The Agency for Toxic Substances and | Disease Registry (ATSDR) protects | communities from harmful health eects | related to exposure to natural and humanmade hazardous substances. ATSDR works | closely with tribal agencies, the ATSDR | Partnership to Promote Localized Eorts to | Reduce Environmental Exposure (APPLETREE state partners), and other stakeholders | to conduct public health assessments (PHAs). | PHAs investigate exposures to environmental contaminants, evaluate potential health | eects, and develop public health action | plans to prevent and reduce these exposures | in communities. During the PHA process, | ATSDR and state partners review various | types of data and information to determine | exposure and potential for harmful health | eects in communities living near hazardous | sites (ATSDR, 2022). The scientific evaluation includes several important steps: | • screening contaminants for further | evaluation, | • estimating exposure doses and concentrations, and | • calculating hazard quotients and | cancer risk. | Conducting scientific evaluation and | assessing public health impacts have become | increasingly challenging due to complex sites, | multiple exposure routes, multiple chemical exposures, emerging contaminants, and | evolving knowledge of chemicals and their | toxicities. To improve the scientific quality | and consistency of PHA work conducted by | health assessors at ATSDR and state health | departments, ATSDR has developed a webbased application called the Public Health | Assessment Site Tool (PHAST; Figure 1).