A method for treating a high water content sludge is disclosed, where the method includes mixing into the high water content sludge, an effective amount of an ash composition. The effective amount of the ash composition is sufficient to convert a portion of the sludge and the ash composition into a treated sludge including an amount of a solidifying matrix to impart properties to a depth of the sludge sufficient to support commercial construction equipment. A treated sludge and sludge pits are also disclosed as is the ash composition used to form the treated sludge.