Concentration Observations: TOB: Transport Observation Package Pane

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The Concentration Observations: TOB: Transport Observation Package pane is on the MODFLOW Features tab of the Object Properties dialog box. All cells intersected by the object will be part of the observation.

MT3DMS has three separate types of observations. Two of them, concentration observations and flux observations are defined in the Transport Observation Package. The other is defined by setting the data set MT3DMS_Observation_Locations to true at the desired locations.

Each separate time at which the concentration was observed is a separate observation in MT3DMS. The user specifies an Observation name for the group of observations at the same location. This name is used to generate a different name for each observation time.

The Observation type determines whether a particular observation will be used in a simulation. The observation will only be used if the Observation type of the observation matches the Observation type of the model.

For each observation, the user must specify the time, the chemical species, the concentration, and the weight. The user may also specify a comment if desired. Note that if [TimeObs] is specified as a negative integer, the calculated concentration is saved whenever the number of transport steps is an even multiple of |TimeObs|. weight—is the user-specified weighting factor for computing the residual error at the current observation, i.e., residual error = (calculated-observed)*weight. If [weight] is assigned a negative value, the observed concentration at the target observation point is not used and only the calculated concentration is saved.

The location of the observation is determined by the location of the object. If the object is not at a cell center, MT3DMS can interpolate to the observation location based on the concentrations in surrounding cells.

If an observed concentration is from a well that is open to several different model layers, the user can specify the layers to which the well is open and the weight assigned to each layer.