US Fish & Wildlife Service


Date of this Version



Published in Contaminant Report Number: R6/710C/98, 1-27, (1998)


Oilfield produced water is generated from the extraction of oil mixed with groundwater. A separator is used to physically remove the water from the oil; however, the produced water can contain residual amounts of oil. Additionally, malfunction of the separator equipment can cause inefficient separation and result in higher amounts of oil in the water. The Wyoming Department of Environmental Quality (WY DEQ) regulates the discharge of produced waters under the National Pollution Discharge Elimination System (NPDES) .WY DEQ permits 10 µg/l of oil in produced water discharged into regulated waters of the state. Produced water discharges are not permitted into Class I waters (surface waters protected from degradation from point source discharges) and semiannual bioassays are required for discharges into Class II waters (streams supporting game fish). Discharges into Class III (streams supporting a non-game fisheries) and Class IV (intermittent streams) waters only require annual water quality analyses. Lawrence et al. (1994) concluded that the criteria allowing 10 µg/l of oil in produced water does not assure protection of aquatic communities.

The original objectives of the study were: 1). to determine if wastewater discharges are contributing potentially adverse concentrations of contaminants into wetlands providing important habitat for aquatic birds or threatened and endangered species; and 2). assess the practicability of using MICROTOX ® and sediment pore water bioassay tests for screening potential contaminant problems. Given the limited amount of funding and staff, we focused primarily on oilfield produced water discharges as they have the most potential of all permitted discharges in Wyoming of contributing adverse concentrations of contaminants into wetlands. Limited staff and time prevented us from adequately pursuing the second objective.