a first container including a permeable bottom closure and means for supporting a first reference electrode in electrically conductive engagement with said bottom closure, said first container being operable to be supported on the surface of a pavement layer over {HEAD ~ a predetermined point} for establishing electrical conductivity between the soil under {TAIL ~ said pavement layer} and said first reference electrode; and 
a first container including a permeable bottom closure and means for supporting a first reference electrode in electrically conductive engagement with said bottom closure , said first container being operable to be supported on the surface of a pavement layer over { HEAD ~ a predetermined point } for establishing electrical conductivity between the soil under { TAIL ~ said pavement layer } and said first reference electrode ; and
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