Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic which can cause contamination of surrounding soil and water resources. Often these sites have important historical and cultural value that requires access to be maintained, despite the potential toxicity of As. In west Cornwall, the potential for As contamination has been recognized within the Industrial World Heritage site focused on the Mineral Tramway and mining sites mines in the Gwennap and Camborne mining districts. The major abandoned mine sites, arsenic calciner and milling sites along a proposed tourist route in this area have been assessed for As toxicity and bioavailability taking into account the proximity of footpaths to areas of potential contamination.
Arsenic concentrations up to 3.3% were found in soils along the proposed footpaths and exposed mine spoil, with 55% of all total As values above the UK criteria for contaminated industrial soil of 640 mg/kg in surface soil. Using a Physiologically Based Extraction Test (PBET), the maximum amount of As observed to be bioavailable varied from 4 mg/kg through to a maximum of 9,000 mg/kg with a positive correlation between total As concentrations and bioavailable As concentrations. Mineralogical and selective extraction evaluation identified that the PBET-released As is not so much associated with total As concentrations, but is positively correlated to As held within the weak ‘ionic-held’ As, strongly adsorbed As, As associated with amorphous iron and calcium oxide phases, and poorly crystallized As(V) salts. The data reported here have been used to develop a risk assessment of the sites and propose management strategies to mitigate these risks.
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.
Leakage over a 35-year period, starting in the 1960s, of approximately 9 × 106l of kerosene from an industrial complex located above fractured Permo-Triassic sandstone aquifer resulted in the potential for a significant dissolved phase. However, a phased, risk-based approach identified no significant risks in terms of dissolved-phase petroleum hydrocarbons, BTEX, or volatile or semi-volatile organic compounds. This is considered to be due to biodegradation of potential contaminants via metabolic pathways using electron acceptors primarily provided by the groundwater recharge (oxygen, nitrate and sulphate). Contaminant concentrations have remained below regulatory limits for protection of the receptor since monitoring was initiated in 2000. This case study demonstrates the potential for biodegradation within the Permo-Triassic sandstone aquifer of the UK: the risk-based approach described and the management plan developed could be applicable at other sites.
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