at 680F) , and the discontinuation of the vapor extraction system (VES) VLEACH was also quite pages