By Gregory C. Delzer and Kimberlee K. Barnes

The U.S. Geological Survey’s National Water-Quality Assessment Program was implemented to characterize, in part, the quality of ambient surface and ground-water resources of about 50 major hydrologic systems with various land uses distributed across the country.  Since 1991, water samples from about 940 public supply wells and 2,700 privately owned (domestic) wells were collected and tested for more than 200 physical and chemical properties. A variety of organic and inorganic compounds were analyzed using low-level, highly sensitive methods.  About 60 of these compounds are considered in the literature to be potential hormonally active compounds (PHACs).  This presentation will characterize the occurrence of PHACs and their mixtures in the Nation’s public supply wells and domestic wells and illustrate the relative vulnerability of the two well types to PHACs.  In addition, the occurrence of PHACs in a smaller data set for selected community water systems supplied only or predominantly by surface water will be presented and compared.