What is the study about?
The Reclaimed Water Infiltration Study was a major scientific research effort. It was intended to answer community questions about residual chemicals that may remain in reclaimed water, and what happens to them when reclaimed water is infiltrated into the ground and used to replenish groundwater. Watch the video for an overview of the study and key findings.
Why conduct the study?
The study was an opportunity to answer community questions about residual chemicals in reclaimed water and ensure long-term plans for managing wastewater are appropriate. It was also an opportunity to advance the science around these topics, especially because existing research tends to be done in areas with climates quite different than the Pacific Northwest.
What are residual chemicals?
Residual chemicals refer to chemicals that come from the many household and personal care products we all use every day, such as medicines, soaps, shampoos, cleaning products, lawn care products, and even some foods. Some of these chemicals get sent down the drain or toilet and end up in wastewater that gets sent to a treatment plant for cleaning before it is released back to the environment.
Why infiltrate reclaimed water?
Groundwater recharge is part of our communities’ long-term plan for overall wastewater management. This practice helps to reduce the amount of flow discharged to Budd Inlet from LOTT’s main treatment plant. It also has the potential to provide additional community benefits, including improved streamflows and mitigation for municipal groundwater withdrawals.
Key Finding
Task 1
Task 2
Task 3
Task 4
Levels of Oversight
Reclaimed Water is Safe
Scientists found that risk to human health from residual chemicals in reclaimed water is very low. No risk to ecological health was found. An independent Peer Review Panel agreed that risks are low and the current use of the water for groundwater replenishment is safe.
Key Finding
Reclaimed Water is Safe
Scientists found that risk to human health from residual chemicals in reclaimed water is very low. No risk to ecological health was found. An independent Peer Review Panel agreed that risks are low and the current use of the water for groundwater replenishment is safe.
Task 1
Task 1: Testing Local Waters for Residual Chemicals
Testing of wastewater and reclaimed water for residual chemicals showed that wastewater treatment is effective at removing chemicals, but some remain in reclaimed water after treatment. Sampling of groundwater and surface water in the area around LOTT’s Hawks Prairie Recharge Basins and in a “control” area in Tumwater showed that residual chemicals are found in our environment where reclaimed water is used for infiltration and also in areas where it is not.
Task 2
Task 2: Tracking Reclaimed Water Underground
A tracer test provided information about where reclaimed water flows underground after infiltration, and how quickly it travels. Sampling showed that residual chemicals decrease as the water travels underground and mixes with groundwater. This occurs as chemicals adhere to soil particles, break down by microorganisms, and disperse. Field data was used to build a computer model predicting conditions 100 years into the future.
Task 3
Task 3: Evaluating Potential Risk to People and Wildlife
Risk assessments were based on a step-wise process that began with a broad list of residual chemicals and gradually narrowed the focus to chemicals with potential effects. Of the 134 chemicals analyzed, 132 were found to be below levels of concern for human health. Two chemicals were identified as slightly above the minimum level of concern, however, the risk assessment scientists indicated the risk was very low. None of the residual chemicals were predicted to harm ecological health.
Task 4
Task 4: Reviewing Options to Address Risks
This cost/benefit analysis reviewed several advanced treatment options to remove residual chemicals from reclaimed water. Costs of the various technologies varied widely, and were substantial compared to risk reduction benefits. Other actions, such as targeted monitoring of chemicals of interest and source control, were identified as ways to further understand and address risks.
Levels of Oversight
Ensuring the Science is Sound
To ensure a credible and scientifically valid study, multiple layers of expertise and review were built into the process, starting with the Project Team led by HDR Engineering Inc, with sub-consultants adding specialized expertise. Review and input from a local Science Task Force of technical experts and a highly qualified national Peer Review Panel ensured the research was rigorous, objective, and based on accepted scientific practices. A Community Advisory Group of local citizens provided insight and reviewed study materials and community engagement plans.
What Comes Next?
Based on study findings, LOTT plans to continue infiltrating reclaimed water. As we do, we will continue to monitor chemicals of interest, track related research and new regulations, and remain flexible and ready to respond to new information. Conditions are expected to change over time and study results will likely need to be revisited. This fits well with LOTT’s long-term management approach, which is based on a constant planning model. Information gathered as part of this study provides a solid foundation to reassess our reclaimed water practices and explore advanced treatment options in the future.
For More Details
This extensive research effort resulted in over 2,500 pages of scientific reports outlining analyses and findings, in addition to Peer Review Panel reports, Community Advisory Group meeting notes, and other supplemental documents. To access this study-related information, please visit the library here.
Reclaimed Water Infiltration Study
Summary Materials
Project Summary August 2022 (PDF) – Reclaimed Water Infiltration Study project summary
Reclaimed Water Infiltration Study Summary (PDF) – high-level overview of study activities, findings, and next steps
Task 1: Water Quality Characterization (PDF) – initial testing of wastewater, reclaimed water, groundwater, and surface water
Task 2: Treatment Effectiveness Evaluation (PDF) – results from a tracer test and chemical monitoring near the Hawks Prairie site
Task 3: Risk Assessment (PDF) – evaluation of potential risks to humans and wildlife from infiltrating reclaimed water
Task 4: Cost Benefit Analysis (PDF) – review of technologies to remove additional residual chemicals from reclaimed water
Reclaimed Water Infiltration Study Introduction (PDF) – overview of study structure and oversight
Reclaimed Water Infiltration Study Outreach Report (PDF) – outreach conducted to inform the community about progress and results
Technical Memos
Cost Benefit Analysis August 2022 (PDF) – costs and benefits of treatment options to reduce residual chemicals in reclaimed water
Final Human Health Risk Assessment (PDF) – human health risk assessment for infiltration of reclaimed water into groundwater
Final Ecological Risk Assessment (PDF) – ecological risk assessment for infiltration of reclaimed water into groundwater
Residual Chemical Fate and Transport Analysis (PDF) – results of hydrogeologic modeling predicting residual chemical concentrations
Tracer Test and Water Quality Monitoring Report (PDF) – results of tracer test and groundwater monitoring
Residual Chemicals in Reclaimed Water, Groundwater, and Surface Water (PDF) – summary of three Task 1 technical memos
Steady-State Groundwater Model Development and Calibration (PDF) – development and calibration of the groundwater model
Background Material
Screening Evaluation for the Human Health Risk Assessment (PDF) – analysis used to inform the Human Health Risk Assessment
Screening Evaluation for the Ecological Risk Assessment (PDF) – analysis used to inform the Ecological Risk Assessment
Hydrogeologic Characterization Report (PDF) – description of hydrogeologic field investigations and results
Groundwater Quality Characterization (PDF) – results of groundwater sampling in the Hawks Prairie and Tumwater study areas
Surface Water Quality Characterization (PDF) – results of surface water sampling in the Hawks Prairie and Tumwater study areas
Wastewater and Reclaimed Water Quality Characterization (PDF) – results of wastewater and reclaimed water sampling
Community Advisory Group Final Report Phase 3 (PDF) – summary of Phase 3
Community Advisory Group Final Report Phase 2 (PDF) – summary of Phase 2
Community Advisory Group Final Report Phase 1 (PDF) – summary of Phase 1