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t Mr. Robert McClellon November 1, 2010 Page 2 October 15, 2010 SCS Response to Environmental Health Department Comment No. 4— Based on conversations with CalRecycle and the EHD, Forward will perform an evaluation to shift the locations of the SVE wells that will be satisfactory to both agencies and that will still be optimal for LFG migration control. Forward will supply this evaluation and new SVE well locations to CalRecycle and the EHD within 5 days. Evaluation by Cornerstone SVE Well Design Review Cornerstone evaluated the proposed locations of the SVE Wells SVE-1 through SVE-10 as shown in the October 1, 2010 Work Plan, their proximity to the existing landfill gas (LFG) monitoring probes (GP-10, GP-11, and GP-12), their well and wellhead design, and local geologic conditions. Based on our evaluation, it is our opinion that the proposed location and design of each of the SVE wells is acceptable if installed as designed and operated using good industry practice. Each SVE well is designed with a vacuum control valve which will control the effective radius of influence (ROI) of the well (see Attachment B, Sheet 8 of 13, of the Work Plan). The control valve allows the applied vacuum at the SVE well to range from zero inches of water column to the maximum system vacuum available within the gas collection and control system(GCCS). The locations of the SVE wells should be in relatively close proximity to the perimeter monitoring probes. The SVE wells will have individual control valves that can limit the amount of applied vacuum, which impacts their effective ROI (turning the vacuum off will reduce the ROI to zero while increasing the vacuum will increase the ROI). Since the effect of the SVE wells on the LFG migration will be determined during initial operation and monitoring (See Operation and Monitoring section below), it is important to locate the SVE wells close enough to the perimeter monitoring probes so that the probes can be utilized to verify that operation of the SVE wells has a positive impact on controlling LFG migration and to verify that the ROIs of the SVE wells are able to control the LFG migration along the entire landfill perimeter including the area between the perimeter monitoring probes and the landfill. Based on review of the LFG migration, the geology as documented in the existing perimeter monitoring probes boring logs, and the available vacuum available to be applied to the SVE wells, as performed by Cornerstone and by Andrew Romolo, a California registered geologist at Terraphase Engineering Inc., the current proposed SVE well locations are appropriate. Locating the SVE wells further apart or further from the probes may not allow for an effective ROI from the SVE wells under full system vacuum to effectively control LFG migration along the full site perimeter including the area between the perimeter monitoring probes and the landfill. In addition, the proximity of the monitoring probes to the SVE wells will allow for the collection of data that can verify the ROI of the SVE wells and the effect that the ROI has on the migration of LFG.