Groundwater is water that has seeped below the Earth's surface. Prior to seeping into sand, gravel and rock, most groundwater begins its journey to Earth as precipitation. A small portion of groundwater seeps into the soil from rivers, lakes and streams.

Aquifers
Unlike a body of surface water, groundwater seeps beneath the surface of the earth and collects in the gaps between pieces of rock and soil. These unique, naturally forming storage spaces are called aquifers. The amount of usable water that collects within an aquifer depends on the aquifer's porosity (the amount of space available for water storage) and its permeability (how freely the water can move through the soil and rock).

There are two main types of aquifers: unconfined and confined. The most common type, an unconfined aquifer, lies beneath the ground close to the earth's surface. Water seeps into it and collects above the aquifer's impermeable layer, (a geological formation at the base of the aquifer that water cannot penetrate). A confined aquifer can form between two impermeable layers. Sometimes, the pressure between the layers is so great that water squirts to the surface of the ground, creating what is called an artesian aquifer.

Wells
Groundwater is brought to the surface by wells. A well is simply a hole in the ground that extends past the water table (the top surface of the groundwater).

Preventing Pollution
Preventing groundwater pollution is everyone's responsibility. The federal government has passed numerous laws to prevent toxic waste and other harmful materials from polluting valuable groundwater resources. The Clean Water Act and the Safe Drinking Water Act of 1974, for example, regulates the water we drink. It also establishes a groundwater protection program for the areas that surround drinking water wells.

However, once the groundwater has been polluted by toxic waste and other harmful materials, its cleanup can be extremely expensive and time-consuming. The Comprehensive Environmental Response, Compensation and Liability Act of 1980, also known as Superfund, was enacted by the federal government for the purpose of cleaning up hazardous waste sites, which usually threaten groundwater resources.

Within Los Angeles County, government agencies such as the Metropolitan Water District of Southern California (MWD), Los Angeles County Department of Public Works (LACDPW), Water Replenishment District (WRD), Sanitation Districts of Los Angeles County (LACSD), Central Basin Municipal Water District and West Basin Municipal Water District work both independently and together to restore local area groundwater aquifers and protect them from overpumping and seawater intrusion.

The West Basin Water Recycling Facility (WBWRF), located in the City of El Segundo, prevents seawater intrusion into the West Coast Basin by injecting a water barrier through wells operated by LACDPW into the aquifer. West Basin's C. Marvin Brewer Desalting Facility, located in the City of Torrance, restores groundwater resources by treating brackish water (a mixture of seawater and fresh water) and treating it to drinking water levels. These efforts help preserve the West Coast Basin Aquifer.

Spreading Grounds
Central Basin works with WRD and LACSD to prevent a shortage of available groundwater through a series of spreading grounds located in Montebello and Pico Rivera. The spreading grounds allow water from various sources to artificially seep down into the Central Basin Aquifer. These and other government agencies, including cities within the Southeast Water Coalition, are also heavily involved in monitoring a Superfund site in neighboring San Gabriel Valley to ensure that the Superfund site doesn't contaminate local groundwater sources. For more on Central Basin 's efforts in this project, please visit the Water Quality Protection Project.

The close working relationships between these local government agencies prove that everyone should have an interest in protecting and restoring a valuable local resource - groundwater. This also lessens the area's dependence on expensive imported water from the ecologically sensitive San Francisco Bay/San Joaquin Delta and the Colorado River .

How Can You Help Prevent Contamination?

Though it may seem well-protected underneath layers of soil and rock, groundwater quality can be very sensitive to what occurs on the surface. Certain human activities can lead to groundwater contamination. Some human activities that contaminate groundwater include:

• Incorrectly using and disposing of agricultural chemicals

• Leaks and spills of hazardous chemicals from factories, commercial sites, underground storage tanks and landfills

• Incorrectly disposing of industrial waste

• Releasing harmful chemicals into the atmosphere

• Incorrectly using salt and other chemicals to de-ice roads

• Saline (saltwater) intrusion from improper land uses

• Incorrectly locating and designing septic tanks and sewer systems