Water can travel from the soil and from the bottoms of rivers and lakes down into the aquifer. This is called groundwater recharge. Water in aquifers is usually found in the spaces between the particles of sand or rocks. Layers of sandstone make good aquifers because there are many holes between the sand grains. These holes let water travel into the sandstone. Layers of clay trap water on top because water does not travel through clay. Clay creates the bottom and, sometimes, the top of aquifers.

Santa Margarita Basin: Made up of Lompico Sandstone, Butano Sandstone, Monterey Formation and the Santa Margarita Sandstone. Provides water to Scotts Valley, Lompico and San Lorenzo Valley.

Purisima: Provides water to Capitola, Live Oak, Soquel, and part of Aptos.

Aromas Red Sands: Provides water to Watsonville, Pajaro Valley, Corralitos, Larkin Valley, La Selva Beach, and part of Aptos.

Pajaro Valley Alluvium: This shallow aquifer used to be a major source of water for the Pajaro Valley until it became too contaminated with nitrates and salt to use for drinking water. It is separated from the Aromas Red Sands by a very thick layer of clay (50-150 feet thick).

Dangers to our groundwater

Overdraft occurs when groundwater is used faster than it is recharged. Most of Santa Cruz County aquifers are either in overdraft or are very close to being in overdraft.

Seawater intrusion happens when there is too much overdraft near the ocean and saltwater seeps into the aquifer. When saltwater gets into the aquifer, that part of the aquifer is contaminated and can never be used again. Some coastal wells have been shut down because of seawater intrusion.