groundwater development and drilling

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WASH Cluster – Emergency Training GWD

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Groundwater Development and Drilling

Session 5

Protecting Groundwater Sources

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Session Aims

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•Demonstrate the potential impacts on groundwater that may affect security of the water source,

•Discuss systems that must be put in place to determine whether the water supply is able to be sustained for on-going use, and

•Demonstrate what issues need to be understood for on-going use

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Question 1: What are some of the risks to the use of groundwater for emergency water supply?

Key Risks to Groundwater

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•Reduction of groundwater availability / Depletion of aquifer yield due to excessive drawdown, sustainability, interference from other bores •Water quality impacts - contamination in the catchment and near the bore -eg salt water intrusion, latrines, other pollutants•Protection of the bore itself -eg animals, agricultural runoff, dirty equipment, including vandalism•Contamination from up-gradient contaminants, salt water intrusion•Set up costs, time lags, proper investigation and design•Costs of pumping, maintenance of pumps and fuel supply•Interruption to power or fuel supply (related to well infrastructure and delivery–session GWD4)

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QUIZ 2:• What factors will affect the amount of

water that can be extracted from a well? • What will happen if the well is pumped at

too high a rate

• What happens when the pump stops?

• Does this apply to all wells?

• What might the long term effect of this be?

Reduced Yield from a Well

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Relevance to Emergency

• Reduction of flow from well or spring related to the balance between the amount of water removed from an aquifer and the amount that recharges.

• Unless there is adequate seasonal recharge into the aquifer, the volume of groundwater stored in the aquifer will be reduced - ultimately unsustainable supply.

• If extraction is too great on a particular day, the yield of the well on that day may drop off

• Changes due to pumping drawdown and recovery due to recharge need to be carefully monitored to make sure supply is maintained

Reduction in Availability

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Groundwater potentially protected by being below the surface

Potability can be influenced by:– Natural variations in salinity– Naturally occurring chemicals – Man-induced contamination

Water Quality Effects

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• Salinity – Potable (<1000mg/L) based on palatibility

• Turbidity– Can be serious in hand dug wells and

poorly constructed drilled wells

• Dissolved Iron– Unpleasant taste and colour

• Dissolved Carbonate / bicarbonate– Unpleasant taste, precipitation on pipes

Naturally occurring quality issues

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• High Fluoride and Arsenic occur in some groundwaters

• Can be naturally occurring • Can be detrimental to health • Tend to be due to long term exposure

– but requires careful assessment

Natural Toxicants

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Contamination by Humans

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WASH Cluster – Emergency Training GWDMicrobiological contamination

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The bacterium Escherichia.coli is found in the intestines of warm blooded animals,

- present in the faeces of humans

Latrines can be a source of contamination with E.coli –

Bacteria and viruses have relatively short lives in groundwater

Latrine siting is important - not in the groundwater flow path

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WASH Cluster – Emergency Training GWDMicrobiological contamination

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Protection of Well surrounds

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Poorly maintained well head at pumping well with pathway for contamination down the well, Osire Refugee Camp, Namibia

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Filthy surrounds to shallow well and likely contamination introduced to a well by rope.

Note the broken hand pump has compromised the security of the well head. To access the well buckets are used. Gassire, Eastern Chad

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Sanitary well conditions at the well head but a contamination source (pig pens) is immediately behind the fence (Nias, Indonesia, 2006).

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• Emergency can cause additional demand – Increased drawdown on existing wells – Over-extraction pressure on the aquifer

• Too many people at a well (eg open well) can lead to contamination

Maintenance of Aquifers and Well Infrastructure

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WASH Cluster – Emergency Training GWDRepairing and disinfecting wells

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Litter in well after Tsunami, Band Aceh, Indonesia

Rubbish removed from the base of an open well during well rehabilitation, Gassire, Chad

After rubbish removal, disinfection with a chlorine solution

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Refurbishing well surrounds

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Original unsanitary well surrounds,

Rehabilitated apron with drainage point bottom left.

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Repair of deep wells

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Deep wells can be degraded by:•Microbiological contamination – can be disinfected with chlorine solution•Casing and screen corrosion – repair or replacement•Build up of bacterial slime (fouling) on screens– chemical treatments

Treatment / repair of existing wells needs careful assessment and specialist inputs

•Not a focus for first phase emergencies.

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Spring Protection

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Dedicated buckets and collection cell, Nias,Indonesia

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Monitoring

• QUIZ 2: MONITORING QUIZ

• Why monitor?

• What to consider in a monitoring program

• What type of information is collected for a groundwater source?

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Monitoring

Monitoring of water level, usage and quality is important

fundamental to record and store the data

Data must be looked at and used to make best use of the groundwater resource

Monitoring groundwater levels in new water supply well

groundwater development and drilling

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