Disposal of brackish water desalination concentrates will in many cases involve downhole injection into deep formations.  The potential for chemical reaction between injectate and deep groundwaters might ultimately limit the economic disposal of desalination concentrates.  Mineral precipitation (and/or dissolution) has the potential to drastically alter local hydrologic conditions in the receiving body.  Borehole clogging is a particular obstacle to sustainable waste injection.  We have performed a series of geochemical reaction-path calculations to limit the range of potential injectate interactions and to anticipate the geochemical consequences of large scale waste injection.  Compositions of New Mexico brackish wasters were modified to reflect reverse osmosis extraction of water.  These waters were then "reacted" with the fluids and minerals of likely receiving bodies in New Mexico.  The calculated reaction paths set some limits on the controls over sustainable injection and highlight critical data gaps.