Potential of sewage and green waste for acidic pit lake bioremediation

Bacterial sulfate reduction-based bioremediation was trialled in an acidic pit lake, divided into two sections by an earth wall. Sewage and green waste was added to the smallest section, while the other was kept untreated as a control. Bioremediation initially increased the pH of the hypolimnion of the treatment lake but after 12 months the pH suddenly returned to pre-treatment levels. This proved to be only temporary and pH bounced quickly back to previous highs. The pH decreases appeared to be associated with heavy rainfall events. These rainfall events affected the bioremediation by mixing the lake and increasing acidity inputs from the catchment

What do elevated background contaminant concentrations mean for AMD risk assessment and management in Western Australia?

Water quality contaminants include a range of naturally occurring chemicals that can cause degradation of aquatic ecosystem water values when concentration ranges exceed biological tolerances. Both acid and metalliferous drainage (AMD) and acid sulfate soil (ASS) can increase contaminant concentrations through reduced pH and increased solute concentrations especially of toxic metals and metalloids. Water quality guideline criteria are typically used to maintain existing end use value objectives when managing AMD/ASS-affected waters. However, surface and ground waters of catchments comprising mining resources often show elevated solute concentrations in baseline conditions due to their unique geologies. From an AMD and ASS risk assessment perspective, regional water quality may therefore be unique and locally-relevant such that site-specific water quality guidelines may therefore be required to most reasonably manage water quality objectives. We provide case study examples from iron ore and coal mining from the Western Australian regions of the Pilbara, and the South-west to show that defining water quality criteria for closure is more than just using generic national guidelines, but an explicit consideration of the baseline regional bio-physico-chemical context

Ecological Restoration of Novel Lake Districts: New Approaches for New Landscapes

Mine void pit lakes often contain water of poor quality with potential for environmental harm that may dwarf other mine closure environmental issues in terms of severity, scope, and longevity. This is particularly so when many pit lakes occur close together and thus form a new ‘‘lake district’’ landscape. Pit lakes that can be developed into healthy lake or wetland ecosystems as a beneficial end use provide opportunities for the mining industry to fulfil commitments to sustainability. Clearly articulated restoration goals and a strategic closure plan are necessary to ensure pit lake restoration toward a new, yet regionally-relevant, aquatic ecosystem, which can achieve sustainability as an out-of-kind environmental offset. Such an approach must also consider obstacles to development of a self-sustaining aquatic ecosystem, such as water quality and ecological requirements. We recommend integration of pit lakes into their catchments as a landscape restoration planning exercise with clearly-identified roles and objectives for each new lake habitat and its surrounds

Recreational Use of Acidic Pit Lakes—Human Health Considerations for Post Closure Planning

Pit lakes may form in mining voids that extend below groundwater level after mining ceases and many have been found to have elevated metals concentrations and low pH through acidic and metalliferous drainage (AMD). Pit lakes are often used for recreational activities including swimming, fishing and boating and poor water quality may present health risks to recreational users. Pit lakes also provide the opportunity for additional water resource uses. The Collie Coal Basin in south-western Australia currently has a number of pit lakes with moderate AMD effects which are also used for recreational pursuits. Twelve hundred questionnaires were mailed to selected addresses in the Collie shire with an additional 170 questionnaires to specific interest groups. Participants were asked about the type of activity, frequency and duration and any health symptoms experienced after use of the lakes. Two hundred and fifty questionnaires were returned, which comprised 176 returns from the random sample and 74 from the targeted sample. Three pit lakes with elevated metals concentrations and low pH were used for recreational purposes by 62% of respondents. This was mostly in summer with swimming the most common activity. Of all respondents 52% were concerned about lake water quality and 38% using the lakes reported a variety of symptoms. Recreational use of Collie pit lakes did not represent a health risk for most of the surveyed population due to the low frequency and duration of use, however health risks may be elevated in sensitive users such as children and those consuming seafood from the lakes. Comprehensive water quality monitoring for chemicals and further characterisation of recreational use of pit lakes is warranted to more comprehensively assess the potential health risks to recreational users. Post closure mine plans need to consider potential future community uses combined with assessments of water quality and physical characteristics to reduce the potential for adverse health and safety impacts

Pit lakes as evaporative \u27terminal\u27 sinks: an approach to best available practice mine closure

Pit lakes may form when open cut mining operations extend below groundwater level and then fill at cessation of mining and associated dewatering operations by ground and surface water influx. Pit lake hydrogeology may function as an evaporative “sink” when pit lake water evaporation rates exceed influx rates. Although not ideal closure, management of local surface and groundwaters contaminated by Acid and Metalliferous Drainage (AMD) through entrainment toward an evaporative terminal pit lake may provide a best-case scenario for protection of regional water resources required by typical mine closure time scales of hundreds to thousands of years. We present two case studies from Western Australia; the first where closure of above ground landforms such as waste dumps by covers would arguably not be successful over long terms (1,000 years or more) and another where Potentially Acid Forming waste (PAF) management is limited by current waste rock dump location and suitable cover materials. Pit lake water balance modelling indicates both case study pit lakes will function as hydraulic sinks if they are not backfilled above their equilibrium water levels. A best closure outcome for these pit lakes may be to be backfilled with PAF encapsulated with alkaline/neutral waste and then filled as rapidly as possible to minimise PAF oxidation and ensure an evaporative sink pit lake is formed

Closure planning in a developing country - a case study from the Phu Kham Mine, Laos, Southeast Asia

Mining in developing regions face significant challenges for effective closure planning. A maturing mine closure regulatory environment and limited capacity within government to regulate mine closure issues can present considerable risk from an operation to the regional community and environment. Alternatively, if the operation adopts leading practice international standards in recognition of their corporate responsibilities and social license‐to‐mine in developing countries, there may be significant opportunities for enhanced social and environmental outcomes for host country and mining company. Using a case study from the Phu Kham Mine, Lao People’s Democratic Republic (Laos), we discuss some of the key challenges to closure planning, including the limitations of closure regulation and community capacity to assimilate closure issues, in a developing country. We describe how leading mine closure planning can be achieved in a developing country using leading practice international standards. The practical application of these standards is already leading to significant social outcomes in the areas of community development through initiatives targeting health, education and economic opportunities. When planning for closure, the focus must shift towards a longer term view, which endeavours to use the remaining years of the operation to prepare local communities for post‐mining independence and sustainable benefits. We highlight the potential for both social and environmental benefits post‐closure and the degree of planning required to get there

Regulation of artisanal small scale gold mining (ASGM) in Ghana and Indonesia as currently implemented fails to adequately protect aquatic ecosystems

Artisanal small scale gold mining (ASGM) operations are largely unregulated, informal and transient. Rudimentary mining and processing techniques used in ASGM often result in degraded environmental, safety, health and social conditions. ASGM requires permanent sources of water, placing most operations close to natural water bodies. Until recently, the impact on these environments has been largely overlooked, with most studies focussing primarily on mercury contamination and health concerns. Based on Ghanaian and Indonesian experiences, regulation of ASGM is a good step toward improvement, but here we argue that regulation alone is insufficient to improve environmental performance, particularly when the impacts of ASGM on aquatic ecosystems are largely unknown