Groundwater is the largest and most reliable source of freshwater on earth. In the United States 26% of public supplied water is from groundwater in addition, 15% of households in the United States with private wells pump directly from groundwater for their drinking water. Groundwater and surface water are connected in many ways, not all of them fully understood. When streamflow is low due to lack of precipitation (drought) or withdraws (pumping for irrigation or water supply), groundwater serves to help maintain the baseflow. When conditions are dry, rivers, streams and ponds can serve to recharge groundwater.
In addition wastewater from agricultural irrigation is used to recharge groundwater and effluent discharge from wastewater treatment plants is intentionally and accidently finding its way into groundwater. In Los Angeles waste water effluent is used to recharge the groundwater, septic systems return their effluent water to groundwater and several studies by the U.S. Geological Survey (USGS) scientists Paul M. Bradley and Larry B. Barber (and others) have shown that waste water contaminants including pharmaceuticals are carried not only downstream into drinking water intakes, but into the shallow groundwater at least 65 feet from the stream.
The most recent study by Bradley and Barber et. al. was carried out at Fourmile Creek, near Des Moines, Iowa in October and December 2012. Fourmile Creek has been extensively studied by these scientists because wastewater dominates the streamflow. (Wastewater also dominates the flow of the Occoquan River and many others in our area.) Due to a drought in the Des Moines area, the wastewater represented 99% of streamflow in October and 71% of streamflow in December. Scientists chose to track the movement of pharmaceuticals between the stream and shallow groundwater because pharmaceuticals are bioactive, can be highly mobile, are good indicators of domestic wastewater, and wastewater is the only source of pharmaceuticals in Fourmile Creek.
Both stream and shallow groundwater samples were analyzed for 110 pharmaceuticals. The scientists found that 43% and 55% of pharmaceuticals analyzed for were detected in the stream’s water in in October and December, respectively. Fewer pharmaceuticals were detected in shallow groundwater; however, 16% and 6% of the pharmaceuticals were detected at a distance of 65 feet from the stream bank during October and December, respectively. The pharmaceuticals detected included antivirals and antibiotics, muscle relaxants, and antidepressants and tranquilizers, as well as medications for treating cancer, diabetes, and hypertension; in concentrations as high as 87 nanogram per liter (ng/L).
Both carbamazepine and sulfamethoxazole (a common antibiotic) were found in shallow groundwater at detectable levels at 65 feet from the river bank. The levels of these pharmaceuticals were higher close to the riverbank during the drier period, and appeared to fluctuate in response to drought; the larger portions of the river flow were made up of wastewater the higher the concentrations of sulfamethoxazole and carbamazepine in the groundwater. However as distance increased, the concentrations dropped, but it appeared that the rate of biodegradation of wastewater contaminants in groundwater is slower than in surface water and trace contamination of the groundwater may become ubiquitous.
USGS scientists have previously documented adverse impact to trace levels of sulfamethoxazole far below levels used to treat diseases on native soil bacteria. Since many studies by the USGS have found sulfamethoxazole in surface waters, the scientists conducted a series of laboratory experiments to determine the effect of the antibiotic on native soil bacteria. They found that sulfamethoxazole concentrations commonly found in aquatic environments (approximately 1 microgram per liter [ug/L]) delayed the start of cell growth, limited denitrification (a critical component of global nitrogen cycles), and altered bacterial community composition. In short, our contamination of water supplies with traces of antibiotics may impact the ability of the earth to feed us.
Other impacts of water pollution have been to the aquatic ecology. For over 15 years the USGS has been studying fish kills. Work done by Vicki Blazer and others has documented endocrine disruption and immune-suppression in aquatic life as contributing to fish kills. The earliest work did not find a cause. Dr. Blazer and others believe that methodology used to detect these chemicals in past studies may not have been sensitive enough, and may indeed be above the concentration thought to impact these fish. Dr. Blazer and others believe based on research studies in more than 25 fish species, that 1 ng/L (parts per trillion) may be the “no effects level” for estrogen concentrations in stream water on fish. We eat the fish, we drink the water, and we intentionally recharge groundwater with our waste water and pass all manner of chemicals and pharmaceuticals through our septic systems. For many of us, the closest septic system to your well is our own septic system. Any drugs you take (or flush down the toilet), chemicals you spray in your yard, use or pour down the drain may reappear in trace levels in your well especially during dry months or drought.
Water is our most valuable resource and how we manage its use or allow its abuse may determine the fate of our country and mankind. Groundwater is an important natural resource, especially in those parts of the country that don't have ample surface-water sources, such as the arid West and in times of drought. Groundwater is a renewable resource, but not in the way that sun light is. Groundwater recharges at various rates from precipitation and surface water. Wastewater reuse is necessary to meet water supply needs, but we are contaminating our environment and our drinking water supplies with what we do not remove from our wastewater.
Wastewater has become a complex mixture of chemical and biological contamination. Pharmaceutical contamination in wastewater is a particular problem because the pharmaceuticals are highly soluble in water, highly mobile in the water compared to other wastewater contaminants, and pharmaceuticals are designed to be highly bioreactive with long shelf-lives. At the low levels found they can be toxic to stream ecology, cause endocrine disruption, immune-modulation and suppression and serve for antibiotic resistance selection. Water contamination will challenge mankind’s survival long before climate change.
Related blog posts and articles:
Barber, L., Keefe, S., LeBlanc, D., Bradley, P., Chapelle, F., Meyer, M., Loftin, K., Kolpin, D., Rubio, F., 2009. Fate of sulfamethoxazole, 4-nonylphenol, and 17bestradiol in groundwater contaminated by wastewater treatment plant effluent. Environ. Sci. Technol. 43, 4843e4850.
Barber, L., Antweiler, R., Flynn, J., Keefe, S., Kolpin, D., Roth, D., Schnoebelen, D., Taylor, H., Verplanck, P., 2011a. Lagrangian mass-flow investigations of inorganic contaminants in wastewater-impacted streams. Environ. Sci. Technol. 45, 2575e2583.
Barber, L., Keefe, S., Brown, G., Furlong, E., Gray, J., Kolpin, D., Meyer, M., Sandstrom, M., Zaugg, S., 2013. Persistence and potential effects of complex organic contaminant mixtures in wastewater-impacted streams. Environ. Sci. Technol. 47, 2177e2188.
Bradley, P., Barber, L., Kolpin, D., McMahon, P., Chapelle, F., 2007. Biotransformation of caffeine, cotinine, and nicotine in stream sedimentseImplications for use as wastewater indicators. Environ. Toxicol. Chem. 26, 1116e1121.
Bradley, P., Barber, L., Kolpin, D., McMahon, P., Chapelle, F., 2008. Potential for 4-nnonylphenol biodegradation in stream sediments. Environ. Toxicol. Chem. 27, 260e265.
Bradley, P., Barber, L., Duris, J., Foreman, W., Furlong, E., Hubbard, L., Hutchinson, K., Keef, S., Kolpin, D., 2014. Riverbank filtration potential of pharmaceuticals in a wastewater-impacted stream. Environ.Poll. 193, 173-180.