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Kansas Geological Survey, Open-File Rept. 96-1a
Proposed Management Areas--Page 13 of 16

Management Area IV

The boundaries between Management Areas VA and IVA and between VB and IVA define the upgradient extent of the area where ground-water withdrawals from the Dakota may slightly reduce discharge to shallow aquifers and surface waters in the Smoky Hill and Saline River valleys. The boundary between Management Area IVA and IVB is the approximate location of the 1,500 mg/L total dissolved solids isocon in the upper Dakota aquifer (Figure 4). The boundary between Management Areas IVB and III is approximately coincides with the 1,500 mg/L total dissolved solids isocon. Management Areas IVA and IVB are located where the Dakota is overlain by the dissected Upper Cretaceous aquitard in central Kansas. Where it is present, the thickness of the Upper Cretaceous aquitard is 400 ft or less. The southern part of Management Area IVB in Ellis, Rooks, Rush and Russell counties includes the regional discharge area of the Dakota and the Cedar Hills Sandstone aquifers (Macfarlane, 1993). Throughout both management areas, the hydraulic head gradient indicates a potential for upward flow from the Cedar Hills Sandstone aquifer into overlying aquifers, including the Dakota aquifer (Macfarlane et al., 1988; Macfarlane, 1993). The Kiowa shale aquitard is not present in most of Management Area IVB but is present in the western and southern parts of Management Area IVA. Saltwater intrusion in the upper Dakota from sources in the lower part of the Dakota and underlying Cedar Hills Sandstone aquifer is widespread. Limited recharge across the Upper Cretaceous aquitard has flushed some of the salinity from the most permeable zones in the uppermost Dakota aquifer (Smith, 1995). Test drilling by the cities of Hays and Russell and the Kansas Geological Survey (Frye and Brazil, 1943; Swineford and Williams, 1945; and Macfarlane et al., 1988) has shown that salinity generally increases with depth within the Dakota aquifer.

Pumping wells situated within either management area will produce water entirely from storage in the aquifer until their cones of depression extend to the discharge area (Smith, 1995; Macfarlane, in review). Initially, most of the flow to producing wells will come from storage in the sandstone aquifer and the surrounding mudstones in the Dakota Formation will not contribute significant flow to the pumping well (Macfarlane et al., 1994). With continued pumping, the mudstones will begin to contribute recharge to the sandstones because of head gradients between the sandstone and the surrounding mudstone created by pumping acting over a large area of contact between the two porous media (Butler and Liu, 1991). Once the cone of depression has reached the discharge area, discharge from the aquifer will be reduced and flow from the discharge area may eventually be drawn into the aquifer. These effects may not occur with intermittent pumping at reduced rates because of recharge from regions of the aquifer not affected by pumping during the recovery period. Water quality in area IVA is acceptable for most uses. Water quality in area IVB is marginally usable and would require additional treatment to remove dissolved solids for most uses.

Pumping centers need to be spaced far apart and pumping rates monitored closely so as not to diminish regional discharge from the Dakota or induce additional saltwater intrusion from lower Dakota aquifer. Smith (1995) investigated the potential effects of pumping from the heterogeneous uppermost Dakota aquifer in southwestern Ellis County (T. 1315 S., R. 1720 W.) using MODFLOW (McDonald and Harbaugh, 1988) to produce a 3-D numerical simulation. A geostatistical analysis of the sandstone distribution in the study area revealed greater regional connectivity of the sandstones in an east-west direction than in a north-south direction in the fresher part of the aquifer. A single well was allowed to pump continuously at 200 gal/min over a 10 yr period near the center of the model area. At the end of the pumping period, the cone of depression had extended nearly across the entire model, a distance of 20 mi in an east-west direction, but was slightly less than 6 mi wide in the north-south direction. Smith concluded that a well spacing of at least 20 mi in an east-west direction and 5 mi in a north-south direction is needed to avoid the possibility of developing overlapping cones of depression where there are multiple wells pumping simultaneously.

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Kansas Geological Survey, Dakota Aquifer Program
Original report available from the Kansas Geological Survey.
Electronic version placed online July 1996
Scientific comments to P. Allen Macfarlane
Web comments to webadmin@kgs.ku.edu