SYLMAR >> Michael Grahek trudged through the murk of a historic Los Angeles Department of Water and Power water tunnel, his flashlight sweeping its century-old concrete walls.

His light then settled on some a strange outlines in the Sylmar shaft.

“Notice the footprints,” said Grahek, LADWP manager of southern aqueduct and Owens Lake Operations and maintenance, pausing inside the arched tunnel. “Somebody stepped in the wet cement almost 100 years ago.”

“It’s exciting working on the south aqueduct: always something new.”

An unused water system known as the Maclay Highline is being restored from the L.A. Aqueduct Cascades in Sylmar to a group of meadows in Pacoima as an innovative means to create more Los Angeles drinking water.

For the first time in decades, a torrent of water from melting snow from the Sierras is slaking the thirst of Los Angeles homes and businesses. The LADWP now aims to capture some of the excess mountain runoff by storing it below ground for future use.

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Enter the Maclay Highline, a series of concrete tunnels and channels first dug in 1915 — the year residents of the San Fernando Valley voted to join Los Angeles.

The 6-by-5 foot tunnel conveyed unfiltered water from the newly opened L.A. Aqueduct to a now defunct Maclay Reservoir, which served the scattered homes and farms in Sylmar and Sunland-Tujunga.

The line was retired 30 years ago when state regulations required a new filtration plant be built nearby to treat L.A. drinking water.

LADWP crews are now bringing the 2-mile horseshoe-shaped tunnel back into service. The $4.5-million project, begun last spring, will restore caved-in or missing sections stemming from the L.A. Aqueduct.

By fall, officials say, it will help transport 130 acre-feet of water per day along a roughly 8-mile route to the Pacoima Spreading Grounds — a series of above-ground basins near Devonshire Street west of Interstate 5 — where it can percolate down into the city aquifer.

One acre-foot of water is equal to 326,000 gallons, or about enough to supply two households with water for a year.

“We’re now going to be able to spread mountain water into the spreading grounds to deep water storage 425 feet down,” Grahek said, a 32 LADWP veteran emerging from the tunnel amid oak-covered foothills above Sylmar. “It’s part of our ongoing effort to maximize the use of available water for our customers.”

“We do have, on the books, a huge groundwater treatment system being constructed. This ties into that. We will have groundwater for years to come.”

Los Angeles, which imported nearly 60 percent of its water from the Colorado River and northern California during the drought, now gets all its water from Sierra runoff via its L.A. Aqueduct. By 2040, it aims to get 17 percent from its supply of aquifer groundwater.

The LADWP was recognized as one of the world’s top water utilities at a global water summit that took place last spring in Madrid, Spain. Officials say reviving its historic water tunnel to replenish its groundwater supply ties in with Mayor Eric Garcetti’s water sustainability goals.

“It’s going real good, real smooth” said LADWP Labor Supervisor Tim Page, among a crew of proud utility workers around the tunnel. “We’re doing a lot of restoration.

“And we’re taking this one foot at a time.”