07-06-2020 Council Work Session Packet

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Feasibility Study Water Treatment Plant City of Lino Lakes, MN WSB Project No. 015822-000 Page 11 Tooth discoloration and/or pitting is caused by excess fluoride exposures during the formative period prior to eruption of the teeth in children. The secondary standard of 2.0 mg/L is intended as a guideline for an upper boundary level in areas which have high levels of naturally occurring fluoride. The level of the SMCL was set based upon a balancing of the beneficial effects of protection from tooth decay and the undesirable effects of excessive exposures leading to discoloration. The standard related to this effect includes Fluoride. Technical Effects Corrosivity and staining related to corrosion not only affect the aesthetic quality of water but may also have significant economic implications. Other effects of corrosive water, such as the corrosion of iron and copper, may stain household fixtures, and impart objectionable metallic taste and red or blue-green color to the water supply as well. Corrosion of distribution system pipes can reduce water flow. Standards related to corrosion and staining include: Chloride, Copper, Corrosivity, Iron, Manganese, pH, Total Dissolved Solids, and Zinc. Scaling and sedimentation are other processes which have economic impacts. Scale is a mineral deposit which builds up on the insides of hot water pipes, boilers, and heat exchangers, restricting or even blocking water flow. Sediments are loose deposits in the distribution system or home plumbing. The EPA recommended Secondary Maximum Contaminant Levels are summarized in Table 3-1. Lino Lakes’ water currently complies with all of the recommended Secondary Maximum Contaminant Levels except for manganese, iron, and total hardness. Producing effluent water quality below these levels should be a treatment goal for Lino Lakes in addition to complying with the Primary Drinking Water Standards, Health-Based Values (HBVs), and Health Risk Limits (HRLs). Many of Lino Lakes’ customers are already treating hardness with in-home water softeners. Table 3-1 Secondary Maximum Contaminant Levels Contaminant Secondary MCL Noticeable Effects above the Secondary MCL Aluminum 0.05 to 0.2 mg/L*colored water Chloride 250 mg/L salty taste Color 15 color units visible tint Copper 1.0 mg/L metallic taste; blue-green staining Corrosivity Non-corrosive metallic taste; corroded pipes/ fixtures staining Fluoride 2.0 mg/L tooth discoloration Foaming agents 0.5 mg/L frothy, cloudy; bitter taste; odor Iron 0.3 mg/L rusty color; sediment; metallic taste; reddish or orange staining Manganese 0.05 mg/L black to brown color; black staining; bitter metallic taste Odor 3 TON (threshold odor number)"rotten-egg", musty or chemical smell pH 6.5 - 8.5 low pH: bitter metallic taste; corrosion high pH: slippery feel; soda taste; deposits Silver 0.1 mg/L skin discoloration; graying of the white part of the eye Sulfate 250 mg/L salty taste Total Dissolved Solids (TDS)500 mg/L hardness; deposits; colored water; staining; salty taste Total Hardness 150 mg/L hardness; scale deposits on plumbing fixtures; Zinc 5 mg/L metallic taste * mg/L is milligrams of substance per liter of water