Installation Date:
08/01/1995

Contaminants:
Nickel, Iron, Sulfate

Reactive Media:
Organic Carbon

Construction:
Cut and Fill

Point of Contact:
David W. Blowes
University of Waterloo
Tel: 519-888-4878
Fax: 519-746-5644
Waterloo Centre for Groundwater Research
Waterloo , Ontario Canada

A full-scale continuous permeable reactive barrier (PRB) was installed in August 1995 downgradient from an inactive mine tailings impoundment at the Nickel Rim Mine site in Sudbury, Ontario, Canada. Nickel Rim was an active mine from 1953 to 1958. Primary metals extracted were copper (Cu) and nickel (Ni). Tailings have been undergoing oxidation for approximately 40 years. The ground-water plume emanating from the tailings is discharging to a nearby lake. The primary contaminants on site are nickel (Ni), iron (Fe), and sulfate. Initial concentrations were 2400-3800 mg/L sulfate, 740-1000 mg/L Fe, and up to 10 mg/L Ni.

The contaminated aquifer is 10-26 ft thick and composed of glacio-fluvial sand. The aquifer is confined to a narrow valley, bounded on both sides and below by bedrock. Ground-water velocity within the aquifer is estimated to be 49 ft/yr.

The PRB was installed across the valley using a cut-and-fill technique. The barrier spans the valley and is 50 ft long, 14 ft deep, and 12 ft wide. It is composed of a reactive mixture containing municipal compost, leaf compost, and wood chips. Pea gravel was added to the mixture to increase hydraulic conductivity. Coarse sand buffer zones were installed on both the upgradient and downgradient sides of the reactive material. A 12-in clay cap was placed on top of the PRB to minimize entry of surface water and oxygen into the PRB. Remediation at the Nickel Rim Mine Site was accomplished by sulfate reduction and metal sulfide precipitation resulting from the presence of the organic material.

The cost was approximately $30,000. This includes design, construction, materials, and the reactive mixture.

Monitoring wells were installed along a transect parallel to ground-water flow. Samples were collected one month after installation and again nine months after installation. Passing through the PRB resulted in a decrease in sulfate concentrations to 110-1900 mg/L. Iron concentrations decreased to <1-91 mg/L. Dissolved nickel decreased to <0.1 mg/L within and downgradient of the PRB. In addition, pH increased from 5.8-7.0 across the barrier. As a whole, the PRB converted the aquifer from acid-producing to acid-consuming. Monitoring is planned to continue for a minimum of three years with sampling occurring biannually.

SITE-SPECIFIC REFERENCES