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i !I Workplan for Additional Assessment and Sensitive Receptor Survey Tracy Office Plaza 324 E. 11th Street,Tracy,CA January 27,2017 Additional Site Assessment Report dated October 8,2014. The additional site assessment was completed in accordance with the approved Workplan for Additional Assessment and Subslab Gas Sampling dated November 22,2013.This additional site assessment was performed to define the lateral and vertical extent of contamination identified in Pangea's Phase II Environmental Assessment Report dated July 23,2013. Site Geology& Hydrogeology Soil from site borings consisted primarily of silty clay to a depth of approximately 5 to 9 ft bgs,underlain by more permeable sandy clays or clayey sands observed to a depth of approximately 25 ft bgs. Wet soil(possible groundwater) was encountered in the more permeable sandy clay or clayey sand layers encountered at approximately 8 to 11 ft bgs. Soil contamination is primarily located between 1 and 10 ft bgs based on field observations and analytical results. REGUALTORY GUIDANCE In the Additional Site Assessment Report(Report)dated October 8,2014,Pangea recommended conducting a well survey within a 1,000 ft of the site to determine if the site meets LTCP criteria for groundwater.In a letter dated March 15,2016,San Joaquin County Environmental Health Department(SJCEHD)requested additional assessment for the following reasons: 1)the usage of each of the six former USTs has not been documented;it is possible that one or more may have been utilized for waste oil, and 2)the B-1 and B-6 soil data can be interpreted as having a shallow source and the groundwater data from borings B-1 and B-6 can be interpreted as potentially indicating two separate sources if groundwater flow is predominately north-northwest, so additional data from the east margin of the site should be obtained to test the one-source model. In response to Pangea's well survey recommendation,SJCEHD requested that Pangea review records for Tracy High School to determine if a sensitive receptor survey had already been completed.Pangea found elements of a sensitive receptor survey were completed in the No Further Action Required Request Report by Conestoga- Rovers&Associates,dated September 2009. However,this report did not include a well survey.Therefore, Pangea will perform a well survey within 1,000 R of the site to determine if the site meets LTCP criteria for groundwater. PROPOSED INVESTIGATION The proposed scope of work to address these concerns is provided below. The objective of the proposed investigation is to determine if there is impact from a waste oil tank and to delineate the contamination in the eastern margin of the site. To facilitate this assessment Pangea proposes to install two soil borings to 10 ft depth and one contingent soil boring to 5 ft depth. 2