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Because the bottom line for the Ramat Hovav researchers was an understanding of the movement of pollution down to the water table, they required a system for accurately monitoring aquifer contamination. For this task, geologists drill wells or narrow-diameter boreholes, through which they extract groundwater samples for analysis of toxic elements. The early series of boreholes through which pollution was initially detected were not satisfactory for long-term, reliable monitoring, as they were drilled vertically and did not always intersect the major fractures through which precipitation and contaminants flowed. Therefore, a novel approach was proposed by the researchers, namely the use of slanted, nonvertical boreholes and core-holes that would increase the number of major fractures crossed by the drilling and increase the underground flow entering the groundwater monitoring system.
To determine where to position these boreholes, the Ramat Hovav geologists and structural geologists took advantage of techniques that enable mapping and characterizing a fracture network in detail. Using aerial photographs, computerized identification techniques, and field measurements, they located major, deep-penetrating surface fractures and the joints between layers of the deposited chalk. In addition, by examining cracks that were atop cliffs that also had openings along the cliff wall, ILLUSTRATION FIG. 4b, OF NATIV, ADAR, BECKER, Designing a monitoring Network, Ground Water 37, 41 (1999) or by digging deep trenches perpendicular to surface cracks, ILLUSTRATION ibid. FIG. 4c, they could determine how a family of fractures was tilted. This made possible three-dimensional mapping of the cracks, along with their orientations, inclinations, and apertures.
With this fracture map, along with knowledge of the locations of the potentially contaminating Ramat Hovav facilities, ILLUSTRATION ibid. FIG. 6, the researchers could pass their slanted well holes through numerous fractures to reach the water table, ensuring that water or pollution passing through the active cracks would be trapped by the monitoring borehole. Over the last decade, 101 well holes, most of them slanted, were drilled to an average depth of 50 meters below surface. For more advanced measurements, four of the holes are over 100 m deep and one reaches 350 m underground. By examining the chemical and physical features of fractures exposed on the walls of this well, it is also possible to determine how much water and pollution passes through each of them. These wells are still regularly monitored to ensure that aquifer pollution at Ramat Hovav remains at a minimum. In fact, this is the world’s first and most extensive system for monitoring the health of a chalk-based aquifer.
