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' Harding Lawson Associates <br /> exposed to the same intensity of vacuum. The piping will extend <br /> through the trench to the treatment area. <br /> A storm drain discharge line, an auxiliary vapor line, and <br /> auxiliary groundwater extraction line will be installed in the <br /> 1 trench with more crushed rock at a depth of approximately 1-1/2 <br /> ' feet below surface grade. The auxiliary two-inch PVC vapor line <br /> will not be screened and will extend along the trench to an <br /> I <br /> approximate horizontal latitude even with MW-8 . This line can be <br /> i <br /> used for future modifications, such as using MW-8 as a vapor <br /> 1 extraction well to increase the radius of influence of the VES, <br /> ' if necessary. Another two-inch PVC line will also be installed <br /> to accommodate future discharge of treated groundwater to the <br /> storm drain. A four-inch PVC line and a one-inch PVC line will <br /> also be installed at this depth for potential use as a conduit <br /> ' for groundwater extraction lines to facilitate any future <br /> ' extraction well in the eastern area of the site. <br /> Class II aggregate base rock will be placed between two feet <br /> ' to four inches below grade and compacted to 95 percent. A four- <br /> inch asphalt layer will seal with the surrounding asphalt. <br /> D. Soil Vapor Extraction System and Treatment Design <br /> ' The soil vapor extraction system (VES) will extract from the <br /> laterals placed in the trench, and the laterals placed in the <br /> tank pit area. A total of five 2-inch PVC vapor conduit lines <br /> will extend through the common conduit trench to the treatment <br /> area alongside the store. Two 4-inch PVC conduits will extend <br /> ' 23 <br />