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Mr. Cervantes 16 October 2012 Page 3 µg/m3) exceeded the CHHSL of 603 µg/m3 for commercial use. Therefore, SVE system optimization testing will be conducted in the vicinity of these sampling locations and will include vapor extraction from the following wells(Figure 3): • Soil vapor extraction wells SVE-3, SVE-4, SVE-5, and SVE-7 in the northern portion of the Site near SG-1; • Soil vapor extraction wells SVE-1, SVE-2, SVE-17, SVE-19, and SVE-23 in the central portion of the Site near SG-3; and, • Soil vapor extraction wells SVE-26, SVE-27, and SVE-30 in central portion of the Site near SG-4. To evaluate the residual mass of PCE in the vadose zone and determine if mass removal rates can be significantly improved, the SVE wells listed above will be pulsed such that they are operated for one week, shut down for four weeks to allow concentrations to equilibrate, and then restarted for one week. This pulsing cycle will be repeated at least twice. The need for additional pulsing cycles will be determined based on the magnitude of change in PCE concentrations over the course of the pulsing cycle. If significant rebound in PCE concentrations between pulsing events is not observed or PCE concentrations remain below the CHHSL, pulsing will cease and the system will be shut down. If significant increases in PCE concentrations (by more than 501/o) are observed during the pulsing cycle, an additional pulsing will cycles will be conducted. The test will include a maximum of three pulsing cycles. Vapor samples will be collected for laboratory analysis from four key SVE wells within 30 minutes after starting or 30 minutes prior to shutting down the SVE system. The key wells were selected based on their proximity to the areas where PCE concentrations have exceeded the CHHSL and include SVE-5, SVE-17, SVE-19, and SVE-26. Soil vapor samples intended for laboratory analysis will be collected in Summa canisters and analyzed using USEPA method TO-15 by Test America Laboratories. A minimum of three well volumes will be purged from the SVE wells using a vacuum pump prior to sample collection. In addition to the samples collected for laboratory analysis described above, vapor from each SVE well operated during the SVE system optimization testing will be analyzed in the field using a part per billion photoionization detector (PID) during each sampling event. Soil vapor samples collected for field measurement using the PID will be collected and analyzed in dedicated Tedlar® bags. Wells will be purged a minimum of three well volumes prior to collection of soil vapor samples for PID analysis. The PID will be calibrated at least once per day during use. 20121000-SVE Optimization and Confirmation Testing engineers I scientists I innovators