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This option allows the user to incorporate one or more passive sinks or a phase change with depth into a model. A passive sink is a depth interval in which there is a horizontal velocity which will have the effect of removing contaminant from beneath the landfill. Typically, a passive sink is used to represent intermediate aquifers or secondary leachate collection systems [Rowe and Fraser, 1993].
In the Passive Sink feature the model is divided into a number of depth intervals, and in each interval the user can specify the Darcy velocity, rate of removal, rate of inflow, and phase parameter. The set of depth intervals should cover the entire thickness of the model, between the top and bottom boundary. If a fixed outflow bottom boundary is used, the depth interval should stop at the top of the base aquifer (i.e., it should not include the base aquifer).
Note: When using both the Variable Properties option and the Passive Sink option, the Darcy velocity used is the product of the Darcy velocity specified in both of the options. For clarity, it is generally recommended the user specify the Darcy velocity on the Variable Properties option as 1, and vary the Sink Darcy velocity with time.
WARNING: This option should only be used by someone with the hydrogeologic and engineering background necessary to appreciate the subtleties associated with the physical situation and the steps necessary for appropriate modelling of the physical situation.
THIS OPTION SHOULD NOT BE USED FOR AN IMPORTANT PROJECT WITHOUT THE GUIDANCE OF THE PROGRAM DEVELOPERS.
To use this feature, select the Passive Sink option from the Special Features menu. The Passive Sink form will be displayed. This form has either two or three tabs, one for the sink data, one for the interval data, and if the bottom boundary condition is not Fixed Outflow one for the landfill size.
If the Variable Properties feature has also been selected then the Passive Sink properties will need to be specified for each time period. In this situation,, at the top of the form the current Time Period is indicated and there are buttons to move to the first, previous, next, and last time period. If the Variable Properties feature is not selected the time period information will not be displayed.