Paso sends Nacimiento water to river to help recharge supply

City is taking its allocation for the first time and filtering it into a pooling system on the sandy surface of the Salinas riverbed

tstrickland@thetribunenews.comJuly 17, 2013 

For the first time, the city of Paso Robles has turned on the tap to its share of Lake Nacimiento water.

It’s doing so by filtering about 2,000 gallons per minute into a new pooling system on top of the bone-dry Salinas riverbed to offset the city’s summer shortages.

The new supply comes from the city’s annual 4,000-acre-foot share in the Nacimiento Water Project, a 45-mile pipeline that carries millions of gallons from the lake to residents and businesses within San Luis Obispo County.

Paso Robles can’t use the full allotment until a treatment plant is operational, which is expected around the end of 2015. Citizen protests led to a delay in the plant’s construction.

“The purpose of this is to serve as a drought buffer to recapture water in times of below-normal rainfall,” city water resources manager Christopher Alakel said.

The well field area where they’ve built the new system can’t absorb additional water during wet years, he said, so they can’t use it year-round.

The new system begins at a well field on Paso Robles’ south side near the city’s access point to the Nacimiento pipeline. From there, the city connected a short underground pipe along a bluff overlooking the Salinas River, which always has a steady stream of underflow that the city pumps from.

That pipe was outfitted with a connection point sticking out of the ground, to which the city attached a large hose. The hose stretches about 200 feet down the bluff to the riverbed and filters into an aboveground pool where the water can softly overflow and sink into the sandy river bottom.

The idea behind the project, which has been in the works since last year and cost about $18,000 to build plus additional electricity costs, is to recharge the river’s underflow during the hot summer months — and in periods of drought — when the water levels typically fall.

“It’s not the best way to use our Nacimiento water. But for a drought buffer, it’s fantastic,” Alakel said.

As the water sinks into the riverbed, it percolates into the underflow so city wells can recapture some of it and introduce it into the city’s overall water supply. If the city continues operating the pooling system through October — a period when the city typically sees little rain — it will have used nearly 14 percent of its annual Nacimiento share, Alakel said.

City officials are often asked why Paso Robles needs a treatment plant — why can’t it percolate the lake water into the Salinas River to treat it naturally with the rocks and soils, similar to the new pooling system and to what its neighbors in Atascadero do.

The reason, Alakel said, is, “Due to the geology of the area, we’re only able to recapture about 25 percent of the water.” That’s because the city’s wells physically can’t capture the water fast enough before it trickles out of reach.

But the amount of water the wells do capture is making a difference, Alakel said.

As of Wednesday, the new system had discharged a total of 44 million gallons into the river since the end of June and noticeably increased production at two of the city’s river wells, Alakel said. Groundwater monitoring data also show that the underflow levels in the well field increase when the system is turned on and decrease when it’s turned off, he added.

“I think it’s going to play a pretty important role for us during drought,” he said.

Paso Robles has struggled to keep up with its water customers’ summer demands after poor rain years. Conservation has helped, but the hot, dry months have exacerbated the problem.

On Wednesday, afternoon temperatures topped nearly 100 degrees — a typical summer day in Paso Robles.

“Look how fast it soaks it in,” Alakel said of the lake water as he moved his hand through the wet, gravely sand. “It’s just a big sponge.”

With a five-year permit, the city is looking to continue the pooling process as needed. It may also use it for any extra lake water its treatment plant won’t have room for when it’s built.

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