26 September 2006
The construction and sampling from the last test borehole at Pine Walk, St Catherine has been completed successfully. A previous test borehole at La Rocque was successfully completed last week.
Both boreholes are part of a scientific investigation to determine whether or not flowing freshwater streams enter Jersey from mainland Europe.
The water diviners and well drillers, who believe the streams exist, were asked to identify two locations along the east coast of Jersey where they thought underground streams entered the Island.
Two test boreholes were drilled at the precise coordinates specified. The boreholes were drilled to a depth just short of the predicted streams and then completely sealed off with a cement plug and grouting to exclude shallower groundwater from entering the borehole. They were then drilled to the final depth at which the streams were believed to exist; 55 metres deep for La Rocque and 80 metres deep for St Catherine.
The experimental drilling went according to plan and was observed throughout by interested parties and properly supervised. Effective seals against shallower groundwater were achieved at both sites.
The water chemistry, geology and the flow rates of groundwater throughout the borehole were fully documented. In addition special water samples to determine the number of heavy and light isotopes (the isotopic signature) were taken throughout the borehole. By using this ‘signature’ it will be possible for scientists to conclude whether the water sampled at the depth fell as rain on Jersey or whether it derived from a source in mainland Europe. The samples have been sent to specialist laboratories in the UK for analysis.
The results from the analysis of the isotopic signature are expected to be available in four weeks.
Initial results show that the water flow rates arising from the two boreholes, at the depths where streams were believed to exist by the diviners, were lower than they had predicted. The average yield of water at this depth was approximately one litre per second at La Rocque and 0.3 litres per second at St Catherine.
The borehole was constructed as part of the work of the Deep Groundwater Advisory Group. The members have agreed to adhere to the findings of the investigation.
The construction of the borehole and sampling was supervised by a Senior Hydrogeologist from the British Geological Survey. ENTEC Consultants have also overseen the methodology.
The Minister for Planning and the Environment, Senator Freddie Cohen said “I am delighted that both boreholes had now been completed successfully. The analysis of the isotopic signature of the deep groundwater will determine whether or not underground water enters Jersey from mainland Europe. Before bringing a Water Resources Law back to the States, it is essential that this matter is settled once and for all.”
Notes:
The Deep Groundwater Advisory Group was set up by the previous Environment and Public Services Committee following the publication of the Scrutiny Panel report on the Draft Water Resources (Jersey) Law 2000-.
Members of the group include:
Dr Ralph Nichols (chair) - geologist
Dr John Renouf - geologist
Mr Lewis de la Haye - well driller
Mr Neville George - well driller
Mr George Langlois - water diviner
Mr Howard Snowden - Managing Director of Jersey Water
Mr Chris Newton - Director of Environment
Deputy Sarah Ferguson - States Member
Deputy Rob Duhamel - States Member
Isotope testing
The water molecule consists of H20. The stable isotopes of hydrogen (1H and 2H) and oxygen (16O and 18O) have identical chemical properties but have slightly different physical properties. During rainfall events the heavier 2H and 18O isotopes tend to fall out as rain at a higher rate than the lighter isotopes (16O and 1H). Thus is it possible to make maps of the isotope composition of water and use it to determine the area that groundwater originally fell as rain.
Further information:
Senator Freddie Cohen 07797-714550 or Chris Newton 01534-441610
gov.je