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I <br /> vadose zone. The soil vapor flow rate is directly related to the length of the <br /> screened interval. A longer screened interval gives the soil vapor more area <br />' to flow through, thereby increasing the flow rate at a given applied vacuum <br /> compared to a shorter screened interval. <br />' Due to the limited soil vapor flow rate and relatively low concentration of <br /> petroleum hydrocarbons in the soil vapor extracted from well MW-13, the <br /> calculated mass removal rate was relatively low (0.1 pound per day). <br /> Based on these conclusions, EMCON Associates has considered the <br /> following options: <br />' 1 . extracting soil vapor from well MW-1 <br /> 2. installing a SVE well near well MW-13 in the suspected <br />' center of the petroleum hydrocarbon-impacted soil <br /> 3. extracting soil vapor from the piping gallery <br />' Extracting from MW-1 (screened interval from 27 to 47 feet) is not likely to <br /> be efficient since the well head did not appear to be sealed properly. A <br /> leaking well seal will allow atmospheric air to enter the well, diluting the <br />' concentration of petroleum hydrocarbons in the soil vapor extracted <br /> (thereby reducing the mass removal rate), and will decrease the radius of <br /> influence of the well. Since data is not available regarding the effectiveness <br /> of this well as an extraction point, its use is not recommended. <br /> Extracting from an SVE well near well MW-13 may yield a higher mass <br /> removal rate than the other two options. A higher mass removal rate would <br /> be the result of installing the well with a long screened interval (30 to <br /> 80 feet) within the unsaturated zone in the suspected center of the <br />' petroleum hydrocarbon impact. Potential disadvantages of installing this <br /> SVE well include delay in initiation of remediation and the possibility that the <br /> zone of influence may not be as large as the zone of influence measured <br />' while extracting from the piping gallery. <br /> Extracting soil vapor from the existing piping gallery is likely the better of the <br />' three options for beginning remediation of impacted soil. This option is <br /> proposed because (1)the piping gallery is already in place and (2) test data <br /> are available to indicate that the lateral and vertical zone of influence <br />' includes the areas of petroleum hydrocarbon-impacted soil. A possible <br /> drawback to using the piping gallery is that a large portion of the soil vapor <br /> may originate from soil with low concentrations of petroleum hydrocarbons <br /> relative to soils adjacent to well MW-13. This may result in a lower than <br /> optimum petroleum hydrocarbon mass removal rate. <br /> Based on the evaluation above, EMCON Associates recommends installing <br /> an SVE system and extracting soil vapors from the piping gallery. As part <br />' pj010f9010f900020.1 ag 6 - 2 Rev. 0 December 15, 1992 <br />