An American senator who has promoted the importance of carbon- capture technology is suggesting that he's been misled about its success in Saskatchewan.

Sen. Joe Manchin says the carbon-capture facility at the Boundary Dam power plant has "failed to operate successfully for any meaningful period of time."

Manchin is also critical of the U.S. Environmental Protection Agency for including the Saskatchewan project in its greenhouse gas emissions standards.

"Many of the glowing performance results cited by EPA in the final rule have been found to be nothing more than marketing spin and hyperbole, with the true results reflecting a very troubled project, particularly in the CCS technology area," Manchin wrote in a letter last week to Gina McCarthy, administrator of the U.S. Environmental Protection Agency.

He also questions how much time the EPA spent at the Boundary Dam site and asks how the agency missed "the persistent unsuccessful performance and shutdowns throughout 2015."

Saskatchewan Energy Minister Bill Boyd said the senator's comments are unfortunate and he's drafting a letter to send to Manchin.

"We are going to be very, very clear on it, that the project is not performing to the standard that we would like it to perform at, that it has captured though about 400,000 tonnes, the equivalent of about 100,000 cars," Boyd said Monday at the legislature in Regina.

"We're also saying that this is a very, very technical project and I think requires some patience to perform adequately."

Manchin is from the coal-producing state of West Virginia and says carbon capture could help mitigate CO2 emissions for countries that rely on fossil fuel energy.

The senator met with Saskatchewan Premier Brad Wall last year to talk about the facility at Boundary Dam. At the time, Wall posted on Facebook: "Thanked Senator Joe Manchin III for his leadership on CCS & clean coal. Told him about our clean-coal technology at Boundary Dam 3."

That was before reports started surfacing about troubles at the carbon-capture complex.

The facility opened with much fanfare in October 2014. It was to have opened the previous April, but faced construction delays. The goal is to reduce carbon-dioxide emissions by one million tonnes annually. The facility has removed 400,000 tonnes so far this year.

Documents leaked to the Opposition NDP show the $1.5-billion facility has been working 45 per cent of the time since it opened.

It was the NDP that raised the Manchin letter in the legislature Monday.

Boyd said he's "very, very concerned about the project" and getting regular updates from SaskPower.

"The last few days, the last several days, have been going pretty well. I think there's a lot of time that needs to go by here performing well before we certainly want to look at the project any further," said Boyd.

"It is a project that's had a troubled past, there's no question about it, our government has admitted that, maybe not as explicitly as we should have done at the outset of the project, but I think this is still a good project for the people of Saskatchewan."