TY - JOUR
T1 - Ground Water Chemistry Evolution Under Unsaturated Zone Sulfate Salt Dissolution in a Great Basin Lacustrine Aquifer, Western United States
AU - Bohm, B.
AU - Thomas, J.
AU - Dahan, O.
AU - Ralston, J.
AU - McKay, A.
PY - 2006/12/1
Y1 - 2006/12/1
N2 - Sulfate and chloride ions in combination with stable isotopes of water
turned out to be a powerful tool to decipher the complex aquifer
geochemistry in the Fernley Basin aquifer system, in the western Great
Basin of the Western United States. The results permitted identifying
the underlying hydrologic processes and conceptualizing a
three-dimensional model of basin geochemistry. The primary causes of
high total dissolved solids (TDS) in this lacustrine sediment aquifer
system are dissolution of unsaturated zone Na-SO4 salts by infiltrating
irrigation water. By irrigating an area of 2,185 hectares between 0.5
and 1.3 million metric tons of salts were washed into the underlying
aquifer, increasing aquifer TDS from pre-irrigation values of about 600
mg/l to more than 5000 mg/l. Irrigation also raised the ground water
table which adds to unsaturated zone salt dissolution. The high TDS
ground water eventually discharges into the Truckee River, which is the
only source of surface water for Pyramid Lake, a large hydrologically
closed lake. At present most of the unsaturated zone salts beneath the
irrigated areas have been dissolved. About 25 years' worth of water
quality records from nine municipal wells show that the historically
high TDS ground water is now gradually diluted by continued application
of low TDS irrigation water. Due to the complex interaction of salt
dissolution, mixing and dilution, the Fernley aquifer system is now
characterized by three water types: 1) about 150 mg/l TDS mixed-cation-
HCO3 river water; 2) 500 to 3000 mg/l TDS Na-Cl water and 3) 250 to 5000
mg/l TDS Na-SO4 water. Mixing of these three water types results in wide
ranges of ground water chemistry. Mixing was identified between low TDS
river water and high TDS Na-SO4 ground waters, and Na-SO4 and Na-Cl
ground waters. Deep well samples from the central part of the basin
indicate that the pre-irrigation ambient Na-Cl ground water type at
depth has been mixed with Na-SO4 water in the upper 200 m of the
aquifer, which is now discharging north into the Truckee River. A
smaller source of high TDS water is ambient Na-Cl ground water flowing
through a fault zone into the Truckee River at the northeastern basin
periphery. Discharge of these two high TDS ground water sources are
evident in the Truckee River's water chemistry during the low streamflow
season.
AB - Sulfate and chloride ions in combination with stable isotopes of water
turned out to be a powerful tool to decipher the complex aquifer
geochemistry in the Fernley Basin aquifer system, in the western Great
Basin of the Western United States. The results permitted identifying
the underlying hydrologic processes and conceptualizing a
three-dimensional model of basin geochemistry. The primary causes of
high total dissolved solids (TDS) in this lacustrine sediment aquifer
system are dissolution of unsaturated zone Na-SO4 salts by infiltrating
irrigation water. By irrigating an area of 2,185 hectares between 0.5
and 1.3 million metric tons of salts were washed into the underlying
aquifer, increasing aquifer TDS from pre-irrigation values of about 600
mg/l to more than 5000 mg/l. Irrigation also raised the ground water
table which adds to unsaturated zone salt dissolution. The high TDS
ground water eventually discharges into the Truckee River, which is the
only source of surface water for Pyramid Lake, a large hydrologically
closed lake. At present most of the unsaturated zone salts beneath the
irrigated areas have been dissolved. About 25 years' worth of water
quality records from nine municipal wells show that the historically
high TDS ground water is now gradually diluted by continued application
of low TDS irrigation water. Due to the complex interaction of salt
dissolution, mixing and dilution, the Fernley aquifer system is now
characterized by three water types: 1) about 150 mg/l TDS mixed-cation-
HCO3 river water; 2) 500 to 3000 mg/l TDS Na-Cl water and 3) 250 to 5000
mg/l TDS Na-SO4 water. Mixing of these three water types results in wide
ranges of ground water chemistry. Mixing was identified between low TDS
river water and high TDS Na-SO4 ground waters, and Na-SO4 and Na-Cl
ground waters. Deep well samples from the central part of the basin
indicate that the pre-irrigation ambient Na-Cl ground water type at
depth has been mixed with Na-SO4 water in the upper 200 m of the
aquifer, which is now discharging north into the Truckee River. A
smaller source of high TDS water is ambient Na-Cl ground water flowing
through a fault zone into the Truckee River at the northeastern basin
periphery. Discharge of these two high TDS ground water sources are
evident in the Truckee River's water chemistry during the low streamflow
season.
KW - 1806 Chemistry of fresh water
KW - 1829 Groundwater hydrology
KW - 1831 Groundwater quality
KW - 1834 Human impacts
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VL - 41
JO - Geophysical Research Abstracts
JF - Geophysical Research Abstracts
SN - 1029-7006
ER -