Advances in Water Treatment and Enviromental Management

6 WATER TREATMENTpollution control has operated. Nevertheless, until now any water qualityobjectives which have been used have been non-statutory in character.Once the Secretary of State has set such water quality objectives it will bethe NRA’s duty to ensure that as far as is practicable the water qualityobjectives are achieved. The NRA is considering the criteria which will benecessary in order to establish water quality objectives and is currentlycreating categories for the various uses to which water may be put, in orderto be able to derive specific water quality standards appropriate to eachuserelated objective.WATER QUALITY SURVEYSRiver water quality has been reviewed on a quinquennial basis since 1958under a scheme operated by the Department of the Environment. The nextsuch review is due in 1990. The NRA has now embarked on a two-partreview—the first part a survey designed to replicate as closely as possiblethose previous surveys. It has been recognised however, that earlier surveyssuffered from the differences in approach adopted by the former RiverAuthorities and Regional Water Authorities, and, furthermore, that littleattention was given to biological criteria. For these reasons the NRA isconducting an overlapping survey based on a standard set of proceduresand incorporating a biological survey making use of a river invertebratepredicting and classification model (RIVPACS), which has been developedby the Institute of Freshwater Ecology, through funding from the DoE andthe Natural Environment Research Council. The use of such a system willenable a biological override to be attached to the results of chemical analysisto give a more reliable assessment of water quality which relates to thetopographical and other features of the assessment point.The results of the 1985 survey of river quality which were published by theDoE showed that 90% of rivers included in the classification were generallyof satisfactory quality—in classes 1 and 2 of the old classification system—but the report identified marked regional variations. The largestconcentrations of polluted rivers were located in the densely populated andindustrialised areas of England and Wales. Major problems relating to thedischarge of untreated sewage were identified in the Mersey and Humberrivers. River quality problems in England and Wales were mainly connectedwith the quality of effluents from sewage treatment works, and pollutionfrom intensive agriculture and forestry. A significant conclusion from thelast survey was that the reductions in the lengths of seriously pollutedrivers and canals which had been achieved in the 1970s had not beenmaintained in the early 1980s. Whilst in some regions improvements werecontinuing, there had been a small net deterioration in overall qualitybetween 1980 and 1985. The results of the 1990 survey, which will becarried out on comparable data and by similar assessment techniques, will