2020-09-09 CC Packet - Laserfiche WebLink

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moderately vulnerable DWSMA, the main point sources of concern are storage tanks. Tanks are a potential threat because they may contain a high volume of contaminants at one location, but may also contain certain compounds (such as petroleum products) which can break down protective geologic layers if leaks are allowed to go unchecked for an extended period of time. The City investigateddatabases containing information about registered storage tanks, including both above ground and underground tanks. Once this information was collected, it was reviewed for accuracy and was also reviewed with City staff in order to identify sites that are currently withinthe delineated DWSMA.Figure 5 shows the mapped storage tanks, while Tables A-3 in Appendix A contain information about thesemappedsites. A total of nine storage tank sites were identified during this planning effort, containing a total of 28registered storage tanks. The majority of these tanks contain petroleum products, including gasoline, diesel,and fuel oil. Management strategies will be implemented to raise awareness of best management practices among tank owners in the DWSMA, to ensure that steps are being taken to reduce the risks for spills or leaks from these tanks. 5.6 Public Utility Services Another potential source for contaminants within the DWSMA is from infrastructure-related failures. In moderately vulnerable areas, storm sewers and sanitary sewers are mapped, particularly where they intersect the 1-year capture zone of the City’s wells, also known as the Emergency Response Area. Figure 4 shows a layout of the storm and sanitary sewers line operated and maintained by the City of Centerville.Sanitary sewers for Lino Lakes and Hugo are displayed in Appendix B. Public water supplywells are also components of the public utility infrastructure. The locations of the Centervillemunicipal wells are shown on Figure 1. The City of Hugo Wells 3 and 4 are located in the western portions of the Centerville DWSMA. Table A-1 in Appendix A lists all wells located within the groundwater portion of the DWSMA. Well locationsare shown in Figures 2A and 2B. 5.7 Former and Active Sites of Contamination Figure 3 contains an inventory of mapped spill and contaminationsites, with Table A-1 in Appendix A summarizing each of these sites. This inventory isnot required by the MDH for moderately vulnerable DWSMAs, but is being included for informational purposes as it provides information about what sites have posed threats to the aquifer in the past. Additionally, these sites are mapped in case thehave any residual contamination that is capable to migrating to the bedrock aquifer.A total of 20 sites were inventoried in the DWSMA, with all sites now being listed as “closed” by the MPCA, meaning they are no longer being actively investigated, remediated, or monitored. Should any new contamination sites be identified within the DWSMA, they will be prioritized in order of the threat they pose to the City’s municipal wells. Site specific soil conditions, geology, surface runoff, and estimated time of travel to the City’s wells will be investigatedto assess the level of threat to the City’s water supply. 13 193803358 Stantec Consulting Services, Inc.