AWWA WQTC64137

The distribution system for the City of Clearwater, Florida provides 13 MGD of chloraminatedwater through approximately 588 miles of pipeline. Since the inception of the total coliform rule(TCR), routine monitoring of 110 distribution system samples per month has rarely yieldedpositive samples. However, an increased incidence of positive total coliform samples occurredduring the height of Florida's 2004 hurricane season. In response to the positive TCR samplingresults, the City of Clearwater embarked on an extensive sampling campaign and expanded waterquality monitoring efforts throughout the distribution system. In conjunction with the additionalmonitoring, a comprehensive audit was conducted to identify potential reasons for the coliformexcursions and to develop measures to prevent future occurrences. The audit included geographic information systems (GIS)mapping of water quality patterns, hydraulic modeling of the variable flows and pressuresassociated with hurricane preparation and evacuation activities, operational simulations, fieldinspection of sampling sites, and a detailed analysis of water quality and supervisory control and data acquisition (SCADA) data.An extensive GIS database was developed to allow for mapping of sampling sites, watertreatment plant and storage tank locations, interconnects, customer complaints, and the locationof construction and flushing activities. A hydraulic model was integrated with the GIS databaseand used to assess flow and pressure variations throughout the distribution system under normaland abnormal operating conditions. System dynamics were examined further with a review ofSCADA data, simulations of abnormal operations, and field testing. In addition, comprehensivereviews were conducted of historical water quality data, treatment system operations, disinfectionresiduals, sampling and testing procedures, cross connection control practices, flushing activities,and construction activities in an effort to simulate the conditions associated with the positive TCRresults.While the increased incidence of positive total coliform samples could not be traced to a singlecause, it is likely that the storm-induced shutdowns and post-storm start-up operations resulted inshort-term localized perturbations in water velocities and flow directions. Collectively, changes inflow direction and velocity may have mobilized bacteria from biofilms or introduced bacteriathrough intrusion or other mechanisms. In addition, some samples may have been contaminateddue to flooding of sampling ports. Based on the findings of the audit, the City of Clearwater hasmodified its hurricane response plans for management of water treatment and pumping facilities,updated procedures and operational controls, implemented above-grade dedicated sampling taps,and modified sampling protocols. The lessons learned from this experience are presented inthis paper and should be of interest to other utilities in hurricane-prone or flood-prone regions. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

7

File Size:

1 file , 800 KB