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EXECUTIVE SUMMARY This report documents the delineation of the wellhead protection areas and drinking water supply management areas for the City ofCenterville, PWS ID No. 1020036. The delineation was performed in accordance with rules (Minnesota Rules 4720.5100 to 4720.5580) for preparing and implementing wellhead protection measures for public water supply wells. The rules are administered by the Minnesota Department of Health (MDH), and the results described in this report were prepared as a group effort involving staff from the following organizations: Anoka County, the City of Centerville, and the MDH. Key documentation relative to the City of Centerville's wellhead protection effort is contained in Appendix A. The City of Centerville obtains its drinking water supply from two wells (Table 1) completed in the Prairie du Chien - Jordan Aquifer System, which is comprised of the separate Prairie du Chien Dolomite and Jordan Sandstone. The Prairie du Chien and the Jordan each exhibit confined hydraulic conditions, and while they together are considered an aquifer on a regional basis, each has unique characteristics. Well No.1 is completed in the Jordan and Well No.2 is completed in the Prairie du Chien. W ell logs for the city wells are presented in Appendix B. The wellhead protection areas (WHPAs) for the city wells were delineated using a multi-aquifer groundwater flow model developed for the MDH by a private contractor (EOR, KDB Consulting, 2000). This model simulates groundwater flow in the Prairie du Chien and Jordan Aquifer systems, as well as in the overlying materials (where applicable). The model input set runs using a groundwater flow code known as MLAEM. The MLAEM model was used to delineate capture zones for all city wells. The drinking water supply management areas (DWSMAS) were determined by overlaying the boundaries of the WHP As on an aerial photograph and a map showing property parcel boundaries and roadways. The DWSMA was delineated using these features as boundaries. Figure 1 shows the boundaries of both the WHPA and the DWSMA. The amount of geologic protection documented in well logs from the city wells is sufficient to classify Centerville Well No.1 (511091) as nonvulnerable. In addition, results ofa tritium analysis of a water sample from the well showed non-detectable levels of tritium, another indicator that the well is not vulnerable. Because of this result and the nature of geologic protection in the area, this well and the aquifer it draws from in the DWSMA are not vulnerable to current land uses and, thus, the principal means by which they could be affected by land use activities is through wells or boreholes of equal or greater depth. Well No.2 (512748) is completed in the Prairie du Chien at a shallower depth than Well No.1, and water samples collected from the well contain tritium. The tritium results (4 t.u. in 1997) mean some of the water pumped from the well has infiltrated from the ground surface after 1953. Accordingly, the well is vulnerable to contamination from the ground surface and land use within the area of the DWSMA has the potential to affect the Prairie du Chien Aquifer. The city wells meet the construction standards of the State Well Code and are not considered a likely avenue for contamination to reach the aquifer from which they pump.