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II a CONDOR EARTH TECHNOLOGIES INC -� 188 Frank West Circle Suite I Stockton CA 95206 Phone 209.234.0518 FAX 209.234.0538 CONDOR www, condorearth .corn June 1 , 2011 Ms. Derry Wasson Assistant Director Facilities Management County of San Joaquin 44 N. San Joaquin Street, Suite 590 Stockton, CA 95202 Re: Historic UST Investigation, 630 N. California St., Stockton, San Joaquin County, California Condor Project No. 5960B Dear Ms. Wasson: Condor Earth Technologies, Inc. (Condor) prepared this report of findings for the Historic Underground Storage Tank (UST) Investigation conducted at 630 N. California Street, Stockton, California (Site) (Figure 1 , Attachment A) . This report includes Site background information, a description of field activities, laboratory analyses, and conclusions. This report presents results of subsurface soil sampling conducted on May 5, 2011 at the Site. The primary objective of the work described herein was to determine whether a UST and associated contamination is present at the Site. SITE BACKGROUND INFORMATION A vent pipe consistent with those typically found associated with historic USTs is located immediately south of the west doorway to the warehouse along the exterior wall (Figure 2, Attachment 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 hydrocarbons quantified as gasoline (TPH-G); and total petroleum hydrocarbons quantified as diesel (TPH-D). Condor acquired historic Sanborn@ Fire Insurance Maps and City Directories to ascertain the history of the-Site.. Prior to 1917, the Site-was the location of-th"tockton 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.