Agenda - Council Work Session - 10/20/2020 - Special

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6 source water aquifer for both a water quantity and a water quality standpoint. The source water aquifer is underneath protective 'confining" units that appear to inhibit the influence of new water from brining contaminants to the City's wells and will likely produce consistent water quality unlikely unconfined sources such as surface water that may have a highly variable water quality. Additional considerations for well Sites should take into account the thickness of the two hydrogeologic units that make up the source water aquifer. The Tunnel City is not as prolific as an aquifer as the Wonewoc Aquifer !meaning that the Wonewoc aquifer is more economical source of water_ Figure 15 in Appendix 0 depicts three potential well sites taking into account these issues. Well Site Area A has Tunnel City Aquifer thickness range from 100 to 150 feet and Wonewoc Thickness range from 45 to 60 feet. Well Site Area B has Tunnel City Aquifer thickness range from 0 to 80 feet and Wonewoc Thickness range from 35 to 100 feet. Well Site Area C has Tunnel City Aquifer thickness range from 90 to 1100 feet and Wonewoc Thickness range from 15 to 35 feet. All of these sites have potential for potable water sources but a test well will need to be installed to confirm their viability. As opportunities to investigate these well sites present themselves the City of Ramsey should consider these as potential well sites. Regional Water Supply Study Metropolitan Council Environmental Services in conjunction with the Cities of Ramsey, Dayton, Rogers, and Corcoran prepared a study in 2020 that looked at various options for a regional water system. SEI-1 was the consulting engineer on the project. The Northwest Metro Area Regional Water Supply System Study (Study) evaluated four approaches to water supply: • Approach 1: Regional Surface Water Treatment Plant • Approach 2: Regional Lime Softening Groundwater Treatment Plant • Approach 3: Regional Conjunctive Use System (Surface Water Augmented with Groundwater) • Approach 4: Status Quo (communities construct individual lime softening groundwater treatment plants) So that similar treated water qualities were being evaluated, Approach 2 and Approach 4 assumed that the communities would construct lime softening groundwater treatment plants. A potential driver ultimately requiring lime softened groundwater or the use of surface water is a chloride discharge limit in wastewater. A finding in the report as it relates to surface water treatment in the vicinity of Rarnsey was that "The Mississippi River has sufficient water quantity to serve the Northwest Metro communities. The water quality in the Mississippi River appears to be acceptable for a conventional surface water treatment plant. St. Could, St Paul, and Minneapolis utilize the Mississippi River as their source of drinking water." The capital cost of a surface water treatment plant is significantly higher than an iron and manganese groundwater treatment plant. Based on costs presented in the report, the project cost for a 10 IVIGD surface water treatment plant would be $50 million or more. In addition, the Operation and Maintenance costs of treating surface water is approximately twice as high as iron and manganese treatment. It should be noted that a surface water treatment plant could provide softened water to the residents of Ramsey; whereas an iron and manganese treatment plant would not provide FEASIBILITY STUDY -DRAFT RAMSY 154354 Page 24