A method for neutralizing in situ pore water associated with a subsurface waste material body, the pore water having a pH of less than 2, the method includes the steps of adding a non-carbonate alkali to the pore water to produce a pH-modified acidic pore water having a pH between about 4 and about 5; and adding a carbonate alkali to the pH-modified pore water in an amount sufficient to raise the pore water pH to between about 6 and about 8.