WASHINGTON - The powerful U.S. Environmental Protection Agency has once again rebuked the State Department over its positive environmental assessment of TransCanada's proposed Keystone XL pipeline.

In a lengthy, highly technical letter sent Monday to the top State Department officials overseeing the pipeline permit process, the EPA raises serious concerns about the project's carbon footprint and criticizes the department's draft analysis.

It urges the State Department to rethink its finding that the controversial pipeline would not significantly spur production of Alberta's carbon-intensive oilsands or boost greenhouse gas emissions.

The letter, signed by EPA official Cynthia Giles, said the State assessment included "insufficient information" on environmental issues and added that officials failed to adequately consider alternative routes for the pipeline.

It's the second time the EPA has publicly denounced the State Department's environmental review of the pipeline.

In July 2010, as TransCanada awaited a decision from the White House on its first permit application, the EPA sent a letter to the State Department calling its draft environmental assessment of the project “inadequate.”

Then, as now, it chastised analysts for failing to address the greenhouse gas emissions associated with Keystone XL. The letter also urged the State Department to further examine pipeline safety and spill-response planning, as well as the impact on Canadian aboriginal communities.

The EPA is one of several federal agencies that’s been advising the Obama administration on the $7.6-billion pipeline, a project that would carry millions of barrels of bitumen a week from Alberta’s oilsands to the U.S. Gulf Coast.

President Barack Obama rejected the pipeline early last year, but invited TransCanada to file a new application with an altered route that would skirt Nebraska’s ecologically sensitive Sand Hills region.

TransCanada did so, earning the thumb's up from the state of Nebraska and the draft assessment from the State Department that suggested it posed minimal environmental risks. The State Department is analysing the pipeline because it crosses an international border.

In Round 2 between the EPA and the State Department, Giles says State officials have mistakenly concluded that oilsands bitumen would find buyers with or without the pipeline, most likely via rail lines. The State review used an outdated "energy-economic modeling effort" to reach that finding, she wrote.

“Because the market analysis is so central to this key conclusion, we think it is important that it be as complete and accurate as possible,” she added.

The EPA response was one of hundreds submitted to the State Department following the release of its draft ecological assessment of Keystone in March. The public comment period ended on Monday.

The State Department will now review all the public comments, including the input from the EPA, before finalizing its draft report. Ninety days later, State officials will then determine whether Keystone XL is in the national interest of the United States.

After that, it will be up to Obama to either block or bless the pipeline. A final decision is expected this summer.

The State Department released a brief statement on Monday night saying it had always anticipated that it "would conduct additional analysis and incorporate public comments" in the final version of its environmental report on the pipeline.

Environmental groups urged Obama administration officials to heed the EPA.

"We hope that the State Department will listen closely to the EPA and try again to measure the true impact of this proposed pipeline, which almost every evaluator who doesn’t work for the Canadian government or an oil company has found to be not in the national interest," May Boeve, executive director of 350.org, said in a statement.

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  • The 181 million metric tons of (CO2e) from Keystone XL is equivalent to the tailpipe emissions from more than 37.7 million cars. This is more cars than are currently registered on the entire West Coast (California, Washington, and Oregon), plus Florida, Michigan, and New York – combined.

  • Between 2015 and 2050, the pipeline alone would result in emissions of 6.34 billion metric tons of CO2e. This amount is greater than the 2011 total annual carbon dioxide emissions of the United States.

  • If approved, the Keystone XL pipeline would be responsible for emissions equal to that of 51 coal-fired power plants.

  • The International Energy Agency has said that two-thirds of known fossil fuel reserves must remain undeveloped if we are to avoid a 2 degree C temperature rise.

  • U.S. demand for oil has declined since 2005 by 2.25 million barrels per day or the equivalent of almost three Keystone XL pipelines.

  • More on the oilsands and Canada’s environment:

  • Syncrude Upgrader and Oil Sands

    The refining or upgrading of the tarry bitumen which lies under the oil sands consumes far more oil and energy than conventional oil and produces almost twice as much carbon. Each barrel of oil requires 3-5 barrels of fresh water from the neighboring Athabasca River. About 90% of this is returned as toxic tailings into the vast unlined tailings ponds that dot the landscape. Syncrude alone dumps 500,000 tons of toxic tailings into just one of their tailings ponds everyday.

  • Boreal Forest and Coast Mountains / Atlin Lake, British Columbia | 2001

    This area, located in the extreme northwest of British Columbia, marks the western boundary of the Boreal region. On the border of the Yukon and Southeast Alaska, the western flank of these mountains descends into Alaska's Tongass Rainforest and British Columbia's Great Bear Rainforest. Far from the oil sands, the greatest remaining coastal temperate and marine ecosystem is imminently threatened by the proposal to build a 750-mile pipeline to pump 550,000 barrels per day of oil sands crude to the coast. Once there, it would be shipped through some of the most treacherous waters, virtually assuring an ecological disaster at some point in the future.

  • Tailings Pond in Winter, Abstract #2 / Alberta Tar Sands | 2010

    Even in the extreme cold of the winter, the toxic tailings ponds do not freeze. On one particularly cold morning, the partially frozen tailings, sand, liquid tailings and oil residue, combined to produce abstractions that reminded me of a Jackson Pollock canvas.

  • Aspen and Spruce | Northern Alberta | 2001

    Photographed in late autumn in softly falling snow, a solitary spruce is set against a sea of aspen. The Boreal Forest of northern Canada is perhaps the best and largest example of a largely intact forest ecosystem. Canada's Boreal Forest alone stores an amount of carbon equal to ten times the total annual global emissions from all fossil fuel consumption.

  • Tar Sands at Night #1 | Alberta Oil Sands | 2010

    Twenty four hours a day the oil sands eats into the most carbon rich forest ecosystem on the planet. Storing almost twice as much carbon per hectare as tropical rainforests, the boreal forest is the planet's greatest terrestrial carbon storehouse. To the industry, these diverse and ecologically significant forests and wetlands are referred to as overburden, the forest to be stripped and the wetlands dredged and replaced by mines and tailings ponds so vast they can be seen from outer space.

  • Dry Tailings #2 | Alberta Tar Sands | 2010

    In an effort to deal with the problem of tailings ponds, Suncor is experimenting with dry tailings technology. This has the potential to limit, or eliminate, the need for vast tailings ponds in the future and lessen this aspect of the oil sands' impact.

  • Tailings Pond Abstract #2 | Alberta Tar Sands / 2010

    So large are the Alberta Tar Sands tailings ponds that they can be seen from space. It has been estimated by Natural Resources Canada that the industry to date has produced enough toxic waste to fill a canal 32 feet deep by 65 feet wide from Fort McMurray to Edmonton, and on to Ottawa, a distance of over 2,000 miles. In this image, the sky is reflected in the toxic and oily waste of a tailings pond.

  • Confluence of Carcajou River and Mackenzie River | Mackenzie Valley, NWT | 2005

    The Caracajou River winds back and forth creating this oxbow of wetlands as it joins the Mackenzie flowing north to the Beaufort Sea. This region, almost entirely pristine, and the third largest watershed basin in the world, will be directly impacted by the proposed Mackenzie Valley National Gas Pipeline to fuel the energy needs of the Alberta Oil Sands mega-project.

  • Black Cliff | Alberta Oil Sands | 2005

    Oil sands pit mining is done in benches or steps. These benches are each approximately 12-15 meters high. Giant shovels dig the oil sand and place it into heavy hauler trucks that range in size from 240 tons to the largest trucks, which have a 400-ton capacity.

  • Oil Sands Upgrader in Winter| Alberta Oil Sands | 2010

    The Alberta oil sands are Canada's single largest source of carbon. They produce about as much annually as the nation of Denmark. The refining of the tar-like bitumen requires more water and uses almost twice as much energy as the production of conventional oil. Particularly visible in winter, vast plumes of toxic pollution fill the skies. The oil sands are so large they create their own weather systems.

  • Boreal Forest and Wetland | Athabasca Delta Northern Alberta | 2010

    Located just 70 miles downstream from the Alberta oil sands, the Athabasca Delta is the world's largest freshwater delta. It lies at the convergence of North America's four major flyways and is a critical stopover for migrating waterfowl and considered one of the most globally significant wetlands. It is threatened both by the massive water consumption of the tar sands and its toxic tailings ponds.

  • Tar Pit #3

    This network of roads reminded me of a claw or tentacles. It represents for me the way in which the tentacles of the tar sands reach out and wreak havoc and destruction. Proposed pipelines to American Midwest, Mackenzie Valley, and through the Great Bear Rainforest will bring new threats to these regions while the pipelines fuel new markets and ensure the proposed five fold expansion of the oil sands.