About two miles off the coast of Rancho Palos Verdes, on a sunny morning last week, a crew of marine biologists prepared to launch a trawl about 200-feet deep into the ocean — intent on catching a diverse array of sea flora and fauna for analysis.

The catch, reeled in by the Los Angeles County Sanitation Districts’ Ocean Monitoring team on Thursday, July 24, included hundred of creatures: Scorpion fish. Sea stars. Red octopus. During such routine trips, the creatures get tested to determine the impact of the agency’s operations on the local marine ecosystem.

The catch-and-test trips are just one of many crucial studies undertaken by LASAN’s team of biologists aboard the agency’s research vessel, the Ocean Sentinel.

Since 1970, the Ocean Sentinel has monitored how treated wastewater from LASAN’s A.K. Warren Water Resource Facility, in Carson, impacts the ocean.

“We split our monitoring into three main pieces,” Josh Westfall, LASAN’s senior environmental scientist, said aboard the research vessel. “We have our core or local monitoring,  regional monitoring, and we have special studies.”

Though tours on the Ocean Sentinel are typically reserved for LASAN stakeholders, the agency recently opened them up to media for the first time.

Since the agency began its ocean monitoring efforts — which include dive teams that conduct scuba surveys, a remotely operated vehicle that roams the ocean floor to inspect LASAN’s outfall system, trawls of the ocean floor to check on marine life and much more — in the 1970s, the health of the local ecosystem has vastly increased, in line with better wastewater treatment procedures, Westfall said.

“We have more clean water going out into the ocean,” Westfall said. “Now, we are looking into our partnerships to reduce the amount of clean water that’s going out into the ocean and instead repurpose that clean water for beneficial reuse.”

Those efforts, though recently disrupted by a partial LASAN tunnel collapse, could have immense benefits for drought-ridden Southern California — which has long relied on imported water supplies from the Colorado River and the Sierra Nevada snowpack — by transforming treated wastewater into purified drinking water.

The Los Angeles County Sanitation Districts is a public agency consisting of 24 independent districts that, cooperatively, serve about 5.5 million people in 78 cities and unincorporated areas throughout the county. LASAN is responsible for wastewater management across that jurisdiction.

The agency operates 10 different water reclamation plants — from Valencia to Long Beach — that produce 150 million gallons of recycled water every day.

The Warren Facility in Carson, meanwhile, isn’t just an isolated water treatment plant.

Instead, it’s a key component in a wastewater treatment network  — called the Joint Outfall System — that consists of seven treatment facilities and more than 1,200 miles of sewers running from Long Beach to La Canada-Flintridge.

It serves a vast majority of LASAN’s clientele — about 5 million people — and has the capacity to treat up to 400 million gallons of wastewater daily, making it one of the largest such facilities in the world.

Six of the JOS plants, according to LASAN, convert less salty waste water into higher-quality recycled water, which is then sent off and used for landscape irrigation, groundwater replenishment and other uses.

The remaining wastewater, with a higher salt content and solids, are sent to the Warren Facility, where it’s converted into green energy and reusable biosolids (think fertilizer, compost and other agricultural products). The Warren facility has also increased its organic and food waste recycling, as recent changes to state law now require local municipalities to divert the greenhouse-gas producing matter from landfills.

“A lot of that food waste actually goes to this facility, and we’re able to reuse that in a few different ways,” Westfall said. “We’re always looking to expand those partnerships, and how many resources can we recover from our facilities.”

After the wastewater has been treated and converted into recycled water, energy and other resources, the leftovers are cleaned — disinfected to ensure bacteria, viruses and harmful chemicals aren’t present in the water.

It then makes a six-mile journey from the Carson facility through a two-tunnel network, traveling under Carson, Lomita, Rolling Hills and Rancho Palos Verdes, and released back into the ocean about two miles off the coast of Royal Palms Beach, where LASAN’s Ocean Monitoring team routinely inspects to make sure that treated water isn’t harming marine ecosystems.

Those two tunnels, constructed in 1937 and 1958, play a crucial role in the Warren Facility’s operations. Since the second tunnel was constructed, in fact, LASAN hasn’t been able to take either offline for inspections or repair — because of how extensively they’re used.

And if tunnels and LASAN ring a bell, that’s likely because a new one — the Clearwater Tunnel, which is being constructed to replace the older two — recently made headlines after a portion of it collapsed.

A portion of the Clearwater Tunnel collapsed on July 9, about 370 feet underground and five to six miles from its only access point at the Warren facility, temporarily trapping more than two dozen workers. While the workers made it out of the tunnel unharmed, the collapse, which remains under investigation, has put the $630 million project at a standstill for the foreseeable future.

“The Clearwater Tunnel project right now is at a full stop, full halt,” LASAN spokesperson Michael Chee said aboard the Ocean Sentinel. “There’s no work going on in there. We don’t know when, if or how we’re going to be able to get back into that tunnel.”

The California Department of Industrial Relations’ Division of Occupational Safety and Health — better known as CalOSHA — has closed the tunnel completely, Chee said.

“There’s currently a plan of access being worked out, which has to be submitted to CalOSHA, (which) is the oversight authority,” Chee said. “That could be anywhere from weeks to months before we actually are able to get into the breach area.”

The Clearwater Tunnel project, which has been in the works since 2006, is necessary to replace the existing tunnels because of their aging infrastructure. The current infrastructure also isn’t built to modern seismic standards, despite crossing two fault lines; and because capacity was nearly exceeded during major rainstorms in recent years.

“Any of these concerns could result in the existing tunnel capacity being exceeded,” according to LASAN. “Such an event would require partially treated or untreated wastewater to be discharged to surrounding waterways, which could lead to environmental degradation for an extended period of time.”

Beyond those concerns, the Clearwater Tunnel is intended to serve as a crucial piece of infrastructure for an even larger LASAN project, in collaboration with the Metropolitan Water District of Southern California.

The project, dubbed Pure Water Southern California, will build a new water purification plant at the Warren Facility. When completed, the plant will be able to purify treated wastewater that currently gets released into the ocean into drinking water, effectively creating a new, and much-needed, local source of drinking water for 19 million people in MWD’s service area.

At full scale, according to LASAN, the new facility would be able to produce 150 million gallons of purified water every day — enough to meet the yearly needs of 500,000 homes.

“So the (Clearwater) tunnel is not operational, but when it does become operational, which now has been set back for an undetermined amount of time,” Chee said, “it will be integral to the system.”

The Pure Water Southern California facility project is still a long way — and many billions of dollars — from actualization, however. As it stands, the project is undergoing environmental review. Construction could start as soon as 2026, according to LASAN, with start up operations beginning in 2032.

Besides creating a a new, reliable source of water, the facility could also create 47,000 new jobs and upward of $8 billion in yearly economic output, according to a 2021 study by the Los Angeles Economic Development Corporation.

The saline-laden treated wastewater from the Warren Facility, instead of being discharged out into the ocean, would instead be purified and reused as drinking water.

“Times change, both in terms of what technology is available, and really what alternatives are cost-effective in terms of things like importing water and groundwater extraction,” Westfall said. “That will be the final piece of our resource recovery puzzle.”

The Ocean Sentinel, meanwhile, won’t be decommissioned any time soon, officials said — as there will always be a need for LASAN’s sailing scientists.

For more about the Pure Water Southern California project, visit mwdh2o.com/rrwp.