Craven County Water: Change in Operating Strategy Utilizing Hydraulic Modeling

Prepared for the 2014 NC American Water Works Association & Water Environment Association (AWWA-WEA) Annual Conference by Brian T. White, PE and Christopher L. Windley, PE

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The purpose of this paper and presentation is to discuss the implementation of hydraulic modeling to assist Craven County with major operational changes in its water distribution system in conjunction with the design and construction of a new water treatment plant.

In the Central Coastal Plain of North Carolina, groundwater from the Cretaceous aquifer system is being withdrawn at a rate that exceeds the available recharge. In 2002, the Central Coastal Plain Capacity Use Area (CCPCUA) regulations were established to reduce existing groundwater withdrawals from the Cretaceous aquifer system. The regulations call for a 25 percent reduction every five years over a 15-year period, equivalent to an overall withdrawal cutback of 75 percent. The cutback will result in a raw water supply shortfall for the county. Therefore, McKim & Creed teamed with the county to design and construct a new water treatment plant with water supply wells from the Lower Castle Hayne Aquifer.

The preferred site for the new plant is located in a central area of the county, proximate to the most populous area of the county and the higher water demands. The existing water supply wells, however, are more remotely located in the northern portion of the county. Adding a second major water supply source located in a different area of the distribution system required major changes in the county’s operational protocols.

The county and McKim & Creed collaborated to create a hydraulic water system model for the proposed improvements. The model served as an important tool in helping to develop a control strategy that would optimize how the proposed water system improvements would be integrated into the existing system, while minimizing impacts to existing infrastructure and customer supply.

The county staff provided valuable feedback on the system configuration and current operations, and assisted with providing calibration data from the county’s SCADA system. The team modeled several new operating scenarios. A well-calibrated extended period model proved to be the key to optimizing the operational changes necessitated by the new facility. At the same time, the new control strategy helped to reduce infrastructure and costs by eliminating one booster pumping station and reducing run times at a second booster pumping station. These changes in operations will also increase turnover volumes in the elevated storage tanks, in turn helping improve water quality within the distribution system.

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