Cryptosporidium contamination hazard assessment and risk management for British groundwater sources

Contamination of aquifers by Cryptosporidium oocysts has only recently been recognised as a risk to the security of important groundwater-based drinking water supplies in the UK. The predominance of dual porosity aquifers with complex flow systems, the fact that UK water utilities hardly ever own or control the catchments overlying the aquifer supplying their abstractions and the diverse designs of the wells/springs themselves renders hazard assessment necessary but not simple. A tripartite approach is proposed which is a modification of standard contaminant transport sourcepathwayreceptor principles. The complex interaction of factors and uncertainty of underpinning data greatly limit the applicability of a strictly numerical approach to risk assessment. Instead the importance is emphasised of understanding the blend of hydrogeological and operational factors which makes each site and its setting unique.