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MC TDecember 13,2016 N T Page 4 of 8 SENSITIVE RECEPTORS In August 2011, ATC Associates, Inc. performed a '/-mile sensitive receptor survey for the site. ATC reviewed Water Well Drillers Reports on file with the North Central Region branch of the California Department of Water Resources (DWR) in West Sacramento, California. Based on information provided by the DWR, one municipal well, three domestic wells, and two irrigation wells were identified within '/-mile of the site; ATC omitted inclusion of any wells identified as being used for monitoring, remedial, or cathodic protection purposes. The closest well, an irrigation well, was identified as being located approximately 1,350 feet west of the site; all other identified wells were determined to be located at distances of greater than 2,000 feet from the site. Two additional wells may be located within'/-mile of the site, but due to a lack of information, the precise locations of the wells could not be determined. ATC did not attempt to field-verify the presence of any of the identified wells. In August 2011, ATC performed an internet-based search for other potential receptors located within '/z-mile of the site. The search attempted to identify any hospitals, schools, or nursing homes located within '/2-mile of the site. Based on a review of identified receptors, one elementary school, Rio Calaveras Elementary School, was identified approximately 1,450 feet east-southeast of the site. Heald College, a private school catering to part-time students is located approximately 1,000 feet northeast of the site. Rio Las Palmas, a retirement home, is located approximately 1,050 feet west-northwest of the site. No hospitals were identified within Yz-mile of the site. CHARACTERIZATION STATUS Based on a review of recent and historical soil analytical data, the observed distribution of petroleum hydrocarbons in soil beneath the site suggests the impact observed at depths of 40 feet bgs and greater are related to hydrocarbons adsorbed to soil. An apparent confining unit at 68 feet bgs may separate the impacted soil from deeper depths and a deeper water bearing zone at approximately 80 feet bgs. Recent assessment results indicated groundwater is defined laterally to the northeast, east, and southeast. Groundwater does not appear to be defined vertically. REMEDIATION STATUS Other than over-excavation of impacted soil conducted in 1991 during UST removal and replacement activities, active remediation has not been performed at the site. On December 17, 18, 19, and 20, 2012, Cardno ATC performed SVE and AS pilot testing at the site. Recently-installed SVE wells SVE-1, SVE-2, and SVE-3 were utilized as the extraction points for the SVE pilot test utilizing a mobile thermal oxidizer. The SVE wells were connected to the thermal oxidizer utilizing aboveground temporary PVC pipe. Well AS-1 was used as the sole injection point for the air sparge pilot test. The air sparge well was connected to a portable air compressor utilizing a temporary air hose. Results of the pilot testing concluded that AS combined with SVE was a viable approach for remediating soil and groundwater beneath the site. The effective radius of influence for this alternative was estimated to be less than 40 feet for the vapor extraction wells based on field observations and less than 30 feet for the air sparge wells. PROPOSED SCOPE OF WORK In correspondence dated October 5, 2016, the RWQCB requested additional assessment to evaluate the lateral and vertical extent of petroleum impacts at the site. ATC proposes to advance