Paul Eger Minnesota Department of Natural Resources Division of Lands and Minerals September 2010

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Paul Eger Minnesota Department of Natural Resources Division of Lands and Minerals September 2010

What are constructed treatment wetlands? Why would you use them? Questions to ask Data needs Types of wetlands Mine drainage Performance Example Dunka Mine

Man made Built to remove contaminants Wide variety of removal processes Generally not designed to recreate natural wetlands Used to treat mine water in US for several decades

Lower cost, lower maintenance alternative to standard chemical treatment

Active Requires ongoing human operations, and maintenance Based on external sources of energy using infrastructure and engineered systems Passive Processes do not require regular human intervention Employs natural construction material, natural materials and promotes natural vegetation Gravity flow Global Acid Rock Drainage (GARD) Guide, 2009

A perfect passive system would operate indefinitely with no maintenance

Is a wetland appropriate? Is this the right design? Is the wetland big enough to handle changes over time? How long will it treat? Substrate disposal? Consistent compliance? Any ecological impacts?

Fundamental mechanisms of wetlands function Characteristics of the water being treated Chemistry Flow Site characteristics (Climate and Topography) Removal rates Regulatory Limits

Abiotic Settling & sedimentation Sorption Chemical Oxidation & Reductionprecipitation Photo oxidation Volatilization Biotic Aerobic or anaerobic Biodegradation/ Biotransformation Phytoaccumulation Phytostabilization Rhizodegradation Phytodegradation Phytovolatilization

Surface Flow (SF) Subsurface Flow (SSF)

Surface Flow Wetland Water flows above the substrate Contaminants predominantly removed by aerobic processes Inflow Control Structure Wetland Plants Effluent Collection System Outflow Control Structure Flow 2-12 Influent Distribution System Organic Substrate Liner To Pond or Receiving System

Subsurface Flow Wetland Water flows surface through substrate Horizontal Vertical Influent Inflow Control Structures Planting Substrate Water Level Outflow Control Structures Influent Distribution System Treatment Media (gravel, sand, soil) Hydraulic Gradient Liner Effluent Collection System To Receiving System

Water contacts rock containing reactive minerals Primarily iron sulfides Impacts in US ~ 12,000 miles rivers/streams ~ 180,000 acres of lakes Mine waste stockpiles

Net Acid: Acidity> Alkalinity Generally ph < 6 Subsurface wetland Net Alkaline: Acidity< Alkalinity ph > 6 Surface or Subsurface wetland

Parameter Coal Mine Drainage Metal Mine Drainage Net Acid Net Alkaline Net Acid Net Alkaline ph 3-4 6.5-7.5 3-4 6.5-7.5 Acidity 100 10,000 0 100-10,000 0 Sulfate 1,000 10,000 100 3,000 1,000-10,000 100-3000 Iron 100 1,000 < 10 100 100-1,000 <10 Aluminum 10 1,000 < 1 1-100 < 1 Manganese 5-100 < 5 2 25 < 2 Copper ND 1 ND 1-100 0.1 1 Zinc ND 5 ND 10-1,000 1-10 Cadmium ND ND 0.05-1 0.01-0.1 Lead ND ND 0.5-10 0.01-0.1 Except for ph all concentrations are in mg/l ITRC Technical and Regulatory Guidance Document for Constructed Treatment Wetlands

Parameter Coal Mine Drainage Metal Mine Drainage Typical removal efficiencies ph >6 >6 Acidity 75-90% 75-90% Sulfate 10-30% 10-30% Iron 80-90+% 80-90+% Aluminum 90+% 90+% Copper NM 80-90+% Zinc NM 75-90+% Cadmium NM 75-90+% Lead NM 80-90+% Typical removal efficiencies

Dunka Mine

Waste rock stockpiles

Virginia Formation Mineralized Zone Dunka Pit Duluth Complex Giants Range Granite

Duluth Complex, Copper-Nickel Deposit Fresh sulfides Oxidized sulfides

5 major seeps Flow Average 20 850 L/min ph Generally >7 One site ph ~ 5 Trace metal concentrations, mg/l Nickel, ~ 1-10 Copper ~ 0.01 1 Cobalt ~ 0.01-0.1 Zinc ~0.01-2

Cap stockpiles Limit infiltration Treat residual drainage with wetlands

-W2D/3D -W1D -Seep 1 -Seep X - Em 8

Site ph Nickel input Nickel output % removal W2D/3D 1 7.0 1.9 0.036 >90 W1D 7.3 0.76 0.10 87 Seep 1 7.3 6.6 3.3 50 Seep X 7.4 1.8 1.1 40 Em8 7.4 2.1 1.4 33 Average concentrations for 1999-2004, Nickel in mg/l 1 Estimated

Metals bound to peat Over 99% in solid phase Tightly bound ~1 2% water extractable

Site needed initial 1 as built Final treatment area Needed after closure 1 % final removal W2D/3D 5000 4200 6200 3000 >90 W1D 23000 7000 17000 1200 87 Seep 1 4100 2500 50 Seep X 5000 10000 40 Em8 32200 16000 33 Area in square meters 1 Calculated based on areal removal rate 40 mg Ni/m 2 / day Undersized relative to design value

Nickel Concentration Nickel versus time W1D 10 1 0.1 0.01 wetland outflow inflow Design Value 0.001 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Date

Assumptions Model based on nickel accumulation in substrate Removal capacity = 10,000 mg Ni /kg substrate Mass of Active Substrate Total treatment area Density of substrate Removal depth = 20 cm Input of new removal sites

Lifetime > 100 years