In addition to adding mass to an Aquifer via an initial/boundary condition, and adding/removing mass via mass flux links, GoldSim allows you to instantaneously add species The chemical (or non-chemical, such as bacterial or viral) constituents that are stored and transported through an environmental system in a contaminant transport model. In GoldSim, the Species element defines all of the contaminant species being simulated (and their properties). mass to an Aquifer.
This is done using the Discrete Changes field in the Aquifer dialog:
This field only accepts discrete change signals.
The discrete change signal A discrete signal that contains information regarding the response to an event. must be a vector A one-dimensional array. by species and have dimensions An output attribute for an element that defines the dimensionality (in terms of Length, Time and other fundamental dimensions) of the output. of mass. Typically, such a discrete change signal will be the output of a Discrete Change element An element that generates discrete change signals that can subsequently modify stock elements. that has been triggered by an event.
Discrete change signals have an instruction associated with them. Two types of instructions are possible: Add and Replace. The Discrete Changes field for an Aquifer only accepts Add signals.
When an Add signal is sent to an Aquifer during a simulation, the specified amount of mass of each species in the discrete change vector is added to pathway. If the Source Zone Length is zero (the default), the mass is applied at the beginning of the Aquifer (the first Cell). If the Source Zone Length is greater than zero, the mass is distributed uniformly over the specified length.
Note: The discrete change vector cannot contain negative numbers (i.e., you can NOT discretely remove mass from an Aquifer; you can only add mass).
Like most input fields that accept discrete change signals, you can specify multiple discrete changes. You can do this in two ways:
- You can enter multiple discrete changes into the input field by separating the entries using a semi-colon; and
- You can use the Multiple Discrete Changes button to the right of the input field (i.e., the small button with red lightning bolt) to access a table listing the Discrete Changes (to which you can add or delete entries).
In the latter case, any Discrete Changes which are added to the list are also automatically added to the input field, separated by semi-colons.
The Discrete Changes field can be very useful for instantaneously modifying your system in response to discrete events. Note, however, that this feature should be used with care, since when it is applied, conservation of mass in the system is the responsibility of the user.