Dominion Consultant Discusses Karst Topography
Since the announcement of the planned Atlantic Coast Pipeline, concerns have been raised around the impacts of construction in the region’s karst topography. Robert Denton is a certified professional geologist, a licensed soil scientist in the state of Virginia and senior geologist at Concepts Engineering. He is serving as the karst geography consultant for Dominion for the project, and addressed these concerns at the Highland open house.
He explained the nature of karst, and the process to avoid potential issues.
“Really, karst is a terrain, and that terrain is identified by the presence of sinkholes, caves, large springs – it’s a consequence of the presence of soluble bedrock, like limestone and dolomite, which can dissolve very, very slowly from the effects of rainwater, and it forms the cavern systems. In the construction of the pipeline, one of the things that we do is an initial survey, an advance survey, to identify any and all karst features – that would be a cavern or a cave opening, or a sinkhole. Of particular interest to us is any sinkhole that has what we call an “open throat”, meaning a hole in the bottom of it, or even a hole that’s clogged in the bottom of it, because that’s where water from the surface could percolate rapidly into the ground, and we want to make sure that we’re not causing sedimentation or soil running into those openings, and possibly impacting local groundwater. That’s a really big concern.”
“It’s a three stage process – initial survey; re-route of the line based on that survey to come up with a finalized route; and then inspections during the process of construction – if we do intercept something, to have it looked at, have it characterized, and then remediated if necessary.”
Mr. Denton touched on the history of pre-existing pipelines.
“There’s already just one pipeline alone, a pre-existing pipeline that runs across the Shenandoah Valley. It goes through five counties, 76 linear miles of karst, and there’s never been any kind of collapse or failure, anything associated with that pipeline through the Shenandoah Valley that we could point our finger at and say “see, this is what the karst did.” All totaled in the Appalachian region, pre-existing already, there’s probably hundreds of miles of natural gas pipeline that goes through karst terrain. You know we, as engineers, we always look at track record – we want to identify where there have been failures before, especially so we can study them and see how to prevent them in the future, and the interesting thing is, you just can’t find it. There’s really no place to find a failure that can be associated necessarily with karst geology.”
The trench for the pipeline will be 8-12 feet deep.
“This line is really barely scratching the surface of the earth. It’s very shallow – it’s seated in mostly soil. Some places it will go through bedrock, but it doesn’t go very deeply into the bedrock. Cutting through bedrock is expensive.”
The steep mountainous slopes will require extra care.
“That’s always an issue, whether it’s in karst topography or not. Obviously, they try to plan line so that it’s not ascending or descending the steepest slopes. But when you do, it’s just extra care has to be taken – the erosion and sediment control has to be done very carefully – the installation of water breaks – it’s very tightly regulated, it’s inspected, and it has to be very carefully done.”
Mr. Denton had praise for working with Dominion.
“As somebody who is both an engineering geologist, and also an academic geologist, but also is very conservation minded, environmentally minded – it’s a pleasure to be able to work with these folks. When I tell them, they listen to me. I get every impression that they really do have conservation uppermost.”
Tune in Thursday for an interview with F.E.R.C. representatives for upcoming steps, and how to comment publicly on the project.