Site History - The discharge impacted for several kilometres of the Long Burn which sits in a woodland area managed by Durham Wildlife. The Coal Authority constructed the mine water treatment wetland at Edmondsley in 1999, with consultants SRK (UK) Ltd and contractors Rockbourne Civil Engineering Ltd. Water Chemistry - The minewater at Edmondsley is net alkaline, the pumping flows were measured and were between 3.2 l/sec and 6.6 l/sec with an average value of 4.4 l/sec. The average inflow levels for total Iron were 13.4 mg/l with an average pH of 6.4 Site Design - The treatment site at Edmondsley comprises three cells in series, with the facility to input water into each cell separately to allow maintenance. The minewater is pumped from the emergence point in the valley to the treatment site some 45m higher up the valley side. Inlet to the first cell is through gabion baskets and to the second and third cells through the separating weir walls. The three cells measure: Cell 1 - 1,165m2, Cell 2 - 1,200m2 and Cell 3 - 870m2, with the retention time being 3.4 days assuming sequential flow through each of the cells. Average area adjusted removal of Fe is 1.6 g/m2/day which is considerably lower than the levels at which the scheme was developed for. The system is therefore thought to be ‘oversized’ for the volume of water entering the site, but this should mean that the site will remain effective for a extended time period. The costs of construction at Edmondsley £277,000. |
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