Farnsworth Group

Green Infrastructure Impact on Combined Sewer Overflows 

Federal, state, and local governments are all focusing efforts on reducing the destructive impacts of storm water runoff.  The major impacts of runoff include pollutant delivery to surface waters, flooding, and erosion. In Illinois, we see evidence of storm water runoff after rainfall events in our yards, streets, fields, streams, and rivers. Green infrastructure is being proposed in many communities to provide relief not only to storm water runoff, but also to combined sewer overflow issues, which several of our local communities are working to resolve.

Central Illinois Conditions

Locally, in the communities of Peoria, Pekin, and Havana, which are served or partially served by combined sewers, the negative impacts of storm water runoff are even more significant. Combined sewers carry both storm water and sanitary sewage in the same pipe. With minimal rain events, the storm water is transported within the sewer pipe to the wastewater treatment plant for proper treatment and discharge to the Illinois River. But, during periods of heavy rainfall, the combined sewer system and treatment plants are not able to handle the storm water runoff, resulting in a combined sewer overflow (CSO) to the Illinois River. These discharges contain water with pollutant levels that violate the Clean Water Act.

The Illinois Environmental Protection Agency (IEPA) has been focusing attention on all combined sewer systems within the state since the 1970’s. Communities have developed solutions to meet the “then current” regulations, but with time there have been ever more stringent regulations aimed at reducing pollutant discharges into the receiving streams. The costs of these solutions to meet current regulations are very high, with Peoria estimating a cost of up to $250 million to meet current CSO regulations.

The IEPA requires each combined sewer community to prepare a Long Term Control Plan (LTCP) defining proposed projects and schedules to meet the regulations. Pekin and Havana have submitted and received IEPA approval of their LTCP and have completed many of the projects defined in their plan for compliance. The City of Peoria has submitted their LTCP, and are in negotiations with the Agency to reach approval.

Status of Pekin & Havana

The City of Pekin’s LTCP proposes additional treatment capacity at their primary wastewater treatment facility, expansion of their storm water holding facilities, and increased interceptor sewer capacity, in addition to other system modifications to reduce the number of combined sewer overflows into the Illinois River. The City also requires storm water retention and detention, a type of green infrastructure, in new developments to reduce the storm water runoff rate entering storm sewers and the combined sewer system and provide for infiltration. These improvements were approved by the IEPA and considered the most cost-effective approach for the City of Pekin. Much of this work is complete, with remaining work limited to storage and interceptor sewer improvements. The total cost of Pekin’s improvements are estimated to be in the $50 to $60 million range.

Each community’s combined sewer system is unique, and Havana took a different approach to meeting the regulations. While they also require storm water retention/detention for new developments within the City, they chose sewer separation combined with better utilization of storage within the existing interceptor sewers at a cost of under $2 million. The City is complete with the improvements and are currently analyzing overflow data to determine if the combined sewer system complies with regulations. 

Implementing Green Infrastructure in the City of Peoria

The City of Peoria combined sewer system experiences an average of 20 to 30 overflow events each year. The downtown and bluff areas, the older parts of the City, are served by combined sewers. Sewer separation within these areas would be cost prohibitive, so the City has proposed green infrastructure improvements as their most cost-effective solution to the CSO issue.

Numerous studies have been done across the country, assessing the effectiveness of green infrastructure projects. The United States Environmental Protection Agency claims managing wet weather impacts are accomplished in a cost-effective method utilizing green infrastructure. When included in site design, green infrastructure reduces and treats storm water at its source while at the same time delivering environmental, social, and economic benefits. There are a variety of green infrastructure projects, including many that have already been constructed within Peoria.

One example of effective green infrastructure are the planter boxes in the Warehouse District that can collect and absorb runoff from the street, sidewalk and parking areas while enhancing the appearance of the area.

The permeable interlocking pavers along the parking lot of the Murray Building not only add to the appearance of the site but also collect the runoff from the parking lot and allow it to absorb into the underlying soil.

Bioswales are vegetated channels that provide storm water treatment and retention. Bioswales were included in the site designs for Glen Oak Birth-8^th Community Learning Center, Peoria Public North Branch Library, and Northminster Presbyterian Church, among other recent local developments. These channels slow the flow of the runoff, allow the vegetation to filter the water, and provide time for water infiltration into the soil or more slowly enter into the existing storm sewer system.  

Green techniques not only reduce the damaging impact of storm water runoff, but also enhance our built environment, by providing aesthetic benefit, habitat, educational opportunities and many other benefits not always associated with buried pipe solutions.  Based on the effectiveness of green infrastructure projects at reducing the impact of storm water runoff, we are likely to see more of them in the future.