Advances in Water Treatment and Enviromental Management

246 WATER TREATMENTwhich indicated that the waters off both Southport and Lytham did not consistently complywith the microbiological standards. North West Water was asked by the government todetermine how the quality of these bathing waters could be improved to ensure compliance.Preliminary investigations of the location of sewage discharges to the area, and a detailedexamination of ways to achieve compliance for the bathing waters off the nearby Fylde coast(Crawshaw & Head, 1989; Head et al., in press), showed that solutions to the problems atSouthport and Lytham would only be possible within the context of an integrated programmeto reduce polluting inputs to the Ribble estuary as a whole. It was apparent that, in additionto the effects of discharges of sewage and storm water near the bathing waters, the quality ofthe outer estuary could be influenced by discharges from Preston via the sewage works atClifton Marsh, and possibly combined sewage overflows within the town itself.Figure 1. Ribble Estuary showing bathing waters and existing sources of pollutionAdditionally, sewage effluents from areas draining to the River Douglas were also liable tohave an effect (Figure 1). It was important to ensure that any scheme to improve the conditionof waters near the bathing areas did not result in a worsening of microbiological or otherconditions elsewhere. In particular it was essential to ensure that the important salmonfishery in the estuary and further upstream was not adversely affected. Investigations todetermine the most appropriate scheme involved mathematical modelling and bacteriologicalinvestigations of the sewerage systems and receiving waters, along with tracer experiments todetermine the significance of the existing inputs.EXISTING CONDITIONSThe effects of the discharges from the most significant of the existing discharges to the estuarywere investigated by means of a series of tracer releases carried out during 1988 and 1989.