Using data for 81 coal mine discharges in the UK, the influence of discharge hydrogeology on discharge chemistry is assessed and typical chemical parameters derived for five discharge types. A combination of modified and new classification schemes is used to differentiate between the various discharge sources. Drainage from spoil tips generally has a pH below 5 and net-alkalinity values as low as — 2500 mg l−1 CaCO3. Drainage from flooded workings and pumped discharges are net-alkaline, while drainage from flooded and free draining workings are either moderately net-alkaline or net-acidic. Iron is the major contaminant of concern, although many mine waters contain less than 30 mg l−1 and Fe/SO4 ratios are less than unity. The classification schemes developed can be used to assess mine water treatment requirements and processes operating in passive treatment systems.
Wetlands were constructed between 1995 and 1999 to treat discharges from abandoned coalmines in the Pelenna Valley, South Wales. This was one of the first and most comprehensive demonstrations of passive minewater treatment technology in Europe, incorporating aerobic and anaerobic cells, including ‘reducing and alkalinity‐producing systems. The wetlands were monitored to assess their performance and longevity and were found to remove 82‐96% of the incoming iron, with no decline in treatment performance over the monitoring period to 2002. Oxidation was found to be the dominant iron‐removal process, even in vertical‐flow cells which were designed to utilise anaerobic processes. Factors limiting the longevity of iron‐removal processes were identified. maintenance requirements were highlighted and life‐span predictions were calculated for the systems. The wetlands were shown to be an effective and low maintenance (but not maintenance‐free) method of treating net‐acidic and net‐alkaline minewater.
The ecology of the River Pelenna (in South Wales) was impoverished by polluted discharges from abandoned coal mines. A series of passive constructed wetlands was created in order to treat these discharges and to improve the ecology of the river. A three‐year Environment Agency R&D project investigated the performance, environmental benefits and sustainability of the constructed wetlands. It showed that the treatment systems were removing most of the iron contamination. In the reaches downstream from the minewaters, the dissolved‐iron concentration quickly dropped below the target level. Invertebrate abundance, trout and riverine bird populations increased in following years. However, occasional overflows from the systems have significantly affected the ecology of one stretch of river. The research work has provided an insight into the potential for ecological recovery associated with future minewater treatment.
Abstract. From the 1960s to the late 1990s, the River Pelenna in South Wales was impacted for a distance of 7 km by five significant discharges from abandoned coal mines. Elevated iron and low pH caused significant orange staining and had detrimental effects on the river ecology. The River Pelenna Minewater Project constructed a series of passive wetland treatment systems to treat these discharges. Monitoring of the performance and environmental benefits of these has been undertaken as part of an ongoing Environment Agency R&D project. This project has assessed the changes in water quality as well as monitoring populations of invertebrates, fish and birds between 1993 and 2001.Performance data from the wetlands show that on average the three systems are removing between 82 and 95% of the iron loading from the minewaters. Downstream in the rivers the dissolved iron concentration has dropped to below the Environmental Quality Standard (EQS) of 1 mg/l for the majority of the time. Increases in pH downstream of the discharges have also been demonstrated.Trout (Salmo trutta) recovered quickly following minewater treatment, returning the next year to areas that previously had no fish. Intermittent problems with overflows from the treatment systems temporarily depleted the numbers, but the latest data indicate a thriving population. The overflow problems and also background episodes of acidity have affected the recovery of the riverine invertebrates. However there have been gradual improvements in the catchment, and in the summer of 2001 most sites held faunas, which approached unpolluted controls. Recovery of the invertebrate fauna is reflected in marked increases in the breeding success of riverine birds between 1996 and 2001.This study has shown that constructed wetlands can be an effective, low cost and sustainable solution to ecological damage caused by abandoned mine drainage. ___________________
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