Wetland-based sewer system is being constructed for Spring Hill

This article submitted by Michael Jacobson on 9/8/99.

work at spring hill The city of Spring Hills is on the verge of having a new main street and a new municipal septic system that utilizes a constructed wetland to treat the city's wastewater.

Road construction on County Road 80, which runs north-south through the heart of the small town, should start this week, and take a little more than a week.

The city-wide collection system for the municipal sewer system was started on Aug. 17 and is done already, as is the dirt work on the two wetlands on the north side of town. The liners should be installed in both ponds this week. They will need to be tested against leaks, and then the rest of the wetland can be constructed. Two septic tanks should be installed next week.

The entire system could be approved and operational by the end of the month. When that approval is final, individual hook-ups for the 72 residents of the town can begin. Some hook-ups should be done this fall, and the rest will be done next spring.

Workers from Traut Wells of Waite Park worked Thursday at installing the tubing for the drip irrigation field at the Spring Hill city sewer project.

Discovery of a problem
Hill learned it had a problem in October of 1997. The county was planning on rebuilding County Road 80 back then. "Before they do any road construction, they check to see if they are going to disturb any storm sewer or septic sewer," explained Karen Voz, of Stearns Country Environmental Health.

What they found is the city's septic tank had a common drain field that discharged into a nearby creek. Mary Wuertz, Spring Hill's mayor, remembers taking office that year amid the regional media interest in the story.

Voz said the community was easy to work with and focused on solving the problem, even before they received their grants. "They were very, very cooperative. Their attitude was, 'If we've got to get this done, let's do it now,'" she said. Wuertz and Voz were pleased by the community participation at a series of meetings held to discuss the problem and decide on the remedy. "I can't say enough about how cooperative the residents were," Voz added.

Reuben Bertram is an example of that cooperative nature. His sewer system is only five-years-old. At first he thought that he might not opt to hook up to the city system, but in the end he decided it would be easier, and cheaper, to hook up now instead of later. That way he won't have to worry about his system failing or about a decreased value for his property if he decides to sell. "I think it'll be nice," he said, of the city's sewer system. "It would have been nice to know it ahead of time...but that's the way it goes."

The community had five options for a legal septic system, according to Voz: a city lagoon, individual septic systems, hooking up to the Greenwald, Elrosa, Meire Grove (GEM) lagoon, an aerobic tank with drip irrigation, and a wetland-based system. Lagoon systems are expensive and require considerable maintenance. The GEM system doesn't have enough capacity to include Spring Hill without additional construction.

Individual systems might have worked for one generation, but with private wells and city lots meeting setbacks requirements, it would have been difficult. When the systems started to wear out in ten to 15 years, residents might have had a more difficult problem.

The aerobic tank has more mechanization and consequently requires more maintenance than the wetland system, which was ultimately chosen. "I think (the residents) liked that one for simplicity reasons, and I think it will blend in nicely with the landscape, too," said Voz.

The solution
Spring Hill treatment The sewer system for Spring Hill will consist of a gravity-flow collection system, which is scheduled to service 40 units and a population of 72. After collection, the waste will flow to the north side of town, where the treatment system will be located. The system is designed to handle 9,200 gallons of waste per day.

The first component will be two 6,000-gallon septic tanks. These tanks, like septic tanks in private home systems, will provide primary treatment by breaking down organic material. Heavy solids will be collected in the bottom of the tanks, which will need to be removed periodically.

The wastewater will then flow into the wetlands for the main treatment. Scott Wallace, vice president of North American Wetland Engineering, which subcontracted the designing of the wetlands for Spring Hill, said constructed wetland technology started in Germany in the 1950s. The first application in the southern United States wasn't until the 1970s, according to Wallace, and key design breakthroughs that allow the wetlands to work in cold weather weren't made until the 1990s.

Two identical wetlands are being built for Spring Hill. Both start with a PVC liner that will prevent seepage into the soil and the groundwater. Eighteen inches of gravel will be put on top of the liner, and a mulch layer will be put on top. Wetland plants will be planted on the mulch layer and their roots will reach down into the waste water flow. "They'll actually extract nitrogen and phosphorus from the water to help them grow," said Wallace.

"The main part of the treatment is really done by bacteria growing on the gravel substrate," explained Tim Bayerl, of Widseth Smith Nolting and Associates, the city engineer for Spring Hill. "The plants do take up some nutrients, but bacteria by far will do the most."

Wallace estimated 80 percent of the treatment will be done by bacteria and 20 percent by the plants through the absorption of nutrients. The bacteria will turn the nitrogen into a gas, which will be released to the atmosphere.

One of the two mechanical components of the Spring Hill system will be forced aeration in the wetlands, which will provide the bacteria with enough oxygen to break down the waste. That oxygen supply will be especially critical in winter, when plant growth obviously will not be helping and when snow on the ground could limit the oxygen. "The more oxygen you provide, the more microbacterial action you get," said Voz. The foot of mulch provides insulation in the winter, keeping the bacteria alive and working. "We've been able to prove pretty conclusively that when you have this mulch layer to prevent freezing, they're able to operate in the wintertime," said Wallace.

According to Wallace, North American Wetland has done 75 wetlands-treatment projects in the state. (Only a few have been done by others, mostly for research.) While Spring Hill will be the first municipality in Stearns County, and possibly in the state, with a wetland-based treatment system, North American Wetland has done treatment projects of a similar size for residential areas and for other sources of waste.

After the wastewater has been treated, the water will be disposed in a drip irrigation field. Spring Hill bought 4.3 acres of farm land for the irrigation field. The water will need to be pumped up a hill, and it will flow through the underground tubing and out into the soil. Trees will be planted on top of the irrigation field.

The city's current system will be used only as a storm sewer in the future: for rainwater runoff, flooded basements, etc.

Funding the project
To fund the sewer project, the city of Spring Hill received a $382,400 rural development grant and a $47,000 loan from the United States Department of Agriculture. Jim Merrick, who works in the USDA office in Waite Park, said the loan and grant was based on the estimated cost of the project and the median income of the community. The grants and loans are competitive, he stressed. "This funding is federal," he said. "We have a lot more demand for the funding that we have (funding) to help."

The city of Spring Hill also received a $165,600 grant from the Minnesota Pollution Control Agency. The total cost was projected at $595,000, but the bids came in $50,000 less.

Wuertz said the bids for the project came in $50,000 under the projections, leaving the city with $90,000 in contingency funds. Excess USDA funds will need to be returned, but Wuertz said the MPCA grant might cover up to 50 percent of hook-up costs for some private homeowners. Residents should pay their expenses and submit their bill to the mayor, who will forward it to the MPCA for consideration.

Each homeowner will be responsible for materials and installation of the piping from the main to their house. The cost per unit could be $1,000 or more.

The city ordinance requires every resident who can to hook up to the system. Hook-ups will need to be completed by July 1, 2000, giving residents time in the spring to finish if time runs out this fall.

Wuertz said that all the contractors, engineers, and government workers for the project have been very helpful.

The project is working out wonderfully for Spring Hill, according to Wuertz. "We'd never have been able to fund a sewer and a road," she stated. "We'd never have been able to do it." The road construction will cost the county about $300,000.

When the problem was discovered, Wuertz remembers asking their local priest to pray for the town. With the end now in sight, she said, "I told him last week, 'Father, I think your prayers have been answered.'"

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