Soil Stabilization Brings New Life to Old Utility Site (2004)
Today, “green building” is ubiquitous—it’s rare that project designers don’t at least explore their sustainable options. But the green building movement has a broader view than just new construction. Building renovations and site rehabilitation are also on the radar.
In Appleton, Wisconsin, We Energies is taking sustainability seriously, bringing new life to the former site of a manufactured gas plant (MGP). Located next to the Fox River Canal, the plant operated in the late 1800s through the early 1950s. When the plant equipment was later removed, the land was contaminated, and in some cases, contaminants in the form of a black, viscous, tarry material were coming into contact with groundwater.
Soil stabilization/solidification (S/S) is a process that immobilizes contaminants, mitigating the risk of exposure and potential harm to human health and the environment. Cement material is mixed with impacted soil and hardens to form a soil-cement matrix that encapsulates the impacted materials. In this case, the process was performed on site soils in-place, otherwise known as in-situ stabilization/solidification (ISS).
We Energies chose ISS as its remediation strategy because the company prefers to limit its landfill liability, says Mark Collins, senior hydrogeologist for the company. “A lot of companies will transfer their contaminated media off-site, but in the long term, we don’t feel that’s the best approach—why transfer the problem from one location to another?”
Before work could begin, a treatability study was required, performed by Compass Environmental (known then as Williams Environmental Services). The company has practiced ISS since 1991, and has used slag cement in its mixes for the past four years. “The material has recently gained a lot of acceptance because of noticeably increased compressive strengths and lower permeability,” explains Jim Brannigan, project manager with Compass.
“We utilized the product on previous successful projects (in Macon, Georgia, and Des Moines, Iowa), so we looked at utilizing slag cement as a potential component,” says Brannigan. “The treatability study showed it to have a far superior performance over other additives, and because we’re able to utilize it like portland cement, we didn’t have to change any of our equipment.”
Scope of Work
The team developed three mix designs, including one that blended 25 percent portland cement and 75 percent slag cement. Chris Robb, project manager for Natural Resource Technology, Inc. (which provided consulting engineering services and construction management oversight), says the different mix designs were needed to accommodate a variety of work. “We had requirements for a typical mix design, we needed high-strength around structures on-site, and low-permeability mix designs to minimize contaminant leaching and groundwater flow,” he explains.
Initial work (in Fall of 2003) included stabilizing approximately 1,612 cubic yards of material along 630 feet of riverbank, with depths ranging from 1 to 7 feet, and widths ranging from 7 to 19 feet. Once the riverbank soils were stabilized, Compass returned in Spring of 2004 to finish work on the remaining land, performing ISS on approximately 34,000 cubic yards of material spread over 2.5 acres, at depths ranging between 8 and 18 feet. This second stage included stabilization with high-strength material around bridge piers for an overpass that crosses the site.
Robb says quality assurance tests showed that the final material exceeded design criteria, creating a stronger, less-permeable material than specified. “Slag cement would now probably be our leading candidate for future similar projects,” he says.
The method is so reliable, says Compass Environmental Vice President Bruce Culbertson, that slag cement “is one of the products we are evaluating on almost every S/S project, not only for petroleum-based products, but also for pesticides, herbicides, heavy metals, semi-volatile polycyclic aromatic hydrocarbons—even nuclear waste.” There is no doubt that the material’s use will continue to grow in these applications, he says.
Serving nearly 2 million electric and gas customers in Wisconsin and the Upper Peninsula of Michigan, We Energies places a high value on contributing to its customers’ communities, and in this case, hopes that once site work is complete, the land can be used by the city of Appleton for public recreational space.
Owner: We Energies, Milwaukee, Wisconsin
Engineer: Natural Resource Technology, Pewaukee, Wisconsin
Contractor: Compass Environmental, Stone Mountain, Georgia
Slag Cement Supplier: Lafarge North America, Pewaukee, Wisconsin