Transboundary Aquifer Assessment Program |

Transboundary Aquifer Assessment Program

Arizona/Sonora (TAAP-A/S) 

Project News

The International Boundary and Water Commission, United States and Mexico (IBWC) have completed the San Pedro River Aquifer Binational Report. The study marks the first time researchers from both countries have collaborated to collect data and jointly prepare binational maps of the San Pedro River aquifer, which spans the border between the States of Arizona and Sonora near the communities of Sierra Vista, Arizona and Cananea, Sonora. The binational database and bilingual maps created for this study, and the resulting technical analysis, are an important contribution to scientists’ understanding of the aquifer.

The report is the result of a dedicated group of scientists from both countries that worked with IBWC according to an IBWC-approved binational cooperative framework to allow them to exchange ideas and information to improve the state of knowledge in the basin.

“The cooperation between our two countries resulted in the collection of key information about our shared groundwater resources,” said U.S. Commissioner Edward Drusina. “These types of partnerships benefit scientists and water managers in both countries.”

“The information included in this joint study improves our understanding of the San Pedro River transboundary aquifer and provides a more solid basis for decision making related to water management in both countries,” said Mexican Commissioner Roberto Salmon.

The technical team for this study included personnel from the U.S. Geological Survey (USGS), Mexico’s National Water Commission (CONAGUA), and two state universities, the University of Arizona and the University of Sonora, working together under the auspices of the IBWC. Funding came from IBWC, USGS, CONAGUA, and the University of Arizona. 

Spanish language version of the San Pedro River Aquifer Binational Report is soon to be released!


Para la versión español, haz clic aquí

 Click on the "States Map" to download a print quality jpeg file
TAAP-A/S (the transboundary Santa Cruz and San Pedro aquifers) is a federally funded program co-hosted between the USGS Arizona Water Science Center in Tucson, Arizona and the Water Resources Research Center (WRRC) at the University of Arizona. The program originates from U.S. Public Law 109-448, signed by the President on December 22, 2006 as the Transboundary Aquifer Assessment Act. The Act applies to the states of Texas, New Mexico, and Arizona where four transboundary aquifers have been designated for priority assessment; those being the Hueco Bolson and Mesilla Basin aquifers in the greater El Paso / Ciudad Juárez region, and the Santa Cruz and San Pedro aquifers across the Arizona – Sonora border (see maps). TAAP-A/S is designated to operate for 10 years, with $50 million authorized for appropriation over that time period.

Aside from the USGS, WRRC and Udall Center for Studies in Public Policy at the University of Arizona, a variety of other U.S. and Mexican stakeholders participate in priority setting for the assessment process. TAAP-A/S has been designated a case study by the UNESCO Internationally Shared Aquifer Resource Management (ISARM) program.

Click on the "Basins Map" to download a print quality jpeg file
The upper San Pedro and Santa Cruz river basins, south to north drainages which are bisected by the international border, harbor unique human-environment issues. The upper Santa Cruz is marked by the sister cities of Nogales, Arizona and Nogales, Sonora with the Mexican side having an approximate population 10-times that of its northern neighbor. Within the upper San Pedro basin, the cities of Cananea, Sonora and Sierra Vista, Arizona are the urban centers in which the majority of the regional population resides. Economic activity in Cananea is driven by copper mining while the U.S. Army’s Fort Huachuca is a major source of employment for residents of Sierra Vista. Federally mandated sustainability within the Sierra Vista Subwatershed is a driver for regional water conservation efforts. 

Materials and Activities


Callegary, J.B., Minjárez Sosa, I., Tapia Villaseñor, E.M., dos Santos, P., Monreal Saavedra, R., Grijalva Noriega, F.J., Huth, A.K., Gray, F., Scott, C.A., Megdal, S.B., Oroz Ramos, L.A., Rangel Medina, M., Leenhouts, J.M., 2016, San Pedro River Aquifer Binational Report: International Boundary and Water Commission, 170 p. 

Five-year interim report of the United States-Mexico Transboundary Aquifer Assessment Program: 2007--2012

Localizing Decision-Making in the Bi-National US-Mexico upper San Pedro River-July 12-14, 2011

The Importance of Institutional Asymmetries to the Development of Binational Aquifer Assessment Programs: The Arizona-Sonora Experience


2015 UA CALS Poster Forum on October 29, 2015

Fact Sheet 

The TAAP-A/S Fact Sheet can be downloaded in .pdf format. The bilingual/bilingue Fact Sheet is here


International Conference on Water Scarcity, Global Changes, and Groundwater Management Responses: Irvine, California; December 2, 2008

Scientific Segment of the 19th Session of the Intergovernmental Council of the UNESCO International Hydrological Programme (IHP): Paris, France; July 7, 2010

World Water Week- Responding to Global Changes: Accessing Water for the Common Good, with Special Focus on Transboundary Waters: Stockholm, Sweden; August 20, 2009.

UNESCO-IHP, ISARM and PCCP Programmes International Conference- Transboundary Aquifers: Challenges and new directions: Paris, France; December 7, 2010   

Aside from the above presentation, the paper written for this conference can also be downloaded, either inEnglish or Spanish.

Arizona Hydrological Society Symposium- Dryland Hydrology: Global Challenges, Local Solutions: Tucson, Arizona; September 3, 2010.

Arizona-Mexico Commission Plenary Session - Water and Environment Committees;  June 8, 2012

Binational Border Water Resources Summit: Past, Present and Future.  Ciudad Juarez, Chihuahua, Mexico and El Paso, Texas, USA;  September 28-29, 2012.

Workshop on Cooperation Across and Within Jurisdictions and Levels for Good Water Governance – Local to Global; September 3, 2013

Arizona-Mexico Commission Water and Environment Committee; June 14, 2013

Session on Managing the National Water Sector. Tel Aviv, Israel; October 22, 2013



TAAP-A/S has compiled two databases of published materials related to groundwater in the binational upper Santa Cruz and San Pedro basins. These databases are available for download in both Adobe Acrobat PDF and MS Excel format, though due to character input limits, certain fields in the Excel version will be incomplete.

The TAAP-A/S database is currently in draft format, and certain fields have not been completely reviewed. The files are being made available in draft format. For reference purposes, please cite as: Santa Cruz (or San Pedro) Database, Transboundary Aquifer Assessment Program- Arizona/Sonora. University of Arizona, 2010. Include the date that file was accessed and web address. 


On November 3 and 4, 2009 TAAP-A/S hosted a workshop entitled “Developing a Work plan for the Santa Cruz and San Pedro Aquifers”. The purpose of this event was to review progress of TAAP-A/S and confirm or modify priorities in the draft work plan that will guide assessment of the Santa Cruz and San Pedro aquifers. Over 50 participants gathered during the two-day event, which culminated in breakout groups providing feedback on the TAAP-A/S work plan for priority assessment activities. The workshop agenda contains links to all presentations made. 
Download workshop agenda 
Download workshop report






Municipal provision of groundwater to Cananea, Sonora requires pumping facilities to push the water uphill from the well field on the San Pedro River to the urban area.


Surface flow of the Santa Cruz River at the Tubac Bridge is largely composed of treated effluent released by the Nogales International Wastewater Treatment Plant, located approximately 20 kilometers upstream, to the south.