Sewer project earns state accolades

Tuncer Edil (27K JPG)

Workers prepare a geotextile cover for a Madison Metropolitan Sewerage District lagoon. (14K JPG)

What was once contaminated sludge has been converted into a section of Wisconsin's newest state park, thanks to the help of Professor Tuncer Edil and a team of students.

Edil, working with David Taylor from the Madison Metropolitan Sewerage District, devised an innovative method for capping an MMSD lagoon system filled with very soft sludge contaminated by high levels of polychlorinated biphenyls (PCBs). The project recently was honored with the Engineering Achievement Award by the Wisconsin Section of the American Society of Civil Engineers. "It saved a lot of money for water users in the Madison area and it also converted a contaminated and unsightly area into part of a state park and wildlife refuge," Edil said.

The department has a long history of working with MMSD on projects to treat wastewater and provide economical and effective sewage systems. Edil began working with the district on the lagoon project in 1997, with construction of a new lagoon capping system beginning in January 1998.

The challenge was considerable. The lagoons were originally constructed in the 1940s to provide storage of municipal wastewater sludge generated by the district. In 1990, the lagoon system was designated as a priority for clean-up under the U.S. Environmental Protection Agency's Superfund program because portions of it had high concentrations of PCBs.

Studies done in the mid-1990s suggested the cost of cleaning up the contaminated lagoon system could run as high as $168 million. MMSD contacted the department and Edil, a specialist in geo-engineering, to find an affordable method for capping 22 acres of the lagoon system.

Edil and his team of students developed a method that involved covering the lagoons with a layer of ice as a platform to support construction equipment. A mixture of soil and woodchips was placed on top of a geotextile (a woven sheet of polymer) that sat atop the layer of ice. During the spring thaw, the ice layer melted, allowing the geotextile cover and the soil/chip mixture to cap and seal off the lagoons. The sealed-off lagoons were then seeded for a vegetative cover. Work on capping the lagoons was completed during four winter construction seasons.

All told, the capping project cost $600,000, a considerable savings from the highest estimates projected for the cleanup. One way that Edil's team kept down costs ­ it got soil and woodchips at no cost from local municipalities looking for a place to dispose excavated soils and chipped brush.

The capped lagoons have worked out so well that they were recently included within the boundaries of Wisconsin's new Capital Springs Centennial State Park.

"This was not straight-forward stuff," Edil said of the methods used to cap the lagoons. "But the result was a much more affordable capping system, and enhanced use of the land."