Drilling and testing

Groundwater Training CourseGroundwater Training Course

SOPAC, April 2005SOPAC, April 2005

Drilling & TestingDrilling & Testing

Selected methodsSelected methods

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)

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

Drilling and Drilling and testingtesting

Rotary drilling rig

Rotary drill rigRotary drill rigCocos (Keeling) Islands, AustraliaCocos (Keeling) Islands, Australia

‘Mud’ tank

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

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)

Down the hole hammer drilling using foamDown the hole hammer drilling using foam

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)

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)

Christmas Island (Australia) deep monitoring boreholesChristmas Island (Australia) deep monitoring boreholes

Depth to base of lowest monitoring tube = 190m

Christmas Island (Australia) deep monitoring boreholesChristmas Island (Australia) deep monitoring boreholes

Volcanic rock basement (intersected in BH1 at 22m below sea level)

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

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)

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)

Measuring level and obtaining water sample in deep Measuring level and obtaining water sample in deep monitoring boreholesmonitoring boreholes

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

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

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

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

Groundwater mappingGroundwater mapping

TabiteueaTabiteueaisland, island, Tarawa Tarawa atoll, atoll, KiribatiKiribati

These freshwater contours were mapped using both borehole salinity measurements and geophysics data

Dating of water

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)

Time• >20,000 BP• recent

Tritium

CFC-12

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