Kansas Geological Survey, Open-file Report 2007-20
by
P. A. Macfarlane
KGS Open File Report 2007-20
Historically, the Ozark Plateaus aquifer system has been the single most important source of water in the Tri-State region of southeast Kansas, southwest Missouri, and northeastern Oklahoma. Recent concerns that the available supply from this source may become inadequate, rendered unusable, or require additional water treatment in the near future stem from: (1) recent and projected population growth that will create increased demand for water by public supplies and some industries; (2) potential upward vertical or eastward migration of saline water into public supply wells due to pumping, if pumping rates or wellfield size are increased to keep up with demand; and (3) possible contamination of ground-water supplies by downward moving leachate derived from mine tailings piles and the mine water contained in the abandoned open shafts. In response to these concerns the Kansas Water Office (KWO) contracted with the Kansas Geological Survey (KGS) to evaluate and redesign the existing ground-water-level monitoring network in southeast Kansas in Phase 1 of the project.
In Phase 2 of the project, the KWO contracted with the KGS to (1) site and construct new wells that would serve as dedicated monitoring wells to track water levels and quality in the Ozark Plateaus aquifer system into the future, (2) continue conducting semi-annual water-level surveys of wells in the monitoring network designed in Phase 1, and (3) provide support to the Ozark aquifer Water Issue Strategic Plan (WISP) group through participation in their meetings, and participation in the technical advisory board (TAC) formed in connection with the USGS project to develop a management model of the Ozark aquifer in the Tri-state region.
Contract specifications were developed and let for bid on (1) Ozark aquifer and a Springfield Plateau aquifer monitoring wells sited within the City of Pittsburg wellfield with the objective of conducting high-frequency water-level monitoring using pressure transducers and well tests to derive estimates of aquifer properties and (2) an Ozark aquifer well near McCune, Kansas, in southwest Crawford County to monitor water level and quality changes near the back edge of the water quality transition zone in the Ozark aquifer. The Ozark aquifer monitoring well in the Pittsburg wellfield site (OW-O) is 900 feet deep and was completed as an open borehole from near the top of the Ozark aquifer at 515 feet below surface down into the lower part of the Roubidoux Formation at 900 feet below surface. The total depth of the Springfield Plateau aquifer well (OW-S) is 375 feet where it ends in the lower part of the aquifer. The well is completed as an open borehole from 200 feet below surface down to total depth. The Ozark aquifer monitoring well at the site near McCune is 1,206 feet deep and was completed as an open borehole from 830 feet down to total depth. Based on an examination of the drill cuttings it is believed that the well bottoms in the lower part of the Roubidoux Formation.
Two sets of well tests were conducted using Pittsburg wells 8 and 10 to derive aquifer properties data that could be incorporated into the USGS modeling study. Each test set consisted of a pumping (pump on) and recovery (pump off) phase during which water-level data were collected at high frequencies using pressure transducers that had been installed in OW-S and OW-O. The drawdown and recovery data were processed and analyzed using standard procedures to derive estimates of Ozark aquifer transmissivity and storativity. The average of the transmissivity and storativity values from the tests conducted using Pittsburg well 10 as the pumping well are 16,350 ft2/day and 9.47 x 10-5, respectively. The average of the transmissivity and storativity values from the tests conducted using Pittsburg well 8 as the pumping well are 13,992 ft2/day and 9.16 x 10-5, respectively. Factors that influenced the test results include pumping by other nearby wells and variability in the rate at which water was being withdrawn from the aquifer by the pumping wells in each test.
The water-level data from all of the Phase 1 and Phase 2 semiannual surveys were plotted as hydrographs to assess trends. Hydrograph interpretation is problematic because: (1) the collected survey data are more likely to be representative of pumping conditions than static conditions in the aquifer beyond the cone of depression, (2) the long intervals of time between individual measurements may provide a distorted picture of water-level trends locally within the aquifer depending on when the initial survey measurement was taken and on the spacing between measurements, and (3) human error associated with taking the water-level measurements may be significant even under the best of circumstances. If the goal of these surveys is to assess regional water level change in the aquifer, the interpretation uncertainty can be reduced by investing in additional dedicated observation wells strategically placed in areas of the aquifer outside of the immediate influence of pumping wells. At the moment, only the Ozark aquifer monitoring well near McCune fills this need. Furthermore, some of the future monitoring wells in the transition zone should be completed to the bottom of the Ozark Plateaus aquifer system because the water quality transition within the transition zone is likely three-dimensional and may extend far to the east in the lower part of the Ozark aquifer. If so, pumping stress that lowers the hydraulic head in the upper part of the Ozark aquifer may induce upward flow of poorer quality water from deeper zones to active wells.
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Kansas Geological Survey, Geohydrology
Placed online Feb. 9, 2009
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