Laserfiche WebLink
Geological rec"Cs&C Page 2 <br /> George's Service <br /> Feasibility Study <br /> Pioject No 425 2 <br /> April 28,2004 <br /> R G , SJCEHD, found the work proposed to be adequate and necessary with some <br /> conditions The work was performed by GTI and the details are discussed in GTI's <br /> ' Additional Soil and Groundwater Investigation and P Quarter 2004 Groundwater <br /> Monitoring Report dated March 22, 2004 <br /> ' The following Feasibility Study reviews the variety of remedial alternatives available to <br /> treat the site For site-specific details please refer to GTI's Additional Soil and Groundwater <br /> Investigation and P Quarter 2004 Groundwater Monitoring Report dated March 22, 2004 <br /> ' The appropriateness and cost effectiveness of these remedial alternatives is explored in the <br /> following report <br /> ' 2.0 REMEDIAL ALTERNATIVES <br /> 2.1 Air Sparging <br /> Air sparging is the process of injecting air into the aquifer to volatilize contaminants from <br /> the groundwater These contaminants are captured in the vadose zone and removed with the <br /> use of a vapor extraction recovery system The addition of air into the aquifer also aids in <br /> increasing the rate of natural degradation <br /> Air sparging presents a couple of concerns at the site <br /> • Shallow depth to groundwater Depth-to-water fluctuates between approximately 9 to <br /> 12 feet bgs, there is very little unsaturated soil zone where the vertically migrating <br /> vapors could be captured There would be a high possibility that short-circuiting of the <br /> ' vapors could occur, petroleum vapor could be pushed under buildings or into utility <br /> trenches, or uncontrolled emissions to the atmosphere of petroleum hydrocarbon vapors <br /> could occur <br /> ' • Moderate permeability of materials The vadose zone soil is predominately clays and <br /> clay-sand mixtures, which do not conduct airflow very well through the subsurface <br /> • Capture and control of sparged vapors requires an expensive inventory of equipment, <br /> ' including extraction wells and effluent treatment by thermal oxidizers or units of <br /> granular activated carbon <br /> 2.2 Vapor Extraction <br /> Vapor extraction is the process of drawing a vacuum on the vadose zone to produce an air <br /> flow through the subsurface, which removes volatile compounds from the soil and soil pore <br /> spaces through evaporation and concentration gradient diffusion Typically, the extracted <br /> air is treated using thermal destruction (a thermal oxidizer or internal combustion engine) or <br /> granular activated carbon There are two factors, which limit the effectiveness of the VETS <br /> ' • Low permeability of vadose zone materials The vadose zone materials at the site are <br /> primarily composed of clays and clay-sand mixtures, which have low permeability <br /> Low permeability soils create problems for vapor extraction systems by limiting the <br /> radial influence of the extraction wells <br /> • Shallow depth to groundwater, 9 to 12 feet bgs Thin vadose zones are problematic to <br /> vapor extraction due to the tendency. of the air to short circuit to the ground surface <br /> 1 <br />