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/; -1 Lomurvo G bmmv J. <br /> M... "Hooxro... <br /> WaterBoards `/ ,.,Vran­„r.N,a 1-F-TCTI— <br /> Central Valley Regional Water Quality Control Board <br /> 28 October 2013 <br /> OCT 3 02013 <br /> ENVIRONMENT HEALTH <br /> Mr. Kevin Dyer PERMIT/SERVICES <br /> Shell Oil Products US <br /> 17 Junction Drive, PMB #399 <br /> Glen Carbon, IL 62034 <br /> REVIEW OF INVESTIGATION REPORT AND UPDATED SITE CONCEPTUAL <br /> MODEL, FORMER SHELL OIL PIPELINES CORDES RANCH, HANSEN ROAD, <br /> SAN JOAQUIN COUNTY <br /> Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 13 May 2013 Subsurface Investigation Report and Updated <br /> Site Conceptual Model submitted on your behalf by Conestoga-Rovers and Associates <br /> (CRA) for the subject site. In the report, CRA used current and historical site data to <br /> update the site conceptual model (SCM) for the former crude oil pipeline located within <br /> a portion of the Cordes Ranch commercial development, which is adjacent to the City of <br /> Tracy. As CRA indicated in the SCM, 126 borings and 19 well borings were drilled at <br /> the site along the former two mile pipeline section of interest. Concentrations as high as <br /> 79,000 mg/kg consisting of primarily total petroleum hydrocarbons as crude oil (TPH-c) <br /> were detected in soil samples from the borings. Depending on the boring, contaminants <br /> were detected at depths ranging from five to seventy feet below ground surface (bgs), <br /> with the majority of soil impacts occurring above 35 feet bgs. The SCM also shows that <br /> groundwater is impacted with TPH-c and other petroleum contaminants. During the <br /> third quarter 2013 monitoring event, contaminants were detected in groundwater <br /> samples from seven of the wells. The table below shows contaminant concentrations <br /> detected during the monitoring event. <br /> Third Quarter 2013 Monitorin I Results /I <br /> Well TPH-c1 Benzene Toluene Ethyl- Total <br /> Benzene Xylenes <br /> MW-2 9,300/5,500 320 1 <2.0 2.2 <2.0 <br /> MW-5A SPH = 0.02' <br /> MW-9 2,900/2,100 <0.5 <1.0 <1.0 <1.0 <br /> MW-10 280/<250 <0.5 <1.0 <1.0 <1.0 <br /> MW-13C 350/<250 <0.5 <1.0 <1.0 <1.0 <br /> MW-14B 1,400/1,100 <0.50 <1.0 <1.0 <1.0 <br /> MW-15 SPH = 0.02' <br /> 1 =Concentrations before and after Silica Gel Cleanup <br /> <=Less than detection limit <br /> SPH=Separate phase hydrocarbons measured in feet <br /> KARL E _oNCLev Sc[) P.E. CHAIR I PAMELA C. CREEooN P.C.. BCEE EXEOOTIVL Orr'CER <br /> 11020 Son Center[rive 9200, Rancno Co rOova.CA 95670 1 wvrw waterbo a rCs.ca nov/cen Iva i va I!ey <br /> Cir I c.am.,�,morn <br />