Presumptive sources and relative heat index of 6PPD-quinone at the NHDPlus HR scale in the Delaware River Basin

Geospatial datasets of sources and landscape characteristics expected to contribute 6PPD-quinone, a compound intended to increase the life span of tires, to surface waters were acquired and integrated into a relative heat index framework across the Delaware River Basin. 6PPD-quinone is known to be the cause of coho salmon (Oncorhynchus kisutch) kills following storm events, and recent studies indicate susceptibility of multiple other species to 6PPD-quinone exposure and negative effects. Sources and influential factors associated with this compound and the hazard it poses to fish include tire-related manufacturing and industry facilities, road densities and traffic, airports, imperviousness, and consecutive dry days. These characteristics among others were identified and given weights by a team of geographers, toxicologists, biologists, hydrologists, and chemists in an effort to best identify NHDPlus High Resolution (NHDPlus HR) catchments with coincident network flowlines that could be most useful for sampling efforts. This effort builds on the previous conterminous U.S.-scale heat index effort (Gordon and others, 2025, https://doi.org/10.5066/P1WBVJEU) with higher resolution data sources, smaller more management-relevant stream catchments (NHD High Resolution 1:24k scale) and multiple years of data for some source layers to support future modeling efforts. This data release includes raw values of sources and influential factors, ranked and weighted values of sources and influential factors and the final assigned relative heat index value for each NHDPlus HR catchment.