A WATER-QUALITY MODEL FOR A RIVER RECEIVING PAPER-MILL EFFLUENTS AND CONVENTIONAL SEWAGE

During low flow periods in summer, portions of the Pigeon River, North Carolina, have experienced depressed dissolved oxygen concentrations. The Pigeon River receives multiple point source effluents from several wastewater treatment facilities and a large kraft paper mill located in Canton, NC which contribute the oxygen-demanding and nutrient loads to the river. A water quality model was constructed, from survey data specifically collected to meet the model's requirements, to examine the processes and sources contributing to the observed oxygen declines and the evaluate specific management alternatives. The model was validated using two independent data sets. Simulations showed that relatively little of the CBOD materials released by the mill were degraded within the river and were subsequently 'deposited' in the reservoir at the end of the modelled river segment. Reductions in CBOD concentrations could be generally accounted for by tributary dilution. However, nitrogenous oxygen demanding materials released by the mill (e.g., NH3) created a considerable demand for oxygen within the modelled segment of the river. Model results showed this relatively rapid degradation of NBOD could depress oxygen levels to low levels (i.e., < 4 ppm) if artificial oxygenation was not used to supplement existing concentrations. The model also showed the majority of this oxygen supplement was released to the atmosphere and not maintained within the water column. Model analyses showed that the effluents associated with the wastewater treatment facilities had little effect on the water quality of the Pigeon River.