ABSTRACT
Subsurface investigations into the presence and extent of contaminated groundwater are primarily geological investigations. The site subsurface geology forms the physical framework through which groundwater and contaminants move. Understanding the site geology provides the fundamental basis for understanding site hydrogeology and defining contaminant movement. Groundwater occurs in subsurface rock and strata called aquifers, which comprise porous and permeable material. Aquifers may be composed of alluvium, sedimentary rocks, and fractured crystalline or metamorphic rocks. The vadose zone is geologically a very heterogeneous region. Typically soil formation occurs at the surface and soils may be buried sequentially in fluvial and alluvial depositional processes. Fluid movement is governed by fluctuations in local pressure gradients. Capillarity occurs due to available porosity immediately above the saturated zone as a response to water surface tension allowing vertical movement against gravity. Sedimentary rock contain lithified and semilithined sediments, as well as chemical sediments such as limestone.
