Chemical Well Rehabilitation

Review this simple primer on chemical well rehabilitation guidelines in the field.

By Edd Schofield

Routine well maintenance is a misnomer as typically no one takes the time nor needed effort to routinely chlorinate or disinfect, let alone properly acidize, a minerally affected well.

However, a more standard protocol for a complete well rehabilitation is to remove the pump, and clean to the bottom of the well with brush swabs—in other words, mechanically.

Once that is complete, you need to run back in and circulate out all the disrupted loose debris and pre-existing fill from the well. Only then would you typically introduce chemistry to the well screen interval and follow that chemical solution with agitation once again.

The agitation is intended to physically disperse the chemistry, introducing new chemistry against new deposits throughout the well column and into the filter pack.

Everyone needs to understand the silver bullet belief that dumping chlorine or any acid mix down a well is just “lipstick on a pig.” In addition, you need to treat the static water zone in addition to the screen interval.

The potential of scraping material above the well screen when rerunning the pump offers the potential to introduce deposits back into the screen interval. It is a fact that fully concentrated or heavy well rehab chemistry—regardless of what you may have been told—will have limited success in treating an impacted well screen and submerged blank casing without some means of agitating the solution across the well.

The dumping of undiluted or strong acid into the well without any diffusion or dilution whatsoever can potentially cause significant damage to the well’s lower structure as the heavy acid simply rests on the bottom of the well, and will likely do little to the total well screen interval.

Along these lines, you need to account for the water column in your calculations of chemistry to prevent dilution that occurs when just trying to target the screened zones.

As to chlorinating any well, you need to first check the initial pH prior to adding more chlorine solutions to the well. If your well water is neutral or around a pH of 7, adding chlorine (sodium or calcium hypochlorite) will migrate the pH up past 8. At that range or higher, the generation of hypochlorous acid (the biocidal component of chlorine) is reduced to less than 5% disinfection potential.

So, you’ll need to adjust the base water pH to 5.5 to 6 prior to adding in the chlorine.

This can be done with a small amount of acid or specially formulated chlorine enhancer. Such an enhancer typically contains organic acid, a biodispersant, and a surfactant.

Using an enhancer or simply adding acid will effectively lower the pH and enhance the generation of hypochlorous acid to more than 90%. When the pH is too low (below 4.5), you can push that to 100% which is chlorine gas (deadly).

Please note that sodium isocyanates, a dry powder chlorine alternative that offers a 55% reactive chlorine, does not need any of the buffering of other chlorine products. They are far simpler on the surface, are NSF-approved, and have no shelf life.

These chlorine alternatives offer a simpler and far more effective solution to nearly all well disinfection applications, thanks to advantages over that of any other chlorine product.

General Acid or Chlorine Treatment Application Recommendations

The following procedure should be followed to prepare the well for chemical addition and subsequent cleaning.

Remove the pump from the well.

1. Brush the casing present unless video review shows a clean existing surface.
2. Evacuate any debris from the well, starting at the bottom and working upward. Spend 10 minutes to 15 minutes at each 20-feet interval to draw off as much loose debris as possible. Clean to the bottom one last time.
3. Add the chemical blend to the well by placing approximately equal portions at prescribed intervals, beginning just off the bottom and finishing at the static water level.

The cleaning process can be assisted greatly by swabbing, jetting, or the recirculation of the cleaning solution thoroughly to ensure that the acid solution comes directly in contact with the entire well screen interval. The mechanical action should incorporate a minimum of 30 minutes to 45 minutes of jetting action at each 50-feet interval.

The pH of the solution should be checked periodically to maintain a pH of 3.0 or less in the recirculating cleaner. If the pH rises above 3.0, add a small quantity of treatment food-grade acid to the downhole solution. Repeat this each time the pH rises.

After the jetting or swabbing is complete, allow the well to stand overnight. Make sure the pH is at and remains at 3.0 or below. Repeat the mechanical process the following day by spending 20 minutes to 30 minutes at each 50-feet interval. Once the mechanical agitation is complete, evacuate the well, starting at the bottom and moving upward.

Spend at least 10 minutes at each 50-feet interval moving upward. Repeat moving toward the bottom. Check the pH. If the pH returned to normal and total evacuation equaled five or more well volumes, only then can the well be prepared for chlorination.

Edd Schofield is the technical sales manager–chemicals for Johnson Screens and has been with the company since 1988. He served as the Groundwater Foundation’s McEllhiney Distinguished Lecturer in Water Well Technology in 2007. He can be reached at edd.schofield@johnsonscreens.com.