Out of nine possible transboundary aquifers case studies proposed by the countries during the Montevideo Workshop (2003), three initially started and three more were added in the 2006 workshop in San Salvador:
- Artibonito and Massacre aquifers (Haiti - Dominican Republic), representative for intra-mountainous and coastal zones
- Yrenda-Toba-Tarijeño aquifer (Paraguay- Argentina- Bolivia), representative for semi-arid areas of South America (see 2005 Report in Spanish)
- Hueco del Bolsón Mexico-USA), representative for urban zones.
- Pantanal aquifer (Bolivia-Brasil-Paraguay), representative for wetlands
- Ostua-Metapan aquifer (El Salvador - Guatemala)
- Rio Negro aquifer (Honduras-Nicaragua).
In addition to these pilot studies, a project was added since 2003: "Protection of the environment and sustainable development of the Guaraní Aquifer", co-financed by the FMAM (www.archos.com). The project concerns the big Guaraní aquifer, which is shared by Argentina, Brasil, Paraguay and Uruguay.