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Introduction to the New River/Mexicali Sanitation Program

Salton Sea Transboundary Watershed

The present day channel of the New River was created in 1905-07 when the Colorado River washed out diversionary works, and the entire Colorado River flow coursed into the Salton Basin creating the New and Alamo River channels and the present Salton Sea, thus the name "new" river. These surface waters are within the Salton Sea watershed, which is a transboundary watershed that includes the Coachella and Imperial Valleys in the United States and a portion of the Mexicali Valley in Mexico.

Currently, the New River's headwaters originate about 15 miles south of the City of Mexicali, in the Mexicali Valley, Mexico. The New River carries urban runoff, untreated and partially treated municipal wastes, untreated and partially treated industrial wastes, and agricultural runoff from the Mexicali Valley into the United States. After it crosses the International Boundary at Calexico, California, the New River travels about 60 miles through Imperial County before it discharges its entire flow into the Salton Sea. By the time the New River reaches the Salton Sea, about 2/3 of its flow consists of wastewater in the form of agricultural runoff from Imperial County. The New River flow is approximately 200 cubic feet per second (cfs) (or 144,800 ac-ft/yr) at the International Boundary. At its delta with the Salton Sea, its flow is approximately 600 cfs (or 434,400 acre-feet/year), which makes it one of the two main tributaries to the Salton Sea--the other main tributary being the Alamo River.


Historically, the New River has been recognized as a significant pollution problem since at least the late 1940s, primarily because of its extremely high concentrations of fecal coliform bacteria and offensive odor at the International Boundary. The early history of New River pollution is vague, but it is believed to be closely aligned with population growth. In 1920, the total population of Mexicali was only 6,200 people. In 1955, it was estimated that raw sewage from approximately 25,000 people was being discharged into the New River from Mexicali. In 1975, the population jumped to over 100,000 people. The present population of Mexicali is reported as 764,902 (INEGI 2001) by Mexico, but some believe it is close to 1 million. A focal point of early complaints regarding New River pollution was odor. In the early fifties, the odor of the river near the boundary, particularly at night, was oftentimes overpowering. Beginning around 1956, the flows of the New River at the boundary increased considerably due to development of agricultural drainage return flows from Mexicali Valley. This dilution water temporarily alleviated the odor problem, but in the sixties the problem became increasingly noticeable as sewage loading increased with the population. Similarly, due to the recent industrial growth in Mexicali, industry is now also a significant source of New River pollution. In the mid 1980's the extent of the problem was finally recognized, and Mexico and the United States began to work cooperatively to address New River pollution from Mexico.



The California Regional Water Quality Control Board, Colorado River Basin Region, has been actively involved in the cleanup of the New River and has been a significant force in molding the proceedings. The Regional Board has monitored the water quality of the New River since 1975. In 1995, the United States Environmental Protection Agency (USEPA) provided funds to the Regional Board to monitor and document the water quality at the International Boundary on a monthly basis. The main purpose was to assess to what degree the sanitation projects improve water quality of the New River at the boundary. Monitoring data indicate the New River is polluted by bacteria, silt, nutrients (e.g., nitrate and phosphate), and volatile organic constituents. See water quality data for the New River at the International Boundary.

The Regional Board has primary responsibility for addressing the New River's water quality problems attributable to activities in the United States. It is controlling pollution from nonpoint sources of pollution by implementing the State's Nonpoint Source Management Plan and the State's Watershed Management Initiative, which calls for development and implementation of Total Maximum Daily Loads
for the constituents
impairing the river. It also controls pollution from Imperial Valley point sources discharging into the New River (e.g., domestic wastewater treatment plants) through the National Pollutant Elimination Discharge System (NPDES) regulatory program. The United States Environmental Protection Agency (USEPA) and the US Section of the International Boundary and Water Commission (US IBWC) are the two US agencies with responsibility for Border pollution.

In 1980, the Unites States and Mexico Sections of the IBWC adopted Treaty Minute 264, which established water quality standards for the New River at the International Boundary and called for the elimination of Mexico's raw sewage discharges into the New River by 1982. In spite of this, the discharges of 10 to 20 million gallons per day (mgd) of raw sewage have continued due to an inadequate and dilapidated sewage infrastructure in Mexicali. It was not until 1992 that both governments recognize that the problem was more significantly extensive than envisioned in Minute 264. In 1992, US and Mexico adopted Treaty Minute No. 288 in 1992. Treaty Minute No. 288 established a long-term sanitation strategy for the New River at the Border and divided the sanitation project into Immediate Repairs (a.k.a. quick fixes"), the Mexicali I, and the Mexicali II projects. The projects total about $50 million dollars are being funded by both countries through the North American Development Bank (NAD Bank)-a binational organization created by the North American Free Trade Agreement (NAFTA). The Border Environment Cooperation Commission (BECC)-the NAD Bank's sister institution-is responsible for certifying the projects meet a series of environmental criteria and qualify for funding. The Mexicali I and II sanitation projects originally received certification by the BECC on December 5, 1997, and January 7, 1998, respectively.


The Quick Fixes were funded through a cost sharing agreement between both countries. The U.S. 55% and Mexico contributed 45% of the $7.5-million total cost for the Quick Fixes. These emergency projects were implemented under the supervision of a Binational Technical Committee (BTC). The BTC has representatives from CILA (IBWC, Mexican Section), CESPM (State Public Services Commission of Mexicali), CNA (National Water Commission), SAHOPE (Secretary of Human Settlements and Public Works) and the Municipality of Mexicali for Mexico; and the US IBWC Section, USEPA, California State Water Resources Control Board, Regional Water Quality Control Board, County of Imperial, and the Imperial Irrigation District for the United States. The BTC has led to improved communication and technology transfer between the two countries. IBWC declared the Quick Fix projects 100% complete in 1999. The Quick Fixes are summarized below:

  • Improvements to the collection system, either by lining or replacing existing sewer pipes and acquiring modern sewer cleaning equipment;
  • Rehabilitation and upgrades to pumping facilities that lift and deliver wastewater to the treatment facilities, including installation of standby power equipment; and
  • Improvements to the existing lagoons at the Ignacio Zaragoza (Mexicali I) and Gonzalez Ortega wastewater treatment facilities in Mexicali to increase their reliability and capacity.


The Mexicali I projects focus on providing sewage collection services for neighborhoods on septic systems. As of June 2004, these projects are about 95% complete and consists of the following infrastructure:

  • Installation of sewage collection systems in 52 colonies located in the western part of Mexicali.
  • Reposition of 36 kilometers of sewage collectors
  • Construction of 7.650 km of new sewage collectors
  • Installation of telemetry equipment for the municipal collection and pumping systems
  • Rehabilitation of Pump Stations No. 1, 2, 3, and the Gonzales Ortega lift station
  • Construction of the Orizaba, Orizaba II, Pump Station 8, and the Santorales Pump Station.


The essence of the Mexicali II projects is the construction of a new 20-mgd wastewater treatment plant to handle the current raw sewage bypasses. The main project components are:

  • Construction of a 20-mgd pumping plant (a.k.a. "Pumping Plant No. 4")
  • Construction of a new 20-mgd Waste Water Treatment Plant (a.k.a. "Mexicali II WWTF")
  • Installation of 26 Km of a 48-inch pressure force main
  • The construction of the following collectors; Periferico, Nutrimex, Robledo, Tula, Solidaridad Entronque with PB4, Condor, Villas del Colorado, Valle Dorado, Lagunas, Garzas, Garita, Aeropuerto, Carranza, Benassini
  • Reposition of the collector Calle Primera-Gonzales Ortega.

The Mexicali II projects were supposed to be completed in 2002. Construction of Pumping Plant No. 4 and construction and reposition of the sewage collectors proceeded on schedule. However, construction of the new Mexicali II WWTF and its force main as originally certified by the BECC did not materialize because residents in the area of El Choropo, which was site originally certified for the WWTF, successfully opposed the construction of the WWTF there. In December 2003, the BECC granted conditional certification for construction of the Mexicali II WWTF at a site known as "Las Arenitas," which is outside the Salton Sea Transboundary Watershed. Effluent from Las Arenitas is discharged to a tributary of the Rio Hardy in Mexico. In October 2006, Mexico completed installation of the 48-inch force main for Las Arenitas WWTP, the modifications to Pumping Plant No. 4 to meet the new pumping requirements for Las Arenitas, and construction of the Las Arenitas WWTP. The WWTP is fully functional. The cost for this project was approximately $26 Million. Las Arenitas WWTP was designed to prevent any remaining untreated municipal sewage in Mexicali from being discharged into the New River. As a result of Las Arenitas, 15-20 million gallons per day of raw sewage that were routinely present in the New River at the Border have been eliminated. Board staff and USIBWC staff continue to monitor the New River every month. Board staff continue to participate in binational technical committee meetings to address New River from Mexico and bi-national tours to assess and enhance water quality improvements. Our monitoring data show that New River bacteria were significantly reduced by about 10-fold, and that volatile organic compounds were reduced to below detection limits as a result of Las Arenitas. The dissolved oxygen in the River at Border has also improved dramatically and significantly to a point that it eliminated the stench that used to characterize the River at the Border. Further, the improvements and new WWTP have reduced the nutrient loading into the Salton Sea by about 20%. The tables below show a comparison of New River water quality at the Border before and after completion of the binational projects, including Las Arenitas going on line.

Fecal, E. Coli > 1,000,000 ~ 100 - 60,000
Dissolved Oxygen < 1.0 mg/L ~ 5.0 mg/L
Nutrients (PO4) 40% of Load to Salton Sea 20% of Load to Salton Sea
VOCs Some detected Non-detect
Trash > 150 cu yds/year > 150 cu yds/year
Pesticides Detected Still a problem


The 10 to 20 mgd of raw sewage that were historically present in the New River at the Border have been eliminated and resulted in significant, measurable improvements in water quality of the New River at the Border, particularly as it relates to pathogens, nutrients, bacteria, and dissolved oxygen. In spite of these significant water quality improvements, there are still New River water quality impairments at the Border caused by dumping of trash, non-point sources of pollution: pesticides from agricultural runoff; nutrients, and pathogens from confined animal feeding operations as well as from slaughterhouses in Mexicali. Additional measures must be taken to address the indiscriminate dumping of trash into the New River and its tributaries, the nutrients and pathogens from Mexicali's Zaragoza wastewater treatment lagoons, the untreated and partially treated discharges of industrial wastes from Mexican-owned facilities, agricultural runoff (and the pesticides associated with it) from the Mexicali Valley, and urban and storm runoff from the municipality.