Bruce D. Lindsey Bryant C. Jurgens Kenneth Belitz 2019 tabular digital data U.S. Geological Survey Data Release DOI:10.5066/P9DU94RV Suggested citation: Lindsey, B.D., Jurgens, B.C., and Belitz, K., 2019, Data for Tritium as an Indicator of Modern, Mixed and Premodern Groundwater Age: U.S. Geological Survey data release, https://doi.org/10.5066/P9DU94RV. https://doi.org/10.5066/P9DU94RV Bruce D. Lindsey Bryant C. Jurgens Kenneth Belitz 2019 publication U.S. Geological Survey Scientific Investigations Report 2019-5090 Suggested citation: Lindsey, B.D., Jurgens, B.C., and Belitz, K., 2019, Tritium as an Indicator of Modern, Mixed and Premodern Groundwater Age: U.S. Geological Survey Scientific Investigations Report 2019-5090, https://doi.org/10.3133/sir20195090. https://doi.org/10.3133/sir20195090 Categorical classification of groundwater age based on concentrations of tritium (3H) in groundwater can provide useful information for the assessment and understanding of groundwater resources. These data present a three-part groundwater age classification system for the continental United States based on tritium thresholds that vary in space and time: modern (recharged after 1952), if the measured value is larger than an upper threshold; premodern (recharged prior to 1953) if the measured value is smaller than a lower threshold; or mixed if the measured value is between the two thresholds. Inclusion of spatially-varying that vary geographically on the basis of the location of the sample rather than a single threshold accounts for the observed systematic variation in 3H deposition across the U.S. Inclusion of time-varying thresholds rather than a single threshold accounts for the date of sampling given the radioactive decay of 3H. The efficacy of the three-part classification system was evaluated at national and regional scales. The system was evaluated at a national-scale by classifying samples from 1,788 public supply wells distributed across 19 Principal Aquifers (Tritium_PublicSupply_CONUS.csv and Tritium_CentralValley_CA.csv) and comparing those results with expectations based on hydrogeologic principles. The regional-scale data are from five paired networks of shallow and deep wells (287 wells; Tritium_PairedNetworks_CONUS.csv). As expected, modern groundwater is more prevalent in shallower wells than in deeper wells; in fractured-rock and carbonate aquifers as compared to clastic aquifers; in unconfined areas as compared to confined areas; and in humid climates as compared to arid climates. The results from the three-part classification system were also compared to results for groundwater ages from previously published studies. For 14 previous age-dating studies available for comparison, results from this method compare favorably with the previous studies. This work improves on previous work by developing methods: for choosing post-1952 3H thresholds that minimize the misclassification of modern samples as mixed; choosing a pre-1953 threshold to estimate pre-bomb background concentrations; and adds a mixed category to classify samples that are clearly neither entirely modern nor entirely premodern. As with any tritium-based approach, it can fail when the 3H record in precipitation does not accurately reflect the record of 3H in recharge. This data release includes water-quality data (tritium), sample collection date, and selected physical characteristics of wells (depth, region, principal aquifer) used to classify groundwater age and evaluate the resulting classifications nationally and regionally. The purpose of this data release is to present the data used to create and evaluate a three-part groundwater age classification system. Estimates of groundwater age are often used to enhance groundwater studies. Groundwater age is used to estimate recharge rates, to calibrate groundwater models, and to infer susceptibility of groundwater to contamination by activities at the land surface. 1997 2017 ground condition Complete None planned -125.0 -65.0 49.0 25.0 USGS Thesaurus Tritium Groundwater age Recharge Water quality National Water-Quality Assessment project USGS Metadata Identifier USGS:5bfff281e4b0815414cad45b Common geographic areas Conterminous United States Iowa New England Nevada Utah Wisconsin Biscayne aquifer Basin and Range carbonate-rock aquifers Basin and Range aquifers Central Valley Coastal lowlands aquifer system Columbia Plateau basin-fill and basaltic-rock aquifers Cambrian-Ordovician aquifer system Colorado Plateaus aquifers Edwards-Trinity aquifer system Floridan aquifer system Glacial aquifer system High Plains aquifer Mississippi Embayment-Texas Coastal Uplands aquifer system Northern Atlantic Coastal Plain aquifer system Ozark Plateaus aquifer system Piedmont and Blue Ridge crystalline-rock aquifers Rio Grande aquifer system Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers None. Please see 'Distribution Info' for details. None. Users are advised to read the data set's metadata thoroughly to understand appropriate use and data limitations. Bruce D. Lindsey U.S. Geological Survey GW Status & Trends Coordinator mailing address

215 Limekiln Road

New Cumberland PA 17070 United States 717-730-6964 717-730-6997 blindsey@usgs.gov Funding for this work was provided through the National Water-Quality Assessment (NAWQA) project. This data release consists of 3 comma-separated values (csv) files and 1 metadata document. No formal attribute accuracy tests were conducted. 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 carefully for additional details. A formal accuracy assessment of the horizontal positional information in the data set has not been conducted. A formal accuracy assessment of the vertical positional information in the data set has either not been conducted, or is not applicable. Craig J. Brown Jeannie Barlow Charles A. Cravotta Bruce D. Lindsey 2019 publication Applied GeoChemistry Volume 101 Suggested citation: Brown, C.J, Barlow, J.R., Cravotta, C.A., and Lindsey, B.D., 2019, Factors affecting the occurrence of lead and manganese in untreated drinking water from aquifers in the Atlantic and Gulf Coastal Plain, Eastern United States, Appl. GeoChem., Vol, 101, https://doi.org/10.1016/j.apgeochem.2018.10.017. https://doi.org/10.1016/j.apgeochem.2018.10.017 Digital and/or Hardcopy 2019 publication date Lead and Manganese in Drinking Water Background information about lead and manganese in untreated drinking water. Data from this publication appear in Tritium_PublicSupply_CONUS.csv, column J (Relative Distance from outcrop). U.S. Geological Survey 2018 tabular digital data U.S. Geological Survey, 2018, National Water Information System—Web interface, accessed October 22, 2018, at http://dx.doi.org/10.5066/F7P55KJN. http://dx.doi.org/10.5066/F7P55KJN Digital and/or Hardcopy 2018 publication date NWIS Data Results from public water supply wells, domestic-supply wells, and monitoring wells collected by the National Water-Quality Assessment (NAWQA) project across the nation. Determine a modern threshold: For each value of 3H in the precipitation record (precipitation data is not included with this data release), calculate a decayed concentration of 3H based on the time span between the date of the precipitation sample and the date of the groundwater 3H sample. The lowest post peak concentration of decayed 3H in precipitation is the threshold above which the groundwater is considered modern. We compute the minimum post-peak, decay corrected 3H activity based on semi-annual (half-year) 3H values so that some intra-annual variability is captured. 2018 Determine a premodern threshold: Calculate the average concentration of 3H in precipitation from the 2008-2012 period of record (to use as an estimate of 3H concentration in 1952) then calculate the decay of that 3H concentration from 1952 to the date of the groundwater 3H sample - this is the threshold below which groundwater is considered premodern. 2018 Concentrations of 3H in groundwater that are between the premodern and modern thresholds are considered mixed. A sample would have to have some fraction of premodern and modern groundwater in order to fall between these thresholds. This approach assumes 3H travels through the aquifer under piston-flow behavior. This assumption is made because it will give the maximum concentration for the premodern threshold and a minimum value for the modern threshold. Any mixing that occurs within an aquifer would tend to lower the 3H threshold of the premodern period or increase the 3H threshold of the modern period. 2018 A more in-depth discussion of the process used to develop and evaluate the groundwater age classifications is fully described in the journal article by Lindsey and others (2019). 2019 Table Tritium_PublicSupply_CONUS.csv Comma-separated values (csv) file. Tritium data and well information for public-supply wells in the conterminous United States. Producer defined Principal Aquifer Aquifer that is the primary source of water for the site. National Water-Quality Assessment (NAWQA) Project A complete list of principal aquifers and their locations can be found on Figure 1 in U.S. Geological Survey Circular 1279, at: https://pubs.usgs.gov/circ/2005/1279/. Well_ID Site identifier assigned by the NAWQA Project as a combination of the well network name and a project identification number. National Water-Quality Assessment (NAWQA) Project The first 4 letters are the study unit abbreviation (see list below). The remainder of the code is as follows: PAS = Principal Aquifer Study; 1 = First study; 2 = Second study; 3 = Third study; A = part a of the study; B = part b of the study; C = part c of the study; -BW = Black Warrior aquifer; -C = Chattahoochee Aquifer; U = wells sampled to enhance understanding. The number following the dash represents the project identification number. BISC, Biscayne aquifer BNRC, Basin and Range carbonate-rock aquifers BNRF, Basin and Range basin fill aquifers CLOW, Coastal Lowlands aquifer system CLPT, Columbia Plateau basaltic-rock aquifers CMOR, Cambrian-Ordovician aquifer system COPL, Colorado Plateaus aquifers EDTR, Edwards-Trinity aquifer system FLOR, Floridan aquifer system GLAC, Glacial aquifer system HPAQ, High Plains aquifer METX, Mississippi Embayment/Texas Coastal Uplands aquifer system NACP, Northern Atlantic Coastal Plain aquifer system OZRK, Ozark Plateaus aquifer system PIED, Piedmont and Blue Ridge crystalline-rock aquifers RGAQ, Rio Grande aquifer system SECP, Southeastern Coastal Plain aquifer system VPDC, Valley and Ridge/Piedmont and Blue Ridge carbonate-rock aquifers Date Sample collection date, in mm/dd/yyyy. National Water-Quality Assessment (NAWQA) Project 05/22/2012 12/05/2017 Date Remark Code, Tritium Remark code for the Tritium data. National Water-Quality Assessment (NAWQA) Project R Radchem non-detect; also below Sample-Specific Critical Level Producer defined M Presence verified but not quantified Producer defined Tritium value, in picocuries per liter Tritium concentration, in picocuries per liter. National Water-Quality Assessment (NAWQA) Project -1.39 52.38 Picocuries per liter Tritium, in Tritium Units Tritium concentration, in Tritium Units. National Water-Quality Assessment (NAWQA) Project -0.44 16.42 Tritium Units Tritium Category Classification system of groundwater age. National Water-Quality Assessment (NAWQA) Project Modern Recharged after 1952 Producer defined Premodern Recharged prior to 1953 Producer defined Mixed Mixture of water recharged after 1952 and prior to 1953 Producer defined Well depth Well depth, in feet below land surface. National Water-Quality Assessment (NAWQA) Project 22 4261 Feet Sub-Aquifer Sub-aquifer within the Edwards-Trinity aquifer system. National Water-Quality Assessment (NAWQA) Project For more information about the Edwards-Trinity aquifer system, see https://pubs.usgs.gov/ha/ha730/ch_e/E-text8.html. Confinement Type of aquifer. National Water-Quality Assessment (NAWQA) Project Confined Aquifer below the land surface that is saturated with water Producer defined Unconfined Aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall Producer defined Semiconfined Aquifer that is partly confined by layers of lower permeability material through which recharge and discharge may occur. Producer defined Relative Distance from outcrop Distance from the outcrop relative to the widest aquifer width (Brown and others, 2019). National Water-Quality Assessment (NAWQA) Project 0.034 0.962 Ratio Relative depth to bottom of aquifer Depth of well relative to the deepest well depth (Brown and others, 2019). National Water-Quality Assessment (NAWQA) Project 0.022 1.0 Ratio Table Tritium_CentralValley_CA.csv Comma-separated values (csv) file. Tritium data and well information for wells in the Central Valley, California, United States. Producer defined Principal Aquifer Aquifer that is the primary source of water for the site. National Water-Quality Assessment (NAWQA) Project Central Valley Located entirely within California's Central Valley. See https://pubs.usgs.gov/circ/2005/1279/pdf/circ1279.pdf for more information Producer defined Well_ID Site identifier assigned by the NAWQA Project as a combination of the Central Valley study-specific identifier and the well identification number. National Water-Quality Assessment (NAWQA) Project The study-specific identifier may be followed by one or more of the following that indicate how the well was used in the study: FP = Flowpath; QPC =Located at places where older Quaternary-Pleistocene consolidated sequences outcropped as opposed to the alluvial unconsolidated Quarternary-Holocene deposits in the valley trough; U = Deeper understanding of the groundwater flow system. Date Sample collection date, in mm/dd/yyyy. National Water-Quality Assessment (NAWQA) Project 12/13/2004 07/08/2010 Date Remark Code, Tritium Remark code for the Tritium data. National Water-Quality Assessment (NAWQA) Project R Radchem non-detect; also below Sample-Specific Critical Level Producer defined Tritium value, in picocuries per liter Tritium concentration, in picocuries per liter. National Water-Quality Assessment (NAWQA) Project -1.58 40.62 Picocuries per liter Tritium, in Tritium Units Tritium concentration, in Tritium Units. National Water-Quality Assessment (NAWQA) Project -0.5 12.73 Tritium Units Tritium Category Classification system of groundwater age (Brown and others, 2019). National Water-Quality Assessment (NAWQA) Project Modern Recharged after 1952 Producer defined Premodern Recharged prior to 1953 Producer defined Mixed Measured value is between the Premodern and Modern thresholds Producer defined Well depth Well depth, in feet below land surface. National Water-Quality Assessment (NAWQA) Project 30 2109 Feet Tritium_PairedNetworks_CONUS.csv Comma-separated values (csv) file. Tritium data and well information for paired networks in the conterminous United States. Producer defined Principal Aquifer Aquifer that is the primary source of water for the site. National Water-Quality Assessment (NAWQA) Project Glacial aquifer system Extends from Maine to Montana and southward almost to Kentucky, encompassing parts or all of 22 North-Central and Northeastern States. Producer defined Basin and Range aquifers Located mostly in Nevada and parts of eastern and southern California but also extend into eastern Utah and southern Arizona Producer defined Network type Description of the paired network depth National Water-Quality Assessment (NAWQA) Project Shallow 10 to 176 feet Producer defined Deep 18 to 1385 feet Producer defined Region State or region in which the well is located. National Water-Quality Assessment (NAWQA) Project Locations include Iowa, Nevada, Utah, Wisconsin, or New England. Well_ID Site identifier consisting of a 15-digit value composed of the latitude and longitude of the well plus a 2-digit code indicating the well number. National Water-Quality Assessment (NAWQA) Project 390708119450301 462416088191901 Number Date Sample collection date, in mm/dd/yyyy. National Water-Quality Assessment (NAWQA) Project 06/10/1997 09/21/2016 Date Remark Code, Tritium Remark code for the Tritium data. National Water-Quality Assessment (NAWQA) Project R Radchem non-detect; also below Sample-Specific Critical Level Producer defined Tritium value, in picocuries per liter Tritium concentration, in picocuries per liter. National Water-Quality Assessment (NAWQA) Project -0.41 59.5 Picocuries per liter Tritium, in Tritium Units Tritium concentration, in Tritium Units. National Water-Quality Assessment (NAWQA) Project -0.13 18.65 Tritium Units Tritium Category Classification system of groundwater age (Brown and others, 2019). National Water-Quality Assessment (NAWQA) Project Modern Recharged after 1952 Producer defined Premodern Recharged prior to 1953 Producer defined Mixed Mixture of water recharged after 1952 and prior to 1953 Producer defined Well depth Well depth, in feet below land surface. National Water-Quality Assessment (NAWQA) Project 10 1385 Feet GS ScienceBase U.S. Geological Survey 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. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital Data https://doi.org/10.5066/P9DU94RV None 20200826 Jennifer B. Sharpe U.S. Geological Survey Geographer mailing address

405 N. Goodwin Avenue

Urbana IL 61801 United States 217-328-9731 217-328-9770 jbsharpe@usgs.gov FGDC CSDGM FGDC-STD-001-1998 Record created using USGS Metadata Wizard tool. (https://github.com/usgs/fort-pymdwizard)