EPA Superfund Site

COLORADO SMELTER

CO | EPA ID CON000802700

About this site’s exposure pathways: As of September 2025, the Colorado Smelter Superfund Site is considered “Current Human Exposure Not Under Control” (HENC). Separate Remedial Investigations/Feasibility Studies (RI/FS) for both Operable Unit 1 (OU1) (Community Properties) and Operable Unit 2 (OU2) (Former Smelter Area) began in 2014. A plan proposing an early interim action was issued for the residential properties' indoor dust and soil cleanups in OU1 in July 2017 due to exposures to lead- and arsenic- contaminated soil and indoor dust. EPA signed the Interim Record of Decision (i-ROD) in September 2017 and residential soil and indoor dust sampling and cleanups are complete, but institutional controls are not in place.
The soil exposure and indoor dust-inhalation/exposure pathways are considered unacceptable based on EPAs Site-specific i-ROD cleanup criteria not having been met for all the OU1 properties. Site-specific i-ROD cleanup criteria are Lead: 350 ppm soil, 275 ppm indoor dust; Arsenic: 61 ppm soil and indoor dust. In January 2024, EPA released an Updated Soil Lead Guidance lowering the screening level for lead to 200ppm. EPA is currently evaluating how this change may impact the cleanup that was conducted or is planned within the Site boundary. EPA currently anticipates that human exposure will be under control by 2034 for this OU because we anticipate having our cleanup complete and Institutional Controls in place.
The OU2 RI/FS is ongoing. "Caution" and "No Trespassing" signs were placed around the former smelter area in 2015. Despite the signage, there are several unhoused people continually living on OU2 and an active railroad prohibits fully limiting access to OU2 slag areas. All OU2 media, pathways, and contaminants of concern have not been fully characterized; however, one year of quarterly air monitoring (March 2018 to March 2019) showed that smelter area contaminants are not being entrained into adjacent neighborhoods. In 2019, quarterly surface water sampling with collocated sediment and pore water samples were collected and Bipartisan Infrastructure Law/Infrastructure Investment and Jobs Act (BIL/IIJA) funding received in 2022 allowed OU2 RI Work Plan updates and RI/FS tasks, including groundwater investigation. Groundwater investigations are expected to be completed in 2026.