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Observational Method 

 
Author: Jack Caldwell

Summary

This review discusses the observational method and its application in mining, specifically acid mine drainage. The Cannon Mine tailings impoundment is also discussed.

INTRODUCTION

The Observational Method was first applied by those masters who built cathedrals in the Middle Ages. They did not call the principal by that name, but I suspect they consciously applied it. The first formal enunciation of the method was in the 1940s in the context of soil mechanics; and it has been applied fitfully in geotechnical engineering since. Mining engineers always have and continue even today to apply the method-but mostly unconsciously I suspect.

In this review, I go well beyond the material on the Observational Method that you will find via Google or even in expensive books. I basically stick my neck out, in an attempt to explore possibilities as yet, to my knowledge, unexplored.

I do this because recently I have heard a lot of people talk about the method; but most do not even know what it means, let alone know how to apply it in the situations to which they propose it be applied. For example, last week an old professor satiated with expensive wine and fancy food proclaimed: "I think we must manage mine acid rock drainage using the Observational Method." Profound, but vague.

Maybe we can go some way to clearing up this vague pomposity. Help me with your comments, so that I may keep adding to and improving this review.


THE OBSERVATIONAL METHOD DEFINED

PECK'S FORMULATION

The classic paper that describes the Observational Method is by the late Ralph B. Peck. It is called Advantages and limitations of the observational method in applied soil mechanics. The method has never been better explained than by him:

(a) Exploration sufficient to establish at least the general nature, pattern and properties of the deposits, but not necessarily in detail.

(b) Assessment of the most probable conditions and the most unfavorable conceivable deviations from these conditions. In this assessment geology often plays a major role.

(c) Establishment of the design based on a working hypothesis of behavior anticipated under the most favorable conditions.

(d) Selection of quantities to be observed as construction proceeds and calculation of their anticipated values on the basis of the working hypothesis

(e) Calculation of values of the same quantities under the most unfavorable conditions compatible with the available data concerning the subsurface conditions.

(f) Selection in advance of a course of action or modification of design for every foreseeable significant deviation of the observational findings from those predicted on the basis of the working hypothesis.

(g) Measurement of quantities to be observed and evaluation of actual conditions.

(h) Modification of design to suit actual conditions.

A 21ST CENTURY FORMULATION

In 2005, a much more complex statement appeared: The Observational Method in Geotechnics. In this publication by ARUP we are brought right up date with European practice and implementation of the method. They define it thus:

The Observational Method in ground engineering is a continuous, managed, integrated, process of design, construction control, monitoring and review that enables previously defined modifications to be incorporated during or after construction as appropriate. All these aspects have to be demonstrably robust. The objective is to achieve greater overall economy without compromising safety.

I have found nothing about the application of the method in mining. So let us proceed to think about it ab initio.


ACID MINE DRAINAGE APPLICATION

GENERAL

First let us try to explore the old professor's proposal: manage acid rock drainage via the Observational Method. Let us assume that you are planning a new mine and the prudent have identified acid rock drainage as a potential problem. Let us further assume that the old professor's advice prevails: manage the anticipated problem by the Observational Method. The proposal to invoke the Observational Method is supported by the environmental group, the licensing experts, and the community relations people.

MAKE A MODEL

Here is my advice on how to invoke and implement the Observational Method with respect to acid rock drainage-other consultants (there are 17 listed in the InfoMine Consultants database) will no doubt give you other advice more specific to the particulars of your mine.

First you need to define the site's surface water regime and then the site's groundwater regime. Not particularly difficult to do, but at this stage of mining you will be facing head-on Peck's "exploration sufficient to establish at least the general nature, pattern and properties of the deposits, but not necessarily in detail." In the normal course of events and in the absence of invoking the Observational Method it is likely the average groundwater specialist and especially the regulators would have required you to define the precise nature, pattern, and properties of the groundwater. That, afterall, it the altar of belief of the profession.

Next, I recommend that you compile a decent mine water and chemical mass balance model. Again this is not difficult to do at this stage of planning; particularly if you are committed to the Observational Method. In particular, I would recommend more than one water and chemical mass balance: one for the most likely conditions and a few for reasonably anticipatable deviations. Recall the second Observational Method Principle: "Assessment of the most probable conditions and the most unfavorable conceivable deviations from these conditions."

REGULATORY COMPLIANCE

The objective of multiple runs through the water and chemical mass balance model is to identify the concatenation of conditions that may lead to excedance of regulatory limits on discharge water quality. I assume that your mine will be in one of those transparent regulatory places where the only real regulatory requirement is that your discharge does not exceed preset limits. In the United States these are referred to as the NPDES permit requirements.

Of course if there are no reasonably conceivable set of conditions that your water and chemical mass balance model predicts will lead to an exceedance of discharge water quality standards, you are a luck investor. I would proceed post-haste through the environmental impact process and get the mine opened as soon as possible. Conversely, if most of the cases you analyze for predict exceedances of discharge water quality standards, you may have to abandon the mine, radically change the design of the pit and waste disposal facilities, or invoke an independent panel that hopefully will validate the socio-economic benefits of your mine over the impact of perpetual acid drainage.

So that we may proceed, let us assume that you can come up with a suitable pit layout and acceptable designs for the heap leach pad, tailings impoundment, waste rock dump, and other mine facilities that may generate excess quantities of acid drainage. By "suitable" and "acceptable" I mean that for most of the runs of the water and chemical mass balance model you predict compliance with the discharge standards. In the words of the Observational Method Third Principle, let us assume you have: "Established a design based on a working hypothesis of behavior anticipated under the most favorable conditions."

MONITOR

Thus we may proceed to the Observational Method Forth Principle, namely "Selection of quantities to be observed as construction proceeds and calculation of their anticipated values on the basis of the working hypothesis." Now you have to designate what you will measure and where you will measure it. In the context of our example, here are some possibilities: actual rock quality as regards actual acid generating potential; actual rainfall, runoff, and seepage; actual placement locations and layout for the pit and waste disposal facilities; actual affected water quality-surface and below grade. I suspect you will easily identify others. The idea is to select places and things to monitor that are easy to access, easy to measure, and easy to quantify in the model.

As you gather all these data, you will compare them to the values you predicted with your water and chemical mass balance model. Don't forget that as part of implementing the Observational Method you should have long ago run the model for a range of conditions and you should have tabulated the anticipated values of the things you proposed and are actually monitoring. More: you should have already have identified the range of the possible values of the things you are monitoring. This is simply the Observational Method Fifth Principle: "Calculation of values of the same quantities under the most unfavorable conditions compatible with the available data concerning the subsurface conditions."

ALTERNATIVE ACTIONS

The hard part of applying the Observational Method is the Sixth Principle, namely: "Selection in advance of a course of action or modification of design for every foreseeable significant deviation of the observational findings from those predicted on the basis of the working hypothesis."

Nobody ever advanced their career on a mine by telling the boss to change things, to do things in a way that takes more time or costs more. But the advantage of the Observational Method Sixth Principle is that you will have documented the changes well in advance of having to tell the boss to implement them. If you have written your plan well, all you will have to say is: "Now is time to implement Plan 5C. Plans 5A and 5B do not accord with the pre-approved Observational Method approach for achieving regulatory compliance."

All you will need to do is send a brief and courteous note to the regulator telling them that henceforth you are implementing Plan 5C. They will see in the stamped and approved plan that 5C is stamped and approved, and you may not even have to trudge down the hill to meet them.

Let us think for a moment about the things you may include in your modified plans-i.e., the ones you may have to implement if your working hypothesis is proven wrong. The worst is to stop mining and cover it all up with low permeability clay. But we assume things do not get that bad. You may have to increase the amount of rock going to the special encapsulation area, which is that disposal facility where really nasty acid generating materials are to go. You may have to add more lime or flyash to the rock you do place in the waste dump-on the basis of your geochemist's calculations that the increased amount of lime will forever preclude acid drainage.

You may have to improve the surface water management facilities to keep water out of the dump or to get more in to achieve greater dilution. You may have to face the face that you are going to have to triple the size of the acid water treatment system and commit to relocating the dump back into the open pit at close so you can cover it all with a lake into which you perpetually dump fertilizer.

There really is no end to these options. Most will be scary and objectionable to management, investors, and environmentalist alike. I submit, however, that if you have not thought through the possibilities and identified the worst that can happen and come up with a practical plan to deal with the worst that can happen, then you simply have not got the right to claim you are using the Observational Method.

WHAT NOT TO DO

All too often the Observational Method is invoked because of the nice sounding final Principle: "Modification of design to suit actual conditions." All too often this principle is invoked as a substitute for hard work and honesty. All too often it is invoked as a lazy-man's way of saying "I'll come up with something when is see what happens." This is to ignore the earlier principle which I repeat: "Selection in advance of a course of action or modification of design for every foreseeable significant deviation of the observational findings from those predicted on the basis of the working hypothesis."

ASSOCIATED DOCUMENTS

If you are successful in invoking the Observational Method at your mine as a way to deal with acid mine drainage, I bet you will inexorably be drawn into all those other nice-sounding approaches: Failure Mode Analysis; Rick Assessment; Value Engineering; Peer Review, Emergency Response; Design for Closure . Each of these is valid, in its time and place. Each used properly can augment and expand the power of the Observational Method implementation as we have discussed it here.

Be careful, however, for you may get too busy compiling and administering plans and committees to do any meaningful engineering, scientific, or technical work. It is more fun, of course, to go to conferences and attend meetings than to think and write and analyze. But meetings and talking-heads are no substitute for the hard work that makes for a successful Observational Method implementation. At the very least you should be examining data, rerunning your models, and persuading the boss to do the right thing. That is much more beneficial than trotting around nice sunny spots with co-workers agreeing on the obvious.


CANNON MINE TAILINGS IMPOUNDMENT

Many years ago, I designed and built a large tailings impoundment using a pale simulacrum of the Observational Method. Today the impoundment if full, closed, and so well-blended with the surroundings that I cannot see it on Google Earth even though I know where it is supposed to be.

Those were the heady days when we moved fast to open mines. I proposed a full-scale site investigation in accordance with standard geotechnical principles. The mining engineer looked me straight in the face across the old deal table and said: "You will do it like a mining engineer; we know generally where the ore is and we go for it; we adjust our plans as we proceed and see what we see."

Thus I looked at the miner's geology maps of the area, read up in the local library, consulted a local geologist, and designed a 300-ft high earth and rockfill embankment. We captured the complete layout on two drawings. I also uprooted my family from Vancouver and we moved down to Leavenworth and 2-acres of land surrounding a seven-bedroom house. And every day for two years I went down to Wenatchee and the tailings impoundment construction site.

I watched ever scoop of overburden removed. I examined every exposed face of friable sandstone. I designated every hole drilled to grout the foundations. I saw as many loads of granite from the hilltop quarry as I could stand to see. And I did the standard geotechnical testing myself in the old trailer we dragged to site.

I consulted with the experts. They would fly in and out and tell me what they knew and advise me what to do. I went to the regulators and brought them along on this exciting construction exercise.

We were conservative: the embankment is above the town. I could hold water and does hold tailings. It is on friable sandstone just like those that failed a dam in a nearby state. We place sand filters. We tried to compact rockfill. We watched and debated, and adjusted the design and construction procedures every day.

I would like to claim that we had a formal Observational Method Plan to guide us. But we did not. I did have expert geotechnical engineers guiding me. We all knew, in general, where we were going. We had basic principles to guide us. We had a supportive client, and understanding regulators. And we had the impetus to change as we saw what was there.

The process worked. The dam was built, operated, closed, and reclaimed. It is a testament to the power of the informal application of the Observational Method.

There are a number of papers in the InfoMine library on the dam - look for them using the keyword cannon mine. We never formally published them. It was judged too mundane a project to warrant publication.


In Memory of Dr. Ralph Brazelton Peck

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