Distribution of total trihalomethane (TTHM) concentrations in Martin County, Kentucky from Winter 2018-Winter 2019.

We obtained the GIS data comprising the county boundary polygon data for Fig 2 and, thus, the base layer for these maps—from the Kentucky Geography Network (https://kygeonet.ky.gov), the spatial data clearinghouse for Kentucky. A ZIP file containing this publicly available shapefile can be downloaded from https://ky.app.box.com/v/kymartian-KyBnds-County/folder/137608414025. We used state cartographic boundary files from the U.S. Census for the inset U.S. map (https://www.census.gov/geographies/mapping-files/time-series/geo/carto-boundary-file.2015.html), and the National Hydrography Data (NHD) from the United States Geological Survey (USGS; https://www.usgs.gov/national-hydrography/national-hydrography-dataset) for the Tug Fork River.