Garden City Hall goes green

Garden City is building a bioswale to collect and filter storm-water runoff near City Hall. City officials said they hope their example will help lead the way toward better storm-water management throughout the Treasure Valley. (Photo by Page Warren)

Garden City is building a bioswale to collect and filter storm-water runoff near City Hall. City officials said they hope their example will help lead the way toward better storm-water management throughout the Treasure Valley. (Photo by Page Warren)

By Page Warren, IRU Intern

In response to federal Clean Water Act storm-water regulations, officials from Garden City are taking steps to manage their storm water on site through implementation of green storm-water infrastructure.

The Environmental Protection Agency (EPA) estimates that storm-water runoff is responsible for approximately 70 percent of pollution in lakes, rivers and creeks. Pollution from runoff negatively affects aquatic ecosystems as well as the communities that live downstream from pollution sources. Some of the most common pollutants found in storm-water runoff include pesticides from heavily treated lawns, animal waste, salt and other chemicals used to de-ice surfaces, grease and oil from parking lots and roadways, and litter. During a major storm, all of these pollutants are flushed into drainage systems, which often flow directly, without treatment, into main waterways like the Boise River.

Construction is already underway at Garden City Hall and Library where the city is replacing its outdated drainage system, which currently flows into the Boise River, with two Bioswales (channeled depressions that collect rainwater runoff).  Kevin Wallis, environmental division manager for Garden City Public Works, hopes to set an example for other businesses who have yet to redesign their storm-water infrastructure to be more cost effective, sustainable, and environmentally friendly.

“Garden City is embracing a new vision leading the way in environmental responsibility to be the first to disconnect all city-owned MS4 (Municipal Separate Storm Sewer System) outfalls,” Wallis said.  “Disconnection provides for better risk management and improved water quality.”

Under the 1987 addition to the Clean Water Act, EPA is required to issue National Pollutant Discharge Elimination System permits for municipal storm-water systems. Garden City Hall qualifies as an MS4 and is required to have a permit for its storm-water runoff. Businesses, industries and private land owners are also heavily encouraged by Idaho’s Department of Environmental Quality to use storm-water Best Management Practices such as “Source Control” which includes taking measures to minimize or eliminate the ability of polluted runoff to reach drainage systems.

According to Wallis, the swales will be filled with layers of sand and gravel on top of an impermeable sheet of plastic. Storm-water runoff from City Hall, parking lots, and the adjacent street and apartments, will be directed underground and overland toward the two large swales.  As the swales fill with water the sediment layers and plastic sheet will serve to prevent contamination of groundwater and effectively remove silts and pollutants from the surface runoff water before it drains into the surrounding soil. In addition to slowing and filtering storm-water runoff, the swales will also increase groundwater recharge and provide additional water for vegetation. The infrastructure is beneficial; it will be more cost effective, sustainable, and environmentally friendly.