Take a look while it's still visible.

A new concept for safeguarding the water supply in Los Angeles is taking shape in full view of travelers on the 134 Freeway passing by Griffith Park.

"What you're seeing is construction of a 55-million-gallon tank," said Susan Rowghani, Director of Water Engineering for the Los Angeles Department of Water and Power (LADWP).

The massive enclosure, 35 feet deep and sitting on 7 acres, is being made of reinforced concrete, and unlike surface reservoirs, will be fully enclosed.

As soon as what's called the "Headworks" project is completed, it will disappear from sight, covered with three feet of soil, with a new park to be landscaped on top. The project is part of the LADWP's response to federal EPA water quality requirements that effectively make open reservoirs obsolete, according to Martin Adams, LADWP's director of Water Operations. Construction began early in 2012.

"I didn't realize how big it was going to be when they started," said Noel de Paz of Van Nuys, a frequent visitor to Griffith Park who was been watching the construction progress. Completion of the first Headworks reservoir is targeted for next vember. A sister reservoir is expected to be finished in 2017.

Together, the Headworks reservoirs will replace Silver Lake and its companion Ivanhoe Reservoir. At the urging of the community, water will remain in the reservoirs, but not as part of the city's drinking water supply. The feasibility of using recycled water, or perhaps Los Angeles River runoff will be explored, Adams said.

As a stopgap covering measure, the Ivanhoe Reservoir currently is covered with thousands of "shade balls" to block UV radiation to discourage the growth of algae and other biological contaminants. Silver Lake has already been removed from the water supply.

The combined 110-million-gallon capacity of the Headworks reservoirs amounts to only a day's supply for the 4 million Angelenos supplied by the LADWP.

But in conjunction with other reservoirs and new pipelines, the Headworks serves as a "buffer" that will better enable the DWP to distribute water and respond to temporary disruptions of supply, Adams said.

Early on, the DWP considered upgrading and covering the Silver Lake Reservoirs, but ultimately concluded it would be better, and likely less expensive, to build at a new location, Adams said.

"We couldn't put bandaids on the system," Adams said. More than a century ago, the Headworks location had been one of the first locations where city officials tapped the Los Angeles River into a municipal water system.

Later, it served as a spreading basin, with water diverted from the river allowed to percolate through the soil to recharge natural underground aquifers. That role ended in the early 1980s when the water in the LA River was deemed no longer suitable for spreading basin use.

Industrial comtaminants, including the carcinogen hexavalent chromium, have been detected in much of the groundwater beneath the San Fernando Valley, and the possibility had to be explored that soil at the Headworks site might also have been contaminated, and samples were tested.

"There were a lot of concerns that we may have spread water that had contaminants, but we did not find any evidence of that in the soil. We were very fortunate," Adams said.

Had contaminated soil been found, the challenge of dealing with it might have made the Headworks Project impractical. Building a system to decontaminate the tainted groundwater and be able to use it for the water supply is a major initiative the LADWP intends to pursue.

It is expected to take years and cost half a billion dollars, Adams said. The Headworks will draw on existing LADWP water sources, including aqueduct water from the Eastern Sierra, and wells that draw on uncontaminated groundwater.

In addition to the park envisioned atop the Headworks reservoirs, there are also plans to create a wetlands at the west end of the property, using runoff diverted from the LA River. The wetlands will be underlain with a water resistant barrier to keep the river water from percolating through the soil, and it will be diverted back to the concrete riverbed downstream.

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