Why do some passive treatment systems fail while others work?

This technical paper by James J. Gusek, P.E. explains the design and technological factors affecting the successful implimentation of passive treatment systems such as those planned for use in the Elizabeth Mine Site.

Cleanup Options Under Consideration in EE/CA

All Options

• Divert surface water around TP1
• Capture flow from TP3 and treat with passive systems (constructed wetlands or other natural passive systems)
• Collect flow from base of TP1 (seeps) and treat with passive systems (constructed wetlands or other natural passive systems)

Option 2B

Multi-barrier cap with consolidation of TP2 on to TP1 and grading the slope of TP 1 to be less steep. TP3 is preserved in place.

• Remove TP2 and place on TP1
• Reduce slope of TP1
• Place multi-barrier cap (plastic with clay blanket) over entire TP1, including slope areas. Cap would include topsoil, common fill, plastic drain layer, geomembrane barrier, clay blanket barrier. Soil thickness is assumed to be 30 inches.

Option 2C

Multi-barrier cap w/ retaining wall to preserve slope profile. TP3 is preserved in place.

• Build a retaining wall to retain slopes and profiles of TP1 and TP2.
• Same cap as in 2B

Option 3B

Evapo-transpiration soil cover with reinforced wall to preserve slope profile. TP3 is preserved in place.

• Build a retaining wall to retain slopes and profiles of TP1 and TP2.
• Place soil cover of sufficient thickness to retain water for use by plants, trees, etc. to minimize infiltration into tailings. Soil thickness is assumed to be at least 42 inches.

Option 3C

Minimal soil cover to stabilize surface with vegetation and reinforced wall to preserve slope profile. TP3 is preserved in place.

• Build a retaining wall to retain slopes and profiles of TP1 and TP2.
• Place soil cover of 6 - 12 inches to establish vegetative growth on surface of tailings.

Option 3D

Soil cover with hardpan barrier and retaining wall to preserve slope profile. TP3 is preserved in place.

• Build a retaining wall to retain slopes and profiles of TP1 and TP2.
• Place soil cover of sufficient thickness to support vegetative growth over a hardpan layer. Add lime/limestone to tailings to create a hardpan layer as a barrier to infiltration. A plastic drainage layer (geonet) may be needed to prevent ponding of water on hardpan. 18 inches of soil would be placed over the hardpan.

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