Statewide Assessment of New York’s Karst Aquifers With an Inventory of Closed-Depression and Focused-Recharge Features

Science Center Objects

Background: The New York State Departments of Environmental Conservation (NYS DEC) and Health (NYS DOH) are concerned about groundwater contamination in the carbonate-bedrock aquifers in New York, especially relating to the unintended introduction of volatile organic compounds (VOCs) and liquid manure to these aquifers. These carbonate rocks form extensive aquifers that transmit, and can yield,...

Background:
The New York State Departments of Environmental Conservation (NYS DEC) and Health (NYS DOH) are concerned about groundwater contamination in the carbonate-bedrock aquifers in New York, especially relating to the unintended introduction of volatile organic compounds (VOCs) and liquid manure to these aquifers. These carbonate rocks form extensive aquifers that transmit, and can yield, water from solution-enlarged fractures, bedding planes, and other openings (Olcott, 1995). Groundwater contamination from liquid manure application (fecal coliform bacteria [E. coli] and nitrate) has been on the increase over the past decade as these incidents have been reported to the NYS DEC. Nitrate is highly water-soluble and thus can move readily through the soil and enter the groundwater system. E. coli bacteria are not water soluble, but because of their small size, can move through larger soil pores and in bedrock fractures, especially solution-widened fractures in the carbonate bedrock. The high water content and organic nature of liquid manure may enhance movement of some contaminants under certain conditions. Carbonate-bedrock aquifers have also been contaminated by improper chemical disposal or spills (i.e., TCE – trichloroethylene).
 
Contamination issues continue to be reported along and within carbonate-rock units throughout New York. The bedrock units include: Limestone – Onondaga, Helderberg Group, Trenton Black River Group, and Beekmantown Group; and Dolostones –Bertie Formation, and Lockport Group (fig. 1). While not a carbonate unit, the Camillus Shale, north of the Onondaga Limestone, from Erie to Madison Counties in western and central New York, has an evaporite (gypsum) unit where gypsum is present as beds or as scattered deposits throughout the upper 100 feet of the unit and has the potential for groundwater contamination issues similar to the carbonate-rock units in New York. The Camillus Shale, can develop karst-like subsidence features due to dissolution of gypsum deposits and can result in localized groundwater contamination via these karst-dissolution features.
 
In 2008, the US Geological Survey (USGS), in cooperation with the NYS DEC Division of Water, initiated a pilot study to characterize the recharge settings of the carbonate bedrock in Genesee County after a number of groundwater contamination issues were reported over the previous decade (Reddy and Kappel, 2010). A series of 1:24,000 maps were constructed showing areas where focused recharge (surface water that can recharge the groundwater system through karst features or other closed-depression features in the land surface) can most readily infiltrate into the karst carbonate bedrock and potentially contaminate the groundwater-flow system (fig. 2). Similar to the Genesee County case, gently dipping carbonate-rock crops out along a 2-to-5 mile wide band that trends east-west for 250 miles across the State (fig.1). Karst features such as sinkholes, swallets, solution channels, and caverns can locally transmit large amounts of groundwater into these formations, which can move quickly and over large distances. Many homeowners, farms, municipalities, and businesses use these carbonate aquifers for potable water.
 
The carbonate-rock units that run from east-to-west in the western and central part of the state (Onondaga-Helderberg and their Dolostone counterparts), along with their associated aquifers are bounded on the south by unconsolidated deposits, bedrock or both, which may be in hydraulic contact with the underlying carbonate rock. This southern “buffer zone” is where karst-like development may occur in these overlying units when they are generally less than 50-75 feet thick. The Onondaga Limestone forms an escarpment at its northern outcrop in several locations across the western part of New York State and is typically near land surface along its escarpment due to glacial erosion. South of the escarpment, the carbonate bedrock becomes buried by progressively thicker glacial deposits (mostly till and glaciolacustrine fine sand, silt, and clay, but locally by sand and gravel). All carbonate units described above are at risk for rapid, focused recharge and possible aquifer contamination. The Trenton-Black River, and Beekmantown Group limestones throughout northern New York have variable regional bedrock dips, different than the units in western and central New York, so they may not have as wide of a buffer zone as the east-west trending carbonate-rock units.
 
Potential focused recharge to carbonate-bedrock aquifers is greatest where the rocks crop out at, or near to the land surface. Sources of recharge include (1) precipitation that directly falls over the aquifer and infiltrates into the fractures, (2) channelized runoff that seeps into the rocks through swallets, sinkholes and fractures at the land surface, and (3) runoff derived from adjacent uplands, generally to the south of the carbonate unit, in the western and central part of the state, which lose water where it flows northward onto the carbonate-bedrock aquifer units. Any contaminant associated with the recharge water would also readily infiltrate into these aquifers.
 
Problem:
New York’s carbonate-bedrock aquifers are poorly characterized. Accurate aquifer boundaries at larger scales (1:24,000 scale) are not available, and for most of the carbonate aquifers, the sources and amounts of recharge and direction of groundwater flow are unknown. Such information is critical for the management and protection of this important groundwater resource. Groundwater can flow very quickly with minimal filtration or adsorption through solution-widened (karst) fractures in carbonate-rock aquifers. Water and associated contaminants in this situation can move long distances, sometimes in short periods of time, and affect areas far from where the surface contamination entered the bedrock aquifer.
 
The objective of this proposal is to determine the extent of the susceptible carbonate bedrock, and where recharge would most-likely enter the aquifer system. Information on locations where aquifer contamination has occurred over or near carbonate bedrock is crucial in understanding the surface water/ground water connections that facilitate focused recharge. Compilation of this initial statewide information will be useful in determining which parts of these carbonate bedrock units in the State need detailed assessment. These detailed assessments will provide information to DEC and other agencies to develop guidelines for agricultural and industrial operations, and assessment of the potential for chemical-spill and chemical-waste problems in these aquifers.
 
Approach:
A statewide study is proposed, delineating the carbonate-rock areas of concern, and adjacent “buffer areas” where the carbonate rock is thinly covered by unconsolidated or weathered, non-carbonate bedrock. Mapped and reported contamination events near carbonate bedrock will also be used to further define vulnerable areas of potential focused recharge. After the statewide assessment, detailed studies could be undertaken in county-sized areas as was completed in Genesee County (Reddy and Kappel, 2010) where these carbonate-rock aquifers have been identified as being vulnerable to focused recharge.
 
For this statewide assessment the carbonate-rock boundaries and associated buffer areas will be mapped, using GIS applications and visual interpretations to depict the carbonate aquifer and its potential contributing areas; locating former well contamination incidents from records of County Health Departments and County Soil–Water Conservation Districts; and locating closed-depression features (no inlet or outlet for water flow) which might be associated with recharge to the carbonate aquifer.
 
The following data will be collected, analyzed, and mapped in consultation with NYS-DEC:
 
1. Carbonate bedrock extent—the extent of selected carbonate-rock units using the New York State Geological Survey’s 1:250,000 scale bedrock surface map as a starting point.
 
2. Buffer areas for each mapped carbonate-rock unit—this additional area will extend to the south (in western and central New York) from the mapped carbonate contact to include an additional area that may have karst-like features, including closed depressions. This buffer area is related to the underlying carbonate rock as it dips below overlying non-carbonate bedrock and unconsolidated sediments. This buffer area will be extended using the regional bedrock dip for a distance of approximately one mile, especially in western and central New York areas.
 
3. Buffer areas for evaporite karst (gypsum dissolution)—this additional area is only found north of the Onondaga Limestone/Bertie Dolostone contact and is within the upper 100 feet of the Camillus Shale which has easily-erodible gypsum deposits. This evaporite buffer area may be extended approximately 2 miles north of the Onondaga/Bertie contact due to the regional dip of the bedrock (~ 50 feet per mile) and the exposure of the gypsum-rich layer within the Camillus Shale over that distance.
 
4. At the request of the NYS DEC, delineate closed-depression features within the carbonate-rock unit, its associated buffer area(s), and an additional one quadrangle from these buffers. These closed-depression features derived from NYS DOT topographic quadrangles might represent karst sinkholes, swallets, areas that have undergone karst solutioning, or are present for other geologic/anthropogenic reasons (i.e. glacial kettle holes, regional bedrock fracture zones, former gravel pits). These features will be analyzed and mapped using both topographic contour and digital elevation model (DEM) data. Those features outside the carbonate rock zones and associated buffer areas will only be mapped, but their significance as potential focused-recharge areas will not be assessed.
 
5. With the assistance of the NYS-DEC, request information on former aquifer-contamination events from County Health Departments and Soil-Water Conservation Districts that might be related to incidents where a contaminant entered groundwater in the carbonate bedrock or associated buffer area(s) and affected the quality of groundwater. These will be used to further evaluate the buffer boundaries. If these agencies mentioned above are not able to supply this information, this aspect of the project will not be pursued.
Information requested by the NYS-DEC should include:
a. Latitude-Longitude coordinates for the centroid of the incident area,
b. The type and amount of contaminant suspected of causing the problem, if available,
c. A brief summary of the incident, including 1) the date, 2) possible source(s) of contamination, 3) identified focused-recharge location(s) that is, type of feature—sinkhole, losing stream, spill to surface, 4) number of affected homes or businesses, 5) implemented remedies, and 6) any resource modifications designed to prevent future reoccurrence of the incident.
 
6. Closed-depression verification. Lidar imagery, if available, may be utilized to supplement the DOT topographic contours to identify closed-depression areas.
 
SELECTED REFERENCES
Olcott, P.G., 1995, Ground water atlas of the United States- Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, Vermont: U.S. Geological Survey HA 730-M
 
Reddy, J.E., and Kappel, W.M., 2010, Compilation of existing hydrogeologic and geospatial data for the assessment of focused recharge to the carbonate-rock aquifer in Genesee County, New York: U.S. Geological Survey Scientific Investigations Map 3132, 17 p., 20 sheets, at http://pubs.usgs.gov/sim/3132/.
 

Project Location by County

Clinton County, NY, Essex County, NY, Franklin County, NY, Fulton County, NY, Hamilton County, NY, Herkimer County, NY , Lewis County, NY, Oneida County, NY, Saint Lawrence County, NY, Saratoga County, NY, Warren County, NY, Washington County, NY, Erie County, NY, Niagara County, NY, Genesee County, NY, Orleans County, NY, Seneca County, NY, Wayne County, NY, Monroe County, NY, Ontario County, NY, Onondaga County, NY, Oswego County, NY, Cayuga County, NY, Jefferson County, NY, Madison County, NY, Otsego County, NY, Montgomery County, NY, Dutchess County, NY, Albany County, NY, Rensselaer County, NY, Greene County, NY, Orange County, NY, Rockland County, NY, Ulster County, NY, Putnam County, NY, Westchester County, NY, NYWSCStatewide