Monitoring of Blasting Operations Techniques and Assessment of their Impacts on Groundwater in the Context of Underground Mining: Case of ROXGOLD SANU, Burkina Faso

Abstract

This study focused to study the blasting operations and to evaluate their impacts on Groundwater at the ROXGOLD SANU underground mine in Burkina Faso. ROXGOLD SANU is a mining and exploration company, under Burkinabe law and the State is a non-contributing shareholder up to 10%. The seismic vibration values measured on the ground are between 0.075 and 8.45 mm/s. These values are therefore all below the limit value of 10 mm/s defined by the Burkinabe law for mining operations carried out in quarries and mines and in compliance with the IFC standard. The values of acoustic overpressure were also all below 122 dB, i.e. below the limit value of 125 dB allowed for blasting in quarries and solid rock mines. The analysis of groundwater levels recorded since 2014 showed that the different water tables on the site do not communicate with each other. The impact of mining activities on groundwater levels is limited mainly to one piezometer. ROXGOLD SANU has therefore implemented good blasting practices, as the average values of the data collected during blasting are well below the recommended thresholds. Nitrate values measured in mine water in 2016 ranged from 7.1 mg/l to 1054 mg/l. However, in 2018 an average concentration of 484 mg/l was measured. Nitrite values ranged from 0.015 mg/l to 51.5 mg/l in 2016. In 2018, a concentration of 1.9 mg/l of nitrite was observed in the study area. As for ammonium, its concentrations measured in the field in 2016 vary from 0.08 to 145 mg/l. Thus, it emerges that the concentration values of Nitrites, Ammoniums and Nitrates measured in the field are higher than the limit of the regulations in force. These high values of Nitrites (NO3-), Ammoniums (NH4+) and Nitrates (NO2-) observed in mine water of the study area could be directly linked to the blasting operations which release nitrogen into the environment. The mine water of the study area is not dumped on the ground. It is carefully managed and controlled, in case of flooding it is sent to the TSF and does not flow into nature. Nevertheless, It is therefore important to set up a mechanism for complaints and requests from the local population to study the effects of blasting in depth.