Two types of modeling was done for the Río Tinto in its relationship with the effects from the Peña de Hierro mine. The first one is an analytical model and the second is a synthetic model. This to give an idea on what affects the water flow through the ground to the river.

 

For these analysis nine parameters that influences the system were taken out. Here is a short definition of each parameter;

The gradient (dh/dl) expand from the pit to the one of the bigger ponds in the southwest, same as used in Assignment 2. The pH stands for the values measured in the Río Tinto. The porosity has the value of the general estimated one. The metal content is the amount of metals that are leaching out from the mine/waste deposits. The parameter named mining activity/waste stands for how the mining industry affect or affected the area, depending on the scenario. The distance is same as dl in the gradient.  Bedrock defines what type of rock and the influences (e.g. acid rock drainage and the possibilities of mining). The infiltration refers to the general infiltration capacity for the area, and the precipitation is just the rainfall.

 

The parameters were put in a cross-impact matrix and evaluations on how big their influence on each other where categorized from 0-4 (Tab. 1). The parameters that has the biggest effect on the other ones where the bedrock and the mining activity/waste, where bedrock stands out. Precipitation is not affected by any of the other parameters, while the pH and metal content is affected by all the other parameter generally with a moderate to strong influence strength.

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To make it easier to visualize, a cause-effect diagram (Fig. 1) were made to illustrate what table 1 is showing. In fig 1, the more or less dominating parameters are the precipitation, distance, mining activity/waste, porosity and bedrock which are plotted above the trendline. The more affected parameters are the infiltration, pH, metal content and in some extent the gradient plotted below the trendline. The gradient is interpreted as changeable due to that mining activity/waste can change the topography. The bedrock is slightly changeable in an environmental perspective, due to the mining that can increase the natural process of acid rock drainage (or acid mine drainage).

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The parameters that were more stable and influenced the other parameters more, where used in the synthetic modelling. These five parameters were firstly put in a Multi-Criteria evaluation (MCE) where they was evaluated against each other (Tab. 2). This evaluation is based on which of the parameters that has the biggest influence in the system.

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From the summations from the Multi-Criteria evaluation, two hypothetical scenarios were arranged (fig. 2), there each summation were multiplied with a specific utility value (0-1) derived from the possible scenarios.

 

In the scenario 1, the mining industry is ongoing in a maximal capacity, and the question is to what grade each parameter will influence the pH and metal content in the river. In the scenario 2, environmental changes are in focus and deals with the spreading risk when the precipitation increases.  The mining is not ongoing and only consider the waste.

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It is interesting that both scenarios turned out to contribute more or less equally with contaminations. Even if the mining is terminated in scenario 2, the infiltration of precipitation through the waste is abundant to the spreading of pollutions. The porosity is also therefore more important due both for the infiltration process and the transport towards Río Tinto.

 

It is a complex system and more accurate data would be need to give better simulations over effects in the system. However, the results gives a good visualisation about how the system works and how the parameter interact with each other.

 

For a more detailed study, read the report.

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