Artificial recharge by injection wells

Bruce Florquist
Public Works Director
City of Rawlins, Wyoming

One of the absolutes that we have to face is, there is only a finite amount of water on the planet. Although earth is called the water planet, the amount of fresh water is limited. The reality is that much of that fresh water is not where it is needed. Some of the more populous regions on earth are some of the most deficient in fresh water. That is certainly true here in the United States. Many of the fastest-growing areas are in deserts where the average annual rainfall is less than eight inches per year. Historically, we have met this challenge by building large dams and water projects, but the likelihood of building such facilities in the future is very slim considering the environmental requisites that must be met.

So, a challenge is presented to hydrologists and water managers: "What are you going to do to meet the growth in water demands?" The answer is not simple, and there are many ideas and schemes out there. Some of these are practical and cost effective; some are "pie-in-the-sky" schemes that will probably never make economic sense in the foreseeable future.

One solution that shows promise for many areas is water banking through artificial recharge. This is being done around the world using varying techniques such as spreading basins, recharge pits and shafts, ditch infiltration, and recharge wells. This latter method shows some promise, but is often limited by subsurface geology, incompatible water chemistries, and other factors.

Recharge wells are used to introduce water into subsurface water bearing zones (aquifers). These aquifers can be relatively shallow such as alluvial deposits or deep, confined aquifers under artesian pressure. The artificial recharge of groundwater has some distinct advantages:

1. Groundwater is not subject to evaporation and transpiration. These factors account for significant losses in surface reservoirs and wetlands and, in fact, can contribute to the degradation of the water supply by concentrating salts and alkalinity by rapid evaporation. There are many places in the arid west where this has happened over the years. The Great Salt Lake and the Bonneville Salt Flats are some of the more visible examples, but many smaller "alkali flats" attest to the process.

2. Excess water can be stored at times of the year when the demand is low, and recovered for use during peak use periods. In some areas, state water laws complicate this, and anyone contemplating such a project would do well to familiarize themselves with state water laws, river compacts, and other legal matters before starting such a project.

3. Groundwater is inherently less susceptible to contamination and pollution than surface waters. In this time of possible terrorist activities, groundwater is easier to protect than large rivers, or reservoirs.

4. Groundwater quality can actually be improved in some areas by injecting higher quality water into a formation. This dilution factor is being considered in many areas where the groundwater is high in constituents such as radium, sodium, fluoride and others. In many areas, the spring runoff is lost downstream because of the inability to use that water. Often, the early spring runoff from mountain areas is very high quality, but is not needed at that time of the year. If that water could be captured and stored in existing aquifers, it will, in many instances, greatly improve the quality of the formation water.

There are also possible disadvantages to injection recharge of aquifers:

1. Careful economic analyses must be made to assure that the project is cost effective. If one has a reliable source of nearly free water from a groundwater aquifer, does it make sense to install expensive injection pumps and pay the power costs to inject that water for future use? The cost of the injection wells may be prohibitive. In some instances, nothing short of oil field techniques such as artificial fracturing and sand injection into these fractures will help an aquifer take additional water.

2. One must clearly understand the local surface and subsurface geologic conditions. Faulting or other cross-connections with other wells or aquifers could cause all or part of the water to be lost. In the case of confined aquifers under artesian pressure, the head may be too high to overcome without inordinate effort. It is also necessary that one understand the history of water withdrawal from the aquifer. If it is an area that has subsided because of years of groundwater withdrawal, there is little likelihood that the aquifer can be forced to take additional water.

3. Well design, construction, and maintenance are extremely important. The wells must be constructed to meet the demands of the condition, and they must be maintained in perpetuity or until they are properly plugged and abandoned. A well that is not properly maintained can lead to future contamination and degradation of the aquifer.

4. Source water and wellhead protection must be maintained. It wouldn't make sense to invest in a series of injection wells if the natural recharge area is subject to development and possible contamination. An activity as innocuous as building a rural subdivision with septic tanks and leach fields over a recharge area could have long-term impacts on the groundwater.

5. Although it may sound ludicrous at first blush, proponents of injection recharge must understand the local geologic conditions to be sure that they do not exacerbate an existing condition. In the 1960s a series of deep injection wells for the disposal of hazardous wastes at the Rocky Mountain Arsenal north of Denver, Colorado were drilled and put into service. There followed a series of earthquakes in the region. After years of study the cause of these quakes could be traced to the lubrication and pressures of the injected fluids. Although it is unlikely that any injection recharge of groundwater would be at these depths (in excess of 10,000 feet), such factors must be considered.

6. As mentioned earlier, the water laws of the state must be considered, particularly in the west where the doctrine of prior appropriation is prevalent. It may be necessary to show that the project will not have a negative impact on any senior water user.

Water banking is being done worldwide, and there is a wealth of published information available on various concepts, practices, techniques and results. A good primer is Artificial Recharge of Groundwater by Kumar and Aiyagari of the Civil Engineering Department at Virginia Tech (www.ce.vt.edu).

Other good links include:

For more information, please contact Bruce Florquist at 307-328-4599 or at brucef@trib.com.

On the morning of September 8, 2001, the APWA Water Resources Management Committee was meeting around a table at the Pennsylvania Convention Center. We were nearly done for the morning, and were discussing possible articles for the Water Resources issue of the APWA Reporter. Earlier in the meeting, we talked about injection storage of water or "water banking," and our staff liaison, Ann Daniels, suggested I write a piece for the Reporter about the issue. I agreed, but little did any of us know that three days later, events would change our perspective on many things. As I started outlining the framework of the article, I listed bullet points to discuss, and I recalled a conversation I had over 20 years ago with a groundwater hydrologist from the Soviet Union who told me that most of the community water supplies in the Soviet Union were from wells as they were fearful of radiological contamination of surface water supplies in the event of a nuclear confrontation. Her name is lost to me now, but her message has come back with great clarity in the months after September 11.