by Bill Goosman, Office of Environmental Services,
Colorado Department of Transportation, Denver

At the end of this summer, the Colorado Department of Transportation (CDOT) completed two years operating its first wetland mitigation bank. Located in Limon, the project resulted from a unique partnership between local, state, and federal agencies.
While reclaiming a landfill for bike paths and parks, the Town of Limon was approached by Warren Cummings, a state wildlife officer who had an idea — combine the reclamation with improvements to nearby wetlands to increase waterfowl habitat. Things continued to grow with another idea — use water from the town’s nearby wastewater treatment plant to expand the habitat further. During the same period, CDOT, the U.S. Army Corps of Engineers (COE), and the Federal Highway Administration were also discussing creating Colorado’s first wetland mitigation bank. These efforts were joined and the parties agreed to use the Limon site as a pilot project to better understand the mitigation banking process. Limon’s participation solved two major problems — available land and, especially in the West, available water rights.
The site is a 14-acre abandoned sewage lagoon owned by the town and dominated by non-wetland, weedy annuals. Four different ponds of varying depths were created to provide a variety of wetland types and habitats. About 8.2 acres of wetlands are expected, with another 1.25 acres of open water. Water for the wetland is taken near the discharge point for the town’s treatment plant. Two pumps alternate moving the water some 2,700 feet north at 200 gallons per minute. Valves at three of the ponds, along with programmable pump operating times, control the amount of water entering the ponds. Pipes and flumes move water between the ponds. Removable gates of different heights at these points allow the water levels in each pond to be adjusted. The overflow is eventually returned to a nearby drainage. Total costs at the end of construction are estimated at $350,000.
In May and June 1997, non-wetland areas were seeded and wetland areas were planted with approximately 12,000 nursery plants, plus 2,000 plugs from adjacent wetlands, 820 shrubs, 42 trees, and 2,000 willow brush layer cuttings. The ponds were planted based on the species and zonation observed in nearby wetlands that have similar clay soils and alkaline conditions. No wetland topsoil was used. Plant placement at this wetland is crucial because saturation of the soil is a product of surface water soaking down, not the water table moving up. Given this, changes in wind direction can shift the saturation zone as much as two feet laterally in a matter of hours.
“Withdrawals” from the bank are approved on a case-by-case basis by COE and impacted wetlands must be located in designated EPA ecoregions on the plains of southeast Colorado. Success at the bank is defined by three criteria: wetland acreage achieved, overall plant cover, and percent coverage by wetland community type, such as palustrine emergent persistent.
To date, the wetland plants have covered large areas in the first two years. The size of the bank also enhances its value. Wetlands in this region that are affected by highway construction are often small, isolated strips containing a few species, factors that limit their functions and value. The replacement of these wetlands with a large, consolidated site with a variety of habitats and plant species provides benefits beyond mere replacement. The wildlife response in the first two years is also encouraging. State wildlife personnel note that bird species new to the area have been seen at the wetland and that some bird species appear to be staying longer. Local schools use the area for study, and the wetland is providing a laboratory for investigating the process of cattail invasion. By these measures, the wetland bank is considered a success at this point. Once the bank is judged a success by the agencies involved, it can be turned over to the town of Limon and may be used for banking purposes at that time. The bank site will exist as a wetland in perpetuity thereafter.

Colorado Riparian Association