The groundwater system as a whole is a three-dimensional flow field where the vertical components of groundwater movement in shallow aquifers affect the interactions of groundwater and surface water.

Surficial aquifers recharge through rainfall and infiltration into the upland areas between drainages and discharges into local streams and rivers.

Groundwater flow is an important aspect of hydrogeology because it is used to demonstrate groundwater movement principles. Groundwater moves from areas of higher elevation or higher pressure/hydraulic head (recharge areas) to areas of lower elevation or lower pressure/hydraulic head, along the hydraulic gradient. The magnitude of groundwater flow depends on both the hydraulic gradient and the soil characteristics.

Groundwater flow in aquifers ultimately is released into streams, lakes, wetlands, or springs (discharge areas). The direction of groundwater flow normally follows the general topography of the land surface. The more permeable the aquifer material, the higher the rate of groundwater flow and discharge.

The geologic conditions of a site are used to understand the elements that create the natural infrastructure of the land that includes the following: physiographic setting; the general nature of geologic units; controlling regional geologic features; geologic units beneath the site and their thicknesses; and origin of deposits (channel sand, lake deposits, etc.).

The hydrogeology specialty area has identified approaches for Conceptual Site Model, or CSM, development to explain critical geological issues, complex hydrological flow, and contaminant movement at site-specific and base-wide locations. The development of CSMs presents a three-dimensional picture of site conditions that illustrates environmental radionuclide distributions, release mechanisms, exposure pathways and migration routes, and potential receptors.

The CSM demonstrates current site conditions supported by maps, cross-sections, lithostratigraphic/hydrostratigraphic columns, and site diagrams that illustrate human and environmental exposure through contaminate release and migration to potential receptors. These approaches are responsible for accelerating the process for defining the nature and extent of contaminants, as well as addressing site restoration in a systematic and efficient manner.

Effective site management and restoration are dependent on a clear understanding of surficial and subsurface conditions and how installation activities ensure the protection of human health and the environment. The hydrogeology specialty area provides support in understanding complex geological and hydrological issues through expert advice in evaluating site contamination, specifically at challenging sites, through groundwater modeling and review services for contaminant fate and transport.

Human activities commonly affect the distribution, quantity, and quality of water resources. The range in human activities that affect the interaction of groundwater and surface water is broad. For nearly every type of water use, water possesses increased concentrations of dissolved constituents or increased temperature following its use. Therefore, water quality of the aquatic bodies that receive discharge or return flow are affected.