There are two types of permitted recharge facilities in Arizona: underground storage facilities and groundwater savings facilities. An underground storage facility is typically a shallow basin or series of shallow basins where water is discharged into the basin and percolates into the soil below the facility known as the aquifer.
A groundwater savings facility is not a constructed facility but rather a water user, typically an irrigation district, that agrees to reduce its groundwater pumping for an equal amount of renewable supplies delivered to its facility. The renewable supplies are also referred to as "in-lieu" water. By leaving the groundwater in the aquifer, water is in essence "saved" underground.
The AWBA currently holds or has held water storage permits at 26 recharge facilities. Eleven of these projects are underground storage facilities and the other 15 are groundwater saving facilities. Those facilities have a collective capacity of about 1.5 million acre-feet, close to 75% of all permitted recharge capacity. Of the 1.5 million acre-feet of capacity, approximately 820,000 acre-feet of capacity is located in the Phoenix AMA, 330,000 acre-feet in the Pinal AMA and nearly 300,000 acre-feet in the Tucson AMA.
Through 2019, the AWBA has developed approximately 4 million acre-feet of long-term storage credits in these facilities. Nearly 75% of those credits are stored in 7 of the facilities. The largest number of AWBA credits stored at a single facility are stored at the Maricopa Stanfield Irrigation & Drainage District, a Groundwater Savings Facility (GSF) in the Pinal AMA. Approximately 644,000 acre-feet of credits were stored at this facility through 2019. The largest number of credits stored at a single Underground Storage Facility (USF) is approximately 480,000 acre-feet stored at the Tonopah Desert Recharge Project in the Phoenix AMA.