Degradation and production of substances in groundwater can be both chemical and biological in nature.

Degradation and production processes can be taken into account in the mass transport calculation. In theory, a distinction is made between production and degradation rates of the solution in the fluid and the adsorbate in the matrix. As these processes cannot be clearly separated or assigned to each other in nature, the mass transport calculation does not take the processes within the matrix into account. Instead, all production or degradation processes are only considered in the fluid.

 

Various approach functions can be selected for the degradation and production rates in the fluid. (Degradation: negative values, production: positive values)

The approach function determines the functional rule with which the existing concentrations increase or decrease in the next transient time step.

Possible attachment functions:

• No degradation and production processes are considered (default setting!).

• A constant degradation or production process is considered:

f(c) = c = const.

The parameter c corresponds to the intercept of the function, in the example c = 1.0.

 

 

• A linear degradation or production rate can be entered:

f(c) = Intercept + gradient * c

 

In this example, the intercept = 1.0 and the gradient is also = 1.0.

 

 

• A step function for the degradation or production rate can be entered (starting with f(c=0)=0), which is limited from a certain concentration (lower limit) by a maximum rate (maximum). From a maximum concentration to be entered (upper limit), the degradation or production is then set to 0 again:

 

In the example the lower limit is = 10.0, the upper limit is = 20.0 and the maximum is 10. 0.

 

 

• If the substance parameters have been zoned (attribute Z-AP), a tent function for the degradation or production rate can also be entered as the 4th approach function, which drops again after reaching a maximum until the upper limit is reached. The extraction or production is then set to 0:

In the example the lower limit is = 20.0, the upper limit = 30.0 and the maximum = 200.0.

 

 

 

The respective parameters axis section, maximum, lower limit and upper limit of the function are defined in the Advanced – Production/degradation.

 

Radioactive or biological decay (half-life calculation)