Full Description

Two fluoride tracer tests were performed by the City of Fort Collins, Colorado during the period ofFebruary 20, 2006 through March 17, 2006. The first test was conducted with fluoride in decreasingmode. The second test was conducted immediately following the first test with fluoride in increasingmode.The purpose of this study was to provide data to:verify and refine the hydraulic and water quality calibration of the City's existing H2OMAPmodel and increase confidence in predicted velocity and flow patterns;increase understanding of factors influencing water quality within the WDS as well as evaluatethe formation potential of, and appropriate sampling locations for, disinfection byproducts andother water quality parameters in the WDS;examine the influence of treated water supplied from neighboring water district inter-connectionson water quality;comply with Initial Distribution System Evaluation (IDSE) requirements; and,examine various scenarios related to the introduction of contaminants directly into the WDS.Successful tracer tests require extensive planning. This includes identification of sampling sitelocations, frequency of sample collection, time to start each tracer test, determination of WDSoperational conditions, communication with the public and participating facilities, identification ofstaff to support sampling, assembling field equipment, documentation of sampling protocols,coordination with the laboratory analyzing samples, etc. Anticipation of, and preparation of responseplans to, changed conditions during the tracer test is also essential. Planning for the tracer tests wasbegun approximately six months prior to the first tracer test and culminated with the development of a75-page planning document outlining procedures for tracer test execution and contingency planning.The City's existing H2OMAP hydraulic model of its WDS was used as a tool to support preparationof the tracer test plan. Demand data sets were developed using historic February-March demand datafor the previous seven years of record. Using the H2OMAP model, response times todecreasing/increasing fluoride concentrations were estimated and considered in the selection ofsampling site locations, frequency of sampling, and time to begin each test. Sensitivity analyses wereperformed over the range of anticipated demand conditions to validate sampling protocols.During the tracer test, the H2OMAP model was used to predict the likely movement of the tracerthrough the WDS under the hydraulic conditions observed during the initial phases of each test toensure that the fluoride front was captured during sampling. Following the tracer test, results wereused to verify and re-calibrate the hydraulic model such that it more closely matched observed data.The results of tracer tests suggest excellent correlation between the H2OMAP water qualitysimulation and the field sampling results leading to a high degree of confidence in the hydrauliccalibration of the City's H2OMAP model and its use for Initial Distribution System Evaluation(IDSE) compliance. Includes figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 15File Size: 1 file , 820 KB