Approach Used in This Compilation


Tracer data collected between FYs 1992 and 2005 from 1,417 Land-Use Study (LUS), Major-Aquifer Study (MAS), Reference (REF), and OTHER sites were identified in table A1 (appendix A). Of these 1,417 sites, 47 were not compiled in this report. A description of these 47 sites and explanations for their exclusion from this compilation are provided in table B1 (appendix B). Most of these 47 sites were excluded because superior, alternative tracer data were available or because interpretation and publication of tracer data in a separate publication was planned (table B1). Tracer data collected between FYs 2006 and 2007 from 29 LUS and REF sites were added to this compilation. A description of these 29 sites and a list of reasons for inclusion in this compilation are provided in table C1 (appendix C). This report thus summarizes tracer data that were collected from 1,399 sites [1,417 sites (appendix A) – 47 sites (appendix B) + 29 sites (appendix C)], with a total of 43 (of 48) Study Units represented. Table D1 (appendix D) summarizes the number of sites in this compilation along with the types of well networks associated with these sites. Table E1 (appendix E) summarizes the well characteristics of these 1,399 wells.


Previously Interpreted Environmental-Tracer Data


Tracer data from 618 of the 1,399 sites had been evaluated in various publications as part of earlier studies. Tracer-based piston-flow ages assigned in these earlier publications for most of the 618 sites are listed in table F1 (appendix F). References for the publications that contain the piston-flow ages also are given in table F1.


Newly Interpreted Environmental-Tracer Data


Environmental-tracer data that previously had not been interpreted were compiled for 781 of the 1,399 sites. Analytical methods are described elsewhere (Busenberg and Plummer, 1992; Plummer and Mullin, 1997; Busenberg and Plummer, 2000). For internal consistency, CFC concentrations, which originally were measured over a range of analysis dates using various calibration standards, were rescaled to the Scripps Institution of Oceanography (SIO) 2005 scale of atmospheric CFC mixing ratios (Walker and others, 2009). Rescaled CFC concentrations changed by as much as 2.3 percent. All SF₆ data were scaled to the National Oceanic and Atmospheric Administration 2000 scale of atmospheric SF₆ mixing ratios (National Oceanic and Atmospheric Administration, 2008). 


First posted January 27, 2011