Michael E. Wieczorek Shannon E. Jackson Gregory E. Schwarz 20230802 tabular digital data Reston, Virginia U.S. Geological Survey https://doi.org/10.5066/F7765D7V This tabular data set represents the number and density of major National Pollutant Discharge Elimination System (NPDES) sites, as defined by Environmental Protection Agency (EPA), compiled for two spatial components of the NHDPlus version 2 data suite (NHDPlusv2) for the conterminous United States; 1) number and desnity of major sites per individual reach catchments and 2) number and density of major sites accumulated upstream through the river network. This dataset can be linked to the NHDPlus version 2 data suite by the unique identifier COMID. The source data was acquired by James Falcone (USGS, written commun., 2010) from the EPA. Reach catchment information characterizes data at the local scale. Reach catchments accumulated upstream through the river network characterizes cumulative upstream conditions. Network-accumulated values are computed using two methods, 1) divergence-routed and 2) total cumulative drainage area. Both approaches use a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the metrics derived from the reach catchment scale. (Schwarz and Wieczorek, 2018). This data set was created by the U.S. Geological Survey's (USGS) National Water-Quality Assessment Project (NAWQA) which is part of the USGS National Water Quality Program (NWQP). This effort was undertaken to estimate the number of major NDPES sites for NHDPlusV2 flowline catchments and upstream river networks to support statistical analysis, map display, and model parameterization. The data processed here uses a modified routing data base for the NHDPlusV2 flowline network (ENHDPlusV2_us, Schwarz and Wieczorek, 2018). The NHDPlusV2 flowline network serves as the spatial infrastructure for many water-quality modeling efforts included under NAWQA Cycle 3 status and trend assessments including the SPARROW (SPAtially Referenced Regressions On Watershed attributes) model (Rowe and others, 2009). The NHDPlusV2 flowline network is a publically available digital geospatial framework (database) that depicts the network of stream segments and their catchments within the conterminous United States (see Moore and Dewald, 2016 for more detail). The NHDPlusv2 data set includes catchments for each reach covering the conterminous U.S. which includes the catchment boundaries in neighboring Canada and Mexico. These catchments are used as the spatial units for zonal statistics. A statistic (summation, average, minimum or maximum) is calculated for each zone (catchment), based on values from the source ancillary data set (See Process_Description for more details). The output of these values are used as the source input data for an accumulation program which uses a routing database to allocate and accumulate landscape metrics. This database (ENHDPlusV2_us) is based on a topologically reconditionedversion of the NHDPlusV2 hydrography network and is used for routing purposes only. No cartographic changes were made to the original NHDPlusV2 in either the flowline or catchment line work. 2006 unknown acquisition date Complete As needed -127.910792 -65.327751 51.657387 23.243486 CONUS United States None National Pollutant Discharge Elimination System SPARROW NPDES NHDPlus Catchment NAWQA USGS Metadata Identifier USGS:57c9d89ce4b0f2f0cec192da None Conterminous United States none One should use caution and read this document before using these data to estimate smaller areas. These data should not be used for site-specific evaluation, surveying, or engineering purposes. They should also not be used beyond the limits of the source data's scale. Use of this data is considered acceptance of the limitations of this data and that the user has read and understood this metadata prior to its use in any form. Michael E. Wieczorek US Geological Survey, Maryland Water Science Center mailing and physical

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Baltimore MD 21228 USA 443-498-5550 mewieczo@usgs.gov We would like to acknowledge the following USGS employees. The original conception and rationale for creating these data is from Robert Gilliom and Daren Carlisle. We also acknowledge Andrew LaMotte in helping to process and format much of this data as well as the helpful colleague reviews provided by Alison Appling and Daren Carlisle. We also would like to thank Dave Wolock, Curtis Price, Roland Viger, and Drew Ignazio for their invaluable input. Gary L. Rowe Kenneth Belitz Hedeff I. Essaid Robert J. Gilliom Pixie A. Hamilton Anne B. Hoos Dennis D. Lynch Mark D. Munn David W. Wolock 2009 Reston, Virginia U.S. Geological Survey http://pubs.usgs.gov/of/2009/1296/pdf/OF09-1296.pdf Richard B. Moore Thomas G. Dewald 2016 American Water Resources Association (JAWRA) 1-10.DOI: 10.1111/1752-1688.12389 http://dx.doi.org/10.1111/1752-1688.12389 James A. Falcone Daren M. Carlisle David M. Wolock Michael R. Meador 2010 Ecology 91 (2), 621 Data Paper in Ecological Archives E091-045-D1 http://esapubs.org/Archive/ecol/E091/045/metadata.htm Basin metrics were compared to values for the same variables available in the GAGESII data set (Falcone, 2010). The following steps were performed before making the comparisons: 1) GAGESII point file with the most current COMIDs associations was joined to the routing database file which contains accumulated basin areas (Schwarz and Wieczorek, 2018). 2) Only those GAGESII points that have a basin area within 1% or less of the accumulated basin areas were processed and used for comparisons. This resulted in 4,713 locations. 3) Using those COMIDs for GAGESII sites, the associated record in the accumulation files were pulled and used in the comparison of one to one plots. Results demonstrated a Pearson's r-squared of over 99%. Outliers can be attributed to either the difference in the basin delineations of GAGESII basins compared to that of the catchment representations in NHDPlus version 2 or to the fact that this data set only reports data from the downstream end of reaches and their upstream contribution. GAGESII basin outlets can occur anywhere along a reach segment which can result in different results depending on the variability of the source data being compiled and the distance between the GAGES II basin outlet and the downstream endpoint of the reach segment. NHDPlus version 2 reach segments can be as long as 95 kilometers and some source data can be widely variable within an NHDPlus reach catchment. As a result, some data processed from the location of a GAGESII pour point compared to the downstream end of a reach segment can result in differences in accumulated variables. None None No formal positional accuracy tests were conducted No formal positional accuracy tests were conducted Gregory E. Schwarz Michael E. Wieczorek 2018 tabular data Reston, VA U.S. Geological Survey https://www.sciencebase.gov/catalog/item/5718d2f8e4b0ef3b7cabdc17 online 2018 publication date nhdplusus_v2.sas The source data provided routing information for the NHDPlusV2 flow line network. U.S. Environmental Protection U.S. Geological Survey 2012 vector digital data Reston, VA U.S. Geological Survey http://www.horizon-systems.com/NHDPlus/NHDPlusV2_data.php online 2012 publication date NHDPlus The source data is the basic hydrologic framework used to process these data. 1) Acquired the source data point file from James Falcone (USGS, 2010). 2) The number of major NPDES sites was calculated using ESRI's "IDENTITY function in python using the point coverage and NHDPlus version 2 reach catchments as input. The "FREQUENCY" function was then used to count the number of NPDES sites for each NHDPlus version 2 reach catchment. 3) An aggregation algorithm was performed on the assigned variables. See the metadata for "Database of Modified Routing for NHDPlus Version 2.1 Flowlines: ENHDPlusV2_US" by Schwarz and Wieczorek in Source_Information for more details on the routing databse. See the landing page for "Select Attributes for NHDPlus Version 2.1 Reach Catchments and Modified Network Routed Upstream Watersheds for the Conterminous United States" for a copy of the aggregation script and its details. 4) Exported results into a comma separated text file format. 20151221 Common Identifier Code for each catchment and reach segment (COMID) NPDES_MAJ_CONUS.txt comma separated tabular data U.S. Geological Survey COMID Unique ID to relate to each NHDPlus version 2 catchment and flow line. http://nhd.usgs.gov/NHDDataDictionary_model2.0.pdf Unique numbers that are automatically generated. CAT_NPDES_MAJ Number of major NPDES sites per NHDPlus version 2 catchment. U.S. Geological Survey 0 10 Count. ACC_NPDES_MAJ Accumulated number of major NPDES sites based on divergence routing. U.S. Geological Survey 0 100 Count. TOT_NPDES_MAJ Accumulated number of major NPDES sites based on total upstream accumulation. U.S. Geological Survey 0 2263 Count. NPDES_DENSITY_CONUS.txt comma separated tabular data U.S. Geological Survey COMID Unique ID to relate to each NHDPlus version 2 catchment and flow line. http://nhd.usgs.gov/NHDDataDictionary_model2.0.pdf Unique numbers that are automatically generated. CAT_NPDES_MAJ_DENS Density of major NPDES sites per NHDPlus version 2 catchment. U.S. Geological Survey 0 27777.78 sites per 100 square kilometers. ACC_NPDES_MAJ Accumulated density of major NPDES sites based on divergence routing. -9999 denotes flow line reach is disconnected from the network and cannot be accumulated. U.S. Geological Survey 0 5555.56 sites per 100 square kilometers. TOT_NPDES_MAJ Accumulated density of major NPDES sites based on total upstream accumulation. -9999 denotes flow line reach is disconnected from the network and cannot be accumulated. U.S. Geological Survey 0 5555.56 sites per 100 square kilometers. Michael E. Wieczorek U.S. Geological Survey - ScienceBase mailing and physical

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Denver CO 80225 USA 443-498-5550 mewieczo@usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the U.S. Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. 20260326 Michael Wieczorek US Geological Survey mailing and physical

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Baltimore Maryland 21228 USA 443-498-5550 mewieczo@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998