Leadville Cleans Up Watershed
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Situated at the uppermost origins of the Arkansas River in the heart of the Rocky Mountains west of Denver, the city of Leadville, CO, carries the scars of decades of mining for gold, silver, copper, and other valuable metals. Starting out as a prospectors’ mining camp in the 1860s, Leadville has the highest elevation of any incorporated city in the U.S., which presents a number of unique problems.
In spite of its remote location, the area surrounding Leadville was mined heavily, leaving countless tunnels deep in the mountain sides. During times of the most intensive digging, there was no easy way to get natural ground and rain water out of the mines, so miners cut horizontal channels underneath the tunnels and mining infrastructures so water could flow down and out to the Arkansas River. To help this process, the Leadville Mine Drainage Tunnel (LMDT) was built by the U.S. Bureau of Mines to drain off water from certain areas of the mining district. Completed in 1952, the tunnel runs approximately 120,000 feet to the south-southeast to an area just outside of Leadville.
By the 1980s, tremendous amounts of water had collected and were continuing to accumulate in abandoned and deteriorating mines; metals and residues that collected in this water made it very acidic. Water that drained out of these mines was so reactive that it could scald the feet and legs of animals that would wade through affected waterways. After an EPA assessment, multiple areas in and around the Leadville Mining District were declared unsafe for human occupation and designated a U.S. EPA Superfund sites.
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The Bureau of Reclamation acquired the LMDT in 1959 and assumed sole responsibility for it after the U.S. Bureau of Mines was disbanded in 1996. Since 1992, it has treated water flowing out of the tunnel to remove dissolved metals and bring water quality into compliance with the regulations and standards for safe discharge into the Arkansas River. Eugene Csuti of the Bureau of Reclamation has been principally responsible for the automation and electronics ised in this water treatment plant since 1996. He has specified, implemented, and maintained a comprehensive process control system to monitor water levels, provide warning of changing conditions, and to remove metals such as cadmium, lead, silver, and zinc. The system also adjusts the pH, reduces turbidity, and otherwise treats the water before releasing it in a cleaner state than everyday drinking water.
Early on in his work with the treatment plant, Csuti did a thorough study of the already-installed Opto 22 Mistic control platform, which included multiple G4LC32 controllers. He decided to update the system software to a newer platform that featured more intuitive Microsoft Windows-based programming, and an HMI development tool.
To manage the upgrade, Csuti worked with Opto-Solutions, an engineering and design firm specializing in machine automation, building and energy management, and other applications. That effort guided him to Opto 22’s Snap PAC System platform. The new system features Opto 22’s distributed architecture with standalone controllers communicating to I/O devices that monitor and control thousands of points. Opto 22 I/O includes individual processors capable of time-critical, processing-intensive, and repetitive tasks, such as high-speed counting, input latching, quadrature counting, and, perhaps most significantly, PID loop control. Because Opto 22 products are designed to be backwards compatible, Csuti was able to upgrade to the new software with its new features and added commands without having to alter his functioning controllers, field wiring, or I/O.
Part of Leadville’s treatment process involves adding sulfuric acid and other chemicals to the water to help contaminants solidify so they can be pumped out as sludge. Use of PID effectively regulates the sulfuric acid injection process and helps keep the pH in an acceptable range, typically from 7.8 to 8.0.
“We set up our Opto system to connect to chemical dosers; the PID program speeds up or slows down the injection process to keep the pH correct,” explains Csuti.
The PID loop control that this process relies on is not performed by the PAC controller, but instead, is executed by the remote processors. Off-loading the processing-intensive PID loop control to these processors situated throughout the facility effectively pushes control to the I/O level, and this type of distributed architecture offers Csuti many benefits.
“With Opto’s distributed Snap PAC System, the central controller runs the control programs and delegates many functions to the remote processors,” says OptoSolutions president Anthony Dern, who consults regularly with Csuti on implementation and support issues. “This includes tasks ranging from simple I/O reads and writes, to more advance functions like high-speed counting, pulse generation and measurement, and thermocouple linearization. So by design, the Snap PAC System reduces the chances of a system-wide failure because if the host PAC should malfunction in any way, you still have independent cells operating and performing their own set of tasks without interruption indefinitely.”
In Csuti’s case, this means that if his central controller gets knocked off line or out of service for any reason, any Snap PAC brains he has distributed across his facility performing PID calculations will not be affected and will continue dosing the water as prescribed.
Another benefit of Opto’s distributed architecture relates to wiring, since Csuti’s water treatment operations take place in a massive facility with a main control room that communicates via fiber optic cables to six remote I/O panels plus two remote sites. These are all wired to I/O points that open and close valves, turn devices on
and off, and monitor instrumentation. During the daytime shift, the system operates in manual mode and the panels are used for local control. After hours, overnight, and on holidays, the system is switched into automatic mode and the control room takes precedence. Using distributed architecture minimizes the need for long wiring runs to multiple places given the size of the physical layout and more than 2,500 I/O points.
One unique aspect of this water treatment project is that upgrading to the Snap PAC System meant that Csuti had to wire the entire facility in parallel, literally duplicating the architecture already in place. He and his crew installed the new hardware and wired it to the I/O alongside the old hardware prior to bringing the new system online. Although this approach was more time-consuming than a typical hardware removal and replacement, it proved to be necessary to avoid any shutdown. The nature of operations at the LMDT, and the considerable impact these operations have on the health and well-being of the surrounding population and environment, left no other choice.
“Our plant is a 24/7/365 facility that processes about 2.8 million gallons per day and our water treatment operations are absolutely critical to this community,” says Csuti. “We’re in a position where we just can’t shut things down for any significant period of time. As a result, we have fewer options in terms of how we can perform our system upgrade. Wiring everything in duplicate has been tricky—we’ve got I/O and components with jury-rigged mounting all over the place.”
Ultimately the upgrade will be well worth it, as the new system is a hundred times faster, has better PID handling capabilities, and offers higher-density I/O that will save the Bureau a good deal of space.
With the entire control system configured in parallel as it is, Csuti is able to switch over from his old Mistic architecture to his new Snap architecture, fine tuning it to his exact operating specifications and preferences. With the new system functioning, Csuti evaluates and makes note of adjustments that need to be made. He can then switch back over to the old system and make these adjustments while still keeping the facility operational. Csuti plans to continue flip-flopping like this until everything is perfect, at which time he will then strip away the old system completely, including controllers, wiring, racks, modules, and other hardware.
Alarming and reliability
Regulators continue to monitor the water in and around Leadville. If tests show too much metal is present, or it is otherwise unclean, the Bureau of Reclamation faces major fines. To guard against this, Csuti designed control strategies which dictate that if any processes are not operating within their defined operational guidelines, the control system will issue commands to divert water output from the river to a secure holding pond until the problem can be addressed, corrected, and the system reset.
Similarly, when the plant is monitoring in automatic mode, if a valve is detected in a wrong position or any analog readings are out of their parameters, the control strategy will attempt a restart. If the system cannot restart normally, the entire process shuts down in a safe fashion. During emergency situations such as this, an autodialer activates and calls one of four individuals (a supervisor, an operator, a mechanical expert, or electronics expert Csuti) who immediately acknowledges the call and hurries onsite.
The Opto system also monitors generator sets for power outages sending instant notifications if any should occur. Uninterruptible power supplies keep the controllers and control strategies running at all times.
“Extensive programming has enabled this system to respond to many different scenarios and conditions,” says Csuti. “The sophistication of our strategies—nearly eighty of them—and the decision-making that takes place within them makes our system something of a living entity.”
|David Crump is marketing communications manager for Opto 22. Reach him at firstname.lastname@example.org .|