Carbonate Geology

Landforms in Carbonate Areas

Karst topography is a landscape form created by the dissolution of layers of soluble carbonate bedrock such as limestone or dolomite and results in unusual subsurface drainage.

 

Carbonate features also pose a potential risk to existing and proposed development if not managed properly. Many carbonate areas in PA display one or more of the following distinctive surface and subsurface features :

  • sinkholes

  • closed depressions

  • vertical shafts

  • disappearing streams 

  • springs

  • lineaments, faults, or fracture traces

  • ghost lakes

Groundwater Contamination

Groundwater in karst areas is as easily polluted as surface water.  Overloaded or malfunctioning septic systems in these areas may allow sewage to flow directly into underground channels or caverns. Contamination also occurs when sinkholes are used as trash dumps.

Dissolving limestone produces conditions that can lead to:

  • extremely high permeability rates 

  • reduced opportunities for contaminants to be treated

 

As a result of  waters bypassing naturally- filtering non-carbonate soil and rock, water supplies in carbonate regions may become unsafe.  

If you suspect your water supply has been contaminated, Penn’s Trail staff can develop a sampling plan for laboratory analysis. Please refer to Penn’s Trail's Hydrogeology page for a more detailed description of our water related services.

Weathering and Erosion of Carbonate

Weathering in a carbonate area may result in a variety of large or small-scale features both on the surface and subsurface. Beneath the surface, complex underground drainage systems and extensive caves and cavern systems may form.

The need for care when dealing with carbonate soils and bedrock is clear.  Sinkholes can develop gradually as surface openings enlarge, but often erosion is unseen until the roof of an underground cavern suddenly collapses.  Such events have swallowed homes, cars, and even highways, as on PA Rte. 33 in Nazareth in 2004.

Penn's Trail Carbonate Investigations

Many municipalities underlain by carbonate bedrock have a “Carbonate Geology” ordinance for new development. Whether for stormwater management, grading, drainage ditches, new structures, or even swimming pools, Penn’s Trail’s Professional Geologists have the experience to conduct a comprehensive carbonate evaluation to ensure your project will comply with all municipal and state land development requirements. Inspections include a combination desktop review, site inspection and subsurface investigation by a Professional Geologist who will:

  • correlate published geologic and topographic mapping, historic aerial photographs, and open-source karst features mapping with current surface and subsurface indicators of carbonate features.

  • use remote sensing techniques for parcels located within or adjacent to mapped carbonate bedrock.

  • evaluate sites for indicators of carbonate weathering features

  • provide verification of either the presence or absence of carbonate bedrock.

  • establish soil test pits to evaluate subsurface soils and/or bedrock geology for potentially regulated carbonate features when carbonate bedrock is present.

  • issue a report of methodology and findings to satisfy regulatory requirements.

  • make recommendations for further testing if necessary.

No method to accurately predict future carbonate feature development has been developed to date.  Our work and subsequent reporting cannot guarantee future behavior of the carbonate bedrock or its overburden.  Recommendations and opinions are based on information gathered at the time of the site evaluation and are subject to revision as new information becomes available.

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