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George's Service Remedial Action Work Plan Project No.425.2 June 30,2011 The site meets the key parameter criteria for air sparging, such as: / i • No floating product remaining at the site; n MWZ , • No confined spaces or basements on the site; • Groundwater is not in a confined aquifer; • TPH-g and BTEX are contaminants of concern: o Boiling point of TPH-g of 40 to 225°C indicates effective vapor/dissolved phase partitioning; o Henry's Law constants greater than 100 atmospheres o Vapor pressures of higher than 0.5 mm Hg. • Intrinsic permeability of the gravel backfill in excavation area(estimated to be 10�) is within suitable range for air sparging. Along with phase transfer, air sparging has the potential for introducing atmospheric oxygen into the saturated zone, which can increase the dissolved oxygen content in the groundwater. A significant effect of air sparging is to enhance the biodegradation process by supplying oxygen to an otherwise anaerobic environment. Concerns and Limitations Problems associated with the use and design of an air sparging system include those generic to any gaseous sparging system, and include the following: • The movement of vapors in the subsurface is influenced by the permeability of the soil. Fine grained and/or heterogeneous geology can prevent the upward migration of the vapor. • The presence of low permeability soils could cause preferential channeling of vapor movement thereby limiting the radius of influence from sparge points. • As pore water is displaced by vapors groundwater mounding could occur and cause lateral spreading of contaminants. • The effect of mounding is minimized by continuously rotating the sparging from one well to the next. 5.6. Soil Vapor Extraction Soil vapor extraction (SVE) is the process of removing volatile organic compounds in the subsurface by drawing air through the subsurface sediments, which allow a transfer of petroleum compounds from the liquid state to the vapor state. As vapor, the petroleum compounds are removed from the subsurface in the extraction air stream and destroyed above ground via thermal oxidation or removed with the activated carbon. Soil vapor extraction has proven to be an effective in situ remedial method for soils of a permeable nature and can also be used to mitigate volatile hydrocarbons in groundwater by drawing air through permeable geologic units above the capillary fringe. The site meets the key parameter criteria for SVE, such as: yeologica[TeckrtiaInc. 12 4252 RAP.docx