Sewer losses and interactions with groundwater quality.

Inflow/infiltration (I/I) and infiltration/exfiltration (I/E) are interactive processes which dynamically affect sewer and groundwater performance. The incidence and condition of "critical" sewers in the UK are identified together with chemical and bacterial methods of quantifying I/E and its potential impact on sewer performance and on urban groundwater pollution. Whilst the impacts of I/E do not appear to be substantial on the basis of existing evidence, some caution is advocated in respect of long term sewer sustainability.