Put a Lid on It
March 1, 2010
Beginning around 1800 and continuing until the economic recession of the 1970s, Duluth, Minn., was one of the most active industrial areas in the United States, particularly during the world wars. Coking plants, coal refiners, tar manufacturers and similar heavy industries were concentrated on the banks of the St. Louis River, where they could take advantage of extensive shipping facilities.
The region’s manufacturing legacy left quite a mark on the river. Contaminants and wastewater were discharged more or less continuously for about 170 years; in the ‘70s and ‘80s, it was common to see tar and oil oozing to the surface of the shallow wetlands and man-made peninsulas that characterize the area. Subsurface analysis revealed a stew of toxins, including residual tar chemicals, polycyclic aromatic hydrocarbons, volatile organic compounds, cyanide, naphthalene and heavy metals like mercury.
Short Learning Curves Needed
The area being capped was quite large--more than 90 acres−and 95 percent of it was submerged. Water depths ranged from 1 to 20 feet with the majority less than 6 feet deep. Work was done primarily by a combination of wading and working from boats retrofitted with spud poles to hold the boats in place as the technicians took the measurements. Work was also done from contractor barges and even with a telescopic manlift extending out over the water from the dock.
The project specs called for placing monitoring points on a 25-foot grid, and elevation had to be measured at least four times at each point--once on the original ground for a reference and again after each layer was added. Layer thickness was important. Each dolomite layer had to be at least 6 inches thick to be effective but no more than 9 inches thick to avoid heavy patches that would disturb contaminated soil. The project was a little like a dynamic topographic survey with surveyors scrambling to track a changing landscape.
There was little room for error, and the schedule would be extremely demanding. AMI staff would be working on the project alongside heavy equipment operators who would give them instant feedback on layer thickness to ensure that enough material had been placed. The surveyors would need to get to unmarked points quickly, without landmarks to steer by, and then measure and calculate elevations almost instantly. Usually, surveyors stake out points and operators come by later. Here, the surveying and grading would be happening simultaneously.
Frontier Precision Inc.’s solution consultant Wes Schneider quickly rounded up the equipment needed by the team, including two Trimble R8 GNSS receivers and two Trimble R6 GPS receivers. One of the R6s was used as a base station, and the rest of the receivers were used as rovers with Trimble TSC2 Controllers and Trimble Survey Controller field software. “I was impressed with the interface and the fast learning curve,” Bergman says. “The menus made sense, and it was like using a good computer program.”
Additionally, Bluetooth connectivity worked consistently, which made for lighter loads and less bulk. And after a day’s fieldwork was over, Bergman appreciated smoother data handling and file structures. “Three members of our crew had almost no surveying experience using Trimble equipment,” he says, “and they were able to start working productively right way.”
The surveying and capping work began in mid-May 2009. Days were extraordinarily long and tedious. The crew assembled at 7 a.m. for a safety meeting then donned chest waders and got to work by 7:30. “We went through a lot of waders,” Bergman says a little ruefully. Because most of the work was in shallow water or mud, waders were essential, but they added a bulky element to a job that was already cumbersome. Additionally, dolomite packs relatively hard (allowing dozers to work on a set layer), but in order to give feedback to dozer operators, the AMI team was checking points shortly after the material was placed. As a result, they were usually tramping about in conditions that, quite literally, sucked. “We had to keep moving,” says Ryan Jarvis, an engineering student at University of Wisconsin-Madison who interned for the summer project. “Because of the way dolomite sets, if we stood still too long, we’d get stuck.”
Work days routinely lasted 12 hours or more. “Because Nathan and I were processing data after fieldwork, a lot of our days ended up being 15 to 16 hours long,” Jarvis says. The long hours were necessary to provide the contractor with the latest data to keep the project moving as operators struggled to cap toxins in a short window of time. There were, however, some unpredictable breaks--for example, lightning would periodically force shutdowns of half an hour or more.
After recording an elevation and comparing it to previous shots, the crew would tell equipment operators if more cover was needed or if material needed to be removed. When dolomite layers were going down, Bergman strived for horizontal tolerances of about one-half foot. After the root barrier was placed, work was a little tighter horizontally to ensure that the barrier was evenly weighted down. Even though thousands of points were being monitored, there were usually just a few hundred being monitored on any given day as operators filled in relatively small patches at a time. This was especially true when placing the root barrier, which was 18 feet wide and went down in strips that overlapped by 3 feet.
At the end of each day, Bergman and Jarvis doffed waders, downloaded data, condensed point files, edited mistakes, checked labels and handed the results over to The Shaw Group. Shaw then produced topo maps that verified layer thicknesses.
In addition to recording elevations with GNSS receivers, the AMI team also took core samples at each point--a procedure that Jarvis said was “probably the worst part of the job.” The coring procedure involved bending over and ramming a clear PVC tube into the mucky soil, then extracting it and noting layer depths. The procedure had to be repeated at least twice for each point, which added up to thousands of core samples. This dull, simple task quickly turned into a back-breaker.
A Team Effort
Overall, the SLRIDT Superfund Site cleanup is generally held to be a highly successful project. Several mega-companies associated with the industrial work participated effectively in the cleanup, and a large-scale plan that employed state-of-the-art techniques, large workforces, long timetables and big budgets was administered effectively.
The capping and monitoring operation, which was completed in August, was a relatively small part of the multiyear, multimillion-dollar project, but it was critical. By effectively containing remaining contaminants, the capping procedure protects plant, animal and human life and enables restoration of a healthy ecosystem. What’s more, the successful use of GNSS equipment on this project demonstrates how effective interfaces and reliable equipment are considerably expanding the potential uses of GNSS technology.
“The reliability of the equipment allowed [our team] to focus on providing service to our client rather than fighting technical issues with the GNSS,” says AMI Principal Craig Jouppi, PE, SE, adding, “The success of this project wouldn’t have been possible without Ryan and Nathan’s dedication to excellence, attention to detail and tremendous work ethic. We just had a great team, and it showed in the performance.”
Sidebar: Words for the Wise· On projects where numerous points are being gathered, be sure to spend some time organizing filing schemes before starting work.
· When evaluating equipment, technical specs aren’t everything; the interface and the user experience are also important.
· When bidding, keep in mind that even simple tasks are hard when they have to be repeated thousands of times.
· Even on jobs with no obvious hazards, exhaustion is a risk factor if the days are long enough.
· When you’re walking in mud, keep walking! Otherwise, you might lose your waders.