Continuous Porous Medium (CPM) models are considered the appropriate models for certain types of rock and porous materials, in which flow is predominantly through an interconnected network of pores between the solid grains making up the rock or material, such as for many sandstones, soils, clays, unconsolidated deposits, and backfill material. The model assumes continuity in three dimensions and hence a high degree of connectivity between points in the modelling domain. Connectivity is only reduced when very low conductivity layers or flow barriers are incorporated in to the model. The flow through such domains is modelled by Darcy's law, which relates specific discharge (Darcy flux) to the driving force, i.e. the pressure gradient and/or buoyancy force.

It is generally not appropriate to represent fractured rocks as a CPM as it does not represent the discontinuous, heterogeneous and anisotropic characteristics of flow in such rocks. However, it can be used to represent parts of the system such as the backfilled tunnels that behave like porous media, or far from the region of interest where it is only necessary to provide an approximate representation of bulk properties over large volumes. The concept can be elaborated to represent some of the characteristics of fractured rock by use of an Equivalent Continuous Porous Medium (ECPM) representation where hydraulic properties within each finite-element are anistropic and differ between each finite-element to represent the underlying structure and properties of a fracture network.

In ConnectFlow, CPM models can be used to represent the following:

• Complex distributions of lithology;
• 3D volumes of enhanced or reduced permeability;
• Conductive or semi-impermeable fracture zones;
• Stochastic models of permeability and porosity;
• Boreholes, tunnels and shafts;
• Specified value (Dirichlet) and specified flux (Neumann) boundary conditions;
• Infiltration boundary conditions for surface recharge/discharge areas;
• Hydrostatic and outflow boundary conditions for vertical boundaries;
• Time-varying boundary conditions (e.g. used to model land uplift, or time-dependent contaminant discharge);
• Sources of contaminants, salinity or heat.
• Level of saturation.
• Transport of solutes, radionuclides or heat.
• Chemical reactions.

ConnectFlow CPM models have been used in the following applications:

• Calculations in support of safety assessments for radioactive waste disposal programmes:
• Regional groundwater flow;
• Site investigation;
• Pump test simulation;
• Tracer test.
• Modelling for groundwater protection schemes:
• Aquifer;
• Saline intrusion.
• Modelling to design and evaluate remediation strategies:
• Aquifer contamination;
• Landfill site.