『Abstract
　The paper explores the application of a unit area loading (UAL) approach to address the requirements of the US Clean Water Act (CWA) for the identification and quantification of diffuse urban pollution sources. The UAL approach defines the spatial distribution of pollutant loadings within an urban catchment as a basis for the assessment of in-stream hazards and the implementation of source control BMP measures. Calculated annual outflow concentrations for a specific catchment for two pollutants, zinc and hydrocarbons, illustrate the different levels of dilution/control, which can be required to achieve receiving water quality standards and objectives. Methodological issues relating to traditional volume-concentration probabilistic modelling on which the UAL approach is based are discussed, and the application of the UAL approach to non-point diffuse pollution load management is reviewed.

Keywords: Urban runoff loads; Diffuse pollutant sources; Unit area loadings; Environmental quality standards』

1. Introduction
2. Non-point urban pollutant loadings
　2.1. Sources of data
　2.2. Pollutant loading estimations
3. Unit area loading (UALs) approaches
　3.1. Methodology and applications
　3.2. Methodological issues with the UAL approach
4. Assessment of receiving water impacts
5. Implication for diffuse urban pollution load management
6. Conclusions
References