RICHARDSON FLAT TAILINGS
PARK CITY, UT
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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.
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.
EPA’s Involvement at the Site
EPA originally proposed to add the Richardson Flat Tailings site to the National Priorities List in 1988, but decided not to pursue final listing on the NPL. In 2005, the site owner, United Park City Mines, agreed to complete remedial actions, with EPA oversight, at the Richardson Flat tailings impoundment (OU1). UPCM and EPA agreed to address the site as an “NPL equivalent” site, using the same process for investigation and cleanup required for an NPL site.
Cleanup activities at OU1 were led by UPCM, in cooperation with the Upper Silver Creek Watershed Group (UPCWSG), with oversight from EPA. The UPCWSG is composed of federal, state and local agencies, local elected officials, and community representatives who have been working together since 1999 to address environmental contamination in the watershed left behind from historical mining activities.
The site’s long-term remedy includes excavation of contaminated sediment and tailings; placement of the excavated materials in an on-site impoundment; cover of diversion ditch sediment with clean gravel; embankment fortification; wetland restoration; institutional controls; and surface water monitoring. Remedy construction began in 2008 and has been completed.