Mapping salinity

Setting:

The Danish Hydrology Research Center, HOBE wanted to balance the water budget calculations of a catchment area. They suspected the aquifer was discharging into a lagoon via a buried channel and investigated the area to determine the channel’s significance in submarine groundwater discharge (SGD).

Technology:

The SkyTEM 304 was flown at an average speed of 50 kph. The transmitter was set for low (LM)and high (HM) transmitter moments of 5000 and 179000 Am2 respectively. This permitted measurement of 20 unbiased gates (11.7 ?s – 450 ?s) in LM and 21 gates (94 ?s- 8 ms) in HM and maximized the response from the upper layer concurrently while mapping to a depth of over 300 m.

Findings:

The hydrogeological setting was found to be complex as the geology was dominated by stratified deposits with a homogeneous structure of alternating layers. In addition to mapping the stratified geology SkyTEM mapped the buried valleys beneath the lagoon. The system was able to penetrate through the layers to a depth greater than 300m and showed that the valleys were saturated with sea water (see slice at 100-110 m depth). Mapping salinity distribution helped to outline an intricate flow system beneath both the coastal area and the lagoon and answered questions on how and where freshwater was moving. This changed previous assumptions on the heterogeneity of the area.

 

Conclusion:

Because of the extremely high SNR, sensitivity and accuracy are enhanced and subtle differences in resistivity can be resolved. An interesting discovery is that accurate bathymetric and salinity level maps can be produced from the SkyTEM method. It suggests as well that the method can be used for mapping layered features within a water column, such as haloclines.

SkyTEM Surveys has completed project in Maniitsoq, Greenland

 

SkyTEM Surveys has completed a project in Maniitsoq, Greenland for North Americal Nickel Inc.

The skyTEM system arrived in Maniitsoq on September 15, flying commenced on September 17  and the survey was completed on October 6. In all, a total of 2,217 line-kilometers of electromagnetic and magnetic surveying was done over two flight blocks.

Examination of the preliminary data indicates it is of good quality and that the helicopter was able to hug the terrain despite the rugged topography. A final, levelled dataset and initial interpretation is expected from SkyTEM within 7 to 8 weeks.

Read North American Nickel’s full news release here.

Mapping fresh water and saltwater encroachment

Setting:

The Galapagos Island of Santa Cruz. Santa Cruz supports 13,000 inhabitants and 120,000 annual visitors and there is very little evidence of groundwater on the island. Drilling restrictions and challenging terrain prevent traditional hydrogeological investigation.

Solution:

The Darwing Foundation and several universities employed the SkyTEM304 to collect data over the island. Helicopter flying speed was 45 km/h sensor altitude was 35-45 m and South-North flight lines had a spacing of 200 m. A few lines were flown cross island to obtain a full picture of the salt-fresh water interface. SkyTEM filters avoid smoothing of early time data and the near-surface resistivity variations were enhanced. Later times data were more severe filtered to obtain as much depth penetration as possible. The data were gathered into soundings with a spatial distance of about 25 m. The SkyTEM method was sensitive to low-resistivity layers of hydrogeological interest [50-200 ohm-m] to a depth of approximately 300 m.

Findings:

The resistivity data below shows the electrical properties of the Santa Cruz rock. High resistivity values (reds) indicate competent rock, or basalts, while low resistivities (reds) represent gravels and soils. Unit IV, shown in blue-green to yellow is a perched aquifer that lies beneath the weathered, vegetated and permeable layer (yellow). Downward movement of water is constrained by impermeable Unit I (orange) basalts that make up the bulk of the volcano’s composition. Unit II is electrically conductive and is a seawater intrusion wedge underlying the island. Unit III, outcrop, has the same geophysical signature of Unit IV but is interpreted differently based on existing geological data. Large-scale faults that facilitate internal drainage were identified and helped explain the absence of surface seepage.

 

Conclusions:

An aquifer can be difficult to identify due to similarities in resistivity of the aquifer and the layers masking it. SkyTEM however was able to delineate the subtle contrasts required for accurate interpretation. The unique spatial resolution and 3-D view of the subsurfface resistivity structures allowed identification of the previously unknown perched aquifer and the salt-water wedge in the basal aquifer, located with an accuracy of a few meters. Beyond the vital implications for water resource and ecosystem management the high resolution SkyTEM data has forced scientists to reconsider their established conceptual flow models of volcanic islands.

Postscript:

The identification of weathered layers in a volcanic edifice may help to explain the cuase of potentially catastrophic landslides. In 2011 the US Geological Survey contracted SkyTEM to map the slopes and bases of Mt St Helens and Mt Iliamna, two volcanoes in the USA, to study slope stability and the presence of water.

Electromagnetic giant scanner in the battle for pure water

SkyTEM has conducted a survey in Denmark for GEUS (the Geological Survey of Denmark and Greenland) with the purpose of identifying the washing out of nitrogen in streams.

SkyTEM Survey in Greenland

North American Nickel has signed a contract with SkyTEM Surveys for a survey on its Maniitsoq Project in Southwest Greenland.

Read the press release here.

Eagle Plains Resources

Eagle Plains Resources Ltd. and Drexel Resources Ltd. have commenced a 500 line-km SkyTEM survey on the Titan gold-copper property in northwestern British Columbia.

Large-Scale Groundwater Exploration in Selangor, Malaysia

A SkyTEM airborne TDEM survey performed by SkyTEM ApS and DanWater Malaysia Sdn Bhd is being carried out as part of a groundwater exploration programme by Sime Darby Water Resources Sdn Bhd. The TDEM data are modelled by SkyTEM ApS.

Client:
Sime Darby Water Resources Sdn Bhd Malaysia

Survey operator and data modelling:
DanWater Malaysia Sdn Bhd Malaysia
SkyTEM ApS Denmark

Download complete case study –
Large-Scale Groundwater Exploration in Selangor, Malaysia (PDF)

Introduction

The Kuala Lumpur area has an estimated population of 7.6 million people, and almost all fresh water supply for the city is provided by large surface reservoirs dependent on rainfall.

In 1998 the vulnerability of these reservoirs was demonstrated by a long period of drought causing a massive water shortage. Since then, the Malaysian government is focusing on extending the water supply of Kuala Lumpur to include alternative sources such as groundwater.

A SkyTEM airborne TDEM survey performed by SkyTEM ApS and DanWater Malaysia Sdn Bhd is being carried out as part of a groundwater exploration program by Sime Darby Water Resources Sdn Bhd. The TDEM data are modelled by SkyTEM ApS.

SkyTEM airborne system setup:

  • Dual TDEM moment
  • 314 m2 transmitter loop
  • Peak moment of 150000 Am2 (high moment) and 15000 Am2 (low moment)
  • Two receivers recording the Z-and the X-component of secondary magnetic field

Benefits

  • The high peak moment enables great penetration depth and the low peak moment ensures detailed resolution of near surfaces anomalies within the same flight
  • The two-component receiver system secures more information of shape and orientation of a recognized conductor

Survey objectives

The short term objective is to localize possible groundwater resources in selected areas in the state of Selangor using the SkyTEM TDEM airborne system. The results from the geophysical survey will be applied to choose optimal drilling locations in the selected areas.

The long term objective is to establish a sustainable groundwater abstraction and supply the treated water to the cities of Kuala Lumpur and Putrajaya as well as the state of Selangor.

Prospecting for Gold-Copper mineralizations in Archean Greenstone, Qussuk, Greenland

 

Download complete Case Study for Qussuk (PDF)

Introduction

The Qussuk gold-copper project operated by the Greenlandic prospecting  company NunaMinerals is located near the Qussuk bay in West Greenland 60 km North-East of the Greenlandic capital, Nuuk.

Combined geochemical and geophysical exploration located at least five exploration targets within a 20-km belt of altered volcanic rock. Several of the geophysical anomalies match known gold- and copper bearing zones.
Surface samples contain up to 35.8 g/t gold and 1.3% copper. Visible gold was first found in this area in 2007.

SkyTEM Survey

In 2007, a combined TDEM and magnetic SkyTEM survey was performed at the Qussuk project covering 48 km2 at a line spacing of 100 meters. The survey was flown with a peak moment of 130 kAm2 (high moment only) and with two receivers recording the response from both the z-and the x-component. Flight height was 20-60 meters and flight speed was relatively low, 30-50 km/h, due to the rapidly changing topography.

Environmental assessment pollution plume related to groundwater in Ribe, Denmark

From 1956 until 1973, untreated wastewater from a chemical plant was dumped into 6 pits in a plantation in the south-western part of Jutland, Denmark 0.5-1.0 km from the coastline. Today, it is one of the worst pollution scenarios in Denmark with high concentrations of e.g. chlorinated organic solvents.

As an alternative to a costly offshore drilling campaign, a small SkyTEM TDEM survey starting 1.0 km inland and ending 1.0 km offshore was flown in 2006.

Download complete case study  – Environmental assessment pollution plume related to groundwater Ribe, Denmark (PDF)

Large-Scale Groundwater Exploration in Selangor, Malaysia

A SkyTEM airborne TDEM survey performed by SkyTEM ApS and DanWater Malaysia Sdn Bhd is being carried out as part of a groundwater exploration programme by Sime Darby Water Resources Sdn Bhd. The TDEM data are modelled by SkyTEM ApS.

Client:
Sime Darby Water Resources Sdn Bhd Malaysia

Survey operator and data modelling:
DanWater Malaysia Sdn Bhd Malaysia
SkyTEM ApS Denmark

Download complete case study –
Large-Scale Groundwater Exploration in Selangor, Malaysia (PDF)

Introduction

The Kuala Lumpur area has an estimated population of 7.6 million people, and almost all fresh water supply for the city is provided by large surface reservoirs dependent on rainfall.

In 1998 the vulnerability of these reservoirs was demonstrated by a long period of drought causing a massive water shortage. Since then, the Malaysian government is focusing on extending the water supply of Kuala Lumpur to include alternative sources such as groundwater.

A SkyTEM airborne TDEM survey performed by SkyTEM ApS and DanWater Malaysia Sdn Bhd is being carried out as part of a groundwater exploration program by Sime Darby Water Resources Sdn Bhd. The TDEM data are modelled by SkyTEM ApS.

SkyTEM airborne system setup:

  • Dual TDEM moment
  • 314 m2 transmitter loop
  • Peak moment of 150000 Am2 (high moment) and 15000 Am2 (low moment)
  • Two receivers recording the Z-and the X-component of secondary magnetic field

Benefits

  • The high peak moment enables great penetration depth and the low peak moment ensures detailed resolution of near surfaces anomalies within the same flight
  • The two-component receiver system secures more information of shape and orientation of a recognized conductor

Survey objectives

The short term objective is to localize possible groundwater resources in selected areas in the state of Selangor using the SkyTEM TDEM airborne system. The results from the geophysical survey will be applied to choose optimal drilling locations in the selected areas.

The long term objective is to establish a sustainable groundwater abstraction and supply the treated water to the cities of Kuala Lumpur and Putrajaya as well as the state of Selangor.