Each spring, large quantities of dissolved nutrients (such as nitrogen and phosphorous) are transported from the upper Midwest into what is called the Gulf of Mexico Dead Zone — an oxygen-deficient area that grows to approximately 8,000 square miles each year and cannot support marine life.
In Chicago, the public right of way includes more than 4,000 miles of streets and 2,100 miles of alleys — paved impermeable surfaces that contribute significantly to urban runoff that eventually makes its way to the Gulf.
The Chicago DOT (CDOT) is addressing this problem with a comprehensive sustainable streetscape project that will use several environmentally friendly techniques commonly associated with LEED-certified buildings but not typical in streetscape designs. The department will evaluate the techniques to assess their suitability for future projects and create a model for watershed planning in the combined sewer area.
Construction is scheduled to begin in late 2009. It is funded largely through a tax increment financing district, but it has also received several grants, including nearly $450,000 through the Illinois EPA 319 nonpoint source pollution program (which funds best management practices such as rain gardens, permeable pavers, and bioswales) and $73,200 from the Federal Highway Administration's Ecological Grant Program in addition to in-kind services from the Metropolitan Water Reclamation District of Greater Chicago.
The project, designed and implemented by AEC firms Wight & Co. and Knight E/A, is located on the city's near south side along two major arterials — Cermak Road and Blue Island Avenue between Halsted Street and Western Avenue.
Cermak Road is a five-lane truck route with no on-street parking and 10- to 15-foot-wide parkways. It divides the Pilsen neighborhood from an industrial district along the south branch of the Chicago River.
Blue Island Avenue is a five-lane truck route with street parking and 20-foot-wide parkways just north of the project area.
The project began when CDOT set out to determine what the equivalent of a platinum-rated streetscape might look like and what environmental, cultural, and economic benefits it may provide. The platinum rating is the highest level of achievement awarded by the U.S. Green Building Council (USGBC) for a project's level of commitment to sustainability. Wight and Knight developed a series of environmental categories and identified goals similar to a LEED scorecard:
Recycled Content. Recycle at least 90% of construction waste (excluding landscape debris) based on total weight or volume similar to the USGBC's LEED-NC criteria. The sum of post-consumer recycled content plus one-half of the pre-consumer content must constitute at least 20% (based on cost) of the total value of the materials in the project.
Energy Conservation. Reduce energy use by a minimum of 40% below the streetscape baseline typical of new construction; use reflective surfaces on sidewalks/roadways; use dark-sky-friendly fixtures. Use materials or products that have been extracted, harvested, or recovered, as well as manufactured, within 500 miles of the project site for a minimum of 40% (based on cost) of the total materials value similar to LEED-NC criteria.
Stormwater Management. Divert 80% of the typical average annual rainfall and at least two thirds of the rainwater that falls within the catchment area into stormwater best management practices that promote infiltration, provide water for new landscape, improve water quality, and reduce stormwater that enters the combined sewer system.
Urban Heat Island Mitigation. Reduce ambient summer temperatures on streets and sidewalks through the use of high-albedo pavements and coatings on roadways and sidewalks, use trees for shading, increase landscape, and incorporate permeable pavements.
Alternative Transportation. Improve bus stops with signage, shelters, and lighting where possible; facilitate use of bikes with new bike lanes. Improve pedestrian mobility with new fully accessible sidewalks and improved crosswalks.
Beauty & Community. Create attractive places that celebrate the community, provide gathering space, and allow for interaction and observation of both people and the natural world.
Water Efficiency. Eliminate use of potable water sources for irrigation. Specify native or climate-adapted, drought-tolerant plants for all landscape material.
Education. Provide public outreach materials/self-guided tour brochures to highlight innovative, sustainable design features of the streetscape.
Commissioning. CDOT, in partnership with the water reclamation district, will model and monitor various aspects of the project, including stormwater initiatives and air quality. Both pre- and post-construction data will be gathered to determine the efficacy and long-term performance of these initiatives.
When complete, the 1.5-mile-long streetscape project is expected to be one of the most environmentally friendly stretches of roadway in Chicago. The project team has designed several simple and cost-effective best management practices to collect and infiltrate street runoff.
On the north side of Cermak Road, runoff will be collected in sidewalk storm-water planters connected to large expanses of engineered soil below the sidewalk. Engineered soil (¾-inch limestone rock coated with soil) is used to both encourage tree growth and provide stormwater detention. When it begins to rain, initial stormwater flow will bypass existing city infrastructure, enter the stormwater planters, migrate into the engineered soil, and be infiltrated or absorbed by tree roots.
This strategy allows for maximum infiltration while taking advantage of existing infrastructure and provides a cost-effective solution within the existing urban fabric. In addition, curb extensions on many of the side streets will be equipped with rain garden planters that interrupt the gutters' flow line to redirect water into the planters.
Street runoff will enter the bioswale through perforated curb sections on either side of existing stormwater inlets. The bioswales will be interconnected beneath cross streets when possible and have one raised overflow structure per block. The existing sewer infrastructure will remain to accommodate large storm events that may overflow into the street.
To intercept the “first flush” pollutants and improve the quality of street runoff before it enters landscape areas along Cermak Road, a layer of zeolite will be incorporated into the stone infiltration zones of both best management practices. Zeolite is a unique type of microporous volcanic mineral that will trade positive ions with those of phosphorous, nitrogen, calcium, and other water-borne pollutants.
For stormwater management along a half-mile stretch of Blue Island Avenue, new dedicated bike lanes and on-street parking lanes will feature permeable pavers. A 3-foot-deep catchment of stone below the pavers will act as detention with overflow pipes connected to existing infrastructure. In addition, infiltration planters, similar to those proposed on the north side of Cermak Road, will catch stormwater that flows over the permeable pavers and will redirect it back into the stone storage layer below.
Sidewalk planters hydrologically connected to the stone catchment areas below the street will provide long-term access to water and encourage deep root growth in the native and drought-tolerant plant species being specified. The permeable pavers themselves will be topped with high-albedo photocatalytic cement (smog-eating concrete). The photocatalytic cement also resists pollutants that gather on its surface, thus keeping its light color and ability to reflect light back up to help achieve uniform light levels. This technique contributed to a lighting design that specifies a white light source in the street fixtures and achieves an anticipated 49% energy savings below the streetscape baseline.
Finally, a stormwater plaza at Western and Blue Island avenues will take advantage of an empty city-owned lot that has a slight drop in elevation. With cascading planter beds and a backdrop of trees in an area with little vegetation, the storm-water plaza will create a place for people to sit and provide a location for an educational identifier and future community art installation.
Stormwater from Western Avenue will be directed into the highest planter via a runnel. Water will build up 2 inches in the first planter and then cascade into lower planters, repeating the movement with each planter. The lowest planter will be equipped with an overflow-connected existing sewer system.
These stormwater best management practices work in combination with the city's goals and initiatives to redefine the role that urban infrastructure can play to improve a city's vitality and quality of life. Daylighting stormwater highlights a natural resource — water — that is often ignored in dense urban areas, and not only helps to educate the public but helps make the city more attractive.
— Womack, ASLA, LEED AP, is director of sustainable design for Wight & Co. Attarian, AIA, LEED AP, is the project director for the Chicago DOT's Streetscape and Sustainable Design Program.