Brent T. Aulenbach Joshua C. Henley Kristina G. Hopkins 20230404 tabular digital data Reston, VA U.S. Geological Survey https://doi.org/10.5066/P9G8HZTY Brent T. Aulenbach Joshua C. Henley Kristina G. Hopkins 2023 publication USGS Scientific Investigations Report 2023-5035 Reston, Virginia U.S. Geological Survey This dataset contains a list of outlier sample concentrations identified for 17 water quality constituents from streamwater sample collected at 15 study watersheds in Gwinnett County, Georgia for water years 2003 to 2020. The 17 water quality constituents are: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), suspended sediment concentration (SSC), total nitrogen (TN), total nitrate plus nitrite (NO3NO2), total ammonia plus organic nitrogen (TKN), dissolved ammonia (NH3), total phosphorus (TP), dissolved phosphorus (DP), total organic carbon (TOC), total calcium (Ca), total magnesium (Mg), total copper (TCu), total lead (TPb), total zinc (TZn), and total dissolved solids (TDS). 885 outlier concentrations were identified. Outliers were excluded from model calibration datasets used to estimate streamwater constituent loads for 12 of these constituents. Outlier concentrations were removed because they had a high influence on the model fits of the concentration relations, which could substantially affect model predictions. Identified outliers were also excluded from loads that were calculated using the Beale ratio estimator. Notes on reason(s) for considering a concentration as an outlier are included. The purpose of this dataset is to document streamwater sample constituent concentration outliers that were identified. These outlier concentrations were excluded from comparisons of base-flow and stormflow concentrations, from model calibration datasets used to estimate streamwater constituent loads, and from load calculations using the Beale ratio estimator--in support of the U.S. Geological Survey (USGS) Scientific Investigations Report "Hydrology, water-quality, and watershed characteristics in 15 watersheds in Gwinnett County, Georgia, 2002-20". This study is part of a long-term program to monitor and analyze the hydrologic and water-quality conditions of 15 watersheds in Gwinnett County, Georgia by the USGS in cooperation with Gwinnett County Department of Water Resources. 20021010 20200929 publication date Complete None planned -84.2721 -83.8468 34.1514 33.7676 ISO 19115 Topic Category inlandWaters USGS Thesaurus surface water quality USGS Metadata Identifier USGS:63503f4fd34e47431c15c5b6 Geographic Names Information System Gwinnett County State of Georgia None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Brent T Aulenbach U.S. Geological Survey, Southeast Region Research Hydrologist mailing address

1770 Corporate Drive Suite 500

Norcross GA 30093 US 678-924-6626 678-924-6710 btaulenb@usgs.gov Funded through a cooperative agreement between Gwinnett County Department of Water Resources and the U.S. Geological Survey MacOS Big Sur, version 11.7.1; Microsoft Excel for Mac, version 16.67, 11_GwinnettCoGa_WaterQualityOutliers.csv 69 KB Water-quality accuracy is dependent upon representativeness of the water-quality sampling to actual conditions and the analytical errors of the laboratory analyses No formal logical accuracy tests were conducted. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. U.S. Geological Survey 20210524 application/service https://doi.org/10.5066/F7P55KJN Digital and/or Hardcopy 20021001 20200930 publication date NWIS Stream water-quality data for 15 study watersheds in Gwinnett County, Georgia. Stream water-quality data for the 15 Gwinnett County study watersheds were downloaded from the U.S. Geological Survey (USGS) National Water Information System (NWIS) Web interface at https://waterdata.usgs.gov/nwis on May 24, 2021. Possible outliers were first identified by plotting concentrations versus the explanatory variables used in the models (logarithm of streamflow, logarithm of turbidity, and day-of-year) and identifying observations that greatly deviate from any observed relations. Consideration for outlier identification was also given to concentrations that did not fit overall patterns with other related constituents, but this assessment requires corroboration with multiple constituents to ensure that the observed concentration was the outlier and not the concentration of the constituent it was plotted against. Groups of constituents where relations might be expected to exist and for which plots were examined include: total dissolved solids, field specific conductance (SC) and laboratory SC; sediment related constituents (total lead, zinc, total organic carbon, total nitrogen, and total phosphorus), total suspended sediment, and suspended sediment concentration; total calcium and total magnesium; nitrogen constituents (total nitrogen, total nitrate plus nitrite, total ammonia plus organic nitrogen, and dissolved ammonia); and total and dissolved phosphorus. Further evidence of an outlier was determined from LOADEST (Runkel and others, 2004) output plots of model residual concentrations versus explanatory variables--these concentrations reflect deviations after accounting for relations with all model explanatory variables at once and more directly indicate possible influences on the model fit. LOADEST also identifies possible outliers by providing the Grubbs and Beck outlier test criteria (Grubbs and Beck, 1972) along with the range of normalized model residuals (errors), with outlier residuals falling outside the test criteria range. Iterative use of these identification approaches was avoided as removal of outliers reduced the model variance and the Grubbs and Beck criteria range. This can result in a tendency for additional sample concentrations to be identified as outliers, possibly resulting in the removal of good data. Outliers identified June 2021 – January 2022. Grubbs, F.E., and Beck, G., 1972, Extension of sample sizes and percentage points for significance tests of outlying observations: Technometrics, v. 14, no. 4, p. 847-854, accessed May 10, 2022 at https://doi.org/10.2307/1267134. Runkel, R.L., Crawford, C.G., and Cohn, T.A., 2004, Load estimator (LOADEST)--A FORTRAN program for estimating constituent loads in streams and rivers: U.S. Geological Survey Techniques and Methods, book 4, chap. A5, 69 p., accessed July 11, 2020, at https://doi.org/10.3133/tm4A5. NWIS 20210610 11_GwinnettCoGa_WaterQualityOutliers.csv Comma Separated Value (CSV) file containing outlier sample concentrations Producer Defined Outlier_nu Outlier number Producer Defined 1 885 Site_nu U.S. Geological Survey site number Producer Defined "02207120" Yellow River at Ga 124, near Lithonia, Ga. Producer defined "02207185" No Business Creek at Lee Road, below Snellville, Ga. Producer defined "02207385" Big Haynes Creek at Lenora Road, near Snellville, Ga. Producer defined "02207400" Brushy Fork Creek at Beaver Road, nr Loganville, Ga. Producer defined "02208150" Alcovy River at New Hope Road, near Grayson, Ga. Producer defined "02217274" Wheeler Creek at Bill Cheek Road, near Auburn, Ga. Producer defined "02334885" Suwanee Creek at Suwanee, Ga. Producer defined "02336030" North Fork Peachtree Creek at Graves Rd, near Doraville, Ga. Producer defined "02218565" Apalachee River at Fence Road, near Dacula, Ga. Producer defined "02334480" Richland Creek at Suwanee Dam Road, near Buford, Ga. Producer defined "02334578" Level Creek at Suwanee Dam Road, near Suwanee, Ga. Producer defined "02335350" Crooked Creek near Norcross, Ga. Producer defined "02205865" Sweetwater Creek at Club Drive near Lilburn, Ga. Producer defined "02205000" Wildcat Creek near Lawrenceville, Ga. Producer defined "02206500" Yellow River near Snellville, Ga. Producer defined Watershed Watershed names used in the associated U.S. Geological Survey Scientific Investigations Report. Watershed drainage area defined by site specified in value definition shown in parentheses Producer Defined Yellow River near Lithonia Yellow River at Ga 124, near Lithonia, Ga. (USGS site number 02207120) Producer defined No Business Creek No Business Creek at Lee Road, below Snellville, Ga. (USGS site number 02207185) Producer defined Big Haynes Creek Big Haynes Creek at Lenora Road, near Snellville, Ga. (USGS site number 02207385) Producer defined Brushy Fork Creek Brushy Fork Creek at Beaver Road, nr Loganville, Ga. (USGS site number 02207400) Producer defined Alcovy River Alcovy River at New Hope Road, near Grayson, Ga. (USGS site number 02208150) Producer defined Wheeler Creek Wheeler Creek at Bill Cheek Road, near Auburn, Ga. (USGS site number 02217274) Producer defined Suwanee Creek Suwanee Creek at Suwanee, Ga. (USGS site number 02334885) Producer defined North Fork Peachtree Creek North Fork Peachtree Creek at Graves Rd, near Doraville, Ga. (USGS site number 02336030) Producer defined Apalachee River Apalachee River at Fence Road, near Dacula, Ga. (USGS site number 02218565) Producer defined Richland Creek Richland Creek at Suwanee Dam Road, near Buford, Ga. (USGS site number 02334480) Producer defined Level Creek Level Creek at Suwanee Dam Road, near Suwanee, Ga. (USGS site number 02334578) Producer defined Crooked Creek Crooked Creek near Norcross, Ga. (USGS site number 02335350) Producer defined Sweetwater Creek Sweetwater Creek at Club Drive near Lilburn, Ga. (USGS site number 02205865) Producer defined Wildcat Creek Wildcat Creek near Lawrenceville, Ga. (USGS site number 02205000) Producer defined Yellow River near Snellville Yellow River near Snellville, Ga. (USGS site number 02206500) Producer defined Constit Chemical constituent abbreviated name Producer Defined BOD Biochemical oxygen demand (USGS parameter code 00310) Producer defined COD Chemical oxygen demand (USGS parameter code 00340) Producer defined TSS Total suspended solids (USGS parameter code 00530) Producer defined SSC Suspended sediment concentration (USGS parameter code 80154) Producer defined TN Total nitrogen (USGS parameter code 00600) Producer defined NO3NO2 Total nitrate plus nitrite (USGS parameter code 00630) Producer defined TKN Total ammonia plus organic nitrogen (USGS parameter code 00625) Producer defined NH3 Dissolved ammonia (USGS parameter code 00608) Producer defined TP Total phosphorus (USGS parameter code 00665) Producer defined DP Dissolved phosphorus (USGS parameter code 00666) Producer defined TOC Total organic carbon (USGS parameter code 00680) Producer defined Ca Total calcium (USGS parameter code 00916) Producer defined Mg Total magnesium (USGS parameter code 00927) Producer defined TCu Total copper (USGS parameter code 01042) Producer defined TPb Total lead (USGS parameter code 02051) Producer defined TZn Total zinc (USGS parameter code 01092) Producer defined TDS Total dissolved solids (USGS parameter code 70300) Producer defined Strt_SDate Sample collection start date - this is the collection date of discrete samples and the start date of composite samples Producer Defined 10/10/2002 8:30 9/29/2020 7:45 m/d/yyyy h:mm Conc Chemical concentration Producer Defined 0 35200 milligrams per liter; TCu, TPb, and TZn in micrograms per liter Notes Notes with reason(s) for outlier identification [abbreviations: G&B, Grubbs and Beck outlier test criteria; vs., versus; Q, streamflow; lnQ, natural logarithm of streamflow; lnTurb, natural logarithm of turbidity; other constituent abbreviations are documented in the Constit column] conductance; SCFld, field specific conductance; other constituent abbreviations are documented in the Constit column] Producer Defined Notes with reason(s) for outlier identification [abbreviations: G&B, Grubbs and Beck outlier test criteria; vs., versus; Q, streamflow; lnQ, natural logarithm of streamflow; lnTurb, natural logarithm of turbidity; other constituent abbreviations are documented in the Constit column] conductance; SCFld, field specific conductance; other constituent abbreviations are documented in the Constit column] An outlier analysis was performed by plotting concentrations versus the explanatory variables used in the models (logarithm of streamflow, logarithm of turbidity, and day-of-year) and versus constituents that varied similarly and then identifying observations that greatly deviate from any observed relations. Outliers were also identified during the model fitting process from plots of model residual concentrations versus explanatory variables and from the Grubbs and Beck outlier test criteria (Grubbs and Beck, 1972). Outliers were identified for 17 water quality constituents: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), suspended sediment concentration (SSC), total nitrogen (TN), total nitrate plus nitrite (NO3NO2), total ammonia plus organic nitrogen (TKN), dissolved ammonia (NH3), total phosphorus (TP), dissolved phosphorus (DP), total organic carbon (TOC), total calcium (Ca), total magnesium (Mg), total copper (TCu), total lead (TPb), total zinc (TZn), and total dissolved solids (TDS). 855 outliers were identified. Outlier concentrations were excluded from comparisons of base-flow and stormflow concentrations, from model calibration datasets used to estimate streamwater constituent loads, and from load calculations using the Beale ratio estimator (Beale, 1962) in Aulenbach and others (2022). These outliers were not necessarily in error but may represent some condition that occurs infrequently where it would be inappropriate to include for such an ephemeral condition. Furthermore, outliers can have an undue influence on model fits due to the minimization of the squared errors fitting process that gives outliers greater weights. Further details on the water-quality datasets are available in Aulenbach and others (2023). Aulenbach, B.T., Henley, J.C., and Hopkins, K.G., 2023, Hydrology, water-quality, and watershed characteristics in 15 watersheds in Gwinnett County, Georgia, water years 2002-20: U.S. Geological Survey Scientific Investigations Report 2023-5035. Beale, E.M.L., 1962, Some uses of computers in operational research: Industrielle Organisation, v. 31, p. 51-52. Grubbs, F.E., and Beck, G., 1972, Extension of sample sizes and percentage points for significance tests of outlying observations: Technometrics, v. 14, no. 4, p. 847-854, accessed May 10, 2022 at https://doi.org/10.2307/1267134. U.S. Geological Survey GS ScienceBase mailing address

Denver Federal Center, Building 810, Mail Stop 302

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 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 on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P9G8HZTY None 20230404 Brent T Aulenbach U.S. Geological Survey, Southeast Region Research Hydrologist mailing address

1770 Corporate Drive Suite 500

Norcross GA 30093 US 678-924-6626 678-924-6710 btaulenb@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998