Kansas Geological Survey, Open-file Report 2004-32
James J. Butler, Jr., Donald O. Whittemore, Xiaoyong Zhan, and John M. Healey
Kansas Geological Survey
Prepared for the
Kansas Department of Agriculture, Division of Water Resources
KGS Open File Report 2004-32
Two multi-day pumping tests were performed by the Kansas Geological Survey at the O'Rourke Bridge site adjacent to the Arkansas River in Pawnee County, Kansas, near the city of Larned. The first test was performed in the alluvial aquifer of the Arkansas River over two days in September of 2002, while the second test was performed in the High Plains aquifer over four days in October of 2003. The major objectives of these tests were to obtain information about the hydraulic and geochemical responses of the aquifers to extended periods of pumping, the degree of hydraulic connection between the two aquifers, and the impact of pumping on streamflow in the Arkansas River. An extensive network of observations wells was installed for the two tests using direct-push electrical conductivity logging to delineate the stratigraphy and to select the intervals over which the wells were screened. Pumping-induced changes in water level (drawdown) were measured using both automatic and manual methods, and water samples were collected before, during, and after the pumping tests. Type curve analyses were performed on the drawdown data from two observation wells for each pumping test. The transmissivity and specific yield of the Arkansas River alluvial aquifer estimated from the first test were 3800 ft2/d and 0.31, respectively. There was no indication of vertical flow from the underlying High Plains aquifer during the test, so no information about the hydraulic conductivity of the confining unit separating the two aquifers could be obtained. The transmissivity and storage coefficient of the High Plains aquifer estimated from the second test were 5400 ft2/d and 1.7x10-4, respectively. The pumping in the High Plains aquifer induced flow from the overlying alluvial aquifer, and the hydraulic conductivity of the confining unit separating the two aquifers was estimated to be 7.0x10-3 ft/d. The parameter estimates obtained from both tests are consistent with the geologic composition of the unconsolidated aquifers and confining unit.
The Arkansas River rarely flowed at the O'Rourke Bridge site during 2002 and 2003, so these pumping tests could not provide direct information about the impact of nearby pumping on the flow of the Arkansas River. Regardless, the chemistry data collected during the first test indicate that pumping of the alluvial aquifer will draw in water from the Arkansas River. The results of the second test indicate that pumping of the High Plains aquifer will induce downward movement of water from the alluvial aquifer through the confining unit. Thus, pumping in the High Plains aquifer in the vicinity of the O'Rourke Bridge would also be expected to impact flow in the Arkansas River, but the timing and magnitude of that impact will be dramatically different from that for pumping from a well in the alluvial aquifer located close to the stream.
The details of the well construction for the pumping well used in the second test are not known. However, it appears that the gravel pack extends upward from the High Plains aquifer through the confining unit to the alluvial aquifer, a common design for irrigation wells installed prior to the last two decades. This design appears to have resulted in movement of water from the alluvial aquifer to the High Plains aquifer through the gravel pack prior, during, and after the pumping test. This flow through the gravel pack must always be considered when interpreting the results of analyses of water samples collected in the vicinity of older irrigation wells in the High Plains aquifer.
larned_pumping.pdf (2.2 MB)
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