Hollywood Stays Green with World's Largest Underground Water Tanks November 2000

When you literally can't move mountains, you must figure out a way to work around them. That's what contractors did to assist the Los Angeles Department of Water and Power (DWP) in building two of the world's largest underground water tanks in the mountains of Hollywood.

In November 1998, over 1 million cubic yards of dirt was removed to create a huge "pit" for placing two mammoth-sized underground tanks, each capable of storing 30 million gallons of water. Called the Toyon Tanks, they are situated next to the upper and lower Hollywood Reservoirs on the southern slope of the Santa Monica Mountains. With this rugged terrain surrounding over three-quarters of the 52-foot deep hole, accessibility to the job proved challenging.

However, D&N Concrete Pumping of Gardena, Calif. — the exclusive pumping contractor for this project — worked around this major obstacle when it got in the way. Fortunately in the beginning, a dirt ramp into the pit provided access for ready-mix trucks to discharge into the company's 36-Meter Putzmeister boom pump.

With the unit's high volume .20H pump cell, the largest on the market today, well over 200 cubic yards an hour were attained. This method worked efficiently for about 70 percent of the first tank's completion; however, then the ramp had to be removed.

D&N kept their 36-Meter Putzmeister in the hole for mobility, and set up a Putzmeister 14000 HP-D high-pressure and high-volume trailer pump on an edge above the hole for mixer truck access. Between the two pumps, a 5-inch slick line was positioned along with 700 linear feet of pumping system supported by thrust blocks. Bypassing the hopper of the 36-Meter, the delivery line connected directly into the boom's pipeline to deliver smooth outputs over 120 cubic yards an hour. Via two-way radio communications, the two pump operators were able to effectively communicate, thus minimizing any potential problems and avoiding costly downtime.

Due to the large size of the tanks — each 360 feet in diameter and 42 feet high — work was handled in sections. Several concrete slab pours, each about 700 to 800 cubic yards at a time, were pumped over 18 inches of gravel and drainage pipe. D&N also handled pumping the 256 concrete columns inside each tank along with the 2-foot-thick concrete roof the columns supported.

Upon completion of the two tanks, over 87,000 cubic yards of a 4,500 to 5,000 psi, 3-sack slurry mix will have been used. This unusually large amount of concrete was needed as extra ballast to prevent the tanks from floating away from atop a de-watered lake originally found 10 feet below grade.

Although the 36-Meter handled the lion's share of the tanks' construction, various other Putzmeister models from D&N's extensive fleet were also used in other related aspects of the project. The Hollywood Pump Station, which will regulate water pressure between the storage tanks and the distribution system, was pumped with 16- and 24Z-Meter Putzmeister units. Again, access proved difficult with only a two-lane road and the need to allow passage by local residents. Only the compact outrigger footprint of these smaller models allowed setup using only one lane to solve this dilemma.

Another Putzmeister model — the 32S-Meter needed for its compact outrigger spread of only 18 feet — was involved with concrete back-filling a bypass tunnel to hold 72-inch-diameter steel pipes in place. This 5,474-foot underground pipeline will bypass the two Hollywood Reservoirs to carry treated water directly to the Toyon Tanks and the current distribution system.

The 28Z and 32S-Meter Putzmeister pumps will also be used to construct a 70-foot high concrete wall to surround an inlet/outlet vault structure, which will house piping that connects to the Toyon Tanks.

In addition, the larger 46X and 52Z Meter Putzmeister pumps were used for about a third of the work, especially when a longer reach was required to finish the thick concrete roof. In this application, the five-section Multi-Z boom of the 52Z showed its versatility. Using only one boom section to vertically reach up, and the remaining four sections to extend over the 42-ft high tank, the Putzmeister 52Z could provide more "effective reach" than anything in its class. This was particularly helpful for placing concrete in the middle of the roof as some pours were done with the units in the hole.

Dan Navarro, owner of D&N Concrete Pumping, said, "This is an amazing project and our coordinated setup plans have worked flawlessly. We've relied on the high-pressure and high-volume output of our Putzmeister pumps to quickly finish various sections and depended on the compact outrigger spreads and unique Multi-Z features to successfully handle some difficult-to-reach areas. The operators, the crew, and all the pumping equipment has performed beyond expectations."

To date, the concrete work on the South Tank is complete and ready to be wrapped with post-tensioned cable to provide additional support to its sides when filled with water. The North Tank is in progress but faces losing access to "the pit" as sections of concrete are completed and space becomes non-existent in the hole. A crane will then lift the boom pump from its temporary underground home and work will be completed from above. Various sized boom pump and trailer pump models will be used to meet changing reach requirements.

To keep its local residents content, the tanks won't be visible. They will be covered with soil and planted with native vegetation to preserve the Hollywood Hills image. The remaining leftover soil excavated will be placed in four canyons using a technique called landform grading. This special grading will make the fill sites resemble natural hillsides with foliage planted for aesthetics and erosion control.

In May 2002, upon completion of the entire $73 million project, the two tanks will store 60 million gallons of treated water, with new pipelines linking the tanks to the current distribution system. These improvements will provide a safe and dependable water supply that meets both water quality standards and aesthetic issues for the 500,000 residents in the "water-full" land of Hollywood.