Scenario Analysis of the Impact on Drinking Water Intakes from Bromide in the Discharge of Treated Oil and Gas Wastewater

Elevated levels of bromide have been shown to contribute to increased formation of disinfection byproducts (DBPs). Both produced water from unconventional oil and gas wells, which are hydraulically fractured using high volumes of fluids, and produced water from conventional oil and gas wells, which are also typically hydraulically fractured but with lower volumes of fluids, can contain high levels of bromide. If these produced waters are treated in conventional commercial wastewater treatment plants, bromide may not be removed from the effluent and is discharged to receiving water bodies. Elevated bromide levels at drinking water plant intakes is a concern for public health reasons if elevated bromide levels cause elevated levels of DBPs. This study used data from commercial wastewater treatment plants and river flow data in western Pennsylvania to construct generic discharge scenarios that illustrate the potential impacts from disposal of five classes of water that were developed from flowback and produced water bromide concentrations. Months with the historical high and low flows in the Allegheny River (Pennsylvania) and Blacklick Creek (Pennsylvania) were chosen for simulation, and treatment plant discharge rates were set at 100, 50, 33, and 25% of the permitted value for the purpose of varying the mass loading. Steady-state simulation results showed the highest probably of impact, defined as concentrations above target levels of 0.02 and 0.10 mg/L, for produced water in the creek at both high and low flows (100%), and produced water in the river at low flows (>75%). High probability of impact (>50%) occurred in the river at low flows and all flows in the creek with treated mixed/flowback water discharge. Modeled reduction in the effluent discharge rate reduced downstream impacts proportionally. Transient simulation showed that transient peak concentrations may exceed time-averaged concentration by up to a factor of four when mixing conditions are met.