When I was an undergraduate, which really wasnt that long ago--okay, 30 years ago--the prevailing wisdom was that there wasnt life below the soil zone. The idea was that since all life was based on energy from the sun (another assumption thats no longer valid), you couldnt have life too far away from the suns reach. Well, we have found microbes pretty much everywhere weve looked, and the question now is where will we NOT find life.
We have known for several years that there can be viruses in shallow groundwater, especially in wells near septic systems. But because viruses are thought to survive at most one to two years in the subsurface environment, we didn’t expect them to migrate very far in groundwater. So it was a big surprise to many geoscientists when researchers in Wisconsin detected human viruses in deep wells in the Madison region, wells greater than 650 feet in depth in a confined aquifer. [Borchardt, M.A., et al. 2007. Human enteric viruses in groundwater from a confined bedrock aquifer. Environ. Sci. Technol. 41(18):6606–6612.]
At the Geological Society of America annual meeting this past week in Denver, these scientists presented several talks updating that research. [Abstracts for those talks are here, here, and here.] They have continued to detect viruses in public supply wells in Madison, and though the concentrations are extremely low, they apparently are high enough to potentially cause disease. The source appears to be leaky sewer pipes, and most virus detections appear to occur not long after precipitation events. The actual mechanism for transporting the viruses to the well screen is still unknown.
The rather sobering implication of their research is that deep wells, which we generally believe are protected from surface contamination, may be more vulnerable than we think. In the Chicago region, hundreds of wells have been drilled into deep bedrock aquifers since the late 1800’s. Many are open to multiple aquifers, and many were not properly sealed when they were abandoned, thus allowing for cross-flow across aquifers. I’d be very interested in sampling some of the wells in the Chicago region for viruses.
