Scientific Approaches to Assess Impacts Associated with Seawater Desalination Susan C. Paulsen, Ph.D., P.E. Vice President and Senior Scientist Desal Conference October 5, 2006

Figure 2 Outline  Scientific Approaches to Address Key Management Issues:  Source Water Quality Issues  Entrainment/Impingement Issues  Receiving Water Quality Issues  Evaluation of Impacts Through Modeling

Figure 3 Evaluation of Possible Desal Configurations Intake –Co-located with power plant –Separate intake –Beach or subsurface wells Discharge –With power plant effluent –With treated wastewater –Surface discharge –Diffuser discharge Dynamics are well understood, and can be accurately modeled

Figure 4 Flow Schematic – Co-Location Source Water Power Plant Heated Water Brine Concentrate Desalination Plant Drinking Water Heated Water with Concentrate To Receiving Water Body MGD MGD 100 MGD 50 MGD

Figure 5 Intake Issues: Source Water  Contaminants may enter the plant and may or may not be removed by the desalination processes –Bacteria –Heavy metals –Etc.  Sources of Contamination –Wastewater treatment plant discharges –Storm flows, urban runoff –Recirculation –Other  Sanitary Surveys & Source Water Analyses are Conducted  DHS Approval is Required

Figure 6 Intake: Impingement and Entrainment Function of velocity, volume, location Biology! –Time of year –Duration –Local Dynamics Effects can be quantified, including cumulative impacts (studies by others – MBC, Tenera)

Figure 7 Alternatives to Ocean Intakes Test Slant Well - Section Ocean Surface Land Surface Fresh Water 200 to 250 feet ± Test Slant Well Infiltration Drill Rig Ocean Bottom Main Aquifer 40 to 130 feet ± Salt Water 23 o 350 feet ± Thanks to MWDOC

Figure 8 Slant Well Intake System Concept SOCWA Outfall Desalination Plant Site Subsurface Slant Wells & Buried Collector Intake System Thanks to MWDOC

Figure 9 Receiving Water Issues  Typically, desalination of seawater yields 50% brine (68 ppt)  Mixing in ocean is a function of density (temperature, salinity)  Unless diluted, the brine may cause an environmental impact  Besides a few added chemicals, brine is concentrated seawater Seawater Desalination Plant Brine Residue To Disposal Fresh Water

Figure 10 Use of modeling to assess impacts Model must evaluate –Near-field mixing –Far-field mixing –Stratification –Meteorological and oceanic processes Validate model against existing data Apply model to predict future conditions Used ELCOM (Estuary and Lake Computer Model) to evaluate Encina discharge

Figure 11 Case Study: Encina Power Station – Regional Seawater Desalination Project  Located at Cabrillo Power Plant  SDCWA is seeking to produce 50 MGD  Work done in conjunction with RBF Consulting  SDCWA is not pursuing project

Figure 12 Southern California Bight Region

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Figure 16 Regional Seawater Desalination Project ELCOM 328 ft (100 m) Computational Grid

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Figure 18 Model Application  Encina Desalination Plant Movie 1: Temperature Movie 2: Salinity

Figure 19 Conclusions Source and receiving water issues must be quantified Multiple configurations can be simulated Modeling needs to consider all relevant physical processes Analysis must consider hydrodynamic (physical), chemical, and biological processes Science can and should be used to quantify impacts

Figure 20 Extra Slides

Figure 21 Inflow Intrusion Source: Textbook “Mixing in Inland and Coastal Waters” by N.H. Brooks, Hugo Fischer,Bob Koh, Jorg Imberger, and John List. Pergamon Press Entrainment flow arrows added to original.

Figure 22 Receiving Water Regulations  Temperature: Thermal plan for new coastal discharges says that a plume cannot exceed 4 o F at the shoreline, the surface of any ocean substrate (including bottom) or 1,000 ft away on sea surface for more than 50% of any tidal cycle. Older plants generally have exceptions, but not all.  Salinity: There are no clear regulations for salinity. However, there are some concerns: –If maximum salinity outside of the immediate area of the discharge exceeds a ppt in the low to mid 40s, then there may be biological concerns if the exposure time is in the range of hours to days. –If the maximum possible increase is about 37 to about 40 ppt, then there may be biological concerns if the exposure is in the range of days to a week. How do we evaluate and quantify these potential impacts?

Figure 23 Evaluating Water Quality: Model Overview  Used Estuary and Lake Computer Model (ELCOM) –Developed at Centre for Water Research at University of Western Australia –In use in 60 countries –State-of-the-art code with continuous development –Applied in both research and practical applications –3-Dimensional –Solves approximate flow equations in stratified environments –Included tides, meteorological forcing, and currents

Figure 24 Regional Seawater Desalination Project Calibration Fall 2004 Comparison of Simulated to Observed Water Temperature

Figure 25 ELCOM Calibration: Temperature Profiles