Green infrastructure is practices or facilities that reduce the volume, rate or pollutant load of stormwater runoff before it goes into the sewer system and creeks.
Green infrastructure is practices or facilities that reduce the volume, rate or pollutant load of stormwater runoff before it goes into the sewer system and creeks. They do this by capturing stormwater and diverting it to where it can be detained, infiltrated into the ground, evaporated, taken up by plants, or reused. There are several types of green infrastructure best management practices. These include:
- Bioretention cells, planter boxes and other rain garden techniques
- Amended soils, tree plantings and native plantings
- Pervious pavements and green roofs
- Wet ponds and constructed wetlands
- Tree trenches and native plantings
- Rain barrels and other rainwater harvesting techniques
Combined sewers are pipes that carry both wastewater and stormwater which go to MSD’s wastewater treatment plants during dry weather and small rain events. During heavy rainfall, the combination of stormwater and wastewater may exceed the capacity of the combined sewer system. The excess flow, called combined sewer overflow (CSO), is discharged directly to the Mississippi River or to one of the river’s tributary streams through permitted outfall pipes. As part of MSD’s Combined Sewer Overflow Long Term Control Plan (CSO LTCP), MSD is creating a green infrastructure program in the combined sewer area that flows to CSOs along the Mississippi River. The purpose of the program is to reduce the volume of stormwater runoff that enters the combined sewer system during rain events. There are a number of challenges to launching a green infrastructure program. Where to find land that could be used for green infrastructure in the target area? What kinds of facilities work best for St. Louis? Who will maintain the facilities? MSD is working through these challenges with a five-year pilot program. The first hurdle was overcome with the help of the Land Reutilization Authority (LRA), which is one of St. Louis City’s economic development authorities. The LRA owns about 10,000 properties. Many of these properties have abandoned buildings in need of demolition, and many of the properties are in the target area for the green infrastructure program. So, a partnership opportunity was born! The green infrastructure pilot program works like this:
- Over the past year, MSD funded the LRA’s program to demolish about 220 abandoned buildings, which reduces runoff in the short term by removing the impervious rooftops and pavement on those parcels
- In demolition and other agreed upon LRA owned locations, MSD will build green infrastructure best management practices (BMPs) or will reserve areas for future green infrastructure BMP construction
- Larger “Neighborhood-scale” facilities built during the pilot program will be owned and maintained by MSD
- Smaller “Site-scale” facilities sized for a single lot will be in a BMP Reserve Area, and these lots will be maintained by LRA and future property owners. All reserve areas are recorded with a maintenance agreement that will transfer to the new property owners
- Demolition locations where it does not make sense to build a facility now will have a development agreement recorded with the property for future green infrastructure to be built in cooperation with redevelopment of the property
- The projects built in the pilot program will be an opportunity to show the community different green infrastructure practices, learn which practices are most desirable and collect information that will be used to create the broader green infrastructure program
Why is MSD interested in a green infrastructure program? Besides being a cost effective means for reducing the amount of runoff that enters the combined sewer system, green infrastructure can also improve groundwater recharge, improve the water quality of the runoff, enhance property values, and increase awareness of stormwater and water quality issues. More information on the green infrastructure program, including the pilot program, can be found in MSD’s CSO Long Term Control Plan. Details of the green infrastructure program can be found in Chapter 12 and Appendix Q. For additional information on the green infrastructure pilot program, please contact 314-768-6260.