Kansas Geological Survey, Open-File Rept. 96-1a
Proposed Management Areas--Page 13 of 16
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. 13Ð15 S., R. 17Ð20 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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