Groundwater Primer

Groundwater is just one part of the continuous water cycle as water moves on, in, and around planet Earth. Groundwater is defined as the water occupying the pore space between sand and gravel below ground surface as in the below image.

The area between the ground surface, and the area where the pores are all saturated is called the vadose zone. There are many places at Hanford where the vadose zone is contaminated. In some locations, the soils may be dug up and moved to a safe storage area such as the Environmental Restoration or Disposal Facility. In others, the contamination goes too deep to simply dig up. We face difficult decisions about how to deal with those areas and prevent the contaminants from reaching groundwater.

The water table is the top of the saturated area which also is known as an aquifer. Aquifers may be perched or separated from one another by clay or rock layers through which water will not flow unless a fracture is available.

Some groundwater was trapped in the ground over the course of geologic time and is in deep aquifers underground. Some water is near the surface and must be recharged regularly to maintain its flow. At Hanford the stratigraphy - or layers of rock, sand, and clays determine where water is trapped.

The hyphoreic zone is an area where a river or stream and adjacent groundwater mix. The water table along a river may rise or fall in direct relation to the surface (river) water level.

Hanford groundwater used to be closer to the surface because manufacturing weapons materials required millions of gallons of water. Much of that water was discharged to the ground, recharging the groundwater at a faster rate than would occur naturally through precipitation.