Model archive explanation for the models used in: Skinner, K.D., and Rupert, M.G., 2012, Numerical model simulations of nitrate concentrations in groundwater using various nitrogen input scenarios, mid-Snake Region, south-central Idaho: U.S. Geological Survey Scientific Investigations Report 2012—XXXX, x p http://pubs.er.usgs.gov/publication/sir20125237 This model archive contains 5 directories with subdirectories as needed. Each directory contains a RedMe.txt file describing the contents and provided any other needed information. The first directory, 1_Contents, contains this ReadMe.txt file. The second directory, 2_Source_codes, contains the source and binary files needed to run the models. This includes MF2K-GWT and UCODE_2005. The directory, 3-4-5_Simulations, contains the actual model files used. The directory mod158d_NL_ML contains the UCODE_2005, mf2k-gwt, and python script files used to calibrate the updated modflow model. The original modflow files are also included in the Software.zip compressed file with the associated report sir20065137.pdf. The scenario model files are included in three separate directories named for the scenario type: ..._dectrend for the decreasing nitrogen input scenario ..._flattrend for the constant nitrogen input scenario ..._inctrend for the increasing nitrogen input scenario All model input and output files are contained in each corresponding directory. The GIS subdirectory in the 6_AncllaryData directory contains two GIS datasets that provide the components necessary for the model nitrogen input. The last directory, 7_Report, contains the report describing the modeling work. The model calibration, mod158d_NL_ML, is run by starting UCODE_2005 from a dos window prompt. UCODE_2005 then automatically runs mf2k-gwt and the python script, ConFactor.py. The three scenarios are run by starting mf2k-gwt from a dos window prompt.