UNCONFINED AQUIFER WITH INFILTRATION

Solve the following problem analytically and using MAGNET and compare the results.

A water supply well at a paper factory is tapping an unconfined aquifer which is exposed to significant infiltration from precipitation.  An incomplete record shows a fairly constant drawdown in the well and the two nearby abandoned wells (see Figure 20. 1) of 5.80, 1.65, and 0.95 m, respectively.  At the time of well completion, the static water table was at 100.80 m above mean sea level.  The diameter of the well is 400 mm and the hydraulic conductivity of the aquifer was determined to be 9.3 x10^-5 m/s.  According to the production record, the installed water supply system has been consistently using 137,500 gallons of water per day for the last three years.  Although there is no exact data on the well pumping rate, it is suspected that there is a loss of water somewhere in the system.  The average annual precipitation in the area was 29 inches for the last three years.

From the available data find the average pumping rate of the well and the average annual infiltration rate.

MAGNET/Modeling Hints:

• Use 'Synthetic Mode' to set up your flow model ( 'Other Tools' > 'Utilities' > 'Go to Synthetic Case Area'). The default model domain for synthetic mode is identical to the domain depicted in the figure above.
• Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.
• Use the given input data parameterize your flow model. 
• Monitor the drawdown at the two abandoned wells. Your numerical model should reproduce the observed drawdowns if the infiltration rate and pumping rate of the well is correct.