The Illinois Sports Facilities Authority (ISFA), developer, owner, and operator of U.S. Cellular Field in Chicago, unveiled what it claims is the first permeable paving parking lot to be used by a Major League sports facility. The new, 265,000-square-foot lot is expected to substantially reduce the amount of water entering Chicago’s stormwater system, improve overall water quality, and help reduce the urban heat island effect.

Permeable pavement design

Permeable Pavers—software developed for use with the U.S. Environmental Protection Agency’s SWMM—to allow planners and designers to simulate the response of permeable pavements in long-term modeling applications.

According to Unilock, performance of a permeable pavement installation is controlled by the infiltration capacity of the permeable pavement, storage capacity of the reservoir in the base, and the infiltration capacity of the underlying soil. The company determined parameters such as the infiltration capacity of the permeable pavement in field and laboratory studies. Additionally, since permeable pavers are used for long-term applications, the program was written for continuous simulations, and accounts for degradation over time and regeneration of infiltration capacity by mechanical means.

However, certain hydrological design conditions must be met, Unilock says. Because of the relatively small areas involved, short computational time steps, such as 1 minute, are required, as are short duration design events (1 hour). Secondly, the reservoir in the pavement sub-base must be properly sized based on its drainage outlet capacity and the porosity of the constituent crushed rock.

“This environmentally friendly project sets a precedent for sports facilities across the country and further enhances Chicago as one of the ’greenest’ cities in America,” said Perri Irmer, ISFA’s chief executive officer. The ISFA is a government unit created by the Illinois General Assembly in 1987 to construct and renovate sports stadiums for professional sports teams in Illinois. U.S. Cellular Field is the home of the Chicago White Sox.

The new, permeable paving parking lot, claimed to be the largest such lot in the United States—more than 6 acres—meets Chicago’s 2008 Stormwater Management Ordinance, which is designed to promote programs that minimize stormwater runoff and erosion control impacts of new development and redevelopment. The permeable paving system allows water to infiltrate and collect below the paving surface, substantially reducing or eliminating the amount of water entering the city’s stormwater system and reducing localized flooding. Detained water is eventually absorbed into the subgrade below the surface and released naturally back into the environment, filtering out most contaminants.

ISFA worked with Unilock, a manufacturer of paving stones and retaining walls; Site Design Group, Inc., a landscape architecture design firm recognized for their work in sports facilities; Rose Paving Co.; and Environmental Design International, Inc., a full-service national engineering firm committed to green initiatives. ISFA broke ground on the permeable paving project in November 2007 and unveiled the new parking lot in early April 2008.

Paving stones installed on top of a gravel bed provide a drainage capacity of 154,583 cubic feet. Workers installed approximately 20,000 square feet of paving stones daily. Granite and charcoal color variations delineate parking areas.

According to Unilock, using the permeable paving system, which meets both low-impact development and Leadership in Energy and Environmental Design (LEED) guidelines, typically costs less, lasts twice as long, requires less maintenance, and is more durable than traditional bituminous asphalt projects. Additionally, the system uses recycled materials, helps recharge groundwater, improve stormwater quality, and reduces urban heat island effect.