Philip T. Harte 20260408 groundwater model Reston, VA, USA U.S. Geological Survey https://doi.org/10.5066/P14LJKCX Philip T. Harte Andrew L. Collins 2026 Scientific Investigations Report U.S. Geological Survey Scientific Investigations Report 2026-5008 Reston, VA, USA U.S. Geological Survey https://doi.org/10.3133/sir20265008 A MODFLOW-NWT groundwater-flow model of the Coakley Landfill (CL) area in southeast New Hampshire was constructed from a previously published hydrologic model of the southeast New Hampshire region (https://doi.org/10.5066/P909PUIP). The CL model was used to evaluate groundwater-flow patterns and advective transport pathways from the CL as a proxy to solute transport of per- and polyfluoroalkyl substances (PFAS) compounds. The CL model was rediscretized and upgraded to include local information associated with the CL. A combination of trial-and-error and parameter estimation was done to calibrate model-computed water-level and streamflow data to observed water-level and streamflow data. The model was run in steady-state conditions indicative of a modified 2015 hydrologic condition then used to delineate groundwater discharge zones from the advective transport of particles from the CL. Several advective transport simulation scenarios were done including forward-tracking of particles and delineation of pathlines from the shallow bedrock aquifer underlying the footprint of the CL under conditions with and without the CL cap, and scenarios forward-tracking of particles from the deep surficial aquifer underlying the footprint of the CL, also with and without the CL cap. The cap was constructed in 1999 and scenarios without the cap are meant to identify the effect of the CL cap on groundwater-flow patterns. Further information on the model is provided in the associated U.S. Geological Survey Scientific Investigation Report (SIR) at https://doi.org/10.3133/sir20265008. This USGS data release contains all the input and output files for the simulations described in the associated report. The model was developed to assess advective transport emanating from the CL to groundwater discharge zones. Mapping of transport pathways allows for delineation of potential risk receptors, such as drinking-water wells or streams, from contaminants associated with the CL. The contaminants associated with the CL include per- and polyfluoroalkyl substances (PFAS). Given that the PFAS compounds are primarily recalcitrant and do not degrade, advective transport approximates the average non-dispersive movement of PFAS compounds in groundwater. This USGS data release contains all the executables and input and output files needed to reproduce the results presented in the associated SIR. Limited support is provided for correcting errors in the data release and clarification of the modeling conducted by the U.S. Geological Survey. Users are encouraged to review the associated SIR to understand the purpose, construction, and limitations of this model. This model is derived from the Seacoast Regional groundwater-flow model; users should review the reports by Mack (2009, 2017, 2023). The model will run successfully only if the original directory structure is correctly restored. The model archive is broken into several pieces to reduce the likelihood of download timeouts. Instructions for reconstructing the original directory structure and running the model included in this data release and described in the model documentation report can be found in the README_Coak_FEB26.txt ASCII file which can be downloaded as part of this data release. Files in this data release include: -fiweldpicsResized_20181024_114320-landfill.jpeg: Picture of landfill showing crown capping. -README_Coak_FEB26.txt: ASCII text file that describes the model data release. This file also includes instructions on how to run the models contained in this data release. -modelgeoref.txt: ASCII text file that defines the four corners of the model grid, in decimal degrees. -ancillary.zip: ZIP file containing ancillary data including graphic file of the top view of the grid, ArcGIS files of the active and inactive area of the model grid, ModelMuse file used to create the input files to run MODFLOW-NWT, the ModelMate files used to run UCODE_2014, and output of groundwater flow from cells by the CL extracted using GW_Chart program and the '.cbc' file. -bin.zip: ZIP file containing the 64-bit executables for MODFLOW-NWT, MODPATH-6, UCODE_2014, ModelMate, ModelMuse, ZoneBudget, and GW_Chart used to run the simulations, complete the particle-tracking analyses, and do post-processing analysis as documented in this data release. -georef.zip: ZIP file containing a shapefile which defines the extent of the model domain in New Hampshire State Plane Coordinates. -model.zip: ZIP file containing the input files for the model simulations and associated particle-tracking and Zonebudget analyses documented in this data release. -output.zip: ZIP file containing the output files for the model simulations and associated particle-tracking and Zonebudget analyses documented in this data release. -source.zip: ZIP file containing source files for standard code versions of MODFLOW-NWT, MODPATH-6, UCODE_2014, ZoneBudget, and GW_Chart used to run the simulations, complete the particle-tracking analyses, and do post-processing as documented in this data release. 20150101 20151231 publication date Complete Not planned -70.9016 -70.7232 43.0591 42.9386 ISO 19115 Topic Category geoscientificInformation inlandWaters environment USGS Thesaurus groundwater water quality none Superfund MODFLOW-NWT MODPATH-6 advective transport hydraulic conductivity groundwater model PFAS UCODE_2014 ZoneBudget USGS Metadata Identifier USGS:666866dad34e9bcc607b7bfa Geographic Names Information System New Hampshire None. Acknowledgement of the U.S. Geological Survey would be appreciated in products derived from this data release. These groundwater model input and output files are provided to support the analyses documented in the associated SIR. Although the information contained in the model files may be useful for other purposes, it is incumbent on the user to understand the purpose, construction, and limitations of this model. Data have been checked to ensure consistency with the accompanying report. If any errors are detected, please notify the originating office. Andrew L. Collins U.S. Geological Survey mailing and physical

196 Whitten Rd

Augusta ME 04330 USA 207-626-6611 alcollins@usgs.gov U.S. Environmental Protection Agency (EPA), Region 1 and U.S. Geological Survey None Unclassified None Richard G. Niswonger Sorab Panday Motomu Ibaraki 2011 Publication Techniques and Methods 6-A37 Reston, VA, USA U.S. Geological Survey Detailed description of the MODFLOW-NWT model input and output files included in this data release can be found in this model code documentation report. https://doi.org/10.3133/tm6A37 David W. Pollock 2012 Publication Techniques and Methods 6-A41 Reston, VA, USA U.S. Geological Survey Detailed description of the MODPATH model input and output files included in this data release can be found in the MODPATH Version 6-A model code documentation report. https://doi.org/10.3133/tm6A41 Richard B. Winston 2000 Publication Open-File Report 00315 Reston, VA, USA U.S. Geological Survey Procedures for extracting and analyzing model output using GW_Chart is included. https://doi.org/10.3133/ofr00315 Eileen P. Poeter Mary C. Hill Dan Lu Claire R. Tiedeman Steffen Mehl 2014 publication GWMI 2014-02 Golden, CO, USA IGWMC Procedures for running UCODE_2014 https://geology.mines.edu/igwmc/ucode/ Edward R. Banta 2014 publication Techniques and Methods 6-E4 Reston, VA, USA U.S. Geological Survey ModelMate is a graphical user interface (GUI) designed to facilitate model analysis by software applications that invoke model simulations using UCODE_2014 https://doi.org/10.3133/tm6E4 Arlen W. Harbaugh 1990 publication Open-File Report 90-392 Reston, VA, USA U.S. Geological Survey Procedures for calculating subregional water budgets from MODFLOW https://doi.org/10.3133/ofr90392 Richard B. Winston 2019 publication Scientific Investigation Report 2109-5036 Reston, VA, USA U.S. Geological Survey ModelMuse is a graphical user interface (GUI) for MODFLOW https://doi.org/10.3133/sir20195036 The groundwater-flow model of the Coakley Landfill was calibrated using a combination of trial-and-error and parameter estimation to match simulated water-level and streamflow data to observed water-level and streamflow data. The initial parameter definitions were taken from Mack (2009, 2017, 2023). There are 21 parameters to represent spatial variability in horizontal and vertical hydraulic conductivity, 3 parameters to represent spatial variability in recharge, and 1 parameter to represent streambed conductance. No formal logical accuracy tests were conducted Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record and the associated model report for additional details. No formal positional accuracy tests were conducted No formal positional accuracy tests were conducted Thomas J. Mack 2023 tabular digital data data release P909PUP Reston, VA, USA U.S. Geological Survey https://doi.org/10.5066/P909PUIP Digital and/or Hardcopy 2009 2023 publication date Seacoast model update Model data sets for the Seacoast Region Thomas J. Mack 2009 tabular digital data Scientific Investigations Report 2008-5222 Reston, VA, USA U.S. Geological Survey https://doi.org/10.3133/sir20085222 Digital and/or Hardcopy 2003 2009 publication date Seacoast model Model data sets for the Seacoast Region The process used to identify advective transport from the Coakley Landfill, to develop and compare the model output to observed data, and to simulate pathlines is fully described in the associated SIR. 2026 Raster Grid Cell 334 347 6 NAD 1983 State Plane New Hampshire FIPS 2800 0.9999666667 -71.6666666666667 42.5 984250.0 0.0 coordinate pair 50 50 survey feet North American Datum of 1983 (NAD 83) Geodetic Reference System 1980 6378137.000000 298.257222 North American Vertical Datum of 1988 1.0 feet Attribute values GRID_OUT3_R122.shp ESRI Polygon shapefile U.S. Geological Survey Area Text string indicating if polygon area is active or inactive in the model. Producer defined groundwater-flow model Delineation of active and inactive areas in the model. Producer defined FID Internal feature number Producer defined This model application data release contains all the model input and output files needed to replicate the simulations described in the associated report (https://doi.org/10.3133/sir20265008). https://doi.org/10.3133/sir20265008 GS ScienceBase U.S. Geological Survey mailing and physical

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Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although the data, software, and related material have been processed successfully on a computer system at the U.S. Geological Survey (USGS), reviewed for accuracy and completeness, and approved for release by the USGS, no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Although the data have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the data are released on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from authorized or unauthorized use. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital datasets None 230 https://doi.org/10.5066/P14LJKCX None. No fees are applicable for obtaining the dataset. 20260513 Andrew L. Collins U.S. Geological Survey Physical Scientist mailing

196 Whitten Rd

Augusta ME 04330 United States 207-626-6611 alcollins@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998