Aquifers in AZ

Figure 3: Aquifer materials

An aquifer is an underground geologic formation capable of producing (yielding or transmitting) usable quantities of water to a well or spring.  Depending on the geologic formation, water is typically held in interconnected pores and void spaces between grains of clay, silt, sand and gravel size minerals or in subsurface fractures and cracks of rocks, see Figure 3.  Aquifer material types include unconsolidated and consolidated rock materials, examples of which range from the unconsolidated alluvial sands and gravels of river valleys and southern deserts, to the dense consolidated basalt of the Mogollon Rim.

In these two aquifer types, ground water is filtered through pores (porous flow) or through fractures and cracks (fractured flow) and/or in a combination of these flow types.  Water flow through fractures can rapidly transmit contaminants through the subsurface as there is little opportunity for natural filtration of pollutants. It is important to understand which flow type is prevalent in your aquifer to protect your water supply from contamination.

Figure 4: Arizona physiographic provinces

Arizona’s geologic history resulted in the formation of three physiographic  provinces: the Colorado Plateau; the Central Highlands Region (also known as the Transition Zone between the other two provinces); and, the Basin and Range Province, see Figure 4.

Each of these provinces exhibit aquifer types and ground water flow characteristics unique to that region.