Hydraulic performance assessment of passive coal mine water treatment systems in the UK

Hydraulic performance assessment of passive treatment systems has been conducted for UK's Coal Authority mine water treatment systems. The study aims to improve the understanding of the hydraulic factors that govern contaminant behaviour, such that future design of treatment systems is able to optimise treatment efficiency and make performance more predictable, and improve performance over the long-term. Assessment of the hydraulic behaviour (i.e. residence time and flow pattern) of the treatment systems was accomplished by means of tracer tests. The tracer tests were undertaken at eight UK Coal Authority mine water treatment systems (lagoons and wetlands) within Northern England (main study areas) and part of southern Scotland. A modelling approach using a tanks-in-series (TIS) model was adopted to precisely analyse and characterise the residence time distributions (RTDs), in an effort to account for the different flow patterns across the treatment systems. Generally, lagoon RTDs are characterised by a greater flow dispersion compared to wetlands (i.e. higher dispersion number, D and lower number of TIS, n). Consequently, the hydraulic efficiency, eλ for lagoons is much lower than wetlands (mean of 0.20 for lagoons compared to 0.66 for wetlands). Implications for design and maintenance of mine water treatment systems are discussed.