Pilot Test for Using Dolomite in Engineered Caps for the Fox River Sediment Remediation Project

摘要

The Lower Fox River sediment megasite in Wisconsin includes dredging,capping, and sand covering of PCB–impacted sediment at selected locations over an approximate13.3 mile (21.4 kilometer) stretch of the Fox River. The remediation area isdivided into Operable Units (OUs) 2 through 5. Several engineered cap designs will beused on the project, involving placement of a chemical isolation sand layer, followed by aprotective layer of armor stone. The sand layer and armor stone are to be transferredhydraulically to spreading equipment that places them in the remedial areas, and thequarry spall is to be placed mechanically. Conceptual design plans anticipated the use ofstandard bank-run glacial gravel and quarry spall for the armor stone, however, it wasrecognized that the use of crushed dolomite instead of bank-run glacial gravel for thearmor-stone layer could offer significant remediation savings. Dolomite is a sedimentarycarbonate rock composed chiefly of the mineral dolomite, calcium magnesium carbonateCaMg(CO_3), and is readily available near the project site. Bank-run glacial gravel wouldbe imported to the project site from a distance of approximately 60 miles (96.5 kilometers),thus increasing the overall cost of this capping material. The potential alternativeuse of dolomite is an example of adaptive management and value engineering that is activelypracticed on the project.