AWWA WQTC62615

The City of Sioux City (City) obtains a large percentage of its drinking water supply fromboth a horizontal collector well and vertical wells located adjacent to the Missouri River.These wells are screened in either the Missouri Alluvium or the Dakota Sandstoneaquifers. Several of the collector well's laterals extend beneath the Missouri River. Thissituation led to Sioux City's groundwater system being classified as "Groundwater Underthe Direct Influence of Surface Water" by the Iowa Department of Natural Resources(IDNR). This classification led to the IDNR requiring Sioux City to expand its treatmentprocess to deal with potential surface water contaminants.With several options available to the City, all of which carried expensive price tags, theCity and Olsson & Associates (OA) conducted a riverbank filtration study. The results ofthis study and the statistical data gathered provided all parties with a clearer picture ofthe plant improvements that would be necessary to meet the IDNR requirements. TheCity and OA proceeded with design and construction of a contact chamber to improvethe disinfection contact time of the treatment system. The Iowa Department of NaturalResources granted Sioux City 4.0 log removal for Giardia and 3.5 log removal forCryptosporidium through the riverbank and treatment plant, provided Sioux City metagreed upon lower turbidity levels and surrogate parameters and required at least 0.5log removal through disinfection (contact time).Construction of the contact chamber and additional plant upgrades including theelimination of bottlenecks within the treatment plant, chemical system upgrades andreplacement of filter media were part of this process. Following the improvements, SiouxCity experienced treatment problems and ultimately Treatment Technique Violations forTurbidity. This led to an extensive investigation of the causes of the turbidity problems.Many parameters were investigated, with the conclusion determined to be that with thenew media and the increased contact time, manganese was being oxidized in thecontact chamber and was the cause of the turbidity problems. This presentation outlinesthe investigation, cause and operational changes to control the manganese oxidationand turbidity levels. Includes 2 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

8

File Size:

1 file , 470 KB