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CAMBRIA 0 <br /> Mr. Timothy R- O'Brien, PG, CEG, CHG <br /> Regional Water February 2,2007 <br /> Central Valle Quality Control Board <br /> 11020 Y Region <br /> Sun Center Drive, Suite 200 <br /> Rancho Cordova,California 95670 <br /> Re: Sol'lnvesti ation <br /> Workplan Addendum and Background Groundwater <br /> CamancheD Monitoring Well Installation <br /> am Powerhouse <br /> 23900 E.Buena Vista Road <br /> Clements,San Joaquin County, California <br /> ® Dear Mr. O'Brien: <br /> I <br /> On behalf of East Bay Municipal Utility District(the District),Cambria Environmental Technology, <br /> Inc. (Cambria)has prepared this addendum to the Soil lrrvestigation and Background Groundwater <br /> Monitoring Well In+rallation Workplan (the workplan) dated January 17 2007 in response to the— <br /> Regional Water Quality Control Board's (RWQCB) conditional approval letter dated January 30, <br /> 2007(AttxhmentA).Presented below is the additional information requested by the RWQCB <br /> 1. As stated on page 4, paragraph 2 of the workplan, Cambria inferred the groundwater flow <br /> direction and depth based on local topography,and the elevation of the Mokelumne River.At this <br /> time,this is our interpretation ofthe limited data we have available.Afterthe monitoring wel)s are <br /> installed and developed we will have data to determine the groundwater flow direction and if the <br /> Mokelumae River is a gaining or losing stream. The wells have been proposed in a triangular <br /> configuration to anticipate either flow direction. <br /> 2. Currently,we only have site specific data for the tap 6.5-feet of sediments.However, the site is <br /> located mihe flood plan of a major stream and we suspect at depth that we will encounter coarser <br /> stream channel deposits that will require a drilling method that can advance through cobbles and <br /> boulders Thereforz w,e propose using the ODER Casing system, which advances the casing <br /> simuhasously win the air-rotary hammer. Soil samples will be collected with an 18-inch <br /> Californh Modifid Split Spoon Sampler lined with stainless steel liners in advance of the casing <br /> and air rotary haiff r- <br /> 3. As sbow in F igc 1,we propose to construct the bottom of the monitoring wells with a threaded <br /> rambTia 4-inch diamete inyl chloride(PVC)well cap. <br /> Environmental <br /> Technology,Inc. <br /> 5900 Hollis Street - <br /> $uite h <br /> �Q�yV���8,�a94606 <br /> Tel(510)420-0100 <br /> Fax(510)420-990 <br />