Combined sewer systems were the best solution for city water management in the 1800s, but their pollution of waterways is a struggle for today's communities. Aurora, the second largest city in Illinois, knows this fact firsthand.
The city has made it a priority to use green infrastructure to better manage stormwater in an effort to reduce pollution to the nearby Fox River, a 202-mile-long tributary of the Mississippi that weaves through several counties in Southeastern Wisconsin and Northeastern Illinois. The river has been deemed an impaired waterway by the state of Illinois.
In 2011, Aurora's innovative and environmentally responsible stormwater management practices earned it recognition from the Natural Resources Defense Council (NRDC).
From 2007 to 2009, Aurora conducted a study funded by the Illinois Environmental Protection Agency (IEPA) on how to best implement green infrastructure to mitigate the impact of stormwater on the Fox River. The study was initiated by Mayor Thomas Weisner, who has been the driving force behind Aurora's environmentally responsible initiatives. The goal was to find ways to reduce nonpoint source (NPS) pollution that reaches the river, reduce the stormwater runoff peak discharge rate and total volume amount, and develop a naturalized dispersement stormwater management system.
As a result of the study, the city developed an innovative green infrastructure implementation plan that includes several successful naturalized stormwater management projects, a stormwater management toolkit for redevelopment and a corridor plan that identifies future water quality improvement opportunities.
Aurora identified three stormwater management projects that would treat stormwater through natural processes instead of using traditional gray infrastructure. Using funds from an IEPA grant through the Federal Clean Water Act, the city began work in October 2009, using multiple contractors on each of the three projects.
Over the past 30 years, Aurora has invested over $100 million to separate the combined sewer system. While those steps have helped prevent sewage backups in basements, they did not significantly improve the river's water quality.
"One thing we found is that stormwater is just as dirty as combined sewage because of some pollutants," says Eric Schoeny, city drainage and underground coordinator. "That's how we recognized that green infrastructure needed to be a part of efforts to mitigate combined sewer impacts."
To reduce runoff into the river from a 4.5-acre commuter parking lot, Aurora upgraded an existing retention basin that was originally built in 1990. The original 3,100-
square-foot retention basin had been designed so that small storm events bypassed the pond, and only large storm events would activate the basin. With such a large impervious area, the city saw the need for improvement.
"You get a lot of pollutants from parking lots because vehicles have an opportunity for dirt and oils to get washed off onto the pavement," Schoeny says. "Due to the original design of the commuter parking lot, 100 percent of the pollutants that washed off the parking lot during small storm events bypassed the detention pond and discharged directly into the river. From a water quality standpoint, that is exactly the opposite of what we wanted. We saw that as a great opportunity to improve water quality."
The retention basin was retrofitted with piping to divert stormwater from small events to the pond. However, the challenge was that it was located alongside a railroad embankment, with lower ground on the other side. Due to the significant grade differential and the heavy fill that had been installed at the turn of the century, piping could not be installed to allow water to infiltrate into the ground. Instead, the basin bottom was covered with an impermeable lining and a sand filter was installed to allow for biofiltration. Native vegetation was planted to help evapotranspirate the water and uptake some nutrients. Now the updated retention basin treats the first 3/4 inch of stormwater runoff. The project cost $65,100 to complete.
To intercept, treat and infiltrate the first 3/4 inch of runoff from a parkway in a residential neighborhood, a series of five rain gardens was installed. Curb cuts divert runoff from the gutter to the rain gardens, which are constructed over a newly installed, 18-foot-deep decombination storm sewer trench. Native sand and gravel were used for the trench backfill and provide excellent infiltration rates.
A topsoil mixture of sand, black dirt and leaf/mushroom compost creates the nutritive bed for native vegetation. The plants were chosen for their tolerance of water submersion and have deep root systems to keep the soil open and allow for infiltration.
In larger storm events, the rain gardens fill with runoff, overflowing from one garden to the next. A portion of the rainwater infiltrates into the ground or is evapotranspirated by the plants. Two of the rain gardens have catch basins that direct non-infiltrated runoff into the storm sewer. The gardens, which fill a 2,700-square-foot area, cost $27,500 to install.
Some residents who were previously unaware of the project happening right in front of their homes expressed objection to the rain gardens. Schoeny and Ken Schroth, city engineer and director of Public Works, talked to the concerned citizens to explain the goals and functions of the rain gardens.
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"Public participation is very important," Schoeny says. "It speaks to the saying 'Bring me in at the beginning, I'll be your ally. Bring me in at the end, I will be your critic.'"
From that experience, the Aurora team learned the importance of educating the public on activities and getting them involved in the planning. Today, Aurora continually shares information with residents through exhibits and displays at public events, speaking engagements, public meetings and an educational website.
In stark contrast to the initial objections to the first rain gardens, the Aurora downtown business association has embraced the use of rain gardens as part of a larger reconstruction project to replace two bridges and beautify the business district. Aurora won an Illinois Green Infrastructure Grant from the IEPA to add rain gardens to newly created landscaped areas that are aimed at bringing more foot traffic to downtown shops.
"The entire experience has been a valuable lesson learned," Schoeny says. "Green infrastructure is different from gray infrastructure because it is more visible and interacts with the public. You really need to get the public involved early on."
A large impervious 5.2-acre space along a four-lane highway and industrial parking lot became the site of a stormwater wetland bioswale. The 6,500-square-foot bioswale works similarly to a rain garden, but because it is adjacent to a river, it acts like a wetland because it is full of water for most of the year.
In the bioswale, water is filtered a couple ways. Stormwater runoff from an existing separate storm sewer is diverted to an underground U-shaped detention area. Large solids are filtered out and collected in a tank, which is periodically emptied with a sewer vac truck and treated. The remaining water then enters the bioswale and filters through native vegetation before discharging into the river. The bioswale treats the first 3/4 inch of runoff and helps decrease the peak discharge rate from the drainage area. Total cost for construction was $99,500.
Handbook for redevelopment
To help meet Aurora's stormwater management ordinance for redevelopment projects, the city's team assembled a Stormwater Management Toolkit. Redeveloping in a heavily urbanized area provides challenges for meeting stormwater storage requirements because there isn't enough space. The toolkit defines water quality improvements to give developers some guidance on how to meet the ordinance requirements.
For example, in lieu of retention requirements, the toolkit provides a metric to remove 40 percent of suspended solids from stormwater discharged from the development site as a result of a 3/4-inch rainwater event. Then it is up to developers to decide how to achieve that net benefit in water quality.
Bioinfiltration at McCarty Park
In 2009, the IEPA made the City of Aurora aware of potential green infrastructure funding through the American Recovery and Reinvestment Act. At the same time, Schroth's team was working to prepare and submit a combined sewer overflow (CSO) long-term control plan, a $120 million unfunded plan that had been mandated by the U.S. EPA and IEPA. The team decided that there was an opportunity to use the ARRA funding to help mitigate CSOs as part of the long-term plan.
The city's beloved McCarty Park was chosen as a site for the project to reduce peak runoff rates to the combined sewer system and reduce discharge of stormwater pollutants to the Fox River. The city had previously planned on installing several hundred feet of storm sewers to serve that area. Instead, three bioretention basins were installed along the parkway. Openings in the existing curb and gutter were created to allow stormwater runoff to enter the basins. An overflow pipe at the downstream end of the basins provides a secondary outlet in the event that rain exceeds the basins' infiltration capacity. A flow meter has been installed in the downstream overflow pipe in order to gauge the long-term performance of the basins.
The McCarty Park project proved to be a huge success due to its operational and cost efficiencies. While installing the storm sewers would have cost $140,000, the bioretention basins cost just $70,000.
"The basins eliminated the need to install expensive storm sewers," Schoeny says. "We were able to remove the same stormwater from the combined sewer at half the cost. Plus, with the green infrastructure, it accomplishes a great water quality improvement and a real nice aesthetic amenity for the public. The McCarty Park project taught us how to identify other locations that are going to be cost-effective for combined sewer control."
To identify and assess NPS pollution sources in the area, Aurora developed a Naturalized Stormwater Management Corridor Plan. The plan recommends and prioritizes locations where future water quality projects will be most effective. The document is also a resource to help people understand the impacts of stormwater on the receiving streams and the advantages to implementing naturalized improvements like rain gardens and bioswales.
Using grant money from the IEPA, Aurora will be installing more rain gardens in 28 intersections in 2013. The cost for the rain gardens will be $1.7 million, however, costs to construct gray infrastructure to provide similar improvements to the combined sewer system would cost $3.5 million.
"That is some serious money that helps us with our struggle to fund the long-term control plan for combined sewer overflows," Schoeny says.