Groundwater age dating in fractured rock using 4He data

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

“…A multi‐rate model better represents the geometry of exchange in real systems (Haggerty & Gorelick, 1995). In addition, this study assumed that mobile‐immobile exchange is addressed analytically for any subsurface geometries; there is evidence that exchange processes are more complicated in fractured media specifically (Trinchero et al., 2019; Trinchero and Iraola, 2020). Note that mobile‐immobile exchange can also be modeled more precisely using the phase exposure‐dependent exchange (PhEDEX) approach (Ginn et al., 2016).…”

“…When using appropriate correction and interpretation techniques, isotope sampling conducted at one point in time can instead reveal long‐term groundwater recharge behavior (Cartwright et al., 2020; Ginn et al., 2009; McCallum, Cook, et al., 2014; McCallum, Engdahl, et al., 2014; Turnadge & Smerdon, 2014). The ability of isotopes to reflect groundwater age is influenced by the groundwater transit through slower‐moving and faster‐moving components of the aquifer system—this includes aquitards (Sanford, 1997; Sudicky & Frind, 1981), general heterogeneity (Weissman et al., 2002) and fractures (Cook et al., 2005; Cornaton et al., 2011; Trinchero et al., 2019; Trinchero and Iraola, 2020; Underwood et al., 2018). Assuming a homogeneous medium creates an oversimplification reducing the possibility of applying the findings to realistic systems (Haggerty & Gorelick, 1995).…”