GroundwaterGroundwater TrainingTraining CourseCourse SOPAC,SOPAC, AprilApril 20052005

DrillingDrilling && TestingTesting

SelectedSelected methodsmethods DrillingDrilling andand testingtesting

• 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) DrillingDrilling methodsmethods

• 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 DrillingDrilling andand testingtesting

Rotary drilling rig RotaryRotary drilldrill rigrig Cocos (Keeling) Islands, Australia

‘Mud’ tank RotaryRotary drillingdrilling rigrig

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 RotaryRotary drillingdrilling rigrig withwith ‘mud‘mud pit’pit’

Rock 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) DownDown thethe holehole hammerhammer drillingdrilling usingusing foamfoam DownDown thethe holehole hammerhammer drillingdrilling usingusing foamfoam

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 boreholes

• 5 monitoring boreholes in ‘Smithson Bight’ area • Closer look at 3 of these (BH1, BH2 and BH3) Christmas Island (Australia) deep monitoring boreholes

Depth to base of lowest monitoring tube = 190m Christmas Island (Australia) deep monitoring boreholes

Volcanic rock basement (intersected in BH1 at 22m below sea level) Monitoring data, boreholes BH1 & BH3

Borehole BH1 • 1,200m from coast • Freshwater to > 30m

Borehole BH3 • 400m from coast • No Freshwater SimpleSimple monitoringmonitoring boreholeborehole (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--levellevel monitoringmonitoring boreholeborehole

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 monitoring boreholes SalinitySalinity monitoringmonitoring atat boreholesboreholes

usingusing •• monitoringmonitoring pumppump andand •• salinitysalinity metermeter

Procedure at each borehole • for each tube, pump sample to bucket & test • repeat 2 to 3 times to ensure stable reading • plot salinity v depth for all tubes SalinitySalinity monitoringmonitoring boreholeborehole datadata

LIF1 salinity profiles 0.0

-5.0

table (m) -10.0 Depth below water Depth below -15.0 0 2,500 5,000 7,500 32,500 35,000 37,500 40,000 42,500 45,000 47,500 50,000 52,500 55,000 10,000 12,500 15,000 17,500 20,000 22,500 25,000 27,500 30,000 Electrical Conductivity (uS/cm)

Aug 98 Sept 98 Oct 98 Nov 98 Dec 98 Jan 99 Apr 99 Jul 99 Oct 99 PermeabilityPermeability teststests

Falling head test (during drilling process)

Refer to paper on Tarawa and Christmas Island for equation and example of use PermeabilityPermeability teststests

Constant head test (during drilling process)

Refer to paper on Tarawa and Christmas Island for equation and example of use GroundwaterGroundwater mappingmapping

Tabiteuea island, Tarawa atoll, Kiribati

These freshwater contours were mapped using both borehole salinity measurements and geophysics data Dating of water Concepts

• Atmosphere Ù 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) • >20,000 BP Time • 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