Method of sealing contaminated wells

This patent describes a method of in situ treatment of wells having a first perforated casing extending to an aquifer through a subterranean layer that inhibits percolation of surface water. It comprises positioning a second generally cylindrical imperforate well casing about the first well casing, the second well casing depending a predetermined depth to at least the layer and defining an annulus between the outer diameter of the first casing and inner diameter of the second casing; and filling the annulus with a sealant to seal the perforations in the first casing along an upper portion of the first casing to form a barrier to the entry of surface water into the well through the upper portion of the well structure