Human health risk associated with direct potable reuse - evaluation through quantitative relative risk assessment case studies

Quantitative relative risk assessment (QRRA) evaluations were conducted for two hypothetical direct potable reuse (DPR) case studies. The goal of a risk assessment is to estimate the severity and likelihood of harm to human health or the environment occurring from exposure to a risk agent. Each case study compares a No Project Alternative (raw water that has undergone drinking water treatment) with a potential DPR Alternative (treated wastewater that has undergone advanced water treatment and drinking water treatment). Neither DPR scenario accounts for blending with raw drinking water prior to drinking water treatment, blending after drinking water treatment in the potable distribution system, or blending via directly distributing the purified reclaimed water into a drinking water distribution system. The QRRA focuses on chemicals that are currently regulated and chemicals that are not yet regulated but are of broad interest, such as pharmaceuticals and personal care products. Pathogen risk evaluation was not conducted but could follow a similar approach. The results illustrate how QRRA can inform water supply decisions that are made with respect to industrial pretreatment/source control, wastewater treatment, drinking water treatment, and advanced treatment for DPR. In these case studies, the DPR alternatives are projected to provide protection from regulated constituents and constituents of emerging concern that are comparable to or better than the No Project Alternatives. The results also indicate that future QRRA studies would benefit from specific information that could be obtained through targeted research. Two hypothetical quantitative relative risk assessment (QRRA) case study evaluations illustrate how QRRA can inform risk management decisions for direct potable reuse.