It must be done unique to each well but restores groundwater quality when done right.
By Michael Schnieders, PG, PH-GW
In the medical field, rehabilitation services and programs are as unique as the individual in need and the ailment they suffer from. The goal is to return a patient back to a normal, healthy condition, whether it is following an illness, an injury, or surgery.
Well rehabilitation must have a similar goal—to return the well back to an operational state with no lingering impacts to efficiency or produced water quality. As with medicine, the rehabilitation methods should be unique to the well and the problem impacting it.
Well rehabilitation is a broad term that is used to indicate everything from the dumping of chlorine at the top to full cleaning and structural modification. Well rehabilitation can include mechanical and chemical efforts used to target bacteria, hard mineral scale, and migrating sediments. These efforts can vary greatly across the industry and country.
Rehabilitation is typically broken down into three distinct categories: disinfection, cleaning, and redevelopment.
Disinfection is likely the most commonly applied method of rehabilitation, partly because it’s required by many states following work on the well but also because it is typically a relatively low-cost procedure. Cleaning generally targets fouling mechanisms within the well comprised of chemical and biological components and can involve a variety of mechanical and chemical methods, depending on the contractor’s toolbox and nature of the offending material. Development and redevelopment are efforts specifically designed to target drilling fluids and migrating sediments that are impacting flow into the borehole.
When discussing well rehabilitation, there are several questions that should be considered prior to the initiation of work.
- How is the well constructed?
- How has the well been maintained?
- How impacted is the well?
- What is causing this impact?
These questions are commonly overlooked as we rush to respond to an out of water emergency, but they are paramount in accurately responding to an impacted well.
Prior to being placed into active service, a well should be developed. Development is a key aspect of good well construction and effectively sets the stage for well health over the life of the well.
Development should be conducted in a timely manner on all wells regardless of the methodology used. Development should include at least two methods and should have a means of evaluation or determination of success. There should be a particulate goal, a turbidity and clarity goal, and a production goal to indicate when sufficient development has occurred.
If a well was drilled and development was incomplete, rushed, or occurred during a drought, redevelopment should be included in any rehabilitation effort. Alluvial aquifers and areas of rapid recharge tend to suffer from increased sediment migration towards the well. These wells generally require redevelopment periodically over the course of their operational life.
In addition to development concerns, identifying the well construction helps determine possible influences on the well and what treatment methods will limit impacts on the well structure. For example, when dealing with wells that have low carbon steel or galvanized metal components, use of aggressive acids is generally avoided to limit the potential for corrosion to occur. Use of aggressive acids or high doses of acids could result in structural damage to the well when dealing with reactive materials.
Sadly, the run to failure mindset is pervasive among well owners—be it the homeowners or large municipalities. Overcoming this is best achieved with education. Compiling the data following cleaning is a good time to initiate the well owner on the importance of proactive maintenance.
When approaching a cleaning procedure, review what maintenance has been conducted on the well: successes, failures, and challenges. This information is important when approaching a well rehabilitation effort.
Level of Impact
Identifying the extent to which a well is impacted is an important step in the rehabilitation process. The most reliable means of evaluating the level of impact is to look at the specific capacity (SC).
The specific capacity of a well is the pumping rate (gpm) divided by the drawdown in feet. Regular monitoring of the specific capacity can help to identify impaction of the producing zones, ahead of a run to failure event. We generally advise clients to begin planning for maintenance efforts as the loss of specific capacity exceeds 15%.
The level of impact can be assessed by examining the use and ability to produce water. In a municipal setting, evaluating the effectiveness of treatment efforts such as filtration or the chlorine demand can give you good insight. If filters or other conventional means of treatment are requiring more frequent and aggressive backwash or if chlorine demand has increased, fouling within the well can be responsible.
A video survey of the well is an effective tool to identify the extent of fouling. In addition to confirming the type and extent of fouling, a video can help identify areas that may require additional treatment or physical repair.
Causes of Well Fouling
Well fouling can be a result of a number of issues, including microbial presence such as a coliform occurrence, the buildup of biofilm, the accumulation of mineral scale, corrosion and corrosion by-products, mechanical blockage caused by fine sediments, or a combination of these issues.
Fouling generally occurs as one of several issues but can include an impact to water quality or the use and treatability of the produced water, influence on the production capacity, or a decline of the well’s efficiency.
Well fouling does not follow a set schedule. Fouling can develop quickly in one well and occur over decades in the next, so as stated initially, every well should be treated individually.
Monitoring and testing, when conducted, require routine evaluation of a number of issues including chemical, biological, and operational aspects to identify problems early.
As noted, the rehabilitation aspect should be tailored to the well, the level of impact, nature of the fouling mechanisms, the environment the well is located in, and the abilities of the contractor. Preferences vary widely, but historically, combined chemical and mechanical efforts show the best effectiveness.
Mechanical agitation has proven beneficial in all types of rehabilitation. Mechanical cleaning, such as brushing, helps to break down bulk material that can consume or neutralize the chemicals being employed.
The methods should be tailored to the well and the problem—without endangering the “patient.” For example, splayed high tensile strength cable brushes are useful in breaking down hard mineral scale, but when employed against low-carbon steel casing can leave scratches or reactive surfaces in the metal, increasing the potential for iron mobilization.
The chemicals employed for well rehabilitation vary significantly by the nature of the fouling mechanisms. When selecting the right chemical, you need to confirm that it is designed for the identified problem; won’t damage the well or aquifer; is compatible with the well structure and mechanical methods being employed; is NSF Standard 60–approved for potable well use; and can be removed from the well, neutralized (on the surface), and disposed of without additional challenges.
Regardless of the size, ownership, or use of the well, once rehabilitation is complete, your job is not done. As with all projects, take the time to assess the usefulness of your actions. This should go beyond simple regulatory requirements to a means of assessing the well and actions taken.
Is the problem resolved? Has the well’s efficiency or capacity loss been restored? Is the offending odor or bacterial presence resolved? If possible, document and quantify the successes or failures of your efforts so that the well can be operated and maintained moving forward in the best manner
Some means of evaluating performance include water quality testing, a pump test, wire-to-water efficiency calculation, and a downhole video survey. However, this information is only beneficial if evaluated and shared with the customer.
Well Rehabilitation Is a Process
In summary, well rehabilitation, in whatever form it takes, is a process. To be successful, it cannot be approached or executed lightly and should vary with each well. Each well is designed, constructed, and operated differently, and as such, resolutions to problems should be well-specific.
The early identification of problems and timely response saves time and money but can extend the operational life of a well considerably. Post-treatment evaluations can be as useful as pre-treatment investigation efforts and can help to establish new use and maintenance guidelines for the well when utilized.
Michael Schnieders, PG, PH-GW, is the president and principal hydrogeologist at Water Systems Engineering Inc. in Ottawa, Kansas. Schnieders was the 2017 NGWA McEllhiney Lecturer in Water Well Technology. He has an extensive background in groundwater geochemistry, geomicrobiology, and water resource investigation and management. He can be reached at firstname.lastname@example.org.