YANKTON, S.D. – The U.S. Army Corps of Engineers, Omaha District, is seeking comments on a draft environmental assessment for a proposal to implement additional underseepage control measures at Gavins Point Dam near Yankton, South Dakota. Comments on the draft EA will be accepted until May 27, 2020.
In March 2019, extreme runoff into Lewis and Clark Lake resulted in record loading on Gavins Point Dam. Project staff observed one to three foot diameter boils downstream during this event which contained dam foundation material. To prevent the movement of additional material, also referred to as underseepage, it is necessary to implement additional measures.
Proposed measures 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. Also, the additional weight of the blanket would help counteract any uplift pressure from the upstream side of the dam.
The public is encouraged to provide comments on the draft environmental assessment which can be downloaded at: www.nwo.usace.army.mil/Missions/Civil-Works/Planning/Project-Reports/. Comments can be mailed to: U.S. Army Corps of Engineers, Omaha District; CENWO-PMA-C; ATTN: Chris Weber, Gavins Seepage; 1616 Capitol Avenue; Omaha, NE 68102-4901. Comments can also be emailed to cenwo-planning@usace.army.mil. Comments must be postmarked or received no later than May 27, 2020.
This draft EA is consistent with the National Environmental Policy Act of 1969, as amended, the Council on Environmental Quality's regulations for implementing NEPA (40 CFR 1500-1508), the Corps' regulations for implementing NEPA (33 CFR 325 and Engineering Regulation 200-2-2) and other applicable laws and regulations.
Release no. 20-046