Background:
A sequence of gently dipping carbonate bedrock - the Bertie Formation, Akron Dolostone, and Onondaga Limestone crop out along a 2- to5-mile wide band in western and central New York. These bedrock units trend east-west for 250 miles across the State and form extensive carbonate-bedrock aquifers which transmit and yield water from solution-enlarged fractures, bedding planes, and other openings (Olcott, 1995). Bedding planes or sub-horizontal fractures typically are the most enlarged and important water conduits. Karstic features such as sinkholes, swallets, solution channels, and caverns can locally transmit large amounts of surface water into the ground where the groundwater can move quickly and over large distances. Many homeowners, farms, municipalities, and businesses use the carbonate-bedrock aquifers for potable water. In addition to being a widely-used important groundwater resource, these carbonate units are an important mineral resource for agricultural lime, aggregate (road base, rip-rap), and building stone.
In western New York, the Onondaga Limestone of lower Devonian age unconformably overlies the Bertie Formation and Akron Dolomite of upper Silurian age. The Bertie Formation consists mostly of dolomite and dolomitic limestone with interbedded shale and gypsum seams particularly in its lower part. Its maximum thickness is about 55 feet. The Akron Dolomite is a fine-grained dolomite whose thickness is between 7 and 9 feet. The Onondaga Limestone, which has a maximum thickness of about 110 feet, forms the upper two-thirds of the carbonate-rock sequence. The Onondaga consists of three lithologies: a lower coarse-textured, crinoidal limestone that is about 10 feet thick; a middle cherty limestone that is about 45 feet thick; and an upper limestone that is about 55 feet thick. Together the Bertie Formation, Akron Dolomite, and Onondaga Limestone sequence form an approximately 160-ft thick sequence of carbonate rocks in western New York.
In central New York, the Akron Dolostone is discontinuous, however, another sedimentary carbonate group (the Helderberg Group of Upper Silurian and Lower Devonian age) is present between the Onondaga Limestone and Bertie Formation and this unit thickens to the east. In Cayuga County NY the Helderberg Group is about 80 ft thick, the Onondaga Limestone is about 75 ft thick, and the Bertie Formation is about 80 ft thick. Together these carbonate units form a sequence that is about 235 ft thick. Further to the east the carbonate sequence is over 350 ft thick.
The carbonate-bedrock aquifers are bounded on the south by the overlying Marcellus Shale and on the north by the underlying the Camillus Shale. The Camillus Shale has evaporite deposits (halite and gypsum) and where the gypsum beds are near the land surface, an evaporite karst may develop in this humid area with similar attributes as those of carbonate-rock karst.
The Onondaga Limestone is hard and resistant to erosion and forms an escarpment in western New York. South of the escarpment, the bedrock becomes buried by progressively thicker glacial deposits (mostly till and fine sand, silt, and clay, but locally by sand and gravel) and the overlying Marcellus Shale. Potential recharge to the carbonate-bedrock aquifers is greatest where the rocks crop out at land surface. Sources of recharge include (1) precipitation that directly falls over the aquifer and infiltrates into the fractures, (2) channelized runoff that infiltrates bedrock through swallets, sinkholes and fractures at the land surface, and (3) runoff derived from adjacent till- or glaciolacustrine-mantled shale uplands which lose water where the runoff flows northward into the carbonate aquifer. Any contaminant associated with the recharge water would also readily infiltrate into these aquifers.
Problems:
The New York State Departments of Environmental Conservation (NYSDEC) and Health (NYSDOH) are concerned about groundwater contamination in the carbonate and evaporite-bedrock aquifers, especially relating to the inadvertent introduction of volatile organic compounds (VOCs) or manure to these aquifers. Bacterial (E. coli) and nitrate contamination of groundwater in the region has been recognized as a problem in these aquifers (reference). 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 area over the carbonate bedrock aquifers is heavy in agriculture and application of liquid manure is prevalent. The high water content of liquid manure allows quick movement of some contaminants under certain conditions. Carbonate-bedrock aquifers have also been contaminated by improper chemical disposal or spills (TCE –trichloroethylene) in Cayuga and Livingston Counties.
Groundwater can flow very quickly with minimal filtration or adsorption through solution-widened fractures in carbonate-bedrock aquifers. Therefore, large amounts of water and associated contaminants can move long distances, sometimes in short periods of time, and affect large areas of groundwater users. If these underground pathways are tapped by drinking-water wells, they can pose a significant health threat. Once introduced into the bedrock, contamination can persist long after the source has been removed as in the case of Dense Non-Aqueous-Phase Liquids (DNAPLs) commonly associated with VOCs.
Also, these same carbonate units are utilized for their mineral resources and are mined in open pit quarries across the State, and in some instances large volumes of groundwater must be removed to dewater a quarry. Quarry dewatering may lower groundwater levels in surrounding areas and impact nearby water wells. These wells may have to be deepened or a new well may have to be drilled to find another source of water (Staubitz and Miller, 1987). Quarry dewatering may significantly affect the water level in wells 1,000 ft from a quarry and have some effect on water levels in wells up to a mile or more away (Staubitz and Miller, 1987). Additionally, lowering groundwater levels can locally change the direction of groundwater flow and affect the movement of contaminants in the aquifer.
Because the Bertie and Camillus units in the western part of the State contain thin seams of gypsum (3-5 feet thick) that were mined (underground) in the past, the abandoned caverns are now filled with mineralized water that is sometimes used for industrial purposes (cooling water). These caverns sometimes are utilized as a repository for surface-water runoff (i.e., from parking lots) or to provide for shallow dewatering of a locally high water table and can affect the quality and quantity of water in the carbonate-bedrock aquifers.
In general, the carbonate-bedrock aquifers across western and central New York State are poorly characterized. Accurate aquifer boundaries at a 1:24,000 scale are not available, and for most of the aquifer area, 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. One of the first steps to better understand this resource is to determine the character, extent, and thickness of the carbonate bedrock, and delineate where most recharge is likely to be entering the aquifer system. Karst settings with swallets and sinkholes are obvious areas of high and rapid recharge. Significant recharge also may occur in areas where carbonate or evaporite bedrock is at land surface or covered by thin permeable soils. Compilation of such information will be useful in the development of guidelines for agricultural and industrial operations, and assessment of chemical-spill and waste-disposal problems in these aquifers. Agencies such as the NYSDEC, NYSDOH, Cornell Cooperative Extension, Natural Resource Conservation Service, Soil and Water Conservation Districts, NYSDOS, and NY State Agriculture and Markets could utilize this information if it were provided in an easy-to-use, accessible format.
Approach:
The area underlain by the carbonate and evaporite-bedrock aquifers is large and funds are limited, therefore NYS-DEC has proposed a county-sized study area for this proposal that can be manageably mapped, interpreted, and presented in the form of a map and narrative report. In this case, the study area will include portions of Livingston and Monroe Counties which overlie the carbonate-evaporite system (fig. 1).
For the study, a Geographic Information System (GIS) will be used to facilitate the mapping of the extent of the carbonate-evaporite bedrock aquifer and the location of contaminant sites, quarries, mines, karst and closed-depression features, and water-supply wells at a scale of 1:24,000.
For this study area (Livingston-Monroe Counties), the following data will be collected and analyzed:
1. Base map— Compile digital base map using topographic maps, digital orthoimagery, and other existing digitally mapped information.
2. Well and Geologic data— Refine the outcrop extent of the carbonate aquifer in the two-county area by modifying the New York State Geological Survey map (scale (1:250,000), using other published data (contaminant sites, university theses, etc.), and examining well records already in USGS Ground Water Site Inventory (GWSI) and new records compiled from NYSDEC Well-Reporting Program. The well records will be useful in identifying (1) areas where the carbonate bedrock appears at or near land surface, (2) the type and thickness of unconsolidated deposits that overlie the bedrock aquifer, and (3) the probable location of the contacts between the carbonate and evaporite bedrock units and their adjacent bedrock (shale) units.
• NYS-DEC will verify the locations of new wells from their Well-Reporting Program prior to entry into the USGS GWSI database
• Collect, geo-reference, and interpret hydrogeologic data, when available - (horizontal and vertical fracture patterns from State maps, formation thickness from bedrock quarry and contaminant site data, presence of water-bearing zones if available from drinking water-well and other stratigraphic logs, for the carbonate-bedrock sequence).
• Delineate karst features such as swallets, sinkholes, and areas that have undergone extensive dissolution and the associated drainage area of these features/areas (if data are available) from interpretation of lidar and other elevation data, aerial photos, and interviews with local land and water resource managers. The karst features exist in the carbonate bedrock in specific areas across Livingston and Monroe County but also appear to the south of the carbonate/shale interface and may also be found where evaporite (gypsum) karst has developed in the Bertie-Camillus bedrock north of the Onondaga Limestone. Closed depressions in the land surface will also be identified as part of this project.
• Collect and analyze water-use? data from public water-supply wells, and other well information as available. Any public-supply well information will be entered into the USGS SWUDS database.
• Where data are made available from County Health Departments and Soil-Water Conservation District offices, locate spill, contaminant, landfill, mine, and quarry sites on the GIS coverage.
3. Soils Data—compile surficial geology and the appropriate county-based National Resources Conservation Service (NRCS) digital soils database to help to identify areas with potential for recharge to the carbonate-bedrock aquifers. Livingston County soils data are quite old but an attempt will be made to update soil nomenclature to that of the soils maps in surrounding counties in this effort to identify thin, permeable soils over bedrock. Soils with similar hydrogeologic characteristics will be grouped together.
4. Field verification—field check areas where GIS and hydrogeologic interpretation require verification that features are karstic in nature. This is especially true when relying on soils classification for bedrock, which in the previous Genesee County study turned out to be just piles of loose rock in some cases. The field personnel will coordinate with the local Soil and Water Conservation District to help gain access to private landowners fields. Use HSVR (passive seismic) in areas where depth to bedrock is uncertain and conditions are acceptable for passive seismic exploration.
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, Hydrologic Investigations Atlas 730-M, 28p.
Staubitz, W.W. and Miller, T.S., 1987, Geology and hydrology of the Onondaga aquifer in eastern Erie County, New York, with emphasis on ground-water-level declines since 1982: U.S. Geological Survey Water-Resources Investigations Report 86-4317, 44 p.
Project
Location by County
Livingston County, NY, Monroe County, NY
