Technology Review

Liners

At a Mine in Arizona, From Field Lining Systems

 

 

 

 

 

Jack A Caldwell

August 2006


Table of Contents

 

Introduction.. 3

General Sources of Information.. 4

Mining Related.. 4

Landfill Related.. 4

Heap Leach Piles. 6

Uranium Mill Tailings Impoundment Liners. 6

Waste Rock Dumps. 7

Tailings Impoundments. 7

 

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Engineered Linings (South Africa)

 


Introduction

Liners may be used at mines beneath tailings impoundments, heap leach pads, water reservoirs, rock piles, or wherever the mine needs to limit seepage to the ground and hence protect groundwater quality. 

There are as many types of liners as there are potential uses of liners at a mine.  For the purposes of this review we identify these basic liner types:

·       Geologic Liners such as natural geologic strata in the form of soil or rock of low permeability.

·       Clay Liners which may be natural in-place clay or imported and compacted clay. 

·       Synthetic Liners such as geomembranes, gunnite, asphalitic concrete, concrete, or any other of the many products being manufactured and distributed by the gemembrane manufacturing industry.

I have never been persuaded that the tailings or any other low permeability waste constitutes a liner in and of itself per se. so I do not address that concept, although is used to be popular in the tailings industry.


General Sources of Information

Mining Related

The U.S. Environmental Protection Agency’s (EPA) 1997 report “The Feasibility of Lining Tailings Impoundments” summarizes a series of reports that evaluate the design and installation of tailings impoundments at hard rock mines.  The EPA report concludes that the size of land-based mining units, the character of mining wastes, and technical factors do not necessarily preclude the use of liners or leachate collection systems.

Closure activities at the Kennecott Utah Copper Mine include use of liners in the closure of mine waste disposal facilities'

The Nevada state regulations for mine closure include requirements to use liners in specified instances.

An interesting case study of mine closure that included the construction of a lined waste disposal facility where mine closure wastes were consolidated is described at this site.

The Oregon Department of Environmental Quality requires that new heap leach pads and mine pits that contain water at closure should be lined.

PVC may be used in liners for heap leach pads. 

Landfill Related

In the U.S. it is required by law that new landfills be lined.  As a result, websites and publications from the landfill industry contain considerable information of interest to the mine and miner charged with selecting and installing a liner beneath a mine facility. 

First stop should be the Geosynthetic Institute where you will find all the information you are likely to need on liners in landfills.

Here are some sites where the liner requirements are set out by state agencies and others:

·       Oregon

·       New Mexico

·       Massachusetts

·       US Army

·       Guam

 

The manufacturers all have web sites; some looked at in preparing this report are

·       Bentofix

·       Cetco

·       Colorado Lining

·       Tensar

·       XR-5

·       Secugrid

Never forget that liners leak.  As contrary a view as any is to be found at any one of these sites, none of which appear to have formal names:  http://www.stopwmx.org/liner.html. http://www.nwqmc.org/98proceedings/Papers/61-lee.htm http://www.frtr.gov/matrix2/health_safety/chapter_2.html.

Heap Leach Piles

Liners are required beneath heap leach piles in order to preclude loss of leachate that must be directed to outlet points for collection and ore extraction. 

Uranium Mill Tailings Impoundment Liners

This topic is easily dealt with. Generally liners should not be installed beneath uranium mill tailings impoundments.  The reason is that the long design life requirements put the focus of seepage control on the site that is selected and the final closure cover.  If you need to line the area of the new tailings impoundment, you probably have the wrong site; start your selection process again and find one characterized by naturally low permeability materials that will preclude impact to the groundwater by the inevitable seepage from the pile. 

At closure put a proper cover over the pile, for any water that gets in will come out at the toe or seep into the groundwater and nobody wants to deal with that forever.  The idea is that once water has infiltrated the pile, it will get out.  You cannot rely on somebody to collect the leachate 1,000 years hence and treat it before discharge.  So the cover must be able to limit infiltration to the point where the resultant seepage from the base of the pile into the ground will not impact groundwater quality either because of the limited quantity of seepage or because of geochemical attenuation by the pile’s foundation soil and rock strata. 

I know some uranium mill tailings piles do have liners and some that should have had liners do not.  But that is the past, and I cater here only for those who may have to select a new liner for a new facility. 

Waste Rock Dumps

I am not aware of any waste rock dumps where liners have been installed.  Any such liner would have to be able to withstand the impact of waste dumping and the large size of the rock that could tear the liner. 

It is conceivable that the need to control acid seepage would make a liner an attractive option at a rock dump.  Any such facility would have to be designed to deal with the long-term seepage that would then appear at the outlet from the dump and which would have to be treated indefinitely.

As with uranium mill tailings impoundments, my belief is that if you need to line your waste rock dump you have the wrong site. 

Tailings Impoundments

Tailings impoundments are another class of mine waste disposal facilities that should not, in my opinion, be lined.  Whatever may be said of the longevity of geosynthetics, they will not last long by comparison with the length of time the tailings will be a new geomorphic form.  If seepage from the impoundment is going to impact the groundwater, find a better site. 

I recognize the benefits of lining an impoundment in environments where water is scarce and the reason the liner is installed in water collection and recirculation. 

This opinion is likely to be unpopular and I can already hear my friend and critics alike.  So be it---send me your views on the matter and as long as they are objective and to the point I will put them here. 

Other Mining Applications

I am not much good at thought experiments, but I tried this one.  What other applications are there on mines for liners that are not currently tapped? 

I got a partial answer at the site of Western Environmental Liner.  Having lived two happy years in Tucson, I cannot resist a site with pictures of cacti and the South West.  So here is a picture from their site. 

I also copy some of their text, for it goes someway to answering my questions: 

Western Environmental Liner Co. has  specialized materials that are blended for the containment of oil and oil based liquids, sludge, salt water, waste water and contaminated soil containment.  For temporary containments, Standard  or Oil Resistant PVC's may meet your needs.  For long-term containment, or containment situations that require high puncture resistance, durability and extreme UV resistance, XR-5® may be the liner of choice.