The EPA has established a National Dioxin Air Monitoring Network (NDAMN) to detennine the temporal and geographical variability of atmospheric polychlorinated dibenzo-p-dioxins (CDDs), polychlorinated dibenzofurans (CDFs), and dioxin-like polychlorinated biphenyls (PCBs) at rural locations throughout the United States. Consisting of 31 sampling stations (Figure A-2), NDAMN has three primary purposes: (1) To provide measurements ofbackground atmospheric levels of dioxin-like compounds in different geographic regions of the United States; (2) To detennine the atmospheric levels of dioxin-like compounds in agricultural areas where livestock, poultry and animal feed crops are grown; and (3) To provide data to evaluate results from long-range transport and deposition air models. In 1997, EPA developed and designed NDAMN based on the following criteria: (1) NDAMN must provide reasonable geographical coverage of the continental United States; and (2) whenever possible, NDAMN sites are to be located in rural and other non-impacted areas. To enhance cost savings, many of the sites were co-located at pre-existing air monitoring network stations located in rural areas. The EPA intends to continue to operate the NDAMN for the next several years. As data becomes available and are evaluated, the NDAMN may be extended or modified as necessary to achieve the three original purposes or future goals.