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August 18,2015 Paul Palzer,Public Works Director Page 4 of 7 Reference: Part 1 Wellhead Protection Plan Amendment,City of Centerville The Met Council Metropolitan Model 3 is proposed to be used for the delineation effort. While this model is likely the best starting point for the delineation effort, the model will still require updates to reflect current understanding of local geology, current pumping volumes of nearby high capacity wells, current understanding of the recharge and interaction of relevant aquifer units, and current data for model calibration, including groundwater level data from nearby wells. The wellhead protection delineation generated by the model must, at a minimum, show the one-year and 10-year time-of-travel capture zones for all active primary water supply wells. Wellhead protection areas will be mapped on ArcView GIS using UTM NAD 83 coordinates, as required by MDH rules. Other coordinate projections can be provided to Centerville, if requested. Fracture Flow Delineation Since the wells that Centerville uses are in connection with the fractured Prairie du Chien aquifer, an additional delineation step is required to calculate the potentially flow paths within the fractures of the bedrock formation. This calculation efforts typically adds additional area onto the delineations produced by the computer groundwater model. Conuunctive Delineation Aquifers that are highly vulnerable and are in hydraulic connection with surface water require an additional delineation step that calculates the drainage area for storm water around the 10-year capture. This analysis is done using a combination of LIDAR data to map the topography for gravity drainage and using maps of man-made structures that are designed to divert stormwater flow. Where storm water is determined to be draining towards the capture zone, that area is added onto the overall wellhead protection area delineation. DWSMA Delineation The modeled capture zone and fracture flow delineation must then be combined to form integrated management zones. Since the mapped zones cannot be easily identified using surface features, a Drinking Water Supply Management Area (DWSMA) is created to correlate the capture zones with the nearest surface features, such as roads, parcel boundaries, water bodies, and other surveyed features that can readily be identified. The DWSMA will be mapped on ArcView GIS using UTM NAD 83 coordinates, oe!;gn wit;,cc n„,T', ety if;mina 24