ARCHIVED REPORTS_XR0004784 - Laserfiche WebLink

Home Browse Search

- 06 December 1995 AGE-NC Project No, 95-0100 Page 7 of 13 when high concentration hydrocarbon vapors necessitate frequent canister replacement and disposal. Thermal oxidation systems operate by destructing hydrocarbons utilizing open-flame combustion. Natural gas is commonly used as the supplemental fuel, heating the extracted vapors to a combustion _ temperature of approximately 1400°F. Relative to internal combustion systems, these systems may be slightly more expensive to purchase and install. I lowever, they can operate at higher air flow rates, and can remediate suitable sites at a faster rate. Thermal oxidation systems can be used when hydrocarbon concentrations exceed 20,000 ppm, but have a more efficient destruction rate at lower hydrocarbon concentrations, such as exist at the Four Corners Market site. They also operate at much lower noise levels than internal combustion systems. Catalytic oxidation units provide another option for treating hydrocarbon vapors, particularly after other extraction systems have reached their economic efficiency lirnits due t 3 decreased hydrocarbon concentrations. These systems operate at temperatures under 1,000°F, re]uiring less supplemental fuel than either thermal oxidizers or internal combustion engines. Other requirements and limitations for the technology are similar to those for internal-combustion and thermal oxidizer systems. 5.1,2. REQUIRED SOIL CONDITIONS Operation of the blower utilized for a vapor extraction system creates a vacuum in the subsurface, inducing air movement through the soil pore spaces. Vapors move by convection toward the area of lowered air pressure (the extraction point). The efficiency of this process is a function of soil porosity and permeability. Neither of these parameters has been measured at the Franklyn Cole site, but qualitative information has been gained through examination of soil samples and the performance of a vapor extraction pilot test (see section 4.4.). Based on soil composition and the results of the SVE pilot test, it appears that site conditions are satisfactory for the operation of a vapor extraction system. 5.1.3. EXTRACTION WELLS At least one extraction well is required for a vapor extraction system. At the Franklyn Cole site, both _ VE1 and VE2 are completed for use.(if necessary) as extraction wells. Well VE1 was drilled near the center of the hydrocarbon-impacted soil plume and was screened through the entire zone of contamination. VE1 should serve as the main extraction well. Well VE2 was placed approximately 30 feet southeast of VEI and can be used as a passive air-intake well. To increase the effectiveness of the VES, one additional extraction well will be required. The optimal location of the additional vapor well is directly west of B2. Soil samples obtained during the installation of the addtional extraction well will serve to further delineate the extent of the contaminare,i soil plume to the west.