The new DuPage County Courthouse and government complex will be a study in contrasts when it's completed. On the one hand, it will be a state-of-the-art judicial facility designed to serve the needs of one of the nation's fastest growing counties. And yet, bordering the distinguished building will be a re-created wetland, engineered to correspond as closely as possible with the original character of the land.

This feat of intelligent engineering will be made possible through the collaboration of -Wight & Company of Dowsers Grove, Illinois; the planners of DuPage County, Illinois; and the Kane-DuPage Soil and Water Conservation District.

Wetland History and Legislation
The preservation of natural wetlands has gained considerable attention in the last two decades. Wetlands have disappeared at an alarming rate since the pilgrims came to America, but between 1947 and 1967 alone, the nation lost an estimated 21 to 36 percent of its wetland area. Under the 1972 Clean Water Act, the Army Corps of Engineers and the Environmental Protection Agency are charged with protecting this dwindling natural resource with benefits that far exceed wildlife conservation alone.

Even the U .S. Supreme Court has been involved in the conservation effort, giving the Army Corps of Engineers broad power to curb development on millions of acres of marshy land in every state. Since 1975, the Corps has claimed that the Clean Water Act requires federal permission to develop any wetlands adjacent to navigable waters — even wetlands entirely within a single state.

While the Corps approves the development of about 500, 000 acres annually, it has halted some projects and limited the size of others. In 1984, a U.S. appeals court said that the Corps had overreached its authority in barring the development of a wetland, but a unanimous Supreme Court upheld the sweeping Corps regulations.

DuPage County is located in northeastern Illinois. Most of Illinois' remaining wetland territory is in this section of the state. A large portion of this wetland area has been lost to development — a cause for alarm because of the substantial stormwater detention and water quality benefits that this type of ecosystem offers,

Wetland Characteristics and Benefits
The wetlands themselves are characterized by soil saturated with water and plants adapted to life in this type of habitat. Few ecosystems can compare to wetlands in the variety of wildlife — especially endangered species — that they support. By slowing water runoff and temporarily storing excess water, wetlands also help to protect communities from flooding. In addition, they are chemical and biological oxidation basins that cleanse both surface and groundwater systems.

Wetland as a Stormwater Management Tool
At the DuPage County government center, the new courthouse will be the fourth large scale building on the 120-acre site. Wight & Company, in collaboration with HOK, St. Louis, Missouri, designed the new court- house, now under construction, as well as an addition to an existing jail planned for groundbreaking in 1992. The construction of these two structures, in tandem with two new parking structures, has reduced on-site water storage, fostering the need for a complex stormwater management system.

Two retention ponds flanking the new7 courthouse are an important component of the plan: an existing pond designed for an additional two feet of storage and a new detention facility with wetland characteristics.

The larger pond will hold 30.3 acre feet of water, while the smaller detention basin will have a capacity of 29.4 acre feet. According to Wight & Company vice president and project director, Ottavio Finaldi, a complex pumping system will bring water to the detention basins from all areas of the site.

"The stormwater pumping system will be located underground, running from the north side of the complex to the south," Finaldi explained. "An underdrain system will be installed around the courthouse. Parking deck grades have been designed to ensure positive drainage away from the structure."

February 1991 / Illinois Municipal Review / Page 15

"In the early design stages, observation wells were established at various points around the site to monitor water depths," Finaldi continued. "This data was integrated with historic rainfall records to establish the necessary water storage area as well as pumping rates."

The Kane-DuPage Soil and Water Conservation District offered several recommendations to planning engineers. The Kane-DuPage authority pointed out that stormwater retention facilities should be designed to retain and slowly release all additional storrmwater run- off at a maximum release rate of .10 cubic feet per second per acre.

Soil erosion and sedimentation, the authority pointed out, are another concern since excessive erosion on construction sites is a contributing source of water pollution. Eroded soil sediments are capable of choking storm sewers, reducing the capacity of detention/retention areas, increasing the risk of flooding, degrading water quality and destroying aquatic ecosystems.

Wight & Company has made provisions for controlling costly erosion including keeping disturbed areas to a minimum, maintaining vegetative ground cover and reducing runoff velocities.

DuPage County Government Center Wetland Design
The pervasive need for additional water storage at the county site furnished planners with an ideal opportunity for incorporating wetland characteristics into the expansion, an activity typically known as "wetland mitigation." Since wetland shelves will be constructed at levels below7 the normal pond elevation, no loss of stornnwater storage capacity will result.

A 1988 soil analysis of the government complex site revealed prior wetland characteristics. Wetland features are established on the basis of three primary characteristics: presence of a hydric or wet soil, a predominance of hydrophytic or water-tolerant vegetation, and evidence of seasonal or periodic flooding.

Wetland mitigation is gaining popularity as a tool for stormwater detention/retention, preferable from an ecological standpoint. Wetland mitigation has also been found to be superior for preventing soil erosion.

Performing a Wetland Restoration
To create the new7 wetland, the perimeter of the retention pond will be shelved in steps between one tenth of a foot and two feet below water level. Different varieties of wetland plants require varying water levels to flourish. The shelving system also permits fish to swim in and amongst the plants and eat mosquito larvae.

"An important consideration in the particular design of the wetland shelves is the fact that wetland plants need water to survive, but they can also be drowned," explained Joe Chaplin, Engineering Technician, Department of Environmental Concerns for the DuPage County Stormwater Division. "Therefore, we have to be careful about the change in water level in the pond. For example, if the water level rises for a brief period because of a storm, they could probably survive. But over longer periods, they would die."

According to Randy Stowe, a natural resource planning consultant to the county, another critical factor in wetland mitigation is the soil quality. "You can usually have some degree of success in re-creating the plant community, and from an engineering standpoint, it is possible to restore water quality, but the wetland soils have a complex profile which involves many layers."

"One alternative the county is considering," Stowe said, "is to obtain topsoil stripped from an existing wetland site. The mitigation process, in this case, would be to carry out rough clay grading and then top dress the wetland shelves with at least one foot of this organic wetland topsoil. Often, the numerous seeds, rhizomes and tubers found in this soil will bring back much of the wetland on its own."

A period of three to five years will be required to establish the wetland plant community. In its first year, virtually no top growth will be apparent, since most of the early wetland plant activity is in its roots. Not unlike a prairie ecosystem, wetlands are managed with controlled burning which kills off the more invasive yet shallow-rooted cattails and canary reeds which tend to take over a wetland area to the detriment of the other plant varieties.

Engineers have chosen approximately 10 hardy plant species to begin the wetland mitigation. A buffer area of native prairie plants will help to protect the tenuous plantings. Native tree material is also planned for the wetland perimeter, chosen for both aesthetic and stabilizing benefits.

When the new courthouse is completed, the pond waters will lap at the south side of the building where a generous terrace will capture a view of both the wetland wildlife and a magnificent fountain to be set in the center of the pond.

The combination of complex stormwater management techniques and wetland mitigation benefits at the DuPage government center will make it a model facility from the standpoint of both stormwater and environmental planning. DuPage County planners anticipate that the project will generate considerable interest as a prototype for other county governments as well as municipalities and commercial land developers. •

Page 16 / Illinois Municipal Review / February 1991