HYDROGEOLOGICAL CHARACTERIZATION OF AN ABANDONED MINE POOL USING FEFLOW-3D TO MITIGATE AGAINST BREACH AND POTENTIAL ACID MINE DRAINAGE

Inadequate hydrogeological characterization of abandoned mine sites can lead to possible breach and adverse environmental impacts during remediation and reconstruction. Many abandoned mine impacted sites expend tremendous effort trying to understand attenuation due to remediation, flow paths, and quantification of transport parameters. It is widely known that the effects of acid rock drainage (ARD) can persist for long periods of time after mining operations have ceased due to chemical and physical weathering of sulfidic minerals. This study presents hydrogeological modeling results of an abandoned mine site near Ward, Colorado. The abandoned site presents a novel remediation technique where a section of the adit is lined with limestone to treat mine water as the mine pool accumulates. The adit is plugged by a bulkhead with a flow-through pipe, where recirculation can be implemented. The concrete bulkhead has been sealed using shotcrete and pressure grouting to prevent leakage. Regional groundwater quality and hydraulic heads are assessed using a series of monitoring wells. FEFLOW-3D modeling was applied to characterize site hydrogeology in terms of the rate of infiltration of water in the adit, estimation of the size of the mine pool behind the bulkhead, and estimation of the effective hydraulic conductivity. The results provide insights on how fast the mine water behind the bulk head rises, and on whether there is sufficient time for the water to be treated prior to recirculation. If the remediation strategy succeeds, it can be applied to other abandoned mine sites with similar hydrogeological characteristics.