Project Summary/Abstract This project proposes to monitor illicit drug and prescription opioid consumption trends at the population level in six cities in Washington State over a three year period. This study overlaps with two other major events: 1) the initiation of a state-wide drug take back program and 2) the 2020 census. This, first in the nation, statewide drug take-back program is aimed at reducing prescription opioid abuse and to reduce environmental contamination. Wastewater provides an excellent approach to provide an indicator of the effectiveness of this program. Prescription opioids and their metabolites will be measured as part of the three year monitoring program and the change in hydrocodone/norhydrocodone (metabolite) will be used as a take-back program indicator. Hydrocodone and its metabolite will be used because it is highly prescribed, highly wasted, and recommended by the DEA for disposal by flushing. Wastewater-based approaches to population level drug consumption include many data inputs with population being the largest source of uncertainty. This project will identify and monitor compounds in wastewater that reflect human populations. Levels of these population biomarkers (drugs and food additives) in wastewater will be used to develop a more accurate account of the population size contributing to the wastewater sample and thus to develop better per capita consumption estimates. Levels of these population markers will be validated with 2020 census data and the dynamic trends in populations will be evaluated with mobile device data. These population biomarkers will thus provide the project’s illicit drug and prescription opioid three-year consumption trends with updated and reliable per capita data.