Water system optimization is important for all municipalities, including Goochland County, Virginia, a community located northwest of Richmond. In 2013, new leadership at the Department of Public Utilities (DPU) started an initiative to optimize the existing water system while planning for the future. As a result, they hired us to prepare Goochland County’s first-ever water and wastewater utility master plan.  

At the beginning of the project, we sat down with DPU staff to discuss the water system issues they had observed, which included low water pressures and fire flow availability as well as isolated areas of higher water age. The DPU staff was looking for us to develop solutions that would not only adequately solves these issues, but were also cost effective. In order for us to be able to accomplish their goals, we first had to build and calibrate a hydraulic model of the county’s water distribution system to allow us to evaluate and identify the sources of these issues.

Establishing Best Practices

The model was initially used to help identify areas where routine flushing was needed. We identified several areas where auto-flushers could be installed to reduce water age without overburdening DPU’s staff. We also developed the county’s first unidirectional flushing program by working with the operations staff to understand field conditions so that the plan was executable. Following the initial evaluation, we turned our focus to more holistically assessing the water distribution system and identifying potential projects that would improve water quality for the system overall.

An Obsolete Elevated Water Tank

This model helped us determine that many of the water system issues were caused by an elevated water tank in the southern zone, which was constructed roughly 40 years ago. When the tank was first constructed, it was set at the correct elevation and location for the surrounding area; however, as the system expanded the tank ultimately served a larger area and was not at an optimum location or hydraulic grade line. We found that this was the source of the low pressures and fire flow availability and significantly contributed to high water age. We recommended that Goochland County take the tank offline or remove it from operations. Although this may seem counterintuitive, we proved through our evaluation that keeping the tank operational did more harm than good for the customers of the water distribution system.

Interconnectivity Between Pressure Zones

The next issue we identified centered on the interconnection between two pressure zones. The existing system was designed with a 24-inch water main that connected the northern and southern pressure zones of the water system. This water main contained a control valve that separated the two pressure zones and was designed to open during a high flow event in the southern pressure zone; however, this meant that the main was not consistently turned over, which resulted in high water age. We recommended modifying the control valve to continuously allow flow from the northern to the southern zone with the addition of a parallel low-flow pressure reducing valve (PRV). This allowed us to utilize the storage capacity of the one-million-gallon elevated storage tank in the northern zone to supplement the storage needs in the southern zone. It also allowed for continual turnover of the 24-inch water main and decreased the water age in the entire system.

Chloramine Booster Station

Last but not least, we wanted to have the ability to accurately control the chloramine residual entering the county’s water distribution system. The chloramine residual entering the system was highly variable, which led to lower residuals in some areas of the system. In order to control this, we recommended and designed a chloramine booster station at the point of supply. This provided DPU’s operation staff with the ability to precisely control the influent chloramine residual, which helps minimize the low chloramine residual areas within the county water system.

In October 2018, we assisted DPU in developing standard operating procedures for chemical addition at the point of supply to decrease chlorine decay rates throughout the system. DPU selected an electrically bonded oxidizing agent, which specifically targets organic material anywhere in the distribution system, including private service lines. We worked with DPU to update the control logic at the chloramine booster station and provided recommendations for metering so that the chemical was dosed adequately. This, coupled with the previously described improvements, provided the county with significant control over the water system while maintaining a cost-effective project budget.

Delivering Cost-Effective Solutions

There was one main goal for this project: identify cost-effective solutions to address the water system issues. Through close collaboration with the client and dedicated individuals on both sides of the project—engineering and operations staff—we were able to develop these solutions in a timely manner, allowing DPU staff to have the tools they need to operate the water system efficiently. The key in achieving DPU’s goals was to develop a calibrated water distribution system model. The identification of these improvements would have been very difficult, if not impossible, without this valuable tool. While the development and calibration of a water distribution system model is an expense, it pays for itself many times over by helping to identify cost-effective solutions to optimize water distribution system operations.