By Jack Caldwell - Mining Engineer - Robertson GeoConsultants

Today, July 11 is the deadline for submission of papers to the Tailings and Mine Waste 2011 conference. In preparation of one of my papers, I read through the proceedings of the 1994 conference. I am amazed at how bold the folk were in those days, how little theyknew by comparison with today, and yet how much we owe them for efforts over the years. Here are some of my notes on reading the 1994 conference proceedings.

By 1988 the uranium market had declined, mills had closed, and support for a symposium on uranium mill tailings had declined. In 1994, Colorado State University, the sponsor of the uranium mill tailings conferences resuscitated the conference series as Tailings and Mine Waste, the title by which the series goes today. As the organizers noted: “It is hoped that this conference will serve the same function for the general mining industry that the previous symposia served for the uranium mining industry.”

The four keynote lectures capture the change in the years since 1978. J.A. Marjerison in Construction activities in flood plain tailingswrites of Superfund or CERCLA-driven cleanup of old mine workings. Superfund was by now a reality and other papers in this conference predict dire consequences to the mining industry from Superfund. In reality the consequences have not been as dire as the nay-sayers predicted. In fact it may be postulated that threat of Superfund and other new regulations from that time drove the changes we implement today of responsible mining.

Charles D. Shackelford in Hydrogeotechnics of clay liners for waste disposal concludes what we all know today:

  • A low hydraulic conductivity measured on a laboratory compacted clay specimen is a necessary , but not sufficient condition to ensure a low hydraulic conductivity for a filed compacted liner.
  • A low hydraulic conductivity for a field compacted clay liner is a necessary but not sufficient condition to ensure containment of contaminants.

Thus started the long march of double liners, seep detection systems, and the complexities of modern tailings impoundment liners.

James M. Link in Tailings transport and deposition writes briefly of selection of pipes for tailings transport. If this was truly the state-of-practice in 1994 we have come a long way.

Finally David A. Bird et al in An assessment of hydrogeochemical computer codes applied to modeling post-mining pit water geochemistry tell of using MINTEQA2, PHREEQE, WATEQ4F, and BALANCE to do what is still hard to do: predict the post-closure water quality in a pit filling with water. The codes have advanced, changed, died, and new ones come into being, but the issues are still germane and essentially unsolved.

Also in the 1994 conference are papers by three people I know, admire, and who are still active in tailings. They are Rick Frechette, Don Poulter, and Mine Gowan. Rick writes of the initial work on covering the Cannon Mine Tailings Impoundment in Wenatchee. I designed and was on site during construction of this impoundment. My colleagues at SRK took over when I left. It is to Rick’s immense credit that he had the courage, when faced with construction of a closure cover, he had the courage and engineering guts to try placement of a geofabricout over the top of the soft tailings and to construct a soil ramp atop this geofabric. He finally succeeded and today we owe him acknowledgement for being amongst the first to do this – or at least write about it. For today with FLAC and advanced geosynthetics, we know how difficult this is to do. Recall what we did at the Suncor Pond 5 impoundment as described in papers in this series in the past three years.

John Hughes in 1994 was still introducing and selling the idea of CPT testing in tailings. Today this is routine. We can only admire his paper with Bryan Ulrich STP/CPT correlation for mine tailings and admire their pioneering work that we take so much for granted today.