Abstract

The U.S. Geological Survey (USGS) in cooperation with the city of Sioux Falls conducted several rounds of sampling to determine the occurrence of organic wastewater compounds (OWCs) in the city of Sioux Falls drinking water and waste-water effluent, and the Big Sioux River in or near Sioux Falls during August 2001 through May 2004. Water samples were collected during both base-flow and storm-runoff conditions. Water samples were collected at 8 sites, which included 4 sites upstream from the wastewater treatment plant (WWTP) discharge, 2 sites downstream from the WWTP discharge, 1 finished drinking-water site, and 1 WWTP effluent (WWE) site.

A total of 125 different OWCs were analyzed for in this study using five different analytical methods. Analyses for OWCs were performed at USGS laboratories that are developing and/or refining small-concentration (less than 1 microgram per liter (μg/L)) analytical methods. The OWCs were classified into six compound classes: human pharmaceutical compounds (HPCs); human and veterinary antibiotic compounds (HVACs); major agricultural herbicides (MAHs); household, industrial,and minor agricultural compounds (HIACs); polyaromatic hydrocarbons (PAHs); and sterol compounds (SCs). Some of the compounds in the HPC, MAH, HIAC, and PAH classes are suspected of being endocrine-disrupting compounds (EDCs). Of the 125 different OWCs analyzed for in this study, 81 OWCs had one or more detections in environmental samples reported by the laboratories, and of those 81 OWCs, 63 had acceptable analytical method performance, were detected at concentrations greater than the study reporting levels, and were included in analyses and discussion related to occurrence of OWCs in drinking water, wastewater effluent, and the Big Sioux River.

OWCs in all compound classes were detected in water samples from sampling sites in the Sioux Falls area. For the five sampling periods when samples were collected from the Sioux Falls finished drinking water, only one OWC was detected at a concentration greater than the study reporting level (metolachlor; 0.0040 μg/L).

During base-flow conditions, Big Sioux River sites upstream from the WWTP discharge had OWC contributions that primarily were from nonpoint animal or crop agriculture sources or had OWC concentrations that were minimal. The influence of the WWTP discharge on OWCs at downstream river sites during base-flow conditions ranged from minimal influence to substantial influence depending on the sampling period. During runoff conditions, OWCs at sites upstream from the WWTP discharge probably were primarily contributed by nonpoint animal and/or crop agriculture sources and possibly by stormwater runoff from nearby roads. OWCs at sites downstream from the WWTP discharge probably were contributed by sources other than the WWTP effluent discharge, such as stormwater runoff from urban and/or agriculture areas and/or resuspension of OWCs adsorbed to sediment deposited in the Big Sioux River. OWC loads generally were substantially smaller for upstream sites than downstream sites during both base-flow and runoff conditions.

In general, HPCs and HVACs accounted for relatively small portions of the total OWC concentrations in water samples collected from all sampling sites. MAHs generally accounted for a relatively small part of the total OWC concentrations during base-flow conditions for all sites, and for a substantial part at the river sites during some but not all stormrunoff sampling periods. HIACs generally accounted for a substantial part of the total OWC concentrations in samples collected from the WWE site during all sampling periods. In samples collected from downstream sites, HIACs generally accounted for a substantial part of the total OWC concentration during base-flow conditions and during some but not all of the storm-runoff sampling periods. PAHs only were detected at Big Sioux River sites that might be substantially affected by stormrunoff from roads. PAHs were not detected during any baseflow sampling period and were detected during some but not all storm-runoff periods. SCs generally comprised a substantial part of the total detected OWC concentrations for WWE and Big Sioux River sites during both base-flow and storm-runoff conditions. Results indicate that the WWTP discharge substantially contributed to the occurrence of OWCs in the Big Sioux River during below-normal base-flow conditions.

There were no human-health concerns apparent in the results of this study. Occurrence of EDCs in aquatic systems is a very complex and sensitive issue. A complete assessment of potential effects of EDCs in the Big Sioux River in or near Sioux Falls based on the results of this study is not possible. However, EDC concentrations in the Big Sioux River generally were less than concentrations reported to have substantial endocrine-disrupting effects on aquatic organisms. The relatively large frequency of detection for atrazine might indicate a cause for concern with respect to endocrine-disruption effects for aquatic organisms.