Advances in Water Treatment and Enviromental Management

256 WATER TREATMENTThe long term effect of storm discharges on the stream is being measuredin biological, bacteriological and chemical terms. Biological analysis examinesthe presence of invertebrate fauna using the BMWP score and ASPTtechniques. Bacteriological and chemical sampling involves the measurementof coliforms, faecal streptococci, BOD, suspended solids and ammonia fromfive sites along the receiving stream.The project is ongoing and the findings to date are reported in this paper.1. INTRODUCTIONIn the United Kingdom pollution of beaches and inland waterways hasbecome a serious environmental issue demanding urgent attention. Thedemands of EC directives have increased public awareness of bacteriologicaland other standards to be achieved at bathing beaches and there has beena lot of activity on the control of pollution in the environment. Stormwateroverflows are regarded as transient, intermittent point sources of pollution.There are numerous reports (1) which conclude that pollution arising fromstormwater overflows can account for the majority of pollution problemsexperienced in watercourses and on beaches. But, more information isrequired on the effects of stormwater on the environment.2. PRESENT PRACTICEIn general, standard practice in the United Kingdom concentrates on thefunction of a stormwater overflow as a “flow splitter” to remove excessvolumes of storm sewage from a foul sewer with inadequate hydrauliccapacity. In consequence, there has been much attention paid to stormwateroverflow settings.For example, the recommendation by the original Ministry of Health of settingstorm overflows at 6×DWF, providing full treatment for 3×DWF andsettlement for flows from 3–6×DWF in storm tanks regardless of thesomewhat obscure origins of these recommendations, have been in use formany years.This recommendation was modified on slightly more rational grounds bythe Technical Committee on Storm Overflows(2), with the production ofFormula ‘A’commonly regarded as the present standardThe development of computers and advanced mathematical techniques hasenabled further refinement and it is now normal to assess a sewerage systemand the impact of an overflow on the hydraulics of a system using a designpackage such as WASSP or WALLRUS.The question of the polluting influence of stormwater overflows on thereceiving waters environment has been basically neglected.