Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010

Shapiro, Stephanie D.; Plummer, L. Niel; Busenberg, Eurybiades; Widman, Peggy K.; Casile, Gerolamo C.; Wayland, Julian E.; Runkle, Donna L.

Abstract:

Piston-flow age dates were interpreted from measured concentrations of environmental tracers from 812 National Water-Quality Assessment (NAWQA) Program groundwater sites from 27 Study Units across the United States. The tracers of interest include chlorofluorocarbons (CFCs), sulfur hexafluoride (SF₆), and tritium/helium-3 (³H/³He). Tracer data compiled for this analysis were collected from 2006 to 2010 from groundwater wells in NAWQA studies, including: * Land-Use Studies (LUS, shallow wells, usually monitoring wells, located in recharge areas under dominant land-use settings), * Major-Aquifer Studies (MAS, wells, usually domestic supply wells, located in principal aquifers and representing the shallow drinking water supply), * Flow System Studies (FSS, networks of clustered wells located along a flowpath extending from a recharge zone to a discharge zone, preferably a shallow stream) associated with Land-Use Studies, and * Reference wells (wells representing groundwater minimally impacted by anthropogenic activities) also associated with Land-Use Studies. Tracer data were evaluated using documented methods and are presented as aqueous concentrations, equivalent atmospheric concentrations (for CFCs and SF₆), and tracer-based piston-flow ages. Selected ancillary data, such as redox data, well-construction data, and major dissolved-gas (N₂, O₂, Ar, CH₄, and CO₂) data, also are presented. Recharge temperature was inferred using climate data (approximated by mean annual air temperature plus 1°C [MAAT +1°C]) as well as major dissolved-gas data (N₂-Ar-based) where available. The N₂-Ar-based temperatures showed significantly more variation than the climate-based data, as well as the effects of denitrification and degassing resulting from reducing conditions. The N₂-Ar-based temperatures were colder than the climate-based temperatures in networks where recharge was limited to the winter months when evapotranspiration was reduced. The tracer-based piston-flow ages compiled in this report are provided as a consistent means of reporting the tracer data. The tracer-based piston-flow ages may provide an initial interpretation of age in cases in which mixing is minimal and may aid in developing a basic conceptualization of groundwater age in an aquifer. These interpretations are based on the assumption that tracer transport is by advection only and that no mixing occurs. In addition, it is assumed that other uncertainties are minimized, including tracer degradation, sorption, contamination, or fractionation, and that terrigenic (natural) sources of tracers, and spatially variable atmospheric tracer concentrations are constrained.

Genre:

USGS Numbered Series

ProdID:

70039424

Citation Author:

Shapiro, Stephanie D.; Plummer, L. Niel; Busenberg, Eurybiades; Widman, Peggy K.; Casile, Gerolamo C.; Wayland, Julian E.; Runkle, Donna L.

Citation Contributing Office:

National Water Quality Assessment Program

Citation Datum:

North American Datum 1983

Citation Day:

Citation Edition:

Citation Editor:

Citation End Page:

Citation Issue:

Citation Keywords:

Citation Language:

English

Citation Larger Work Title:

Citation LatN:

0492300

Citation LatS:

0243000

Citation LonE:

-0665700

Citation LonW:

-1244800

Citation Month:

Citation No Pagination:

Citation Number Of Pages:

112

Citation Online Only Flag:

Citation Phsyical Description:

Title Page; Table of Contents; List of Figures; List of Tables; PDF: viii, 100 p.; Table 1 XLS; Table A1 XLS; Appendix B PDF; Appendix B Tables XLS ZIP

Citation Projection:

Albers Equal-Area Conic

Citation Public Comments:

National Water Quality Assessment Program

Citation Publisher:

U.S. Geological Survey

Citation Series:

Scientific Investigations Report

Citation Series Code:

SIR

Citation Series Number:

2012-5141

Citation Search Results Text:

Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010; 2012; SIR; 2012-5141; Shapiro, Stephanie D.; Plummer, L. Niel; Busenberg, Eurybiades; Widman, Peggy K.; Casile, Gerolamo C.; Wayland, Julian E.; Runkle, Donna L.