Frequently Asked Questions

What are canyon collectors?

Canyon collectors are conveyance structures used to capture and divert dry weather transboundary flows occurring in the canyons on the United States/Mexico border to the South Bay International Wastewater Treatment Plant (SBIWTP). United States International Boundary and Water Commission (USIBWC) operates and maintains canyon collector structures at Smugglers Gulch, Goat Canyon, Canyon del Sol, Stewart's Drain, and Silva Drain. Map of the canyon collector locations.

What is dry weather?

Weather is considered dry if the preceding 72 hours have been without precipitation greater than 0.1 inch (>0.1 inch), based on the Goat Canyon Pump Station rain gauge. All other weather is considered wet weather. What is a transboundary flow? Wastewater and other water flows that cross the international border from Mexico into the United States. Transboundary flows include treated and untreated wastewater/sewage, groundwater, runoff, and stormwater.

What is a Type A transboundary flow?

A dry weather transboundary flow through a conveyance structure owned and operated by the United States Government into Smuggler Gulch, Goat Canyon, Canyon del Sol, Stewart's Drain, or Silva Drain and not diverted into the canyon collector system for treatment at the Facility.

What is a Type B transboundary flow?

A dry weather transboundary wastewater or other water flow occurring at the Tijuana River (main channel), Yogurt Canyon drainage, other unnamed drainages or coastal marine waters.

Does USIBWC sample transboundary flows?

USIBWC is required to sample Type A transboundary flows. The monitoring requirements are contained in Attachment E section VII.B.3 (page E-33) of Order No. R9-2014-0009. No monitoring is required for Type B transboundary flows or transboundary flows occurring during wet weather.

What transboundary flow events must be reported by USIBWC?

USIBWC is required to report all dry weather transboundary flows. No reporting is required for wet weather transboundary flows. The report must contain information such as the location(s), date(s), volume, and cause of the transboundary flow(s).

Why are transboundary flows tracked and reported?

Transboundary flows can degrade water quality in the Tijuana River Estuary and adjacent beach coastal waters and also pose a significant public health risk to residents and visitors along both sides of the border. Dry weather transboundary flows are reported to collect information to allow the San Diego Water Board, other regulatory agencies, and the public to analyze the extent of transboundary flows and potential impacts on water quality, the beneficial uses of the receiving waters, and public health. The reports are also needed to ensure that all reasonable steps are taken by USIBWC to prevent and contain transboundary flows, and to minimize or correct any adverse effect on the environment resulting from the transboundary flow. Reporting dry weather transboundary flows is a requirement of Order No. R9-2014-0009.

How does/should USIBWC respond to transboundary flows to protect public health and the environment?

USIBWC submitted the Spill and Transboundary Wastewater Flow Prevention and Response Plan (Spill Plan), as required by section VI.C.2.a.ii (pages 16-22) of Order No. R9-2014-0009. The Spill Plan states USIBWC may use sandbags or containment barriers to prevent the flows from bypassing the collectors, alter the containment in the downstream storm drains, and plug the downstream storm drains outlets to capture the spill and/or transboundary wastewater flow, if possible.

Does USIBWC mitigate or cleanup the transboundary flow?

The Spill Plan states that USIBWC may excavate contaminated soils, collect solid and liquid material and other debris, use a vacuum truck to recover the transboundary flow, and cleanup impacted storm drains.

Does USIBWC treat flows in the Tijuana River main channel?

All dry weather flow in the Tijuana River that would otherwise flow into the United States is currently diverted from the Tijuana River main channel at the international border using the River Diversion Structure and Pump Station CILA located on the Mexico side of the border. During low flow/ dry weather conditions, the Tijuana River water is conveyed by the CILA Pump Station to a 72-inch diameter sewage line where the flow can be diverted to a Pacific Ocean shoreline discharge point approximately 5.6 miles south of the U.S./Mexico border. Alternatively, the flow can be diverted to SBIWTP or another wastewater treatment plant in Tijuana, depending on how Tijuana's public utility department (CESPT) configures the collection system