Jeffrey G. Chanat 20251209 1.0 spreadsheet Jeffrey G. Chanat Christopher A Custer 20251208 Manuscript is currently in review and being prepared for submission to Water. This data release documents the inputs and outputs for a coupled water-chloride mass balance model at Long Branch in Fairfax County, VA. Data inputs include daily measurements of various hydrologic conditions including precipitation, temperature, discharge and specific conductance. Output data include daily predicted values of discharge, chloride concentration, and volume for the different reservoirs hypothesized in the model. This data was used in support of “A 10-year continuous daily simulation of chloride flux from a suburban watershed in Fairfax County, Virginia, USA” by Jeffrey G. Chanat and Christopher A. Custer. The data were collected to monitor hydrologic conditions of Long Branch in Fairfax County. This data release provides the hydrologic data used to fit a coupled water/chloride mass-balance model in order to gain insights into storage, residence time, and transport processes in the Long Branch watershed. The data release also contains the model outputs used for analysis and inferences regarding research objectives. 20131001 20230930 observed Complete None planned -77.28564 -77.23367 38.84046 38.80891 ISO 19115 Topic Category inlandWaters None road salt residence time legacy storage urbanization USGS Thesaurus salinity water quality USGS Metadata Identifier USGS:682dfba9d4be020ae7e19e00 No access constraints. Please see 'Distribution Information' for details. These data are marked with a Creative Common CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Christopher A Custer USGS - Northeast Region Hydrologist mailing and physical

VA/WV WSC Richmond Office

Richmond VA 23228 +18044049094x115 cacuster@usgs.gov Fairfax County Department of Public Works and Environmental Services Data were downloaded from various sources and manually checked for missing values. Data were assumed accurate. Missing data were estimated using linear interpolation. Values fall within expected ranges The dataset is complete with respect to the timeline of the study. PRISM Group 20240205 tabular digital data PRISM Time Series Data Location: Lat: 38.8271 Lon: -77.2881 Elev: 390ft Climate variables: ppt,tmin,tmean,tmax Spatial resolution: 4km Period: 2013-09-01 - 2023-11-01 Dataset: AN91d PRISM day definition: 24 hours ending at 1200 UTC on the day shown Grid Cell Interpolation: On (data are interpolated at the source and downloaded after these calculations) https://prism.oregonstate.edu/explorer/ Digital and/or Hardcopy 20130901 20231101 publication date PRISM Temperature and daily precipitation for input data NCEI NOAA 20240206 tabular digital data https://www.ncei.noaa.gov/access/us-climate-normals/ Digital and/or Hardcopy 20131001 20230930 observed Vienna, Virginia climate station Daily snowfall and snow depth data for Vienna, VA U.S. Geological Survey 20231207 tabular digital data https://doi.org/10.5066/F7P55KJN Digital and/or Hardcopy 201404 202309 observed Accotink Creek Accotink Creek water quality data was used to estimate the linear relationship between chloride concentration and specific conductance as a surrogate model for Long Branch (the system of interest). Interstate Commission on the Potomac River Basin 202012 publication https://www.novaregion.org/DocumentCenter/View/13054/SaMS_Toolkit_final?bidId= Digital and/or Hardcopy 20131001 20130930 publication date Virginia Salt Management This report was used to estimate chloride inputs from road de-icing material. U.S. Geological Survey 20250829 tabular digital data Multiple chapters published separately by various authors between 1967 and 1995 https://pubs.usgs.gov/twri/index090905.html Digital and/or Hardcopy 20200323 publication date USGS Water Resource Techniques Citation for methods used to collect hydrologic data U.S. Geological Survey 20231207 tabular digital data https://doi.org/10.5066/F7P55KJN Digital and/or Hardcopy 20120605 20230802 observed Paint Branch Paint Branch water quality data was used to verify estimated relationship between chloride concentration and specific conductance. U.S. Geological Survey 20231207 tabular digital data https://doi.org/10.5066/F7P55KJN Digital and/or Hardcopy 20131001 20230930 observed Long Branch This provided all the relevant water quality and hydrologic information for Long Branch. Robert M Hirsch Douglas L Moyer Stacey A Archfield 20100907 tabular digital data This is a statistical framework for analyzing long-term surface water quality data. Digital and/or Hardcopy 20131001 20230930 publication date WRTDS Estimated chloride output. Obtain the PRISM data at the URL. Enter the coordinates - Lat: 38.8271 Lon: -77.2881. Check the 'interpolate grid cell values' button. Download 'Daily values' data for ppt, tmin, tmax, and tmean from 9/1/2013 - 11/1/2023 20240205 PRISM Mass inputs were estimated as the sum of inputs due to public transportation de-icing operations and inputs due to private application. Inputs due to road de-icing operations were estimated on a per-snowfall-event basis using example per-lane-mile application rates published in the Virginia Salt Management tool kit. Snowfall depth and air temperature were used to classify distinct snowfall events into 5 categories of severity, ranging from a trace of snow and above-freezing temperatures to greater than 6 inches of snow and temperatures well below freezing. Each category was associated with a typical NaCl application rate ranging from 325 to 625 pounds per lane mile. Edge-of pavement area and road length were used to estimate the number of lane-miles of road in the watershed, assuming a lane width of 11 feet. Estimates of private application were obtained by assuming that private application roughly equals 40 percent of total salt inputs. The summed estimated inputs were then converted from mass of NaCl to mass of Cl- and assigned to the beginning day of each snowfall event. Chloride mass outputs were estimated by direct integration of the product of streamflow and estimated chloride concentration. Trends in chloride output, both overall and in relation to season and streamflow, were estimated using the Weighted Regressions on Time, Discharge, and Season (WRTDS) model. Virginia Salt Management PRISM 20240302 WRTDS Daily in-stream chloride concentrations were estimated using a regression relation between paired observations of chloride and specific conductance. Two data sources were used: The first consisted of discrete depth-and width-integrated water quality samples (n = 111) collected between January, 2010 April 2014 and September 2023 at the Accotink Creek near Annandale streamgage (USGS 01654000), located on Accotink Creek 0.5 km above the outlet of Long Branch. The area of the Accotink Creek watershed above the Annandale streamgage is 61.9 square kilometers. Data from Accotink Creek were used in favor of data from Long Branch due to the longer period-of-record and greater number of observations. To test the generality of the relation at Accotink Creek and explore the range over which the relation applies, paired data were also obtained from nearby Paint Branch near College Park, Maryland (USGS station ID 01649190). These observations (n = 330) were collected using a combination of depth- and width-integrated measurements and point measurements collected using an ISCO autosampler. Like Accotink Creek, Paint Branch is located in the Piedmont physiographic province and has a similar degree of urbanization. Specific conductance data were measured at the Long Branch stream gage (USGS station 01654500) at 15-minute intervals with a YSI water-quality sonde using standard USGS methods (USGS, variously dated). Data were then aggregated to mean daily values. The daily specific conductance record was 91 percent complete. Most gaps were less than 3 days in length; the longest gap was 37 days. Five gaps longer than 10 days were filled by duplicating existing data from the period immediately preceding the gap, and the remaining gaps were filled by linear interpolation. Specific conductance was used to estimate chloride concentration using the estimated relationship (between specific conductance and chloride concentration) from Accotink Creek. Accotink Creek Long Branch 20240302 The hydrologic sub-model was first executed to generate the time series of volumes in the soil-moisture, quick-flow, and slow-flow reservoirs, along with the corresponding discharges from each reservoir. The solute model was then run in top-to-bottom order, calculating the concentration first in the soil-moisture reservoir, then in the quick-flow reservoir, then in the slow-flow reservoir. Final streamflow and stream concentration were computed from the outflows of the quick-flow and slow-flow reservoirs by simple mass-balance. Full equations governing the volumes and concentrations in each reservoir, along with the outflow discharge and concentrations, are given in Appendix A-Supplemental Equations from Chanat and Custer, 2026. LongBranchInput.csv 20240302 LongBranchOutput.csv LongBranchInput.csv Comma Separated Value (CSV) file containing data. Producer Defined Date Date of sample Producer Defined 2013-10-01 through 2023-09-30 ppt_mm.day Daily precipitation Producer Defined 0.0 125.73 mm snow_mm.day Daily snowfall Producer Defined 0.0 457.2 mm snowDepth_mm Daily snow depth Producer Defined 0.0 635.0 mm tmin_degC Daily minimum temperature Producer Defined -17.167 25.056 degrees Celsius tmax_degC Daily maximum temperature Producer Defined -9.67 36.33 degrees Celsius tavg_degC Daily average temperature Producer Defined -12.861 30.472 degrees Celsius Q_m3.sec Discharge Producer Defined 0.000283 11.383265 cubic meters per second Q_mm.day Discharge Producer Defined 0.00254 102.07981 mm per day SC_us.cm Specific conductance Producer Defined 49.0 7400.0 Microsiemens per cm Cl_mg.l Chloride concentration Producer Defined 5.6896 3798.7415 mg per liter Cl_kg.day Total chloride mass discharged Producer Defined 1.139 135693.776 kg per day logQ_mm.day Log-scaled discharge Producer Defined -5.976 4.626 Log-scaled mm per day LongBranchOutput.csv Comma Separated Value (CSV) file containing data. Producer Defined Date Date of simulated data Producer Defined 1/1/2014 9/9/2023 Q.t Simulated streamflow Producer Defined 0.0176 31.901 mm per day C.t Simulated chloride concentration Producer Defined 0.0407 1502.880 mg per liter PPT.eff.t Effective rainfall/Discharge from soil moisture reservoir Producer Defined 0.0 74.52 mm per day C.sms.t Chloride concentration in soil moisture reservoir Producer Defined 0.0 193.83 mg per liter V.sms.t Dead storage volume in soil moisture reservoir Producer Defined 82.0 152.98 mm Q.q.t Discharge from quick flow reservoir Producer Defined 0 42.33 mm per day C.q.t Chloride concentration in quick flow reservoir Producer Defined 0.0 428292.57 mg per liter V.q.t Volume of water in quick flow reservoir Producer Defined 0 39.62 mm Q.s.t Discharge from slow flow reservoir Producer Defined 0.001 1.25 mm per day C.s.t Chloride concentration in slow flow reservoir Producer Defined 24.02 63.18 mg per liter V.s.t Dead storage volume in slow flow reservoir Producer Defined 137.03 175.015 mm ACPB_SCvCl.csv Comma Separated Value (CSV) file containing data. Producer Defined sample_dt Sample date Producer Defined Dates range from June 5, 2012 to September 13, 2023 sc Specific conductance (microsiemens per cm) Producer Defined 24 3910 uS/cm cl Chloride concentration Producer Defined 5.1 1280.0 mg/L site Sample site (Accotink Creek or Paint Branch) Producer Defined Paint Branch Sample site is Paint Branch USGS station ID 01649190 Producer defined Accotink Creek Sample site is Accotink Creek USGS station ID 01654000 Producer defined WRTDS Output RData object containing the output from the WRTDS model. Producer Defined U.S. Geological Survey - ScienceBase mailing address

Denver Federal Center

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Denver CO 80225 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 these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (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. Digital Data https://doi.org/10.5066/xxxxxxxx None 20251209 Christopher A Custer USGS - Northeast Region Hydrologist mailing and physical

VA/WV WSC Richmond Office,North Run VI

Richmond VA 23228 +18044049094x115 cacuster@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998