The future of San Diego (California) County's water supply relys strongly on the Olivenhain Dam. The dam is a part of the San Diego County Water Authority's $827 million Emergency Storage Project, which will protect the region's $117 billion economy, job base and quality of life by increasing the amount of water available within the county for use during emergencies. County planners fear that a drought or major earthquake could interrupt San Diego's water supply for as long as six months, and some communities could go without water for three or four days.

The Emergency Storage Project is part of the Authority's $1.2 billion Capital Improvement Program, which was initiated in 1989 to make necessary improvements to the pipeline delivery system and increase operational flexibility to supply water throughout the county. As one of the first components of the project, the Olivenhain Dam and Reservoir costs about $200 million. When completed, it will be the first roller-compacted concrete (RCC) dam in California and, at 318 ft. high and 2,400 ft. long, will stand taller than any other RCC structure in North America.

The $8.4 million excavation contract was awarded to California-based Ladd Associates. This work involved about 700,000 cu. yds. of material being blasted and removed for the dam's foundation.

Construction on the dam began in 2000 and will require 1.3 million cu. yds. of RCC supplied by California's Kiewit Pacific. Designed by a joint venture of California's JV Parsons Engineering Science, Inc. and Chicago's Harza Engineering Co., the dam will not actually control a river or stream; it will box off a canyon to contain 24,000 acre-ft. (or 7.8 billion gal.) of imported water from the Colorado River and Northern California, enough to sustain 192,000 people for one year.

Because RCC is placed in layers that are compacted with rollers similar to those used in asphalt road building, interruption of work must be minimized to facilitate bonding of the layers. Therefore, crews have often worked 24 hours a day, seven days a week during a 10- to 12-month period to construct the dam. Having begun in 2000, construction of the dam by Kiewit Pacific is expected to finish in spring 2003. The placement work for Olivenhain has been performed during the night and early morning hours because RCC requires placement during the coolest periods of the day to maintain high quality and strength.

In May 2000, a $1.25 million test program was completed by Kiewit Pacific to determine the optimum strength of the RCC and proper mix of materials to build the dam. The outcome was to build the concrete in 12-in. lifts. The test established the suitability of site-mined and crushed granite in combination with a binder of 50 percent portland cement and 50 percent fly ash. Developed by Gannett Fleming, Harrisburg, Pa., the mix design yields a 3,000 psi material.

The dry RCC mixes have been transferred from a massive, four-mixer batch plant to the point of placement via a covered conveyor system, minimizing contamination by soil, dust and other materials. Cement tankers or other vehicles delivering supplies to the site have been restricted to a Monday to Friday, 7 a.m. to 4 p.m. schedule so as not to interfere with local traffic patterns. Enough materials were brought in using that schedule to facilitate evening and weekend construction.

A PVC membrane installed on the dam's upstream face will prevent leaks through the lift joints, which is common on wet downstream faces. Also, the face of the dam will be stained with a color that blends into the natural surroundings of the area. Encircling the dam and reservoir is a 750-acre open-space park and recreational area, which offers 17 miles of hiking, mountain biking, equestrian trails and viewing points. The wildlife and natural resources on this reserve are all closely monitored.