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Californiam-'Llegional Water Quality Coil Board <br /> Central Valley Region <br /> IJKarl E. Longley,ScD,P.E.,Chair <br /> Sec S.Adams ecremryfor Sacramento Main Office Arnold <br /> Environmental 11020 Sun Center Drive#200,Rancho Cordova,California 956766114 Sehwarzenegger <br /> Protection Phone(916)464-3291 •FAX(916)464-4645 Governor <br /> http://www.waterboards.ca.gov/centralvalley ,—,Ir�^r� �y j; r(�- DD <br /> I UBAAPRRR I1 4\P200888 <br /> 8 April 2008 <br /> ENVERRMH <br /> IT/SERVICES <br /> P <br /> Mr. Jeff Whitworth <br /> Shell Oil Products US <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> REVIEW OF SITE INVESTIGATION REPORT, rORMIEFR SHELL CENT PAL VALLEY <br /> CRUDE OIL PIPELINES, HANSEN ROAD NEAR SCHULTE ROAD, TRACY, SAN JOAQUIN <br /> COUNTY <br /> Staff of the California Regional Water Quality Control Board, Central Valley Region (Regional <br /> Water Board) has reviewed the 6 August 2007 Site Investigation Report, Former Shell Central <br /> Valley Crude Oil Pipelines, Cordes Ranch, Tracy (Report) submitted by Science Application <br /> International Corporation (SAIC) on behalf of Shell Oil Products US (Shell). The Report <br /> details the results of further investigation of petroleum hydrocarbons dissolved in groundwater <br /> through vertical profiling. In addition, soil vapor samples were collected to evaluate the <br /> potential threat to indoor air quality of future developments. It is our understanding that the <br /> property is slated for development as a commercial property. <br /> Two borings were advanced using a cone penetrometer testing (CPT) rig approximately 100 <br /> feet northeast (inferred down gradient direction) of the former pipeline in the area of Trench 3 <br /> where previous deeper groundwater samples had been collected. Groundwater samples were <br /> collected using a Hydropunch sampling tool at 15 to 30-foot depth intervals between 40 and <br /> 150 feet below ground surface (bgs). The samples collected from B-75 contained <br /> concentrations of Total Petroleum Hydrocarbons (TPH) as crude oil (TPHcr) ranging from less <br /> than the detection limit of 470 micrograms per liter (pg/L) at a depth of 40 feet BGS to a <br /> maximum concentration of 14,000 pg/L at a depth of 120 feet BGS. Similarly TPH as diesel <br /> (TPHd) ranged in concentration from 51 Ng/L at 40 feet BGS to 2,700 Ng/L at 120 feet BGS. <br /> Whereas TPHcr was not detected in any of the groundwater samples collected from B-76 <br /> (detection limits of 470 to 490 pg/L), TPHd was detected in most of the B-76 groundwater <br /> samples with a maximum concentration of 100 pg/L. <br /> Soil vapor samples were collected through temporary soil gas probes advanced using a CPT <br /> rig in four boring locations near where benzene had previously been detected in groundwater. <br /> Soil gas samples were collected at depths of 6, 16, and 30 feet in each of the four locations. <br /> Three of the vapor probe boring locations contained benzene at depths of 16 and 30 feet bgs <br /> with higher concentrations at the greater depth. Concentrations at 30 feet bgs in B-70 through <br /> B-72 ranged from 1,800 to 390,000 micrograms per cubic meter (Ng/m3) whereas <br /> concentrations at 16 feet bgs ranged from 4.5 to 530 Ng/m3. Benzene was detected in one of <br /> California Environmental Protection Agency <br /> Qa Recycled Paper <br />