A review was used to identify the major factors leading to priority substances (PS) & priority hazardous substances (PHS) loading from WWTPs, integrated and conceptualised into a basic conceptual model. The focus is on readily-available data relevant to major PS/PHS risk factors identified by conceptual modelling, developing appropriate indicators. Databases were compiled for Local Authority and EPA licensed discharges, and agglomeration traffic. Results from these databases were integrated into the risk model for agglomeration PS/PHS loading, combined with basic WWTP (e.g. capacity and treatment level) and agglomeration (e.g. population and area) data, and finally expressed as elevated risk in a national context following normalisation procedures.