Groundwater Recharge and Aquifer Storage and Recovery: Injection Projects, Challenges, and Impacts

     The U.S. EPA defines and distinguishes aquifer recharge (AR) and aquifer storage and recovery (ASR) as follows:

“Aquifer recharge (AR) and aquifer storage and recovery (ASR) are manmade processes or natural processes enhanced by humans that convey water underground. The processes replenish ground water stored in aquifers for beneficial purposes. Although AR and ASR are often used interchangeably, they are separate processes with distinct objectives. AR is used solely to replenish water in aquifers. ASR is used to store water, which is later recovered for use.”

     They also note that both AR and ASR projects are increasing in number, often as a way to address water shortages in areas of high population density, intense agriculture, and high groundwater withdrawal rates. The projects occur more in the drier regions of the U.S. in the southeast, southwest, and west. There are projects in coastal areas as well where freshwater is injected into aquifers to stave off saltwater intrusion. The EPA mentions three methods of aquifer recharge, including surface spreading, infiltration pits and basins, and injection wells. Injection wells are used where surface methods are impractical.

     AR and ASR injection wells are regulated under the EPA’s Underground Injection Control (UIC) program. The main goal of AR and ASR regulations is to protect underground sources of drinking water. States granted primacy for regulating these wells may have additional requirements.

“no owner or operator shall construct, operate, maintain, convert, plug, abandon, or conduct any other injection activity in a manner that allows the movement of fluid containing any contaminant into underground sources of drinking water, if the presence of that contaminant may cause a violation of any primary drinking water regulation under 40 CFR part 142 or may otherwise adversely affect the health of persons.” (40 CFR 144.12L)

     Water injected into AR and ASR wells may have different origins, including drinking water from a public water treatment system, untreated groundwater and surface water, treated effluent, and reclaimed or recycled water.

     Below are some potential contaminants that may be inadvertently introduced into an aquifer if the water is not treated properly before injection. These include pathogens which can be removed by disinfection, disinfection byproducts which can be reduced by pretreatment before disinfection, and leaching of metals from the surrounding rock, or precipitation of carbonates if water pH and red-ox potential are not ideal. There are some cases where injecting water into aquifers has improved the groundwater quality of naturally poor-quality groundwater. However, it is more typical for groundwater quality to remain the same or go down where it is being withdrawn fast enough to lower the water table significantly.

Natural Groundwater Recharge

   Groundwater is recharged naturally from rain and snowmelt. Human activities like paving and development can reduce groundwater recharge. Loss of topsoil can result in decreased infiltration rates. Soil infiltration rates also depend on soil grain size. Larger soil grain sizes, such as soil with abundant sand or gravel and low amounts of clay, will be more permeable than clay and loamy soils. Low infiltration rates often lead to lower recharge rates. Groundwater hydrologists are often interested in the areas where groundwater recharge is highest and, in the case of drinking water aquifers, in protecting those areas from contamination. These are known as groundwater source protection areas. Salts that accumulate in the root zones of plants can be washed out by infiltrating water, improving the quality of the lower soils.

     Wetland soil is often impermeable and impedes water flow, but areas around the perimeters of wetlands are often good recharge areas. Thus, areas with abundant small wetlands with high perimeter-to-wetland ratios can be very good recharge areas. In the U.S. Upper Midwest and Plains areas, groundwater recharge areas can be areas with abundant prairie potholes.

     One method of natural groundwater recharge that is enhanced by human activity is depression-focused groundwater recharge. This method involves natural or constructed depressions, ponds, or basins that collect water and let it infiltrate into the subsurface. These depressions concentrate water in places where the soil is highly permeable, enhancing flow into the aquifer.

 

Artificial Aquifer Recharge

     As noted by the EPA, artificial aquifer recharge may involve streambed channel modification, bank filtration, water spreading, and recharge wells. In urban areas, stormwater runoff retention basins may become aquifer recharge areas. In hot, dry agricultural areas where groundwater levels have dropped due to depletion caused by over-withdrawal, like much of India, where over 60% of irrigation water is groundwater, there are many ongoing aquifer recharge projects. Over-pumping groundwater also causes land subsidence, and this has occurred in some U.S. cities. Adequate recharge can prevent such land subsidence if it is done in time.

     According to a 2021 paper in Environmental Research Letters and Wikipedia, estimating and measuring rates of groundwater recharge is inherently difficult:

“Rates of groundwater recharge are difficult to quantify. This is because other related processes, such as evaporation, transpiration (or evapotranspiration) and infiltration processes must first be measured or estimated to determine the balance. There are no widely applicable method available that can directly and accurately quantify the volume of rainwater that reaches the water table.”

“The most common methods to estimate recharge rates are: chloride mass balance (CMB); soil physics methods; environmental and isotopic tracers; groundwater-level fluctuation methods; water balance (WB) methods (including groundwater models (GMs)); and the estimation of baseflow (BF) to rivers.”

“Regional, continental and global estimates of recharge commonly derive from global hydrological models.”

 

Gutter-Based Recharge in Urban Areas

      In dry areas, individual residents can help by helping rainwater to percolate into the soil rather than run off into surface water bodies. 

     In urban and suburban areas, especially in arid regions, gutter and downspout systems can increase local aquifer recharge and decrease runoff to storm sewers. Gutter-based recharge in urban areas can also help to mitigate urban flooding. 

     Gutter water management company Euroguard gives some recommendations.

     They also give some factors that affect soil infiltration rates and recharge.

 

Induced Seismicity is Apparently a Potential Issue with Recharge, but I Doubt It Will Become a Concern

     Alluvial groundwater aquifers beneath rivers are one major source of water, including my own water, which comes from such aquifers under the Ohio River. Such aquifers are typically unconsolidated and very permeable, which means the water recharging them is younger than for many consolidated hard rock aquifers, which may naturally take years or decades to recharge.

     A project recharging the Potomac Aquifer under the James River in Virginia has installed seismometers to listen for seismic events, but none have yet been found. Such events due to water injections at high pressures are common in oil & gas fields where wastewater is injected into disposal wells in high volumes at high pressures. The risk for seismic events depends on geology, depth, and injection pressures. I doubt that this will be a concern in the future, even as more recharge projects are initiated. It is rare for freshwater aquifers to be hydraulically connected to subsurface faults, especially basement faults, which are more susceptible to slipping with high-pressure injection.  

 

References:

 

Replenishing sapped groundwater could trigger small earthquakes: A boom in aquifer injection projects could unlock long-quiet faults. Hannah Richter. Science Advisor. December 10, 2025. Replenishing sapped groundwater could trigger small earthquakes | Science | AAAS

Aquifer Recharge and Aquifer Storage and Recovery. U.S. EPA. Aquifer Recharge and Aquifer Storage and Recovery | US EPA

Groundwater Recharge: A Vital Solution for Sustainable Water Management. Euroguard. July 25, 2025. Groundwater Recharge: Methods, Benefits & Importance Explained

Groundwater recharge. Wikipedia. Groundwater recharge - Wikipedia

Mapping groundwater recharge in Africa from ground observations and implications for water security. Alan M MacDonald, R Murray Lark, Richard G Taylor, Tamiru Abiye, Helen C Fallas, Guillaume Favreau, Ibrahim B Goni, Seifu Kebede, Bridget Scanlon, and James P R Sorensen. February 16, 2021. British Geological Survey. Environmental Research Letters, Volume 16, Number 3. Mapping groundwater recharge in Africa from ground observations and implications for water security - IOPscience