On the Level: Under-appreciated surveying.
From time to time engineers and surveyors make it into the news, but the notice is often short-lived and under-appreciated. Such was the case in the ABC television production “The Pennsylvania Miners’ Story” aired on Nov. 24, 2002. The special recounted the accidental flooding of the Quecreek coal mine in Somerset, Pa., on July 25, 2002.
Nine miners were trapped 240 feet below ground and over a mile from the mine entrance after an accidental breakthrough occurred, allowing millions of gallons of water to pour into Quecreek from the nearby abandoned Saxman mine. Water quickly filled the tunnel leading from the mine entrance to the area of the mine where the men were working. They were able to scramble to a slightly higher section, but were trapped in a bubble of air while they watched the water level slowly rise to their precarious position. A separate crew of nine men was able to escape and sounded an alarm, bringing managers, other miners and families to the scene.
For those on the surface there was no way to communicate with the trapped miners, to know their position or even to know if they were alive. There was no hope of pumping the mine dry in time to save anyone who might be alive; the only logical approach was to drill down from the ground surface to the suspected location of the miners. The mine managers were aware of the assigned location for the men for that day’s mining and had current maps of the network of tunnels, “entries” and “crosscuts.” This is where the science of surveying played such a crucial role in the operation to save the men.
Two local engineers, Sean Isgan and Randy Musser, were assigned the task of reproducing, on the surface, the suspected location of the men calculated from the coordinates of the mine entrance and using the map of the mine. For quality control and precision assurance, Isgan and Musser ran independent surveys, Musser’s surveyors using conventional survey equipment and Isgan’s surveyors using GPS. Both surveying teams arrived at the pre-determined location within a few inches of each other—after a mile of open-ended, unadjusted overland surveying. But ABC saw more drama in the agonies of the trapped miners and their frantic families than in the wonders of modern day surveying, and that part of the episode passed by very quickly on the television.
Hollywood has never been greatly impressed with the drama of surveying, but surveyors and surveying have appeared as bit-part players in a number of Hollywood productions over the years. Watching the “Pennsylvania Miners’ Story” one could wish that the producers had made more note of the remarkable feat of those two surveying teams, working under the direct time constraint in less than ideal conditions—over farmland at night.
Rescue LogisticsThe rescue was begun by drilling a 61⁄2 inch diameter hole down to the calculated location of the men. When the drill bit broke through the roof of the chamber where the men were trapped, they were able to signal their presence and notify rescue workers that all nine men were alive. The joy and relief the people on the surface felt was quickly replaced by a new threat: the air bubble in which the men were located was under pressure from the weight of water forcing its way up the tunnel and into their nearly air-tight chamber. The hole drilled through the roof relieved that pressure as the workers above discovered by the blast of air blowing up through the hole. New problems presented themselves: if the air pressure in the chamber was holding back the advance of water, by piercing the chamber they had allowed water to rise at a greater rate. There was also the danger of rapid decompression and the risk of reduced oxygen levels in the confined space. The immediate solution was to pump air down into the chamber through the drill rig at a rate of almost a thousand cubic feet per minute and a pressure of 90 pounds per square inch, while sealing the 61⁄2 inch hole around the drill rod.
The rescue hole was to be drilled 20 feet from the air hole. For this, a large drill rig with a 30-in-diameter, diamond-tipped drill had been brought on the site in a four-vehicle caravan escorted by Penn State Police. The nine miners had entered the mine Wednesday afternoon. Drilling of the rescue hole began Thursday evening with an estimate of 18 hours to complete the drilling. But at 1:30 Friday morning, the big drill bit broke off under ground and drilling stopped for another 18 hours until it could be repaired.
In the meantime, a controversy had arisen between the miners and mine managers on the surface, and the chief of the federal mine agency’s Mine Waste and Geotechnical Engineering Division, Dr. Kelvin Ke-Kang Wu. Miners above ground wanted to drill immediately into the chamber to rescue their brothers. Medical personnel were concerned about hypothermia for the trapped miners who had been immersed in 55 degree water for over 24 hours. But Dr. Wu argued that the greatest threat to the men was not hypothermia but drowning; engineers had calculated that water was pouring into the mine at a rate of 80,000 gallons per minute. He would not allow penetration of the air bubble by the big rig until the water level in the mine could be lowered to elevation 1829. It was at this point in the discussion that the drill bit broke off.
A huge pumping operation was underway, sucking water out of the mine and into a nearby cornfield. By Saturday afternoon the big drill was back in operation and was within 20 ft of the roof of the men’s underground chamber. Finally, at 10 p.m. Saturday, the water level was down and the men drilled the final few feet into the chamber. The rest is history. All nine men were brought to the surface in a special escape cage lowered by crane into the mine. After 77 hours underground, immersed in cold water, without food and unable for most of the time to communicate with their rescuers, all nine men were in reasonably good shape physically. But all nine men said they did not plan to return to work underground.
Disaster PreventionThe Disney organization paid the miners $1.35 million for their story. Seven of the miners signed with an attorney to begin liability actions, and the U.S. Senate began hearings on the matter in October. The breakthrough from the Saxman mine to Quecreek has been plugged and new federal mining safety rules have been written. By Nov. 22, 2002, production of coal at the Quecreek mine had resumed (with an estimated 13 years of production remaining at a rate of about 50,000 tons per month), but mining must stay at least 500 ft from the Saxman mine and the miners now drill a 2,500-foot pilot hole horizontally ahead as they continue to extract the coal.
A final note of interest to surveyors: the value of as-built or post-construction mapping is emphasized by the Quecreek accident. The miners, based on the available maps of Saxman, which had been out of operation for 40 years, thought they were at least 200 ft from any part of the Saxman mine. For 40 years Saxman had been accumulating groundwater. The flood that occurred when they broke through was the fault of inaccurate maps. How many of us have experienced the reluctance of clients and government officials to require good post-construction documentation? Underground pipelines and cables, and infrastructure of all kinds get built with the only archived documentation being design plans, which may or may not reflect the actual as-built conditions. Modern mining practice, we are told, includes good mapping of mines in operation. It is unfortunate that other industries have not yet learned that lesson, and it’s a shame that surveyors and good surveying is so often under-appreciated.