Groundwater Under the Influence: What to Do When Process Changes Cause Turbidity Problems

Abstract

Sioux City, Iowa, obtains a large percentage of its drinking water supply from a horizontal collector well and 12 vertical wells adjacent to the Missouri River. Because the water supply is classified as groundwater under the direct influence of surface water, the city was required in the late 1990s to expand its treatment process to deal with potential surface water contaminants. After constructing a chlorine contact chamber to improve the disinfection contact time and replacing filter media to lower iron and manganese levels, the city's treatment plant experienced elevated, fluctuating turbidity levels and manganese oxidation after filtration. The treatment problems led to treatment technique violations, and the city had to conduct an extensive investigation into what caused the problems. After many parameters were investigated, the elevated turbidity levels were attributed to manganese oxidation after filtration, new filter media, and increased contact time. This article discusses the investigation, causes, and the operational changes implemented to control manganese oxidation and turbidity levels.