EPA spokeswoman Laura Williams said the agency is continuing to investigate samples taken from the creek to see whether the metal content in the water is higher than historic levels.
Officials said that samples collected did not show the presence of some of the metals the EPA tests for, but, as of Monday, they had not explained what metals were present in the samples and in what concentration.
The tests look for aluminum, antimony, arsenic, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, manganese, magnesium, nickel, potassium, selenium, silver, sodium, thallium, vanadium and zinc.
The deluge of water from the Swathmore Mine on Sept. 21 temporarily turned the creek orange and led officials to briefly shut down water intake systems downstream.
Boulder and Nederland use the creek as part of their water supplies.
EPA officials said soon after the spill that the discharge from the mine was not toxic, but sent water samples for testing. They expect further results to be available later this week.
Todd Hartman, a spokesman for the Colorado Department of Natural Resources, said the mine has discharged at a “low flow rate,” less than 15 gallons a minute, for as long as the landowner can remember, but had apparently never surged before…
The Colorado Division of Reclamation, Mining and Safety has identified six old or abandoned mining sites in the county that impact water quality or likely do: Bueno, Emmett, Evening Star, Fairday, Captain Jack and Golden Age.
Four of the mines — Bueno, Emmett, Evening Star and Fairday — likely impact water quality, but currently have no active water treatment programs, records show.
Hartman said the six mines are designated as “legacy mines” because they were mined prior to modern mining reclamation laws that came into effect in the 1970s.
The Captain Jack Mill is designated as a Superfund site because of multiple contaminants, including lead, arsenic and thallium, along with several other heavy metals, according to the EPA.
Mary Boardman, a project manager with the Colorado Department of Public Health and Environment, said the Captain Jack Mill Superfund Site was added to the national priorities list in 2003 and a decision was made to begin clean-up in 2008. That project remains ongoing.
Hartman said the Golden Age Mine is still in the investigative stage, so officials can determine the best approach to managing it.
Boulder County has several waterways deemed “mine related impaired streams” and one state-run “nonpoint source mine reclamation project” that includes removing mine tailings, waste piles and restoring streams, according to the Colorado Division of Reclamation, Mining and Safety.
Hartman said “mining impacted” means the streams have been degraded by acidity or metals from a combination of mining sources and natural background geological sources in such a way that they fall below Clean Water Act Standards.
He said it’s difficult to determine how many old or abandoned mines are in Boulder County, but nearly 1,200 safety closures have been conducted in the last 25 years, and the owner of Swathmore Mine has asked that one be installed by the Colorado Division of Reclamation, Mining and Safety.
“Those are grates and other measures to prevent people and animals from entering (or) falling into old mines,” Hartman said.