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Feature Story

        Tonka Bay’s $1.9M Water

        Treatment Plant Renovation                                                   By Kathy Laur, MPA, City Administrator
                                                                                     City of Tonka Bay, MN

        There’s nothing like a shiny “new” water   especially for water softening and arsenic   a year of discussion, the city council
        treatment plant, said no one ever, until   removal. However, this is not the case   made the decision to move forward
        now. After a year and a half of having   in Hennepin County, the largest county   with the renovation. Fortunately, the
        to work around sandblasters, painters,   in the state. Using salt in individual   city was able to secure a low-interest
        floor refinishers and having all their   customer water softeners is still the   loan from the Drinking Water Revolving
        equipment covered in plastic, the    prominent method in the area. Indeed,   Fund administered by the Minnesota
        Public Works department in Tonka Bay,   the American Water Works Association   Public Facilities Authority (PFA) and the
        Minnesota is thrilled with their new   has issued standards that provide for   Minnesota Department of Health (MDH)
        surroundings.                        the use of the lime softening process in   for all of the $1.9M cost.
                                             drinking water treatment.
        In May 2017, the Minnesota Department                                     There was a lot of renovation that
        of Health strongly recommended       In water softening, hydrated lime is used   needed to be done starting with the
        that the city complete an engineering   to remove carbonate “hardness” from the   removal of the old lime slaker equipment
        evaluation of the water treatment plant   water. Lime-enhanced softening can also   and adding a new lime tank slurry system
        (WTP) due to its age and condition and   be used to remove arsenic from water.   in the base of the lime silo. By doing this,
        the resulting challenges to maintaining   Stricter drinking water regulations for   most of the lime dust is kept out of the
        consistent water quality. The city   arsenic have increased the need for this   water plant. The water plant itself came
        retained WSB to provide an engineering   treatment. 2                     next. The clarifier was reconditioned
        evaluation of the WTP and water tower                                     and that included the removal of
        in November 2017. WSB presented an   Hydrated lime is widely used to adjust   unnecessary equipment, welding of
        evaluation report to the city council in   the pH of water to prepare it for further   holes, sandblasting and painting, and
        February 2018. The evaluation report   treatment. Lime is also used to combat   new ball bearings, sprockets and chain.
        included a priority ranking of the   “red water” by neutralizing the acid   Almost all the valves that run the water
        proposed improvements, and the lime   water, thereby reducing corrosion of   plant were replaced. A hydropneumatic
        feed system replacement was identified   pipes and mains from acid waters. The   tank that is used as a backup to the water
        as the highest priority improvement.   corrosive waters contain excessive   tower was also replaced. The media and
        The WTP Lime Softening Feed System   amounts of carbon dioxide. Lime      wash troughs in all three filters were
        improvements were designed in the    precipitates the CO2 to form calcium   replaced. The entire WTP was painted;
        spring of 2018, bid in April 2018, and   carbonate, which provides a protective   ceilings, walls, pipes and flooring. Pipes
        constructed in the fall of 2018. Most of   coating on the inside of water mains. 3  were labeled to help identify them. An
        the improvements were completed as                                        all new roof system was also installed.
        part of the WTP improvements project   Of course, the catalyst for the new   Additionally, a new generator was
        and were constructed from summer 2019  renovation in Tonka Bay was the    installed that will run the water plant
        to summer 2020.                      Minnesota Department of Health       in cases of emergency, as well as the
                                             recommendation, and after about      city’s largest lift station pumps. The
        With a population of                                                                     WTP upgraded to a
        about 1,600, Tonka                                                                       full SCADA system
        Bay has a central                                                                        (Supervisory Control
        water treatment plant                                                                    and Data Acquisition)
        that uses lime for                                                                       so the effluent water
        precipitative softening                                                                  quality will be more
        instead of salt for                                                                      consistent with pH
        cation exchange to                                                                       probes that tell the
        treat its water. Cation                                                                  rest of the plant to
        exchange capacity                                                                        add more or less lime
        (CEC) is a measure                                                                       and CO2 as needed for
        of the soil’s ability                                                                    better water softening.
        to hold positively                                                                       This also allows the
        charged ions. It is a                                                                    Public Works operators
        very important soil                                                                      to monitor the water
        property influencing                                                                     plant remotely from
        soil structure stability,                                                                their phones.
        nutrient availability,
        soil pH and the soil’s                                                                   In addition to the
        reaction to fertilizers                                                                  city of Tonka Bay,
        and other ameliorants.                                                                   the water treatment
        Lime is used by many                                                                     plant provides
        municipalities to                                                                        water to six homes
        improve water quality,                                                                   in the neighboring

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