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' and 6.3 m respectively. Well MWO-lx (pumped for 4.4 hours sustained a flowrate of 1 gPP P approximately 6.0 gpm. Average.MTBE concentrations in the influent water streams from the three wells were 240, 87 and 196 µg/L, respectively. SECOR estimated a mean transmissivity of 940 gallons per day(gpd), a hydraulic conductivity of 3.8x7 0-3 cm/sec, and a capture zone of 127 feet downgradient. This report concluded that GWE was not a cost-effective alternative for the site. Results of these investigations were summarized in SECOR's Additional Assessment Report, dated June 27, 2006. During February and March 2007, Environmental Remediation Group (ERG) installed seven additional groundwater monitoring wells to further evaluate the vertical and lateral distribution of MTBE impact in Sand A (MW-14A and MW-15A), Sand B (MW-14B and MW-15B), and l Sand C (MW-12C and MW-13C). In addition, one well (MW-13A/B) was installed with a screen length spanning both the Sand A and B intervals. Analytical results of groundwater samples collected from the newly installed wells showed very low MTBE impact in C zone well MW-13C and moderate concentrations (ranging from 58 to 72 gg/L) in downgradient wells MW-13A/B and MW-15A. Results of this investigation were summarized in ERG's Additional Groundwater Assessment Report, dated April 16, 2007. In August 2009 in anticipation of regulatory case closure, Stratus advanced and sampled eight temporary soil vapor points (V-1 through V-8) on the site property and on the Storage-Pro property to the north of the site. A comparison of the results of the soil gas samples against RWQCB-SF's ESLsI using the residential values indicate that ESLs were not exceeded for any chemical analyte in any of the eight samples collected. Given these results, Stratus concluded that the potential risk for vapor intrusion concerns at the site and in areas surrounding the site 4✓ above the residual impacted groundwater appears low and the performance of an HHRA does not appear warranted. Results of this investigation were summarized in Stratus' Soil Gas Investigation, dated September 10, 2009. 2.3 Sensitive Receptor Survey In January 2000, Avalon conducted a sensitive receptor survey. The sensitive receptor survey consisted,of identifying any domestic, municipal, agricultural, industrial, and any other wells within a 2,000-foot radius of the site. This included contacting the California Department of Water Resources (DWR), municipal suppliers, and any other nearby industries to search for wells. In addition, the survey included a physical search of the area to locate wells, conduits or other receptor risks. Based on the information reviewed and the physical search of the area, no domestic or commercial wells were identified within the search radius. Avalon's sensitive receptor survey report is included as Appendix B. In October 2009, . Stratus augmented the original sensitive receptor survey by reviewing topographic maps, satellite images, and other online resources. According to the USGS 7.5' ( quadrangle topographic map of the:area (photorevised 1980) and Google Earth satellite photos, no surficial water bodies are located within the 2000-foot survey radius; the nearest surficial RWQCD-SP's Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater INTERIM FINAL.—November 2007 a (Revised May 2008),Table E-2(Shallow Soil Gas Screening Levels for Evaluation of Potential Vapor Intrusion Concerns) Page 9 STRATUS