Summary: Proposed measures would include filling relief well channels with sand filter material and constructing a sand seepage blanket in the marsh area along the backside of the dam embankment. The seepage blanket, consisting of approximately 30,000 cubic yards of sand, would assist in preventing underseepage (movement of foundation material), and the additional weight of the blanket would help counteract any uplift pressure from the upstream side of the dam.
Geographic Scope: Gavins Point Dam, Yankton, SD
Decision/Date: Made following close of public comment period.