Summary of Issues Strategies Benefits & Costs Key Uncertainties Additional Resources

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1 Summary of Issues Strategies Benefits & Costs Key Uncertainties Additional Resources KEY POINT: The primary environmental concern associated with direct disposal to the ocean is the potential adverse impacts to marine species and surrounding habitat. SUMMARY OF ISSUES Concentrate quality. The quantity and quality of desal concentrate depends on source water quality, type of pretreatment process used, membrane type, and recovery rate. Salinity. SWRO concentrate discharge is typically about 1.5 to 2.5 times higher in salinity than ambient seawater (assuming 35 60% recovery). High levels of salinity in the concentrate can have significant adverse effects on receiving water quality and the surrounding marine environment. Source water quality contaminants. In addition to salts, naturally occurring elements and contaminants in the source water will be concentrated in the discharge, which can result in adverse impacts to the marine environment (depending on the type and concentration of the contaminant). When desal plants are co-located with power plants, the desal concentrate may also contain excess heat that may pose concerns (NRC 2008). Process chemicals. Desal concentrate can include desal process chemicals used for pretreatment, cleaning, corrosion prevention, and membrane anti-fouling. These substances include heavy metals, weak acids and detergents, and unreacted chemicals from pretreatment processes. The nature and concentration of these chemicals in the concentrate vary and are site-specific, depending on which chemicals are used, the amounts used, how frequently they are used, and whether they are discharged in the concentrate or disposed of via sewage treatment plants or other disposal options. The nature and potential impacts of these chemicals are discussed in detail in NRC Thermal pollution. Thermal pollution is a concern associated with concentrate discharge. Although the rise in temperature resulting from RO processes is relatively low, brine concentrate from thermal desal processes has an elevated temperature compared to ambient seawater. Increased temperature can affect levels of dissolved oxygen in the seawater. However, ss discussed elsewhere in the PIM, there are no municipal thermal desal plants in the U.S (and likely will not be). Thermal desal concentrate is therefore not addressed here. 1

2 Hazardous metal substrates, such as copper and lead, may be introduced to brine as a result of corrosion of pipes and equipment. Desal concentrate combined with other industrial discharges will include other substances characteristic of the secondary discharge. Outfall infrastructure. Construction of discharge infrastructure also contributes to the overall environmental impact of a desal facility. Construction of pipes for open ocean outfalls have direct (temporary) impacts on surrounding terrestrial and marine habitats. The severity of impacts depends on construction methods and the type of habitat impacted. Site- and species-specific impacts. The impacts of concentrate discharge on the marine environment vary based on discharge method, receiving water characteristics, source water salinity and quality, and ecosystem and species type. Due to the site-specific nature of potential impacts, it is necessary to conduct pre-construction experiments and postconstruction monitoring on a site-by-site basis. Mitigation measures. There are several mitigation measures that can reduce the negative impacts of seawater desal brine discharge on the marine environment. Some of these measures are technological and some come with a greater understanding of the ecosystems near the desal facility. Regulations and permitting. In addition to state and local regulations, the National Pollutant Discharge Elimination System (NPDES) program (part of the Clean Water Act) applies to ocean water discharge. Concentrate from municipal desal treatment plant is currently regulated as an industrial waste under the Clean Water Act. This designation imposes stringent, cumbersome, and potentially costly regulations. In addition, the associated stigma may generate wariness about the project among the public (AMTA 2007). STRATEGIES Understand potential environmental impacts Thorough examinations of areas around proposed desal facilities can help minimize environmental impacts of discharge. Infrastructure design should be based on an understanding of 1) the composition of the desal discharge (including average conditions and extreme conditions), 2) the physical properties of the receiving water body (wave and current action, 2

3 seafloor topography), and 3) the species composition of the marine community around the outfall. Each desal facility will need to monitor its own discharge to characterize its composition, and to understand potential impacts on the marine community. This monitoring should take place throughout the year in order to capture fluctuations due to the operation of the desal facility and to seasonal variability in receiving waters. The physical properties of the receiving water body are important in determining the impacts of the discharge plume. The concentrate will sink towards the ocean floor once it is discharged from the outfall, but a water column with strong currents and wave action can help to dilute the brine and disperse it in various directions, preventing it from settling on the ocean floor. The topography of the ocean floor and the type of sediment are also important. Discharging into an area where the ocean floor slopes away from the coast will help to mix the brine plume as it moves towards deeper water. There is limited knowledge of the behavior of actual brine plumes; thus, the impacts of desal discharge on receiving body water quality have mostly been studied through modeling (see Jenkins 2006). The results of this modeling can be combined with knowledge of the marine habitats near the desal facility, as well as the salinity tolerance of the marine biota, to project potential impacts of brine discharge on the marine community. This type of modeling can assist utilities in selecting appropriate discharge infrastructure and in evaluating potential brine discharge impacts before construction of the facility begins. It is difficult to rely on models for understanding impacts on biological organisms. Each marine species exhibits a certain level of tolerance to salinity fluctuations, and there is typically an upper-limit threshold to this tolerance. While this threshold is known for some species, it is unknown for the vast majority of potentially affected marine species. The impacts of brine plumes on the biological community should be studied on a site-specific basis through experimental manipulations. Before these tests are performed, however, it is necessary to identify the range of salinities that will result from the brine concentrate disposal. Hydrodynamic models are useful for this purpose. Potential impacts of pretreatment chemicals and other parameters should also be evaluated. One method of testing effects of increased salinities on marine organisms is whole effluent toxicity (WET) tests. While this method was not specifically designed for testing increases in salinity, it has been useful for this purpose, and it may be used more successfully for testing potential effects of other chemicals in desal discharge. 3

4 Mitigate or reduce adverse environmental impacts There are several mitigation measures that can reduce the negative impacts of concentrate discharge on the marine environment. Methods of enhancing mixing and dilution of the brine discharge, such as installing diffusers on the outlets, modifying the angle of the outfall, and constructing discharge outfalls in areas of high ambient mixing can help minimize adverse effects. Diffusers and proper discharge pipe construction can also reduce the impacts of thermal pollution discharged with brine concentrate. Combining desal concentrate with other types of discharge (power plant cooling water or wastewater, for example) can also serve to reduce the impacts of each individual discharge. In some cases, the actual siting and construction of a desal plant may be affected by the potential impacts of brine discharge. The Desalination Task Force convened by the California Department of Water Resources (CDWR) has agreed that proper siting of desal facilities and application of mitigation measures can offset most impacts associated with coastal concentrate discharge. To further minimize impacts, desal facility operators should consider the use of process chemicals that have least environmental impact. In addition, the use of pipes that minimize the corrosion of hazardous substances (polyethylene or titanium is preferable to copper nickel) can reduce potential impacts. Be familiar with the regulations and required permits Both federal and state regulations require monitoring and permitting of discharge from coastal desal facilities. Desal discharge is characterized as an industrial discharge through the Clean Water Act, which is enforced by the U.S. Environmental Protection Agency and state environmental agencies. Further, desal facilities must be permitted through the National Pollutant Discharge Elimination System (NPDES) in order to discharge brine concentrate and other chemicals. NPDES requires monitoring of concentrate toxicity through whole effluent toxicity (WET) tests for major ion toxicity. Construction of desal facilities, including discharge infrastructure, is subject to environmental review through the National Environmental Policy Act (NEPA) as well as applicable state requirements (e.g. California Environmental Quality Act). Other regulations that a facility may need to consider include federal and state threatened and endangered species laws and designations of protected marine or terrestrial habitats (e.g., Monterey Bay National Marine Sanctuary). An extensive discussion of the applicability of regulations such as the Clean Water Act and Safe Drinking Water Act is provided in the United States Bureau of Reclamation report Membrane Concentrate Disposal: Practices and Regulation (Mickley 2006). 4

5 BENEFITS & COSTS Benefits Open ocean discharge is typically the least expensive technology for desal brine. Costs Costs associated with studies of physical properties of marine environment and composition of surrounding marine communities. Costs of mitigating impacts on marine biological communities. Costs of ongoing monitoring of discharge composition and effects on marine biota. Potential reduction in individual fitness, population size, and species composition and diversity in affected marine communities. Impairment of water quality near discharge outfall. KEY UNCERTAINTIES While discharge may contain other substances, the increase in salinity is the primary concern. The impacts of increased salinity on marine organisms from desal brine discharge are largely unknown. However, there is a general consensus in the literature that discharge salinity should be within 1% of the receiving water salinity (Mickley pers comm. 2009). Although models can help predict the behavior of brine plumes and their impacts on marine organisms, it is not until discharges from actual desal facilities are studied through experiments and monitored over time that will we know the full extent of impacts. Continuing observational and manipulation experiments are necessary to more fully understand salinity tolerance thresholds of marine organisms. It is especially important to understand these thresholds in threatened and endangered species. 5

6 ADDITIONAL RESOURCES AMTA Disposal of Desalting By-Product. Publication FS-4, February CDWR (California Department of Water Resources) Water Desalination Task Force, Issue Paper. Revised Draft August 26, Office of Water Use Efficiency and Transfers. Campbell, R. L., and A. T. Jones Appropriate disposal of effluent from coastal desalination facilities. Desalination 182: Cooley, H., P. H. Gleick, and G. Wolff Desalination, with a Grain of Salt: A California Perspective. Pacific Institute, Oakland, CA. Damitz, B., D. Furukawa, and J. Toal Desalination Feasibility Study in the Monterey Bay Region. Association of Monterey Bay Area Governments, Marina, CA. Einav, R., K. Harussi, and D. Perry The footprint of the desalination processes on the environment. Desalination 152: Fernandez-Torquemada, Y., J. L. Sanchez-Lizaso, and J. M. Gonzalez-Correa Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of Alicante (SE Spain). Desalination 182: Hoepner, T., and J. Windelberg Elements of environmental impact studies on coastal desalination plants. Desalination 108: Jenkins, P. D., Scott A Dilution modeling of brine discharge from desalination plants in southern California coastal waters. in Evaluating Environmental Issues with Desalination in California, Santa Cruz, CA. Khan, S., D. Waite, G. Leslie, and R. Cox Management of Concentrate Waste Streams from Desalination and Water Recycling Membrane Treatment Systems. Report Prepared for Queensland Environmental Protection Agency and ARUP. Draft No. 3. Report Number: CWWT2006/3. 28 February Latorre, M Environmental impact of brine disposal on Posidonia seagrasses. Desalination 182: Malfeito, J. J., J. Diaz-Caneja, M. Farinas, Y. Fernandez-Torrequemada, J. M. Gonzalez-Correa, A. Carratala-Gimenez, and J. L. Sanchez-Lizaso Brine discharge from the Javea desalination plant. Desalination 185:

7 Mauguin, G., and P. Corsin Concentrate and other waste disposals from SWRO plants: characterization and reduction of their environmental impact. Desalination 182: Mickley, M Membrane Concentrate Disposal: Practices and Regulation. USBR Desalination and Water Purification Research and Development Program Report No. 123, 2 nd Ed. April Available at: < Miri, R., and A. Chouikhi Ecotoxicological marine impacts from seawater desalination plants. Desalination 182: NRC (National Research Council) Desalination: A National Perspective. Washington, D.C.: National Academy Press. Available: < Purnama, A., and H. H. Al-Barwani Some criteria to minimize the impact of brine discharge into the sea. Desalination 171: Raventos, N., E. Macpherson, and A. Garcia-Rubies Effect of brine discharge from a desalination plant on macrobenthic communities in the NW Mediterranean. Marine Environmental Research 62:1-14. Roberts, P.J.W., A. Ferrier, and G. Daviero Mixing in inclined dense jets. Journal of Hydraulic Engineering, 123(8): Sadhwani, J. J., J. M. Veza, and C. Santana Case studies on environmental impact of seawater desalination. Desalination 185:1-8. Voutchkov, N. Date unknown. Innovative Method for Evaluation of Tolerance of Marine Organisms to Desalination Plant Discharges. Voutchkov, N Alternatives for ocean discharge of seawater desalination plant concentrate. In Proceedings of 20th Annual WateReuse Symposium Water Reuse & Desalination: Mile High Opportunities. Denver, Colorado, Sep 18-21, 2005: WateReuse Association. WHO (World Health Organization), Desalination for Safe Water Supply: Guidance for the Health and Environmental Aspects Applicable to Desalination. WHO/SDE/WSH/07/0?, Geneva. Available at: < Xu, P., T. Cath, G. Wang, J.E. Drewes and S. Dolnicar Critical Assessment of Implementing Desalination Technology. Denver, Colorado: Water Research Foundation 7

8 Younos, T Environmental issues of desalination. University Council on Water Resources Journal of Contemporary Water Research and Education 132: