Abstract: Method of treating subsurface layers of the earth for controlling movement of subsurface water and building strength of the subsurface layers characterized by injecting at a plurality of predetermined depths and at a plurality of predetermined spaced-apart locations a lime-fly ash slurry consisting essentially of water, particulate hydrated lime and particulate fly ash; the particulate lime and fly ash being present as particulate solids and a proportion of from twenty-five percent by weight of the water to as much as two hundred percent by weight of the water when employed along. The particulate solids comprise lime and fly ash in proportions ranging from three parts lime to one part fly ash to one part lime to ten parts fly ash. The injection is carried out by pumping the slurry of one of the particulate solids and water through a jet slurry mixing apparatus for aspirating in the other dry particulate solid. Preferably the fly ash will be aspirated into a slurry of the lime in water.