Superfund Information Systems: Site Profile

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The Richardson Flat Tailings site is located near Park City, Utah. The site is comprised of multiple Operable Units, or areas, including a tailings impoundment that holds about seven million tons of tailings (Richardson Flat tailings impoundment – OU1), an approximately six-mile-long reach of Silver Creek with an unknown amount of upland, riparian and instream tailings deposits, and draining water from a second tailings impoundment (Prospector Square tailings impoundment). EPA proposed the site for listing on the Superfund Program’s National Priorities List (NPL) in 1988, but ultimately decided not to pursue final listing on the NPL. EPA and two potentially responsible parties (PRPs) are currently evaluating the Silver Creek tailings deposits and the water draining from the second tailings impoundment. For these portions of the site, EPA and the PRPs are currently collecting environmental data to understand the nature and extent of contamination and to inform remedy selection.

The Richardson Flat tailings impoundment (OU1) consists of a tailings dam and an impoundment area. Historic aerial photos show that a tailings pile existed as early as 1953. The most recent tailings disposal in the area took place from 1975 to 1981, when United Park City Mines (UPMC) leased its mining operations to Noranda Mining and Park City Ventures. The location of the tailings impoundment is owned by UPCM. In 1989, EPA and State of Utah officials observed mine tailings at the site sinking into an on-site diversion ditch and Silver Creek. During the 1990s, UPCM did some voluntary work at the site, including covering most of the tailings pile with clean, low-permeability soil and reseeding the site. The diversion ditch was also improved.

Remedy construction at OU1 was completed by UPCM, with EPA oversight, included consolidating tailings material within the main impoundment, installing a wedge buttress to support the main embankment, and removal of sediments within the wetland area. All of these actions are complete. The Richardson Flat tailings impoundment is to be capped after remedial actions are completed at other portions of the site, which may affect the tailings impoundment.

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What Is the Current Site Status?

The Richardson Flat tailings impoundment remedy addresses mine tailings in several areas of the site and sediments and surface water within the site boundary. Cleanup activities at OU1 include excavation, containment, future disposal of mine tailings from the Park City area within the tailings impoundment, placement of restrictions on future land and groundwater use, and surface water monitoring. Since waste remains on site, EPA will continue to conduct five-year reviews to make sure the remedy remains protective of human health and the environment.

The second five-year review, completed in 2018, found the remedy at OU1 currently protects human health and the environment because tailings and sediments have been excavated, tailings are contained through capping with clean soil, and surface waters exiting the site are below water quality standards. However, for the remedy to be protective in the long term, the following action needs to be taken: implement institutional controls that include restrictions on future land and groundwater use. Additionally, it was noted that a final operations and maintenance plan has not been prepared.

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