THE OCCURRENCE OF PERCHLORATE IN THE UNITED STATES' DRINKING WATER

In the fall of 2004 the authors completed an American Water Works Association (AWWA) sponsored study of perchlorate occurrence in drinking water systems. This study the documented the national occurrence of perchlorate in drinking water and geographically mapped its occurrence by compiling data from existing perchlorate occurrence surveys. The existing surveys included studies by USEPA and by the States of Arizona, California, Massachusetts, and Texas.

Perchlorate occurrence in drinking water was found to be national in scope, with detections in 26 states and Puerto Rico. Perchlorate was detected in at least one entry point to the distribution system of approximately 5% of the nation's large (>10,000 population) Community Water Systems. Geographically, the highest density of perchlorate detection was found to be in Southern California, west central Texas, along the east coast between New Jersey and Long Island and in Massachusetts. At time the study was completed no perchlorate had been detected in drinking water in the northern Great Plains, the central and northern Rocky Mountains, Alaska or Hawaii. If detected, perchlorate was typically present at concentrations of less than 12 ug/L. The frequency of perchlorate detection increased with lower detection limits, indicating that perchlorate will be more frequently detected if analytical methods of greater sensitivity are used. Perchlorate was often detected in drinking water in areas for which there was no documented environmental release of perchlorate. This implies that the environmental release of perchlorate is more wide spread than anticipated or that undocumented mechanisms of perchlorate formation exist. Since two of the occurrence surveys summarized by this study are still in progress, it is likely that the estimates of perchlorate occurrence made by this report represent a lower bound of the actual number of drinking water systems impacted by perchlorate contamination.

The purpose of this paper will be to present the study results. The presentation will also discuss the “data gaps” in the study and what additional data would be required to fill these gaps.