# HydroGeoSphere/Specified Concentration

This is also known as a first-type, Dirichlet, or constant concentration boundary condition. It is a nodal property so you should first choose the subset of nodes for which you want to apply the condition and then issue one of the following instructions.
If the node was assigned a specified concentration, mass flux or third-type value by a previous instruction then it will not be modified by subsequent specified concentration instructions.

## Specified concentration

* npanel Number of panels in the time-variable concentration function. For each panel, enter the following:
       (a) ton_val,toff_val,(bc_val(j),j=1,nspeciesmob) Time on [T], time off [T], and specified concentration [M L$^{−3}$] of each species.
Chosen nodes in the currently active media (see Section 5.8.1) are assigned a time-variable concentration value. If a node was previously assigned a specified concentration, it will remain in effect.
A panel is a point in time at which the specified concentration is set to a new value. The first panel would normally start at time zero. The concentration given for the last panel will be maintained until the end of the simulation. You can assign a static concentration for the duration of the simulation by setting npanel to 1, ton_val to 0.0 and toff_val to a large number.
Note that if nspeciesmob is greater than 1, additional values of bc_val should be included.

## Specified concentration from file

* fname Name of the file which contains the time-varying concentration information.
This file should contain the following input data:
* nnde Number of nodes to be assigned concentration data.
* npanel Number of panels in the time-variable concentration function. For each panel, enter the following:
       (a) ton_val,toff_val Time on [T], time off [T].
3. nde, (bc_val(j),j=1,nspeciesmob) Node number and specified concentration [M L$^{−3}$] of each species.
Listed nodes are assigned the time-variable concentration values contained in the file. If a node was previously assigned a specified concentration it will remain in effect.
Although all nodes in the file share the same time on/time off panel information the concentration values in each panel can vary from node to node.

## Specified well concentration

* iw Identification number of the well to which the concentration is to be applied. For each species defined, enter the following:
       (a) ninjc Number of panels in the injection concentration history for this well and species. For each panel enter the following:
          i. cinjc,toninjc,toffinjc Injection concentration [M L$^{−3}$], time on [T] and time off [T].
All nodes in well iw are assigned a time-variable first-type concentration value, which is uniform along the length of the well.
Since this instruction loops over all defined species, you must supply input even if it is a zero concentration.

## Specified tile concentration

* iw Identification number of the tile drain to which the concentration is to be applied. For each species defined, enter the following:
       (a) ntdc Number of panels in the injection concentration history for this tile and species. For each panel enter the following:
          i. c_tile,ton_c_tile,toff_c_tile Injection concentration [M L$^{−3}$], time on [T] and time off [T].
All nodes in tile drain iw are assigned a time-variable first-type concentration value, which is uniform along the length of the tile.
Since this instruction loops over all defined species, you must supply input even if it is a zero concentration.