HGL prepared 10 Remedial Designs (RDs) for 4 Operable Units (OUs) that encompassed numerous subsites and private properties to delineate soil, mine waste, sediment, and surface water contamination from historical mining operations. The RDs supported an area-wide solution within the Tri-State Mining District (TSMD) for returning affected private properties to beneficial reuse and included revegetation with native plant species.
For OUs 3 and 4, HGL completed a 9-square-mile hydrologic and hydraulic model for the Tar Creek Watershed mine waste areas and surrounding farmland using USACE HEC-HMS and HEC-RAS codes to simulate overland flow, channel flow, and sediment and surface water contaminant transportation processes. Model results were used to estimate how removal and relocation of surficial mine waste contamination along Tar Creek would impact the creek floodplain, including sensitive habitat, and to aid in the selection and design of channel restoration components such as the use of armoring materials, revegetation, and sinuous alignment of stream channels to reduce stream flow velocities and control sediment transport. The RDs stipulated that waste consolidation areas and subsidence pits used for waste disposal be covered with a 1.5-foot-thick cap (1 foot select fill and 6 inches topsoil); however, in floodplain areas or in areas where the land will be returned to agricultural use, the cover will consist of a 4-foot-thick cap (3 feet select fill and 1 foot topsoil).