REMEDIATING THE DAVIS MILL CREEK, TN WATERSHED, PHASE 3: PRIORITIZING ACID-GENERATING SOURCES

Davis Mill Creek (DMC), a tributary to the Ocoee River in southeastern Tennessee, is significantly impacted by the lingering effects of underground mining, chemical production, and waste disposal associated with hard rock mining in the Ducktown Mining District. These impacts include high acidity and metals in surface and ground water, substantial precipitation of iron-bearing phases on the stream substrate, channel modification, sedimentation and habitat disruption. DMC comprises a watershed of about 5.2 square miles, of which approximately one-half is drained by Belltown Creek, a tributary to DMC that was not impacted by mine wastes and materials. DMC is the subject of continuing remedial actions by EPA Region 4.

A phased approach to remediating the watershed was developed during a planning process. Initial efforts concentrated on understanding the nature of impacts and included surface water monitoring; reconnaissance sampling of wastes, soil, and sediment; a mine waste inventory; and waste testing. The inventory identified approximately 9.7 million cubic yards of mine wastes, by-product materials and contaminated soils in the affected area of about 2.5 square miles, including slag, iron calcine, sulfide concentrate, and sulfide-bearing mine rock. Most of these materials are situated on the stream banks, atop the former creek channel, or in the creek bed. In the second phase, studies of the lower creek permitted decisions to be made that will limit discharge of contaminated water from DMC to the Ocoee River. In the third phase, we examined four significant sources of acid to DMC: 1) a pile of sulfide-bearing iron calcine at the creek headwaters; 2) a small pile of sulfide-bearing waste rock; 3) a pile of mixed iron-sulfide and copper-sulfide mill concentrate; 4) a tunnel outlet and French drain that collect seepage from overlying waste materials. These sources were prioritized for remedial action based on increases in contaminant load in DMC, effects on ground water, and source volume and character. Future remedial investigations will target non-acid generating materials, mostly slag, that contribute metals to the DMC system. Once sources are controlled, restoration of the stream channel and rehabilitation of aquatic and riparian habitat can begin.