Optimized risk assessment of ground pollution
AU HydroGeophysics Group mapping
EU-Interreg Topsoil project with Central Denmark Region
AREA: Vildbjerg
GEOLOGY: Moraine clay, mica quartz sand, and mica clay.
SIZE/TIME: 29 ha/<1 day
LINE/KM.: 29
LINE-DISTANCE: 10 m
Purpose:
Mapping of clay cover around a pesticide pollution 200 m upstream from water abstraction
Results
Pollution with pesticides was found near a contractor pool outside Vildbjerg. The water runs southeast and directly towards the abstraction wells of Vildbjerg waterworks. From existing wells (B1, B2, B3) there is a known mica layer of a certain thickness, but it is not possible to ascertain whether the layer is constant and without windows to the aquifer below. The area between the contractor pool and the abstraction wells was mapped with tTEM. tTEM provides a detailed image of the local geology enabling an assessment of the risk of percolate spreading, by mapping the special variation of clay and sand layers.
The figure below shows the thickness of the clay layer as found by tTEM and drilings. As shown, the thickness of the mica layer is more than 15 m all over and there are no windows. This makes for a small risk of the pollution spreading towards southeast. Acquiring this knowledge would have been difficult and costly depending on borehole information alone.
Case 2
Purpuse:
Mapping of clay cover around a pesticide pollution 200 m upstream from water abstraction
Purpuse:
Geological mapping on land and lake to understand the hydrological system, understand and avoid a rising ground water table in and around the town of Sunds.
Results
The town of Sunds surrounds Sunds lake in the middle of the heath plain, characterized by flat topography and sandy deposits. The groundwater table in the town and the surrounding farmland is close to the surface and reacts quickly to precipitation events, which has often led to flooded basements and fields. This is expected to get worse in connection with the renovation of the city’s sewer system and the future precipitation expected due to climate change.
A geological mapping with tTEM and FloaTEM was initiated in order to understand the hydrological system around and under the town and lake of Sunds. Before the start of the project, the general understanding of the area’s geology was that it was a giant sand box down to a depth of more than 20 m. The geophysical mapping has shown that this is far from the truth. Below the first 20 m of glacial sand, glacially deformed clay layers from the Mådegruppen appear interchanging with Miocene sand. The layers are greatly disturbed. Likewise, you find a thick organic silt deposit (10-20 m) under parts of Sunds Lake. The spatial extent of the clay and organic silt deposits is important to the hydrological circuit, and it is expected that with this new knowledge, climate proofing of the town and surrounding farmland will be possible.
tTEM mapping example - Geological mapping on land and at sea
EU-Interreg Topsoil project with GEUS, Central Denmark Region, Herning municipality and Herning Water.
AREA: Sunds
GEOLOGY: Moorland plain over Miocene quartz-sand and clay fromMåde fm.
SIZE/TIME: 816 ha/8 days
LINE/KM.: 326,4
LINE-DISTANCE: 25 m
Geological mapping on land and lake
AU HydroGeophysics Group mapping
EU-Interreg Topsoil project with Central Denmark Region
AREA: Sunds
GEOLOGY: Moorland plain over Miocene quartz-sand and clay fromMåde fm.
SIZE/TIME: 816 ha/8 days
LINE/KM.: 326,4
LINE-DISTANCE: 25 m
Purpose:
Geological mapping on land and lake to understand the hydrological system, understand and avoid a rising ground water table in and around the town of Sunds.
Results
The town of Sunds surrounds Sunds lake in the middle of the heath plain, characterized by flat topography and sandy deposits. The groundwater table in the town and the surrounding farmland is close to the surface and reacts quickly to precipitation events, which has often led to flooded basements and fields. This is expected to get worse in connection with the renovation of the city’s sewer system and the future precipitation expected due to climate change.
A geological mapping with tTEM and FloaTEM was initiated in order to understand the hydrological system around and under the town and lake of Sunds. Before the start of the project, the general understanding of the area’s geology was that it was a giant sand box down to a depth of more than 20 m. The geophysical mapping has shown that this is far from the truth. Below the first 20 m of glacial sand, glacially deformed clay layers from the Mådegruppen appear interchanging with Miocene sand. The layers are greatly disturbed. Likewise, you find a thick organic silt deposit (10-20 m) under parts of Sunds Lake. The spatial extent of the clay and organic silt deposits is important to the hydrological circuit, and it is expected that with this new knowledge, climate proofing of the town and surrounding farmland will be possible.
Field scale nitrate retention mapping
AU HydroGeophysics Group mapping
Innovation Fund Denmark project, rOPEN
AREA: Javngyde
GEOLOGY: Meltwater sand and clay from Måde fm.
SIZE/TIME: 1001 ha/11 days
LINE/KM.: 400,4
LINE-DISTANCE: 10-25 m
Purpose:
Geological mapping at field scale for developing automated N-retention maps in ID15 catchments
Results
The objective of rOpen is to develop a tool for assessing nitrate retention at field scale. Two 15 km2 catchments (Javngyde and Sillerup) have been chosen as pilot areas, and geophysical, geochemical, and hydrological surveys have been performed in the catchments. tTEM has been used to map the farmland and the results are turned into a hydrostratigraphical model, that will be connected to the agricultural practices and redox mapping in order to produce nitrate-retention maps in a transparent and data driven workflow. The figures below first show the extremely complex geology that is being mapped with tTEM along a profile in the northeastern part of the area. Below is shown a single realization of the auto generated hydro stratigraphic model. An important strength of the rOpen modeling concept is that all uncertainties are being handled in a manner so that together with the final nitrate retention map one also gets an estimation of uncertainties, which is critical for the land use management.
Mapping of raw materials
Purpose:
Mapping of sand/gravel resources to support development of the infrastructure
Development project with Orbicon and the
North Denmark Region.
AREA: StendalMark
GEOLOGY: Meltwatersand and clay deposits. Some marine deposits.
SIZE/TIME: 365 ha/3 days
LINE/KM.: 146
LINE-DISTANCE: 25 m
Results
Stable supplies of gravel are crucial for extending and maintaining the country’s infrastructure such as roads and railways, as well as for the construction industry. There is a need for finding new gravel pits using a cost-effective method, since drilling alone is too costly and time consuming. In a development project with Orbicon and North Denmark Region, 365 ha were mapped with tTEM in order to assess the method’s ability to locate raw material resources; sand and gravel. The mapping was carried out as part of the Region’s raw material resources planning that has to ensure that sufficient areas are laid out to sand and gravel extraction for a period of the next 12 years. The area was mapped in just three days and large areas with high resistivities were located. By means of the tTEM mapping the Region now has a very precise spatial delimitation of potential gravel deposits and a sound basis for follow up borehole surveys. The left figure shows a 3D image of the subsurface resistivities where conductive clay and till layers will be blue to yellow colors and high resistivity sand, gravel and silt layers is shown in red to purple colors. To the right is an iso-resistivity map with a cut-off value of 200 ohm-m showing only the high resistivity layers which would corresponds to sand and gravel deposits.
Mapping from abroad
The following shows an overview of tTEM/FloaTEM/SnowTEM mappings performed abroad since 2018. tTEM has been used in Sweden and in the USA, and SnowTEM in Greenland Grønland. FloaTEM has been used for mapping large areas in the USA.
Sweden - Infiltration of water in the Gråbo delta
Development project with the Geological Survey of Sweden (SGU)
AREA: Gråbo
GEOLOGY: 52 ha/<1 day
LINE/KM.: 16
LINE-DISTANCE: 10-100 m
METHOD: tTEM
Purpose:
In some areas of southern Sweden, clean drinking water is in short supply. Thus, the SGU has initiated a 3D geological mapping of particularly interesting areas to assess whether water can be infiltrated into sand/gravel deposits to establish a sustainable supply of drinking water. In this project, a former gravel pit was mapped to examine the dimensions of the potential groundwater reservoir and the depth of the underlying clay/bedrock.
Sweden - Geological mapping
Development project with Geological Survey of Sweden (SGU).
Sweden - Infiltration of water in the Gråbo delta
Development project with the Geological Survey of Sweden (SGU)
AREA: Gislaved
GEOLOGY: 2000 ha/<1 day
LINE/KM.: 13,6
LINE-DISTANCE: Rekognoscerings linjer
METHOD: tTEM
Purpose:
The Nissan River, a meandering river, runs southwest of the town of Gislaved. The course of the river has formed the landscape in the area, which is characterized by a complex geology of fine-grained sand/gravel deposits and sporadic clay deposits. In parts of the area, bedrock is found at surface level. A series of reconnaissance lines were performed in the 600 ha large fluvial sediment area to achieve an idea of the geological complexity. This knowledge would be difficult to achieve with drilling alone, due to the variation in the geology.
Sweden - 3D Geological mapping
Purpose:
The mapping area in Yllavald is characterized by significant topographis and geological differences. In some areas bedrock is found at surface level, whereas sand or clay is found in other areas.
The areas was recently mapped with SkyTEM, but in the upper 30 m the resolution was not sufficiently adequate to map the complex geological structures. With tTEM the area was mapped in a 3D resolution (25x10m grid). Several thin layers of sand and clay were identified in the upper 30 m and the bedrock could be mapped accurately.
Development project with Geological Survey of Sweden (SGU).
AREA: Yllevald
GEOLOGY: 64 ha/<1 day
LINE/KM.: 25,6
LINE-DISTANCE: 25 m
METHOD: tTEM
Greenland – locating lost engine parts
Development project with the Danish and the French Accident Investigation Board.
AREA: The ice cap
GEOLOGY: 20000 ha/1 måned
LINE/KM.: 4000
LINE-DISTANCE: 5 m
METHOD: SnowTEM
Purpose:
In 2017 an Airbus scheduled flight suffered an engine failure. The engine parts landed in southwestern Greenland. Not all parts have been found and thus it has not been possible to determine what exactly caused the accident. The Accident Investigation Board has designated a 10x20 km large impact area that will be mapped in part with two SnowTEM systems in the hope of locating the lost engine parts. The ice cap is characterized by a high electrical resistivity and any engine parts will appear as coupling in the SnowTEM equipment.
USA - Hydrogeological mapping on the rivers and storm protection in the Mississippi delta
Development project with the US Geological Survey (USGS).
AREA: Mississippi Delta
GEOLOGY: Mississippi
LINE/KM.: 352 km/7 days
LINE-DISTANCE: Not relevant
METHOD: FloaTEM
Purpose:
The Mississippi delta is characterized by rich fauna, fertile land, and agriculture. Along the banks of the river are large fields and farm buildings. The population and the industry in the area depend on the water in the river and the subsoil, and at present, the USGS is setting up a hydrological model for the whole area to ensure clean water for agriculture and fauna and to ensure infrastructure like dikes for flood protection. The USGS has used FloaTEM at several locations in the delta to map the subsoil below the rivers for understanding the inflow and outflow in the complex hydrogeological environment. Additionally they use the resistivity of the river water to assess the water quality.
USA - Hydrogeological mapping on rivers in Connecticut
Development project with the US Geological Survey (USGS)
AREA: Farmington & Rainbow Rivers
STATE: Connecticut
SIZE/TIME: 32 km/2 days
LINE/KM.: 32
LINE-DISTANCE: Not relevant
METHOD: FloaTEM
Purpose:
The USGS has used FloaTEM in 2 locations in Connecticut to map the hydrogeological system of the Rainbow and Farmingtion rivers.
USA - Hydrogeological mapping of rivers, bays and lakes in Massachusetts
Development project with the US Geological Survey (USGS),
AREA: Eel River, Waquiet Bay & Ashumot lake
STATE: Massachusetts
SIZE/TIME: 28 km/2 days
LINE/KM.: 28
LINE-DISTANCE: Not relevant
METHOD: FloaTEM
Purpose:
The USGS has used FloaTEM at 3 locations in Massachusetts to map the hydrogeolocial system of Eel River, the Waquiet Bay and lake Ashumot.
USA – Hydrogeological mapping of rivers in Pennsylvania
Development project med US Geological Survey (USGS).
AREA: Delaware floden
STATE: Pennsylvania
SIZE/TIME: 82 km/2 days
LINE/KM.: 82
LINE-DISTANCE: Not relevant
METHOD: FloaTEM
Purpose:
The USGS has used FloaTEM in Pennsylvania to map the hydrogeolocial system of the Delaware river.
USA – Salt water infiltration and geological mapping in Cape
Development project with the US Geological Survey (USGS).
AREA: Cape cod
STATE: Massachusetts
SIZE/TIME: 28 km/4 days
LINE/KM.: 28
LINE-DISTANCE: Reconnaissance lines
METHOD: tTEM
Purpose:
The USGS has used tTEM at 4 locations in Cape Cod, Massachusetts, to map the salt-water infiltration in the coastal area and to map the upper 30 m of the subsurface.
USA - Mapping of fractures in bedrock
Development project with the US Geological Survey (USGS).
AREA: Haddam
STATE: Connecticut
SIZE/TIME: 10 ha/<1 day
LINE/KM.: 10
LINE-DISTANCE: 10
METHOD: tTEM
Purpose:
The USGS has used tTEM at 1 location in Haddam, Connecticut, to map fractures in the bedrock.
USA - Mapping of geological structures
Development project with the US Geological Survey (USGS).
AREA: Jamestown
STATE: North Dakota
SIZE/TIME: 160 ha/<1 day
LINE/KM.: 21
LINE-DISTANCE: Reconnaissance lines
METHOD: tTEM
Purpose:
The USGS has used tTEM at 1 location in Jamestown, North Dakota to map sand and clay layers.
USA - Mapping of geological structures
Development project with the US Geological Survey (USGS).
AREA: Rapid city
STATE: South Dakota
SIZE/TIME: 19 ha/2 days
LINE/KM.: 10
LINE-DISTANCE: 19
METHOD: tTEM
Purpose:
The USGS has used tTEM at 3 locations in Rapid city, South Dakota to map the distribution of sand and clay layers.
USA - Mapping af saltholdigt grundvand omkring kulmine
Development project with the US Geological Survey (USGS).
AREA: Tully
STATE: New York
SIZE/TIME: 3 km/<1 day
LINE/KM.: 3
LINE-DISTANCE: Reconnaissance lines
METHOD: tTEM
Purpose:
The USGS has used tTEM at 1 location in Tully, New York, to map the distribution of salty ground water at a coalmine.
USA - Infiltration of water in the central valley
Development project with Stanford University.
AREA: Tulare
STATE: Californien
SIZE/TIME: 30 ha/<1 day
LINE/KM.: 10
LINE-DISTANCE: 25 m
METHOD: tTEM
Purpose:
Stanford University has used tTEM to map the ground water resources in Central Valley, California. Specifically, they were surveying the distribution of sand, gravel, og clay layers at field scale to find the optimal place for infiltrating and pumping water.
