Upper Chase Creek - US 191 Relocation and Dam

Freeport-McMoRan Copper and Gold Inc. operates the largest copper mine in the United States in terms of production at Morenci, AZ. With record worldwide demand for copper, production at the Morenci Mine needed to be increased to fulfill its customers’ requirements. Before the mine expansion could begin, however, a new dam on Upper Chase Creek had to be built. The new dam would replace an existing dam located in the pit expansion area. The Upper Chase Creek drainage lies upstream from the Morenci Mine. Upper Chase Creek’s flows are diverted through a pipeline around the mine and into the San Francisco River. The Upper Chase Creek Dam temporarily impounds creek waters for release into the pipeline. Before the new dam could be constructed, a one mile section of US Highway 191 had to be relocated, since the existing highway alignment ran through the new dam’s reservoir area.

Constructing the project

Skanska’s work consisted of building the new alignment on the side of a narrow canyon. Of the 259,000 cubic yards (cy) of excavation, 100,000 cy required drilling and blasting as well as difficult pioneering work. Freeport-McMoRan awarded Skanska a second contract for construction of
the new dam. Major work for the dam included pressure grouting, 221,000 cy of rockfill, colluvium borrow and processed material for the dam embankment construction, a structural concrete spillway, inlet tower, outlet works and a riparian collection and diversion system. A cast in place concrete plinth was built at the upstream toe of the dam to secure the HDPE geomembrane liner that is the upstream face of the dam. More than 9,000 linear feet of pipe was installed to transport water from the dam to a riparian sump and to the pipeline that carries Upper Chase Creek waters around the mine.