Modeling Storm Overflow Impacts on Eutrophic Lake

A mathematical model was developed to predict the transient impact of storm loads on phosphorus, fecal coliform, and dissolved oxygen concentrations in Onondaga Lake and determine the need for control of storm overflows. Model simulations demonstrated that combined sewer and storm loads have a significant impact on lake fecal coliform but little effect on phosphorus, CBOD, NBOD, and dissolved oxygen in Onondaga Lake. Observed variations in lake dissolved oxygen were caused by changes in chlorophyll a, light, and wind. Control of storm loads is recommended to alleviate violations of fecal coliform water quality standards but not for improvement of dissolved oxygen concentrations. As a consequence of the modeling analysis, a limited control program for combined sewer overflows was designed which included only disinfection and removal of objectionable solids. Reductions in storm loads of nutrients and BOD would not provide any significant improvements in lake water quality and were not recommended.