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Multifrequency VLF-R equipment for detection of saline groundwater
65
Geophysical measurements in the Nyiinget Drainage Area, Svartberget Forest Experimental Area, Vindeln, Sweden GUSTAF LINDQVIST*, LENA NILSSON and GUSTAV0 GONZALES Department of Applied Geophysics, liniversity of LuleB, S-951 87 LuleH(Sweden)
This work is part of the “Surface Water Acidification Project” in which long term effects in the ground and in ground and surface water due to atmospheric acid deposition are to be studied. The Nyanget drainage area is a reference area which represents a region with low acid deposition. Geophysical measurements were made to map the thickness of the Quaternary deposits and to detect any fracture zones in the bedrock in the Nyanget drainage area in Sweden. Three refraction seismic profiles were measured, two of them also by the VLF method. Two electrical soundings were done in the southern part of the area. The results showed greater moraine thickness along the profiles than was believed to be the case. It was also found that different moraines could, in some cases, be distin~ished from each other.
Multifrequency VLF-R Equipment for Detection of Saline Groundwater JAN-OLOF ARNBOM’ and GORAN BERGMAN’ ‘Swedish Geological Co. (SGABj, P.O. Box 1424, 75144 Uppsala (Sweden) “Swedish Environmental Research Institute (IVL), Stockholm (Sweden)
The steadily running construction of summer dwellings at the coastal areas and archipelagoes of Sweden has created an ever increasing need for household water. This water is drawn most frequently from drilled wells in the bedrock. The groundwater in the bedrock is however a limited natural resource. At many places along our coastline this natural resource is being destroyed by excessive water withdrawal. In case of an immoderate withdrawal the pressure balance between fresh water and saline sea water is upset, thus facilitating the intru-
*Present address: Swedish Geological Co., P.O. Box 801, S-851 28 LuleH,Sweden.
66
ABSTRACTS 1TTH MEETING
sion of sea water into the well. If the problem is not noticed in time the saline water can disperse from well to well thus contaminating the entire available fresh water reservoir. In order to be able to estimate the hazards of salt water intrusion, one must be familiar with the geological conditions of the area in general and with the joint structures, the recharge of groundwater and with total groundwater withdrawal in particular. To be able to determine - in a rapid way - the location of the boundary between fresh and saline water, one is limited today to analyse chloride ion content in the existing wells in the area. Between these infrequent observation points, one has to resort to approximations and guesswork. In trying to indicate this boundary geophysically, we have tested a multifrequency VLF-R equipment constructed by Dr. Mueller (Hydrogeological Dept., University of Neuchatel, Switzerland). This VLF operates in frequency ranges of 200,50 and 20 kHz. Thus it is possible to obtain information about groundresistivity at different depths. The 20 kHz frequency penetrates very deep while the 200 kHz frequency penetrates only to shallow depths, depending on the bedrock resistivity. Surveys with the multifrequency VLF-R equipment were carried out at three sites in the Stockholm archipelago. We arived at the following conclusions: _ It is impossible to interpret the results according to a standard system with two layers. - At surveys with three frequencies we have obtained good information of fractures at various depths as well as of saline and fresh water aquifers. - By conducting measurements in two different directions from the same point, it is possible to distinguish the principal fracture alignment.
The Application of Magnetic and Mise-&la-Masse Methods, Especially in Drill Holes, in the Discovery of Deep Extensions of the TelkkS Nickel Deposit RISTO PIETIL# and JORMA EERONHEIMO Outokumpu
Exploration,
Tehtaankatu
2, P.O. Box 67, SF-83501
Outokumpu
(Finland)
A small nickel deposit at Telkkala, northwest of Lappeenranta in southeast Finland, was located by Outokumpu Exploration in the 1960’s. During 19691970 about 0.2 Mt of ore, averaging 1.06% Ni and 0.29% Cu, was mined from the open pit. In 1987, after having reviewed some old nickel prospects in east-
Geophysical measurements in the Nyiinget Drainage Area, Svartberget Forest Experimental Area, Vindeln, Sweden GUSTAF LINDQVIST*, LENA NILSSON and GUSTAV0 GONZALES Department of Applied Geophysics, liniversity of LuleB, S-951 87 LuleH(Sweden)
This work is part of the “Surface Water Acidification Project” in which long term effects in the ground and in ground and surface water due to atmospheric acid deposition are to be studied. The Nyanget drainage area is a reference area which represents a region with low acid deposition. Geophysical measurements were made to map the thickness of the Quaternary deposits and to detect any fracture zones in the bedrock in the Nyanget drainage area in Sweden. Three refraction seismic profiles were measured, two of them also by the VLF method. Two electrical soundings were done in the southern part of the area. The results showed greater moraine thickness along the profiles than was believed to be the case. It was also found that different moraines could, in some cases, be distin~ished from each other.
Multifrequency VLF-R Equipment for Detection of Saline Groundwater JAN-OLOF ARNBOM’ and GORAN BERGMAN’ ‘Swedish Geological Co. (SGABj, P.O. Box 1424, 75144 Uppsala (Sweden) “Swedish Environmental Research Institute (IVL), Stockholm (Sweden)
The steadily running construction of summer dwellings at the coastal areas and archipelagoes of Sweden has created an ever increasing need for household water. This water is drawn most frequently from drilled wells in the bedrock. The groundwater in the bedrock is however a limited natural resource. At many places along our coastline this natural resource is being destroyed by excessive water withdrawal. In case of an immoderate withdrawal the pressure balance between fresh water and saline sea water is upset, thus facilitating the intru-
*Present address: Swedish Geological Co., P.O. Box 801, S-851 28 LuleH,Sweden.
66
ABSTRACTS 1TTH MEETING
sion of sea water into the well. If the problem is not noticed in time the saline water can disperse from well to well thus contaminating the entire available fresh water reservoir. In order to be able to estimate the hazards of salt water intrusion, one must be familiar with the geological conditions of the area in general and with the joint structures, the recharge of groundwater and with total groundwater withdrawal in particular. To be able to determine - in a rapid way - the location of the boundary between fresh and saline water, one is limited today to analyse chloride ion content in the existing wells in the area. Between these infrequent observation points, one has to resort to approximations and guesswork. In trying to indicate this boundary geophysically, we have tested a multifrequency VLF-R equipment constructed by Dr. Mueller (Hydrogeological Dept., University of Neuchatel, Switzerland). This VLF operates in frequency ranges of 200,50 and 20 kHz. Thus it is possible to obtain information about groundresistivity at different depths. The 20 kHz frequency penetrates very deep while the 200 kHz frequency penetrates only to shallow depths, depending on the bedrock resistivity. Surveys with the multifrequency VLF-R equipment were carried out at three sites in the Stockholm archipelago. We arived at the following conclusions: _ It is impossible to interpret the results according to a standard system with two layers. - At surveys with three frequencies we have obtained good information of fractures at various depths as well as of saline and fresh water aquifers. - By conducting measurements in two different directions from the same point, it is possible to distinguish the principal fracture alignment.
The Application of Magnetic and Mise-&la-Masse Methods, Especially in Drill Holes, in the Discovery of Deep Extensions of the TelkkS Nickel Deposit RISTO PIETIL# and JORMA EERONHEIMO Outokumpu
Exploration,
Tehtaankatu
2, P.O. Box 67, SF-83501
Outokumpu
(Finland)
A small nickel deposit at Telkkala, northwest of Lappeenranta in southeast Finland, was located by Outokumpu Exploration in the 1960’s. During 19691970 about 0.2 Mt of ore, averaging 1.06% Ni and 0.29% Cu, was mined from the open pit. In 1987, after having reviewed some old nickel prospects in east-