Recovery of Stream and Adjacent Groundwater After Wastewater Treatment Facility Closure

A map of Fourmile Creek study area in Ankeny, Iowa, showing the locations of shallow groundwater piezometers, stream water sampling locations, and the direction of flow in the stream. Solid and dashed red arrows indicate the flow direction of the effluent from the wastewater treatment facility. Figure 1 from Bradley and others, 2016. Aerial photo credit: ArcGIS basemap, ESRI.

Contamination of stream water and adjacent groundwater in wastewater-impacted streams is a concern due to the presence of chemicals including pharmaceuticals in wastewater treatment facility (WWTF) effluent that are mobile in the environment and are specifically designed to be bioactive. In this study, scientists had the unique opportunity to assess hydrologic and chemical recovery processes in a stream and adjacent surficial groundwater system following WWTF closure. A combined pre/post-closure assessment (2012–14) was conducted near a long-term WWTF on Fourmile Creek in Ankeny, Iowa. Water samples were collected and water levels monitored continuously in the stream and adjacent groundwater located upstream and downstream from the WWTFoutfall. Water samples were analyzed for 110 organic chemicals including 107 human-use pharmaceuticals and degradates.

The hydrology and chemistry of the stream and shallow groundwater system responded rapidly to the WWTF shutdown. There was a nearly instantaneous decrease in water levels of surface-water and groundwater, and immediate elimination of the characteristic, diurnal wastewater-discharge pattern. The number of chemicals detected and cumulative concentrations decreased in Fourmile Creek and the adjacent groundwater. Although the numbers and concentrations of detected chemicals were substantially higher in surface water than in the adjacent groundwater system prior to closure, the reverse was true following WWTF closure. This finding is consistent with the adjacent shallow groundwater system acting as a continuing source of wastewater-derived contaminants to the stream for at least a year after WWTF closure. The persistence of wastewater-derived contaminants in adjacent groundwater suggests the potential for the shallow groundwater system to serve as a long-term source of wastewater-derived contaminants to the stream. Improved understanding of the environmental fate and transport of wastewater-derived contaminants is essential for understanding organism exposure and ecosystem recovery.

Before and after photos of Fourmile Creek near Ankeny, Iowa, showing a wastewater outfall from a wastewater treatment facility (WWTF). The top photo is the creek before the WWTFwas closed, and the bottom photo is after the WWTF was shutdown. After the shutdown flow in the creek decreased significantly. Photo credits: Laura E. Hubbard, USGS, Layout by David W. Morganwalp, USGS.

This study is funded by the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program.

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