Minutes - Public Works Committee - 01/20/2004

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water level is recommended so that data can be collected to correlate against the long term trending patterns within the FIG. Permitting: The increase in demand will subsequently require an amended DN'R water appropriations permit. At that time, the DN'R is likely to require the collection of the surficial groundwater data mentioned above. In addition, the DNR may require a pumping test to correlate short term temporal relationships between the two aquifers. The monitoring wells needed for this study should also be designed as groundwater sampling wells that can be used to identify potential contamination of wellhead protection areas. The design of all additional municipal production wells can then be based on information collected during these studies in an effort to mitigate impacts, assuming any exist. Wellhead Protection: The RTC is located directly within the Wellhead Protection Area (WHPA) and Drinking Water Source Management Area (DWSlVIA) determined by the preliminary Ramsey wellhead protection plan (Figx~re 20.1). Additional groundwater modeling information is included in Appendix H. Using the MhDH model for wellhead protection planning purposes and the Maximum Annual Capacity shown in Table 13.3 as the pumping rates for wells 3, 4 and 5, the 10-year capture areas for these wells was recalculated. With the inclusion of well 5, the WHh~A would extend southward from well 5 to the edge of the RTC site. Therefore, this area should be considered a WH:PA for land use'planning purposes. Any contaminating material that is spilled on the permeable sands within the site can potentially migrate into the groundwater system. City wells were tested for tritium as part of the wellhead protection plan delineation. Tritium is a form of hydrogen and can act as an indicator of groundwater age, but does not pose a health risk. Atmospheric tritium levels increased during the 1950's due to testing of atomic bombs. Therefore, tritium levels are used to indicate whether groundwater entered the ground before or after 1950. Public water supply wells with high levels of tritium are 'classified as "vulnerable" to surface processes because of the relatively recent (post-1950) interaction with the surface. Tritium levels in the three city wells around the Town Center are high. A formal well vulnerability assessment has not been completed for well 5 but the preliminary wellhead protection plan identifies it as vulnerable in Table 1. A formal assessment could be done in coordination with a plan addendum for additional municipal wells. The results of the formal assessment will most likely confirm that well 5 is also vulnerable to contamination. The vulnerability of these wells may be caused by the rapid rate of infiltration through the highly permeable sand and gravel materials of the Anoka Sand Plain, by leakage of water around the annular space of the well, or by the interaction. of the quaternary and bedrock aquifers in the bedrock valley to the north of the site (Figure 19.4). To reduce the risk of groundwater contamination, pretreatment of stormwater runoffpr/or to infiltration and community education programs on household chemical and fertilizer use can be implemented. Storm water management practices that encourage the infiltration of treated runoff will be part of the design and are discussed in detail in Items t 7 and 20. -46- 13-8