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URS N N Mr. Robert McClellon January 4, 2005 Page 4 Additional Probes Installation The extent of the methane plume along the northwestern boundary is unknown. Additional probes will have to be installed to further assess the methane plume along the northwestern boundary and along the northern portion of the western boundary of the site.We propose to install two new probes(Figure 1). The first probe will be installed at the northwestern corner of the site. The second probe will be installed along the western boundary of the site, approximately 100 feet south of the northwestern corner of the site(midway between the first probe and VW-I).The probes will be constructed following the same construction protocols described in the work plan dated November 17,2003 and work plan addendum dated December 12, 2003 approved by SJCEHD. In addition, we plan to install two extraction wells. The details of the extraction wells are discussed hereafter. Extraction Well Installation We proposed to install two extraction wells at the site (Figure 1).The extraction wells will be installed approximately 100 to 200 feet south of the northern boundary of the site. Our experience with active soil vapor extraction has shown a radius of influence of at least 200 feet with extraction wells installed in similar types of soil. We propose to install the extraction wells within 100 to 200 feet of each other. We will obtain approval from you before installing the extraction wells.We propose to install each extraction well midway between the probes.The extraction wells will be constructed using 2-inch PVC piping. We propose to place the screen of the extraction wells from the bottom of the debris to 6 feet bgs. The wells will be constructed following the probe construction protocols described in the work plan dated November 17, 2003 and work plan addendum dated December 12, 2003 approved by SJCEHD. Pilot Test Activities Following the installation of the probes and extraction wells, a pilot test will be conducted.The first step will be to measure the methane concentration in each of the extraction wells.This information will be used to size and select a soil vapor extraction system and to select and size a soil vapor treatment method. The pilot test will be conducted in two phases: stepped and sustained. It is our understanding that SJVAPCD does not require a permit for pilot tests with a duration of less than five days. Since the pilot test will be completed in less than five days, an ATC or PTO will not be needed from the SJVAPCD.For the stepped phase,URS will operate the vapor extraction pilot system at a minimum of four different flow rates at each extraction well. The applied vacuum will be measured at each flow rate for each extraction well. For the sustained test,URS will operate the vapor extraction pilot test system at each extraction well for a sustained period of two days. Methane concentrations will be measured using the landfill gas monitor during the pilot test. Vacuum measurements at each of the probes and extraction well also will be measured periodically during the pilot test. Following the completion of the sustained test at each extraction well, a soil vapor sample will be collected and analyzed for landfill gas parameters. The results of the pilot test will be used to select and size an appropriate remediation and treatment system for the site. K:\Wprocess\25532\WorldEnterprise\Remediation Plan\010405-Ltr.doc