The NGWA Managed Aquifer Recharge (MAR) Work Group convened a webinar on June 20 to address virus risk in MAR.
The webinar focused on technical aspects of the issue of virus deactivation in the subsurface and groundwater that is of concern to state regulators for safe water supply. This is a key issue that the NGWA MAR Work Group, chaired by NGWA Board Director Tim Parker, PG, CEG, CHG, is engaging in to clarify that safe groundwater is being recovered from MAR projects.
Deactivation of viruses from treated water and wastewater occurs in the subsurface, but the rate of removal from water depends on site specific conditions.
The webinar panel, moderated by Bill Alley, Ph.D., NGWA director of science and technology, included:
- Charles P. Gerba, Ph.D., of the Department of Environmental Science, University of Arizona, Tucson, Arizona
- Jorg E. Drewes, Ph.D., chair of Urban Water Systems Engineering, Technical University of Munich, Germany
- John Lisle, Ph.D., hydrogeologist, U.S. Geological Survey, St. Petersburg, Florida.
Significant points emerging from the panel and discussion were:
- Laboratory column studies tend to overestimate virus removal because most removal occurs at the surface and decreases with distance from the source.
- Viruses behave as particles that must move through the underground pore space.
- Most virus removal occurs in the soil surface and decreases with distance from the source.
- Regulators take a simple approach and specify a retention time but there are many operational, physical, chemical, and biological factors affecting virus removal that are site specific.
- Site measurements can be entered in a “toolbox” model to estimate virus removal as an evidence-based approach to virus control at MAR sites.
- A MAR example from Florida demonstrated that target inactivation was reached in less than 60 days.
The NGWA webinar is the first in a series of webinars to be developed on problematic contaminants beyond PFAS. Click here to learn more about MAR.