Background:

Problem:

Clean Up:

Concerns:

Implications:

EAGLE MINE SITE

The Eagle mine is located 25 miles northwest of
Leadville in Eagle County, Colorado, and the site
consists of both an underground mine and mill.
Mining activity was initiated prior to 1920, and
zinc, lead, copper, silver, cadmium, and indium
have all been produced at the site. The
underground mill was operated until December 1977
and was then converted to treat mine waste water.
The site was sold to Miller Enterprises in November
1981, and all mining operations and waste water
treatmentwere discontinued after 1984.

Seepage from tailings ponds and discharge of treated
mine drainage have contaminated local surface water.
Soluble iron has been measured in Cross Creek and
Eagle River at concentrations exceeding stream water
quality standards, and fish kills have been
reported. Surface water is also the major source of
domestic water in the area, and the citizens of
Gilman have complained about the discoloration of
drinking water and the increased cost of water
treatment.

Ground water has also been significantly
contaminated by seepage from tailings ponds.

Monitoring wells downgradient from the tailings have
detected lead and cadmium at concentrations
exceeding primary drinking water standards and zinc,
manganese, and iron at concentrations exceeding
secondary standards. Contamination has not been
detected in any domestic supply wells, but there is
a small community (pop. 1,300) which relies upon
ground water for dommestic supply just down gradient
from the tailings.

An RIFS was completed for the site in December,
1985, but no remedial action has been taken.

The underground mine tunnels are flooding due to the intrusion of ground water, and mine portals are expected to begin discharging acid mine water by December of 1986. Discharge of acid mine water would seriously degrade local surface water and most likely result in the contamination of Gilman, Colorado's domestic water supply.

This site provides further evidence that heavy metals can be transported from mine waste sites and abandoned mines in ground water. The site also points out the importance of post closure maintenance of mines and mine waste sites.

INTRODUCTION

LONG TERM PREVENTION OF ACID MINE DRAINAGE

Dr. A. MacG. Robertson, P. Eng.
President, Steffen, Robertson & Kirsten

Suite 801-1030 West Georgia St.
Vancouver, B.C., Canada, V6E 2Y3

Десо

Minie
DRACUAGE:

ROC SMA 89
FL: DAM KIZALES,

MYLALOHLIN MINE.
EDUCATIONAL MATERIAL FROM
MINERAL POLICY CENTER
1325 MASSACHUSETTS AVE, MW, #550
WASHINGTON, D.G. 20005

The long term prevention or abatement of acid mine drainage depends on the continued effectiveness of the control measures. These measures may involve covers of various types including soil, water or synthetic membranes, drainage or infiltration controls, base addition or long term drainage collection and treatment in chemical plants or wetlands. Such control measures are subjected to both extreme disruptive forces such as storms, floods, fires and earthquakes, as well as the lesser but perpetual action of weathering and chemical change, erosion, frost and root action and the burrowing activities of animals and man. Under these forces there is a deterioration which eventually leads to failure of the control measures. Failure can be prevented by an adequate program of monitoring and maintenance.

The period to failure and the nature of the failure mechanism determines the risk of environmental impact, the required monitoring, and frequency and cost of maintenance. Different control measures have different inherent stabilities (resistance to failure). The selection and application of the most appropriate may result in minimal visual monitoring (every few years) with inexpensive minimal maintenance only every few decades, with extremely low risks of environmental impact. Inappropriate controls may require continuous monitoring and maintenance at high cost with a high risk of environmental impact.

A MODEL FOR THE VISUALIZATION OF LONG TERM AMD

The author has found it useful, in his visualization of acid generation and drainage, to develop the analogy illustrated in Figure 1. A description of this analogy follows.

Factors Controlling Acid Generation

Acid generation occurs in a sulphide reactor. This reactor contains a finite load of sulphide. The rate at which the reaction proceeds is dependant on:

The nature of the reactive sulphides; with some oxidizing much more rapidly than others,
EPA, 1977. The form of the sulphide is also important with disseminated framboidal pyrite
oxidizing more rapidly than large cubical crystal forms.

The rate at which the other fuels:

oxygen and

water,

are introduced into the reactor.

The initiation of bacterial oxidation may increase the rates of oxidation from 50 to 1 million
times, Lundgren, 1971. Both the chemical and biological oxidation rates are substantially
dependant on the pH in the reactor as illustrated in Figure 2 (Knapp, 1987). Typically the
reactor starts up slowly with local slow chemical oxidation, and increases rapidly as
biological oxidation starts after the pH has dropped below 5. On a single lump of waste
rock, as illustrated in the inset in Figure 1, individual crystals of pyrite may develop a
surface coating of low pH adhered water, providing the conditions for rapid bacteriological
oxidation long before similar conditions develop on other surfaces of the otherwise
naturally alkaline host rock.