The EPA chose 26 mining sites for interim work to reduce human and environmental risks while a long-term solution is studied.
A task force is expected to wrap up recommendations soon. Denver City Council will begin weighing the proposal by the end of June.
Tests of a well at Sugar Loaf Fire Station 1 found levels 10 times above the EPA's health advisory levels.
In Colorado, the Arkansas benefits from an injection of water from the Fryingpan River on the other side of the Sawatch Range.
Projections show there's a chance that Lake Mead will fall low enough in 2020 to trigger cutbacks under agreements governing the system.
The Colorado River is expected to only carry 43 percent of the average amount of water into Lake Powell this year.
The normal staid diplomacy of Colorado River managers was upended in a spat between Denver Water and the Central Arizona Project.
The allegation was made by Sunnyside Gold Corp., which is fighting the EPA over who should pay for a potentially costly groundwater study.