Prior Lake, Minn., partners with neighboring tribal community on water treatment facility
A few years back, Prior Lake was facing a question all too familiar in rapidly growing communities: How do we meet the growing water demands of our community in an environmentally and economically sustainable way?
I am the mayor of the City of Prior Lake, a suburb of Minneapolis, Minn., with approximately 26,000 residents. To provide our citizens with safe, high-quality water now and into the future, we needed to increase our water capacity from 6.5 million gallons per day to more than 8 million.
Meeting our water demands would require significant investments in our infrastructure. But the facilities we would need — a new water tower and water treatment plant — were two costly projects. A decision to go-it-alone and build would saddle our citizens with significant debt and our ratepayers with elevated water costs.
While this isn’t an uncommon problem, we found an uncommon solution. We looked beyond our borders to seek a collaborative approach partnering with our neighboring tribal nation. Initial conversations led to a solution that was a little outside-of-the-box: we partnered on a joint water treatment facility.
Our Approach
The Shakopee Mdewakanton Sioux Community (SMSC) is a federally recognized, sovereign, Dakota tribal government — and wonderful neighbor. Like our city, the tribe is growing. They were considering a go-it-alone approach of their own to build a new treatment plant to increase their 1.5-million-gallon-per-day capacity. We had partnered with the tribe on many initiatives in the past, from infrastructure to mutual aid agreements, but nothing of the size, magnitude or permanence of a water treatment facility.
We began discussions of a joint water facility with the tribe in 2015, and the next year commissioned a study to evaluate our shared water needs. The findings were promising and we decided to proceed with building a facility.
To ensure the success of our venture, Prior Lake entered into a joint water purchase and facility expansion agreement with the SMSC in 2017. This contract laid out the terms of our collaboration and exactly how the plant would be developed and managed — an invaluable tool to ensure both governments were on the same page before launching such a complex and long-term project. As a part of this agreement, the city and SMSC also jointly own the facility’s equipment.
Improved Technology
Our facility’s treatment process was developed using two major processes in order to deliver safe drinking water to our two communities: sand filtration and reverse osmosis (RO) membrane treatment.
The first step in our joint facility’s process is aeration. The aerator comprises numerous pipes through which the water flows and begins the oxidation of iron and manganese. An induced draft fan draws air through the aerator to further aid in the oxidation process.
Next, the water flows by gravity into a 178,000-gallon detention tank that holds the water for approximately 45 minutes and allows for further oxidation of the iron and manganese. Afterward, the water flows into four filter basins. Each filter basin consists of a media-retaining underdrain system and dual filter media, which is composed of 15 inches of anthracite and 15 inches of manganese green sand to further filter out the oxidized iron and manganese.
The trapped material is then removed by backwashing, which reverses the flow of water through the filter. The process is enhanced by blowing compressed air up through the underdrain blocks, causing the media to scour itself. The backwash water is held in the tank to allow particles to settle out, and the filtered water then flows to a 375,000-gallon clear well where it can be pumped to the City of Prior Lake’s distribution system using one of two high service pumps.
Filtered water is also run through a RO treatment process to filter out and flush away contaminants. An antiscalant and sodium meta-bisulfate are first added to prevent the water from damaging the membrane surface. The RO process then begins with a pump that increases the water pressure, forcing the water molecules through the membrane and filtering out 95–99 percent of dissolved solids like chlorides, sulfates, nitrates, and hardness from the water.
After RO treatment, the water has a pH of 5.0 and is corrosive. The facility adds caustic soda to the product water to increase the pH to approximately 7.8–8.0.
Finally, the water is enhanced to provide disinfection residual and fluoride for public health. A corrosion inhibitor is also added to decrease the corrosiveness, thus minimizing the potential for lead and copper leaching into the water.
Impact
The ribbon has been cut; the plant is now operational and providing water to both our communities. The South Area Water Treatment Plant has connected our city and tribal water together as a fully integrated system. Although the plant is located on SMSC reservation land, our city can access water as needed via integrated control systems that allow our separate systems to function as one.
The plant provides up to 2.1 million gallons of additional water each day to the city, removing iron, manganese, nitrates, sulfates, and other total dissolved solids. It also meets the SMSC’s water demands as well, doubling their total capacity.
This new infrastructure and state-of-the-art process will benefit our communities for years to come. We have a perpetual agreement with no end date. In addition, the joint water treatment plant has enough capacity right now to support the estimated growth rate for our city and the SMSC for the next 20 years.
This partnership has resulted in significant savings for our citizens and the tribe. By collaborating, the city and tribe saved $11 million collectively. Prior Lake has saved $7 million, while the SMSC has saved $4 million. The facility also helps protect our environment, guarding the region’s groundwater from overuse.
Partnering with a Tribal Nation
This project was an incredible opportunity, but not without its own set of challenges. Tribal governments are sovereign nations that operate on a government-to-government basis with federal, state, and local governments. They present regulatory and logistical concerns that are unique and different than working with a city, county or state government.
These differences and challenges may be why these sorts of projects are unique. Cities and tribes don’t always work together, and I know that is a lost opportunity.
This new infrastructure, and all the benefits it delivers to our community, wouldn’t be possible without our partnership with the SMSC.
It’s my hope that our experience partnering with a tribal nation provides an example for others planning for the long-term needs of their citizens. Providing clean water, protecting groundwater, and maximizing efficiencies are something we can all agree on. And by working together, across borders and boundaries, we have a higher likelihood of achieving them. WW
