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girders. The latter method requires the use of a pneumatically -applied mor- tar coating over the wire -wrap. Be- cause of the precast method of con- struction, reservoirs of this type have not employed waterstops in the walls. All joints have been sealed with either polysulfide or polyurethane sealant. As quality control in the manufacture of both polysulfide and polyurethane sealants is not always reliable, the life of the sealant may be uncertain. There- fore, maintenance expense may be rather high. It is believed, however, that modified designs will be available Buried Concrete Reservoirs Because of the rising cost of Iand in urban areas, the underground con- crete reservoir has become more at- tractive to water utility agencies. Maintenance expense can be practically eliminated, and the savings in main- tenance expense alone largely offsets the higher initial cost of this type of reservoir. Thus, the benefits of using the area above the reservoir may be considered a bonus to the community. Buried reinforced concrete reser- voirs can be built in rectangular or ir- Fig. 3. Precast, Post -Tensioned Reservoir, Santa Ana, calif. This 6-mil-gal reservoir was built under the Pritzker system. in the near future that will eliminate the necessity of relying solely upon sealants to insure watertightness of the joints. Several precast prestressed reser- voirs have been constructed on the west coast. They have been expensive for a single reservoir, but if two or more reservoirs of this type are built under a single contract, the cost is competitive with other types of con- crete reservoirs. regular shapes and can accommodate any reasonable live load above the reservoir. This type of structure has been widely used in England and in the eastern United States. A recent sur- vey of reservoir practice in England showed that 64 per cent of the reser- voirs constructed in recent years had cast -in -place concrete roofs, most of which were buried and of flat -slab con- struction. Although very few buried concrete reservoirs were built on the RICHARD BRADY &ASSOCIATES, INC. F-53 25B-131