Aquifer Storage and Recovery

An Update

By Ed Butts, PE, CPI

As we rapidly approach the end of another year, we are also close to the end of this series covering our industry’s changes, both good and bad, along with the advancements that have occurred in the water well market over the past half century.

Our industry has certainly witnessed remarkable improvements in everything from drilling rig technology to water pump materials and efficiencies to variable frequency drives.

All that said, there has likely not been a more obvious change to well drilling applications and aquifer technology than the introduction and increasing use of aquifer storage and recovery (ASR).

It’s difficult to expound on the changes to ASR since 1975, as it wasn’t well known or widely used then. Throughout the history of mankind, water resources have often been polluted, available in inadequate volume, or improperly located for everyday potable use. Civilizations have often risen and fallen in accordance with the fickle nature of rainfall, runoff, and evaporation.

In today’s world, as the population of the world continues to grow and diversify, the luxury of locating cities and large groups of people adjacent to consistently available water supplies will continue to diminish and challenge planners.

The need, therefore, exists to secure and begin using new and sometimes radical technologies to treat, transport, and store additional fresh water in areas with inadequate or non-potable water supplies. These newer technologies such as reverse osmosis, electrodialysis, and ASR are being used today to assist in providing additional water supplies throughout the world, most notably in third world and developing
countries as well as the United States where water supplies are already or becoming often limited or strained.

ASR technology has largely seen widespread use throughout the world, principally beginning during the 1980s. I was somewhat on the cutting edge of the application of ASR in Oregon with our firm designing and building several systems for use in Oregon and Washington during the 1990s and early 2000s. I also wrote two columns on ASR within my first year of this column in Water Well Journal’s December 2001 and January 2002 issues.

This month then, as a fitting wrap-up to this series on updated technology during the last 50 years, we will review the early experimental days of ASR, its increased application and expansion, and a few recent advancements.

History and Current Status

Artificial recharge through wells has been used since 1956 in Israel, and Australia has used ASR to recharge a brackish aquifer with fresh surface water supplies since around 1970.

In the United States, the first known recharge project began during the 1950s in Orange County, California. The storage zone was comprised of sand, and the purpose of the recharge was to provide a salinity intrusion barrier between saltwater sources and freshwater dune wells. In fact, most of the early uses of recharge were to provide a barrier against saltwater intrusion to freshwater supplies either by displacement or by maintaining higher static water levels in the freshwater wells, thereby preventing the saltwater intrusion.

Currently, the most active regions in the United States for recharge activities include southern California, Florida, and Arizona. ASR projects in the U.S. saw substantial growth between 1990 through 2010 (Figure 1).

For example, in July 1999 there were 32 ASR systems in operation throughout the United States, with around 40 more in various stages of investigation, design, construction, or testing. In 2013, a data set on ASR systems in the United States was collected from the U.S. Environmental Protection Agency and state environmental agencies. In addition, data was compiled from literature and through telephone interviews with specific water utilities. This effort yielded 204 ASR sites that included more than 700 wells, with the most sites found in Florida (54) followed by California (28) and New Jersey (19).

The ASR projects in this inventory used water sources that included raw surface water (64%), groundwater (21%), and reclaimed wastewater (14%). Storage periods ranged from months to years depending on the goal, which included storing water to meet the next high-demand period, supplementing supply during an emergency such as a severe drought, and providing water during an interruption of supplies resulting from equipment breakdown.

Approximately 37% of the ASR sites were considered operational, while 25% of the sites were not active, and the rest in various stages of testing (26%) or feasibility studies (12%).

In October of 2019, an updated database added 29 new sites to the previous inventory of ASR sites. Florida still has the most ASR sites, followed by Texas and California (Figure 2).

The applications of aquifer storage and recovery systems include more than just long-term or emergency storage of drinking water. An ASR system can be designed and constructed to accommodate many other objectives, depending on the specific site conditions and water needs. Among the many available uses of ASR are included seasonal or long-term water storage, emergency storage, water quality enhancement,
restoration of groundwater levels, reducing subsidence, supplementary capacity for peak demands, and offsetting saltwater intrusion impacts.

Limitations and Risks Associated with ASR

As with all new technologies, the apparent benefits of ASR are often offset by liabilities and risks. The following list represents the most common potential water quality issues:

• Pathogens may enter aquifers if water is not disinfected prior to injection. Some states allow injection of raw water and treated effluent. In these states, the fate of microbes and viruses in an aquifer is relevant.
• Disinfection byproducts can form in the aquifer if water is disinfected prior to injection. Soluble organic carbon should be removed from the injectate before disinfection. If not, chlorinated disinfectants may react with carbon to form contaminating compounds. Contaminants include
  trihalomethanes and haloacetic acids.
• Metals and radionuclides may be mobilized from the rock, depending on the chemistries of the injected water and the aquifer. Differences in pH and reduction/oxidation potential between the injected water and aquifer may cause arsenic, iron, manganese, or radionuclides that are present in the rock to dissolve into the water.
• Carbonate precipitation in carbonate aquifers can clog wells when the injectate is not sufficiently acidic.

There are also other potential downsides to the use of ASR and the other three types of aquifer recharge. Injection and withdrawal of groundwater through ASR wells can change local and regional flow patterns and water levels in the aquifer used for storage. If improperly managed, these excessive water level head changes can lead to aquifer mounding resulting in overflow, possibly causing undesired increases in the amount of groundwater discharging to springs, streams, lakes, or wetlands, or even spilling over or leaking into other local aquifers.

In some cases, there are also undesirable changes in hydraulic or water chemistry parameters such as well clogging or intermixing dynamics, which may affect well yield and induce changes in water quality to other nearby wells.

Potential changes in aquifer dynamics need to be evaluated during the preliminary design and pilot (testing) phases of an ASR system to estimate the required full-scale injection rate, ASR recovery efficiency, and to anticipate water quality or hydraulic impacts on other users of the aquifer. Geophysical logging, hydraulic and water quality testing, and numerical modeling are effective tools that can be used in this evaluation.

ASR systems may also develop serious problems when not sited, designed, constructed, or maintained correctly. To begin, the wells can clog or plug from various physical causes such as sand, silt, rock, or grit, or chemical precipitation of iron, manganese, or calcium hardness, preventing the injection and recovery of water at a meaningful rate.

This can occur on the well screen face, within the filter pack or confined well fractures, or in the aquifer itself. It can also occur over time due to inaccurate predictions or inadequate pilot testing of the water quality impact or seasonal variations.

Well plugging typically occurs in one or more of these three locations:

• In direct proximity to the well
• The area that exists within the interface between the screen/filter pack/local fractures and aquifer
• Remote (exceeding a distance of 100 feet beyond the wellhead).

Where and how the well plugs can take different forms. Abrasion between sand grains, air binding, biofilm, cementation and chemical dissolution or precipitation are all types of plugging encountered in ASR wells, and all require slightly different approaches and solutions to correct and resolve the issue. Hazardous trace elements such as arsenic or selenium may leach into the stored water from the aquifer materials if the recharge water is chemically incompatible or inadequately treated.

ASR systems require specific and favorable geological conditions to successfully inject, store, and extract water. As such, poor planning or site selection, improper well construction, and inadequate well maintenance may cause the stored water to flow out of the aquifer and capture zone due to the presence of inadequate boundaries, higher head (static water levels), or improper well and seal construction.

Aquifers recharged from infiltration basins must be unconfined and have sufficient transmissivity to allow lateral flow of the water away from the infiltration sites to prevent excessive groundwater mounding. Soils, unsaturated zones, and aquifers should be free of significant contaminants to prevent possible aquifer contamination.

This can result in the possible migration of recharge water to lower or higher aquifers or downgradient to neighboring wells, yielding an unfavorable outcome and potential political and liability issues. To avoid this situation requires careful attention to detail in the siting, design, and construction of wells and sites used for recharge purposes.

As a relatively new and growing technology, aquifer storage and recovery is also susceptible to various technical and non-technical issues and concerns. Most of the technical issues are related to the injection process and geochemistry of the applicable water.

The injection process, whether by injecting the water directly into the well or through a pump or specialized injection control valve, must include some method to avoid air entrainment into the recharge water or cascading (falling) of water down the well. Air, when allowed to be mixed with water, can be injected into the aquifer during recharge, which can create air binding of the aquifer, drastically lowering the efficiency and production of the well as well as causing chemical changes within the water itself.

An air/water mixture can also result in oxidation/precipitation of background levels of iron and manganese, resulting in possible plugging of the well screen, perforations, or fissures. This plugging may lead to increased pumping and recharge head as well as reduced well performance and efficiency, which may ultimately lead to well failure.

Water quality can also become compromised due to inadequate mixing, thermal gradient and water quality differences, head variations, or intermixing instability.

A potential hazard that can occur from ASR/AR is liquefaction, caused by creating a shallow water table in poorly consolidated geologic materials that is subsequently shaken by an earthquake of sufficient magnitude.

Once the system is operable, regular tracking of recharge and pumping water levels and flow rates must be conducted to ascertain and correct any serious deviations before the situation becomes irreversible. To avoid these potential conditions, a proper pilot study of adequate duration must be initially conducted.

An ASR pilot study is performed generally on a scaled basis for a year or more to account for all seasonal changes with lower flow rates and volumes in the pilot extrapolated to greater flows and volumes.

In addition to the normal hydraulic factors of recharge flow, head, and withdrawal (recovery) rates, this study should include a comprehensive water quality examination, including stratification simulations within the recharge zone, geochemistry mixing scenarios with varying recharge levels, well plugging potential, and possible unfavorable water quality issues when remixing with the water from the water system. This generally requires the installation and permanent use of one or more observation or monitoring wells within the recharge zone.

ASR systems can also present possible political problems and liability issues. These systems have the potential to increase tensions between states, nations, tribes, or populations that compete for freshwater from the same surface water source or aquifer.

Capturing and storing excess freshwater in aquifers can dewater surface water sources and basins, which often precludes constructing dams or reservoirs on rivers. This may violate international or tribal treaties or interstate water use agreements.

This often occurs when surface water from one state is transferred to an adjacent state for aquifer recharging. Infringement on a senior water right can result in significant flow restrictions, or in extreme cases, total shutdown and loss of the source.

Local contamination of a widespread and large aquifer due to improper recharge water quality can possibly migrate from one locality or well to another downgradient or nearby water user. In some cases, pushing saline or brackish water back into an aquifer can create detrimental water quality to other nearby users. This can result in a contaminated or unusable aquifer or well on the neighboring property and severe legal repercussions.

Two examples of these types of potential risk are the Ogallala Aquifer, known to underlie a significant portion of the central and southern United States and the Columbia River Basalt Group in the Portland-Willamette Valley region of Oregon and Washington states.

Advancements to ASR Injection Technology

During the infancy years of ASR systems, one of the principal required functions was developing and implementing effective well injection processes. This consisted of systems that utilized controlled pressure to prevent cascading water and column separation, resulting in potential air entrainment and vapor locking of the aquifer.

Downhole injection control is the primary element of a successful ASR system. Whether injection control is provided by back-feeding water through a set of locked pump bowls or through a downhole injection flow control valve (Figure 3), control of the flow rate and backpressure of recharge water is vital to ensure proper system operation and prevent cascading and aerating conditions.

Reverse injection depends on the head loss generated through the locked pump bowls while flowing in a reversed manner. Downhole injection valves typically use pneumatic or hydraulic control, fed through tubing from the control module mounted at the wellhead. This provides variable control over the process and ensures the pump column remains full during injection.

Methods of ASR Injection

Although not necessarily exhaustive, the following section is an introduction to the primary methods of ASR injection control and the unique operation of each method or valve. Most of the descriptive language is derived from the firms’ own description of their particular method and valve.

AGE ASR Valve: The AGE ASR valve provides injection control that also allows aquifer fluids to be injected or pumped to meet either production requirements or to backflush where an injection bore is susceptible to regular fouling due to mineralized deposits forming within the bore, causing clogging issues. The ASR valve is controlled by the same surface control system (SCS) and allows the same user functionality of the flow control valve (FCV) system with the addition of the recovery or backflush cycle.

In this mode of operation, the annular ASR valve is modulated fully closed and aquifer fluids are pumped through the valve by means of a submersible pump installed below the ASR valve. To return to injection mode, the pump is stopped and the SCS is returned to injection mode modulating the ASR valve according to the set parameters.

Injection is accommodated by means of radial injection ports that are specifically shaped to obtain proportional control of injection flow rates. Injected water is then deflected downwards by the injection shroud ensuring that erosion of bore casing does not result.

ASR Resources-BIC-V Injection Valve: The V-Smart BIC-V Borehole Injection Control Valve™ is a sliding sleeve, multi-port, all stainless steel injection control valve for deep-well flow control. The V-Smart BIC-V is designed for use with both vertical turbine pumps and submersible pumps. The valve sits above the bowls of a pump and is submerged below the static water level or maximum expected drawdown
level during pumping operation. The valve maintains a variable backpressure in the drop pipe to maintain well pressure above atmospheric pressure to prevent cascading water and air entrainment, while providing precise flow control into the injection well.

For vertical turbine pumps, the full port internal diameter of the V-Smart BIC-V valve allows the pump line shaft to extend through the center of the valve, while leaving a large flow area for minimal pressure drop. The V-Smart BIC-V is hydraulically actuated by an above-ground hydraulic power unit (HPU) housed in a Nema 3R enclosure. The hydraulic fluid is food grade mineral oil.

Baski-FCV Injection Valve: The InFlex™ Flow Control Valve (FCV™) is a fluid-actuated valve that permits pumping water to the surface or regulating the flow of water from the surface into the well, while using the same column pipe and maintaining a column of water in it at all times. The InFlex FCV may be used in conjunction with a submersible pump or a vertical turbine pump for aquifer storage and recovery and aquifer thermal energy storage applications.

For injection, the annular orifices provide the tortuous path for water that results in the desired non-cavitating pressure loss across the valve. The reinforced element stretches into the area between the channels, which further increases pressure loss in the valve. For pumping, the element is pressurized to provide a leakproof shutoff seal against the area without channels. The valve has a built-in liquid inflation chamber so that gas from the surface may be used to actuate the valve.

IPI ASR Flow Control Valve: The  IPI ASR Flow Control Valve is an innovative and cost-effective tool for minimizing the introduction of air into injection and recovery wells. The flow control element with a tapered, inflated shape in conjunction with PLC control provides a single-point choke that controls high volume flow without causing fluttering and eliminates the need to create a variable tortuous flow path. The inflatable element expands in a tapered shape to control annular area during the injection phase. The packer expands to its full length in the closed position.

This simple approach means that the IPI valve is lighter and more economical than other similar valves. IPI can tailor the valve design to suit precise operational requirements.

Reverse Bowl Injection: Reverse bowl injection involves the direct injection of recharge water through the locked well pump. This method is occasionally called static pump injection, as the bowl assembly and motor are static or not operating during injection. It is used most often with a vertical turbine pump (VTP) equipped with a non-reverse ratchet and relies on the backpressure developed by the locked bowls in a backfed flow direction.

To prevent cascading water, the flow range during recharge should generally be within 70% to 85% of the pump’s design flow at the best efficiency point (BEP) when the recharge head is essentially identical to the pump’s total dynamic head (TDH) value. A booster pump to generate higher recharge head can be applied to provide recharge at higher flow rates or head, if desired.

Although limited in the range of recharge flow, this is usually the least costly option since no added equipment beyond that required for pumping is needed. Generally, the design is predicated on the recharge flow passing through each pump stage and delivered to the well through the suction strainer.

The additive resistance from each stage develops the head loss necessary to avoid cascading conditions in the pump column. In certain cases, a specially cut perforated tailpipe or screen can be placed on the suction to provide a uniform entrance velocity into the pump during pumping and from the pump into the well during recharge activities.

With an alternative shaft coupling design, water can be backfed through the spinning bowls to function as a turbine to generate low values of electrical power. Experience and hydraulics have correlated the recharge head through a locked pump bowl to be related to the specific speed (N_S) of the pump. Figure 4 displays a chart based on actual tested data to enable prediction of recharge through vertical turbine pump bowls of various N_S.

For example, for a specific speed VTP of 4500, a bowl assembly will pass 80% of the design flow at 70% of the bowl’s rated TDH. This means a pump designed for 1000 GPM at 350 feet TDH will pass a recharge flow of 800 GPM at 245 feet or 106 psi (350 feet × 0.70).

3R Valve-Injection Valve: The design of the 3R Injection Valve allows the user to control the flow of water flowing down a pump column by activating two hollow single acting hydraulic cylinders that move a UHMW internal sleeve in front of a group of small holes that allows the water to then move from the inside of the valve through the holes to the outside and out into the aquifer.

The small-diameter holes are located around the valve in a slight upward spiral pattern, so as the UHMW sleeve moves, it exposes only a few holes at a time. This allows the PLC controller to regulate the flow of water more precisely. The small discharge holes in the valve also allow the water that is surrounding the valve to dissipate the energy of the water that is flowing out of the holes and in turn reduces the hydraulic mining that might occur in the borehole.

The valve is constructed out of stainless steel and does not screw together like other valves on the market. This one-piece construction will not allow the valve to unscrew and fail. The 3R Valve also has no moving parts that are on the outside of the valve body that can rub against the borehole or allow rocks or other objects to interfere in the operation of the valve. The 3R Valve does not use any rubber boots to control the flow. These boots are subject to wear that causes the valve to fail and be pulled to be repaired.

The 3R Valve can also be ordered with a spring option that allows the valve to close if there should be a hydraulic failure in the valves control line. 3R Valve also makes a recharge- only valve used in HVAC applications that allows the operator to control the flow of water back into the aquifer.

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This concludes this month’s column and our year-long series on changes in water well technology and science since 1975. We’ll conclude the year next month with a review of some of my past water well projects—the good, the bad, and the ugly.

Until then, work safe and smart.

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Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 40 years of experience in the water well business, specializing in engineering and business management. He can be reached at epbpe@juno.com.