Evaluation of groundwater residence time in a high mountain aquifer system (Sacramento Mountains, USA): insights gained from use of multiple environmental tracers

Land, Lewis; Timmons, Stacy

Evaluation of groundwater residence time in a high mountain aquifer system (Sacramento Mountains, USA): insights gained from use of multiple environmental tracers | Evaluation du temps de résidence des eaux souterraines dans un système aquifère de haute montagne (Montagnes de Sacramento, Etats Unis d’Amérique): enseignements tirés de l’utilisation de traceurs environnementaux multiples Evaluación del tiempo de residencia del agua subterránea en un acuífero de alta montaña (Sacramento Mountains, USA): Los conocimientos obtenidos con el uso de trazadores ambientales múltiples (美国沙加缅度山脉)高山含水层系统中地下水停留时间的评估:使用多种环境示踪剂获得的认识 Avaliação de tempo de permanência em um sistema aquífero em alta montanha (Montanhas de Sacramento, EUA): conhecimentos obtidos pelo uso de múltiplos traçadores ambientais

2016

Land, Lewis | Timmons, Stacy

The New Mexico Bureau of Geology and Mineral Resources (USA) has conducted a regional investigation of groundwater residence time within the southern Sacramento Mountains aquifer system using multiple environmental tracers. Results of the tracer surveys indicate that groundwater in the southern Sacramento Mountains ranges in age from less than 1 year to greater than 50 years, although the calculated ages contain uncertainties and vary significantly depending on which tracer is used. A distinctive feature of the results is discordance among the methods used to date groundwater in the study area. This apparent ambiguity results from the effects of a thick unsaturated zone, which produces non-conservative behavior among the dissolved gas tracers, and the heterogeneous character and semi-karstic nature of the aquifer system, which may yield water from matrix porosity, fractures, solution-enlarged conduits, or a combination of the three. The data also indicate mixing of groundwater from two or more sources, including recent recharge originating from precipitation at high elevations, old groundwater stored in the matrix, and pre-modern groundwater upwelling along fault zones. The tracer data have also been influenced by surface-water/groundwater exchange via losing streams and lower elevation springs (groundwater recycling). This study highlights the importance of using multiple tracers when conducting large-scale investigations of a heterogeneous aquifer system, and sheds light on characteristics of groundwater flow systems that can produce discrepancies in calculations of groundwater age.

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