By Kristen Hays and Matthew Robinson

March 31 (Reuters) - Exxon Mobil on Sunday continued cleanup of a pipeline spill that spewed thousands of barrels of heavy Canadian crude in Arkansas as opponents of oil sands development latched on to the incident to attack plans to build the Keystone XL line.

Exxon spokesman Alan Jeffers said on Sunday that crews had yet to excavate the area around the pipeline breach, a needed step before the company can estimate how long repairs will take and when the line might restart.

"I can't speculate on when it will happen," Jeffers said. "Excavation is necessary as part of an investigation to determine the cause of the incident."

Exxon's Pegasus pipeline, which can carry more than 90,000 barrels per day (bpd) of crude from Patoka, Illinois to Nederland, Texas, was shut after the leak was discovered late Friday afternoon in a subdivision near the town of Mayflower. The leak forced the evacuation of 22 homes.

Exxon also had no specific estimate of how much crude oil had spilled, but the company said 12,000 barrels of oil and water had been recovered - up from 4,500 barrels on Saturday. The company did not say how much of the total was oil and how much was water.

Allen Dodson, Faulkner County judge who is the top executive for the county where the spill occurred, told Reuters in an interview on Sunday that the smell of crude was less potent on Sunday as cleanup efforts continued, saying it was weaker than the smell of fresh asphalt laid on a road.

"The freestanding oil on the street has been removed. It's still damp with oil, it's tacky, like it is before we do an asphalt overlay," he said.

Exxon said it staged the response to handle 10,000 barrels of oil "to ensure adequate resources are in place."

Officials from the U.S. Environmental Protection Agency and the Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) also were on site to investigate the spill.

Fifteen vacuum trucks remained on the scene for cleanup, and 33 storage tanks were deployed to temporarily store the oil.

The pipeline was carrying Canadian Wabasca Heavy crude at the time of the leak. An oil spill of more than 1,000 barrels into a Wisconsin field from an Enbridge Inc pipeline last summer kept that line shuttered for around 11 days.

The 848-mile (1,381 km) pipeline used to transport crude oil from Texas to Illinois. In 2006 Exxon reversed it to move crude from Illinois to Texas in response to growing Canadian oil production and the ability of U.S. Gulf Coast refineries to process heavy crude.

The Arkansas spill drew fast reaction from opponents of the 800,000 bpd Keystone XL pipeline, which also would carry heavy crude from Canada's tar sands to the Gulf Coast refining hub.

Environmentalists have expressed concerns about the impact of developing the oil sands and say the crude is more corrosive to pipelines than conventional oil. On Wednesday, a train carrying Canadian crude derailed in Minnesota, spilling 15,000 gallons of oil.

"Whether it's the proposed Keystone XL pipeline, or ... (the) mess in Arkansas, Americans are realizing that transporting large amounts of this corrosive and polluting fuel is a bad deal for American taxpayers and for our environment," said Representative Ed Markey, a Massachusetts Democrat.

Supporters of Keystone XL and oil sands development say the vast Canadian reserves can help drive down fuel costs in the United States. A report from the Canadian Energy Pipeline Association, put together by oil and gas consultancy Penspen, argued diluted bitumen is no more corrosive than other heavy crude.

A year ago Exxon won a court appeal to charge market rates on the Pegasus line, or rates that are not capped and that can change along with market conditions without prior approval from the Federal Energy Regulatory Commission.

That decision by the U.S. Court of Appeals in Washington D.C. said the Pegasus pipeline is now the "primary avenue" to move Canadian crude oil to the Gulf Coast. The ruling also said Exxon moves about 66,000 barrels per day on the line.

Last week PHMSA proposed that Exxon pay a $1.7 million fine over pipeline safety violations stemming from a July 2011 oil spill from its Silvertip pipeline in the Yellowstone River. The line, which carries 40,000 barrels per day in Montana, leaked about 1,500 barrels of crude after heavy flooding in the area.

Exxon has 30 days from the March 25 order to contest those violations.

According to PHMSA, the U.S. has 2.3 million miles of pipelines.

CLEANUP

Exxon said that by 3 a.m. Saturday there was no additional oil spilling from the pipeline and that trucks had been brought in to assist with the cleanup. Images from local media showed crude oil snaking along a suburban street and spewed across lawns.

Twenty-two homes in the affected subdivision remained evacuated on Sunday, though Mayflower police were providing escorts for residents to temporarily return to retrieve personal items.

Jeffers said a couple of homes "appear to have small amounts of oil on their foundations," but he had no information on damage estimates or claims. Exxon had established a claims hotline for affected residents and said about 50 claims had been made so far.

Dodson said oil that made it to the street went into storm drains that eventually lead to a cove connected to nearby Lake Conway, known as a fishing lake stocked with bass, catfish, bream and crappie.

He said local responders that included firemen, city employees, county road crews, police quickly built dikes of dirt and rock to block culverts along that path that stopped crude from fouling the lake.

"We were just in the nick of time," he said.

Exxon later deployed 3,600 feet of boom near the lake as a precaution.

Dodson said crude also got into several homeowners' yards, which will take longer to clean up.

"We've just gotten used to having pipelines go through cities and counties, and you hope something like this doesn't happen. My heart goes out to all of the people personally impacted," Dodson said.

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  • Niger Delta ExxonMobil Spill, Nigeria - May 2010

    In Nigeria's Akwa Ibom State, an ExxonMobil pipeline ruptured on May 1 and spilled over a million gallons of oil, <a href="http://www.guardian.co.uk/world/2010/may/30/oil-spills-nigeria-niger-delta-shell" target="_hplink">reported the <em>Guardian</em></a>. The leak continued for seven days before it was stopped. <a href="http://www.huffingtonpost.com/omoyele-sowore/the-oil-spill-no-ones-tal_b_649220.html" target="_hplink">HuffPost blogger Omoyele Sowore explained</a> in July 2010 that an oil spill from ExxonMobil operations was nothing new to the country. He wrote that an "environmental catastrophe [had] been going on since December 2009." He described the toll on Nigeria: "There's oil on the surface of the ocean, wildlife coated in crude, fishermen losing their businesses." In 2011, the Nigerian government said there had been <a href="http://articles.latimes.com/2011/aug/05/world/la-fg-nigeria-oil-20110805">more than 7,000 oil spills</a> in the country between 1970 and 2000 that could take up to 30 years and $1 billion to clean up.

  • Trans-Alaska Pipeline Spill - May 2010

    In May 2010, several thousand barrels of oil spilled from the Trans-Alaska pipeline "during a scheduled pipeline shutdown at a pump station near Fort Greely," <a href="http://www.huffingtonpost.com/2010/05/26/alaska-oil-spill-trans-al_n_589974.html" target="_hplink">explained AP</a>. No injuries were reported and officials said the spill was likely "limited to the gravel on top of the containment area's line."

  • Red Butte Creek Spill, Utah - June 2010

    In June 2010, a Chevron pipeline ruptured and spilled oil into a creek near Salt Lake City, Utah. It was first estimated that over 17,000 to 21,000 gallons spilled into the creek, which leads into the Great Salt Lake, <a href="http://www.huffingtonpost.com/2010/06/12/utah-oil-spill-500-gallon_n_610232.html#s99698" target="_hplink">reported AP</a>. Around 150 birds were "identified for rehabilitation." The <a href="http://www.huffingtonpost.com/2010/06/14/utah-oil-spill-officials-_n_611014.html" target="_hplink">oil did not reach the Great Salt Lake</a>, however. <a href="http://www.huffingtonpost.com/2010/07/14/chevron-cited-for-oil-spi_n_646340.html" target="_hplink">Chevron was later cited for the spill</a>, which released an estimated 33,000 gallons in total. In March 2012, <a href="http://www.huffingtonpost.com/huff-wires/20120324/us-oil-spill-utah/" target="_hplink">a group of 66 residents of a Salt Lake City neighborhood sued Chevron</a> for damage caused by the Red Butte Creek spill and a smaller spill in December 2011.

  • Kalamazoo River Spill, Michigan - July 2010

    In late July 2010, an Enbridge pipeline in southwestern Michigan sprung a leak and <a href="http://www.huffingtonpost.com/2010/07/27/michigan-oil-spill-among_n_661196.html" target="_hplink">spilled over 800,000 gallons of oil into a creek</a> which flows into the Kalamazoo River. By August, a regional EPA administrator said that significant progress had been made at the site, but "the agency cautioned that it will take months to complete the cleanup," <a href="http://www.huffingtonpost.com/2010/08/02/michigan-oil-spill-epa-of_n_667556.html" target="_hplink">reported AP</a>. By the end of September, <a href="http://www.huffingtonpost.com/2010/09/27/michigan-oil-pipeline-res_n_741233.html" target="_hplink">the pipeline -- which travels from Ontario to Indiana -- was back in operation</a>. The EPA later <a href="http://www.huffingtonpost.com/huff-wires/20111116/us-michigan-river-oil-spill/" target="_hplink">reported that about 1.1 million gallons of oil were recovered</a>, but pipeline operator Enbridge said that it would stick with previous estimates that only about 843,000 gallons were spilled.

  • Xingag Harbor Spill, Dailan, China - July 2010

    In July 2010, China experienced what was reported as the "<a href="http://www.huffingtonpost.com/2010/07/21/china-oil-spill-grows-off_n_653852.html#s120708" target="_hplink">country's largest reported oil spill</a>" after a pipeline rupture near the northeastern port city of Dailan. Several days after the spill, cleanup efforts were underway over a 165 square mile (430 square kilometer) area of the Yellow Sea. The Chinese government reported that about 1,500 tons or 461,790 gallons of oil had spilled, but <a href="http://www.huffingtonpost.com/2010/07/30/china-oil-spill-far-bigge_n_665038.html#s120708" target="_hplink">experts contended that the spill could have been "dozens of times larger,"</a> reported AP.

  • Peace River Spill, Alberta, Canada - April 2011

    In late April 2011, a pipeline in northwestern Alberta began leaking, and created the worst spill in the province in 36 years, <a href="http://www.calgaryherald.com/news/alberta/Rainbow+pipeline+leak+largest+years/4720888/story.html" target="_hplink">reported the <em>Calgary Herald</em></a>. About 1,176,000 gallons of oil were reportedly spilled from the Rainbow pipeline, which is operated by Plains Midstream Canada. The <em>Globe and Mail</em> revealed that the pipeline operators "<a href="http://www.theglobeandmail.com/report-on-business/oil-on-rainbow-line-halted-8-hours-after-problem-detected/article2013335/" target="_hplink">detected a potential problem nearly eight hours before halting the flow of crude</a>." A nearby school in a First Nation community was closed after residents reported "nausea, burning eyes and other symptoms," and several animals were found dead. In late July, Plains Midstream <a href="http://www.huffingtonpost.ca/2011/07/28/alberta-pipeline-owner-as_n_912796.html" target="_hplink">requested to re-open the pipeline</a> and begin to ship oil to Edmonton again.

  • Bohai Bay Spill, China - June 2011

    In June 2011, an oil <a href="http://www.huffingtonpost.com/2011/07/01/china-offshore-oil-spills-bohai-bay_n_888473.html" target="_hplink">spill occurred about 25 miles off the coast of China's Shandong province</a> in Bohai Bay. A second spill followed in July. In late August, <a href="http://www.huffingtonpost.com/2011/08/26/new-seeps-in-china-spill_n_937809.html" target="_hplink">it was reported</a> that ConocoPhillips had discovered more oil seeps in Bohai Bay, although only "1 to 2 liters (a quarter to a half-gallon) of oil and drilling mud were being released each day." The company reported that the 2011 spills released 29,400 gallons of oil and 2,500 barrels of drilling mud into the bay and that most of it was recovered. In September, <a href="http://www.huffingtonpost.com/2011/09/05/china-oil-spill-conocophillips_n_949745.html" target="_hplink">China's State Oceanic Administration claimed that oil was still seeping</a> underwater. In early 2012, Texas-based ConocoPhillips <a href="http://www.huffingtonpost.com/huff-wires/20120124/as-china-oil-spill/" target="_hplink">reached a settlement deal with the Chinese government</a> for $160 million.

  • Yellowstone River Spill, Montana - July 2011

    In July 2011, a pipeline beneath Montana's Yellowstone River ruptured and sent an oil plume 25 miles downstream, <a href="http://www.huffingtonpost.com/2011/07/02/yellowstone-oil-spill-pro_n_889363.html" target="_hplink">reported AP</a>. Despite reassurances from ExxonMobil that the pipeline was safe, <a href="http://www.huffingtonpost.com/2011/07/06/yellowstone-river-oil-spill-exxon-mobil_n_891246.html" target="_hplink">the July spill released what was originally estimated to be 42,000 gallons of oil</a>. With other 1,000 workers assisting the cleanup, ExxonMobil <a href="http://www.huffingtonpost.com/2011/11/04/yellowstone-river-cleanup-costs_n_1077106.html" target="_hplink">estimated that it would cost $135 million to clean the river</a>. In January 2012, <a href="http://www.huffingtonpost.com/2012/01/19/exxon-yellowstone-oil-spill_n_1216830.html" target="_hplink">it was reported</a> that ExxonMobil had increased its estimate of the spill size by 21,000 gallons. AP later <a href="http://www.huffingtonpost.com/2012/04/06/yellowstone-river-spill-response-plan_n_1408328.html" target="_hplink">reported the estimated spill size as 63,000 gallons</a>. <em><strong>CORRECTION:</strong> A previous version of this slide stated the estimated spill size as 63,000 barrels instead of gallons.</em>

  • North Sea Spill, United Kingdom - Aug. 2011

    In August 2011, <a href="http://www.huffingtonpost.com/2011/08/15/north-sea-spill-uk-oil-spill_n_927078.html" target="_hplink">an oil rig off the eastern coast of Scotland began leaking</a> oil into the North Sea. Royal Dutch Shell, which operates the Gannet Alpha oil rig, initially reported that 54,600 gallons of oil were spilled. A second leak soon occurred, turning the spill into the worst in the North Sea in a decade, <a href="http://www.huffingtonpost.com/2011/08/16/north-sea-oil-spill-shell_n_927941.html" target="_hplink">reported AP</a>. Several days later, Shell announced that it had "closed a valve from which oil was spilling into the North Sea," <a href="http://www.huffingtonpost.com/2011/08/19/shell-says-it-has-closed-_n_931379.html" target="_hplink">according to AP</a>. The spill released about 1,300 barrels of oil, which spread out over a 2.5 square mile (6.7 square kilometer) area.

  • Campos Basin Spill, Rio de Janeiro, Brazil - Nov. 2011

    In mid-November 2011, Brazilian authorities began investigating an offshore spill near Rio de Janeiro, <a href="http://www.huffingtonpost.com/2011/11/17/chevron-oil-spill-brazil_n_1100062.html" target="_hplink">reported AP</a>. Chevron initially reported that between 400 and 650 barrels of oil had spilled into the Atlantic, while a nonprofit environmental group using satellite imagery estimated that the spill rate was at least 3,738 barrels per day. Chevron soon claimed full responsibility for the spill. The brazilian division's COO said, Chevron "<a href="http://www.huffingtonpost.com/2011/11/20/brazil-oil-spill-chevron-_n_1104070.html" target="_hplink">takes full responsibility for this incident</a>," and that "any oil on the surface of the ocean is unacceptable to Chevron," reported AP. In December, Brazilian prosecutors announced that they were <a href="http://www.huffingtonpost.com/2011/12/14/brazil-oil-spill-chevron-payment_n_1149554.html"target="_hplink">seeking $10.6 billion in damages</a> from Chevron for the spill that leaked nearly 126,000 gallons of oil. In March 2012, a Brazilian federal judge <a href="http://www.huffingtonpost.com/2012/03/18/brazil-oil-spill-chevron_n_1355923.html" target="_hplink">allowed prosecutors to file criminal charges against Chevron and Transocean</a> and 17 executives from both companies were barred from leaving Brazil.

  • Rena Spill, New Zealand - Oct. 2011

    In October 2011, a Liberian-flagged cargo ship ran aground on a reef in Northern New Zealand and began leaking oil. With oil washing up on shore, a government minister deemed it <a href="http://www.huffingtonpost.com/2011/10/11/new-zealand-oil-spill_n_1004643.html" target="_hplink">the country's largest maritime environmental disaster</a> a week later. Although over 2,000 sea birds were killed by the spill that spilled about 400 tons of fuel oil, <a href="http://www.huffingtonpost.com/2011/11/22/new-zealand-oil-spill-penguins_n_1107289.html" target="_hplink">343 little blue penguins were rescued and cleaned of oil</a>. <em>[<a href="http://www.huffingtonpost.com/2011/12/22/new-zealand-oil-spill-penguins-released_n_1151788.html" target="_hplink">Watch video of the penguins' release into the wild here.</a>]</em> In January, <a href="http://www.huffingtonpost.com/2012/01/10/new-zealand-oil-spill-ship_n_1196568.html" target="_hplink">half of the stricken Rena began sinking</a> into the sea after breaking apart and spilling over 100 cargo containers.

  • Nigeria Oil Spill - Dec. 2011

    The spill, which took place near the coast of Nigeria, was reported as "likely the worst to hit those waters in a decade," <a href="http://www.huffingtonpost.com/2011/12/22/shell-oil-spill-nigeria_n_1164891.html" target="_hplink">according to AP</a>. After two days, the spill had affected 115 miles (185 kilometers) of Nigerian coastline. Several days after the December 20 spill, <a href="http://www.huffingtonpost.com/2011/12/26/shell-nigeria-oil-spill_n_1170198.html" target="_hplink">Shell reported that the leak -- which occurred about 75 miles offshore -- had been contained before it reached the Nigerian coast</a>. The spill, which covered 350 square miles of ocean at its peak, was reported as having released less than "40,000 barrels -- or 1.68 million gallons" of oil.

  • Red Deer River Spill, Alberta, Canada - June 2012

    In June 2012, 126,000 gallons of sour crude oil leaked from a submerged pipeline into the <a href="http://www.huffingtonpost.ca/2012/06/08/alberta-oil-spill-red-deer-river_n_1581008.html">Red Deer River in Alberta, Canada</a> before being swept downstream to the Gleniffer Lake and Reservoir, a main source of drinking water for several communities near the spill. A $75 million <a href="http://www.huffingtonpost.ca/2012/06/22/red-deer-river-oil-spill-lawsuit_n_1620267.html">class-action lawsuit was filed</a> against the owners of the pipelines, and in October 2012, the Canadian government <a href="http://www.huffingtonpost.ca/2012/08/07/red-deer-river-fishing_n_1752902.html">banned fishing in the river </a>in order to study the long-term environmental impacts of the spill. This was the second major spill in the province and for the company that owns the line, <a href="http://www.plainsmidstream.com/">Plains Midstream Canada</a>, in two years. In 2011, 1.1 million gallons of oil leaked into the Peace River from a damaged pipeline in a remote corner of the province.

  • Arthur Kill Oil Spill - October 2012

    In October 2012, 336,000 gallons of diesel fuel <a href="http://www.huffingtonpost.com/2012/11/01/arthur-kill-oil-spill-new-jersey_n_2054267.html">spilled into the Arthur Kill waterway</a> as a result of Superstorm Sandy when two storage tank were damaged by 13-foot waves. The spill contaminated the narrow band of water that separates Staten Island from New Jersey, releasing a strong chemical odor into the air as the diesel rose to the surface and evaporated. Officials said a <a href="http://www.huffingtonpost.com/2012/11/01/arthur-kill-oil-spill-clean-up-diesel-shell_n_2058723.html">majority of the fuel spilled was captured</a> by booms and that it was fortunate diesel spilled rather than crude oil because cleanup and dissipation would be much faster.

  • Mayflower, Arkansas Pipeline Rupture - March 2013

    In late March 2013, ExxonMobil's Pegasus pipeline ruptured and spilled about 5,000 barrels (210,000 gallons) of Canadian heavy crude oil into a residential area in Mayflower, Arkansas. Exxon later <a href="http://www.huffingtonpost.com/2013/04/15/exxonmobil-pegasus-pipeline_n_3082441.html" target="_blank">removed a damaged 52-foot section of the pipeline</a>. The company's cleanup efforts -- which <a href="http://www.huffingtonpost.com/2013/04/09/rachel-maddow-mayflower-oil-spill-exxon_n_3047331.html" target="_blank">reportedly included using paper towels</a> -- were <a href="http://www.huffingtonpost.com/2013/04/12/colberts-arkansas-oil-spill-exxon_n_3071539.html" target="_blank">criticized in the media</a>. <a href="http://www.huffingtonpost.com/2013/04/10/arkansas-oil-spill-health-_n_3045610.html" target="_blank">Local residents began reporting health issues</a> not long after the spill. Arkansas Attorney General Dustin McDaniel has also expressed his concern for the health of Mayflower residents, <a href="http://www.huffingtonpost.com/2013/05/13/arkansas-oil-spill-health-mayflower-moms_n_3267965.html" target="_blank">reported The Huffington Post's Lynne Peeples</a>. One month after the spill, the <a href="http://www.huffingtonpost.com/2013/05/01/missouri-oil-spill-exxon_n_3194177.html" target="_blank">same pipeline leaked one barrel of oil</a> into a residential yard in Missouri.

  • Mississippi River Oil Spill - January 2013 (and February 2012)

    In January 2013, a <a href="http://www.huffingtonpost.com/2013/01/27/mississippi-river-barge-crash_n_2564418.html">barge carrying 668,000 gallons of light crude oil</a> on the Mississippi River crashed into a railroad bridge. An 80,000 gallon tank on the vessel was damaged, spilling oil into the waterway, which prompted officials to close the river for eight miles in either direction. The spill led to a backup of more than 1,000 barges and the accident is still under investigation. Workers <a href="http://www.sfgate.com/news/science/article/Oil-spill-cleanup-on-Mississippi-River-complete-4257729.php">finished clean-up in early February</a>, but the Coast Guard said 7,000 gallons of crude oil are still unaccounted for. This was <a href="http://www.huffingtonpost.com/2012/02/17/mississippi-river-barge-collision_n_1284166.html">the second collision of an oil tanker</a> on the Mississippi in the past year. In February 2012 two barges collided which led to a five-mile wide closure.

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