Peña de Hierro is an abandoned mine in the Riotinto mining district. It is within the catchment area of the Tinto river and is the first point source of pollution into the river (Fig. 1). The mine was used around a century and were closed 1966 (Romero et. al., 2010). Over an area of 25 ha, 1,5x106 tonnes of waste are dumped during the mining period. Notably is that there are several streams that springs up in the waste deposit that additionally would have an influence of the degree of pollutant spreading (Romero et, al., 2006).

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The modeling was done for a 20-year period and the start for the simulation is year 2002. The starting year is based on when Romera et al. (2006) did their measurement in the area. The time interval is to see how it been since the measurements and to see how it can look in the next couple of years.

 

Three different scenarios are simulated, the first under the estimated conditions during 2002.

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The Scenario is based on the estimated conditions between the Peña de Hierro mine and the Tinto river. With a pH of 2 and a porosity of 0,38 the spreading of the plume will look like the in fig. 2. 

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The results show that after 20 years have the pollution exceeded the chosen distance of 5000 ft through the groundwater towards Río Tinto, and with a plume concentration of 0,0013 mg/L (fig. 2). 

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In this assignment, only two parameters were chosen and changed to predict what parameter that would have the highest impact of the pollutant spreading, the values of pH and porosity. It shows that the pH has the highest influence. In this example, the pH was changed from 2 to 5,75 (fig. 3c), As can be seen in the graphs which displays the evolution of 20 years, it varies a lot more when the pH was changed than the porosity, that in this case was changed from 0,38 to 0,6 (fig. 3b). To see more clearly the differences, fig. 3a illustrates the conditions that were estimated in this case study (with a pH 2 and a porosity of 0,38).

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There are other parameters that has big influence on how long it takes before the spreading reaches the river. This can be the distance they need to travel, or the hydraulic gradient. However, as these parameters are fixed and/or not easily changeable their affect was not tested. To be mentioned, this modeling is based on a lot of estimations and is not 100 percent accurate. However, it gives a good idea on how the system works and what has the biggest influence on it. Even though there are many factors that are not taken in.

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For a more detailed study, read the report.

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