“There’s nothing like a shiny, new water treatment plant,” said no one ever, until now. After a year and a half of having to work around sandblasters, painters, floor refinishers, and having all their equipment covered in plastic, the public works department in Tonka Bay, Minnesota (population 1,600), is thrilled with their new surroundings.

In May 2017, the Minnesota Department of Health strongly recommended that the city complete an engineering evaluation of the water treatment plant (WTP) due to its age and condition and the resulting challenges to maintaining consistent water quality. The city retained WSB, a consulting firm, to provide an engineering evaluation of the WTP and water tower in November 2017. WSB presented an evaluation report to the city council in February 2018, which included a priority ranking of the proposed improvements, and the lime feed system replacement was identified as the highest priority improvement.

The WTP lime softening feed system improvements were designed in the early spring 2018, bid in April 2018, and constructed in the fall 2018. Most of the improvements were completed as part of the WTP improvements project and were constructed from summer 2019 to summer 2020.

Tonka Bay has a central water treatment plant that uses lime for precipitative softening instead of salt for cation exchange to treat its water. Cation exchange capacity (CEC) is a measure of the soil’s ability to hold positively charged ions. It is a very important soil property influencing soil structure stability, nutrient availability, soil pH, and the soil’s reaction to fertilizers and other ameliorants. Lime is used by many municipalities to improve water quality, especially for water softening and arsenic removal. However, this is not the case in Hennepin County, the largest county in Minnesota. Using salt in individual customer water softeners is still the prominent method in the area. Indeed, the American Water Works Association has issued standards that provide for the use of the lime softening process in drinking water treatment.

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Five Things to Keep in Mind When Undergoing a Water Treatment Plant Renovation

1. Allow for plenty of time to review the plans with all necessary parties (such as the city engineer before bidding and the contractor before the work begins) to confirm the list of items that needed to be upgraded.
2. Stay on top of the progress by visiting the water treatment plant throughout the renovation. It keeps the engineer and the contractor, along with their subcontractors, accountable.
3. If something doesn’t make sense to you, question it. (For example, painting the floor with an inferior product that doesn’t hold up well in a sample area of the plant).
4. Know that this undertaking will be a huge inconvenience to the public works staff for several months. They will have to work around all the equipment covered in plastic while sandblasting and painting are taking place.
5. Change orders happen, so expect them.

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In water softening, hydrated lime is used to remove carbonate “hardness” from the water. Lime-enhanced softening can also be used to remove arsenic from water. Stricter drinking water regulations for arsenic have increased the need for this treatment.

Hydrated lime is widely used to adjust the pH of water to prepare it for further treatment. Lime is also used to combat “red water” by neutralizing the acid water, thereby reducing corrosion of pipes and mains from acid waters. The corrosive waters contain excessive amounts of carbon dioxide. Lime precipitates the CO2 to form calcium carbonate, which provides a protective coating on the inside of water mains.

Of course, the catalyst for the new renovation in Tonka Bay was the Minnesota Department of Health recommendation, and after about a year of discussion, the city council made the decision to move forward with the renovation. Fortunately, the city was able to secure a low-interest loan from the Drinking Water Revolving Fund, administered by the Minnesota Public Facilities Authority and the Minnesota Department of Health, for all of the $1.9 million cost.

There was a lot of renovation that needed to be done starting with the removal of the old lime slaker equipment and adding a new lime tank slurry system in the base of the lime silo. By doing this, most of the lime dust is kept out of the water plant. The water plant itself came next. The clarifier was reconditioned and that included the removal of unnecessary equipment, welding of holes, sandblasting and painting, and new ball bearings, sprockets, and chain. Almost all the valves that run the water plant were replaced. A hydropneumatic tank that is used as a backup to the water tower was also replaced. The media and wash troughs in all three filters were replaced. The entire WTP was painted—ceilings, walls, pipes and flooring. Pipes were labeled to help identify them. A new roof system was also installed. Additionally, a new generator was installed that will run the water plant in cases of emergency, as well as the city’s largest lift station pumps. The WTP upgraded to a full Supervisory Control and Data Acquisition (SCADA) system so the effluent water quality will be more consistent with pH probes that tell the rest of the plant to add more or less lime and CO2 as needed for better water softening. This also allows the public works operators to monitor the water plant remotely from their phones.

In addition to the city of Tonka Bay, the water treatment plant provides water to six homes in the neighboring community of Shorewood, including the police and fire departments and Shorewood’s public works department.

No project is perfect, and Tonka Bay did experience some minor problems during the renovation. American Iron and Steel certified parts were hard to get in a timely fashion, and there were unforeseen issues inside the walls near where a new door on the second level was supposed to be installed so that the filter media could be brought in. The natural gas line to the generator had to be dug after the season’s frost set in, making that a challenge. One problem, that no one could have foreseen, was the COVID-19 pandemic. While public works was still on the job, city hall shut down and staff were working from home until the beginning of June. In addition to that, there was an issue with the painting subcontractor. The process of painting the water treatment plant took months longer than it should have. What seemed like a never-ending job finally did end in June, six months after it was supposed to have been done.

Other cities facing the possibility of water treatment plant renovations need to make sure they are clear on what their objectives are and make plans to revisit those objectives during the renovation. Things can change, and frequently do, during the renovation of an aging facility. Good luck!

 

KATHY LAUR, MPA, is city administrator of Tonka Bay, Minnesota.