Summary of Limitations on the Use of Pipe Pathways

While Pipe pathways are versatile and powerful, they do have several limitations, which are worth summarizing here:

• Unlike Cell and Aquifer pathways, GoldSim does not apply solubility limits within Pipe pathways.
• If the properties of a Pipe (e.g., partition coefficients The ratio of the species’ concentration in a medium to its concentration in the Reference Fluid at equilibrium. Partition coefficients are inputs to Solid and Fluid elements., flow rates) change as a function of time, GoldSim has to use an approximation. The approximation is that 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). are discharged from a pathway based on the properties of the pathway (and the outflow rate) at the time the species (or their parents) entered it.
• Pipe pathways with very low dispersivities (<<1% of the pathway length) can produce unstable and inaccurate results (even if using a High Solution precision).

Two additional limitations (that have not been discussed previously) are as follows:

• Pipe pathways with transit times which are much less than a single timestep A discrete interval of time used in dynamic simulations. can produce unstable and inaccurate results. In such a case, a High Solution precision may be necessary to keep the solution stable and accurate.

• "Looping" reaction chains (A decays to B and B decays to A) are not permitted. Defining such reaction loops in a model that uses a Pipe will result in a fatal error message.

If any of these limitations applies, then the Aquifer pathway may be preferred over the Pipe pathway A transport pathway element that is intended to represent a feature that essentially behaves as a fluid conduit, such as a fracture. Pipes are primarily used for simualting matrix diffusion in fractured groundwater pathways..