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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
1
Lime is used by many plant provides
municipalities to water to six homes
improve water quality, in the neighboring

8 MRWA TODAY S SPRING 2021