Groundwater noble gas, age, and temperature signatures in an Alpine watershed: Valuable tools in conceptual model development

Abstract

[1] Bedrock groundwater in alpine watersheds is poorly understood, mainly because of a scarcity of wells in alpine settings. Groundwater noble gas, age, and temperature data were collected from springs and wells with depths of 3-342 m in Handcart Gulch, an alpine watershed in Colorado. Temperature profiles indicate active groundwater circulation to a maximum depth (aquifer thickness) of about 200 m, or about 150 m below the water table. Dissolved noble gas data show unusually high excess air concentrations (>0.02 cm 3 STP/g, DNe > 170%) in the bedrock, consistent with unusually large seasonal water table fluctuations (up to 50 m) observed in the upper part of the watershed. Apparent 3 H/ 3 He ages are positively correlated with sample depth and excess air concentrations. Integrated samples were collected from artesian bedrock wells near the trunk stream and are assumed to approximate flow-weighted samples reflecting bedrock aquifer mean residence times. Exponential mean ages for these integrated samples are remarkably consistent along the stream, four of five being from 8 to 11 years. The tracer data in combination with other hydrologic and geologic data support a relatively simple conceptual model of groundwater flow in the watershed in which (1) permeability is primarily a function of depth; (2) water table fluctuations increase with distance from the stream; and (3) recharge, aquifer thickness, and porosity are relatively uniform throughout the watershed in spite of the geological complexity of the Proterozoic crystalline rocks that underlie it.

Noble gases and coupled heat/fluid flow modeling for evaluating hydrogeologic conditions of volcanic island aquifers

“…Water-table depth information within steep mountainous terrain is scarce and groundwater processes in such regimes are generally poorly understood (Manning and Caine, 2007); this is particularly true for active volcanoes (Hurwitz et al, 2003;Ingebritsen et al, 2010). Groundwater noble-gas measurements from wells and springs at distal discharge locations, however, can provide upland water-table temperature and altitude information (Mazor, 1991;Aeschbach-Hertig et al, 1999;Manning and Solomon, 2003;Manning, 2011).…”

Residence time distributions for hydrologic systems: Mechanistic foundations and steady-state analytical solutions

“…The hydrological literature abounds with studies based on analytical solutions for RTDs: (Bockgård et al, 2004;Chen et al, 2011;Knowles et al, 2010;Manning and Caine, 2007;Osenbrück et al, 2006;Solomon et al, 2010;Zouari et al, 2011) for a few recent examples. Since there is no practical way to empirically measure residence time distributions, a commonly used approach is parametric fitting of trial distributions to chemical concentrations (Turnadge and Smerdon, 2014 …”

Tracing groundwater flow and sources of organic carbon in sandstone aquifers using fluorescence properties of dissolved organic matter (DOM)

“…A basic understanding of these processes is important in order to provide a framework within which chemical and microbiological transport processes can be better understood. Various hydrochemical tracers have been used to understand groundwater movement and sources including dissolved gasses, isotopes (stable, radiogenic and radioactive), dyes and bacteriophage (Manning and Caine, 2007;Harden et al, 2003). Groundwater concentrations of anthropogenic atmospheric trace gases such as chlorofluorocarbons (CFCs) have also been used to understand the dynamics of groundwater movement in the subsurface (Plummer et al, 2000;Szabo et al, 1996;Gooddy et al, 2006).…”