To provide a construction method for a countermeasure against the spread of contamination upon construction work like the excavation of the ground by which secondary contamination caused by ground water existing in a contaminated aquifer is prevented.

Upon excavating or drilling work piercing through a contaminated aquifer 61 and reaching a clean-water aquifer 63 being work for a cast-in-place pile or a boring exploration, for example, a chemical is grouted in the contaminated aquifer 61 of a construction place of the cast-in-place pile or the boring in advance to move the contaminated ground water out of the construction place. The excavation work or the like is carried out in a state that the ground water is prevented from flowing out to the lower layer through a gap between a casing tube of the cast-in-place pile and the natural ground, or through a hole drilled by a boring machine.