BLM Hillside Mine Site

Tailings Consolidation and Groundwater Protection

Department of the Interior – Office of Environmental Policy and Compliance

July 28, 2022

Site

The Hillside Mine Site is in the Eureka Mining District, five miles north of Baghdad, Arizona.

The area of the abandoned mine is partially located on public land. The site is managed by the Department of the Interior’s (DOI) Bureau of Land Management (BLM). The Hillside Mine area consists of the Hillside Mine, the Mill Site, and three distinct tailings piles - designated as the Upper, Middle, and Lower Tailings Piles.

The project site consists of the Mill Site and the Upper Tailings Pile. The two sections of the Upper Tailings Pile were subsequently referred to as the "East and "West" Tailings Piles.

Background

Dilapidated structures and debris from the mill site

Silver and gold, and limited amounts of lead and zinc, were mined at Hillside Mine from 1887 to 1951. In 1946 and 1947, the mine was rehabilitated and a mill was added. In 1951, the mine was shut down, but the mill was expanded and custom milling activities continued until around 1954.

Contamination

A 1999 environmental characterization found arsenic and lead in the tailings piles and in sediment and water samples in Boulder Creek downstream of the Upper Tailings Pile.

Contamination was found to exceed the Arizona non-residential Soil Remediation Levels and Arizona Surface Water Quality Standards.

Remediation

The remediation began with access road improvements in September 2014, followed by the consolidation of the West Tailings Pile and tailings from the mill site into the East Tailings Pile. The East Tailings Pile was consolidated to reduce its square footage.

The consolidated East Tailings Pile was lined with a geomembrane and capped with a geotextile liner, which was subsequently covered in a protective soil cover and graded.

BLM used funds from DOI’s Central Hazardous Materials Fund (CHF) to assist in the environmental cleanup activities. CHF funds are Congressionally appropriated funds, provided to the Department of the Interior and managed by the Office of Environmental Policy and Compliance (OEPC), for the cleanup of environmental contamination on public lands pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). 

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Remediation Slideshow

The West Tailings Pile (shown) was excavated and hauled to the East Tailings Pile.

Structures and debris at the Mill Site were excavated and removed, and tailings from around the mill were added to the East Tailings Pile.

The north slope of the East Tailings Pile was consolidated southward.

The consolidated tailings pile was sub-graded before a liner was put in place.

A 40-millimeter geomembrane provides the bottom layer of the liner, followed by a geotextile layer and protective soil cover.

Geotextile- and riprap-lined control ditches keep surface water away from the tailings pile.

All components of the remedy -- consolidation, earth shaping, liner, soil cover, control ditches, protective boulders, and final grading -- were completed by February 2015, five months after construction began.

Impacts

Boulder Creek is no longer suffering from arsenic and lead contamination from the site, and public lands around the mine have been restored for public access. The site is currently monitored and maintained by the Bureau of Land Management and is available for public use.