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Workplan for Additional Assessment and Sensitive Receptor Survey Tracy Office Plaza 324 E. 11th Street,Tracy,CA January 27,2017 INTRODUCTION On behalf of Tracy Office Plaza LLC, Pangea Environmental Services, Inc. (Pangea) has prepared this Workplan for Additional Assessment and Sensitive Receptor Survey(Workplan). This proposed work was requested in a San Joaquin County Environmental Health Department(SCEHD)letter dated March 15,2016. The purpose of the additional assessment is to evaluate potential impact from a waste oil tank and to delineate contamination in the eastern margin of the site. SITE BACKGROUND Site Description The subject site is an office building operated by Tracy Office Plaza,LLC located at the intersection of East Street and E. 11 th Street in Tracy,CA(Figure 1).The site consists of offices and a large parking lot.Land use surrounding the site is predominantly commercial with residential land use present 275 ft southwest ofthe site (upgradient).Additional site background information is provided in the Phase I Environmental Site Assessment report.The Phase I identified concerns regarding the property being the location of a truck/auto station from the 1950s until 1973. In 1973, a permit was obtained to demolish the station and remove six USTs. No documents confirming the removal of the USTs have been found to date at the San Joaquin County Environmental Health Department or the Central Valley Regional Water Quality Control Board. The Phase I also identified petroleum hydrocarbons north of the site at Tracy High School. The estimated groundwater flow direction at the Tracy High School site was northerly,indicating that the subject property is upgradient of Tracy High.The Tracy High School case was closed in March 2009.The locations of four of the former six monitoring wells is shown on Figure 1.The Phase I also recommended a subsurface investigation to determine if the source of hydrocarbons at Tracy High School is the subject property. As part of a Phase 11 Environmental Assessment,Pangea coordinated a geophysical survey utilizing ground penetrating radar(GPR), electromagnetic utility locating techniques,and a metal detector to survey the area where the former USTs were potentially located. Geophysical surveying did not identify any USTs but did identify a potential 20-ft long underground pipe anomaly near the potential former tank location.Following the completion of the geophysical survey,Pangea coordinated the installation of six soil borings(B-1 through B-6) onsite.Hydrocarbon contamination was detected in soil and/or groundwater in borings B-1,B-4 and B-6.The investigation results were reported in Pangea's Phase II Environmental Site Assessment dated July 23,2013. On July 10,2014,Pangea coordinated the drilling of four soil borings(B-7S,B-713,B-8 and B-9)onsite and one soil boring(B-10)offsite at Tracy High School. The results from this investigation are described in the 1