The United States and Mexico share a nearly 2,000-mile border that stretches from the Pacific Ocean to the Gulf of Mexico. Although more than half of this boundary is delineated by the Rio Grande, communities on both sides of the border are affected by the region’s air quality as well as such common natural resources as groundwater, aquifers, rivers, and watersheds. For example, several communities in and bordering Texas depend on the Rio Grande for drinking water, domestic and industrial uses, and discharging wastewater. The cities of San Diego and Tijuana use the Pacific coastal waters for recreation, fishing, and wastewater discharge. Because of the transboundary character of the border region’s ecosystem and the need to address pollution problems binationally, the United States and Mexico signed the 1983 La Paz Agreement, which defines the border region for purposes of environmental cooperation as the area within 100 kilometers (62 miles) of either side of their international boundary. In the last two decades, border communities have experienced significant population growth. Between 1980 and 1996, the total population of border communities has grown from over 4 million to almost 10 million people. Most of the population is concentrated in 14 pairs of neighboring cities that are distributed across four U.S. and six Mexican states. (See fig. 1.) Almost one-third of the population in the border region lives in the San Diego/Tijuana metropolitan area, while another third is distributed among the following four large metropolitan areas along the Rio Grande in Texas: El Paso/Ciudad Juarez, Laredo/Nuevo Laredo, McAllen/Reynosa, and Brownsville/Matamoros. Most of the remaining population in the border region is scattered among the other nine pairs of neighboring cities. The rapid growth in this region is generally attributed to the potential of northern Mexican communities to provide economic opportunities that cannot be found in Mexico’s interior because of adverse economic conditions. Northern border communities also offer potential access to the U.S. job market. The availability of jobs with maquiladoras—companies located in Mexico’s northern border region that use imported materials to produce finished goods for export—has been a key factor in attracting Mexican workers to migrate to that border. Many of these migrants tend to cluster in and around suburban areas where housing is affordable but basic environmental services (such as trash collection, sewage connections, and a potable water supply) are limited or not available. In developing binational solutions to the border region’s environmental problems, policymakers in both countries face unique challenges because of the transboundary nature of the border environment, differing approaches to addressing problems in public policy, and a substantial lack of financial and technical resources. To address these problems, the United States and Mexico have established several mechanisms; in 1993, both governments signed a supplemental agreement to NAFTA to establish the BECC and the NADBank, which were created to complement existing funding to improve the border region’s environmental infrastructure and to strengthen cooperation on addressing the region’s environmental problems. The BECC’s purpose is to certify environmental infrastructure projects—primarily for drinking water, wastewater treatment, and municipal solid waste—for subsequent financing by the NADBank in the form of loans and loan guarantees at market interest rates with flexible repayment terms. The agreement encourages the private sector to invest in projects that are operated and maintained through user fees paid by polluters and the border communities benefiting from these projects. Because of the low income levels of border communities, both countries have recognized that the ongoing availability of grant funds and low-interest loans from both sides of the border that could be combined with NADBank funds was essential to make environmental infrastructure projects financially viable. The BECC and the NADBank complement an existing binational framework of environmental cooperation dating back to the late-1970s. As border communities grappled with an array of pollution problems linked to the rapid population and industrial expansion at that time, the International Boundary and Water Commission developed recommendations for addressing sanitation issues in the border region. The Commission now plans, constructs, and operates several wastewater treatment plants and projects on both sides of the border. In 1983, the La Paz Agreement, signed by the presidents of the United States and Mexico, established binational workgroups to address various problems with air, soil, and water quality as well as hazardous waste in the border region. In 1990, both governments agreed to implement action plans to bolster efforts undertaken under the La Paz Agreement to respond to various media-specific pollution problems, which appeared to have worsened with the region’s rapid population and economic growth. Although the United States and Mexico have expanded efforts in recent years to address environmental problems in the border region, many environmental infrastructure needs remain unmet and continue to pose serious threats to human health and the environment on both sides of the border. These unmet needs are particularly acute on the Mexican side of the border, where the basic infrastructure is generally insufficient and sometimes nonexistent for connecting outlying communities to services for municipal sewage collection, wastewater treatment, and solid waste disposal. Most U.S. border communities have an adequate basic infrastructure to provide drinking water, wastewater treatment, and solid and hazardous waste disposal. The colonias, however, have many unmet environmental infrastructure needs, and some other communities need to expand or upgrade the capacity of their existing infrastructure to meet the ever-increasing demand from population and industrial growth. EPA believes that insufficient infrastructure on the Mexican side, coupled with rapid population and economic growth, has contributed significantly to severe water pollution problems in the border region on both sides of the border and poses significant threats to human health and the environment. According to Mexico’s National Water Commission, the government agency responsible for national water policy, the Mexican border region has the capacity to treat only about 34 percent of the wastewater it generates, and most treatment plants are also underfinanced and poorly maintained and operated. For example, the municipal sewage connections of Matamoros and Ciudad Juarez reach only about 56 percent and 84 percent of their residents, respectively, and both cities lack wastewater treatment facilities. According to EPA, other sister cities experience similar problems with water pollution that is mostly caused by inadequate wastewater treatment capacity and problems with sewage collection. The sister cities of Mexicali and Calexico have contributed to severe pollution of the New River, which flows from Mexicali and drains into the Salton Sea in California. The domestic and industrial waste generated by Mexicali’s population of nearly 700,000 and its more than 200 industrial facilities exceeds the capacity of that city’s two wastewater treatment plants. As a result, raw and inadequately treated wastewater is routinely discharged into the New River. In Imperial County, California, agricultural runoff and irrigation return flows also pollute the New River. Several border communities, particularly in Mexico, lack the capacity to collect and dispose of the domestic and industrial solid wastes they generate. In such cities as Matamoros and Reynosa, municipal garbage collection trucks are in poor condition and too few in number to meet the needs. Both cities also have problems with their solid waste disposal facilities. According to the city official responsible for environmental control, because the entrance to the municipal solid waste disposal facility for Matamoros is generally unguarded, the site is vulnerable to illegal disposal of hazardous and/or dangerous industrial wastes that threaten the quality of groundwater. Furthermore, several families live at or near the site and rummage through its waste in search of items that can be used or sold. About 1 mile from the facility’s entrance, waste that is incinerated in the open produces a thick, dark cloud of smoke that impairs visibility and the area’s air quality. In addition, an open canal carrying the city’s untreated sewage passes through the site. This official told us that the overall conditions at the Matamoros municipal solid waste disposal facility threaten the health of the area’s residents and the environment. (See fig. 2.) Reynosa also suffers from an inadequate capacity for solid waste collection and disposal. While the city has one municipal dump, it also has 17 large illegal dumps and hundreds of vacant lots used as dumps. According to the Mayor of Reynosa, the inadequacy of the municipality’s domestic waste collection service has prompted the emergence of approximately 700 illegal trash collectors who use horse-drawn wagons and usually dispose of trash illegally, including dumping it into the Rio Grande. Most communities on the U.S. side have an adequate capacity for solid waste collection and disposal. According to officials from the Texas Natural Resource Conservation Commission, most border communities in Texas have adequate capacity to meet their solid waste disposal needs for at least the next 10 years. However, these officials cautioned that this capacity may be reduced as stricter enforcement curbs illegal dumping and solid waste collection service is extended to colonias, where it has often been inconsistent and inadequate. In addition, as Mexico increases its enforcement of solid waste laws, the return of additional maquiladora waste to the United States will reduce the years of landfill capacity that are currently projected. Several communities on both sides of the border have made progress in responding to some of their most severe environmental problems. Prior to the International Boundary and Water Commission’s decision in 1990 to construct an international treatment plant for Tijuana’s wastewater, the uncontrolled flows of untreated sewage crossing the international boundary reached a peak of 13 million gallons per day. As a result of improved sewage collection in Tijuana, the uncontrolled flow has been reduced to between 1 million and 2 million gallons per day. Furthermore, a sewage treatment facility in Nuevo Laredo is nearing completion and undergoing testing and will soon begin treating the city’s domestic and industrial wastewater, which currently drains into the Rio Grande untreated, thereby endangering human health and the environment on both sides of the border. Ciudad Juarez plans to construct wastewater treatment plants and has submitted proposals to the BECC for certification.