Part V provides the background on groundwater recharge (replenishment)---both natural and artificial.
A good understanding of groundwater recharge is necessary before we get into the statutory groundwater requirements in Arizona (AZ).
Many common water resource terms will be explained but you can go to the Water Lingo Tab for more definitions and information. Reference photos are provided of waterworks facilities constructed and/or managed in CT, IL and CA and from other sources in AZ.
Direct Groundwater Recharge
As discussed in Part III-Water Resources, groundwater recharge can be natural or artificial.
Natural groundwater recharge occurs when precipitation percolates down into the aquifer. See diagram (right). This process has been occurring for thousands of years. Some deep aquifers (1,000-2,000 feet) can contain groundwater that is considered ancient!
Artificial groundwater recharge is required to prevent overdraft (groundwater withdrawal exceeds natural and artificial recharge) and restore aquifer groundwater levels. There are two primary methods of groundwater recharge; (1) percolation and (2) injection. Recovery wells are utilized to recover the recharged groundwater.
Percolation
The percolation process is the same as natural recharge except the non-groundwater supply is delivered and stored in a constructed percolation basin (sometimes called spreading pond) and the non-groundwater percolates down through the bottom of the basin/pond into the aquifer. Similar to the wetland shown in the diagram (above).
The non-groundwater supply can also be discharged into a river or stream (usually ephemeral) that has direct connectivity with the aquifer. The non-groundwater blends with any natural river/stream water and percolates down through the river/stream bottom into the aquifer.
Direct Recharge (Palm Springs, CA)-aerial view of the Whitewater River Recharge Facility near Palm Springs, CA (note the windmills & I-10). This facility has 19 percolation basins that can recharge up to 400,000 acre-feet/year of Colorado River water into the Coachella Valley Aquifer. This facility can also recharge the aquifer by diverting Colorado River water directly into the Whitewater River.
Injection
The injection process is the reverse of a groundwater well/pump. Here the non-groundwater is pumped into the aquifer. Injection is utilized when land is not available to construct large percolation basins and/or the subsurface conditions make percolation difficult.
Recovery Well
Recovery wells are standard groundwater wells/pumps strategically located above the aquifer that is being artificially recharged. See well/pump photo in Part III.
Non-Groundwater Utilized For Recharge
There are two sources of non-groundwater utilized for recharge in AZ; (1) surface water and (2) recycled (reclaimed) wastewater.
Surface Water
Surface water can come from any river/stream with available supply. In the arid southwest, the Colorado River is the primary source of surface water utilized for groundwater recharge. In AZ, the Central Arizona Project (CAP) is the infrastructure that transports Colorado River water from Lake Havasu (Colorado River) to Mariposa, Pinal and Pima counties.
Central Arizona Project (CAP)-photo showing Aqueduct & Twin Peaks Pumping Plant in Marana which transports Colorado River water to downstream recharge facilities including Tucson Water's Central Avra Valley Storage & Recovery Project shown in the lead photo.
Recycled Wastewater
Recycled wastewater is municipal wastewater that has been treated to Class A+ water quality standards (almost drinking water). Two wastewater treatment plants in the Tucson region discharge recycled wastewater to the Santa Cruz River which has hydraulic conductivity with the aquifer(s).
Indirect Groundwater Recharge
Indirect recharge occurs when an entity (e.g. farm, golf course, etc.) utilizes a non-groundwater source directly in-lieu of pumping groundwater. The groundwater that would have been pumped stays in the aquifer. The aquifer benefits from reduced groundwater pumping. Indirect recharge is also called "in-lieu recharge" or "source substitution".
Indirect Recharge (Coachella, CA)-photo showing the Coachella Canal providing Colorado River water to an adjacent farm that eliminated groundwater pumping for irrigation.
Factoid: theoretically a molecule of water in Wyoming can find its way by gravity (no pumping) down the Colorado River through the All-American Canal (Imperial County, CA), then up the Coachella Canal (Riverside County, CA) and end up in Lake Cahuilla (Coachella Canal terminal reservoir in La Quinta, CA)!