Right now, it’s just a huge hole in the hills off Ortega Highway in San Juan Capistrano. Really huge, as it’s designed to hold 1.6 billion gallons of water.
It’s still dry as dirt, but promises to be a central component of future water supplies for the 165,000 people served by the Santa Margarita Water District. While the district currently imports 100% of its drinking water from the Colorado River and northern California, the new Trampas Canyon Reservoir is part of a plan to generate 30% of potable water supplies locally and to recycle more wastewater.
That in, in turn, will provide a buffer from droughts and other circumstances that could reduce imported flows.
While water may not start filling the reservoir until December, they opened the valve on Friday to spray in a few ceremonial gallons, as state, county and local officials gathered — both in person and virtually — to celebrate the dedication of what should look like a lake a year from now.
“Trampas Reservoir allows the district to maximize recycled use and bring us closer to zero wastewater discharge into the ocean,” said Betty Olson, president of the water district.
The $109 million reservoir will hold treated wastewater for reuse and will be the largest such recycled water storage receptacle in Southern California, according to Don Bunts, the district’s deputy general manager. Part of its benefit will be to allow the storage of water during wet periods for later use during summer and fall months.
Initially, the reservoir — located at the site of a former sand mining operation — will allow the district to increase the amount of recycled irrigation water from the 6,500 acre feet it used in 2019 to about 8,000 acre feet, he said. At the same time, that would reduce the amount of imported water from 23,000 acre feet used in 2019 to about 21,150. And it will mean the district is reusing 75% or more of its wastewater.
Eventually, the district plans to turn much of that wastewater into potable water, beginning with a system similar to pioneering Groundwater Replenishment System used by the Orange County Water District in the north and central parts of the county since 2008.
After treating the wastewater, the Santa Margarita Water District would allow it soak into the groundwater aquifer and recharge supplies there. The water would then be pumped out, treated a final time, and put into the potable water supply.
Bunts said the district plans to begin introducing the treated wastewater to the groundwater basin in 2 1/2 to 3 years, and begin extracting it in 3 1/2 to 4 years. It would initially be expected to produce about 1,000 acre feet of potable water annually and could eventually reach as much as 5,000 acre feet per year. An acre foot is enough for roughly eight people for a year.
As part of its move toward more local water production, the district will also begin operating San Juan Capistrano groundwater wells as part of its negotiated takeover of that city’s water operations and will be begin buying groundwater from Rancho Mission Viejo, Bunts said.
To reach the goal of having 30% of the district’s potable water produced locally, the recycled water pumped into the groundwater basin may prove the biggest source. But the new groundwater access in San Juan Capistano and Rancho Mission Viejo is also a component, as is a stormwater-capture plan. Reaching that 30% goal would be particularly important during drought or events like earthquakes that interrupt imported flows.
“If we got cut off from imported water, we could provide all the indoor water and firefighting supplies” from local sources, said district general manager Dan Ferons at Friday’s dedication.
The district is also keeping open the possibility of what’s called direct potable reuse — piping treated wastewater directly to customers’ taps. The state doesn’t currently allow this, but the Legislature has directed the state Division of Drinking Water to come up with rules for such use by 2023.
