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The normal annual precipitation for Minnesota (1961-1990) is 27.01 inches. The presence of moist vs. dry air masses also helps to determine the atmosphere's ability to absorb water vapor evaporating from soil and open-water surfaces, or transpiring from leaf surfaces (evaporation plus transpiration is called "evapotranspiration"). Western Minnesota, more frequently under the influence of dry air masses, has higher evapotranspiration rates than the eastern half of the state (see Figure 2). Temperature plays an important role in determining the amount of energy available for evapotranspiration. Because temperature patterns are determined mainly by latitude, southern Minnesota experiences more evapotranspiration than in the north. Due to its position in the continent, Minnesota is located on the boundary between the semi-humid climate regime of the eastern U.S., and the semi-arid regime to the west. Semi-humid climates are areas where average annual precipitation exceeds average annual evapotranspiration, leading to a net surplus of water. In semi-arid areas, evapotranspiration exceeds precipitation on average, creating a water deficit. In Minnesota, the boundary between the climate regimes cuts the State roughly into east-west halves (from Climate's impact on water availability; MN DNR). Centerville The City is within a semi-humid region where average annual precipitation exceeds average annual evapotranspiration, leading to a net surplus of water. No active precipitation gaging stations have been identified within the City of Centerville that can provide consistent data over extended periods. However, the Climatology Working Group (a cooperative effort state and academic organizations) has developed an interactive web site to locate and access precipitation data for the Centerville area. Based on regional data the metropolitan area receives an average annual precipitation of 28 inches. Based on a 20-year compilation of the nearest National Weather Service approved precipitation gage stations the City's average annual precipitation is 33 inches. Local precipitation is presented in Table 1. Soils Soils, within the City's DWSMA, influence the infiltration of water. The General Soil Map of Anoka County (US Dept. of Agriculture - Soil Conserv'ation Service, 1974) indicates that the area of the City's DV'vSMAs consists of the Nessel-Dundas-Webster Soil Association. The Nessel-Dundas-Webster Soil Association consists of nearly level to gently sloping moderately well drained and poorly drained soils formed in loamy glacial till. Figure 3 provides the Centerville section of the Anoka County General Soil Map. A regional study of shallow geology, including soils, has been performed to determine the sensitivity of the uppermost aquifer to contamination [Regional Hydrologic Assessment - Anoka Sand Plain (RHA-1), Minnesota Department of Natural Resources, 1993]. The geologic sensitivity of the uppermost aquifer to pollution is "low" to "moderate" in the City's DWSMAs. Sensitivity ratings are based on the estimated time-of-travel for water-borne contaminants, at land surface, to reach the uppermost aquifer. Low sensitivity rating indicates time-of-travel from decades to a century. Moderate sensitivity rating indicates time-of-travel from years to decades. Figure 4 provides the Centerville section of the Geologic Sensitivity Map. Water Resources Surface water resources in the City consist of Centerville and Peltier Lakes and Clearwater Creek (County ditch 47). The lakes are located in the western portion of the City approximately one-half mile outside of the City's DWSMAs. Clearwater Creek flows through the southern portion of the DWSMA for Centerville Well #2 and defines a portion of the DWSMA. July 3, 2007 DRAFT Centerville Wellhead Protection Plan (Part 2) Page 2