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ISGIITHE <br /> envlmnmental SOURCE GROUP, INC. <br /> March 25, 2008 <br /> Reena Thomas <br /> RBF Consulting <br /> 500 Ygnacio Valley Road, Suite 270 <br /> Walnut Creek, California 94596-3847 <br /> Subject: Monitoring Well Installation Work Plan, Revision 2 <br /> City of Lathrop Water Supply Study <br /> Dear Reena: <br /> In a draft memorandum dated January 21, 2008, The Source Group, Inc, (SGI) identified <br /> uncertainty in groundwater quality characterization as a data gap for the City of Lathrop (City) <br /> Water Supply Study. The memorandum also proposed two potential courses of action to address <br /> the data gap: 1) make a conservative estimate of the water quality that will enter the City wells over <br /> time based on the available data or 2) perform limited subsurface investigation to reduce <br /> uncertainty in the characterization. Based on previous work by SGI in 2004, groundwater quality is <br /> expected to be an important consideration for the alternatives analysis portion of the water supply <br /> study, and the City has decided to proceed with the subsurface characterization option. <br /> This Work Plan for the installation of up to three groundwater monitoring wells has been prepared <br /> by SGI for the City's ongoing Water Supply Study. The well installation activities are planned to <br /> provide groundwater monitoring data with the following goals in mind: <br /> • Determine the location of the poor quality groundwater front defined by total dissolved <br /> solids(TDS) levels above 500 milligrams per liter(mg/1); <br /> • Determine the approximate magnitude of TDS concentrations in groundwater west of the <br /> 500 mg/I front; and <br /> • Determine the groundwater gradient, which indicates the direction and magnitude of flow, <br /> under groundwater pumping conditions (determination only possible if data from three or <br /> more wells are available). <br /> The following sections provide details of the scope of work, schedule and budget for the well <br /> installation, initial sampling and reporting. <br /> 3451-C Vincent Road Telephone:(925)944-2856 <br /> Pleasant Hill,California 94523 Facsimile:(925)9442859 <br /> LaMrop Workplan no markup.Coc <br />