Lee Hall and Harwoods Mill Surface-Water Treatment Plants, VA, USA

Newport News Waterworks (NNWW), one of the 100 largest water utilities in the United States, recently implemented an integrated supervisory control and data acquisition (SCADA) process control system in its two surface-water treatment plants, Lee Hall and Harwoods Mill, in Virginia, USA. This SCADA system provides utility-wide monitoring and control of both in-plant processes and remote distribution system facilities.

PROJECT RATIONALE

In the past, an ageing SCADA system was used at one of the two water treatment plants, (Harwoods Mill), and 17 remote sites (including pumping stations with ground storage tanks, elevated storage tanks, pressure monitoring sites, and raw water pumping facilities). This used out-of-date hardware and software, which would have been unable to cope with future developments and expansions over the coming decade.

Furthermore, the existing SCADA system did not have the expandability or performance capability to control and monitor a new reverse osmosis (RO) facility, a peak-shaving generator facility, and a residuals handling facility.

A further reason why the company's SCADA system had to be upgraded was a result of the NNWW's participation in the Partnership for Safe Drinking Water Program. This program, sponsored by the American Water Works Association (AWWA), requires the utility to monitor water quality parameters by adding monitoring devices with serial communication ports, such as particle counters and other on-line devices.

Finally, the system also had to be able to integrate the Lee Hall Water Treatment plant, eight miles away, so that both plants worked from a single system.

Thus through a public relations program and intensive planning, NNWW changed its disinfection practice from chlorine to chlorimes with a minimum of customer complaints and inquiries.

NEWPORT NEWS WATERWORKS PROJECT MAKE-UP

NNWW worked alongside a team of information technology (IT) and engineering professionals from Westin Engineering, of Rancho Cordova, California, to implement the changes. Ammonia feed processes and their associated in-line monitoring equipment were installed, tested and brought online parallel with the new system.

HSQ Technology was selected as the system vendor, and replaced vintage remote terminals units (RTUs) with modern intelligent RTUs at all of the remote sites. Two Allen Bradley programmable logic controllers (PLCs) were installed inside the Harwood's Mill Water Treatment Plant, each using redundant CPUs with bumpless hot failover.

Hot changeover from the existing control system to the new SCADA/process control system took place while the facilities remained in production. This was done with no degradation in system performance, production, or water quality. A carefully planned and rehearsed sequential cutover of monitoring and control modules, process by process, was undertaken.

Each plant, as well as the remote facilities, was set up with its own server. This enables monitoring of each facility from either plant, protecting the utility from man-made and natural disasters. The Lee Hall plant will be un-manned the majority of the time and controlled from the Harwood's Mill facility. The network between the facilities was designed to support monitoring both through the SCADA system and closed circuit television, and its distributed processes were designed to be monitored and controlled from either of the two plants.

A fibre-optic cable was buried to support a wide band data link between the two plants, and was backed up by an automated failover to frame relay communication, in the event of a break in the cable. Furthermore all I/O points in each plant communicate via campus-wide fibre-optic Ethernet local area network (LAN) between the control system and PLCs.

RTUs communicate with the primary SCADA server via frame relay circuits and an internal dial-up modem provides backup communication capability. At three remote sites, where data is not needed on a continuous basis but only on operator demand, communication is established solely by dial-up modem.

The system comprises two virtual wide area networks (WANs), simultaneously sharing the telecommunications infrastructure and every workstation can log onto either the process control (PC) or process information (PI) virtual WAN.

The SCADA process system is a fully redundant system that provides constant control and monitoring of NNWW's entire storage, treatment, and distribution system