Sewage Effluent

There are 23 sewage treatment works in the Calder catchment serving 790,000 people. The majority of the works treat a mixture of domestic and industrial effluent. many, however, are overloaded and so effluents continue to enter the watercourses. This results in 25% of the rivers having poor or bad water quality. Improvements are being made and the Environment Agency intends that the watercourses should meet their River Quality Objectives (RQOs) and Environmental Quality Standards (EQS) by 1998.

Several sewage treatment works are receiving major loads from chemical works. To protect the rivers from toxic chemicals the Environment Agency carries out tests on sewage effluents and the results are used to set targets.

As well as toxic chemicals raw sewage contains biodegradable organic material. Ammonia levels rise with increasing sewage pollution. The bacteria which feed on this consume oxygen from the water and so the water chemistry and hence the life dependent upon it is altered.

Some pollution reaches the river via sewage and surface water overflows. This is particularly a problem in the Colne and Spen valleys. Improvement schemes are being implemented. Similarly a number of problems arise from the wrong connection of foul drainage to surface water sewers. Once identified the misconnections are remedied. Almost all the sewage trreatment works and overflows are owned and operated by Yorkshire Water Services Ltd.

A considerable number of remote properties use septic tanks for disposal of sewage. These are usually, but not always, covered by planning regulations and so some tanks may escape scrutiny.