In this paper, we investigate land motion and groundwater level change phenomena using differential interferometric synthetic aperture radar (DInSAR) over the Northumberland and Durham coalfield in the United Kingdom. The study re-visits earlier research that applied a persistent scatterers interferometry (PSI) technique to ERS (European Remote Sensing) and ENVISAT (Environmental Satellite) data. Here, the Intermittent Small Baseline Subset (ISBAS) DInSAR technique is applied to ERS, ENVISAT and Sentinel-1 SAR datasets covering the late 1990s, the 2000s and the mid-2010s, respectively, to increase spatial coverage, aid the geological interpretation and consider the latest Sentinel-1 data. The ERS data identify surface depressions in proximity to former collieries, while all three data sets ascertain broad areas are experiencing regional scale uplift, often occurring in previously mined areas. Uplift is attributed to increases in pore pressure in the overburden following the cessation of groundwater pumping after mine closure. Rising groundwater levels are found to correlate to ground motion measurements at selected monitoring sites, most notably in the surrounding area of Ashington. The area is divided by an impermeable EW fault; to the south, surface heave was identified as groundwater levels rose in the 1990s, whereas to the north, this phenomenon occurred two decades later in the 2010s. The data emphasize the complexity of the post-mining surface and subsurface environment and highlight the benefit that InSAR, utilizing the ISBAS technique, can provide in its characterization.
Low temperature heat recovery, cooling and storage schemes, using abandoned flooded mine workings are a viable option for low carbon heating solutions within many abandoned British coalfields. The temperature of mine water is a useful parameter, coupled with depth to water, sustainable yield and recharge potential, to identify suitable locations and calculate the likely performance of heat recovery schemes. This paper aims to provide the first mapping and synthesis of the temperature of Britain's coalfields to support this emerging technology. Using the best available evidence, a median geothermal gradient of 24.1 ˚C/km was calculated for the British coalfields. However, geothermal gradients between separate coalfields can vary from 17.3 to 34.3 ˚C/km. The North East, Cumbria and Yorkshire coalfields all have mean geothermal gradients generally >30 ˚C/km, whilst geothermal gradients of generally <23 ˚C/km are measured in the Warwickshire, South Wales, Staffordshire, Douglas and Fife coalfields. Active dewatering schemes are shown to locally increase the apparent measured geothermal gradient by ingress and mixing of deeper water into the pumping shafts. This baseline spatial mapping and synthesis of coalfield temperatures offers significant benefit to those planning, designing and regulating heat recovery and storage in Britain's abandoned coalfields.
Following the closure of Wheal Jane Mine in 1991, the mine water was allowed to recover and flood the mine workings. In 1992 a release of contaminated, acidic metal-rich (i.e., Fe, Zn, As, Mn, Al, Cu, Cr and Cd) mine water discharged into the River Carnon; in turn, this flowed into the Fal Estuary, causing a large, visual plume within the estuary at Falmouth. After this pollution incident, the National Rivers Authority (later part of the Environment Agency) established a temporary treatment plant and initiated the process of developing a long-term treatment plant. In 2000, the current active mine water pumping and treatment plant was completed, and operations started to remove the contaminants through chemical (lime) dosing using a series of treatment tanks. Prior to April 2011, this operational aspect of the plant was managed, under contract, by the Environment Agency. Since its inception in 1994, the Coal Authority has constructed and currently operates over 60 mine water remedial schemes for treating contaminated coal mine water. In 2011 the Authority was granted permission to take on work regarding non-coal types of mine water, which led to its managing the Wheal Jane Scheme on behalf of the Environment Agency. The knowledge and expertise at the Coal Authority allowed for a much needed assessment of the existing pumping and treatment regimes at the plant in addition to investigating the wider mining catchment as a whole. The main focus of this assessment was to identify any cost savings and efficiencies, thereby making continuous improvements to the scheme and gaining additional wider knowledge for the site. To date, since 2011 the Coal Authority and Veolia Water have implemented changes resulting in lime savings of 7% and polymer savings of 30% whilst continuing to meet all environmental consents. In addition to this, the Authority has undertaken an appraisal of the geochemistry of the water and begun a regional monitoring network of shaft water levels within the catchment to aid understanding and enable future possible scenarios for the plant to be assessed. Currently the Authority envisages a future in which changes in the mine water pumping regime could result in pumping less water and, in the long term, the establishment of a passive treatment scheme. This would ultimately reduce the financial burden of both active treatment and pumping. The Wheal Jane mine site sits within a larger catchment, which in part is drained by the Great County Adit. The discharge from the County Adit also flows in to the River Carnon, causing additional environmental issues. Together with the scheme at Wheal Jane, the investigations undertaken by the Coal Authority could also see some improvements being made to metal contamination originating from the County Adit.
Advances in differential interferometric synthetic aperture radar (DInSAR) processing algorithms, such as the Intermittent Small Baseline Subset (ISBAS), and increased data availability from SAR systems, such as Sentinel-1, provide the opportunity to increase the spatial and temporal density of ground deformation measurements. Such measurements, 2 when combined with modelling, have the potential to make a significant cost-effective contribution to the progressive abandonment strategy of recently closed coalfields.Applications of DInSAR over coalfields have observed heave in coal measures rocks and temporal correlations between the rise of mine water and deformation time-series. The cessation of systematic dewatering can have a variety of detrimental impacts and knowledge of the time-scales (i.e. the rate of rebound) and structure of the mine system are crucial to the remediation strategy. Although mine plans and borehole measurements provide vital information in this regard, mine plans are often incomplete or inaccurate, whereas monitoring boreholes are spatially sparse. Consequently, groundwater can flow in unanticipated directions via goaf, mine shafts and roadways, making it difficult to determine where the impacts of rebound are likely to occur. In this study, ground deformation data obtained using ISBAS DInSAR on ENVISAT (2002ENVISAT ( -2009 and Sentinel-1 (2015 -2019) data are used to develop a simple method to model groundwater rebound in abandoned coalfields. A forward analytical model based upon the principle of effective stress and mine water ponds is first implemented to estimate surface heave in response to changes in groundwater levels measured in monitoring boreholes. The forward model is then calibrated and validated using the ground deformation data. The DInSAR data were subsequently inverted to map the change in groundwater levels in greater detail across the coalfield and forecast surface discharges in order to support mitigation strategies.
Following the reprivatisation of the coal industry in the UK in 1994, the Coal Authority was formed to manage the legacy and liabilities of former nationalised coal mining on behalf of the UK government. Part of this post-mining legacy includes the pollution from the contaminated water in the mine workings. Since 1994, the Coal Authority has constructed and operated over 60 mine water remediation schemes and has implemented an evolving network of nearly 2,000 monitoring points throughout the UK. Due to the organisation's knowledge and expertise in managing mine water and developing treatment schemes, the Coal Authority was granted permission to investigate the remediation of non-coal-related mine water pollution. Over the previous 19 years of managing coal mine water on both a local and regional scale, the Authority has gained a significant amount of knowledge and experience, highlighting a number of important examples of 'lessons learned' for future closing mine sites. This paper is designed to highlight some key factors and methods in understanding, developing and managing mine water pollution postclosure and other mining-associated risks. Part of the historical mining legacy in the UK is the significant problems and potential risks with regard to managing coalfields post-closure. Such issues range from lack of appropriate monitoring sites due to shaft filling, poor maintenance of old mine water drainage adits, blockages or failure of obstructions (e.g., dams) in underground workings and the risks of mine gases due to rising mine water. In addition to these issues, the Coal Authority has continually developed its systems to better manage mine waters and make future predictions in an attempt to understand and mitigate the impact of environmental issues. This paper describes how changes have been made over time to a monitoring network, along with the parameters requiring monitoring. It also uses case studies to highlight problems of previous versus current strategies to prevent aquifer pollution, treat mine water and adapt to changes in environmental regulations over time. After the closure and abandonment of numerous mines and coalfields throughout the UK, with various areas ceasing production during the 1980s and 1990s, the pumping of water from the workings ceased, resulting in the flooding of the mines. Within the mining infrastructure of coalfields and individual mines, various factors influence how the workings fill with water and how the mine water rebounds. Such factors include the type of mine workings, the size and volume of the worked areas, any interconnections between mines and mining units, relationships to surrounding strata and connections to older workings and drainage systems. Each of these factors will have varying effects on how mine waters recover in terms of both the initiation and longevity of the rebound and any future associated risks this may represent. The risks from mine water rebound are not limited to the environment in terms of surface water pollution, they also include the risks to...
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