Rains come, then border pollution

Shorelines from Imperial Beach to Coronado were again shuttered this past week as a result of sewage spilling over the border from Tijuana.

The storms flushed urban pollution into the ocean, triggering swimming advisories across the county. But the South Bay was particularly hard hit as more than 2.8 billion gallons of sewage- and chemical-tainted runoff poured through the Tijuana River and its canyon tributaries, according to federal officials.

Pumps operated by Mexico that suck water out of the river’s main concrete channel were turned off as rains overwhelmed the system’s capacity and debris clogged the intake.

The U.S. Environmental Protection Agency has plans to build a more reliable diversion system north of the border but has yet to secure the funding. The agency currently has $300 million largely slated for an expansion of the South Bay International Wastewater Treatment Plant which services Tijuana.

The agency has cautioned that no amount of spending will completely stop the flood of urban runoff triggered by heavy rains. In fact, these flows, as polluted as they are, help maintain the estuary in Imperial Beach. The wetlands would degrade over time without the infusion of freshwater.

Still, EPA has a roughly $630 million blueprint aimed at reducing cross-border flows by roughly 70 percent. That could significantly curb beach closure days, especially in the summer when sewage pollution floats up the coast from a dilapidated treatment facility about 6 miles south of the border.

Reports of Tijuana sewage leaking over the border into the San Diego region stretch back at least to the 1930s. While significant improvements were made in the 1990s, the city’s plumbing still isn’t keeping pace with population growth.

Real-time conditions are posted at sdbeachinfo.com.

joshua.smith@sduniontribune.com