PULLES HOWARD & DE LANGE INC.

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ENVIRONMENTAL MODELLING OF MINING SITES

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Pulles Howard & de Lange Inc. has experience with the environmental issues associated with the development, operation and decommissioning of mining properties in southern Africa. PHD, through its link with SENES Consultants, is the only company in South Africa which has access to verified and calibrated kinetic geochemical models which, unlike simple acid-base accounting, column leach tests or equilibrium models, are capable of evaluating and predicting pollution associated with mine wastes. Kinetic geochemical models, as developed by SENES, are essential tools for assessing management options for mine waste disposal and the environmental implications they pose. These models can be used to understand physical and geochemical processes occurring within mine wastes; examine current state of acid generation; predict future contaminant loads and concentration profiles; assess future treatment requirements; compare management and decommissioning options and support costing studies.


Computerised water and salt balance programme

PHD has developed a user-friendly computerised water and salt balance model, called AQUABAT, which is a tool, which will calculate and interpret mass water and salt balances. AQUABAT can operate in both a routine monitoring and reporting mode and can also be used for what-if simulations to provide a user-friendly tool to cost-effectively optimise and manage mine water systems.

Development of a water quality prediction model for a combined underground and opencast colliery.

A detailed water quality prediction model was developed for a South African colliery. This model includes subroutines for surface hydrology, acid mine drainage, evaporation, atmospheric deposition, etc. The model is capable of predicting water quality in a major water supply dam located downstream of the mine and will predict the water quality effects of various management actions taken by the mine. Types of management actions which can be simulated include interception of point and diffuse effluent sources, rehabilitation of spoils, discard dumps and haul roads, increase or decrease of dams and reconstitution of water courses. The model was made available as a user-friendly computer package to be used by the mine. User manuals were also prepared.

Prediction Of Mixing Reactions In The Vaal Barrage As A Result Of Discharges From New Vaal Colliery

The prediction of mixing reactions within the Vaal Barrage as a result of discharges from New Vaal Colliery was undertaken in association with Ninham Shand using the water quality model, CE-QUAL-W2. The effect of potential effluent discharges was evaluated at key Rand Water and industrial user off-take points.


Modelling of the Nkongolwana River Phases 1 and 2

The development of a catchment management plan for the Nkongolwana River system is urgently needed for the closure planning of mines within the catchment (including Vryheid Coronation Colliery and Hlobane Colliery) and because the poor water quality is adversely affecting downstream users. A simple mass balance model has been adopted for the river, based on predicted flows and measured water quality. Additionally, because the likely discharge water quality from potential passive treatment systems would be dominated by alkalinity, speciation modelling will be undertaken to determine the chemical make-up of the water. MINTEQA2 and QUAL2E are used for the quality modelling. In order to facilitate the prediction of in-stream quality with high alkalinity levels, blending is being calculated at the key river sections using Stasoft.


Geochemical modelling to define operation and rehabilitation of Durban Navigation Collieries (Durnacol) No. 7 coal discard dump

A comprehensive site characterisation exercise was undertaken, followed by digital elevation modelling and conceptual design of the civil works required to rehabilitate the dump to acceptable standards. This information, together with physical and chemical data collected for the dump were used to undertake detailed kinetic modelling of the dump and the various rehabilitation and cover options. Through comparisons with calculated allowable pollution loads in the receiving river, water treatment requirements were defined and costed. On the basis of this cost-benefit assessment and an accurate understanding of the long-term pollution implications of the different options, the best and most cost-effective rehabilitation strategies were defined.