Agenda - Public Works Committee - 10/19/2021

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Chapter 5 — Regional Groundwater Treatment Plant (Approach 2) 5.1 Overview Groundwater is the most common source of drinking water in Minnesota, including the Northwest Metro communities. To reduce chlorides in wastewater from home softeners and compare the groundwater WTP against a lime softening surface WTP, it is assumed that the potential regional groundwater WTP is a lime softening WTP. The concept regional groundwater WTP is proposed to provide capacity of 25 MGD and would serve the maximum day demands for the Northwest Metro communities through 2040. After 2040, the groundwater WTP will be expanded to 75 MGD to meet ultimate water demands. 5.2 Groundwater Treatment Plant Location A potential groundwater treatment plant location is the same as the surface water treatment plant location in Dayton (Figure 4-1). The water treatment is proposed to be located in Dayton because it is centrally located, less developed than Rogers or Ramsey, and the Tunnel City Wonewoc aquifer is available throughout the entire City. 5.3 Constituents of Interest The primary constituents of interest in groundwater are iron, manganese, and hardness. The following sections describe the potential health and aesthetic effects of these constituents. 5.3.a Manganese Manganese occurs naturally in rocks and soil across Minnesota and is often found in Minnesota groundwater. Your body needs some manganese to stay healthy, but too much can be harmful. The Minnesota Department of Health (MDH) has set a Health Based Guidance Value (HBV)for manganese of 0.1 milligrams per liter(mg/L, equivalent to parts per million). Children and adults who drink water with high levels of manganese for a long time may have problems with memory, attention, and motor skills. Infants (babies under one year old) may develop learning and behavior problems if they drink water with too much manganese in it. The City of Ramsey has manganese in its drinking water above the MDH HBV of 0.1 mg/L. To reduce the level of manganese, Ramsey is currently evaluating the construction of a WTP (separate from this report). 5.3.b Aesthetic Standards Iron and manganese cause red and black staining in toilets and on fixtures and hardness causes scaling. Table 5-1 identifies the secondary (aesthetic) standards for iron, manganese, and hardness. It is very common to have iron, manganese, or hardness above the secondary standards in groundwater wells in Minnesota. Table 5-1.Secondary Standards for Iron,Manganese,and Hardness. Constituent 21 Secondary Standard (mg/L) Iron 0.3 Manganese 0.05 Hardness 80 Page—25 1 METROPOLITAN COUNCIL