Agenda - Public Works Committee - 10/19/2021

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Chapter 10 — Summary of Findings and Implementation Considerations Key takeaways from this concept level study of alternative approaches to a Northwest Metro area regional drinking water supply system include: • The average day water demand in the Northwest Metro is projected to increase from 3.3 MGD in 2015 to 7.8 MGD in 2040 (140% increase). • The ultimate average day water demand in the Northwest Metro is 29 MGD (approximately 800% increase from 2015). • If the Northwest Metro cities continue to utilize only groundwater to meet water demands, an additional 54 wells will likely be needed to meet ultimate demands. A 2016 MCES report indicated drawdown in the Tunnel City-Wonewoc aquifer in 2040 when demands are only 27% of the ultimate demands. It is possible that the aquifer cannot sustain the ultimate demands of the Northwest Metro. • 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. • A regional surface WTP has the advantages of being a cost effective approach, eliminates the need for numerous addition wells, increases groundwater sustainability, provides fully softened water, and reduces chloride discharges to the Mississippi River. The disadvantages of a regional surface WTP is that it changes water taste and odor and relies heavily on one water source. • A regional lime-softening groundwater WTP has the advantages of providing fully softened water and reduces chloride discharges to the Mississippi River. The disadvantages of a regional lime softening groundwater WTP is that it is one of the most expensive approaches evaluated, may not be feasible due to groundwater drawdown, and relies heavily on one water source. • A regional conjunctive use WTP has the advantages of being a cost effective approach, increases groundwater sustainability, provides mostly softened water, reduces chloride discharges to the Mississippi River, and does not rely on one water source. The disadvantages of a regional conjunctive use WTP is that it changes water taste and odor and does not provide fully softened water in the summer. • Constructing individual lime softening groundwater WTPs (Status Quo) has the advantages of providing fully softened water and reduces chloride discharges to the Mississippi River. The disadvantages of individual lime softening WTPs is that it is the most expensive approach and relies on one water source. • A cost of service example indicates that grant funding will be an integral part of implementing a regional surface water supply system to make the project viable. • In the absence of a project driver, Northwest Metro cities are likely to continue to utilize groundwater and construct iron and manganese removal water treatment plants. At this point, none of the Northwest Metro cities have water treatment plants, although 2 are in the planning stages (Ramsey and Corcoran). • The Northwest Metro communities are embarking on this study at an optimal time. The water systems are not fully developed and significant growth is planned. Page—41 1 METROPOLITAN COUNCIL