Simulation of Contributing Areas to Selected Public Water-Supply Wellfields in the Valley-Fill Aquifers of New York State

Science Center Objects

Background For effective wellhead protection, the area where water carrying potential contaminants can enter the groundwater system and flow to the supply well must first be defined, and then best management practices need to be implemented to minimize the opportunity for contamination to occur in areas defined as sources of water to the well. Determination of the sources of water and contrib...

 Background

For effective wellhead protection, the area where water carrying potential contaminants can enter the groundwater system and flow to the supply well must first be defined, and then best management practices need to be implemented to minimize the opportunity for contamination to occur in areas defined as sources of water to the well.  Determination of the sources of water and contributing areas to wells is complex because aquifers and their connection with recharge sources are heterogeneous in nature and hidden from direct observation.

The major groundwater source for public supplies in upstate New York are valley-fill aquifers of glacial and post-glacial origin.  Saturated coarse-grained sediments (sand and gravel) form the aquifers and fine-grained sediments (silt and clay), till, and bedrock are the confining units.  The valley-fill aquifers are particularly susceptible to contamination from surface sources because of their relatively shallow depth of occurrence and the high permeability of the coarse-grained deposits.

Valley-fill aquifer settings in upstate New York vary by hydrophysiographic province as described by Randall (2001) (fig. 1).  Surficial and buried sand and gravel aquifers are commonly present in the Appalachian Plateau and Eastern Hills, which generally sloped away from the glacial ice sheet.    Induced infiltration from main streams to high-capacity wellfields tapping the surficial aquifers is common in this province.  Scattered sand-and gravel aquifers buried within fine-grained sediments and tills from multiple glacial advances are present in the north rim of the Appalachian Plateau, which sloped toward the glacial ice sheet.  Sparse coarse-grained sediments deposited early in deglaciation and very extensive fine-grained sediments are present in the Great Lakes, Lake Champlain, Hudson River, and Port Jervis Trough lowlands, which were inundated by large glacial lakes.  Surficial sand-plain aquifers atop thick fine-grained sediments are locally common in the mid-Hudson section.  Opportunities for induced infiltration from larger streams are limited in this province.

Since the early 1980s, the USGS in cooperation with the New York State Departments of Environmental Conservation (NYSDEC) and Health (NYSDOH) has mapped more than 40 Primary and Principal valley-fill aquifers in upstate New York (https://ny.water.usgs.gov/maps/aquifer/ ).  The mapping has included development of 1:24,000 scale digital coverages of surficial geology and aquifer boundaries along with hydrogeologic sections and well and test-hole data compilations.  Less than ten of these aquifers have been quantitatively evaluated through numerical groundwater-flow modeling, with only half of the models being used with particle tracking for the determination of contributing areas and sources of water to wells (Wolcott and Coon, 2001; Miller and others, 1998; Miller and others, 2007; and Miller and Bugliosi, 2013).  None of the groundwater-flow models explicitly simulated the uplands, which are an important source of recharge to valley-fill aquifers (Morrissey and others, 1987).

Numerical groundwater-flow modeling coupled with particle tracking is by far the most flexible and powerful method to represent valley-fill aquifer frameworks and surface-water connections for the simulation of the factors that influence the sources of water and contributing area to wells (Risser and Madden, 1994).  Recent advances in groundwater-flow modeling and particle tracking have significantly increased capabilities and efficiencies in model construction and calibration, and their use to estimate contributing areas and sources of water to wells, including automated generation of models from digital GIS coverages (Bakker and others, 2016) and regional- and local-scale simulation through single fully coupled models (Panday and others, 2013 and Pollock, 2016).

The USGS National Water-Quality Assessment (NAWQA) Program is developing groundwater models for HUC 8-digit code watersheds in New York State using the auto-generation methods and available regional-scale hydrogeographic digital coverages.   These regional-scale models, which explicitly simulate both the valley-fill and upland areas, are ideal for seamless coupling with focused local-scale models to estimate contributing areas and sources of water to wells.

Objectives

 The objectives of the pilot demonstration project are to:

1)  Add, update, and QA/QC water-use data in the NYSDEC Water-Withdrawal Reporting System for the selected watersheds (>100,000 gal/d users) and wellfield model areas (all groundwater users and return flows);

2) Characterize and classify public-supply wellfields in the selected watersheds according to the hydrogeologic conditions that determine source waters and contributing area distribution including well construction, pumpage, glacial- and post-glacial depositional setting (alluvial, fluvial, glaciofluvial, glaciodeltaic, and glaciolacustrine), aquifer type (water-table, semi-confined, and confined), hydraulic properties as determined from aquifer tests, potential for recharge from channeled and unchanneled upland recharge and induced infiltration from main streams; and

3) Define sources of water and estimate contributing areas to selected representative wellfields that tap valley-fill aquifers in the investigated watersheds through numerical groundwater-flow modeling and particle tracking.

Approach

The HUC 8-digit code watersheds proposed for investigation are the Upper Susquehanna, Chemung, Owego-Wappasening, Mohawk, Middle Delaware, Roundout, Hoosic, Salmon-Sand, Oswego, and Conewango (fig. 1).These watersheds contain more than 100 public-supply wellfields that tap valley-fill aquifers spanning the major glaciated hydrophysiographic provinces in upstate New York. Nearly two-thirds of these wellfields are within aquifer areas that have mapped through the Federal-State cooperative program, and more than 20 of them are within aquifer areas that have been previously modeled. 

Requests for hydrogeologic data from the public-water suppliers will be made through the NYSDOH.  Following hydrogeologic data compilation, analysis, and classification of each of the wellfields in the watersheds, and in consultation with the NYSDEC and NYSDOH, approximately 30 representative wellfields will be selected for evaluation of contributing areas and sources of water through numerical groundwater-flow modeling and particle tracking.  The local wellfield models, which will include from one to more than ten wellfields per focused model, will be developed in aquifer areas that have been previously mapped and simulated, aquifer areas that have been mapped but not simulated, and aquifer areas with no detailed mapping (fig. 1).  The aquifer areas selected for focused modeling will be representative of the range of wellfield hydrogeologic settings to provide a generalized guide to the distribution and character of source waters and contributing areas for each classified wellfield.  

Automated tools as described by Bakker and others (2016) will be used to construct three-dimensional groundwater-flow models of the wellfield areas using available GIS data sets including Federal-State cooperative aquifer maps, lidar, and SSURGO soils coverages and available well and test-hole logs and data from NWIS, SWUDS, NYSDEC, and NYSDOT databases.  Pumpage, groundwater-level, and stream-discharge data will be compiled and analyzed to estimate long-term, average hydrologic conditions for the focused model areas. The MODFLOW 6 code of Hughes and others (2015), which supports general unstructured model grids based on the concepts of the MODFLOW-USG code of Panday and others (2013) that allows flexibility in model-grid design to focus resolution around wells and along rivers and streams, will be used to couple the local models of public water-supply wellfields with the regional models developed by NAWQA.  The MODPATH code of Pollock (2016) will be used for the simulation of flowpaths to the selected wellfields and resulting contributing areas.  Wellfield models will be constructed and contributing areas will be simulated representative of average steady-state conditions for a probable range of subsurface distributions and properties of aquifer and confining units and their hydraulic connections with surface water based on the available hydrogeologic information.

References 

Bakker, M., Post, V., Langevin, C. D., Hughes, J. D., White, J.T., Starn, J.J., and Fienen, M. N., 2016, Scripting MODFLOW model development using Python and FloPy: Ground Water, 54(5), p. 733-739.

Hughes, J.D., Langevin, C.D., and Banta, E.R., 2017, Documentation for the MODFLOW 6 framework: U.S. Geological Survey Techniques and Methods, book 6, chap. A57, 40 p., https://doi.org/10.3133/tm6A57.

Miller, T.S., Sherwood, D.A., Jeffers, P.M., and Mueller, Nancy, 1998, Hydrogeology, water quality, and simulation of ground-water flow in a glacial-aquifer system, Cortland County, New York: U.S. Geological Survey Water- Resources Investigations Report 96-4255, 84 p. https://pubs.usgs.gov/wri/1996/4255/report.pdf .

Miller, T.S. and Bugliosi, E.F., Hetcher-Aguila, K.K., Eckhardt, D.A., 2007, Hydrogeology of two areas of the Tug Hill glacial-drift aquifer, Oswego County, New York: U.S. Geological Survey Scientific Investigations Report 2007–5169, 42 p. https://pubs.usgs.gov/sir/2007/5169/

Miller, T.S. and Bugliosi, E.F., 2013, Geohydrology, water quality, and simulation of groundwater flow in the stratified-drift aquifer system in Virgil Creek and Dryden Lake Valleys, Town of Dryden, Tompkins County, New York: U.S. Geological Survey Scientific Investigations Report 2013-5070, 104 p., http://pubs.usgs.gov/sir/2013/5070/ .

Morrissey, D.J., Randall, A.D., and Williams, J.H., 1987, Upland runoff as a major source of recharge to stratified drift in the glaciated northeast, in Regional aquifer systems of the United States-The northeast glacial aquifers: American Water Resources Association, AWRA monograph series no. 11, p. 17-36.

Panday, Sorab, Langevin, C.D., Niswonger, R.G., Ibaraki, Motomu, and Hughes, J.D., 2013, MODFLOW-USG version 1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly coupled processes using a control volume finite-difference formulation: U.S. Geological Survey Techniques and Methods, book 6, chap. A45, 66 p.

Pollock, D.W., 2016, User guide for MODPATH Version 7- A particle-tracking model for MODFLOW: U.S. Geological Survey Open-File Report 2016–1086, 35 p., http://dx.doi.org/10.3133/ofr20161086 .

Randall, A. D., 2001, Hydrogeologic framework of stratified-drift aquifers in the glaciated Northeastern United States: U.S. Geological Survey Professional Paper 1415-B, 190 p., https://pubs.usgs.gov/pp/1415b/report.pdf .

Risser, D. W. and Madden, T. M., 1994, Evaluation of methods for delineating areas that contribute water to wells completed in valley-fill aquifers in Pennsylvania: U.S. Geological Open-File Report 92-635, 82 p. https://pubs.er.usgs.gov/publication/ofr92635 .

Wolcott, S.W., and Coon, W.F., 2001, Simulation of a valley-fill aquifer system to delineate flow paths, contributing areas, and traveltime to wellfields in southwestern Broome County, New York: U.S. Geological Survey Water-Resources Investigations Report 2001–4171, 17 p., https://pubs.er.usgs.gov/publication/wri014171 .

Project
Location by County

Delaware County, NY, Schoharie
County, NY, Sullivan County, NY, Ulster County, NY, Chautauqua County, NY, Cattaraugus County, NY, Broome County, NY, Cortland County, NY, Tioga County, NY, Onondaga County, NY, Chenango County, NY, Oneida County, NY, Madison County, NY, Otsego County, NY, Herkimer County, NY, Fulton County, NY, Hamilton County, NY, Montgomery County, NY, Saratoga County, NY, Washington County, NY, Rensselaer County, NY, Albany County, NY Jefferson County, NY, Oswego County, NY, Lewis County, NY, Orange County, NY