Notice of Application for State Water Quality Certification

Public Notice (PN) Date: October 22, 2025            PN Reference Number: POA-2019-00122 v1.0
PN Expiration Date: November 6, 2025                                             Waterway: Ugnuravik River

Any applicant for a federal license or permit to conduct an activity that might result in a discharge into waters of the United States, in accordance with Section 401 of the Clean Water Act (CWA), must also apply for and obtain certification from the Alaska Department of Environmental Conservation that the discharge will comply with the CWA and the Alaska Water Quality Standards (18 AAC 70). The scope of certification is limited to the water quality-related impacts of the activity subject to the Federal license or permit (40 CFR 121.3, 18 AAC 15.180).

Notice is hereby given that a request for a CWA §401 Water Quality Certification of a Department of the Army Permit application, Corps of Engineers’ PN Reference Number indicated above has been received0F[1] for the discharge of dredged and/or fill materials into waters of the United States (WOTUS), including wetlands, as described below, and shown on the project figures/drawings. The public notice and related project figures/drawings are accessible from the DEC website at https://dec.alaska.gov/water/wastewater/.

To comment on the project or request a public hearing with respect to water quality, submit comments via (preferred method) DEC website https://dec.alaska.gov/commish/public-notices/ or email to the DEC email address: DEC-401Cert@alaska.gov with the subject line referencing Public Notice Reference Number: POA-2019-00122 v1.0 or on or before the public notice expiration date listed above.

Applicant: Hilcorp Alaska, Keri Iles, 3800 CenterPoint Dr, Ste. 1400, Anchorage, AK 99503, (907) 777-8368; keri.iles@hilcorp.com

Project Name: Phase II, Cell 6, Ugnu Mine Site E

Dates of the proposed activity are planned to begin and end: 11/15/2025 to 05/01/2030

Location: The proposed activity is located within Section 19, T. 13N, R. 10E, Umiat Meridian, in North Slope Borough, Alaska. Project Site (Latitude, Longitude): 70.461513, -149.69594.

Purpose: Hilcorp Alaska, LLC (Hilcorp) proposes to develop Phase II of Ugnu Mine Site E Cell 6 within the Milne Point Unit (MPU). This phase of development is required to support immediate oil resource development projects and field maintenance projects across Hilcorp’s North Slope operating areas, including Omega Pad (POA-2021099361 M1).

Description of Proposed Work: The proposed project would involve new gravel mining operations at Phase II of the existing mine cell 6, resulting in approximately 24.2 acres of total wetland impact, 12 acres to be mined approximately 600 feet wide and 900 feet long and 12.2 acres for completing overburden storage, thermal barriers, and access road accommodation. A maximum of up to 10,000 cubic yards of material would be dredged and disposed of at 5 upland locations above the high tide line for erosion control. The impact from Phase I and Phase II would total 50.5 acres, remaining consistent with the ADNR DMLW Material Sales Contract for Cell 6 and the USACE-approved 2019 Ugnu Mine Site E Mining and Rehabilitation Plan. Final site configuration will be dependent on gravel needs.

Applicant Proposed Mitigation: The applicant proposes the following mitigation measures to avoid, minimize, and compensate for impacts to waters of the United States from activities involving discharges of dredged or fill material.

1. Avoidance: The Ugnu Mine Site E expansion was designed in a phased approach, which avoided immediate impact to roughly half of Cell 6 from the time of its original development in 2019. Additional gravel is now needed to meet gravel demands for field maintenance and development projects. Therefore, Phase II of Cell 6 will be developed beginning in November 2025.

   Phase II of the Ugnu Mine Site E Cell 6 is designed with the minimum footprint practicable given safety and engineering constraints; Instead of developing a new gravel source, Hilcorp is expanding an existing cell on an active mine site. Wetlands in this area are already subject to indirect impacts from ongoing activities in the adjacent mine cells. Phase II of the expansion of the existing cell avoids the following impacts:

   • Avoided impacting as many lakes, ponds, and streams as possible
   • Avoided Anadromous Water crossings to the maximum extent possible
   • Avoided impacting pristine wetlands to develop a new gravel source
   • Will use existing material sites and local existing roads to the maximum extent possible.
2. Minimization: The proposed Phase II expansion has been designed to minimize the disturbance of the area. The overburden for Phase II will be removed to maximize the conservation, segregation, and stockpiling of the organic overburden for use in reclamation and restoration projects. Once mining is completed, overburden will be placed back into the pit to reduce and buttress side slopes and limit the area required for storage. Hilcorp will construct berms around the exterior margin of Cell 6 to serve as a thermal barrier. This barrier will help to preserve the underlying permafrost and prevent the melting of ice wedges and thermokarsting. Without this insulation, exposed ice wedges may melt and erode back from the edge of the pit with the potential to drain adjacent wetlands. The slope stability gained by this practice will ensure that the cell can eventually provide valuable habitat for avian species. The berms will also prevent the transmission of water between mining cells, which is a major safety concern in an active mine site. The result of these berms is a net benefit for wetland preservation. A thermal barrier berm of native overburden was constructed around Phase I as it was opened. As the opening of Phase II begins, the thermal barrier will be shifted to encompass the entirety of the excavated area in Cell 6. Typical dimensions of the thermal barrier will be 60 feet at the base and 10 feet thick. To remain consistent with Phase I, Phase II gravel removal for use in Hilcorp-operated Units will only occur during winter via an ice road. This will eliminate the need for a new gravel road from Ugnu Mine Site E to the Milne Point roads for gravel haul.
3. Mitigation: Through Avoidance and Minimization, Hilcorp has worked to limit the impact on wetlands. Hilcorp examined the permittee's responsible mitigation, including creation/restoration and preservation. Wetland creation/restoration on the North Slope is impracticable because wetlands are primarily developed through permafrost action (taking hundreds of years to develop), and the growing season is only 60 days. This prevents any reasonable success goals from being achieved that would show replacement of lost functions, as required by regulation. Also, the perpetual protection instrument that would be required cannot be accomplished because of land ownership and constitutional protection restrictions.

Hilcorp has avoided potential impacts by methods listed in Section 2 above, including expanding an existing mine site in a phased approach instead of opening a new mine, and minimizing potential impacts by methods including constructing thermal barriers around the mine area. The proposed Avoidance and minimization measures minimize impacts to wetlands to the greatest extent practicable. Due to the temporary and minimal nature of the unavoidable impacts, and given the overall health of the watershed and prevalence of waters of the U.S., including wetlands, on the North Slope and within the project vicinity, we propose that the described avoidance and minimization measures satisfy the mitigation requirements under the Corps’ various statutory authorities and therefore propose that no compensatory mitigation is appropriate or should be required.

After reviewing the application, the Department will evaluate whether the activity will comply with applicable water quality requirements (any limitation, standard, or other requirement under sections 301, 302, 306, and 307 of the CWA, any Federal and state laws or regulations implementing those sections, and any other water quality-related requirement of state law). The Department may certify (or certify with conditions) with reasonable assurance that the activity and any discharge that might result will comply with water quality requirements. The Department also may deny or waive certification.

The permit application and associated documents are available for review. To inquire about or request copies of the documents, contact dec-401cert@alaska.gov or call 907-269-6285.

Disability Reasonable Accommodation Notice

The State of Alaska, Department of Environmental Conservation, complies with Title II of the Americans with Disabilities Act (ADA) of 1990. If you are a person with a disability who may need special accommodation in order to participate in this public process, please contact ADA Coordinator Kristin Mabry, kristin.mabry@alaska.gov, 1-907-334-0884; or TDD Relay Service 1-800-770-8973/TTY or dial 711 at least 3 days prior to the expiration/closure date of this public notice to ensure that any necessary accommodations can be provided.