7A - Wellhead Protection Plan Update

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Chapter 4 - Establishing Priorities and Assigning Risk to Potential Contamination Sources The types of potential contamination sources that may exist within the DWSMA were derived from the information collected to satisfy the data element requirements (Chapter 2). The impact assigned to each data element as part of the assessment process(Table 1)was used to assess the types of potential contamination sources that may present a risk to the city's drinking water supply. The moderate vulnerability assessment for the DWSMA indicates that generally only wells, other types of boreholes, or activities that remove confining material that may allow contaminants to reach the aquifer such as buried tanks or certain types of Environmental Protection Agency Class V Wells are likely to impact the city wells and aquifer. To further safe guard the public water supply used by the City of Pequot Lakes, large above ground tanks, former spills and potentially large contaminant release sources such as pipelines were also considered in completing the potential contaminant source inventory. 4.1 Contaminants of Concern None of the human-caused contaminants regulated under the federal Safe Drinking Water Act have been detected at levels indicating that the well itself serves to draw contaminants into the aquifer as a result of pumping. This generally indicates that most of the recharge the aquifer receives is over a long period of time and not immediately impacted by land uses. 4.2 Inventory Results and Risk Assessment •map and description of the locations of potential contamination sources is presented in Appendix H. •summary of the results for the IWMZ is listed in Table 2 and Table 3 presents these results for the remainder of the DWSMA. The status of former city wells and borings were considered based upon research and information provided by MDH. The report generated for the City of Pequot Lakes showed that former city wells 1 and 2 have been properly sealed based upon well sealing records on file at the department. No other unused unsealed city wells or borings were identified by MDH. (See Exhibit 1) The WHP Team also considered other significant potential contaminant threats such as gas or oil pipelines. None of these types of potential contaminant threats were identified in the DWSMA. The priority assigned to each type of potential contamination source addresses 1)the number inventoried,2)its proximity to a city well, 3)the capability of local geologic conditions to absorb a contaminant,4)the effectiveness of existing regulatory controls, 5)the time required for the City of Pequot Lakes to obtain cooperation from governmental agencies that regulate it,and 6)the administrative,legal,technical, and financial resources needed. A high(I)risk potential implies that the potential source type has the greatest likelihood to negatively impact the city's water supply and should receive highest priority for management. A low (L)risk potential implies that a lower priority for implementing management measures is assigned. Table 2 -Potential Contamination Sources and Assigned Risk for the 1WMZ Source Type Total Level of Risk �-' Water Treatment Backwash Basin/Discharge 1 L 6