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CONESTOGA-ROVERS 19449 Riverside Drive, Suite 230, Sonoma, California <br /> & ASSOCIATES Telephone: 9354850 Fax: (707)935-6649 <br /> www.CRAworld.crld.com <br /> MEMORANDUM <br /> TO: Mike Infurna,SJCEHD REF.No.: 060223-2010-04 <br /> FROM: Jeff Gaarder DATE: August 12,2010 <br /> CC: Jim Whitley,WDC <br /> Brian Taylor,CVR Water Board <br /> RE: Project Update-Well Installation Conductor Casing and Deep Well Specifications <br /> Cordes Ranch,Tracy,California <br /> In response to your July 14,2010 email and telephone call today,Conestoga-Rovers&Associates (CRA) is <br /> providing this supplemental information for the conductor casing and deep well installations scheduled for <br /> the week of August 16,2010. You have requested the following information as detailed in your email: <br /> 1. well construction diagram complete with materials, dimensions, and depths below ground surface <br /> (Figure 1) <br /> 2. a narrative section that details the procedures,drilling methods,and grouting procedures <br /> 3. time between grouting the conductor casing and drilling the well <br /> At this time,the scope of work includes installing one well cluster at the site. The MW-1b and c wells as <br /> detailed on the permit application will not be installed. The MW-7b and c wells have been renamed to <br /> MW-5b and MW-5c. Figure 2 shows the well locations recently installed during July. The drilling and <br /> grouting information for installing two conductor casings and two wells is discussed below. <br /> 1.0 CONDUCTOR CASING DRILLING AND GROUTING PROCEDURES <br /> CRA's subcontractor,WDC Exploration and Wells,will use an air rotary casing hammer to drill the pilot <br /> hole for the conductor casing. The pilot hole boring will be approximately 13.5 inches in diameter and will <br /> be drilled to a depth of approximately 45 feet below grade (fbg). These details are provided on Figure 1, <br /> Typical Well Construction Diagram. <br /> The conductor is an 8 inch nominal diameter steel casing that is approximately 0.25 inches in thickness. <br /> There will be two 20 ft and one 5 ft casing sections welded together. To assure the casing is centered within <br /> the boring,steel centralizers will be welded to the top(near surface) and bottom(near 415 ft sections of the <br /> casing. <br /> Grouting will be performed following the casing installation. A neat cement grout(Type I or II cement)will <br /> be used for filling the annulus between the conductor casing and the borehole wall. The neat cement grout <br /> will be placed within the borehole annulus using a tremie pipe starting at the borehole bottom and filling to <br /> ♦,N tNN...,1W <br /> ISO 9001 <br /> ENGINEERING NESI4N <br />