Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

Abstract

Regional rural water systems construct water storage tanks at strategic locations to maintain water pressure and meet demand variations in their distribution systems. These tanks are typically not artificially mixed and exhibit a wide range of height to diameter ratios, factors which can contribute to stratification during months of warm temperatures. Stratification can cause high water age, leading to loss of chlorine residual resulting in microbiological growth and nitrification in chloraminated waters. Artificial mixing can reduce or eliminate stratification, but equipment and power add to the cost of water. This thesis presents the results of water quality studies of several representative geometries of storage tanks used in South Dakota's regional rural water systems, both by modeling and physical data. Representative tanks were selected based on a survey of regional water systems. Temperature measurement and water sampling systems were installed in these tanks to examine water quality as a function of depth. Stratification was found in several geometries as indicated by temperature profiles and by chlorine, ammonia, nitrite and nitrate concentrations measure at various depths of the tanks. The impacts of operational factors, such as varying water depth, daily water level cycling, and mixing with ice-prevention mixers and pumped recirculation on water quality profiles are presented. Various hydraulic mixing parameters and systematic models were evaluated and compared with experimental data to examine the adequacy of these parameters in predicting mixing in tanks. Results of this study were used by systems to examine strategies to minimize water quality variations in tanks while maintaining adequate pressure and emergency storage requirements. Tall standpipes analyzed in this study experienced substantial loss of disinfectant residuals as a result of thermal and water quality stratification. Three strategies were employed by the systems operating two of those tanks in attempts to restore disinfectant residuals. An ice- prevention mixer was installed in one tank, which proved inadequate at restoring residuals in the upper zone of the tank, and the system elected to overflow the tank. The other system drained a large portion of the tank contents into the system, allowing fresh water to fill the tank. Both overflowing the tank and draining the contents into the system were effective strategies to restore disinfectant residuals in the upper zone of the tank.

Library of Congress Subject Headings

Water-supply, Rural -- South Dakota

Tanks -- South Dakota

Water quality

Format

application/pdf

Number of Pages

287

Publisher

South Dakota State University

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