We examined near-surface soil resistivity of twenty-one locations in the Cerro Chascon science preserve area in the Wenner method with a fixed electrode spacing of 2 m. There were systematic differences in soil resistivity near the surface (down to a few meters): The values in the Pampa La Bola area were around 1000 Ohm-m, whereas those in the Llano de Chajnantor area were much higher and > 4400 Ohm-m in most locations topographically suitable for antenna pads.
Special treatment may be needed for each pad to meet the Chilean regulation for grounding. A factor ~ 1.3 difference expected from the 1.8deg C temperature difference between the Llano de Chajnantor and Pampa La Bola areas is not enough to explain all of the measured difference. The trend that ridges systematically had higher values than their adjacent valleys supports the idea that the difference primarily reflects probable difference of water content due to local topography and drainage.
View a PDF version of ALMA Memo #346.Last modified: February 7, 2001
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