Brackish Water for Inland Water Supply: Hydrologic Challenges

Increasing demand for scarce water supplies in the arid southwestern United States has led water managers to consider alternative sources of water for municipal and industrial supply, including wastewater reuse and development of brackish and saline groundwater resources. In New Mexico there has been considerable interest in brackish groundwater development because of its widespread distribution over much of the state and because its use was not regulated prior to 2009. There are several characteristics of brackish water aquifers that make development of this resource much more difficult than seawater desalination. From a hydrogeological perspective these are: (1) uncertainty regarding the magnitude of the resource, (2) challenges of recovery water from deep low productivity aquifers, (3) identifying methods of desalination concentrate management, and most importantly, (4) recognizing and addressing issues regarding the sustainability of the resource. There is very little information on magnitude of brackish waters resource or its quality because it had no value until recently. Using estimates of hydraulic properties from available studies, it can be shown that development of this resource will be difficult and costly. In particular, low values for conductivity and storage coefficient mean that wells will require very large spacing, produce large drawdowns, and will have larger pumping costs than current supply wells. These hydraulic properties will also have consequences for concentrate disposal as tight formations will require multiple wells for waste injection. Finally, most brackish water aquifers in New Mexico receive little or no recharge. Development of groundwater from them is not sustainable in that it will result in rapid depletion of the resource. An example will be presented in which a proposed urban development, one of several proposed near Albuquerque, would deplete the entire resource in 20 to 70 years.