Let us consider a shallow, homogeneous, isotropic aquifer with a thickness of 10m and a steady uniform average pore water velocity of 1 m/day. A relatively long ditch cuts through this aquifer perpendicular to the direction of the flow. A nonreactive chemical waste is being continuously pored into the ditch. The rate of chemical waste inflow is about 0.1 m³/day per unit length of the ditch. The concentration of a certain nonreactive constituent in this waste is 10 kg/m³. A longitudinal dispersivity of 10 m and porosity of 0.2 are assumed.

A. Given these conditions, perform the following (1) plot the variation of C versus distance for 1,2,and 10 years after the start of the operation, and (2) determine how far downstream from the ditch a concentration of 0.1 ppm or more can be found after 10 years.

B. Develop a MAGNET model to confirm your results using an analytical approach. 

MAGNET/Modeling Hints:

• Use ‘Synthetic mode’ in MAGNET to create a model domain.
• Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.
• Represent the rivers as constant head zone features.