A survey of radioactivity in the Ribble Estuary. 2: Radiological assessment

Beta dose and gamma air kerma rates were measured at sites throughout the Ribble Estuary between September, 1991 and January, 1993. Measurements were made during periods when BNFL, Springfields were discharging effluent from the processing of uranium ore concentrates (UOC) and during periods following shutdown of the process. Above background (excess) beta dose rates of up to 20 μSv.h-1 to skin were recorded over fine-grained sediments deposited towards the tidal limit of the River Ribble and Savick Brook. Similarly, the highest excess gamma air kerma rates (up to 200 nGy.h-1) were measured over the intertidal sediment in Savick Brook. This sediment was very fine grained and was contaminated with fresh Spingfield discharges. Other high gamma air kerma rates were measured on areas of old, deep deposits such as Longton Marsh. Mean background dose rates for the Ribble Estuary of 0.16 ± 0.14 μSv.h-1 beta and 64 ± 8.5 nGy.h-1 gamma air kerma were determined from measurements made at sites beyond the influence of the tide and over sands of the outer estuary. (author)