SITE INFORMATION AND CORRESPONDENCE_2004-2014

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Mr. Maurice Benson January 13, 2010 Page 3 Specific Comments 1.) Sheet #3, P-5A Source Area Soil Gas and Groundwater Well Locations; Comparing the TCE soil vapor analytical results from Figure 6-1 of the comprehensive cone-penetrometer testing results to Sheet #3, identifies that the current placement of SVE wells corresponds in general to locations where elevated concentrations of TCE in soil vapor were detected. For example, the placement of SVE-4 agrees with the TCE vapor detected at CP1145, and SVE-5 corresponds to the high vapor levels at SB1104. DTSC notices that CP1127 recorded TCE vapors as high as 1200 ppbv yet there are no SVE wells proposed in the general vicinity. As presented, the closest SVE well to the known contamination at CP1127 is SVE-1, but this well is over 50 feet to the east of the location leaving the next closest SVE well as SVE-2 which is at least 75 feet to the north of the CPT1127 location. DTSC recommends that the current SVE system layout be re-evaluated to determine whether the current well placement is adequate to remediate the soil vapors present at CP1127. If the evaluation deems the system provides inadequate coverage for the remediation of CP1127 vapors, then the design should be modified with either rotating the current SVE system layout or adding an additional SVE well to the system design. DESJC should clearly identify in the report the planned actions to remediate the TCE vapor concentrations at CP1127. 2.) Page 5, section 3.4.1.2; The design proposes that carbon units are to be sampled before the first and after the second carbon unit. Sampling after the second carbon unit that is in parallel with the first would only provide a composite sampling result, which wouldn't provide any useful information on the individual performance of the carbon vessels, including breakthrough. DTSC recommends that additional sampling ports are installed on each of the carbon vessels' effluent lines for individual assessment of each carbon vessel's performance. 3.) Page 4, section 3.3.3; The report states that the planned SVE blower operating at 1,600 revolutions per minute (rpm) will provide 150 standard cubic feet per minute flow between 2 to 12 inches of mercury vacuum. Reviewing Table 1 for the SVE friction loss and Figure 1 for the blower curves indicates that the current system design at 1,600 rpm will be operating the blower at the upper end of its operational capacity, which would not allow for added flexibility if future modifications to the system are necessary. Additionally, the current design does not specify whether the blower motor includes a variable frequency drive (VFD).