Predetermined quantities of slurried solids wastes are injected into earth formation waste disposal zones (23) having a predetermined in situ stress distribution and compaction rate for a predetermined hydraulic injection pressure and wherein the disposal zones (23) are bounded by zones (24, 26) having greater in situ stresses. Unconsolidated or lightly cemented formation zones may be used for waste disposal wherein it is determined that a substantial compaction of the material defining opposed faces of hydraulic fractures (22) may occur. Fracture volume available for retention of solids in the slurry is calculated based on fracture height, fracture length, elastic deflection of the fracture faces, compaction of the fracture faces and the number of fractures based on either unequal or substantially equal horizontal stress distributions.