Mine water management: recent experience from India

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SRK News | Issue 55: Mine Water Management

Sujit Roy, Senior Consultant - Geology   
 

One of the largest cement manufacturing companies in India, OCL India Limited, produces limestone from its open-cut Lanjiberna mine. With increases in mining depth, the mine is facing significant inflow of water, resulting in the formation of pit lakes. The area experiences significant rainfall during the monsoon months. OCL retained SRK India to help advise on potential water inflows with the deepening of the limestone pits and to develop a cost-effective mine water management solution.

Currently OCL operates three adjacent limestone pits with a fourth used to store pumped out water. During the initial phase of the study, SRK noticed that some water management practices had been overlooked causing high levels of inflow to the pits. The presence of large unlined water bodies and garland drains close to pit edges could be responsible for recirculating water. There were no interception or diversion structures to minimise the impacts of recirculation. Similar oversights were noted at some of theother projects that SRK India is presently involved in. For example, the pit at the Mangampet barytes mine is closely surrounded by unlined garland drains and water impoundment structures. To identify connections between water features, SRK suggested simple fluorescence-based tracer tests and accretion surveys along these drains.

To understand the water management issues at Lanjiberna mine, SRK developed a water balance model. It indicates the split between surface and groundwater inflows: about 5% is from direct rainfall onto the pit lakes, 45% from surface runoff, and the remaining 50% from groundwater seepage.

The Lanjiberna deposit belongs to a Precambrian metasedimentary sequence with multiphase folding and faulting. Landsat 8 satellite images and walk over surveys indicate large-scale lineaments intersect the Lanjiberna pits. Such narrow, elongated fracture zones may act as hydraulic pathways for groundwater flows into the pits. While overall groundwater inflows contribute about 50% of the pit lake water, a good proportion could be due to recirculation from nearby unlined water holding facilities.

Subsequently, SRK mapped the perennial (and seasonal) seepages inside the pit, which indicate reasonable correlation with narrow, linear structures and the regional groundwater flow pattern. Based on the preliminary water balance, SRK developed numerical models to estimate potential groundwater inflows. The results, though preliminary in nature, predict significant water inflows with progressive deepening of the pits.

Overall, it appears that restricting potential recirculation, improving existing storm water management and intercepting groundwater seepages by peripheral dewatering wells along the narrow fracture zones are key solutions for this operation. To validate this, SRK suggested further sitespecific data gathering, including detailed fracture mapping, Electrical Resistivity Tomography along selective transects, pumping tests, tracer tests and accretion surveys along the unlined garland drains.

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