Instream aeration has been used as a supplement to secondary treatment or a substitute for tertiary treatment for meeting dissolved oxygen (DO) standards in rivers.Many studies have used water quality models to determine the number, location, and capacity of instream aeration stations(IASs)needed to meet DO standards in combination with other pollution control measures.DO concentrations have been improved in the North Shore Channel and North Branch Chicago River by the Devon Avenue IAS for more than 35 years.A study was initiated to determine whether it was better to rehabilitate or relocate this station and to determine appropriate operational guidance for the IAS at the selected location. A water quality model capable of simulating DO concentrations during unsteady flow was used to evaluate the proper location for an IAS and operational guidance for this IAS.Three test years,a dry year,a wet year,and an extreme year,were considered in the evaluation.The study found that the Devon Avenue IAS should be rehabilitated as this location performed as well as or better than any of 10 altative locations. According to the new operational guidance for this IAS,the amount of time with blowers operating could be substantially reduced compared to traditional operations while at the same time the attainment of the DO standards could be increased.This study shows that a carefully designed modeling study is key to effective selection, location, and operation of IASs such that attainment of DO standards can be maximized while operation hours of blowers can be minimized.