RISK-EQUIVALENT SEASONAL DISCHARGE PROGRAMS FOR ICE-COVERED RIVERS

Seasonal waste discharge (SWD) programs allow different waste-discharg e rates during different seasons of the year and reduce the cost of wa ste treatment. The efficiency of such programs for managing biochemica l oxygen demand (BOD) and dissolved oxygen (DO) may be affected by red uced reaeration and slowed BOD decomposition on river systems that hav e ice-cover conditions. This paper presents a modified SWD program for managing BOD and DO in river systems that have ice cover during certa in periods of the year. The program designs a set of seasonal uniform treatment removal levels such that the average percent removal over th e year is minimized and the risk of water-quality violation is equal t o that which would occur under a nonseasonal waste-discharge program. The uniform treatment levels during the ice-covered period are evaluat ed by simulating water quality based on reaeration coefficients that a re nearly zero. Application of this program to a section of the St. Jo hn River indicates that the treatment levels for the ice-covered seaso n are not the highest treatment levels required during the year. This suggests that the water-quality responses resulting during the ice-cov er period are not the most critical conditions for the St. John River. A sensitivity analysis shows that such results occur even when the BO D decay rate is increased to a high value during the ice-covered perio d. Evaluation of two- and four-season SWD programs for the St. John Ri ver indicate that in the two-season case there is no advantage to sepa rating the ice-covered period from other times of the year and that on ly marginal savings can be achieved by using a four-season program ins tead of a two-season program.