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.
Highlights
Since 1935, groundwater levels have declined in aquifers of the Palouse River Basin, in the South Fork Palouse River Basin (Basin) in north-central Idaho and eastern Washington (Figure 1) [1,2,3].The Basin aquifers are contained in the fractured basalts of the Columbia River Basalt Group (CRBG)and interbedded sediments of the Latah Formation that compose much of the Basin [4]
Evaluation of isotope and geochemical characteristics of groundwater collected from the study area indicates two major recharge sources to aquifers along the eastern margin of the Basin—a primarily snowmelt-dominant water (Deep source water) and a modified snowmelt/precipitation water (Shallow source water)
These source waters are discriminated by variation in major ion chemistry, water temperature and values of δ18 O, δ2 H, δ13 C and δ34 S
Summary
Since 1935, groundwater levels have declined in aquifers of the Palouse River Basin, in the South Fork Palouse River Basin (Basin) in north-central Idaho and eastern Washington (Figure 1) [1,2,3].The Basin aquifers are contained in the fractured basalts of the Columbia River Basalt Group (CRBG)and interbedded sediments of the Latah Formation that compose much of the Basin [4]. Since 1935, groundwater levels have declined in aquifers of the Palouse River Basin, in the South Fork Palouse River Basin (Basin) in north-central Idaho and eastern Washington (Figure 1) [1,2,3]. The Basin aquifers are contained in the fractured basalts of the Columbia River Basalt Group (CRBG). Interbedded sediments of the Latah Formation that compose much of the Basin [4]. Groundwater provides a primary source for industry and agriculture in the region [5] and is the sole source of municipal water in the Basin [2,6]. Extrapolation of the current trend in declining groundwater levels in the Basin indicates the possibility of insufficient groundwater resources to meet future community needs [6,7].
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