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14 Californi fVegional Water Quality CoarolBoard <br /> Central Valley Region - <br /> v Katherine Hart,Chair <br /> Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Edmund Brown Jr. <br /> Acting Secretaryfor Phone(916)464-3291 •FAX(916)464-4645 Govvee rnor <br /> Environmental Protection http://www.waterbouds.ca.gov/centralvalley <br /> RECEIVED <br /> Mr. Ed Ralston JAN 07 2011 5 January 2011 <br /> ConocoPhillips <br /> 76 Broadway <br /> Sacramento, CA 95818 ENVIIROMI E TA ICHEALTH <br /> S TPERH <br /> LIMITED EXCAVATION REPORT, FORMER UNION OIL BULK PLANT NO. 788, <br /> 8203 EAST 11TH STREET, TRACY, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 16 December 2010 Limited Excavation Report (Report) prepared by <br /> Stantec Consulting Corporation (Stantec) on behalf of ConocoPhillips for the former Union Oil <br /> Bulk Plant at 8203 East 11th Street in Tracy (Site). <br /> The Site is a former bulk fuel storage facility in the City of Tracy. In 1993, Site operations ceased, <br /> and all the tanks and associated piping and structures were removed. The Site is currently <br /> vacant and no longer in use. Since 1989, Union Oil (now ConocoPhillips) has installed 13 soil <br /> borings, sampled 13 test pits, collected 55 soil samples, and installed and sampled <br /> 10 monitoring wells. In the first half of 2009, ConocoPhillips properly abandoned all Site <br /> monitoring wells, excavated contaminated soil to depths of up to 10 feet below ground surface <br /> (bgs), installed five temporary soil .gas vapor probes, and collected soil gas samples. <br /> In November 2010, ConocoPhillips excavated additional soil in the area of the elevated soil gas <br /> sample locations. The excavation dimensions were 22 feet long by 18 feet wide and 8.5 feet <br /> deep. ConocoPhillips excavated soil until all visually contaminated soil was removed and then <br /> collected sidewall and floor samples from the excavation. None of the soil samples contained <br /> petroleum hydrocarbons above the laboratory detection limit. <br /> Central Valley Water Board staff concurs with the recommendation to conduct one additional soil <br /> gas sampling event in February 2011 to confirm that soil gas levels in the area of the excavation <br /> are below the California Regional Water Quality Control Board — San Francisco Bay Region <br /> Environmental Screening Levels for residential scenario. By 30 March 2011, please install and <br /> sample a soil gas sampling point near the previously high soil gas locations and submit a report of <br /> findings. The report of findings needs to include recommendations for additional work, if <br /> necessary. If you have any questions, you may contact me by phone at (916) 464-4819 or by <br /> email at ksheltonaa.waterboards.ca.ctov. <br /> KR SHELTON, P.E. <br /> Water Resources Control Engineer <br /> Aboveground Tanks Cleanup Unit <br /> cc: Ms. Adrienne Ellsaesser; San Joaquin County Environmental Health Department, Stockton <br /> Mr. Mark Bare, Stantec Consulting Corp., Rancho Cordova <br /> California Environmental Protection Agency <br /> 19: He'rvled Paper' <br /> bC <br />