Editor's note: This story corrected on Wednesday, April 17, to reflect that Larimer County commissioners ruled Thornton's pipeline application failed to meet seven of the 12 criteria for a 1041 permit.

Update: Thornton sues Larimer County commissioners in protest of pipeline rejection

Original story:

The city of Thornton plans to sue Larimer County over commissioners' rejection of the Thornton pipeline proposal, according to the county's attorney.

Larimer County attorney Jeannine Haag told the Coloradoan she learned Thornton would be filing a lawsuit when she called the city's attorney and asked whether the city would pursue legal action contesting the pipeline decision.

Thornton will file a lawsuit in Larimer County District Court next week, Haag said. Thornton spokesman Todd Barnes told the Coloradoan the city doesn't comment on issues of potential litigation.

The Thornton pipeline would eventually carry an average of 14,000 acre-feet of Poudre River water from reservoirs north of Fort Collins to the growing Denver suburb. Thornton officials planned to begin construction in 2019 and begin water deliveries by 2025.

Thornton officials have kept quiet about their plans since commissioners unanimously rejected their proposal to build a pipeline to carry Poudre River water through Larimer County. Thornton leaders said they wouldn't decide what to do until they could review commissioners' written explanation of the vote. Commissioners approved that document March 18.

More:NISP pipeline: Will Larimer County approve a route similar to rejected Thornton pipeline?

The rejection followed more than a year of back-and-forth between Thornton and county officials over the pipeline route. Thornton originally wanted to run the pipeline under Douglas Road but scuttled that route after commissioners sent them back to the drawing board.

The city's modified pipeline route opted for County Road 56, but commissioners and community members were unimpressed, saying Thornton leaders didn't do enough to mitigate negative impacts from construction and didn't offer enough benefits to Larimer County residents.

Thornton's water plans wouldn't diminish flows in the Poudre River because the project's water is already diverted from the river for agriculture. But the "Poudre River alternative," which would involve running Thornton's water down the river and nixing the northern segment of the pipeline, picked up considerable public support during a series of hearings on the project. Proponents said the plan would be a boon for a stretch of the river plagued with low flows.

More:'Poudre River alternative' steals the spotlight at Thornton pipeline hearing

Thornton leaders say the plan isn't workable because it would degrade their water supply and more than double the project's cost, among other things.

Pipeline opponents included the No Pipe Dream group and Save the Poudre, both of which supported the Poudre River alternative.

"Save the Poudre will intervene on behalf of Larimer County, and on behalf of county citizens, to fight Thornton every step of the way," said Gary Wockner, executive director of Save the Poudre.

It was also possible that Thornton officials would pursue an agreement with the city of Greeley, which has extra capacity in a water pipeline that might have been useful for Thornton. The cities met on the matter last month.

In the written explanation of their decision on the pipeline, Larimer County commissioners said Thornton didn't meet seven of the 12 criteria for the 1041 permit required to build the pipeline. The commissioners' ruling was the county's first-ever rejection of a 1041 permit.

Commissioners wrote that Thornton didn't meet the following criteria:

The proposal is consistent with the county's master plan for land use and development

The applicant presented reasonable siting or design alternatives or explained why no reasonable alternatives are available

The proposal conforms with county standards and mitigation requirements for environmental impacts

The proposal won't have a significant adverse effect on the land on which it's situated and adjacent land, or will adequately mitigate significant adverse effects

The proposal won't negatively impact public heath and safety

The benefits of proposed development outweigh the losses of any natural resources or resulting reduction of productivity of agricultural lands

The proposal demonstrates a reasonable balance between the costs to the applicant to mitigate significant adverse effects and the benefits achieved by that mitigation

Jacy Marmaduke covers environment and other topics for the Coloradoan. Follow her on Twitter @jacymarmaduke. Support stories like this one with a digital subscription to the Coloradoan.