PARENT SESSION

5A - Uncertainties and Variabilities
Hall 7
1:45 PM - 3:30 PM, Monday, 28 April 2003
Chair: Scheringer, M.¹, ¹
Co-chair: Matthies, D.M.², Green, J.³, ^{2 3}

(MO7/15) Estimating population served by sewage treatment plants from readily available GIS data.

Keller, Virginie¹, Fox, Kay², Young, Andrew¹, ¹ CEH, Wallingford, Oxfordshire, UK² University of Sheffield, Sheffield, South Yorkshire, UK

ABSTRACT- Local and regional exposure assessments often require an estimate of chemical loads to model the quality of the effluent from Sewage Treatment Works. Uncertainties in chemical loading are a major factor in the uncertainty of environmental risk assessment. To estimate chemical loads from domestic consumables, population equivalents are usually used when available. However, the population equivalent is a measurement of organic biodegradable load and the quality of these data is often relatively poor. Therefore a method has been developed for estimating, with more accuracy, the population served by the works so that the domestic component of the flow discharged from the works to the river can be assigned. The method is based on readily available Geographical Information System data. The optimised method has been automated, and applied to UK Sewage Treatment Works within the rural River Exe catchment in Devon and the industrialised Aire & Calder catchments in Yorkshire. An almost fully automated method was applied for the first catchment, whereas a semi-automated method was found to be appropriate for the second. To assess the accuracy of the method, the results were compared with known population equivalents and domestic populations. The average absolute-error (cf. population equivalents) varied between 37% within the Aire & Calder catchments and 42% within the Exe catchments with standard deviations of 25% and 58% respectively. The method was then applied to the Anglian area (316 sewage treatment works) to assess its applicability: The average absolute-error was 48% with a standard error of 96%. Thus environmental exposure uncertainty of this magnitude can be obtained without specific data for the population served by treatment works.

Key words: population served, sewage treatment works, GIS data, domestic flow