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August 18,2015 <br /> Paul Palzer,Public Works Director <br /> Page 3 of 7 <br /> Reference: Part 1 Wellhead Protection Plan Amendment, City of Centerville <br /> conceptual model of the groundwater flow system in the aquifer serving the Centerville <br /> wells.The five criteria are: <br /> • Time of travel - The minimum time-of-travel for delineations is 10 years. A one-year <br /> time-of-travel must also be computed, which will serve as an emergency response <br /> area for wellhead protection management. Other travel times can be modeled and <br /> mapped for little extra cost, if desired. <br /> • Flow boundaries - Hydrogeologic boundaries, such as extents of aquifer formations, <br /> rivers, lakes, etc. impact the size and shape of wellhead protection delineations. <br /> • Daily volume -The amount of water pumped from the aquifer(s) will also impact the <br /> size of the delineated area. Accurate, up-to-date data regarding water usage is <br /> essential. Planned water usage over the next five years must also be considered. <br /> • Groundwater flow field - Any relevant information regarding groundwater flow within <br /> the aquifer must be considered and incorporated into the delineation process. This <br /> data may relate to groundwater elevations, flow direction, flow gradient, recharge, <br /> and withdrawals that may affect the delineation. <br /> • Aquifer transmissivity -The ability of the aquifer to transmit water to a high capacity <br /> well must also be considered. Aquifer transmissivity can greatly affect the size and <br /> shape of the delineation, when groundwater flow is simulated on a computer <br /> groundwater model.Therefore, aquifer pumping test information is used to determine <br /> transmissivity. <br /> Pre-Delineation Meeting <br /> Once the five delineation criteria have been determined and a conceptual model of <br /> the groundwater flow system has been developed, a meeting is held with MDH staff to <br /> review the conceptual model. This meeting will enable Stantec and the MDH to agree <br /> on how best to proceed with the delineation process, to help see that the end result <br /> meets with favorable review from MDH staff. <br /> WHPA Delineation <br /> A computer groundwater model is utilized to create the wellhead protection area <br /> capture zones for Centerville's water supply wells. The criteria determined above are <br /> entered into the computer model in order to produce a delineation that meets MDH <br /> requirements. <br /> Dcsgri v, h corn-r+.rn'1y rn rnric <br /> 23 <br />