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I got no search results for "pipeline + wetland" so I'm starting this thread.
Columbia Gas needs to replace an old steel gas line to comply with state law. There is a preferred route, but it runs along OSU's research wetland, which in internationally famous.
The process is called horizontal directional drilling, which does not require an open trench. But it presents risks such as a "frac-out" where high-pressure drilling mud can erupt to the surface. There is also a risk of equipment getting stuck, in which case they'd have to trench down to recover it.
(Note, this has nothing to do with fracking or with any kind of brine.)
So, how great are the risks? They don't really know. They have information from three test bores but they don't really know what's under the wetland (which surprises me).
Here is the pertinent section from the Ohio Power Siting Board:
Along the Preferred Route, the glacial till is as thick 86 feet deep on the OSU property adjacent to the Wetland Research Park. The sedimentary bedrock underlying the glacial deposits consists of limestone, shale, and sandstone. The Devonian age formations specific to the project area include the Columbus limestone, Delaware limestone, Ohio shale, and Olentangy shale. The limestone is found along the Scioto River valley and the shale is found along the Olentangy River valley.The Ohio shale is the more hardened and dark fissile Devonian age shale. The Olentangy is the more apparent soft, bluish-gray, and highly weathered Devonian shale that outcrops along the Olentangy River watershed region. Boring logs obtained from the Dodridge Bridge Replacement Project just south of the wetland park indicate the presence of the both the Olentangy and Ohio shales. The rock quality description (RQD) indicated that the shale was of very poor quality.
In contrast, the Franklin Soil and Water Conservation District report for the Wetland Research Park indicated the geology in this area as a buried valley. The bedrock was identified as limestone at a depth of 86 feet.
Without additional subsurface information within the wetland area, there is no way of determining what type of rock formation exists and at what depth it would be encountered. The Preferred Route for the natural gas pipeline along the Wetland Research Park raises concerns regarding the possibility of a frac-out and the potential for piping (subsurface soil erosion). Regardless of the type of subsurface material that is encountered, the proposed HDD design, at a depth of at least 40 feet below the surface, would reduce the risk of soil piping and frac-out. More detailed information is needed that describes the lithology, stratigraphy, and other engineering characteristics of the soil and rock strata beneath the wetland area. Based on the known geology, additional precautions are needed to ensure protection of the wetland from fracout and to maintain the integrity of the bore hole.
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