Zone 1 - the one year horizontal time of travel boundary

Proper management of Zone 1 can reduce contamination risks of the drinking water supply from viral, microbial and direct chemical sources. This zone is defined by the surface area overlying the portion of the aquifer which contributes water to the well within a one-year period. Within Zone 1, potential sources of microbial contamination should be strictly managed at the sources to eliminate or reduce the possibility of microbial contamination.

The criterion threshold of a one-year time of travel is considered appropriate to protect the wellfield from microbial contamination. Existing literature suggests that bacteria and viruses survive less than one year in groundwater, therefore travel times of greater than one year are not necessary. A threshold of less than one year may not provide adequate protection against possible microbial or viral contamination.

The one-year time of travel also defines the area for intensive management to protect the wellhead from direct chemical contamination. Within Zone 1, chemicals capable of contaminating groundwater should not be stored or used, or should be stored and used with sufficient precautions to protect the groundwater resource. A serious chemical release within Zone 1 may provide only a very limited time for a purveyor/community to respond aggressively, identify the spill, implement emergency remedial actions and prevent the contamination from reaching the distribution system.

Laboratory confirmation of the contamination, characterization of the contaminant plume, plus development and implementation of an on-the-ground remediation response traditionally takes a minimum of six months. Twelve to twenty-four months is a more typical period for an initial (preliminary) remedial response. Because of these concerns, most management plans for Zone 1 include strong elements for the identification of potential contaminant sources and risk management. For this reason, the one-year time of travel functions as a buffer area and provides response time.

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