Abstract: Seven kilometres of the River Pelenna in South Wales were impacted for approximately 30 years by discharges from abandoned coal mines. Elevated iron and low pH caused significant ochreous staining and had detrimental effects on the river ecology. The River Pelenna Mine water 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 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 mine waters. In the rivers downstream, 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 mine water 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 those found in 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.

Abstract: For the past 40 years various approaches have been developed to treat acid waters coming from abandoned as well as operating mining operations. System designs have evolved to meet increasingly stringent discharge permit limits for treated water, as well as to provide solid disposal within economic constraints. A treatment system for remediation of acid mine drainage (AMD) or acid groundwater (AG) requires two main steps: 1. The addition of chemicals to precipitate dissolved metals contained in the waters, and if necessary, to coagulate the precipitated solids ahead of physical separation. 2. Physical separation of the precipitated solids from the water so the water can be lawfully discharged from the site. Choosing the appropriate technology and equipment results in the most efficient plant design, the lowest capital outlay, and minimum operating cost. The goal of these plants is to discharge liquids and solids able to meet standards. The separation of solids from liquids can be achieved through various means, including gravity settling, flotation, mechanical dewatering, filtration and evaporation. As important as the liquid solids separation unit operations are, they are driven by the chemistry of the water to be treated. The content of the dissolved solids will influence the quality and quantity of the solids produced during precipitation. Thus the two aspects must be integrated, with chemistry first, then mechanical engineering. This presentation will provide an overview of a number of liquid solids separation tools currently being used to treat AMD-AG at several sites in the USA. It will also discuss how their operations are impacted by the chemistry of their particular acid water feeds. The tools used include clarifier-thickeners, solids contact clarifiers, dissolved air flotation, polishing filters, membrane filters, and mechanical dewatering devices (belt and filter presses, vacuum filters, and driers).

Abstract: Much work has been undertaken on the design of treatment systems to remove iron from ochreous mine water discharges. Unlike iron, manganese removal is far more difficult and generally requires active chemical dosing rather than passive treatment. The need for manganese removal can therefore significantly change the economics, management attention and sustainability of a site. Understanding natural attenuation of manganese in river systems is therefore key to deciding whether (active) manganese treatment is needed to protect downstream receptors. Nuttall (2002, this volume) describes the effectiveness of the passive treatment system at Whittle in reducing both iron and manganese concentrations in ochreous mine waters. This paper discusses the results of in-river monitoring and provides evidence for manganese removal downstream of the discharge point. In addition to dilution, attenuation appears to be in the order of 20 to 50%, depending on relative rates of mine water discharge and river flows. Such attenuation means that active treatment may not be needed for the long-term operation of the Whittle scheme. Operation of the scheme commenced in July 2002, with monitoring to further examine evidence for manganese attenuation and any impact on the ecology of the recipient watercourses.