Text String as input parameter

Hello All,

I have a model that runs a two different processes and I would like to have which process to be run based on a user input.
I have done this before by using a feature dataset allowing the user to select a point on the map to run model however, for this I would like to have the user select a text string from a list if possible (i.e. Ammonia, pH, VSS, COD). Then pass that text value to the model and have it run the desired process based on that selection.

So I am guessing that somehow I need to have the model take the value and test it and run the right process. But, I am not sure if this can be done or exactly how.
I have attached a graphic of the model.

Thanks

Eric

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