Civil engineers continue to find new ways to utilize tire shreds. One of the latest, rain gardens, is the storm water management system of choice next to a parking lot for a school district building in St. Louis Park, MN.

Kevin Pheiffer, project designer for Anderson—Johnson Associates, Inc. in Minneapolis, says the void spaces in TDA (Tire Derived Aggregate) are ideal for providing underground holding areas for water runoff at a fraction of the cost for alternatives and, in the case of St. Louis Park, by using less space than traditional holding ponds.

Rain gardens are detention and retention systems to slow down water that runs off of parking lots or other impervious areas. If water isn’t slowed down, it discharges into a storm system at high speed. When it comes out of a watershed, it can flood a river.

Fast-moving water also carries a lot of sediment with it, according to Joe Otte, Wenck Associates. “Most of the contamination that gets into our bodies of water is sediment or things attached to sediment,” he said. “When you slow down water, you increase the resonance time and that allows anything suspended in the water a chance to get out.”

Rain gardens can be more attractive than traditional holding ponds for a number of reasons. A rain garden:

• isn’t a water hazard,

• maintains vegetation, and

• can be made to work in tight quarters.

For the St. Louis Park school, engineers were required to design a new storm water management plan because when they redid the parking lot and added sidewalks they increased the amount of impervious area. Nationwide, storm water management plans are often required for construction projects.

“We looked at many alternatives and TDA ended up being the most cost effective one,” said Pheiffer. Ponds take more space. Plastic storm chambers may offer more storage in less area, but are much more expensive. Rocks would cost two to three times more than TDA, Pheiffer estimates.

At the school, the rain garden was constructed in a previously turfed area covering about 1,300 square feet. Dirt was removed and two feet of TDA put in place. Six inches of decorative rock went on top of the tire shreds. Trees and vegetation were planted on top of that. Now, rain water runs off of the parking lot and sidewalks into the rain garden. Water moves out of the rain garden through a four-inch drain tile that leads to the city’s storm water system.

“Everyone involved is happy. We fully endorse the Tire Derived Aggregate,” Pheiffer said. “We’re trying to find as many uses for it as we can right now.”

Tire shreds for the project were part of a full-circle recycling program offered by First State Tire Recycling. A tire clean-up project in a nearby community provided the scrap tires. Everybody wins, says Monte Niemi, CEO, First State Tire Recycling. “People can see an immediate benefit to recycling when tires get picked up in the morning at a clean-up site, processed and then delivered to a school construction project later in the day,” Niemi said. “There’s a further benefit to supporting the use of rain gardens because they help protect our valuable water resources.”