Restoring Flow through Water Well Rehabilitation
The performance (flow rate and drawdown) of water wells and their water quality can deteriorate over time. This is a natural occurrence and common experience of mechanical structures. The situation is not always bleak when a household water well fails to produce the water it did when it was first installed. Instead of the expense of abandoning the well and installing a new one, a professional contractor can often “rehabilitate” the well and restore flows that provide enough water for household or farm needs.
Upon what does a contractor base the decision to rehabilitate a well? Several factors are involved, including the ground formation that the well is drilled in, the construction of the well, and the problem that has caused the decreased flow. Sometimes, the water table in the area has dropped and simply drilling the well deeper is the answer.
Important points about well rehabilitation: 1) It is not always as straightforward as well drilling, and 2) it takes time, usually more than one day, and often several. An alternative water supply such as a hauled tank, or scheduling when the occupants are away, is recommended.
The following are more answers to questions concerning well rehabilitation.
A professional contractor can do inspections and tests to see if rehabilitating measures will be successful.
The contractor may start by checking the static water level: The well will often be shut off for 24 to 48 hours to see if the static level – the level of the water table in a well when the pump is not operating – returns to or gets near the original level. If so, rehabilitation will usually work, if other factors suggest success. The contractor will then run a short pumping test to check pump function, flow, water quality, presence of sand, etc.
Before proposing to start rehabilitation, the contractor needs to understand the construction and structural integrity of the well: Is it safe to apply flow, pressure, and mechanical force to the well to clean it? Larger municipal and irrigation wells typically have larger and more robust casings. A well may have been constructed “to the minimum” — have a thin-wall casing, or other deficiencies. The contractor usually starts with the well log or well construction record.
What is the diameter? In many parts of the US southeast, two-inch diameter wells are constructed and attached to jet pumps. These are very difficult to clean with available tools. Even 4 or 5-inch wells, especially if constructed with PVC screens, can be risky to clean mechanically. All these factor into the type of treatment proposed and equipment to bring.
A contractor may recommend (or require) performing a borehole (downhole) video inspection using a slim camera on a reel to observe the well’s structure and condition. There is a cost to this service, but it prevents problems later, and helps the well owner understand the well. The pump is removed for this procedure. At that point, the pump and its operation are inspected. Whatever is clogging the well usually clings to the pump and pipe.
Problems that may prevent or complicate rehabilitation may include debris stuck in the well, casing breaks, changes in diameter or crooked boreholes. The video also shows where to concentrate work, making the process more efficient.
Along with the water table dropping, which has happened in several parts of the country because of droughts or overuse of aquifers locally or regionally, there can be other reasons for reduced productivity.
The most common is the plugging of holes or slots along the well’s casing and encrustations forming on the well screens. The amount of water going through the well system will drop significantly if several holes or portions of the screens are clogged. Calcium carbonate, silt, clay, iron sulfides, and iron and manganese bacterial “biofouling”, a combination of sediment and deposits, are all common well cloggers. There may also be collapse in a well that closes off portions of screens or aquifer rock. For example, an earthquake, construction blasting, or even just time may fill in the well. Locally, other materials may clog wells, and it is really important to know, and not to guess, what is causing the issue.
Sometimes it is just the pump. Pumps wear and clog. The contractor will determine this during the inspection.
Two typical methods are (1) using chemicals to loosen and sometimes dissolve the encrusting materials so they can be pumped from the well and (2) cleaning the well using a mechanical action, pressure, or fluid force (air or water). The best results come from “both”. Chemicals aid in loosening deposits, but the action takes it away and removes it from particles and surfaces and out. Along with mechanical action, a good place to start is with a casing brush that can be attached to a drilling rig and then used in the well. This removes deposits on the casing surface, and improves the chances with the rest of the process, much like removing the grease to get at the baked on deposit in a pan.
For mechanical action, there is high pressure jetting, hydrofracturing, and well surging with either a cable tool percussion rig or high-pressure air (or the two in combination). Contractors will often use a combination of these methods.
High-pressure jetting (downhole variation on pressure washing), features a tool with an adjustable, multi-head, water-powered jet that lowers into the well and injects water at a high pressure, dislodging debris from the well.
With hydrofracturing (a lower impact version of oil and gas methods that is actually more like high-pressure impulse development), water is sent into the entire well at a high pressure. The water removes debris from the clogged perforations in the casing and can sometimes crack the formations or loosen existing fractures or joints underground to create new sources of water.
Cable tool surging is a tried-and-true, low-cost, widely available method of developing reciprocal in-and-out motion in a well to clear debris, and to bring in and remove fine sediment. Air surging can be used instead or in combination with cable tool motion.
Where no more effective option is available, well surging can be performed using the repeated injecting and flushing out of water in a well system. With repeated flushing, the debris is washed away.
This cannot be repeated too often: 1) Chemistry chosen to clean a well should be selected based on knowing (not guessing) what the clog is. 2) The chemicals used can be dangerous to handle or if sprayed around. 3) The chemicals used must be safe and approved for drinking water application. Some examples:
For iron- and manganese-related biofouling (bacteria and slime with encrusted iron, manganese, calcite and sediment), a liquid bacteria acid (usually a version of glycolic aka hydroxyacetic acid, sometimes with hydrochloric acid is effective. Some specify other acids. The homeowner should have the contractor explain their choices. For clogs with carbonate scale, sulfamic acids are used with inhibitors and modifiers. It should be noted that treatment with chlorine products is a form of well rehabilitation.
The chemicals are placed in the well and agitated frequently for 24 to 72 hours (thus the reminder to time such work properly and to prepare for the time it takes). Any strong chemical is then safely pumped away in a responsible manner (the homeowner may want to be sure about that) and the well is developed until clear and pH is normal. At that point, a well pump may be reinstalled and pumped until groundwater is within pre-treatment pH range before a water test is given to see if the well system is ready to be put back in service.
The contractor should provide a brief report on this work.
For more information on rehabilitating a water well system, contact a professional contractor in your area. It should be noted that not all well contractors perform well rehabilitation, and we recommend working with one that is experienced in this specialized task. A list of National Ground Water Association-member and certified contractors is available at the Contractor Lookup section of this Web site.