Surface Remediation Overview and Key Concerns Surface Remediation - PowerPoint PPT Presentation

Surface Remediation Overview and Key Concerns

Surface Remediation • Primary components – Baker Creek – Tailings and sludge ponds – Pits – Contaminated soil – Buildings and roadways – Others

Site Overview

Site Overview

Site Overview

Site Overview

Site Boundary

Baker Creek

Baker Creek

Baker Creek • Baker Creek flows through the site – Enters above Baker Pond and exits into Back Bay

Baker Creek • Both “natural” and “constructed” reaches

Baker Creek

Baker Creek

Baker Creek • Reach 4 flowed over arsenic stopes – Relocated and stabilized in 2006 4

Baker Creek • Problem sections of Baker Creek in flood – Narrow diversions above C1 pit and A2 pit 3 1 4

Baker Creek • High value habitat – Reach 4 – Grayling spawning – Reach 6 – Temperature and nutrients 3 1 4 6

Baker Creek • Other fish habitat and uses – Every reach is now known to support some fish uses 3 2 1 4 5 6

Baker Creek • Arsenic in sediments – Reach 2, 5, 6 – But other reaches also have areas of contaminated sediments 3 2 1 4 5 6

Baker Creek • Water quality – Arsenic in Baker Creek comes from water treatment plant – And from upstream 220 kg/yr 3 2 1 4 5 6 300 kg/yr

Baker Creek • Key Concerns – Physically impacted in mine area – Water quality – Sediment quality – Concerns for fish, muskrat and humans? – Disturbance from sediment remediation?

Tailings • South, Central & North Ponds • Northwest Pond

Tailings • Foreshore tailings • Offshore tailings

Tailings • North, Central & South Ponds – 7M tonnes tailings covering 51 ha – Sludge ponds

Tailings

Tailings

Tailings • Seven dams around Original Impoundments • Up to 20 m high • Inspected annually by geotechnical engineer

Tailings • Northwest Pond – 6.5M tonnes tailings covering 44 ha

Tailings

Tailings

Tailings • Six dams around Northwest Pond • 15-20 m high • Well engineered and constructed • Inspected annually by geotechnical engineer

Tailings • Tailings are fine silty powder • About 2,000-4,000 mg/kg arsenic

Tailings

Sludge Ponds • Settling pond and polishing pond – Water treatment residuals

Tailings & Sludge Ponds • Key concerns – Dust – Surface exposure of arsenic – Lack of vegetation – Seepage

Pits • Five major pits • A2, A1, C1, B2, B1

Pits

Pits • Five large pits and three small pits – Table of pits and volumes Existing Void Pit Volume 1 (m 3 ) Pit Plan Area (m 2 ) A1 757,000 48,000 A2 479,000 32,000 C1 372,000 31,000 B1 331,000 22,000 B2 203,000 20,000 B3 56,000 9,000 B4 10,000 4,000 Brock 10,000 2,000 TOTALS 2,218,000 158,000 1 Volume to spill point elevation

Pits • Key concerns – Safety • Steep pit walls are a potential hazard to people • Long-term stability of stopes directly below pits • Openings to surface – If Baker Creek channel issues not addressed • Flooding could allow water into pits and underground

Contaminated Soils

Contaminated Soils • Key concerns – Land use vs soil contamination levels – Soil quality • Human risk – Inhalation / ingestion – Arsenic uptake by vegetation • Wildlife – Disturbance related to soil remediation?

Buildings • Buildings – In general all buildings on the site will be cleaned and demolished – Five areas with different “issues”

Buildings • Townsite Area – City interested in four Townsite homes

Buildings • Townsite and A-Shaft – NWT Mine Heritage Society interested in Community Hall – A-Shaft is a safety hazard

Buildings • Mill Area – Significant arsenic and asbestos contamination – Requires careful sequence of hazardous material removal, demolition and disposal

Buildings

Buildings • Tailings Retreatment, Effluent Treatment, and Akaitcho Shaft – Some short-term uses – Then demolition and removal

Buildings • Key concerns – Many remaining buildings contain hazardous materials which could pose risks to workers and environment during demolition if not controlled – Decontamination will generate hazardous wastes requiring safe disposal (either on-site or special facility off-site) – Demolition will generate a large volume of non- hazardous waste requiring on-site disposal

Roadways

Roadways • Key concerns – Some road sections contaminated • Mine waste rock containing arsenic – Some roadways impede site drainage • Local flooding problems – Many roadways not required for future uses • Occupied land can be rehabilitated

Other • Remediation will create other surface components

Other • Arsenic trioxide management areas

Other • Water management system

Other • Soil borrow sources

Other • Landfill ???

Questions?