AWWA WQTC69453

The city of Raleigh, North Carolinas historical water quality compliance data has revealed that summer is the peakseason for elevated disinfection byproduct (DBP) levels and coliform outbreaks in the distribution systems (DS). The high water usage,however, helps flush the system, thus limiting the water quality deterioration whichaccelerated by the high water temperature. With water conservation enforced, water willstay longer in the DS in the summer season than previous warm weather seasons. Thismay extend the formation of DBPs beyond the regulation levels, lead the chloramineresidual below the minimum effectiveness level to suppress coliform growth, as well asprovide an ideal corrosion environment for lead and copper leaching into water.Evaluation of impacts of water conservation on water quality in the DS is essential to ensurethe city complies with the federal and state regulations. A geographic information system- (GIS-)integrated computermodel was developed to help assess the effects of water conservation on water quality.The model has been used successfully in recent master planning and IDSE study, with itsexceptional functionality for demand analysis, hydraulic simulation and water ageanalysis. The study first evaluated the effectiveness of the water conservation rules on total watersavings. The monthly water billing records were collected and geocoded into GISdatabases. GIS maps were generated to illustrate the demand change in each service areaafter water conservation. The study also investigated the influence of water conservationon daily water usage patterns, which affects water age variation in the DS. The diurnaldemand curve for each pressure zone was calculated based on hourly supervisory control and data acquisition (SCADA) records ina typical operation day.The change of water age in the DS after the water conservation was simulated using themodel with the updated demand, diurnal curves and operation methods. The areas withsignificant water age increase were identified as the high-risk locations of drinking waterregulation violations after implementation of water conservation. Water qualityimprovements were proposed based on the modeling results. The improvements focusedon system modifications to generate more recirculation which would be a more cost-effectivemethod than flushing, especially during the drought. Includes 2 references, table, figures.



Keywords: Water Conservation; Water Quality; Water Demand; Modeling; Disinfection Byproducts; Geographic Information Systems; Distribution Systems; Drought; North Carolina