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Groundwater Freeze And Cherry Pdf

Map showing study area, mountains, streams, eastern Snake River Plain (ESRP), Idaho National Laboratory (INL), saline soil (U.S. Department of Agriculture 2014), deep test well INEL-1, and general direction of regional groundwater flow

Groundwater Freeze And Cherry Pdf


Groundwater in the Mud Lake area resides in the eastern Snake River Plain (ESRP) aquifer, a sole-source fractured-basalt aquifer of significant economic value to the State of Idaho. Recharge to the Mud Lake area occurs from the Camas Creek and Medicine Lodge Creek drainage basins in the extreme northeastern extent of the aquifer, and groundwater in the aquifer flows downgradient (southwest) from the Mud Lake area through the Idaho National Laboratory (INL). Consequently, the water quality of groundwater in the Mud Lake area influences the water quality of groundwater at the INL, and an understanding of the geochemical sources and processes controlling the water quality of groundwater in the Mud Lake area will provide a better understanding of the sources and processes controlling the water quality of groundwater at the INL, a long-term goal of the Department of Energy and the U.S. Geological Survey (Knobel et al. 2005). The geochemical sources and processes controlling the water quality of groundwater of 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 (Parkhurst and Appelo 2013).

Surface water in the study area (Fig. 2) includes Medicine Lodge and Camas Creeks, both of which terminate on the ESRP; Mud Lake; ponds, lakes, and wetlands at the Camas National Wildlife Refuge (CNWR) and Mud Lake Wildlife Management Area; irrigation canals; and applied irrigation water. Camas Creek is the primary source of surface water to Mud Lake and for most surface water irrigation in the study area; pumped groundwater is also used for irrigation. Infiltration recharge from surface water occurs from Medicine Lodge and Camas Creeks; ponds, lakes, and wetlands at Mud Lake and the CNWR; irrigation canals; and excess irrigation water (Spinazola 1994).

The unsaturated zone in the ESRP ranges from a few meters at the CNWR to tens of meters elsewhere and includes a perched groundwater zone that extends south and west of Mud Lake (Stearns et al. 1939). The ESRP aquifer is comprised of hundreds of intercalated, subhorizontal layers of basalt and sediment (Lindholm 1996) and is estimated to be >1,000 m thick in some locations (Garabedian 1992). A clay layer creates confined aquifer conditions in the area around Mud Lake (Spinazola 1994), but the aquifer is unconfined elsewhere. Most groundwater flow in the aquifer is horizontal and occurs in rubble- and sediment-filled interflow zones between basalt flows (Ackerman et al. 2006), although dikes associated with volcanic vent corridors may impede horizontal flow (Anderson et al. 1999). Downward groundwater movement occurs near the margins of the ESRP and southwest of Mud Lake, and upward movement occurs in parts of Camas Creek, Mud Lake, the CNWR (Spinazola 1994), and within vent corridors where fissures and dikes may facilitate upward circulation of geothermal water (Anderson et al. 1999).

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

The hydrochemical facies (Fig. 6) of water was calcium bicarbonate for surface water, most groundwater from the mountains, and 19 of 32 groundwater samples from the ESRP. The hydrochemical facies of other groundwater from the ESRP were various combinations of calcium-, sodium-, and magnesium-bicarbonates and calcium chloride bicarbonate (site 33). Thermal water was calcium sulfate (site 57), calcium bicarbonate (site 58), and sodium bicarbonate (site 100).

Most δ2H and δ18O values (Fig. 7) of groundwater in the study area (plus values for groundwater from the Centennial Mountains; these values are included in Fig. 7 because much of the groundwater in the study area originates from there) plot near and approximately parallel to the local meteoric water line for winter (Benjamin et al. 2004) indicating that most groundwater is of meteoric origin and from winter precipitation. All groundwater from the ESRP plots along a trend line (determined from linear regression of Mud Lake δ2H and δ18O values) for evaporation of Mud Lake water, but only sites 19, 22, and 23 (southwest of Mud Lake; Fig. 4) have large δ2H and δ18O values that indicate evaporated water was a significant source of recharge.

The approximate age of water was estimated from tritium concentrations in water samples, monthly records (from 1953 to 2009) of tritium concentrations in precipitation (Michel 1989 and personal communication, International Atomic Energy Agency 2013), and the decay equation for tritium. Tritium concentrations indicating pre-1952 (old), post-1952 (young), and a mixture of old and young water, for the years 1991 and 2012, are shown in Table 5. Old water was estimated for 2 sites in the mountains and 4 sites on the ESRP; young water was estimated for 3 sites in the mountains, 3 sites on the ESRP, and Camas Creek; and a mixture of young and old water was estimated for 3 sites in the mountains and 4 sites on the ESRP (Table 4). The old water on the ESRP was from sites (sites 5 and 17) in the northeastern part of the ESRP that received recharge from old water in the mountains (water similar in age to site 3, Table 4; Fig. 3) or from sites with unusual chemistry (i.e., anoxic water) located in volcanic vent corridors (sites 25 and 29). Groundwater from the other 7 sites on the ESRP was either young or a mixture of young and old water, indicating that a source of young water provided recharge to most of the shallow groundwater in the ESRP.

Solutes in groundwater are derived from recharge water, anthropogenic inputs, and chemical reactions. Potentially important sources of recharge water to the ESRP aquifer are groundwater from the Beaverhead Mountains, groundwater from the Camas Creek drainage basin (Rattray and Ginsbach 2014), infiltration of surface water (Medicine Lodge and Camas Creeks; lakes, ponds, and wetlands at Mud Lake and the CNWR; and irrigation water), and upwelling of geothermal water from beneath the aquifer (Mann 1986).

Elements included in the models were hydrogen, oxygen, carbon, silica, nitrogen, sulfur, chloride, fluoride, calcium, magnesium, sodium, potassium, aluminum, and iron. Phases included carbonates (calcite, dolomite), evaporites (gypsum, halite, sylvite, bischofite), silicates [rhyolitic volcanic glass, plagioclase (An25 and An60), potassium feldspar], fluorite, calcium montmorillonite, goethite, fertilizer (ammonium nitrate, sylvite), road salt (halite), anti-icing liquid (MgCl2, represented as bischofite), organic matter, and gasses (methane, hydrogen sulfide, DO, CO2). DO was included as a phase because the water sample from Camas Creek (site 78) had a temperature of 19.3 C and was undersaturated with DO; however, most water from Camas Creek would recharge at colder temperatures and be saturated with DO. Based on saturation indices, kinetic considerations, and redox conditions, all phases should dissolve in groundwater except for calcium montmorillonite and goethite (precipitate) and calcite (dissolve or precipitate).

The model results indicate that sources of water to the ESRP aquifer were groundwater from the Beaverhead Mountains and the Camas Creek drainage basin; infiltration of surface water from Medicine Lodge Creek, Camas Creek, Mud Lake, and irrigation water; and upward flow of geothermal water. Because Camas Creek was the primary source of surface water to Mud Lake and for most surface water used for irrigation, and because surface water recharge occurred over most of the ESRP aquifer, Camas Creek was a very important source of recharge to the aquifer.

Mixing of groundwater with surface water or other groundwater occurred throughout the ESRP, and mixing of groundwater with surface water, other groundwater, and geothermal water was modeled for four sites (sites 25, 27, 29, and 34) located in volcanic vent corridors. Evaporation was modeled to reproduce the chemistry of groundwater from sites downgradient of the CNWR (site 8) and Mud Lake (sites 19 and 22).

Carbonate reactions, silicate weathering, and dissolution of evaporites and fertilizer explain most of the change in chemistry in the ESRP aquifer (Table 6). Large amounts of gypsum and halite dissolution support the interpretation that evaporite deposits are present within the Mud Lake subbasin and are a significant source of chloride, sodium, sulfate, and calcium in groundwater. Redox reactions were important at the CNWR and Mud Lake (from oxidation of organic matter) and at locations (sites 25, 27, 29, and 34) where upwelling geothermal water mixed with groundwater (from oxidation of reduced carbon and sulfur species in the geothermal water). For example, anoxic groundwater at two sites (sites 25 and 29) was modeled by mixing geothermal water (site 100) with surface water and groundwater upgradient of these sites and oxidation of reduced species in the geothermal water. The groundwater would only be anoxic at these sites if the groundwater was relatively stagnant because a continual inflow of oxidized groundwater would produce oxidized conditions. Cation exchange was locally important in areas where water had significant contact with sediment, for instance, areas where surface water infiltration occurred through wetlands or from irrigation.

Evaporite deposits within the Mud Lake area are associated with sediment of Lake Terreton. Surficial deposits of lake sediment extend over the southwestern part of the ESRP in the Mud Lake area and westward onto the INL (Figs. 1, 3). Gypsum identified in lake sediment in several wells at depths ranging from 60 to 740 m below land surface (Blair 2001; Geslin et al. 2002) indicates that evaporite deposits may be present at various depths. To determine whether large amounts of evaporite deposits are dissolving within or outside areas defined by surficial lake sediment, or both, and in the unsaturated zone (from infiltration of irrigation water), saturated zone, or both, a plot was made of SpC versus NO3 + NO2 in groundwater (where SpC is related to the dissolution of evaporite minerals and the concentration of NO3 + NO2 is related to infiltration of irrigation water).


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