The Presence of Nitrate in Ground Water

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→ NO2− → NO + N2O → N2

The rate of nitrate neutralization is 2.4 mg/m2 per day.

In its current configuration, the wetland can reduce up to 70% of the nitrate concentration in the water.The parameters affecting the capacity of the nitrate neutralization are the retention time, the centration of nitrate at the intel and the kinetic of nitrate neutralization.

Methodology

The first step of the investigation was to identify all the potential sources of nitrates on the Loulo site.

According to USEPA (2010), the two kinds of nitrates that could contaminate water are the potassium nitrate (KNO3), and the ammonium nitrate (NH4NO3). The first one is used mainly as fertilizer (85%), and the rest in heat transfer salts, ceramics, in matches and fireworks. The second is used as fertilizers (84%) and in explosives and blasting agents (16%).

Whereas agriculture is the primary source of nitrate in the highly developed countries such as European or North. American countries, on site sanitation, is seen as the main human source of nitrate in South Africa (Israel, S., Engelbrecht, P., Tredoux, G., & Fey, 2009). The Mali being less developt than the latter, this issue is even more present.

The surface, ground and discharge water at Loulo gold mines has been monitored by the hydrogeological section of Digby Wells for several impact studies. Data from 2005 to 2016 has been obtained and used in this research to investigate the source of the high nitrates levels on the site. The student was in charge of analyzing those data and determine by correlation the potential sources of nitrates.

First, the data concerning the water analysis for nitrate nitrogen were isolated. The student, then, identified three strategical points. The discharge water from the Gara underground mine (UGDW04), the Maxam warehouse (MAX-D01), as well the groundwater of a drill hole located in Yale mine where a piezometer is installed (LGW064) were chosen. The latter is considered as a comparison sample.

Finally, the data were plotted using Excel and compared.

Results

The curves of UGDW04 ( Figure 8 ) and MAX-D01 (Figure 9 ) show a similar trend when that of LGW064 (Figure 10) is different. Those results allow starting to link the use of explosives and the high nitrate concentration in the groundwater.

Nevertheless, it must be noted that further investigations must be conducted to confirm this theory. Indeed, the method used by the student may not be the most appropriate for this type of study. It must also be added that the database has been compiled by different persons for various purposes over time, making it less coherent.

The supervisors of the student constructed a hypothesis that because the rocks used in the wetland originated from the waste dumps, they may have contaminated with the nitrate contained by the explosives. Indeed, the rocks of the waste dumps are in direct contact with the explosives during the blasting of the face.

Conclusion

The work undertaken by the student is a small part of the project. However, it helped to confirm the initial hypothesis. Upon the end of his work term, analysis were conducted to support this scenario.