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Moscow basin ground water studies. Pamphlet 153 Item Info

Moscow basin is in Latah County, Idaho, or the eastern edge of the Columbia Plateau physiographic province. The area of the basin is about 58 square miles. The principal water users, City of Moscow and University of Idaho, depend exclusively on ground water obtained from wells that reach three zones of artesian aquifers in the basalt flows and sedimentary interbeds of the Columbia River Group of Miocene age. The three artesian zones are designated the upper, middle, and Bower artesian zones, The Columbia River Group is overlain by surficial sediments in which water generally occurs under water-table conditions, The Columbia River Group is underlain by a basement of crystalline rocks of pre-Tertiary age that also crops out beyond the limits of the basalt and forms the mountains that rim the basin on thee sides. Where exposed at the surface, the crystalline basement contains water under water-table conditions. Neither the surficial sediments nor the crystalline basement will yield large amounts of water; the rocks of the Columbia River Group are the only source of water for public supplies. All ground water originates as precipitation that falls within the borders of Moscow basin; natural discharge of ground water is by underflow to the west. Prior to 1960, the entire public supply was obtained from wells reaching the upper artesian zone. The quality of water was unsatisfactory because of excessive amounts of iron and moderate hardness. Between 1960 and 1965, wells were drilled into the middle and lower artesian zones, and by 1965, nearly all water pumped for public supplies was obtained from the middle and lower artesian zones. The waters from the middle and lower artesian zones contain only moderate amounts of iron and are relatively soft. In 1896, water levels In wells in the upper artesian zone were at or slightly above land surface but declined continuously thereafter and, by 1968, static levels were nearly 120 feet below the surface in the vicinity of the City of Moscow wells. This decline led to suggestions that ground water recharge in Moscow basin was insufficient to balance pumpage. Following the phasing out of heavy pumpage of the upper artesian zone in 1960-1965, water levels rose and recovered to within 65 feet of the surface in 1969. In our studies, two lines of investigation indicate that pumpage was not in excess of recharge during the period 1896-1960. We analyzed the pumpage and water level records of the public supply wells, using a mathematical model aquifer that utilizes the theory of image wells and assumes that there is no recharge to the basin. The results indicate that the decline of water levels in the upper artesian zone was actually much less than it would have been if pumpage was greatly in excess of recharge. We also studied the long-term records of water level fluctuations in observation wells in the basin. The water table in the surficial aquifers remained stable during the time that the water levels in the upper artesian zone declined. We attributed the decline in the water levels in the upper artesian zone to barrier boundary effects rather than to lack of recharge. The results of our studies support the views of previous workers who estimate ground water recharge to the basin by use of the equation of hydrologic equilibrium. All such estimates indicate that recharge is in excess of pumpage sufficient to meet the demands of the basin through the year 2000, We also used our no-recharge mathematical model aquifers to estimate the total water in ground water storage in Moscow basin and to predict the decline in water levels that would occur by the year 2000. Although these figures are based on an assumption that we have rejected--no recharge to the basin--they do represent the smallest amount of water and the largest amount of drawdown to be expected. The study indicates that the middle and lower artesian zones would meet the anticipated 1965-2000 demand of 50.1 billion gallons and still have as much as 299.4 billion gallons remaining in storage in the year 2000. Water levels would b e from 50 t o 80 feet lower in 2908 than they were in 1965. This study indicates that ground water can supply the anticipated needs of Moscow basin well into the 21st century regardless of whether the water is derived from ground water storage or from recharge. If need for water should exceed natural recharge at some time in the future, artificial recharge utilizing water from sources in and near Moscow basin could furnish more than 1 billion gallons of additional water annually. During a normal year, spring runoff from intermittent streams in the Palouse Range can provide about 300 million gallons over a 90 day period during February through May. The Moscow Waste Water Treatment Plant now discharges about 300 million gallons annually; the discharge should increase to about 1 billion gallons by the year 2000. The effluent could be further treated, then recycled by artificial recharge. Mathematical model studies show that the existing wells in the upper artesian zone can accept artificial recharge at rates of 1000 to 2000 gpm for as many as 100 consecutive days without the cone of impression reaching the surface. Cost of artificial recharge probably is less than the cost of long-distance importation of water. The waters of the surficial aquifers are relatively soft, averaging 87 ppm hardness as CaC03, and are relatively low in dissolved solids, averaging 127 ppm. As the waters move into the upper artesian zone, average hardness increases to 135 ppm and average dissolved solids increases to 190 ppm., probably as the result of solution of magnesium from magnesium-rich minerals in the basalts . As the waters move through the middle artesian zone and into the lower artesian zone, average hardness decreases to 84 ppm, but average dissolved solids increases to 286 ppm,; the decrease in hardness probably is the result of base exchange of sodium for calcium. Calcium and bicarbonate are the dominant ions in most of the ground waters of Moscow basin, but calcium and sulfate or sodium plus calcium and bicarbonate are the dominate ions in a few of the waters. Excessive amounts of iron are moderately common in waters from the surficial aquifers and very common in waters from the upper artesian zone. The iron originates in high-iron clay deposits in the surficial aquifers on the outer margin of the recharge area of the artesian aquifers. The high-iron waters move laterally from the clay deposits into the upper artesian zone. Waters from the middle and lower artesian zones contained only moderate amounts of iron when the aquifers were first placed into use. Continued pumpage could induce the high-iron waters to move into the middle and lower artesian zones. Silica also is somewhat high for ground waters and the origin of the silica probably is related to the origin of the iron. Some of the waters in the surficial aquifers contain relatively high amounts of nitrates and chlorides that indicate possible contamination from septic tanks, fertilizers, and barn-yard wastes .

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Title:
Moscow basin ground water studies. Pamphlet 153
Authors:
Jones, Robert W.; Ross, Sylvia H.
Date Created (ISO Standard):
1972-03
Description:
Moscow basin is in Latah County, Idaho, or the eastern edge of the Columbia Plateau physiographic province. The area of the basin is about 58 square miles. The principal water users, City of Moscow and University of Idaho, depend exclusively on ground water obtained from wells that reach three zones of artesian aquifers in the basalt flows and sedimentary interbeds of the Columbia River Group of Miocene age. The three artesian zones are designated the upper, middle, and Bower artesian zones, The Columbia River Group is overlain by surficial sediments in which water generally occurs under water-table conditions, The Columbia River Group is underlain by a basement of crystalline rocks of pre-Tertiary age that also crops out beyond the limits of the basalt and forms the mountains that rim the basin on thee sides. Where exposed at the surface, the crystalline basement contains water under water-table conditions. Neither the surficial sediments nor the crystalline basement will yield large amounts of water; the rocks of the Columbia River Group are the only source of water for public supplies. All ground water originates as precipitation that falls within the borders of Moscow basin; natural discharge of ground water is by underflow to the west. Prior to 1960, the entire public supply was obtained from wells reaching the upper artesian zone. The quality of water was unsatisfactory because of excessive amounts of iron and moderate hardness. Between 1960 and 1965, wells were drilled into the middle and lower artesian zones, and by 1965, nearly all water pumped for public supplies was obtained from the middle and lower artesian zones. The waters from the middle and lower artesian zones contain only moderate amounts of iron and are relatively soft. In 1896, water levels In wells in the upper artesian zone were at or slightly above land surface but declined continuously thereafter and, by 1968, static levels were nearly 120 feet below the surface in the vicinity of the City of Moscow wells. This decline led to suggestions that ground water recharge in Moscow basin was insufficient to balance pumpage. Following the phasing out of heavy pumpage of the upper artesian zone in 1960-1965, water levels rose and recovered to within 65 feet of the surface in 1969. In our studies, two lines of investigation indicate that pumpage was not in excess of recharge during the period 1896-1960. We analyzed the pumpage and water level records of the public supply wells, using a mathematical model aquifer that utilizes the theory of image wells and assumes that there is no recharge to the basin. The results indicate that the decline of water levels in the upper artesian zone was actually much less than it would have been if pumpage was greatly in excess of recharge. We also studied the long-term records of water level fluctuations in observation wells in the basin. The water table in the surficial aquifers remained stable during the time that the water levels in the upper artesian zone declined. We attributed the decline in the water levels in the upper artesian zone to barrier boundary effects rather than to lack of recharge. The results of our studies support the views of previous workers who estimate ground water recharge to the basin by use of the equation of hydrologic equilibrium. All such estimates indicate that recharge is in excess of pumpage sufficient to meet the demands of the basin through the year 2000, We also used our no-recharge mathematical model aquifers to estimate the total water in ground water storage in Moscow basin and to predict the decline in water levels that would occur by the year 2000. Although these figures are based on an assumption that we have rejected--no recharge to the basin--they do represent the smallest amount of water and the largest amount of drawdown to be expected. The study indicates that the middle and lower artesian zones would meet the anticipated 1965-2000 demand of 50.1 billion gallons and still have as much as 299.4 billion gallons remaining in storage in the year 2000. Water levels would b e from 50 t o 80 feet lower in 2908 than they were in 1965. This study indicates that ground water can supply the anticipated needs of Moscow basin well into the 21st century regardless of whether the water is derived from ground water storage or from recharge. If need for water should exceed natural recharge at some time in the future, artificial recharge utilizing water from sources in and near Moscow basin could furnish more than 1 billion gallons of additional water annually. During a normal year, spring runoff from intermittent streams in the Palouse Range can provide about 300 million gallons over a 90 day period during February through May. The Moscow Waste Water Treatment Plant now discharges about 300 million gallons annually; the discharge should increase to about 1 billion gallons by the year 2000. The effluent could be further treated, then recycled by artificial recharge. Mathematical model studies show that the existing wells in the upper artesian zone can accept artificial recharge at rates of 1000 to 2000 gpm for as many as 100 consecutive days without the cone of impression reaching the surface. Cost of artificial recharge probably is less than the cost of long-distance importation of water. The waters of the surficial aquifers are relatively soft, averaging 87 ppm hardness as CaC03, and are relatively low in dissolved solids, averaging 127 ppm. As the waters move into the upper artesian zone, average hardness increases to 135 ppm and average dissolved solids increases to 190 ppm., probably as the result of solution of magnesium from magnesium-rich minerals in the basalts . As the waters move through the middle artesian zone and into the lower artesian zone, average hardness decreases to 84 ppm, but average dissolved solids increases to 286 ppm,; the decrease in hardness probably is the result of base exchange of sodium for calcium. Calcium and bicarbonate are the dominant ions in most of the ground waters of Moscow basin, but calcium and sulfate or sodium plus calcium and bicarbonate are the dominate ions in a few of the waters. Excessive amounts of iron are moderately common in waters from the surficial aquifers and very common in waters from the upper artesian zone. The iron originates in high-iron clay deposits in the surficial aquifers on the outer margin of the recharge area of the artesian aquifers. The high-iron waters move laterally from the clay deposits into the upper artesian zone. Waters from the middle and lower artesian zones contained only moderate amounts of iron when the aquifers were first placed into use. Continued pumpage could induce the high-iron waters to move into the middle and lower artesian zones. Silica also is somewhat high for ground waters and the origin of the silica probably is related to the origin of the iron. Some of the waters in the surficial aquifers contain relatively high amounts of nitrates and chlorides that indicate possible contamination from septic tanks, fertilizers, and barn-yard wastes .
Subjects:
water properties chemical composition artesian aquifers water table decline artificial recharge
Location:
Moscow
Latitude:
46.77
Longitude:
-116.96
IWRRI number:
197212
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
Publisher:
Idaho Bureau of Mines and Geology
Contributing Institution:
University of Idaho
Type:
Text
Format:
application/pdf
Cataloger:
wbv
Date Digitized:
2012

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Preferred Citation:
"Moscow basin ground water studies. Pamphlet 153", Idaho Waters Digital Library, University of Idaho Library Digital Collections, https://www.lib.uidaho.edu/digital/iwdl/items/iwdl-197212.html
Rights
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
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