Groundwater Recharge

Groundwater is water found underground in the cracks and spaces in soil, sand and rock. Groundwater is stored in these geologic formations, known as aquifers, and can move through the spaces in the soil or rock, similar to underground lakes and rivers. Groundwater is naturally replenished, or recharged, by precipitation that seeps into the cracks and reaches the aquifer.


Humans use groundwater for many purposes, and rely on it as an important source of drinking water. Just as with surface water, when groundwater is used faster than it is replenished, such as in times of drought, water levels drop and the stores become depleted. In a coastal basin such as the Santa Maria Groundwater Basin, if the groundwater level sinks too far, it is possible for seawater to enter the aquifer and mix with the potable groundwater supplies. This is not safe for our cities and towns, our drinking water supplies, or the environment. In order to combat this potential problem and augment the naturally slow process of groundwater recharge by infiltration, the Regional Groundwater Sustainability Project will create a new source of clean, purified water to put back into the ground. This will create a safe and sustainable supplemental water supply and protect the Santa Maria Groundwater Basin from seawater intrusion.

Groundwater recharge achieved by injecting purified water is also known as Indirect Potable Reuse (IPR). IPR is a type of reuse where water is blended with other environmental systems, such as a river, reservoir, or groundwater basin before the water is reused. Regulations for this type of IPR were adopted by the California State Water Resources Control Board in 2014. The California Water Board strictly regulates all types of reuse projects and thoroughly investigates projects and processes for viability and safety before regulating them.

In order to treat water to the quality required for injection into the groundwater basin, the RGSP project will include an Advanced Treatment Facility (ATF). The ATF will include a multi-barrier process with advanced technologies designed specifically for treating water to potable standards. The advanced treatment of water will include three main technological processes: microfiltration/ultrafiltration (MF/UF), reverse osmosis (RO), and ultraviolet disinfection with advanced oxidation (UV/AOP). These processes take secondary treated water and filter it through a membrane with ultra-small holes, push it through more membranes that only allow water to pass through, and disinfect it with high energy light and oxidizing compounds. For a detailed description of the treatment processes, please go to Advanced Treatment Processes.