Laserfiche WebLink
f.� 19449 Riverside Drive, Suite 230, Sonoma,California 95476 <br /> Telephone: 935-4850 Fax: (707)935-6649 <br /> www.CRAworld.crld.com <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES <br /> May 4,2012 Reference No.2417219 /C <br /> Ms.Kristi Shelton RECEIVED <br /> C® <br /> Central Valley Regional Water Quality Control Board <br /> 11020 Sun Center Drive,Suite 200 MAY 0 7 2012 <br /> Rancho Cordova,California 95670 ENVIRONMENTAL HEALTH <br /> Re: Trend Analysis PERMIT/SERVICES <br /> Shell Stockton Terminal <br /> 3515 Navy Drive <br /> Stockton,California <br /> SAP Code 356164 <br /> Incident No. 300002 <br /> Agency No. 390247 <br /> Dear Ms.Shelton: <br /> Conestoga-Rovers &Associates (CRA) prepared this letter on behalf of Equilon Enterprises LLC <br /> dba Shell Oil Products US(Shell)in response to the Central Valley Regional Water Quality <br /> Control Board's April 19,2012 letter to Shell regarding the referenced site. It was noted in the <br /> letter that our March 15,2012 Feasibility Study and Corrective Action Plan (FSCAP) did not <br /> contain a rationale for selecting the starting dates used in the groundwater petroleum <br /> constituent concentration trend analyses presented in the FSCAP. Our rationale is presented <br /> below. <br /> CRA uses the guidance provided within the United States Environmental Protection Agency <br /> (EPA) document Calculation and Use of First-Order Rate Constants for Monitored Natural <br /> Attenuation Studies (November 2002) to estimate the time to reach water quality objectives. <br /> Additionally,CRA also uses the EPA document On-line Tools for Assessing Petroleum Releases <br /> (September 2004) to assess the proper methodology of determining where to begin a trend <br /> analysis. As described in the latter document on page 24,a receptor(in this case,a monitoring <br /> well) is located some distance from the source,and no impact to the receptor is seen when the <br /> release first occurs. Time is required for the analyte to travel to/reach the receptor. The first <br /> data point that shows an analyte detection is called the first arrival time. The first arrival time <br /> varies for each receptor based upon distance from the receptor and the transport rates through <br /> the heterogeneous medium. As the analyte plume expands and stabilizes,the analyte <br /> concentration will reach the maximum concentration. If the source of the release is finite <br /> (Le,a single release from an underground storage tank),the concentration will eventually <br /> decrease from the maximum to below the concentration of concern. This period is called the <br /> duration. <br /> Equal <br /> Employment Opportunity <br /> Employer <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />