Groundwater movement can be assessed using established hydraulic principles and data on the characteristics of an aquifer. The ability of an aquifer to receive, store or transmit water depends on the rock properties within the aquifer. Groundwater flow theory is based on equations developed from measurements in unconsolidated sediments (porous media).

In Pennsylvania, groundwater typically moves from beneath the hills to adjacent streams. Unfortunately, nearly all groundwater in Pennsylvania flows through fractures, not porous media. This means that porous media equations do not automatically transfer to fractured rock settings. In fractured rocks, actual groundwater flow directions cannot be easily determined. In fact, determining specific flow paths is impossible where the groundwater flows through a complex network of fractures. Even greater complexity exists in carbonate rock areas where topography is not always a defining factor in groundwater flow direction, and caverns and solution conduits form in a seemingly random network.

Hydrogeologists who characterize groundwater flow in fractured bedrock may use different approaches to estimate groundwater flow. A discrete approach attempts to identify individual fractures. This is an expensive method and at this time is not practical because of the intense geologic data requirements. A statistical approach attempts to average the data to get a representative measure of the groundwater flow. Problems may occur in transferring the scale of investigation to cover the entire region. A continuum approach assumes that the groundwater flow in a fractured rock aquifer acts like groundwater flow in porous, unconsolidated formations. This is the most common method to estimate groundwater movement in fractured rocks. Assumptions are made to use this approach. Care must be taken to verify assumptions and meet criteria that justify the continuum approach.