Sustainable Water Quality Monitoring for Developing Countries in the Context of Mining : Monitoring systems and modelling

Abstract: Mining, seen as a source of revenue in most developing countries, threatens seriously the environment. Mining impacts the water quality and one of the main problems of mining is acid mine drainage. Low pH and high concentration of heavy metals characterize acid mine drainage. When a stream is impacted by acid mine drainage both human activities and the ecological system are seriously affected. In Mozambique coal mining is growing faster since 2010 while water quality monitoring programs are not well established and improvements are limited due to lack of skilled people and financial resources. The major coal reserves of Mozambique are located in the riparian area of Zambezi River Basin which is the largest river basin in Southern Africa with 11% of its catchment area in Mozambique. The Zambezi river basin in Mozambique has a high potential for development of human activities and its environment is rich and diversified. There are water quality monitoring systems already developed and successfully implemented in developed countries. However, these systems are not sustainable for developing countries due to lack of resources. A water quality monitoring system that (1) produces consistent and comparable water quality information; (2) provides feedback to outcomes and goals of the government; and (3) promotes continuous improvement of the water quality, in the context of mining development and under the constraint of lack of human and financial resources, is proposed for the Zambezi River Basin in Mozambique. The system includes two alternative monitoring procedures. It is concluded that the best way forward is to implement the first procedure which improves the current situation by using web-based data sharing and slowly move to the second procedure which is centralized and with one company doing water quality monitoring for the entire river basin in Mozambique.Modelling is an alternative solution for reducing the cost of monitoring by: (1) estimating difficult and costly to measure parameters based on others which are easily obtained and (2) simulating contamination and reclamation of already impacted streams thus shifting usage of resources to monitor water quality changes in more vulnerable areas. Existing surface water quality models have limitations in simulating contamination of streams by acidic discharges. OTIS and PHREEQ C are used for simulating mixing and transport of non-conservative pollutants but they fail when the task is to simulate pH in streams which are influenced by equilibrium reactions between the alkalinity species interacting with the surrounding environment.Within the scope of this work two models were developed, model (I) for estimating the concentration of inorganic ions in surface water, and model (II) for simulating pH and alkalinity in streams impacted by acidic discharges. The model (I) estimates the concentration of major ions (〖Na〗^+, K^+, 〖Mg〗^(2+), 〖Ca〗^(2+),〖HCO〗_3^-, 〖SO〗_4^(2-), 〖Cl〗^-, and 〖NO〗_3^-) together with the maximum possible concentrations of minor ions and heavy metals (〖Fe〗^(2+), 〖Mn〗^(2+), 〖Cd〗^(2+), 〖Cu〗^(2+), 〖Al〗^(3+), 〖Pd〗^(2+) and 〖Zn〗^(2+)) based on pH, alkalinity and temperature. The model (II) was developed and tested to simulate pH and alkalinity in the near field, mixing zone considering only the effect of carbonaceous alkalinity. Finally, the model (II) was extended to include the effect of iron (III) in the near field and a modelling methodology is proposed for simulating pH and alkalinity in the far field. The modelling methodology proposed is based on already demonstrated valid principles and the models results while not tested using laboratory or field data are as expected. The modelling methodology can be used for simulating processes in streams. For real cases calibration will be necessary by adjusting parameters such as the dispersion and mass transfer coefficients.