By Michael Schnieders, PG, PH-GW
I had a contractor mention to me the other day that he “knew what I was going to say…you’ve got to pull the pump, brush and bail, clean out the bottom, treat the entire well column, never neutralize downhole, make sure you evacuate everything, and so on…”
I’ll admit, I was a little taken back at first. But then I remembered those are the fundamental steps to doing the job right and we recommended them for good reason—and he wasn’t calling me because everything was going fine; the treatment effort he had made had failed and he had taken shortcuts.
First, realize by the time someone hires a consultant for a fouled well or disinfection problem, they have typically tried multiple things with little or no success. Also realize that more often than not, the well owner has run the well to a point of failure, whether it is a private well or municipal utility.
Yes, generally my well cleaning recommendations follow a similar procedure, but they are made with a purpose. So, as a refresher, let’s review some of the important components and the reasons behind them.
[not_logged_in]Login with your NGWA member account to read the full article.[/not_logged_in]
Pull the pump. This is a time-consuming and expensive component of cleaning a well, yet if you don’t do it, how will you effectively physically clean the lower extension of the well?
How can you be sure you’ve removed fill, debris, and disrupted material from the bottom of the well? How can you agitate introduced chemistry effectively?
The answer for each of these questions is the same, you can’t. Treating the well while the pump is in place only works if you are conducting routine maintenance, the well is relatively shallow and a good producer, and you are lucky.
Mechanical pre-treatment. Whether you are cleaning dishes, the garage, or a well, removing the easy stuff that is in your way first allows you to see, target, and more effectively clean the small stuff.
In the case of a well, this improves your chances at addressing fouling in the filter pack or in the case of open borehole completions, the fractures. By utilizing brushing, swabbing, or low-pressure jetting and dislodging this material, you can treat the well more effectively and more economically. More physical removal of scale and slime allows for less chemical need and more effective removal of the remnant deposition.
Clean out the bottom. Sand, silt, biomass, scale, and other goodies all accumulate in the bottom of the well. The isolation that occurs may be a part of the well design, a reflection of the flow profile, or a result of fouling.
This area is the most common location of nuisance bacteria including sulfate reducing bacteria and environmental coliforms. Removal of this material is important for effective cleaning and disinfection.
When allowed to remain downhole during cleaning, this material can limit effective dispersal of the chemicals, neutralize or consume the chemicals, and block flow into the lower zones. During disinfection, this material reduces the effectiveness of chlorine and other chemical products while providing a shelter for coliforms and anaerobic bacteria.
Treat the entire well. Many well owners neglect maintenance due to economics, so, when it comes time to clean the well, the cost can be overwhelming. Sometimes in an effort to reduce costs, you may want to target the treatment to the producing or offending zones. But this often results in limited success or failure, and the process has to be repeated.
Why? Think about the well. The bulk of most wells are blank cased sections with tens to hundreds of feet of water sitting above a small screened section. What does that water do? It dilutes and it neutralizes, reducing the strength and effectiveness of the introduced chemicals, whether it is chlorine or acids or surfactants.
A common response is that the chemicals are heavier than water and will just fall to the bottom. And while this is true, the time and dilution factors will significantly impact the viability of the products as effective cleaning or disinfection chemistries.
Never neutralize downhole. The negligence behind this still amuses me. Why spend time, energy, and money to leave the same fouling mechanisms that plagued performance and quality downhole?
Neutralization of acid solutions or oxidative chemistries such as chlorine can result in mineral complexes downhole that provide foundations for a rapid return of scale. Similarly, leaving biomass and microbial cells downhole provides a nutrient source and additional carbon for a very quick rebound of the native population.
Monitor the evacuation. Continuing the discussion from the above section, a little additional effort to insure you’ve fully evacuated the well is important. Several common parameters to monitor include visual turbidity, conductivity, and depending on the methods used, pH or chlorine concentration. These small efforts help insure you’ve removed all of the disrupted material as well as any introduced chemicals and returned the well to its best state.
When we experience less than successful results, it is almost always because a fundamental aspect of the process was skipped.
Each well has been operated and maintained—or neglected—differently. While similarities exist in aquifers or drilling methods or materials used, each well is truly an independent and unique structure that requires special attention in its treatment and restoration.
Take the time to fully understand the condition the well is in and what fouling mechanisms are impacting its operation or produced water quality before heading down the path of treatment. Remember these six fundamentals of good maintenance to help in the process.
Michael Schnieders, PG, PH-GW, is a professional geologist currently serving as the principal hydrogeologist and president of Water Systems Engineering Inc. in Ottawa, Kansas. Schnieders’ primary work involves water resource investigation and management, specializing in the diagnosis and treatment of fouled well systems. Schnieders was the 2017 McEllhiney Distinguished Lecturer in Water Well Technology. He can be reached at firstname.lastname@example.org.