financed by Cape Breton Development Corporation (CBDC | “DEVCO”)
Underground mining commonly disturbs the hydraulic behaviour of aquifers and opens additional space for subsurface waters (commonly called “groundwater”). After mining ceases, mines are usually allowed to ﬂood and the groundwater is gradually ﬁlling the open space of the old underground mine workings, eventually becoming “mine water”. As all rock types – and coal is just a special type of rock – contain a certain amount of pyrite, the mine water reacts with that iron-disulphide mineral and, due to the nature of that chemical reaction, the proton acidity of the water increases and the pH as the measure for the proton activity, decreases. Simultaneously, this acidic mine water dissolves other minerals abundant in the host rocks and the coal, commonly metal sulphides and arsenates, and consequently the constituents of those minerals are released into the mine water. Thus, the mine water gets enriched in iron, sulphide, metals, semi-metals (“metalloids”) and acid. In those cases where buffer minerals (e.g. carbonates, mica, feldspar) are available, the acid of the mine water is buffered and the pH stays stable within a particular pH-range depending on the buffer minerals within the rocks (Wolkersdorfer 2008).
More than a century of coal mining in Cape Breton’s Sydney Coal Field interacted with the local aquifers and the host rock in a similar way as described before. Therefore, the Sydney Coal Field can act as a large scale laboratory to study the inﬂuence of underground mining on aquifers and the ocean as well as mine water remediation and management techniques that lessen those impacts. Currently, the mine water in the Sydney Coal Field is ﬁlling or already ﬁlled several hydraulic systems, accounting to a total volume of roughly 190 Million m³. Three of those will be the focus of current research, as they can be seen as representative for other locations (tab. 1). Hawkins & Dunn (2007) describe a mine pool as follows:
“Hydrologically connected ﬂooding mines combine to form large, high-volume mine pools that interact according to the degree of their interconnection”
Though the mine water, and partly the mine water outfalls, has been monitored and investigated since the 1980ies, not much is known about the hydrogeochemical development of the mine water or the hydrodynamic behaviour of the 26 hydraulic systems. Yet, knowing the temporal and spatial development of mine water contamination is crucial to plan remediation actions, such as diversions or mine water treatment schemes.
Tab. 1: Mine pools (“hydraulic systems”) in the Sydney Coal Field that are of special concern within the next couple of years. The allocation of the mines to a hydraulic system is stipulated, based on practical concerns of management.
|Mines within the Pool
|Lingan, Phalen, Nos. 1A, 1B, 2, 5, 9, 10, 20, 26
|5.6 – 9.3 m³/min
|Nos. 12, 14, 16, (18)
|Queen, Princess, Florence
Out of those mine pools within the Sydney Coal Field, the № 1B, the № 12/14/16, and the Princess mine pools are or will become of special concern in the next couple of years. Compared to the 1B mine pool, the other mine pools have not been studied in that detail. Therefore, the mine water research programme of Cape Breton University (CBU) in conjunction with Cape Breton Development Corporation (CBDC) will investigate the hydrogeochemistry and hydrodynamics of the mine water in order to minimize environmental impacts to surface and marine waters by installing active or passive treatment schemes at the most appropriate locations in the Sydney Coal Field. In doing so, the key issues of CBDC’s Board of Directors from February 2008 can be met:
Within MinWaRep, the application of a Geothermal Programme was planned (“MinWaRep”), but the grant was not provided.