Hydrogeology and simulation of water flow in the Kootenai aquifer of the Judith basin, central Montana
Five Jurassic and Cretaceous formations in the Judith basin of central Montana were investigated with a three-dimensional model to improve the understanding of water flow in the Kootenai aquifer. To accomplish this objective, of water flow in the aquifers and two intervening confining layers was constructed from existing data. A steady-state model was calibrated and evaluated using a parameter-estimation procedure. The digital model simulates horizontal flow in the middle (Kootenai) aquifer and vertical leakage through the overlying and underlying confining layers. The top and bottom aquifers are used as constant-head boundaries to aid in simulating vertical leakage. Transmissivity for the aquifer obtained from the calibrated model ranges from 137 to 364 ft super 2/d. Recharge in the form of precipitation on the outcrop is about 2% of total precipitation (5.44 ft super 3/s). The other component of net recharge is 32.48 ft super 3/s of vertical leakage from the Swift aquifer. The cumulative rate of discharge from all known wells completed in the aquifer is about 0.84 ft super 3/s. Other components of net discharge are 1.83 ft super 3/s of underflow and 35.25 ft super 3/s of vertical leakage to the Colorado aquifers. Estimates of vertical hydraulic conductivity are 2.15 x 10- super 2 ft/d for the lower confining layer, and 3.16 x 10- super 3 and 1.33 x 10- super 4 ft/d for the upper confining layer. (USGS)