Public Notice: Water Quality Certification for the Antelope Dam Design Modifications Project
Summary
The U.S. Environmental Protection Agency (EPA) received a request from the Bureau of Indian Affairs for a Clean Water Act (CWA) Section 401 water quality certification (WQC) for the above project. Section 401(a)(1) of the CWA requires applicants for Federal permits and licenses that may result in any discharge into waters of the United States to obtain certification or waiver from the certifying authority where the discharge would originate.
The EPA acts as the certifying authority in areas of Indian country[1] on behalf of those Tribes that have not received treatment in a similar manner as a state (TAS) for Section 401, in this case the Rosebud Sioux Tribe of the Rosebud Sioux Tribe Indian Reservation.
The EPA will act on this certification request by either: (1) granting certification; (2) granting certification with conditions; (3) denying certification; or (4) expressly waiving certification consistent with CWA Section 401 and the EPA’s implementing regulations at 40 CFR 121.
The proposed project would be covered under U.S. Army Corps of Engineers (USACE) CWA Section 404 Nationwide Permit (NWP) 3 and 42. NWP 3 authorizes the discharge of dredged and/or fill material into waters of the United States for repair, rehabilitation or replacement of any previously authorized, currently serviceable structure or fill under section 404 of the CWA and section 10 of the Rivers and Harbors Act of 1899. NWP 42 authorizes the discharge of dredged and/or fill material into waters of the United States for the construction or expansion of recreational facilities under section 404 of the CWA.
Applicant
Bueau of Indian Affairs
Project Location
43.296838, -100.608854
Waterways
Antelope Creek and Antelope Reservoir in South Dakota
Project Description
The project will rehabilitate Antelope Dam to address dam safety issues related to internal erosion and modify the dam to protect the upstream embankment slope from wave erosion. This includes constructing a combined service spillway and outlet works with a control tower and steel pipe conduit. A U.S. Bureau of Reclamation (USBR) Type VI impact basin will be constructed at the bottom of the dam to manage discharge flows. Riprap will be installed about 30 feet downstream to protect the basin and dissipate flows exiting the baffle inlet and steel pipe conduit. To address dam safety issues, the existing dam embankment will be reconstructed, including excavation to bedrock and raising the dam crest 3 feet higher than the existing crest. Existing unauthorized upstream riprap will be removed and replaced with a 2-foot-thick layer of riprap to prevent wave erosion on the upstream slope of the embankment. Riprap size will be based on USBR design criteria. Geotextile fabric will be placed underneath the upstream riprap for added protection.
Auxiliary spillway modifications include widening the channel and increasing the slope. This will increase the auxiliary spillway capacity to manage the inflow design flood to prevent overtopping and protect downstream life and property. A new berm will be constructed along the discharge channel to provide a margin of safety against overtopping failure.
A new boat ramp will also be constructed as well as a floating dock and parking area improvements. Precast concrete blocks connected by steel cables will be placed upon a six-inch layer of base course foundation with geotextile fabric underneath. The top 9 inches of soil will be removed to allow vehicle access to the boat ramp in the parking area. Nine inches of gravel surfacing will be added with geotextile fabric installed underneath. Concrete-filled piles will be driven into the reservoir floor to secure the floating dock.
Reservoir drawdown to the minimum pool elevation will be completed using an unused irrigation conveyance on the downstream side of the embankment. During dewatering, flows in Antelope Creek may approach 100 cubic feet per second (cfs), and maintenance flows are anticipated to be less than 10 cfs. Cofferdams will be used around the work areas to minimize the risk of potential contaminants or turbidity affecting Antelope Creek. Reservoir drawdown will be completed once the water diversion system is established. The replacement service spillway and outlet works will be built and modifications to the auxiliary spillway will be completed after the cofferdams are constructed. The boat ramp will also be constructed during the drawdown phase.
Work will be completed under the EPA’s 2022 Clean Water Act Section 402 National Pollutant Discharge Elimination System Construction General Permit (CGP). A Stormwater Pollution Prevention Plan (SWPPP) will be developed to comply with the CGP. The SWPPP will incorporate best management practices (BMPs) to control erosion and sedimentation to minimize the discharge of pollutants to the maximum extent practicable.
The project will permanently impact 148 linear feet (0.051 acre) of Antelope Creek below the ordinary high water mark, and 60 linear feet (0.021 acre) of Antelope Reservoir below the established pool elevation. The project will permanently impact 0.118 acres of wetland (0.073 acres below the dam/adjacent to Antelope Creek and 0.045 acres above the dam adjacent to Antelope Reservoir). Approximately 0.046 acres will be authorized under NWP 42 and 0.072 acres will be authorized under NWP 3.
Public Comments
Submit comments as described in the “How to Comment” box at the righthand side of this webpage. The EPA must receive comments by 11:59 pm on July 11, 2025.
All comments received prior to the end of the comment period will be considered in the preparation of the Clean Water Action Section 401 Water Quality Certification and will be part of the administrative record. Contact Estella Moore, R8CWA401@epa.gov and 303-312-6357 to request additional information, public notice updates, submit comments or provide additional information relevant to this certification
Notice of any extension of the comment period will be published on this page and sent to those who have requested updates.
Public Hearing
Any person may request, in writing, within the comment period specified in this notice, that a public hearing be held to consider this application. If the Administrator, in his or her discretion, determines that a public hearing is appropriate or necessary, the EPA will schedule a public hearing. You may request a public hearing using the information in the “How to Comment” box on the righthand side of this webpage
Project Applicant
Bureau of Indian Affairs
Delores Herman
720-454-4201
Applicant Agent
DOWL Engineering
Cameron Sapp (Csapp@dowl.com)
406-442-0370
[1] Indian country is defined in 18 U.S.C. Section 1151. Indian country in South Dakota generally includes (1) lands within the exterior boundaries of the following Indian reservations located within South Dakota: the Cheyenne River Reservation, the Crow Creek Reservation, the Flandreau Indian Reservation, the Lower Brule Reservation, the Pine Ridge Reservation, the Rosebud Indian Reservation, the Standing Rock Reservation, and the Yankton Reservation (subject to federal court decisions removing certain lands from Indian country status within the Yankton Reservation); (2) any land held in trust by the United States for an Indian Tribe (including but not limited to the Sisseton-Wahpeton Oyate Tribe); and (3) any other areas that are “Indian country” within the meaning of 18 U.S.C. Section 1151.