drilling and testing
TRANSCRIPT
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Groundwater Training CourseGroundwater Training Course
SOPAC, April 2005SOPAC, April 2005
Drilling & TestingDrilling & Testing
Selected methodsSelected methods
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Drilling and testingDrilling and testing
• Can provide detailed information about: ♦ aquifer thickness♦ geological formations♦ hydrogeological properties (porosity, permeability, major
structural features such as unconformities)♦ groundwater quality
• Boreholes enable:– Pumping (‘production boreholes’)– Monitoring systems to be installed (‘monitoring
boreholes)– Water samples to be obtained– Cores to be obtained (geological information)– Samples for dating (eg CFC)
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Drilling methodsDrilling methods
• Water drilling methods are many & varied. Common ones are:– Auger– Cable tool (percussion)– Rotary drilling (using drilling muds)– Rotary & percussion drilling using rotary rig and down-
the-hole hammer, air compressor, drilling foam
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Drilling and Drilling and testingtesting
Rotary drilling rig
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Rotary drill rigRotary drill rigCocos (Keeling) Islands, AustraliaCocos (Keeling) Islands, Australia
‘Mud’ tank
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Rotary drilling rigRotary drilling rig
Application:• Small coral island (Lifuka, Tonga)• Depth to water table = 3 – 5 m• Reason: investigate groundwater resources and install multi-level monitoring systems (nylon tubes and PVC pipes
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Rotary drilling rig with ‘mud pit’Rotary drilling rig with ‘mud pit’
Rock roller drill bitRock roller drill bit
Mud pit
Application:• Small coral island (Penrhyn, Cook Islands)• Depth to water table = 2 m• Reason: investigate groundwater resources, install multi-level monitoring systems (nylon tubes)
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Down the hole hammer drilling using foamDown the hole hammer drilling using foam
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Down the hole hammer drilling using foamDown the hole hammer drilling using foam
Application:• Raised limestone island (Christmas Island, Australia)• Depth to water table = 30 – 160 m• Reason: investigate groundwater resources and install multi-level monitoring systems (25mm PVC pipes)
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Christmas Island (Australia) deep monitoring boreholesChristmas Island (Australia) deep monitoring boreholes
• 5 monitoring boreholes in ‘Smithson Bight’ area• Closer look at 3 of these (BH1, BH2 and BH3)
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Christmas Island (Australia) deep monitoring boreholesChristmas Island (Australia) deep monitoring boreholes
Depth to base of lowest monitoring tube = 190m
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Christmas Island (Australia) deep monitoring boreholesChristmas Island (Australia) deep monitoring boreholes
Volcanic rock basement (intersected in BH1 at 22m below sea level)
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Monitoring data, boreholes BH1 & BH3Monitoring data, boreholes BH1 & BH3
Borehole BH1• 1,200m from coast• Freshwater to > 30m
Borehole BH3• 400m from coast• No Freshwater
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Simple Simple monitoring monitoring boreholeborehole
(open borehole)(open borehole)
Useful for measuring:– water level– water quality near
groundwater surface
Where the aquifer material is not granular (sand/gravel), a gravel pack is placed around the pipe slots (or well screen)
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MultiMulti--level monitoring boreholelevel monitoring borehole
Multi-level system
• useful for monitoring water quality (e.g. salinity) at different depths
Note: open boreholes, tend to allow mixing of water from different depths (e.g. can underestimate true freshwater thickness on small island due to mixing within the borehole)
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Measuring level and obtaining water sample in deep Measuring level and obtaining water sample in deep monitoring boreholesmonitoring boreholes
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Salinity monitoring at Salinity monitoring at boreholesboreholes
usingusing•• monitoring pump monitoring pump andand•• salinity metersalinity meter
Procedure at each borehole•• for each tube, pump sample to for each tube, pump sample to
bucket & testbucket & test•• repeat 2 to 3 times to ensure repeat 2 to 3 times to ensure
stable readingstable reading•• plot salinity v depth for all tubesplot salinity v depth for all tubes
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Salinity monitoring borehole dataSalinity monitoring borehole data
LIF1 salinity profiles
-15.0
-10.0
-5.0
0.00
2,50
05,
000
7,50
010
,000
12,5
0015
,000
17,5
0020
,000
22,5
0025
,000
27,5
0030
,000
32,5
0035
,000
37,5
0040
,000
42,5
0045
,000
47,5
0050
,000
52,5
0055
,000
Electrical Conductivity (uS/cm)
Dep
th b
elow
wat
er
tabl
e (m
)
Aug 98 Sept 98 Oct 98 Nov 98 Dec 98Jan 99 Apr 99 Jul 99 Oct 99
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Permeability testsPermeability tests
Falling head Falling head testtest
(during drilling (during drilling process)process)
Refer to paper on Tarawa and Christmas Island for equation and example of use
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Permeability testsPermeability tests
Constant head Constant head testtest
(during drilling (during drilling process)process)
Refer to paper on Tarawa and Christmas Island for equation and example of use
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Groundwater mappingGroundwater mapping
TabiteueaTabiteueaisland, island, Tarawa Tarawa atoll, atoll, KiribatiKiribati
These freshwater contours were mapped using both borehole salinity measurements and geophysics data
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Dating of water
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Concepts
• Atmosphere Groundwater interaction– At time of recharge, groundwater concentrations
reflect atmospheric conditions• Types of tracer
– Natural isotopes• Carbon 14• Tritium
– Contaminants• CFC’s• Tritium (atmospheric weapons testing)
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Time• >20,000 BP• recent
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Tritium
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CFC-12
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Outlook
• Sampling & analysis techniques– Have been complex and costly– Some improvements have been achieved
• Environmental changes– Contamination controls lead to a reduction
in sensitivity of dating– New compounds and improved
measurement techniques likely to continue to provide opportunities