A one-dimensional, steady-state, dissolved-oxygen model and waste-load assimilation study for the Mississinewa River, Grant County, Indiana

A digital model calibrated to conditions in the Mississinewa River, Grant County, IN was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The hydrology of the Mississinewa River downstream from Gas City is controlled primarily by two factors; low slopes, typical of the Tipton Till Plain, and a 10-foot dam at river mile 35.9, in Marion. All point-source waste loads affecting the modeled segment of the Mississinewa River are in the four incorporated municipalities of Fairmount, Jonesboro, Gas City, and Marion, in a primarily agricultural area. Model simulations indicate that algal photosynthesis and nitrification are the most significant factors affecting the dissolved-oxygen concentration in the Mississinewa River during summer low flows. Natural reaeration without photosynthesis, is not sufficient to maintain an average dissolved-oxygen concentration of at least 5 milligrams per liter in the stream, the State 's water-quality standard. Projected carbonaceous and nitrogenous biochemical-oxygen demand loads, from the Indiana State Board of Health, for Owens, Illinois, Inc., and the Gas City and Marion wastewater-treatment facility will result in violations of the instream dissolved-oxygen standard. Fairmount and Jonesboro, because of their distance from the Mississinewa, do not significantly affect the water quality of the modeled segment. The model also indicates that, during winter low flows, ammonia toxicity, rather than dissolved oxygen is the limiting water-quality criterion in the Mississinewa River downstream from the Gas City wastewater-treatment facility. (USGS)