Isotopic Discrimination of Aquifer Recharge Sources, Subsystem Connectivity and Flow Patterns in the South Fork Palouse River Basin, Idaho and Washington, USA

Abstract

Groundwater studies in the South Fork Palouse River Basin have been unable to determine recharge sources, subsystem connectivity and flow patterns due to the discontinuity of pathways in the heterogeneous and anisotropic aquifers located in Columbia River flood basalts and interbedded sediments. Major ion, δ18O, δ2H, δ13C, δ34S and temperature for groundwater collected from 28 wells of varying depths indicate a primary recharge source dominated by snowmelt along the eastern basin margin. This recharge can be separated into two distinct sources—a deeper and relatively less altered snowmelt signal (−17.3‰ to −16.8‰ δ18O, −131‰ to −127‰ δ2H, −12.9‰ to −10‰ δ13C, 18–23 °C) and a more altered signal likely derived from a shallower mixture of snowmelt, precipitation and surface water (−16.1‰ to −15.5‰ δ18O, −121‰ to −117‰ δ2H, −15.9‰ to −12.9‰ δ13C, 12–19 °C). A mixing of the shallow and deep source waters is observed within the upper aquifer of the Grande Ronde Formation near Moscow, Idaho, which results in a homogenization of isotope ratios and geochemistry for groundwater at nearly any depth to the west of this mixing zone. This homogenized signal is prevalent in a likely primary productive zone of an intermediate depth in the overall aquifer system.

Pathways and Estimate of Aquifer Recharge in a Flood Basalt Terrain; A Review from the South Fork Palouse River Basin (Columbia River Plateau, USA)

“…The South Fork Palouse River Basin aquifer system is composed of unconfined and primarily confined saturation zones found in the upper sediments, basalt flows, and interbedded sediments with an unconfined alluvial aquifer along the eastern basin margin. The Plio-Quaternary cover (Figure 3a,b) consisting of the loess (Palouse Formation) and sediments of Bovill (Latah Formation) have been hydraulically characterized (K = 0.001-2 m/day; n = 111) through a relatively large number (n) of slug (n = 55) and Guelph permeameter (n = 56) tests [47][48][49][50][51]. The basin creek/river system is relatively stable and has not completely eroded through the relatively thick (10-90 m thick according to water-well and core logs), low-permeability cover in most locations across the basin plain.…”

“…This low-permeability cover contains argillitic soil and clay layers that can act as restriction to vertical flow and may produce translatory flow that is directed towards the streams [35]. Recent investigations have suggested high conductivity flowpaths from the mountain front of the Palouse Range through the unconfined alluvial aquifer into the confined aquifer system of the fractured basalts and interbedded sediments [44,51]. These paleochannels are characterized by higher porosity and moisture content that can be traced from the mountain front to the city of Moscow and are stratigraphically assigned to the sediments of Bovill, Vantage Member, and sediments of Moscow of the Latah Formation [28,35].…”

“…Past research has suggested very limited recharge and paleowaters in the aquifer system [59], spatially uniform recharge across the basin floor [61][62][63], focused recharge around the creek system [31,[64][65][66], and a substantial mountain-front recharge along the basin's eastern margin [45,51]. Hydrologic tracer analysis of groundwater collected at different localities and depths revealed the primary recharge source of snowmelt from the eastern margin in the South Fork Palouse River Basin (Figures 1 and 3c), which aligned with updated geologic perspectives of the relation of mountain-front alluvium and the fractured basalts and interbedded sediments of the confined aquifer system [43].…”

“…Previous research discriminated source waters, recharge pathways, and alteration of the redox environment along with identifying contamination of prior 14 C analysis from mantle CO 2 . A shallow (<150 mBGL) portion of the aquifer system was characterized as containing a mix of mid-basin surface water, mountain-front runoff, and snowmelt as indicated by different source-water signals identified by δ 16 O, δ 18 O, δ 13 C, δ 2 H, and noble gas values [51]. This mixed distribution of source waters in the upper aquifer arises from the mixing of rapidly recharged snowmelt and more slowly recharged surface water.…”

Hydrogeological Behaviour and Geochemical Features of Waters in Evaporite-Bearing Low-Permeability Successions: A Case Study in Southern Sicily, Italy

“…The isotopic analyses were conducted to refine knowledge about the groundwater origins (stable isotopes of oxygen and deuterium) and residence times (tritium). Isotopes, together with chemical features, are among the major groundwater tracers traditionally and widely employed in hydrogeological studies (e.g., [25][26][27][28][29]).…”