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' Gealgtal cluics Inc.l�cPage 3 Sinclair Trucking Feasibility Study Project No. 1030.3 June 25,2003 A number of factors keep vapor extraction from being a promising technology at the site: • Shallow depth to groundwater — 9 to 12 feet bgs. Thin vadose zones are problematic to ' vapor extraction due to the tendency of the air to short circuit to the ground surface. The shallow groundwater would also cause a problem by mounding in and around the vapor extraction wells. ' • Low permeability of vadose zone materials. The vadose zone materials at the site are primarily composed of silts and clays, which have low penneability. Low permeability soils create problems for vapor extraction systems by limiting the radial influence of the ' extraction wells. A blower with high vacuum potential must be used which increases energy consumption. High vacuum would also cause a problem with mounding of the groundwater. • The majority of the contamination is tied up in the smear zone of the aquifer. It would ' be very difficult to target this zone as much of the year it is under the water table and the rest of the year it is within the capillary fringe zone. ' 2.2 Monitored Natural Attenuation Monitored natural attenuation (NINA) consists of long term monitoring of groundwater conditions. Attenuation of a groundwater plume can occur through physical processes such as advection and dispersion, or through biological processes. In theory, biological organisms that can degrade hydrocarbons are ubiquitous in the subsurface. These organisms metabolize the hydrocarbons in oxidation-reduction processes. Under NINA, the laboratory analyses include chemical parameters that indicate whether oxidation-reduction reactions are taking place and natural biological mechanisms are decreasing the mass of residual contamination at a site. The chemical parameters may include dissolved oxygen, sulfate, nitrate, oxidation-reduction potential, conductivity and pH. A decrease in residual mass can be monitored by measuring concentrations of these parameters, along with a demonstrated decrease in contaminant concentrations in the sites' wells. ' In essence, monitored natural attenuation involves monitoring the site over a period of several years to determine if the VOCs are degrading over time. Unenhanced bioremediation is not a viable option for the site because current] there is- bioloeical activityat the site The site has been under investigation for nearly 8 years and the groundwater concentrations remain relatively stable at the site. S { 3y2yp�51. ' 2.3 Enhanced Bioremediation Enhanced biodegradation is an option for the site because currently there is evidence biological activityat the site. The concept for this site would be tout Ey4fogen peroxide ' o t e excavation pit prior o ackfilling the pit. Tubing will be installed in the backfill to facilitate future injection of hydrogen peroxide. The hydrogen peroxide will immediately oxidize the hydrocarbon constituents while supplying oxygen to the subsurface. Dissolved oxygen measured at the site averages less than 1-ppm and needs to be enhanced to assist natural biodegradation. _ Soil samples collecte during the installation of MW-1 in June of 1995 indicated the �`''� ' presence of 13,600 mg/Kg TPH-G. Soil samples collected during the installation of MW- 101 in April of 2002 indicated the presence of 71.2 m /Kg TPH-G. Additional evidence of active biodegradation include: S�(,t csi ��