Aug. 30 --A lawsuit brought by South Bay cities alleging the federal government is not doing enough to prevent and treat the flow of Tijuana sewage into the U.S. can move forward, a San Diego federal judge ordered this week.The ruling, filed Wednesday, comes a day after U.S. District Judge Jeffrey Miller toured pumps and water-capture basins in the Tijuana River Valley to get a first-hand look at the issue.

The order allows the lawsuit to proceed on claims that the U.S. International Boundary and Water Commission violated the Clean Water Act by allowing wastewater from canyon water-capture basins to spill into the surrounding environment without the proper permit. Veolia Water North America -- West, which operates the South Bay International Wastewater Treatment Plant for the government, is also named in the complaint.

However, the judge granted the government's motion to dismiss a second claim under the Resource Conservation and Recovery Act, finding that the U.S. cannot be held liable for the state of water treatment systems in Mexico .

"At best, USIBWC transports waste through the flood control conveyance," Miller wrote. "However, that transportation is passive in nature, merely permitting the waste from Mexico to flow through the system. ... As a result, Plaintiffs have not adequately alleged that USIBWC plays a 'more active role with a more direct connection to the waste' that flows through the flood control conveyance."

The judge is allowing the plaintiffs -- the Port of San Diego and the cities of Imperial Beach and Chula Vista -- to file an amended complaint within 14 days to address legal issues with its Resource Conservation and Recovery Act claim.

The lawsuit is fighting back against a long history of wastewater flows in canyons along the border and toxic, closed beaches.

The government argues that before the $344 million treatment facility was built in the 1990s, millions of gallons of raw sewage would flow into the Tijuana River Valley . The South Bay cities and port contend that the infrastructure needs to be improved.

The South Bay plant, west of San Ysidro , was designed to handle 25 million gallons of wastewater per day, to treat the overflow of sewage that escapes the Mexican treatment facility, either because the facility is over capacity or temporarily malfunctioning.

The wastewater is treated and then channeled to the Pacific Ocean under a federal environmental permit.

The IBWC also collects wastewater at five canyons along the border, routing the sewage to its treatment plant. But the lawsuit alleges that when the collector inlets are closed or the volume reaches the basin's capacity, the polluted water flows into downstream drainages untreated.

The judge found that the water overflowing into the canyons appeared to violate the terms of the environmental permit, which only allows treated water to enter into the ocean.

Much of the legal argument surrounds whether the effluent is considered to be one body of water, or two distinct bodies. Miller said the international border complicates the matter.

"Plaintiffs argue because the polluted water in the flood control conveyance comes from a body of water in Mexico , it introduces pollutants into the waters of the United States for the first time, thereby adding pollutants in violation of the CWA," he said. "The parties could not identify any case, and the court is aware of none, in which a court addressed a CWA claim in which polluted water enters the United States from another country."

Still, he said there was not enough evidence for him to decide the matter at this point, saying it needed to be litigated further.

kristina.davis@sduniontribune.comTwitter: @kristinadavis___(c)2018 The San Diego Union-TribuneVisit The San Diego Union-Tribune at www.sandiegouniontribune.comDistributed by Tribune Content Agency, LLC.