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• CrNMENC. SACRAMENTO REVIEW DRAFT 0 Addendum Letter to qtr. Harlan Knoll August 31, 1990 Page 4 In situ bacteria are difficult to monitor. Different methods may include monitoring CO levels in the extraction wells or the 02/CO2 ratio at the margin o the contamination area against that present at the center. For this pilot study, it is proposed that soil cultures be obtained from several soil samples for an aerobic population count. Later, samples will be obtain if the pilot study is expanded to determine if the population increase can be documented./" The feasibility of adding nitrogen as a nutrient in the form of low concentration gaseous ammonia is being investigated. Vapor Extraction Well Installation The four soil vapor wells will be installed in a manner similar to that used for ground water monitoring wells. At each well site, a borehole will be drilled using a truck mounted drill rig equipped with 10 inch outside diameter hollow-stem augers. Beginning at approximately 15 feet below the surface, soil samples will be obtained at five feet intervals using a decontaminated California-modified, split-spoon drive sampler. From each sampler, one sample will be selected for potential laboratory analyses. That sample will be sealed with foil , plastic end caps, and tape and labeled with the appropriate information. The sample will then be stored on ice in an ice chest until delivered under chain of custody to the mobile laboratory on site. A second sample will be tested for temperature and soil vapor as previously noted. When the borehole has been completed, a vapor extraction well will be installed in the hole. The well will be screened with four inch inside diameter Sch 40 PVC screen with 0.020 inch slots over the complete interval which contained detectable hydrocarbon contamination. The wells will be completed to the surface with four inch inside diameter Sch 40 PVC blank casing. A Coarse gravel pack will be implaced around the screened interval above which will be a two feet thick bentonite seal . The annular space will be cemented to the surface with Portland Type I-II cement with a 5% bentonite mixture. The casing will extend above the surface and be enclosed in a locking monument box which will be seated in concrete. A copy of the well permit application is included as Attachment II . Soil Venting Equipment Soil vapor will be extracted using a Carbtrol SVX Soil Venting System (SVX) . The SVX consists of a dehumidifier and blower with vacuum, temperature, pressure, and flow monitoring capabilities along with in line sampling of vapor. The SVX has a rated capacity of 105 cubic feet per minute (cfm) at six inches of mercury. Versar has . successfully employed this system at several sites and has found it to be