Napa Plant Site Desalting Modeling Summary

1. Napa Plant Site Desalting Modeling Summary November 10, 2009

2. Overview • Background • Approach to Salt Removal • Breach Concept • Field Experiments (Salt Dissolution) • 2-D Modeling

3. Background • DFG Agreement included Cargill removal of residual salt in the plant to the extent possible to facilitate restoration • Cargill successfully harvested and removed approximately 350,000 tons (since 2003) • Estimated 300,000 to 350,000 tons remain in the plant • Pickle Ponds (Unit 3, B1, B2, B3) salt removed • Residual salt remains in crystallizer beds with 2 to 6-inch salt crust • Continued harvesting not physically possible • Cargill explored other ways to meet desalination obligation

4. Background Approach to Salt Removal • Other salt pond breach successes • NSM Pond 4 - temporary, localized effects (within natural variability at 5 days; ambient at 26 days) • NPS Ponds 9 and 10 - met RWQCB requirements within 24 hrs • Develop breach concept to minimize impacts • Field experiments to understand salt crust dissolution • Redwood City • Napa Plant Site • Modeling to size breach for minimal impact • 2-D Model • Validation

5. Napa River Tidal Exchange Two layers exist within Site Less Saline Layer Mudflat Weir High Saline Layer Dissolution tons/day Crystallizer Bed Salt Crust Breach Concept Mudflat Breach

6. Field Experiments • Goal: better understand expected salt dissolution mechanism and rates • Redwood City crystallizer dissolution tests showed dissolution rate over first 12 days <0.05 in/day • Napa dissolution tests showed: • More dissolution in higher velocity areas • Clear stratification within the test area • Middle and top salinity levels 30 to 44 ppt

7. 2-D Modeling • Advection/Dispersion Model • Objective: Evaluate breach concept for desalting the South Unit given restoration breach location • 2-Dimensional for internal Plant Site and Napa River • 1-Dimensional for sloughs and external ponds

8. 2-D Modeling Assumptions • Dissolution is the primary mechanism for salt loss • Salt dissolves at a constant rate (0.05 in/day) • Stratified high salinity layer within internal Plant Site remains throughout simulation • Low velocities exist within internal Plant Site • External breach occurs at Mudflat elevation • Internal breaches per proposed Restoration Plan

9. 2-D Modeling Input Data • Modeling Period (August-October 2000) • Flow (USGS Gauging Stations at Oak Knoll Avenue and Agua Caliente) • Tides (NOAA Tide Stations at Mare Island and mouth of Sonoma Creek) • Ambient salinity (USGS Mare Island Causeway Station) • Seasonally variability > 20 ppt • Daily variability on the order of 5 ppt • Salt dissolution (Schaaf & Wheeler)

10. Salt Mass Estimate B-1 B-2 Unit 3 B-3

11. Rate of Salt Dissolution B-1 & B-2 Salt Mass Dissolved Unit 3 Salt Mass Dissolved B-3 Salt Mass Dissolved Crystallizer Beds Salt Mass Dissolved

12. Input Data -Salinity Average Salinity Readings at Mare Island Causeway Station Salinity Data Typical (1999-2005) Seasonal Variability of 20 ppt

13. Input Data - Salinity Daily Variability of 5 ppt

14. Model Results

15. Modeling Results Evaluation Points Internal External (Breach & River)

16. Modeling Results - Salinity

17. Modeling Results - SalinityMaximum Salinity – after 6 days 70-foot Breach

18. Modeling Results - Salinityafter 8 days 70-foot Breach

19. Modeling Results - Salinityafter 28 days 70-foot Breach

20. Modeling Results - Salinityafter 42 days 70-foot Breach

21. Modeling Results – Location C Loc. C Loc. A Loc. B

22. Loc. C Loc. A Loc. B Modeling Results – Location B

23. Loc. C Loc. A Loc. B Modeling Results – Location A

24. 2-D Modeling Experience demonstrates saline brines can be released in an environmentally acceptable manner Field experiments clarified dissolution mechanism and rates Modeling results showed that Salinity within Napa River remains within natural variability

25. Questions?

26. Input Data - Flow Flow Data Typical (1999-2005)

27. Input Data - Tidal Tidal Data Typical per Historical Means