If Groundwater Is Contaminated, Will Water from the Well Be Contaminated?

Introduction In a recent study of public-supply-well water quality in the United States, nearly two-thirds of all samples from 932 public wells tapping 30 regionally extensive aquifers contained detectable amounts of drinking-water contaminants that originated entirely or primarily from manmade sources. Twenty-two percent of the samples contained at least one contaminant (manmade or naturally occurring) at concentrations greater than drinking-water standards or other human health benchmarks (Toccalino and Hopple 2010). These findings imply that water from nearly one in five public-supply wells in the United States may need to be treated or blended with more dilute water sources to decrease concentrations of drinking-water contaminants before delivery to the public. Removing contaminants from water intended for drinking is difficult and expensive. It also is becoming increasingly necessary (Job 2011). Consequently, understanding factors affecting public-supply-well vulnerability to contamination is important. Public-supply-well vulnerability to contamination is not the same as groundwater vulnerability, but the two cannot be decoupled. Groundwater vulnerability is the tendency or likelihood for contaminants to reach a specified position in the groundwater system (National Research Council 1993). Groundwater vulnerability depends on three factors: (1) the presence of manmade or natural contaminant sources, (2) the combination of chemical and physical processes in the subsurface that affect contaminant concentrations, and (3) the ease of water and contaminant movement to and through an aquifer, or its