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a <br /> r <br /> i <br /> 3 REMEDIAL ALTERNATIVES EVALUATION <br /> Four remedial alternatives are discussed in the following sections. The remedial <br /> objective is to remove petroleum hydrocarbons from soil and groundwater at the USA <br /> site. <br /> 3.1 Description of Remedial Alternatives <br /> This section presents a description of the selected remedial alternatives for addressing <br /> petroleum hydrocarbon impacted soil and groundwater at the site, <br /> 3.1.1 Air Sparging with Soil Vapor Extraction <br /> Air sparging is the injection of ambient air into the groundwater at flow rates and <br /> pressures sufficient to sustain air flow into the subsurface. The introduced air provides <br /> two mechanisms to remediate petroleum hydrocarbons in groundwater. First, when the <br /> injected air is introduced at a high enough flow rate, typically >5 cubic-feet-per-minute, <br /> the air physically strips the petroleum hydrocarbons from the groundwater and carries the <br /> petroleum hydrocarbons into the vadose zone (unsaturated) soil where it is collected by a <br /> soil vapor extraction system. Second, the introduced oxygen in the injected air (21%) <br /> provides the limiting environmental factor for aerobic biological activity to take place. <br /> The microbial utilization of the petroleum hydrocarbons further reduces the amount of <br /> petroleum hydrocarbons in the groundwater. <br /> Soil vapor extraction (SVE) induces vapor flow through the vadose zone and volatilizes <br /> sorbed petroleum hydrocarbons. The petroleum hydrocarbon vapors are extracted and <br /> treated. This approach is well suited to coarse grained, gasoline impacted soil. SVE is <br /> capable of extracting petroleum hydrocarbons in the vadose soil, usually this is associated <br /> with the source area of petroleum hydrocarbon impacted sites. <br /> 3.1.2 Groundwater Extraction and Treatment <br /> A pump is used to extract impacted groundwater from extraction wells or dewatering <br /> trenches. The extracted groundwater is then treated using various techniques including <br /> E3-1S7:\E:\USA10065\REPORTS1006SP201.DOC-98usg:1 Rev.0,1/26199 <br /> 20A41-007.001 <br />