Turning Waste into Water

Las Arenitas has been a joint U.S.-Mexican venture since its conception in the mid 2000s. Prior to the construction of the plant, Mexicali was releasing untreated sewage into the New River, which runs north into California and terminates in the Salton Sea. In an effort to fix this pollution problem, the North American Development Bank helped finance the construction of the treatment plant. Although the New River remains an extremely polluted waterway, the construction of Las Arenitas greatly reduced raw sewage inflows into the river.

Shortly after the plant became operational, two conservation groups (the Sonoran Institute and Pronatura Noroeste) approached the State Commission of Public Services for Mexicali (CESPM), which manages Mexicali’s water, with a proposal to construct a wetland next to the treatment plant. This provided additional treatment capacity to the plant, while also creating habitat for the hundreds of bird species that rely on this area. Seen from the sky, the wetland is a wild oasis in a sea of desert and farmland. 

Polluted Water Threatens People and Nature

As the city of Mexicali grew to a population of 750,000, so did the demand for sewage treatment. At the same time, Las Arenitas’ treatment capabilities declined due to a maintenance backlog. The plant now services half of Mexicali’s wastewater needs and receives about 20% more inflows than it can fully treat. The polluted water is discharged into the Rio Hardy, threatening both humans and wildlife downstream. The public services commission was aware of the problem, but struggled to obtain the funds for the necessary fix.

TNC, along with its partners, saw an opportunity: fund the much-needed improvements, and increase both the quantity and quality of water flowing into the Colorado River Estuary. But first, local residents, the public services commission, and Mexico’s federal water authority would need to be convinced that a project focused on acquiring water for the environment would not mean less water for farmers and cities, a hard sell in this parched region. Making matters more difficult, Mexicali Valley farmers and residents have often had to fight for their water from the Colorado River, causing them to bristle at the idea of deals involving water allocations. 

Collaboration and Community

One skeptical group was the Ecological Association of Users of the Hardy and Colorado Rivers (AEURHYC), which represents the downstream water users of the Rio Hardy. Francisco Javier Mosqueda, the president of AEURHYC and the co-owner of a large tourism camp along the river, explains that agreements in the past had done little to clean up the river. “Previous deals were signed and water quality was not improved much,” says Mosqueda. “Fish are still dying in the Rio Hardy.”

Still, he is hopeful that with advancements to the treatment plant and monitoring by TNC and its partners, the new agreement will bring improvements to the river. “A cleaner Rio Hardy would bring huge economic benefits to the region,” says Mosqueda, going on to detail the fishing and tourism that the upper river has historically supported. “This is the best effort for water quality and quantity improvements in the last 10 years.” 

“It took years of collaboration and trust building between the environmental partners, water authorities and local groups,” says Francisco Zamora, director of the Sonoran Institute’s Colorado River Delta Program. Zamora was one of the central figures in building the first wetland area next to Las Arenitas, so he understood from the beginning that success was possible.

As talks progressed, the Mexicali public services commission felt comfortable sharing sensitive water quality and flow data with the environmental groups. Armed with this information, TNC and its partners helped develop plans for an improved treatment plant, incorporating a new wetland, that would target the specific contamination issues Las Arenitas was experiencing. Negotiations, spearheaded by Carrera and Zamora, led to a plan with which the water managers, environmental groups and local organizations were happy. 

The Las Arenitas Agreement

The agreement signed July 1st provides funding for maintenance and improvements to the existing treatment infrastructure and the construction of a new wetland area, and pledges that a volume of water equal to 50% of the inflow to Las Arenitas will be allocated to the environment. Importantly, these increased environmental flows will come at minimal costs to downstream farmers and residents, who maintain their current water allocations and will have the added benefit of a cleaner Rio Hardy. 

“The most important lesson that we have taken away from this process is that we can all win: the people, the institutions and the environment” says Isaac Vizzuett Herrera, the public services commission’s subdirector of sanitation and water. Herrera is hoping to take the lessons learned in Las Arenitas and apply them to other communities in Baja California that are struggling with wastewater treatment. 

For Carrera, the agreement is a sign of hope for the entire Colorado River basin. “What is happening in Las Arenitas and in the delta allows us to see the connection between the upstream and the downstream in the Colorado River,” he said. “This is one system, one basin, binational, working to restore the delta ecosystem.”