Authorities in Utah were set to release all 21 of the protesters arrested during a demonstration against a Canadian company's efforts to develop one of the first oil-sands extraction projects in the US.
Scores of protesters showed up early on Monday morning to the site in Utah operated by US Oil Sands, locking themselves to equipment used to grade an area ahead of the construction of a bitumen processing plant about 200 miles east of Salt Lake City.
Others sat in the road to as a "blockade" to prevent work from happening, while banners were hung on fences reading "Respect Existence or Expect Resistance".
A total of 21 were arrested including two that came to the Uintah County jail to "provide support" to the protesters after the demonstration, according to the group Utah Tar Sand Resistance.
Two protesters were injured, with one sent to hospital, the group said.
On Tuesday, the group said on Twitter that all were being released from jail.
Calgary-based US Oil Sands has commenced work work on Utah’s first commercial oil sands mine at PR Springs.
The company was informed in a letter from the US Environmental Protection Agency that the project area includes land within the Uintah and Ouray Indian Reservation, a fact that reportedly fueled the protest on Monday.
US Oil Sands has secured all the necessary state permits to begin construction on the 213-acre site. The company won a victory in the Utah Supreme Court several weeks ago when a case was dismissed alleging that a groundwater discharge permit-by-rule, issued in 2008, was not correctly issued.
The court ruled the company’s process of bitumen extraction uses low-impact, non-toxic substances, recycles water, and does not use tailings ponds, and therefore has "negligible impact" on groundwater.
Commercial start-up of the $60 million, 2000-barrel-per-day first phase of the project is expected during the second half of 2015.
US Oil Sands has trumpeted the lower environmental impact of its Utah project compared to the large-scale developments in Canada. The company will use a citrus-based biodegradable solvent to separate oil from the sand, thus eliminating the need for tailings ponds.