ARCHIVED REPORTS_XR0008852 - Laserfiche WebLink

Home Browse Search

27 December 1996 AGE-NC Project No 95-0143 f Page 6 of 19 supplemental fuel than either thermal oxidizers or internal combustion engines Other requirements and limitations are similar to those for internal-combustion and thermal oxidizer systems ' 5 1 2 REQUIRED SOIL CONDITIONS ' Operation of the blower in a vapor extraction system creates a partial vacuum in the subsurface, inducing air"currents"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 proportional to soil porosity and permeability Qualitative information has been gained through the examination of soil samples collected at the site Soil in the upper 18 feet has a relatively high clay content, potentially making vapor extraction less effective for this zone However, soil below 18 feet and in the saturated ' zone consists of sand, rendering vapor extraction as an effective remediation method for this zone Figures 3 and 4 depict cross sections, showing subsurface soil types at the site ' 513 MONITORING ACTIVITIES Monitoring of vapor extraction systems involves weekly measurement of vapor concentrations at the inlet to the destruction unit and periodic service and repair Systems can be equipped with an ' automatic telecommunication system to alert the operator of system malfunction or failure Vapor samples should be collected monthly for laboratory analysis to monitor the efficiency of the remediation program When the concentrations of extracted vapor have decreased and stabilized after a certain period of operation, confirmation borings are drilled to collect soil samples for quantitative analysis in the laboratory to document the degree of cleanup obtained ' 514 FEASIBILITY Generally, a vacuum of at least 0 10 inches of water is required to successfully volatilize subsurface hydrocarbons The radius of influence is often considered to be the distance from the extraction well at which a vacuum of at least 0 1 inches of water is observed (EPA - A guide for Corrective Action Plan Reviewers) A vapor extraction feasibility test has not been performed at the site, however, data obtained during the installation of soil borings and monitoring wells may be useful in determining a theoretical effective radius of influence Installation of extraction wells would be required at the site to implement an SVE system One drawback of SVE is that not all contaminated zones of soil are remediated effectively or at the . same rate For instance, a sandy soil zone will cleanup more quickly than a silty one SVE is not usually effective in soil with high clay content Other drawbacks of SVE include ineffective