Karst and the proposed Bluegrass NGL Pipeline Posted: October 10, 2013
Karst and the proposed Bluegrass NGL Pipeline
Ralph O. Ewers, Ph.D.
The Bluegrass NGL Pipeline (BG pipeline) route in Kentucky poses several critical environmental issues related to karst topography and requires a thorough environmental impact assessment to understand and mitigate potential threats to human beings and the environment. Understanding these threats requires a basic understanding of karst terrane and the interaction of NGL components with these landscapes. I will attempt to briefly explain these issues.
Approximately 120 miles of the proposed BG pipeline crosses through areas of known karst topography and over known karst aquifers. Karst aquifers and karst terrain are areas where soluble limestone and dolostone bedrock lie beneath the surface. These rocks give rise to underground drainage through caves, and the surface is nearly devoid of intermediate sized streams. Its surface is usually pockmarked with conical depressions called sinks or sinkholes. These areas in Kentucky have been mapped by James Currens of the Kentucky Geological Survey and my former graduate student, Randall Paylor (Paylor and Currens 2001).
There are two important reasons why a detailed analysis of these areas with a full environmental impact analysis needs to be made. First, the pipeline will be subjected to extraordinary stresses when crossing areas of karst potential. Second, any leaks or ruptures of the BG Pipeline can have almost immediate consequences at locations miles or tenís of miles distant from these sites. I will treat these two concerns below with examples and background information, in part gained from my own experience of more than three decades of karst investigations in Kentucky and in karst areas around the world.
Karst - A Landscape of Rapid Change
Karst areas are among the most dynamic areas in the Midwestern U.S. Both the surface and subsurface of these areas change at a rapid pace, well within the span of a human lifetime. The Kentucky counties where the BG Pipeline is projected to pass are marked by tens of thousands of sinkholes. These are known, they have been in part mapped, and they are visible in aerial photography. Sinkholes are sufficiently numerous that they cannot be avoided in pipeline construction. However, because they are known they are not the greatest problem. Many more incipient sinkholes also exist, and are a special problem. Both the known and unknown sinkholes are subject to subsidence. In some cases that subsidence is catastrophic, that is to say, major collapse may occur in minutes or hours. In other cases subsidence is more gradual and continual. These are technically known as solution subsidence or compaction subsidence sinkholes.
Karst Bedrock Topography
The bedrock beneath the karst landscape consists of a series of rock pinnacles called clints, and intervening deep depressions called grikes. The grikes often connect directly to cavernous voids in the bedrock through which soil is conducted and carried away by underground streams. Sinkholes are underlain by broader soil-filled grike-like spaces tens to hundreds of feet across.
A natural pipeline system already exists in the karst areas where the Bluegrass Pipeline will pass. These pipeline systems most often follow bedding planes between limestone and as well as dolostone layers. These water-bearing conduits form a tributary system much like surface streams. They function in karst landscapes as surface streams do in non-karst regions. Surface streams are reduced or absent in karst terranes. Hundreds of miles of these conduits have been mapped in areas beneath and surrounding the proposed Bluegrass NGL Pipeline route. Hundreds more have been confirmed by groundwater tracing and partly compiled on maps by the Kentucky Geological Survey (KGS Map Series XII). I have contributed many of these groundwater traces.
Pipeline Stress and Karst Landscapes
In spite of carefully prepared bedding beneath pipelines, they often come to rest on rock pinnacles (clints) as the soil and bedding material is lost by gradual subsidence through adjoining grikes. The weight of the pipeline and the soil above it then rests at a single point on the bedrock pinnacle. Where a pipeline is not given bridging support across a sinkhole a hundred feet or more of pipeline and soil may come to be supported at two bedrock points on either side of the subsiding sinkhole. The tension stress of an unsupported pipeline or one supported at a point creates a well-known and well-understood predisposition to corrosion and failure. Anyone contemplating a pipeline transporting potentially dangerous materials must take karst terrane into account, understand the nature of the subsurface at all points along the pipeline route, and provide appropriate support for the pipe.
Consequences of NGL Leaks in Karst Terrane
The natural conduits in karst terrane provide routes through which both liquids and gasses can move freely. The speed of water movements in these features revealed by tracer testing has shown conclusively that velocities equal to ordinary walking and jogging speeds are not uncommon for waters coursing through them. Thus, locations a mile or more from a leak site could be affected before a leak site is identified. Our experience with gasoline leaks from underground storage tanks has shown that vapors from the karst conduits have invaded homes and schools with explosive vapors. Sinkholes fill with gasoline fumes displacing the air, and caves have become explosion hazards that have killed exploring children and their rescuers. Flammable vapors released during an NGL pipeline leak would react similarly.
Groundwater in contact with flammable vapors from NGL pipeline leaks could result in a fire and explosion hazard associated with well water use in homes as has been the case with coal mining in eastern Kentucky. Dissolved NGL constituents in groundwater pose a health hazard for well water users.
Some areas along the proposed path have been subjected to groundwater tracing and the springs and wells that would be affected by releases from a few specific areas are known. Unfortunately these traced areas are very few. It is impossible to understand from basic geological and hydrological assumptions where released NGLís would affect groundwater users. The conduits frequently ignore surface drainage basin boundaries, passing beneath ridges and surface valleys, even crossing beneath active surface streams.
The Components of an Environmental Impact Study
A credible environmental impact study would include the following:
1- All groundwater users within at least a mile of the pipeline should be inventoried and sampled for constituents related to NGLís prior to pipeline use. In some areas where large springs exist, areas should be inventoried to distances greater than one mile. When establishing such distances, arbitrary measures should not be substituted for informed geological rationale.
2- All public and private water supply sources from streams, impoundments and springs should be inventoried and sampled at a distance of at least two miles. Again, when establishing such distances, arbitrary measures should not be substituted for informed geological rationale.
3- Because it is difficult and at times impossible to predict groundwater flow and contaminant migration in karst from topographic and geological data, selected areas along the pipeline route should be subjected to groundwater tracing. These locations should be selected on the basis of informed geological understanding, likely groundwater basin size, and the potential for adverse affects to human health and environmental degradation. The tracing should be conducted following the protocols outlined in Quinlan, J. F. (1989) and Quinlan, J.F. and Ewers, R.O. (1985).
4- A groundwater monitoring program should be established based primarily on springs. These should be at least as useful as surface-based monitoring of the right-of-way in detecting incipient pipeline problems.
The Purpose Of The Environmental Impact Study
The object of an environmental impact study is not to bless the project it investigates. The studyís true purpose is to adjust and at times abandon projects which have consequences for human health and the environment. The study should assist in selecting the best route relative to these concerns. Too often, the selection of routes where the land is to be put to some new purpose is based upon cost, construction convenience, land availability, or profit for specific land-holders. The study must be used for the purpose of promoting a salubrious environment for present and future generations.
Paylor, R.I. and Currens, J.C. 2001, Karst Occurrence in Kentucky, Kentucky Geological Survey Map and Chart 33, Series XII.
KGS (Kentucky Geological Survey) Map Series XII (Various Dates) Mapped Karst Groundwater Basins.
Quinlan, J. F. 1989, Groundwater Monitoring in Karst Terranes, Recommended Protocols & Implicit Assumptions. USEPA, EPA/600/X-89/050.
Quinlan, J.F. and Ewers, R.O. 1985, Ground Water Flow In Limestone Terranes: Strategy Rationale And Procedure For Reliable, Efficient Monitoring Of Ground Water In Karst Areas. National Symposium and Exposition on Aquifer Restoration and Ground Water Monitoring (5th, Columbus Ohio), Proceedings, National Water Well Association, Worthington, Ohio, p. 197-234.