The Department of Interior’s (DOI) Bureau of Land Management (BLM) is planning to prepare a supplemental environmental impact statement (SEIS) for a proposal to expand oil and gas development to include shale formations on the Southern Ute Indian Reservation in southwest Colorado.

According to the Southern Ute Indian Tribe Growth Fund, the SEIS would supplement several previous analyses conducted by DOI. Specifically, the SEIS would buttress a final environmental impact statement (FEIS) conducted in 2002; a programmatic environmental assessment for an 80-acre infill oil and gas development authorized in 2009; and an environmental assessment (EA) for the North Carracas Plan of Development in 2013.

None of the aforementioned DOI reports considered the development of shale formations, the tribe’s growth fund said. It added that scoping comments will be accepted until April 14. The BLM, the tribe and the Bureau of Indian Affairs (BIA) are the lead agencies for the proposal.

Four shale formations underlie the reservation. Three of them — the Paradox, Mancos and Lewis shales — are expected to produce natural gas, while the fourth, the Niobrara Shale, is expected to yield crude oil.

The proposed shale development includes drilling, completion and ultimate oil and gas production from 1,534 wells on 352 well pads. Associated infrastructure — including access roads, gathering lines, compressor stations and injection wells — would also be constructed.

“The exact locations of wells and other facilities associated with the proposed development are not currently known,” the tribe’s growth fund said in a statement on its website. “Impacts resulting from the proposed development will be assessed quantitatively when methodologies and data are available, and qualitatively when they are not.”

The growth fund said applications for permits to drill and rights-of-way would be subject to site-specific EAs tiered to the SEIS, when required.

The BLM, tribal representatives and a spokesman for Red Willow Production Co., the tribe’s oil and gas production company, did not return several messages seeking comment.

The Southern Ute Indian Reservation covers 1,059 square miles in southwest Colorado, traversing parts of Archuleta, La Plata and Montezuma counties. The tribe’s headquarters are in Ignacio, CO, in La Plata County.