Risk Management in Wellhead Protection

Abstract
The theoretical basis of a risk‐management approach to wellhead protection is developed. Contaminant sources are divided into two categories: chronic sources and spills. For chronic sources, such as residential septic tanks, contaminant influx to the ground water, decay rates, and retardation factors are viewed as random variables with defined probability density functions, and risk‐analysis yields the expected risk of an adverse health effect to the population served by the wells. In the case of spills, risk analysis yields the maximum probable concentration (MPC) in the pumped water for a given design spill. From a regulatory viewpoint, chronic sources must have regulated contaminant loadings, and facilities handling significant quantities of hazardous materials must have design spills. Using the risk‐analysis procedure developed in this study, a defined level of protection is associated with land uses within the zone of contribution of a wellfield. This is an improvement over conventional wellhead protection strategies that do not define a level of protection.