EXECUTIVE SUMMARY

MEND (Mine Environment Neutral Drainage) studies on the subaqueous disposal of tailings material (outlined under MEND project 2.1 1. 1) were subject to critical review by a group of experts, under the direction of the Rawson Academy of Aquatic Science, Ottawa. The review had two objectives. In summary, these were:

To provide technical and scientific assessment of MEND studies on subaqueous disposal of tailings (presented in Part I of this report).

To outline additional requirements necessary for the MEND studies on subaqueous disposal to maintain a credible scientific approach. (presented in Part H of this report)

The following key points were established during the review and subsequent discussions between the scientific review team (SRI) and representatives of MEND.

Technical and Scientific Assessment

Subaqueous disposal of tailings appears to offer physics-chemical advantages over terrestrial disposal, particularly with respect to sulphur oxidation and generation of acid waters.

The process of tailings disposal is potentially highly disruptive of lake ecosystems and normally it would take several decades (possibly centuries in some lakes) before natural sedimentation provided sufficient cover to insulate the lake ecosystem from the influence of the tailings (both the metals flux and substrate effects). However, remedial measures may be applied to reduce the extent of impact and accelerate recovery.

The MEND literature review of geochemical processes controlling metals release is excellent, it is well written and comprehensive (at the time of completion).

The background limnologies of the MEND case-study lakes (Anderson, Buttle and Mandy) are suitable only for gross comparisons. They do not support clear interpretation of cause and effect associated with tailings disposal.

Field studies were designed to obtain limited information, specifically to assess whether or not the reactivity of tailings disposed of underwater (in the real environment) remained low. For this purpose the data are sufficient; however, the data are neither useful to address effects which occur during the process of disposal nor long term ecosystem adjustments to the introductions of tailings. Limitations inherent in chemical extraction techniques may restrict the extent to which available data are used to address study objectives.

Additional Requirements

Suggestions have been made for more detailed field studies of (metals) fluxes in the case-study lakes, rates of accumulation and for measurements of whole lake ecological response and references are provided in the report The reviewers' comments and recommendations, and further documentation are available from the MEND Secretariat-

A more extensive but selective literature review has been suggested to cover aspects of toxic effects, particle behavior in response to in-lake hydrodynamic conditions, improved field and analytical techniques and methods, and biological indices of whole lake effects.

The general view of a joint meeting between the SRT and representatives of MEND was that sites pecific preferences for subaqueous disposal of tailings would include:

• infilling of a small headwater lake;
• disposal in an artificial structure; and
• in-lake disposal (in which tailings represent only a small part of the total lake volume).

It was recognized that in-lake disposal was not a usual practice and may not be acceptable. To some extent, this view could modify future development of subaqueous disposal studies under the MEND program.

Last Modified: 2003-11-26		Important Notices

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