DETECTION OF SALINE-FRESH WATER INTERFACE AT THE ABER COLLEGE FARM COASTAL AREA, NORTH WALES, U.K

Abstract

The paper presents the results of a surface geophysical survey which was performed at Aber College Farm Area, N.Wales, U.K, using resistivity, electromagnetic soundings and chemical methods to detect the extent of the saline intrusion in the area. A total of thirty four Vertical Electric Soundings (VES) and sixteen Electromagnetic (EM) soundings were measured in the study area. Several of these soundings were measured adjacent to borehole sites to aid in correlating the geophysical interpretations to chemically detected water quality data. By correlating the interpreted surface geophysical to water quality data from the boreholes, depth to a bulk resistivity of less than 35 ohm-m (or more than 250 ppm chloride concentration) and depth to a bulk resistivity of less than 7 ohm-m (or more than 500ppm chloride concentration) could be mapped in both the aquifers. The permeability values of the sediments by pumping and other field and laboratory tests gave additional supporting data. The study revealed that the combined electrical and chemical observations provide a dependable means for the detection and mapping of a saline intrusion and that the two aquifers in the area have been intruded. And the extent of saline intrusion is a function of permeability and the volume of fresh water available to prevent inland movement.