The potential environmental impact on the River Frome and its flood plain network from discharges of groundwater resulting from soil dewatering on the Winfrith site

• Main Authors: Hilton, John, Bass, Jon, Rameshwaran, Ponnambalam
• Format: Report
• Language: English
• Published: Centre for Ecology and Hydrology 2007
• Subjects: Agriculture and Soil Science; Ecology and Environment; Hydrology; Leech; Salmo salar; Lutra lutra
• Online Access: http://nora.nerc.ac.uk/id/eprint/1645/; https://nora.nerc.ac.uk/id/eprint/1645/1/0704036.pdf; http://www.nmw.ac.uk/cehstaff/Library/cr/C03220/0704036.pdf

Over the next few years decommissioning work at the UKAEA Winfrith site will require the water table around relevant work areas to be lowered by pumping groundwater from the underlying aquifer. The anticipated discharge for these works is 15 l/s, although occasionally flows may reach 30 l/s, and will discharge into a ditch at the north of the site, which discharges into a sub-channel of the River Frome. Since the River Frome is an SSSI over much of its lower reaches, a preliminary assessment of the likely impacts of this discharge on vulnerable species was made and a list of subsequent work was proposed. The River Frome between Dorchester and Wareham is a Site of Special Scientific Interest (SSSI) and a candidate Special Area of Conservation (cSAC). Maps of the extent of the SSSI are given along with the reasons for its designation as a SSSI. The discharge has potential to disrupt the typical water crowfoot habitat in the river and may affect several vulnerable species, including: Otter (Lutra lutra), Water Vole (Arvicola terrestris), White-Clawed Native Crayfish (Austropotamobius pallipes) [now thought to be extinct in the R. Frome], Southern Damselfly (Coenagrion mercuriale), Desmoulin’s Whorl Snail (Vertigo moulinsiana), Fine-lined Pea Mussel (Pisidium tenuilineatum), Medicinal Leech (Hirudo medicinalis) native Brown Trout (Salmo trutta), Brook Lamprey (Lampetra planeri) and Salmon (Salmo salar). Exploratory investigations suggest that the volumetric flow in the river is two orders of magnitude greater than the flow in the ditch itself. As a result, the volume of the discharge is not likely to affect the main river, although any vulnerable species present could be affected, particularly during natural low flow periods during the summer. In contrast, the quality of the water, particularly pH, alkalinity and some heavy metals, discharged to the ditch from pumping could potentially impact the river. Water Quality will vary widely, depending on the location of the pumped source within the Winfrith site and so the ...