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California�egional Water Quality Cool Board <br /> Central Valley Region <br /> ` Karl E.Longley,ScD,P.E.,Chair <br /> Linda S.Adams Arnold <br /> Secretaryfor 11020 Sun Center Drive 9200,Rancho Cordova,Cal ifomia 95670-6114 Schwarzenegger <br /> Proseectionction <br /> Phone(916)464-3291 •FAX(916)464-4645 <br /> Envrrol htip://wwwwaterboar s.ca.gov/centralvallev Governor <br /> RECE V„ED <br /> 29 September 2009 <br /> SEP 3 0 2009 <br /> Mr. Joe Lentini ENVIRONMENT HEALTH <br /> Shell oil Products US PERMIT/SERVICES <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> REVIEW OF SITE CONCEPTUAL MODEL, FORMER SHELL CRUDE OIL PIPELINES, <br /> HANSEN ROAD NEAR SCHULTE ROAD, TRACY, SAN JOAQUIN COUNTY <br /> In a letter dated 13 March 2009, staff of the California Regional Water Quality Control Board, <br /> Central Valley Region (Central Valley Water Board) directed Shell Oil Products US (Shell) to <br /> conduct a feasibility study to identify the most appropriate course(s) of action to cleanup the <br /> soil impacts and to submit a work plan to install monitoring wells at the former Shell Crude Oil <br /> Pipeline site on Hansen Road near Schulte Road in Tracy. In addition, Central Valley Water <br /> Board staff extended the due date for testing nearby water supply wells or providing <br /> justification for not needing to sample the wells. In response, Conestoga-Rovers & Associates <br /> (CRA) on behalf of Shell discussed alternative steps to completing these tasks with Central <br /> Valley Water Board staff and presented additional details and a proposed schedule of the <br /> alternative steps in a letter dated 15 June 2009. To support the tasks of preparing a feasibility <br /> study and monitoring well work plan and completing the water supply well assessment, Shell <br /> proposed to first prepare and submit a site conceptual model (SCM). CRA on behalf of Shell <br /> submitted the Site Conceptual Model, Former Shell Central Valley Crude Oil Pipeline, Cordes <br /> Ranch, Tracy, California on 1 September 2009. The purpose of the SCM is to describe the <br /> relationship between the source area, transport pathways, and potential receptors based on a <br /> review of available data. The SCM also includes a schedule that proposes submitting a <br /> monitoring well installation work plan by 15 October 2009 and a risk assessment work plan by <br /> 30 October 2009. <br /> BACKGROUND <br /> According to the SCM, Shell removed a pipeline from the Cordes Ranch property in 2001 in <br /> anticipation of scheduled development. During the removal, six areas referred to as Trenches <br /> 1 through 6 were observed to be impacted by petroleum hydrocarbons. Two of the areas were <br /> over-excavated to a maximum depth of 20 feet. Several subsequent investigations showed the <br /> areas of concern to correspond to Trenches 2, 3, and 4 with Total Petroleum Hydrocarbons as <br /> crude oil (TPHc) up to 31,780 milligrams per kilogram in soil and 730,000 micrograms per liter <br /> (Ng/L) in groundwater. Benzene concentrations up to 620 pg/L have been detected in shallow <br /> groundwater. <br /> The investigations conducted to date have identified dissolved phase petroleum hydrocarbons <br /> extending significantly below first encountered groundwater. Groundwater is first encountered <br /> at approximately 30 feet below ground surface. Near Trench 3, some of the highest TPHc in <br /> California Environmental Protection Agency <br /> rbc Reci cred Paper <br />