If you had your druthers about filing or backfilling would you put in a material that flows like a liquid, requires no tamping, hardens quickly to the density specified and saves on overall costs. Such a material is now available through local ready mixed concrete suppliers who can produce it to specifications, under a licensing arrangement, using cement, fly ash and locally available materials. Controlled density fill (CDF) can be made to densities of 90 to 135 pounds per cubic foot and compressive strengths of 0 to 1600 psi. Local site materials are selected for use in the mix, which is designed for the project being considered. Although it can be made as hard as concrete it is not a substitute for concrete because it is not its equal in such properties as wear resistance. CDF is used as backfill and as structural fill for floors, foundations, piers, and pavement bases and subbases. It has been found useful for filing abandoned underground tanks. For this purpose, the material used would not be very hard, so that if the tanks had to be removed at some later time they could be cut open, the CDF excavated with a backhoe and the tanks lifted out.