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(fI ! <br /> 1) Even if the conservative vacuum radius of influence of 25 feet <br /> is assumed, the VES was correctly designed to address the area of <br /> the site containing the highest concentrations of residual <br /> hydrocarbons in the vadose zone. <br /> The screen interval of the VES wells, primarily V-3 , -4, -5 and Vw- <br /> 6, and monitor wells MW-3, -4 and -6, are appropriate for <br /> remediation of the hydrocarbon impacted area of the soil column <br /> (see schematic diagram of VES screen interval - Figure A) . <br /> 2) A summary of pounds/day and cumulative hydrocarbon removal are <br /> shown on attached Table B, and Figures B and C. The hydrocarbon <br /> recovery rate has shown a steady decline with time, indicating an <br /> effective removal of vadose zone petroleum compounds within the <br /> system's vacuum/air flow radius of influence. The final seven <br /> influent readings (October 23, 1991 to February 18, 1992, and <br /> September 1992) indicate a hydrocarbon recovery value of less than <br /> 11 pounds/day; suggesting that the system had reached an <br /> asymptotically low rate of recovery for the period monitored. <br /> 3) The final recovery value of approximately 3. 6 lbs/day is <br /> significant, when it is noted that the September 1992 reading <br /> represents operating conditions following a seven month hiatus of <br /> VES operation. The relatively low hydrocarbon recovery rate after <br /> seven months of inaction indicates that the system had achieved a <br /> steady, diminished rate of volatile hydrocarbon removal. <br /> 4) The impact to groundwater of any remaining hydrocarbons within <br /> the vadose zone is minimal to none, based on recent groundwater <br /> analytical data from MW-9 (see attached Groundwater Analytical Data <br /> - Table 1) . <br /> 5) A comparison of the soil analytical data from wells V-5 and MW- <br /> 4, suggests the marked reduction of residual hydrocarbons in SB-1 <br /> is the result of soil vapor extraction. Figure D graphically shows <br /> the absence of benzene (all BTEX compounds absent) , and virtual <br /> nondetectable concentrations of TPH-G present in SB-1. <br /> The soil data set comparing confirmation borings SB-2 and SB-3 to <br /> wells V-3 and MW-9, show the removal of the BTEX compounds and <br /> reduction of TPH-G, in response to remediation activity. <br /> Please contact Sheldon Nelson at (510) 242-1383 if you would like <br /> to discuss this site further. <br /> 4 i <br />