Master of Engineering Science
Civil and Environmental Engineering
Mine waste rock piles (WRPs) are anthropogenically created landforms at active and former mining sites that can generate and release highly toxic acid mine drainage (AMD) to the environment. A common solution to control AMD generation is the use of cover systems at the WRPs to isolate the reactive waste from water and oxygen in the atmosphere. Geomembranes exhibit the characteristics needed to be highly effective barriers to atmospheric influx; however, knowledge on their performance at in-service WRPs is limited. The objective of this thesis is to comprehensively assess the field performance of geomembrane-lined cover systems for limiting meteoric water to the waste rock. Four coal mine WRPs located in the Sydney Coalfield in Nova Scotia, Canada, were reclaimed with different cover systems and then extensively monitored for seven years. Defect leakage and water balances methods were employed to determine the daily water flux through the cover systems at each WRP over seven years. Results demonstrated that the inclusion of geomembrane liners in cover systems reduced the water influx from 28% of precipitation to as low as 0.05%. Furthermore, the composition of the drainage layer overlying the geomembrane influences the water influx, with native soil, granular material and geocomposite nets providing influx rates of 3%, 0.5% and 0.05%, respectively. This thesis highlights the role of geomembrane liners and drainage layers in engineered cover systems for significantly limiting the influx of meteoric water to mine waste rock.
Summary for Lay Audience
Mining produces a large amount of waste, which can come in many different forms, from liquid slurry to solid rock. Waste rock is commonly placed into large stockpiles on the ground, and can still contain small amounts of minerals that were not much value. However, these little minerals can harm the environment. When these minerals interact with oxygen and water, they can cause a chemical reaction to take place and create a toxic fluid, called acid mine drainage (AMD). This can then be carried with water flow to the outside environment, and pollute the surrounding streams, rivers and fields. The creation of AMD can be stopped by putting a cover around the waste rock, similar to putting saran wrap over a plate of food to avoid anything from getting in. A lot of different covers exist and can be made from sands, clays, gravels and plastics. The plastic option is very expensive but can be the best option; however, it is unknown if they work well over time. What if the plastic has holes in it? What will make the water flow faster or slower through these holes? This thesis looked at four different covers that were put over waste rock located in Nova Scotia, Canada. Seven years of data had been collected and needed careful compilation, analyses and interpretation. Results found that that the plastic was very successful in stopping water (rain/snow) from getting to the waste rock. It took the yearly amount of water getting inside from 28% to only 0.05%. The result also showed that another layer for draining the water away from the plastic is very helpful, especially if the plastic has holes in it. This study shows that plastic covers, while more expensive, are a great solution to stop water and also stop AMD pollution.
Hersey, Deanna, "Long-term Field Performance of Geomembrane-Lined Cover Systems at Mine Waste Rock Piles" (2021). Electronic Thesis and Dissertation Repository. 8182.
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