Answering Community Questions About the Safety of Residual Chemicals in Reclaimed Water

LOTT Clean Water Alliance provides services to treat wastewater for the urban areas of Lacey, Olympia and Tumwater at the southern end of Puget Sound in Thurston County, Washington. Since 2006, LOTT has also produced Class A reclaimed water, which is used for irrigation and other non-drinking purposes or is sent to infiltration basins where it recharges groundwater.

LOTT’s long-range plan for meeting future wastewater needs has centered on expanding reclaimed water production and groundwater recharge. To address questions about possible health and ecological effects from residual chemicals that may remain in reclaimed water, LOTT conducted an in-depth scientific study. The study, led by HDR, was intended to provide local scientific data and elicit community perspectives to help inform decisions about future reclaimed water treatment and uses.

The study, scoped in 2013, was a multi-year, four-task project.

• Task 1 - Water Quality Characterization: This task involved monitoring of surface water, groundwater and reclaimed water to establish baseline water quality conditions.
• Task 2 - Treatment Effectiveness Evaluation: This task utilized tracer testing, water quality sampling and modeling to understand fate and transport of residual chemicals within the study area.
• Task 3 - Risk Assessment: This task was a stepwise analysis to consider potential exposure and risk to human and ecological health. Notably, the infiltration of reclaimed water was found to pose no ecological risk and very low human health risk. Exposure concentrations of two chemicals, NDMA and PFPeA (a member of the PFAS family of chemicals), slightly exceeded minimum thresholds of possible human health risk, while being within ranges of risk defined as acceptable by the U.S. Environment Protection Agency.
• Task 4 - Cost-Benefit Analysis: This task assessed the efficacy of multiple advanced treatment trains to reduce potential risk from these and other chemicals. This analysis considered treatment processes including granular activated carbon, biologically activated carbon, advanced oxidation (ozone and UV-hydrogen peroxide) and reverse osmosis. Through this effort, the cost of constructing and operating advanced treatment was compared against the risk reduction benefit associated with decreased chemical concentrations present in reclaimed water.

Study results support the continued use of reclaimed water for groundwater replenishment. Next steps include continued monitoring and sampling efforts to better understand sources of chemicals of interest and to inform source control and pretreatment activities. It will be important to track industry research, changing regulations and the chemical landscape to gather new information as it becomes available to assess if additional actions are warranted in the future to mitigate risk.

Throughout the course of the project, we also assisted LOTT in its public outreach efforts, including assisting in the facilitation of a 13-member Community Advisory Group and organization of large-scale public workshops at project milestones. The project work was also reviewed by an independent third-party Peer Review Panel, convened by the National Water Research Institute.