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California " ,gional Water Quality Con" l Board a. .> <br /> Central Valley Region <br /> Karl E. Longley,ScD, P.E.,Chair <br /> Linda S. Adams Arnold <br /> � � <br /> 11020 Sun Center Drive P200. Rancho Cordova.Calilornia 9>67f�-61 14 <br /> Phone(916)464-3291 •FAX(916)464-4645 Schwarzenegger <br /> l.m11 unmcnt<<1 Gore rnor <br /> http://xvww Nvaterhoards ca.eovlcemralvalle\ <br /> Prole('ll/)n <br /> FU �l��D <br /> 22 January 2009 <br /> JAi"I ;2 LU; 9 <br /> ENVIRUNMLI, f LEIALTH <br /> Mr. Joe Lentini <br /> Shell Oil Products US PERMIT/SERVICES <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> REVIEW OF WORK PLAN, FORMER SHELL CENTRAL VALLEY CRUDE OIL PIPELINES, <br /> NEIGHBORHOOD B, MOUNTAIN HOUSE, SAN JOAQUIN COUNTY <br /> Staff of the Regional Water Quality Control Board — Central Valley Region (Regional Water <br /> Board) has reviewed the 6 December 2008 Subsurface Investigation Work Plan (Work Plan) <br /> for Mountain House Neighborhood B submitted by Conestoga-Rovers & Associates (CRA) on <br /> behalf of Equilon Enterprises LLC doing business as Shell Oil Products US (Shell). The <br /> purpose of the Work Plan is to propose additional groundwater investigation activities for <br /> areas of potential concern previously identified through investigation and soil remediation <br /> within Mountain House Neighborhood B. <br /> In 2007, soil impacted with petroleum hydrocarbons was excavated from 12 areas in <br /> Neighborhood B. The excavations ranged in depth from 8 feet to about 30 feet below ground <br /> surface. Soil was removed that was impacted as evidenced by visual staining, or that <br /> exceeded a concentration of 5,000 milligrams per kilogram total petroleum hydrocarbons as <br /> crude oil (TPHcr), a remedial excavation goal provided by Regional Water Board staff. <br /> Approximately 35,000 cubic yards of soil were excavated from the site. <br /> Shell proposes to install 20 monitoring wells in the vicinity of 7 of the 12 previously excavated <br /> areas within neighborhood B. The purpose of the monitoring wells is to further delineate the <br /> lateral extent of shallow groundwater contamination. The monitoring wells will be installed <br /> using a hollow stem auger drill rig. Soil samples for lithological characterization will be <br /> collected continuously in the source area monitoring wells and at 5-foot intervals in the up and <br /> down gradient monitoring well boreholes. No soil samples are proposed for laboratory <br /> analysis since soil has been previously characterized and remediated. Source area and down <br /> gradient monitoring wells will be constructed with 4-inch diameter schedule 40 PVC casing. <br /> The up gradient monitoring wells will be constructed with 2-inch diameter schedule 40 PVC <br /> casing. Screen intervals are anticipated to extend from 20 to 35 feet below ground surface. <br /> The monitoring wells will be developed, sampled. and surveyed. Groundwater samples will <br /> be submitted for laboratory analysis of total petroleum hydrocarbons as diesel (TPHd) and <br /> TPHcr using EPA Method 8015M and benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX) using EPA Method 8260B. <br /> Regional Water Board staff concurs with the proposed scope of work. Please note that <br /> Regional Water Board staff has previously requested additional analyses for naphthalene and <br /> California Environmental Prolection Agenc1, <br /> �G Hel.,Irl.1;:Lill, <br />