Public health officials cautioned that, while the spill was a serious event, it did not pose widespread health risks.
Health officials were testing nearby waters for coliform bacteria and any trace of the airport's deicing fluid. Although the official test results will not be available until Friday morning at the latest, crews have not noticed any significant contamination based on initial observations.
Environmental testing suggested the front edge of the spill in Third Creek was nearing the edge of DIA's property at the Adams County line on Wednesday evening.
However, crews have not seen any contamination beyond airport property.
DIA is setting up dirt blockages at the edge of their property to prevent any residual contamination that could result from this weekend's potential snow or rain.
Third Creek feeds into an irrigation canal and eventually into Barr Lake. Barr Lake provides drinking water to parts of the metro area.
However, crews do not believe any sewage has reached Barr Lake.
Tri-County Health Department's director of environmental health, Tom Butts, said the situation is being monitored but the most aggressive response has not been activated.
That would involve DIA crews damming or diverting Third Creek, Butts said.
"A million gallons as not is big as it might sound," Butts said. "Any spill of this size is serious, but it's all relative."
"We did not notice anything in terms of odor or extra materials," Butts said.
The risk to nearby wells is minimal, Butts said, and small fish in the creek appeared to be unaffected.
"The only risk would be to someone who went in the water in the creek," Butts said.
The airport is putting up signs to discourage people from coming into contact with the creek.
The spill might be contained to the creek and irrigation ditches and never reach Barr Lake, Butts said.
DIA spokesman Jeff Green said a pump at a lift station failed at about 7 p.m. Tuesday. A visible and audible backup alarm was not noticed by airport employees, Green said.
The spill was discovered approximately 12 hours later, according to Green, who said the airport was looking at ways to mitigate the human error that prolonged the spill.
DIA said it notified federal, state and local health departments, a farmer downstream, Farmers Reservoir Irrigation Company, Adams County and authorities at Barr Lake.
Green said the estimate of 1 million gallons spilled was based on the maximum capacity of the system, which was unlikely to be reached during the overnight hours.
There is a chance, Green said, that the actual spill amount was well under 1 million gallons.
An engineer from the Colorado Department of Public Health and Environment was at the scene Wednesday.
Butts said testing would continue to determine the severity of the spill and what mitigation efforts are required.
Calls to the Farmers Reservoir and Irrigation Company and the Barr-Milton Watershed Association were not immediately returned.
(KUSA-TV © 2010 Multimedia Holdings Corporation)