Denison Municipal Utilities (DMU) is parlaying a $4 million State Revolving Fund (SRF) loan for improvements to DMU’s wastewater treatment facilities into a $400,000 project to improve stormwater runoff issues at two Denison locations.
Because the stormwater runoff projects are classified as “Water Resource Restoration Sponsored Projects” by the state, DMU will receive an overall interest rate reduction on the SRF loan that will offset the cost of the construction projects.
All the projects will be done for the same amount of money that would have paid for just the DMU project, said Rory Weis, DMU general manager.
Derek Namanny, urban conservationist with the Iowa Department of Agriculture and Land Stewardship (IDALS), is providing technical oversight of the stormwater runoff mitigation projects.
A project near Crawford County Memorial Hospital (CCMH) will involve construction of a terrace; a project at the Denison Middle School will utilize bioretention cells.
Problems have been caused by the amount of runoff from the hill where CCMH sits.
“All the water that flows off that area goes into the stream that runs right along Highway 59, which is creating some erosion in that stream,” Namanny said.
DMU has had erosion issues near the intersection of Highway 59 and Arrowhead Road.
Several high voltage cables surfaced when runoff through the area washed away four feet of soil, Weis said.
A terrace will be added to the hill between CCMH and Highway 59.
“The terrace is going to capture some of the runoff that is coming off the hospital property and temporarily hold it so it’s not a big rush of water like is going down there right now,” Namanny said.
The water will be absorbed or slowly released into the stream to mitigate the highly erosive runoff that happens after a significant rainfall.
At the middle school, bioretention cells will be used near the school building and by the practice football field.
“The ones (bioretention cells) at the middle school will be treating the runoff from the rooftop of the school and the one at the practice field will be treating runoff from the surface of the practice field,” Namanny said.
A large gully has formed south of the field due to concentrated stormwater runoff, he said.
“It’s eroding all that soil there, so we’re going to be putting the bioretention cell right where that gully is to alleviate the erosion.”
Namanny said the bioretention cells use several layers of filtering material to slow the movement of water.
“There is a layer of rock at the bottom, then there is a layer of sand/soil mix and then mulch on top of it,” he said.
Native prairie plants, which will absorb some of the nutrients in the water, will be planted on the surface of the cell.
“It almost looks like a flower bed when it’s completed,” Namanny.
The bioretention cell has a six-inch depression that temporarily holds water, which is then filtered through the lower layers.
“It will go slowly through the filtering layers and then it will either absorb into the ground or go into a tile system that sits at the bottom,” Namanny said. “They’re designed to hold the water for approximately 24 hours.”
The construction schedule is presently tentative, depending on completion of the design stage, he said.
Veenstra & Kimm, Inc. of West Des Moines is in charge of the engineering.
“We (IDALS) work with them to make sure they are following all the design standards,” Namanny said.
Construction will likely begin in July, Weis said.
Both projects should be wrapped up before the beginning of the school year.
“We don’t want a lot of construction equipment at the middle school while school is in session,” Namanny said.
The hospital project will be very visible to the public because of all the dirt that will be moved for construction of the terrace, Namanny said.
The construction at the middle school will use light excavation equipment and will be less obvious, he said.
Some of the materials for the projects will be stored at the middle school.
Namanny sees the new projects as continuations of early stormwater mitigation projects in Denison, such as the bioretention cells added to the “safety zone” area two years ago.
“It’s a partnership effort building off the previous successes,” he said.
Weis said DMU developed intergovernmental agreements – one with CCMH and one with the school – that address issues of responsibility and maintenance for the completed projects.
He said the funding arrangement with the state allowed DMU to create a project that is a win-win for everyone involved,
“We lower our interest rate and we have a long-term project that’s going to improve these watersheds for years to come,” Weis said.