Statistical summaries of simulated groundwater residence times for the 10 regional aquifers of the Northern Atlantic Coastal Plain aquifer system, at a 1 square-mile grid resolution

Dates

Publication Date: 2020-04-01
Start Date: 1900-01-01
End Date: 2018-01-01

Citation

Pope, J.P., Masterson, J.P., DeSimone, L.A., and Starn, J.J., 2020, Statistical summaries of simulated groundwater residence times for the 10 regional aquifers of the Northern Atlantic Coastal Plain aquifer system, at a 1 square-mile grid resolution: U.S. Geological Survey data release, https://doi.org/10.5066/P91F9JTO.

Summary

Groundwater residence times were simulated for the major regional aquifers of the Northern Atlantic Coastal Plain aquifer system from New York to North Carolina using particle tracking in a regional groundwater flow model. Millions of particles were distributed throughout the aquifers of the North Atlantic Coastal Plain in a MODFLOW model with a volume-weighted algorithm, then tracked backwards using MODPATH6 (Pollock, 2012) until termination of their paths at their sources of origin, usually the simulated water table. Particles were tracked under simulated transient hydrologic conditions from the reference time of January 1, 2018 backwards to 1900, then under simulated steady-state conditions prior to 1900 until eventual termination [...]

Summary

Groundwater residence times were simulated for the major regional aquifers of the Northern Atlantic Coastal Plain aquifer system from New York to North Carolina using particle tracking in a regional groundwater flow model. Millions of particles were distributed throughout the aquifers of the North Atlantic Coastal Plain in a MODFLOW model with a volume-weighted algorithm, then tracked backwards using MODPATH6 (Pollock, 2012) until termination of their paths at their sources of origin, usually the simulated water table. Particles were tracked under simulated transient hydrologic conditions from the reference time of January 1, 2018 backwards to 1900, then under simulated steady-state conditions prior to 1900 until eventual termination of their paths. The simulated residence time, or simulated age, of each particle is the time each particle took to travel backwards from its initial (year 2018) location in the aquifer to its source of origin. Simulated residence times of many individual particles were statistically aggregated for every model grid cell within each of 10 North Atlantic Coastal Plain regional aquifer units. From top to bottom, these include the surficial aquifer, the Upper Chesapeake aquifer, the Lower Chesapeake aquifer, the Piney Point aquifer, the Aquia aquifer, the Monmouth-Mount Laurel aquifer, the Matawan aquifer, the Magothy aquifer, the Potomac-Patapsco aquifer, and the Potomac-Patuxent aquifer. All model cells are one square mile in area but vary in thickness depending on the aquifer and the location. For all statistical computations, individual particle residence times were first modified to limit the statistical influence of unreasonably high and low values resulting from limitations in the simulation approach. Simulated particle residence time values less than or equal to 0.001 years were assigned this value as a minimum, which is less than one day. Particle residence times greater than 10,000,000 years were censored at this value, which is the approximate maximum reasonable residence time for the aquifer system. Statistics computed from the modified simulated residence-time values for each model cell for each aquifer unit include the number of particles originating in the cell, mean residence time, median residence time, minimum residence time, maximum residence time, 10th percentile of residence times, 25th percentile of residence times, 75th percentile of residence times, and 90th percentile of residence times. A table of these computed statistics is provided for each of the ten aquifer units, with entries organized by model cell identification number, which may be used to spatially orient the residence time statistics. A polygon shapefile of the groundwater model grid is also provided, with model-cell statistics joined for all aquifers.

Contacts

Point of Contact :: Jason P Pope
Process Contact :: Jason P Pope, Virginia-West Virginia Water Science Center
Originator :: Jason P Pope, John P Masterson, Leslie A Desimone, Jeffrey Starn
Metadata Contact :: Jason P Pope, Virginia-West Virginia Water Science Center
Publisher :: U.S. Geological Survey
Distributor :: U.S. Geological Survey - ScienceBase
SDC Data Owner :: Virginia and West Virginia Water Science Center
USGS Mission Area :: Water Resources

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nacp_residence_time_stats.xml “Metadata file” Original FGDC Metadata	View	203.9 KB	application/fgdc+xml
nacp_surf_rt_stats.csv “Simulated residence times, Surficial aquifer, NACP model”		6.35 MB	text/csv
nacp_upch_rt_stats.csv “Simulated residence times, Upper Chesapeake aquifer, NACP model”		6 MB	text/csv
nacp_loch_rt_stats.csv “Simulated residence times, Lower Chesapeake aquifer, NACP model”		5.99 MB	text/csv
nacp_pipt_rt_stats.csv “Simulated residence times, Piney Point aquifer, NACP model”		6.55 MB	text/csv
nacp_aq_rt_stats.csv “Simulated residence times, Aquia aquifer, NACP model”		6.08 MB	text/csv
nacp_moml_rt_stats.csv “Simulated residence times, Monmouth-Mount Laurel aquifer, NACP model”		6.07 MB	text/csv
nacp_mtwn_rt_stats.csv “Simulated residence times, Matawan aquifer, NACP model”		6.04 MB	text/csv
nacp_mgty_rt_stats.csv “Simulated residence times, Magothy aquifer, NACP model”		6.4 MB	text/csv
nacp_popt_rt_stats.csv “Simulated residence times, Potomac-Patapsco aquifer, NACP model”		6.96 MB	text/csv
nacp_popx_rt_stats.csv “Simulated residence times, Potomac-Patuxent aquifer, NACP model”		5.54 MB	text/csv
nacp_rt_unit_thickness.csv “Hydrogeologic unit thicknesses, NACP model”		15.8 MB	text/csv
nacp_model_rt_stats_shapefile.7z “Model grid polygon shapefile with all residence-time statistics as attributes”		11.57 MB	application/x-7z-compressed
nacp_rt_potomac.bmp “Preview image”		42.8 MB	image/bmp

Purpose

The provided files are output from a model simulation designed to estimate groundwater residence times across ten regional aquifers of the Northern Atlantic Coastal Plain aquifer system. The simulated residence times are intended as approximate and relative estimates of groundwater ages throughout these aquifers, which may inform the understanding of geochemical and water-quality conditions and provide a measure of groundwater vulnerability to possible sources of contamination at the land surface. Statistical summaries of many tracked particles are intended to characterize the variability and uncertainty of residence time at the model grid scale of 1 square mile.

Statistical summaries of simulated groundwater residence times for the 10 regional aquifers of the Northern Atlantic Coastal Plain aquifer system, at a 1 square-mile grid resolution

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