These gradients are similar to those observed for the ESRP aquifer at and near the INL (0.2–11 m/km), and given the similar aquifer materials and stratigraphy for the Mud Lake area and the INL, average linear flow velocities in the Mud Lake area are probably similar to the 0.6–6 m/d velocities estimated at and near the INL (Ackerman et al.Map showing water-table contours (in meters above the National Geodetic Vertical Datum of 1929), water-level measurement sites, generalized groundwater flow directions, and water-quality site locations and numbers ).Groundwater with elevated dissolved-solids concentrations—containing large concentrations of chloride, sodium, sulfate, and calcium—is present in the Mud Lake area of Eastern Idaho.The source of these solutes is unknown; however, an understanding of the geochemical sources and processes controlling their presence in groundwater in the Mud Lake area is needed to better understand the geochemical sources and processes controlling the water quality of groundwater at the Idaho National Laboratory.Mixing of groundwater with surface water or other groundwater occurred throughout the aquifer.
Deep geothermal water from the ESRP (site 100) was hot (57 °C), had a p H of 7.9, was brackish (2,870 µS/cm at 25 °C), was presumed to be anoxic, and had small concentrations of calcium (7.5 mg/L) and magnesium (0.5 mg/L) and large concentrations of sodium (390 mg/L), bicarbonate (900 mg/L), sulfate (99 mg/L), fluoride (13 mg/L), boron (560 μg/L), and iron (1,100 μg/L).
Groundwater from wells (sites 3, 32, and 35) and cold springs (sites 55, 56, and 59) in the mountains had temperatures ranging from 5.8 to 12.8 °C, p H ranging from 6.9 to 7.8, Sp C ranging from 258 to 523 µS/cm at 25 °C, were anoxic to slightly undersaturated with oxygen (1.1–94.4 % saturation), and had moderate-to-large carbon dioxide (CO ranged from −3.25 to −1.72.
Cation and anion concentrations (in mg/L) ranged from 15 to 109 for calcium, 4.6 to 33.0 for magnesium, 9.0 to 85.0 for sodium, 2.0 to 7.2 for potassium, 131 to 457 for bicarbonate, 5.6 to 121 for chloride, 5.3 to 91.3 for sulfate, 0.15 to 1.01 for fluoride, and 0.03 mg/L as N were measured in water from a few sites (sites 18, 25, 27, and 29), and large lithium concentrations were measured at sites 25 (71 μg/L) and 29 (47 μg/L).
The geochemical sources and processes controlling the water quality of groundwater in the Mud Lake area were determined by investigating the geology, hydrology, land use, and groundwater geochemistry in the Mud Lake area, proposing sources for solutes, and testing the proposed sources through geochemical modeling with PHREEQC.
Modeling indicated that sources of water to the eastern Snake River Plain aquifer were groundwater from the Beaverhead Mountains and the Camas Creek drainage basin; surface water from Medicine Lodge and Camas Creeks, Mud Lake, and irrigation water; and upward flow of geothermal water from beneath the aquifer.
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