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HISTORIC UNDERGROUND STORAGE TANK INVESTIGATION WORK PLAN County of San Joaquin 630 N California Street St ckton, California 1.0 INTRODUCTION This work plan was prepared by CondorEarth Technologies, Inc. (Condor) to describe proposed subsurface investigation activities at 630 N. Califomia Street (Site) in Stockton, California (Figures 1, 2, and 3, Appendix A). The purpose of the wo k is to investigate the potential presence of an underground storage tank (UST) and associated potential soil contamination beneath the Site. The Site is owned by the County of San Joaquin (Client). The proposed work includes advancing three direct push borings to inspect soil and collect soil samples for laboratory analyses. All work conducted by Condor will be performed under the supervision of a State of California licensed Professional Geologist. This work plan includes project background information, a description of the field, laboratory, and reporting procedures proposed to conduct the work, and a project schedule. 2.0 PROJECT BACKGROUND A vent pipe consistent with those typically round associated with historic USTs is located immediately south of the west doorway to the warehouse flong the exterior wall (Figure 3, Appendix A). The southern adjoining property is the location of Stallworth Auto Sales (602 N. California St.), a former retail fueling facility with documented soil and groundwater contamination. Groundwater gradient directions measured at this location have been historically northeasterly to easterly, and the depth to groundwater is anticipated to be approximately 30 feet below ground surface (bgs). Groundwater beneath the Site is likely impacted by petroleum hydrocarbons. Groundwater contaminants include: benzene, toluene, ethyl benzene, and total xylenes (BTEX); the fuel oxygenates 1,2-dichloroethane (1,2-DCA) and tertiary-amyl methyl ether(TAME); total petroleum hydro arbons quantified as gasoline (TPH-G); and total petroleum hydrocarbons quantified as diesel (TPH-D). Condor acquired historic Sanborn® Fire Insurance Maps and City Directories (Appendix C) to ascertain the history of the Site. Prior to 1917, the Site was the location of the Stockton Electric Railroad Company car house and blacksmith repair shop. The buildings (current County Records Center and adjoining warehouse) located at 630 N. California Street were originally constructed in 1917, occupied by the Stockton Transfer Company. By 1940, the Site buildings were occupied by the Stockton Transfer Company and H.S. Dawson Van and Storage, possibly one company or two companies sharing the buildings. The warehouse contained vans and automobiles according to the 1950 Sanborn®Map. From at least 1970 until 1984, the warehouse was used for parking, and the main building was occupied by Morris Brothers Office Supplies and Equipment. The County of San Joaquin appears to have purchased the Site in the late 1980s. On March 30, 2011, Condor conducted a Site reconnaissance. The vent pipe was observed to be located immediately south of the west doorway to th warehouse along the exterior building wall. Plastic tubing was inserted into the top of the vent pipe and threaded down to ground level until resistance was encountered. A photoionization detector(PI ) was attached to the free end of the tubing and allowed to purge ambient air from the tubing. After app oximately 10 minutes of continuous operation, the PID did CONDOR