groundwater development and drilling

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WASH Cluster – Emergency Training GWD

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Groundwater Development and Drilling

Session 4

Developing Groundwater Sources

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• Provide guidance on appropriate methods of developing groundwater resources.

• Clarify understanding of the development of groundwater by wells, boreholes, spring enhancement

• Discuss excavation and drilling techniques appropriate to hydrogeological conditions.

Session Aims

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• Wells are holes in the ground that intersect groundwater and enable groundwater to be brought to the surface

• Holes are dug by hand or by drilling machine

• Walls of the hole usually supported • Depth depends on aquifer type,

available yield

Wells and Bores

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Drilling techniques

• How do you……?

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Types of wells

Shallow well• Hand dug• Unconfined water

table aquifer• Groundwater

recovered by hand or low rate suction pump

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Types of wells

Deep well• Machine drilled• Confined and

unconfined aquifers• Groundwater

recovered by pump

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• Hand excavation / boring• Hand drilling

– incl augering and jetting

• Machine drilling – Rotary, percussion, down hole hammer

• Drilled wells– Reach greater depths– Penetrate wider range of rocks

Well installation methods

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• Hand augering a small hole – install narrow casing - tube well

• Hand digging larger diameter (~1m diam)

• Ground must be soft enough to penetrate

• Shallow water table required

Hand completed wells

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• Likely in the very first phase of an emergency– equipment can be mobilised quickly– produced from available materials

• Relatively low cost • Often local expertise available • Can be labour intensive

Application of hand completed wells

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• VIEW Video of hand augering: http://www.youtube.com/watch?v=qq0p_WPwSZo

• Affordable Water Well Drilling in Sierra Leone - Fresh Hope Ministries International 7min

http://www.youtube.com/watch?v=UYay9-2UMwM

Hand Auger drilling

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WASH Cluster – Emergency Training GWDShallow hand auger wells

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A C

B D

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WASH Cluster – Emergency Training GWDHand dug Groundwater wells

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Lining of Hand Dug wells

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From Oxfam Manual on Hand Dug Well Equipment

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WASH Cluster – Emergency Training GWDCompletion of Hand dug wells

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Simple open holes, no protection from contamination

Sanitary surrounds with hand pump

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• Drilling equipment and technique is affected by:– rock type(s) encountered– depth to groundwater – aquifer pressure

Bore Drilling

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Hand operated drilling

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•Narrow diameter (< 100mm diam) bores •Casing installed to construct tube wells (narrow diameter production wells).

VIEW YOUTUBE FILESShallow percussion: http://www.youtube.com/watch?v=N3CUnUrMo6s&feature=related

Shallow percussion in Senegal: http://www.youtube.com/watch?v=VWaTBNt0n9o&feature=related

Deep well in Dhaka slums 200ft (>60m) deep: http://www.youtube.com/watch?v=nIvgg6QTKj4

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Jetting Techniques

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Use water pressure forced down a drill pipe through a nozzle to penetrate the soil Need a source of water and pump to provide the pressure

Source: Water for the World, Constructed Jetted Wells, Technical Note No RWS 2.C.3

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Jetting Techniques

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Use water pressure forced down a drill pipe through a nozzle to penetrate the soil Need a source of water and pump to provide the pressure

20m deep jetted well, near Matatuto, Timor Leste

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Jetting Videos

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A jetting operation in Ethiopia: http://www.youtube.com/watch?v=cHu5yFQn660&feature=related

Jetting in Indonesia: http://www.youtube.com/watch?v=D-pmZe2aQuY&feature=related

A backyard well in USA : http://www.youtube.com/watch?v=FbGUV7GQpMM&feature=fvw

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Machine Drilling

Advantages • Can reach great

depths• Can penetrate wide

range of rock types• Can produce high

yielding wells

Disadvantages• Expensive• Require highly skilled

crews • Can have long lead

time from set up to completion

• May be privately or Govt owned and not available for an emergency

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Percussion Rigs

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VIDEO: of cable tool operation :http://www.youtube.com/watch?v=vEIyPhQdqrw&feature=relatedApplication in the Philippines: http://www.youtube.com/watch?v=mXAS0UUc7Ek&feature=related

crushes the rock under the weight of a tool dropped down the hole on a length of cable

Suitable for unconsolidated and soft formationsRelatively slow

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Photo of Rotary rig, with drill bit and drilling rods visible – white tubing is PVC casing to be installed in the bore. Photo courtesy GHD Pty Ltd

Rotary Rigs

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Can drill to great depths (1000+ m)

Drill bits attached to the end of a segmented string of steel drilling rods

As the drilling rods rotate, the bit grinds through the soil and rock

Air, water or drilling mud used as a circulation fluid to remove cuttings of rock and soil

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Rotary Rigs

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• VIDEO of a mud rotary rig http://www.youtube.com/watch?v=ZVlzCs3686s

• Some rotary rigs require no mud and are powered by air to activate the drilling bit. This is shown on the following video: http://www.youtube.com/watch?v=Qa0SL6h3pF8&feature=related

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• In most drilled wells, the walls need support

• Wells are cased with lengths of factory-made pipe

• Casing can be steel or plastic (Eg PVC, PE, ABS)

• Holes in very strong rock sometimes not cased

Constructing a Well

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Installation of plastic casing in rotary drilled bore, Photo Courtesy GHD Pty Ltd

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Constructing a Well

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Highest flow from an aquifer into a drilled well is ? through the most permeable zonesIdentified through:

Drill cores“Cuttings” pushed to surface during drilling

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WASH Cluster – Emergency Training GWDOpening the well to the Aquifer

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•Cased wells need to have a screen to allow water to flow from the aquifer into the well

•Screens are a length of slotted or perforated pipe

•Typically PVC, steel or stainless steel

•Screens often have a filter pack to improve inflow to the well

•Wells drilled in stable rock sometimes are not cased and have no screen – termed “open hole”

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Positioning Screens in a well

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from Nkhoma and Baumle, (2007)

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Aquifer

Display of constructing a well

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Drilled Bore

(Plastic bottle)

Insert narrow pipe / plastic bottle

Gravel pack

Flour to seal

Soil mixed with flour

Casing

Screen

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Typical Well construction

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Summary of Types of Wells

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Modified From Wikepedia

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Well Development

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•Well development is undertaken after installing casing, screen and gravel pack

•Improves well efficiency•Involves surging or jetting water or air in and out of the well screen to clean out residual drilling fluid.

•May take several days. •Well developed wells have lower pump costs, longer pump life – sand and mud passing through screen damages pumps

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WASH Cluster – Emergency Training GWDGroundwater pumping effects

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Aquifer

Static or pre-pumping water level

Pump

Ava

ilabl

e D

raw

dow

n

Dra

wdo

wn

Radius of Influence

Cone of depressionD

raw

dow

n Dra

wdo

wn

Dra

wdo

wn

Neighbouring Bores

Creek

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• Completed after well development• Tests the potential pumping rate and

resulting drawdown• Assists in determining :

– Long term pumping rate and water level– Size of pump– Impact on surrounding wells or

environment

Test pumping of wells

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• Step drawdown test – short periods of pumping at progressively higher

rates and measuring drawdown in the well– helps work out achievable pumping rate

• Constant rate test– Pumping at constant rate (could be for days or

weeks)– Measure drawdown in well and nearby

“observation” wells– Helps assess pumping impacts on the aquifer under

different pumping scenarios

Pumping tests

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• Measures ratio of drawdown to pumped flow rate

• Allows a check of well efficiency• Helps indicate bore deterioration eg

blocked screens• Reduced capacity (greater drawdown

to pumping rate) indicates reduced well efficiency

Specific Capacity of a Well

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• Groundwater can be developed quickly in some situations – eg springs, shallow wells, available drilling equipment

• Existing deep wells may be available – Could be included in emergency water supply

solution– Need to understand capacity, condition,

constraints on use

• Potential for future development later in emergency

Relevance to an Emergency

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Springs

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From Oxfam technical brief Spring being protected, Zaire - S House / WEDC

•May be harvested in a number of ways•Should always be protected from degradation.

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Springs

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Spring box with discharge pipe leading down hill, Nias, Indonesia

A protective box that enables:

•collection of water by hand

•discharge to a tap for collection at the spring

•discharge downhill by distribution pipe .

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Estimating volume of groundwater available

Q:How you might work out how much groundwater is available?

A: Factors to be considered •Area where rainfall might occur on aquifer •When does it rain•Will all of the rainfall enter the aquifer?•The rock type•Flows of existing bores / springs

groundwater development and drilling

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