SCADA Makes its Way to Northwest Arkansas
By Robert Daffer, Burns & McDonnell
Springdale, Ark., is a city nestled in northwest Arkansas just north of Fayetteville. Springdale`s water and wastewater utilities serve the nation`s largest poultry-producing center, making demands on the city`s water and wastewater utilities disproportionate to the population. Springdale Water Utilities (SWU) purchases finished water from the Beaver Water District located on the beautiful Beaver Lake Reservoir. The utility stores and repumps the water to its 17,500 water connections, but with the industrial resale load, the utility`s storage requirement is capable of rising to 25 million gallons to meet the demands. The wastewater site of Springdale`s operation has 14,000 sewer connections supported by a 15.6 MGD (millions of gallons per day) treatment plant.
Springdale experienced a very positive population growth which equated to more sales for the utility. But, there was a problem. Its existing SCADA system was aging rapidly and not keeping up with needs. SWU`s system, which provided monitoring through a vulnerable VHF radio system, utilized proprietary hardware and software. It was slow and unreliable, especially during storms when it was needed the most. Springdale was experiencing labor overtime during each storm event where operation and maintenance crews had to be called out to physically man certain critical pumping stations. Ultimately Bob Daffer of Burns & McDonnell Engineering Co., was called to take a look at this situation by the utility`s executive director, Rene Langston.
SWU had already taken the first step to improve its situation by applying for a new radio license for its SCADA system. The Federal Communications Commission had granted the utility a licensed pair of multiple address system frequencies in the 928/952 MHz band. Daffer, recognizing the time limit of 12 months to put an operating SCADA system on the new frequencies, advised SWU of several fast-track options that would meet the deadline. The preferred option provided for the design, procurement of equipment, installation and start-up to occur within a three-month window. This plan would meet the deadline of having an operational radio SCADA system on the MAS frequencies. To meet this ambitious schedule, the SCADA system was designed around off-the-shelf, readily available components.
To meet the economic constraints of the budget, a system was designed so the SWU staff could install the equipment itself. To meet this goal at each remote site, the new SCADA remote was designed to fit a backplate panel that would fit inside the existing enclosure. After Springdale`s staff removed the existing equipment, the new SCADA equipment was mounted on a new backplate which was then installed in the existing enclosure. This proved to be the most economic and expedient solution. A qualified SCADA vendor was chosen to provide programming and system start-up.
The new system, as designed, had the following features:
Each remote site had an Allen Bradley PLC consisting of totally off-the-shelf components.
Digital radios were manufactured by Microwave Data Systems.
The radio master was located on top of Dodd Mountain which provided total radio coverage to all the remote sites. The digital radios operated on a clear channel at 928/952 MHz with a data speed of 4,800 baud.
The radio system had built-in diagnostics for remote access. The operator stations consisted of standard 486-type PCs.
The operating software was a Windows-based system by Wonderware, which is extremely user friendly.
The system is operated from three stations. The main operator station is a PC located at the wastewater treatment plant and manned 24 hours a day. From the operator`s station, the plant operators can monitor and control all of the six water sites and the 15 lift stations in the water utility`s service area. Another operator station is located at the SWU office, where it is available to the executive director. Langston can instantly monitor the condition of the utility systems and has the ability to quickly obtain a report on any of the utility`s parameters. The third operator station is located at the Beaver Water District. This station allows the Beaver water personnel the ability to monitor the water delivered to one of Springdale`s major pumping stations. In return, it allows SWU to obtain the flowmeter readings and the run status of the high service pumps at the Beaver Water District. In addition, there is a color laptop computer that is available to the executive director and his staff to dial into the SCADA system via modem from their home. After hours or on weekends, an operator can go on line remotely, thus having total privileges of operation or control of the SCADA system.
This remote dial-in capability also allows Daffer to dial into the system from his office in Kansas City, Mo. Whenever questions about the system arise, it is much easier to call the plant and go on line at an operator station (and answer the questions right on the spot) rather than driving four and a half hours one way to offer the same solution. This is much more convenient and economical for SWU.
In addition, the system design provides for remote diagnostics of the entire radio system. At the Dodd Mountain site, the master radio has a modem connected to its diagnostic port which ties it into the telephone system. The utility`s maintenance staff can dial into the master radio on Dodd Mountain and run a radio diagnostics which gives it a “health” report of all of the radios in the SCADA system. Daffer can also accomplish this from his computer in his Kansas City office. In any radio system there can be a little bit of frequency drift over time, allowing you to tweak all the remotes back on frequency remotely on a periodic basis.
Besides improved reliability, the new SCADA system also solved many operational problems. The water system is designed so that a SCADA system can monitor the water level in each elevated tank. Based on the water level setpoints, which are changeable by the operators, the system automatically keeps the tanks full within pre-established ranges. The operator can easily adjust the start/stop elevation for the pumps or the alarm setpoints if seasonal adjustment is necessary. This makes the water operation totally automatic and operator attention is required only if an alarm goes off.
The wastewater system had a more demanding problem, especially when there was a major storm in Springdale. Some of the lift stations actually pump through force mains into other downstream lift stations. Because of heavy rains they overpump into downstream lift stations causing backup of wastewater into places that are undesirable. Before the SCADA improvements, Springdale needed to dispatch personnel to these pump stations to put them in manual operation and reduce the amount of pumping. By doing this, the wastewater would be curtailed from overflowing into the downstream system. This was a major operational inconvenience and caused extra labor cost for the utility during each of these events.
With the new SCADA system, the operator at the wastewater treatment plant at the SCADA control center has complete control over the situation. When a storm occurs, sometimes the pumping stations begin to overpump. Then, the operator, simply by using the mouse and pointing and clicking on the graphic screen, can inhibit certain pumps in specified stations so they will not overpump. An operator who is already on duty at the wastewater treatment plant can have total control of the situation that normally required the labors of several people who would be called in only for the storm.
In another situation, there was one wastewater line downstream from a pump station that was rather long and flat in nature and had the problem of solid buildups during time of low flow. With the new “Smart” control offered by the PLC at this lift station, the system is now purged on a daily basis. This is accomplished by allowing the wet well to fill up as high as possible and then starting all of the pumps in the lift station to increase the velocity as much as possible through the force main. This has the effect of scouring the line and removing the settled-out solids. This is just another example of how a new advanced SCADA system can solve existing operational problems. “Our new system has allowed us to adopt a proactive approach vs. our former reactive approach,” said Langston. “We have gained more control over critical elements of our systems and an easily retrievable history of past operating information that is useful in forecasting future requirements.”
Robert Daffer is a project manager at Burns & McDonnell. He has worked with Burns & McDonnell for 25 years and specializes in SCADA projects. He has a bachelor`s of science degree in electrical engineering from the University of Nebraska.
Rick McCoy of Springdale Municipal works on the wastewater plant`s operator station.
Master radio for the Springdale SCADA system.