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<br />PART 2. ASSESSMENT OF DATA ELEMENTS USED TO DELINEATE THE WELLHEAD <br />PROTECTION AREA <br /> <br />A. Use of the Wells - The wells provide all ofthe water that is piped to the water <br />distribution system. The wells used by the city provide different annual volumes of <br />water (Table 2). Projected uses for the city's wells are also shown on Table 2. This <br />table indicates which values were used for the WHP A delineation analysis. <br /> <br />B. Wellhead Protection Area Delineation Criteria <br /> <br />1. Time of travel - A 10-year time of travel was selected. <br /> <br />2. Flow boundaries - In general, the aquifers used by the City of Centerville as a <br />water supply are sufficiently deep that they are unaffected by local surface water <br />resources. The bedrock aquifers used by the city are laterally continuous over the <br />area of the city, but are abruptly truncated 1500 meters to the northwest and 2300 <br />meters west of Well No. 1. The escarpment along which the Prairie du Chien and <br />Jordan terminate trends southwest-northeast in this part of southeastern Anoka <br />County (Figure 2) and is currently covered with unconsolidated glacial drift. This <br />feature is represented in the regional model used for the delineations, but likely <br />has little effect on the local flow system because it is downgradient of the city's <br />wells. <br /> <br />Other nearby pumping centers represent hydrologic boundaries in both aquifer <br />systems used by the city that may affect the size and orientation of the city's <br />wellhead protection areas (WHP As). These pumping centers were identified by <br />reviewing the State Water Use Database (SWUD) maintained by the Department <br />of Natural Resources (DNR) and by locating other municipal pumping centers in <br />southern Anoka County. <br /> <br />3. Daily volume - Table 2 shows the reported and projected water use data for the <br />Centerville city wells over a five-year period. The table indicates which annual <br />use was selected for utilization in the WHP A delineation analysis. <br /> <br />4. Groundwater flow field - Regional-scale groundwater flow analysis for the <br />separate Prairie du Chien - Jordan Aquifer systems are summarized in Seaberg <br />and Hansen (2000), Schoenberg (1990), and Woodward and Delin (1984). The <br />data were incorporated into the model development process by using calibration <br />data sets developed by the Minnesota Pollution Control Agency (MPCA) staff to <br />calibrate the groundwater model flow field. Generally, each of the aquifers show <br />groundwater elevations near the City of Lexington that suggest groundwater <br />flowing from east to west. <br /> <br />5. Aquifer transmissivity - An aquifer test was conducted in Centerville Well <br />No.1. The results of this test indicate the transmissivity of the aquifer is on the <br />order of 15,000 if/day and the storativity is in range of 0.00002 to 0.0015. <br />Results from this aquifer test and regional values were used in the groundwater <br />flow model development. A copy of the aquifer test report is presented in <br />Appendix C. <br /> <br />2 <br />