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Well Rehabilitation

In this Section:




What is Water Well Rehabilitation?

Well rehabilitation comprises all measures that are undertaken to restore the functionality of a well, and generally consists of various treatments or redevelopment methods. The treatment method selected must be tailored to the problem, the well construction details and aquifer type. The pump discharge pipe and distribution lines must also be cleaned when biological, chemical or physical plugging has occurred.

Follow-up monitoring and preventative maintenance must continue after the well rehabilitation work has been completed.


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What is the Difference Between Preventative Maintenance and Well Rehabilitation?

Well rehabilitation is performed when the well has deteriorated to the point where preventative maintenance procedures no longer resolve well performance issues. Rehabilitation procedures are generally initiated when the well performance has declined by about 25 per cent, which points to the importance of collecting initial baseline performance data.

When well rehabilitation is required it should always be performed by a licensed well driller ( Canadian Ground Water Association ) or well rehabilitation specialist.


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What are Some Common Well Problems and the Basic Rehabilition Approaches?

No single treatment process or rehabilitation strategy will effectively solve every well problem. However, an experienced local well driller can be an excellent source of knowledge on common well problems in a specific geographical area. The driller should also be able to recommend appropriate treatment options and assist the well owner in selecting the best method of treatment, and determine if the treatment has been effective by performing a specific capacity test and comparing the results to pre-treatment conditions.

Common well problems and rehabilitation strategies include:

  • Overpumping with no evidence of well screen plugging
    • reduce pump rate or extend pumping time
    • install cistern for peaking needs
  • Increased microbiological activity with no decline in well yield
    • identify source of problem
    • pH-adjusted chlorine
  • Corrosion or structural failure
    • identify cause
    • repair or replacement of well
  • Sand pumping
    • identify cause
    • redevelop well to remove sand
    • repair/replace well
  • Pump failure
    • identify cause
    • clean pump assembly
    • replace faulty parts
  • Plugging of well intake area with a decline in well yield
    • identify cause
    • select appropriate mechanical and/or chemical treatment method(s)

An understanding of the cause of the problem is required in order to identify the proper treatment method. The main causes of well problems are usually physical, chemical and/or biological plugging.

Rehabilitation objectives for well plugging problems

The main objectives in performing a well treatment are:
  • Achieve effective deposit removal.
  • Custom-tailor treatment method to the specific problem encountered, well construction details and aquifer type.
  • Good penetration into surrounding formation.
  • Good agitation of chemicals.

Well rehabilitation considerations

The following will need to be considered when preparing for a well treatment:
  • The pump must be removed and the well will be off-line for 2-3 days to complete well treatment.
  • Specialized equipment and trained personnel are needed to complete any rehabilitation work.
  • Both chemical and mechanical methods are generally required for an effective cleaning.
  • The type of deposit and physical condition of the well must be considered.
  • Well construction details and previous treatment or rehabilitation work should be reviewed.

General steps for well rehabilitation

The following are the general steps in a typical well rehabilitation process:
  1. Pre-Treatment Diagnostics
    • pump test, water sampling, pump removal/inspection, video inspection
  2. Mechanical Cleaning
    • dislodge and remove mineral and bacterial slime build-up
  3. Chemical Treatment
    • dissolve mineral incrustations and disrupt biological slimes for easier removal
  4. Redevelopment
    • dislodge and remove spent treatment chemicals and plugging material
  5. Post Treatment Diagnostics
    • compare to pre-treatment results to evaluate effectiveness of rehabilitation work
  6. Chlorination
    • after rehabilitation has been completed, disinfect well and associated works

Observations on Well Rehabilitation

  • Once the cause of the problem has been identified, appropriate well rehabilitation measures can be applied.
  • Rehabilitation work will generally improve the well performance and help to extend well life.
  • Severely plugged wells are difficult to restore to their original state.
  • No treatment produces permanent results; expect deposition of minerals or biofilm to reoccur.
  • Preventative maintenance and monitoring must follow to extend time between rehabilitation work.

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Common Methods for Removal of Mineral Deposits and Biofouling Deposits

There are several methods that can be used to remove mineral or biofilm deposits from inside the well casing and well intake area. Some of the commonly used methods include mechanical and chemical. Although chemicals can assist in breaking down these deposits, chemical application should always be accompanied by some physical agitation to more effectively remove highly entrenched deposits.

Mechanical methods

Common methods include wire brushing, high-pressure jetting, surge block/swabbing. These methods are usually applied in combination with air-lift pumping to remove the loosened deposits

Wire brushing

Wire brushing assists in the removal of mineral or biological buildup, increasing the effectiveness of any chemical treatments applied.

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Surge block/swabbing

In this method surging action of water loosens minerals and aquifer fines, drawing them into the well for removal. This is often combined with air-lift pumping to remove fines from the well.

High pressure jetting



High pressure jetting

High pressure jetting assists in in dislodging plugging material from the well intake area. This is generally combined with air-lift pumping to remove the loosened material from the well.

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Chemical cleaning methods
A number of different types of chemical products are used to remove mineral or biofilm deposits:
  • Mineral Acids - dissolve mineral precipitates, such as calcium, iron and manganese
  • Organic Acids - dissolve organic compounds, such as biofilms
  • Surfactants - improve penetration of treatment chemicals for biofilm removal
  • Dispersants - prevent the reformation of minerals or biofilms and keep materials in suspension for easier removal
  • Proprietary products - formulated products that contains a combination of treatment chemicals designed for specific applications
Table: Effectiveness of common well cleaning acids
Acid Type of Deposit
Carbonate
Scale
Sulfate
Scale
Iron/Mn
Scale
Biofilm
Sulfamic
Acid
Very Good Good Fair Poor
Hydrochloric
Acid
Very Good Good-Poor Very Good Poor
Phosphoric
Acid
Very Good Good-Poor Good Poor
Hydroxyacetic
Acid
Poor-Fair Very Poor Good Moderately
Good
Citric Acid Poor Very Poor Chelates Poor
Oxalic Acid Very Good Good Good Moderately
Good
Source: (to be identified in the future)


Considerations when applying chemical treatments

The following should be considered when appying chemical treatments:
  • Well construction details
  • Aquifer type
  • Concentrations of various chemicals
  • Sequencing of chemicals
  • Residence time
  • Relative temperatures of the groundwater and treatment chemicals


Applying chemical treatments

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Photo: Inflatable packers are used to isolate injection zone
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Photo: Pouring chemicals into well screen
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Photo: Injection of treatment chemicals

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Well Redevelopment

After a treatment process has been completed, the well must be redeveloped to remove the plugging material that has been disrupted, loosened or broken-up, and any remaining treatment chemicals. Redevelopment methods include overpumping the well, mechanical bailing, surge blocking/swabbing and air-lift pumping to restore the well capacity.

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Photo: Well redevelopment procedures will generally produce very turbid discharge water that contains the plugging material (i.e. mineral incrustations, biological material), sediment and residual treatment chemicals. The redevelopment process should continue until the discharge water clears.