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  2. Colorado Smelter
  3. Site Progress

Cleanup Schedule by Operable Unit

During cleanup, a site can be divided into a number of distinct areas depending on its complexity. These areas, called operable units (OUs), may address geographic areas, specific problems, or areas where a specific action is required. Examples of typical operable units include construction of a groundwater pump and treatment system or construction of a cap over a landfill.

MilestoneStart DateCompletion Date
OU 00 - SITEWIDE
Five-Year Review (EPA Performed) 01/23/2023
OU 01 - OU 01 - COMMUNITY PROPERTIES
Removal (EPA Performed)06/20/201608/08/2017
Combined Remedial Investigation/Feasibility Study (EPA Performed)07/29/2014Estimated Dec 2027 - Feb 2028
Record of Decision (EPA Performed) 09/25/2017
Explanation of Significant Differences (EPA Performed) 04/25/2024
Explanation of Significant Differences Estimated Aug - Oct 2026
Remedial Design (EPA Performed)08/09/2017Estimated Jun - Aug 2027
Remedial DesignEstimated Dec 2027-Feb 2028Estimated Jun -Aug 2028
Remedial Action (EPA Performed)09/29/2017 
Remedial ActionEstimated Dec 2027  -Feb 2028 
OU 02 - OU 02 - FORMER SMELTER AREA
Administrative Order of Consent (EPA Performed) 09/29/2022
Removal (EPA Performed)01/07/201601/07/2016
Removal (EPA Performed)12/11/201712/19/2017
RemovalEstimated Sept - Nov 2026Estimated Dec 2026 - Feb 2027
Remedial Investigation (EPA Oversight)09/29/202205/09/2024
Combined Remedial Investigation/Feasibility Study (EPA Performed)07/29/2014Estimated Mar - May 2028
Record of Decision Estimated Mar - May 2028
Remedial DesignEstimated Mar - May 2028 

Showing 1 to 15 of 15 entries

NOTE: Dates and estimated dates will not display for all milestones. Estimated dates only display for milestones planned within the next three fiscal years. Estimated dates and start dates will not display for the following enforcement milestones: Administrative Order of Consent, Consent Decree and Unilateral Administrative Order. Start dates will not display for the following document milestones: Five-Year Review, Record of Decision, Record of Decision Amendment, Explanation of Significant Differences and Partial NPL Deletion.

DISCLAIMER: The data on this page are derived from the Superfund Enterprise Management System and are solely for informational purposes. The data cannot be relied upon to create any substantive or procedural rights or requirements enforceable by any party in litigation with any member of the public, states, tribes, the United States or any federal agency. EPA reserves the right to change these data at any time without public notice.

Colorado Smelter

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Contact Us About the Colorado Smelter
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Last updated on February 10, 2026
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