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The DPE system is permitted for operation through the City of Stockton, authorizing <br /> discharge of treated groundwater to the sanitary sewer, and the San Joaquin Valley Air <br /> Pollution Control District(SJVAPCD),authoring operation of the oxidizer. <br /> 3.3 DPE SYSTEM OPERATION <br /> The DPE system began operation in April 2007. The DPE system was shut off on <br /> February 2, 2009 due to de minimus vapor recovery rates which indicated the system <br /> had reached its effective limit. Tables 1 through 4 present the DPE system operational <br /> data. The following sections discuss the operational data. <br /> 3.3.1 VAPOR CONCENTRATIONS <br /> At the beginning of remediation,starting with the temporary SVE system,influent TPHg <br /> and benzene concentrations were 11,000 and 100 parts per million by volume (ppmv), <br /> respectively. As previously stated, the temporary SVE system was extracting only from <br /> well VEW-7. These influent vapor concentrations decreased with time as shown on <br /> Figure 3. Once the DPE system was started, the extraction wells were routinely <br /> alternated based on field-measured vapor concentrations in order to optimize <br /> vapor-phase mass removal of petroleum hydrocarbons. As depicted in Figure 3, the <br /> influent vapor concentrations have remained low and stable regardless of optimization <br /> efforts. The final vapor concentration, in ppmv, from each extraction well were as <br /> follows; <br /> VEW-1 VEW-2 VEW-3 VEW4 VEW-5 VEW-6 VEW-7 <br /> 25 270 110 <5.0 100 110 355 <br /> 3.3.2 MASS REMOVAL <br /> During DPE, a vacuum of 20 to 25 inches of mercury was applied to the well field in <br /> order to dewater the wells using the stingers. Each extraction well yielded soil vapor <br /> flows ranging from 20 to 40 standard cubic feet per minute (scfm). Figure 4 presents the <br /> TPHg and benzene mass removal rates versus time. Since the flow rate from each well is <br /> fairly consistent, the mass removal rate follows a trend similar to the vapor <br /> concentration trend in Figure 3. Variations are attributed to alternating extraction wells <br /> for optimization. As of February 2, 2009,the DPE system removed in total 2,543 pounds <br /> xxxXx(X%) 5 CONESTOGA-ROVERS S ASSOCIATES <br />