AWWA WQTC69453

The city of Raleigh, North Carolina's historical water quality compliance data has revealed that summer is the peak season 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 which accelerated by the high water temperature. With water conservation enforced, water will stay longer in the DS in the summer season than previous warm weather seasons. This may extend the formation of DBPs beyond the regulation levels, lead the chloramine residual below the minimum effectiveness level to suppress coliform growth, as well as provide 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 ensure the city complies with the federal and state regulations. A geographic information system- (GIS-)integrated computer model 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 its exceptional functionality for demand analysis, hydraulic simulation and water age analysis. The study first evaluated the effectiveness of the water conservation rules on total water savings. The monthly water billing records were collected and geocoded into GIS databases. GIS maps were generated to illustrate the demand change in each service area after water conservation. The study also investigated the influence of water conservation on daily water usage patterns, which affects water age variation in the DS. The diurnal demand curve for each pressure zone was calculated based on hourly supervisory control and data acquisition (SCADA) records in a typical operation day. The change of water age in the DS after the water conservation was simulated using the model with the updated demand, diurnal curves and operation methods. The areas with significant water age increase were identified as the high-risk locations of drinking water regulation violations after implementation of water conservation. Water quality improvements were proposed based on the modeling results. The improvements focused on system modifications to generate more recirculation which would be a more cost-effective method than flushing, especially during the drought. Includes 2 references, table, figures.