Shallow Groundwater Can be Contaminated by Wastewater

In a new study by the U.S. Geological Survey, contaminants such as pharmaceuticals from treated wastewater can travel into and contaminate shallow groundwater once the waters have released to streams.

In a new USGS study that was conducted in Fourmile Creek near Des Moines, Iowa, the results showed that shallow groundwater can still be contaminated by treated wastewater, even after the waters have released into streams. When the water was tested in October, 99 percent of the stream’s flow was wastewater. By December, wastewater made up 71 percent of the water flow. During these months, dry conditions allowed wastewater to contribute to contamination of the shallow groundwater systems.

"Water level measurements obtained during this study clearly show that stream levels drive daily trends in groundwater levels," said Paul Bradley, the study's lead author. "Combined with the detection of pharmaceuticals in groundwater collected several meters away from the stream, these results demonstrate that addition of wastewater to this stream results in unintentional, directed transport of pharmaceuticals into shallow groundwater."

"This research has important implications for the application of bank filtration for indirect water reuse," said Bradley. Bank filtration is the engineered movement of water between surface waterbodies and wells located a short distance away on the streambank. Bank filtration is routinely used to pretreat surface water for drinking water supply (raw surface water moves from the stream to a shallow groundwater extraction well) or as a final polishing step for the release of treated wastewater (treated wastewater moves from infiltration wells or lagoons through the bank to the stream).

The study also found that between 48 and 61 different pharmaceuticals were found in the downstream discharge areas. For more information, please click here.