4.1. ERMUSR 12-17-2019 - Laserfiche WebLink

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Chapter 4 - 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 ERMU supply. Generally, the ERMU considers all types of land- and water-uses as presenting a possible risk to groundwater quality where the source water aquifer exhibits a high or very high vulnerability. Where the source water aquifer exhibits a moderate vulnerability, certain types of potential contamination sources that may release contaminants to the subsurface must be included in addition to wells, excavations that may reach the source water aquifer and certain types of Environmental Protection Agency Class V wells. These additional types include above ground and buried chemical and fuel storage tanks, underground waste disposal practices, pipelines and fuel/chemical spills. Where the source water aquifer exhibits a low or very low vulnerability, certain types of potential contamination sources that may release contaminants to the subsurface must be included in addition to wells, excavations that may reach the source water aquifer and certain types of Environmental Protection Agency Class V wells. 4.1 Contaminants of Concern None of the contaminants that are regulated under the federal Safe Drinking Water Act have been detected in the ERMU water supply wells. However, the vulnerable nature of the aquifer requires that potential contamination sources that may release them be inventoried. These potential sources likely reflect those that could present a threat to drinking water if a contaminant release were to occur because the contaminants have a known impact on public health. 4.2 Inventory Results and Risk Assessment The ERMU Wellhead Protection Team conducted the inventory of potential contaminant sources. The MDH provided the team with a listing of potential contamination sources from state agency databases and team members provided knowledge about other potential sources that are not addressed under state regulatory programs. Most of the work was accomplished at meetings of team members although this was supplemented with driving throughout the DWSMA to confirm some of the information. The inventory began with updating the locations of potential contamination sources in the area that is located within 200 feet of each city well and is referred to as the IMWZ. A description of the locations of potential contamination sources is presented in Appendix II. A summary of the results for the IWMZ is listed in Table 2 and complete IWMZ PCSI reports are presented in Figure 6, and for the remainder of the DWSMA in Table 3. The priority assigned to each type of potential contamination source addresses 1) the number inventoried, 2) its proximity to an ERMU well, 3) the capability of local geologic conditions to absorb a contaminant, 4) the effectiveness of existing regulatory controls, and 5) the time required for the ERMU to obtain cooperation from governmental agencies that regulate it. A high (H) risk potential implies that the potential source type has the greatest likelihood to negatively impact the ERMU 5 399