There are a variety of reasons why a well might need to be cleaned.
Bacteria. In the upper reaches of the well, and often extending deep into the water column due to pumping, the presence of oxygen encourages the growth of aerobic bacteria (bacteria requiring oxygen) and the oxidation of metals such as iron and manganese. Aerobic bacteria tend to cause clogging by the production of large amounts of slime and the entrapment of oxidized iron and manganese as well as other minerals such as calcite.
Debris from bacterial activity in the upper portions of the well tends to accumulate at the bottom of the well. Water in the lower portions of the well can become depleted of oxygen due to chemical reactions and bacterial activity, creating an environment for anaerobic bacteria (bacteria able to live without oxygen). These anaerobic bacteria, natural to the aquifer, are often responsible for methane gas, a fishy taste, various odors, and hydrogen sulfide (which causes a distinctive rotten egg odor). Aquifers, and therefore wells in them, may become anaerobic if hydrocarbons such as fuel oil or gasoline are spilled in them, and downgradient from uncontrolled trash deposits or manure piles. Such contaminant plumes will be preceded by increases in iron and manganese.
Many aquifers are naturally anaerobic, especially if hydrogen sulfide, methane, and carbon dioxide (derived from methane by bacteria) are present. Hydrogen sulfide and methane are common where there are oil and gas deposits, coal, and shale in the rock. Bacteria and other microbes known as archaeans generate hydrogen sulfide and methane as part of their metabolic processes. This kind of sulfide production is different from the process mentioned above. Microbes are versatile!
Sulfide corrodes steel and other metals and causes iron oxides and other minerals to deposit. Sulfide also combines with iron to form iron sulfides, which are hard and clog pores and fractures in rock, well screens, pumps, pipes and other equipment. Compounding these effects, sulfide oxidizing bacteria, which are aerobic, form spectacular light-colored slimes when they oxide the sulfide.
If nitrate is present in abundance, iron may also be oxidized (yes, without oxygen) and the iron oxides deposited. Often these processes occur together as the natural world works to reclaim your well.
Encrustation. This is the process by which a crust or coating is formed on the well intake and/or casing, typically through chemical or biological reactions. The cause may be chemical oxidation, such as that which usually forms calcite deposits, or it may be microbiological, as described. Such deposits may also trap fine sediment particles to form a weak “concrete.”
Fill-in: Over time, wells pumping from sand-containing aquifers may accumulate sediment in the bottom, closing off parts of a well screen or open borehole. Similarly, earthquakes or other vibration may cause parts of the well borehole to collapse, reducing capacity.
A well that needs cleaning can be noticeably more costly to operate. For example, a well screen clogged due to encrustation can reduce the flow of water into the well, causing the pump to work harder. Likewise, clogging in pumps causes them to work harder to pump the water demanded. This results in higher electrical costs and wear on the pump.
Generally, these effects are more noticeably the higher the pump capacity and the deeper the pump setting or drawdown required.
To summarize, proper well maintenance offers a positive payoff in extended pump and water treatment system life, and reduced impacts on plumbing fixtures and appliances.
Some well owners view chlorination as a cure-all for water quality problems. While chlorination might temporarily prevent taste and odor problems, it leaves behind debris or accumulated organic material. Such debris or material provides a food source for future bacterial growth. Chlorination may therefore be ineffective in the long run. Additionally, well chlorination as often performed, is ineffective in providing the agitation needed to remove deposits, and often does not reach deep into the well water column.
There are two basic approaches to well cleaning—mechanical and chemical, with the most effective strategy often being a combination of the two. Within both the chemical and mechanical methods is an array of options. A water well system contractor is best qualified to help the well owner decide which methods to use, depending on the condition of the well.
Mechanical processes for loosening debris and/or encrustations and removing them from the well include the use of:
Pressurized air or water
Wire brushes or scrapers
Agitation of water in the well
See a more detailed description at the “Restoring flow” page or in references on the subject.
Chemical cleaning often involves the use of various acids to loosen or dissolve debris so that it can be pumped out of the well. Depending on the nature of the cleaning job, there are also polymers and “caustic” chemicals (that increase the alkalinity of the water) to remove debris. These chemicals may be used in combination or in sequence. Such chemicals must be selected to be safe to use in a potable water supply, and by a knowledgeable professional for safety and effectiveness.
Before proceeding to clean a residential (or any) well, a contractor will collect information and perform an inspection:
Review of the well log or well record to determine depth and construction, perform a site review (access, etc.): Is it safe or effective to clean it?
Pumping test and pump function test (the well problem may be the pump, not the well) evaluating performance
The contractor may insist on a downhole video inspection to confirm well dimensions, look for obstructions, holes or other unrepairable damage, and try to confirm and pinpoint the location of the well clogging.
Such an inspection may lead to the conclusion that well cleaning is not cost-effective vs. constructing a new well.
The age of a well may determine which methods are used to clean it. If a well’s water intake areas or the well casing have corroded significantly over time, they may be damaged or destroyed by more aggressive cleaning practices. Long-entrenched deposits may resist the mechanical and chemical energy available, and a well’s design (for example slotted pipe intake) may cripple the effectiveness of a cleaning process. In such cases, a well owner may opt to proceed directly to new well construction or prepare for that option if cleaning is ineffective.
Well cleaning should be followed immediately by a thorough disinfection of the well system and its immediate environment. Disinfection of the well should be completed by the water well contractor to ensure that it is done properly. Description of modern well disinfection processes is provided here.
WellOwner.org is supported by the Rural Community Assistance Partnership (RCAP.org) as part of the USEPA-funded program “Improving Water Quality through Training and Technical Assistance to Private Well Owners.”