The use of off-site methods requires treatment of wastes prior to their final disposal to prevent health-relevant contaminants in the effluent from reaching water intended for human use. In almost all cases, the final discharge of treated wastewaters and a significant proportionof untreated wastewater is to surface or marine waters. Risks to groundwater are therefore often dependent on the nature of the relationship between ground and surface water, in particular whether groundwater is recharged by surface water or whether groundwater provides baseflow to surface water bodies.