By Richard Kerns
rkerns@newstribune.info
tribune staff writer
KEYSER — A drilling rig's loud hum echoed over the forested folds and shimmering waters of Dam Site 14 recently, as engineers installed monitoring devices and gathered data in preparation for a $4 million overhaul of the 46-year-old impoundment which provides water to the city of Keyser.
Crews have been at the dam for more than a week, and are expected to remain at the site for another two weeks conducting rock sampling borings and other tests in preparation for final design of the dam rehabilitation, which is expected to begin next year.
Work last week included extension of a camera device through the main spillway to gauge the health of the pipes.
Andrew Deichert, a civil engineer with the USDA's Natural Resources Conservation Service in Morgantown, said the initial findings point to a healthy dam, which may reduce the cost of the rehabilitation. The project is being funded primarily with federal stimulus money.
“So far so good,” he said as the drilling rig churned away atop the breast of the dam. “What we're finding is what we expected to find.”
Much of the drilling work involved the installation of piezometers in the breast of the dam, devices which measure the flow of water through the impoundment. While earthen dams are designed to allow a certain degree of water to pass through, the meters can help detect abnormal seepage, or the movement of soil with the water.
Officials were concerned about such flow by the presence of a line of dark-colored vegetation at the downstream base of the dam, a feature that indicated a water source in the area. With the early findings pointing to a healthy dam structure, Deichert said the water feeding the vegetation may be normal rain runoff from the breast of the dam, or seepage from a nearby spring.
Detailed analysis of the meter readings should confirm the source.
“We want to find out where the water is coming from,” he said.
Piezometers are a standard feature on modern dams but Dam Site 14 predated the technology. The meters now being installed will remain in place after the rehabilitation,
allowing the city to monitor underground conditions for decades to come.
In addition to the drilling, workers also ran a specialized camera through the 600-foot long principal spillway pipe, which discharges water from the dam into New Creek. The spillway is constructed in 20 foot sections, and the camera looked for problems like leaks in the joints and kinks in the line. Officials monitored the video as the camera moved through the pipe, and did not observe any problems.
“The pipe looked good,” Deichert said. “All indications are, it should be good to go.”
Like the other tests, the results from the survey will be reviewed in detail by the Harrisburg, Pa.-based engineering firm of Gannett-Fleming, the design firm for the project. If the preliminary results hold up, the rehabilitation may not require installation of a new sleeve into the spillway pipe, reducing costs.
In the next couple of weeks, the drilling rig will move to the reservoir itself. Positioned on a specialized barge, the drill will dig 50 feet or so beneath the water to check for rock and soil composition.
Dam Site 14 is the first dam in West Virginia being rehabilitated under a program where the USDA spearheads the project and provides the bulk of funding. The 37-acre New Creek impoundment was chose in part because it is considered a “high hazard” dam – a term that does not reflect the health of the structure itself, but rather the potential for loss of life and property damage should the dam fail.
According to NRCS planning documents, an unexpected “sunny day” failure of the dam would unleash a wall of water 93 feet tall that would threaten 384 homes and businesses, and expose 1,500 people to “fatal risk.” Economic losses would exceed $65 million.
The dam was built in 1963, and engineers at the time gave it a 50-year life. As Deichert noted, “We're closing in the end of that service life.”
The rehabilitation project, to include installation of a new riser drain in the reservoir, will bring the structure up to modern standards capable of handling catastrophic storm, roughly defined by 30 inches of rain in 24 hours. The devastating 1985 flooding featured about 9 inches of rain.
“You want to go extra conservative with a high-hazard dam,” Deichert said.
Keyser, W.Va. —
