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Chapter 1 Data Elements and Assessment I. REQUIRED DATA ELEMENTS In accordance with the Minnesota Department 9rHealth's second Scoping Decision Notice (May 15, 2002) the following data elements are presented and assessed as it relates to the City of Centerville's municipal wells. The Wellhead Protection Area (\MiPA) and Drinking Water Supply Management Area (DVVSMA) of Centerville's Well #2 are vulnerable to contamination from ground surface and near surface sources. Well #1 is not vulnerable. The City's DWSMAs are provided in Figure 1. The City has evaluated the following data elements to determine their significance in the preparation and implementation of this wellhead protection plan. Physical Environment Geology The geologic environment, surrounding Centerville's municipal wells, influences the delineation of the WH PAs and well vulnerability classification. The configuration and characteristics of geologic strata directly affects the infiltration of water and aquifer vulnerability to contamination. A county geologic atlas does not exist and focused geologic studies in the metro region do not provide relevant data for the City's wellhead protection plan. No surface geophysical information was identified. The Minnesota Department of Health performed a geologic and hydrologic assessment of the ,region surrounding the City wells to aid in determining the wellhead protection area and vulnerability. Part 1 of this plan describes the geologic strata, WHPA, DWSMA, and vulnerability of the City's well. Review of representative borehole geophysical and well construction records in the DWSMA indicates that the aquifer units used by the City's wells (Jordan and Prairie du Chien) are under low-permeability protective materials typically described as sandy clay with a thickness of greater than 50 feet. The geologic review indicates that regional precipitation, soil characteristics, and surface water resources influence the aquifer units used by City wells. The regional influence of these environmental elements extends beyond the City's DWSMAs and exceeds the scope of this plan. Precipitation Precipitation recharges all aquifers. Recharge of the confined aquifers, used by City wells, takes place on a regional scale encompassing large areas outside the City's DWSMAs. The Minnesota Department of Natural Resources has maintained a system for monitoring hydrologic data that addresses precipitation within the metropolitan region. The primary source of moisture for precipitation in Minnesota is the tropical maritime air that moves into the State from the south and southeast. The spatial variation of average (normal) annual precipitation across Minnesota is determined by proximity to these moist air masses coming northward out of the Gulf of Mexico. Therefore, southeastern Minnesota, averaging near 32 inches, receives more precipitation than northwestern Minnesota,less than 19 inches. July 3, 2007 DRAFT Centerville Wellhead Protection Plan (Part 2) Page 1