Using ecological risk assessment to evaluate environmental impacts of desalination effluent

OUR CHALLENGE

Our client aimed to build a desalination plant to increase the supply of fresh water required for sustaining local communities and supporting future economic growth. They submitted an effluent permit to the state regulator for authorization to discharge high-salinity effluent into an estuarine system. Legal challenges to the permit cited concerns that the effluent would cause unacceptable harm to the ecosystem. These actions resulted in a court hearing on the environmental concerns associated with the permit. The client contacted Integral to seek technical expertise and obtain objective expert testimony on the matter.    

OUR APPROACH

Integral applied the ecological risk assessment paradigm to estimate the potential environmental impacts of the proposed desalination effluent on the regional aquatic ecosystem.  

• The problem formulation identified the estuarine habitats, sensitive aquatic species, life cycle considerations, and natural salinity fluctuations. 

• The exposure assessment used computational modeling to derive conservative salinity estimates in the receiving waters based on anticipated effluent discharge volumes, local and seasonal variations in ambient salinities, water temperatures, and tidal currents. 

• The effects assessment compiled published literature on salinity tolerances to four life stages of representative local species of fish and shellfish with commercial and recreational importance that might potentially become exposed to the desalination effluent.  

• The risk characterization integrated all of these elements, especially comparing the modeled high-salinity exposure durations in the receiving water to the published salinity tolerances. The evaluation showed that exposures lasted from seconds to minutes and would not negatively affect sensitive life stages subjected to these conditions. In addition, the vast majority of fish and shellfish moving through the estuary would not encounter these conditions due to the limited spatial extent of the high-salinity effluent and the presence of alternative access routes.    

OUR IMPACT

Integral, on behalf of the client, submitted science-based written and oral expert testimony to the Court and successfully argued that the proposed desalination effluent would not adversely affect the regional ecosystem. The Court agreed with our arguments and accepted the effluent permit with some additional modifications. This positive outcome allowed our client to continue their engineering design process to supply a sustainable source of fresh water to the surrounding communities.