The U.S. Environmental Protection Agency (EPA) has prepared this Health Effects Support Document for 1,3-dichloropropene to assist in determining whether to regulate 1,3dichloropropene with a National Primary Drinking Water Regulation (NPDWR). The available data on occurrence, exposure, and other risk considerations suggest that, based on monitoring conducted from 1988 to 1997, 1,3-dichloropropene does not occur in public water systems at a frequency and at levels of public health concern at the present time. Based on the low occurrence of 1,3-dichloropropene in the potable water, 1,3-dichloropropene does not present a meaningful opportunity for health risk reduction for persons served by public water systems. EPA presents its determination and data analysis in the Federal Register Notice covering the Contaminant Candidate List (CCL) regulatory determinations.