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tMr. James L. Barton ' January 17, 2008 Page 2 ' vertical and lateral extent of impacted groundwater, the redesign of the remediation system included replacing the existing AS piping, air compressor, and system controls. Additionally, the RSRT recommended the testing of the existing AS piping for integrity (pressurized air flow without leaks)and the ' AS points for operability (pressure, air flow), and to evaluate need to install new AS points to improve the ability to address the extent of vertical groundwater impacts. ENSR conducted the field testing in February and March 2007. Findings from ENSR's field testing included: ' • At 40 to 60 pounds per square inch (psi)of pressure, approximately 30 to 50 standard cubic feet per minute(SCFM) of air flow was being lost in the AS conveyance piping. ' • On the former Wards property, ENSR observed field measurements that confirmed sparging was occurring, but not at the deeper depths of the most impacted monitoring wells. • On the former Unocal property, ENSR observed pressure at the wellheads of the sparge wells, ' however, the sparge pressure was too low to establish air flow at these wells. • Air flow can be established in wells on both sides of Robinhood Drive by using a higher-pressure capacity air compressor than is currently being operated at the Site. The results from the field testing, the basis for the system re-design, are presented in ENSR's memo dated March 28, 2007, which is included as Attachment B. Based on the results from the field testing, ' ENSR designed the upgraded AS/SVE system and presented the design to the RSRT in May 2007 for a review of the design's technical soundness, compliance with EMC's safety devices/specifications, and ability to achieve the desired goals. Once a vault has been installed with a valve to isolate the conveyance ' line under Robinhood Drive and the dedicated piping for the new AS wells, the integrity of the conveyance line under Robinhood Drive can be further evaluated. If the additional testing indicates that the line has been compromised, a remedy will be proposed for implementation at that time. ' Comment No. 2 ' The Workplan does not include labeled geologic cross sectional views of the remediation well construction and the lithological sequence to be remediated. Submit two geologic cross sections oriented as an "X"(at right angles), and include the proposed remediation wells, along with the existing remediation and tmonitoring wells, within the lithology of the remediated zones. Response No. 2 The requested cross-sections are presented as Figures 5 and 6. ' Comment No. 3 Revise the map or plan view to include the lines of above cross sections indicated as an "X"on ' Attachment B Figure 2(attached). Response No. 3 ' Figure 4 shows the locations of the requested cross-sections presented in Figures 5 and 6. ' 01231-154