Decreases in Pollutant Loading from Residual Soda Ash Production Waste

The attenuation of residual industrial loads of chloride (Cl^-) and total ammonia (T-NH₃) from Solvay waste bedsto Ninemile Creek, New York, and downstream polluted Onondaga Lake, is characterized and quantified based on fourteen years ofmonitoring following closure of a soda ash manufacturing facility. Concentrations of these constituents were monitored atleast bi-weekly at two sites on Ninemile Creek that bound the waste bed inputs, and at the mouths of the two other major tributaries to the lake, to quantify inputs from the industrial deposits and to place these residual loads in the perspective of contributions to total lake loading. Variations in the concentrations of these constituents in Ninemile Creek downstreamof the industrial inputs within individual years are well represented by a dilution model; i.e., linearity of concentrationversus inverse stream flow. A relatively uniform ratio of T-NH₃ to Cl^- has been maintained in the residual loading, about 0.42 g T-NH₃ per kg Cl^-. Substantial decreases (～40%) in loading of these constituents fromthe waste beds to Ninemile Creek over the post-closure period are documented through shifts in the dilution model. As a result,the contribution of this source to the total lake loading has decreased from ～45% to <30%. The estimated total residual Cl^- load received from the waste beds since closure of the industry (～1 million metric tons) corresponds to ～1.6 yr of the full operating load of the industry before closure. The time required to reach a Cl^- concentration goal for Ninemile Creek is considered, based onprojections of the post-closure trend.