Case Study: Minding the Gap

:: Wednesday, June 1, 2016 :: Posted By Mary Beth Garrison

Rio Tinto’s Minerals business worked closely with the City of Los Angeles to support the region’s water quality and conservation.

Groundwater basins in coastal Los Angeles are continually affected by salt water from the Pacific Ocean, as well as urban pollution. To keep seawater out of the freshwater basin, the local government uses a network of hydraulic dams to pump imported freshwater along natural geological underground barriers. One such barrier is the Dominguez Gap, located near Rio Tinto Mineral’s Wilmington Operations.

While this process keeps the ocean at bay to the west, it also traps pollutants inland to the east. This means the water pumped into the Dominguez Gap has to be clean enough to restore the quality of the freshwater basin and ensure it’s suitable for beneficial uses, such as irrigation.

With California facing a water crisis, rather than continue to use imported freshwater to feed into the groundwater system it made sense to investigate whether recycled water could be made clean enough at local treatment plants to be used.

One of the initial challenges to this solution was the boron in industrial wastewater produced under the Wilmington Operations’ existing discharge permit. The rate at which boron was discharged by the Operations meant the local water treatment facility could not effectively process it to a level which would meet the basin’s new water quality objective.

The Wilmington Operations team worked collaboratively with the City of Los Angeles’ Industrial Waste Management division to slow the flow of the operation’s industrial wastewater to the water treatment plant. The team discovered that by slowing down the wastewater discharge it was also possible to reduce the total amount of boron in the wastewater, and keep clean water moving as needed.

Today, almost all of the boron is recycled into refined product and the wastewater discharged to the water treatment plant goes where it can do some good for the community – to the Dominguez Gap.

Boron discharged in industrial wastewater to the City of Los Angeles, Terminal Island Water Reclamation Plant:
Year Boron discharged
% reduction vs 2012
2012 11,058  
2013 3,351 70
2014 1,197 89
2015 302 97



U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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