Nestled in Tennessee's Great Smoky Mountains, Pigeon Forge is home to a variety of special events and entertainment venues. During the nine-month tourism season, the town's population of 5500 swells on weekends to more than 70,000. While weekend tourism contributes to local business receipts, increased demands on the town's infrastructure can overwhelm services offered by the public works department, particularly at the water treatment plant.
From daily showers to commercial water rides, water consumption by tourists challenged the output capacity of Pigeon Forge's 4-mgd water treatment plant. On especially high-demand weekends, city officials requested residents adopt special conservation measures. The problem was not a supply issue—the city has an abundant water supply—but rather the ability of its current plant to produce enough drinking water. In 2000, the city took action and agreed to triple the existing water plant's capacity to meet its skyrocketing demands.
In addition to boosting output, city officials sought to streamline the plant workflow. During an average shift, workers were responsible for maintaining, inspecting, and operating the raw water intakes, storage tanks, and filter plant. With the expansion plan, the current staff would be overwhelmed and unable to perform all of the required operations.
The water plant needed to incorporate data management technology to comply with new U.S. Environmental Protection Agency requirements that mandate all water production facilities retain a continuous data log of plant processes and continually create backup data files. The district also needed to improve security for its remote pump house, in response to the U.S. Department of Homeland Security vulnerability assessments.
Pigeon Forge chose to use a design-build approach to handle the automation portion of their plant upgrade. By doing so, plant managers were able to partner with consulting engineers and system integrator Smith Seckman Reid Inc. (SSR), Nashville, Tenn., and Rockwell Automation, headquartered in Milwaukee, to meet the city's goals of tripling water plant capacity, streamlining workflow, meeting documentation requirements, and increasing security.
To meet reporting requirements, immediate access to information at multiple points in the process was crucial. SSR recommended upgrading the existing relay panels to intelligent motor control centers (MCCs) and a computer monitoring system. This system would give operators a view of the entire process, including access to predictive-failure information, EPA compliance reports, and monitoring information-a vast improvement from the previous system that offered limited information throughout the process.
The water treatment process begins 17 miles from the plant site. There, water is drawn from Douglas Lake and pumped into a 300,000-gallon, above-ground concrete basin. From this tank, four transfer pumps are used to convey the raw water through 12 miles of water main to the plant and into one of four blending basins, with a flash mix added to isolate and destroy harmful bacteria. Next, the water is pumped into eight floculation basins, where the chemicals from the flash mix interact with the water to create floc, or chemically bonded clumps for sedimentation.
As water is transferred into the sedimentation basins, the floc settles to the bottom where large paddles scrape the collected floc into troughs and transfer it to the nearby wastewater treatment plant for processing. As treated water moves to the interior filtering basins, it is filtered once more before moving to the plant's clear well. The treated water is stored at system inventory sites throughout the district's service area.
Upgrades to the plant's MCC provided an array of operational and electrical information, including predictive failure alerts, to plant operators allowing for notification of system problems prior to system failures. Motor currents that approach a predetermined excessive value trigger a blinking message on the human-machine interface (HMI). This alert now gives operators time to determine the nature and location of problems and correct them before an overload occurs. In some cases, the programmable controller automatically shuts down the system to protect plant assets.
For central processing and remote terminal unit control, Pigeon Forge selected ControlLogix and MicroLogix controllers from Allen-Bradley, a division of Rockwell Automation. Installing controls at each blending basin allows plant workers to choose which pump to turn on and gives them the ability to adjust the blending speed as needed. A combination of drives and motor starters located inside networked, intelligent MCCs regulate pump and blending speed.