This presentation discusses problems of clogging and encrustation in water wells and presents possible solutions and management strategies

1. MANAGING THE CLOGGING OF GROUNDWATER WELLS
Mike Deed, Geoquip Water Solutions, UK
Martin Preene, Preene Groundwater Consulting, UK

2. SYNOPSIS
• Definitions of groundwater wells
• Clogging and encrustation
• Operational problems
• Strategies to manage clogging and encrustation

3. PRACTICE PROFILE
Preene Groundwater Consulting is the Professional Practice of Dr Martin
Preene and provides specialist advice and design services in the fields of
dewatering, groundwater engineering and hydrogeology to clients worldwide
Dr Martin Preene has more than 25 years’ experience on projects worldwide
in the investigation, design, installation and operation of groundwater control
and dewatering systems. He is widely published on dewatering and
groundwater control and is the author of the UK industry guidance on
dewatering (CIRIA Report C515 Groundwater Control Design and Practice) as
well as a dewatering text book (Groundwater Lowering in Construction: A
Practical Guide to Dewatering)

4. GROUNDWATER WELLS
• Groundwater wells play a key role in many
construction projects: dewatering, geothermal, water
supply
• Typically, water only enters through the lower part of
the well (the well screen)
• If the screen section becomes clogged, the drawdown
in the well will increase, causing operational problems
• There are three potential types of clogging: physical,
bacterial and chemical

5. BACTERIAL CLOGGING
• Iron-related bacteria are one of the most common types of clogging.
• Groundwater wells and pumping systems provide an oxygenated,
turbulent environment in which they can thrive
• The bacteria oxidise soluble ferrous iron (Fe2+) to insoluble
ferric iron (Fe3+)
• The bacteria life cycle produces a biofilm, typically a slimy or gelatinous
red-brown deposit (commonly known as ‘biofouling’)
• Although soft, the biofouling deposits can be tenacious and difficult to
remove from wells

6. CHEMICAL CLOGGING
• Chemical precipitation caused by the pressure
reduction on the water as it moves from the aquifer
into the well
• Dissolved compounds precipitate out of solution and
are deposited as hard scale on well screens, pumps and
equipment
• Common chemical precipitations are iron
oxyhydroxides, iron sulphides and calcium carbonates

7. OPERATIONAL PROBLEMS
• Reduction in hydraulic efficiency of the
well
• Increased drawdown
• Increased pump power consumption
and increased wear and tear on pumps
• Reduced yield
• Ultimately, without good management,
a well can become so clogged it is
beyond rehabilitation and has to be
abandoned
Symptoms
Iron bacteria and iron oxides and oxyhydroxides
Red-brown slime, rusty water on pump start up,
smelly and poor quality water
Manganese oxide
Blackish-brown deposits, cloudy water on pump
start up, smelly and poor quality water
Calcium carbonate
Hard white/pale grey scale

8. MANAGING CLOGGING AND ENCRUSTATION
• Chemical treatments are now widely used to
attempt to remove encrustation, and restore a well
close to its original hydraulic performance
• There are a wide range of products, each with
advantages and disadvantages. Treatments should
be carefully selected
• Combined chemical and physical (e.g.
scrubbing/jetting) treatments are most effective.
Chemical treatments give 40 to 60% of total
performance gain
Chemical treatments used in
groundwater well rehabilitation
Hydrochloric (Muriatic) Acid, HCl
Sulfamic Acid, H2NSO3H
Phosphoric Acid, H3PO4
Sodium Hypochlorite, NaOCl
Acetic Acid, CH3COOOH
Oxalic Acid, COOH2

9. WELL REHABILITATION PROGRAMMES
The optimal solution for managing clogging and encrustation
involves more than treatment alone. The BoreSaver well
management programme includes:
• Pre-rehabilitation survey
• Assessment of borehole condition and required rehabilitation
• Treatment and rehabilitation
• Post-treatment survey
• Continuing monitoring and maintenance

10. CONCLUSION
• Clogging and encrustation is a natural part of the life cycle of a groundwater
well, and it is natural to expect well performance to deteriorate with time
• It is important to have a planned programme to manage well performance
• Programmes should include regular monitoring and physical cleaning
(scrubbing/jetting) combined with chemical treatments
• Chemical treatments should be selected so that they are effective against the
type of clogging identified, have the necessary regulatory approvals and
produce non-harmful post-treatment residues

11. MANAGING THE CLOGGING OF GROUNDWATER WELLS
Mike Deed, Geoquip Water Solutions, UK
Martin Preene, Preene Groundwater Consulting, UK
Contact:
Mike Deed: mike@geoquipservices.co.uk
Martin Preene: mp@preene.com
© M E R Deed and M Preene 2015