Napa Plant Site Desalting Modeling Summary November 10, 2009

Overview 1.Background 2.Approach to Salt Removal 3.Breach Concept 4.Field Experiments (Salt Dissolution) 5.2-D Modeling

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 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

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

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 Field Experiments

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

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 2-D Modeling Assumptions

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) 2-D Modeling Input Data

Salt Mass Estimate BedsSalt Mass (tons) B1+B216,000 B332,000 Unit 332,000 Crystallizers240,000 Total320,000 Unit 3 B-2 B-3 B-1

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

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

Input Data - Salinity Daily Variability of 5 ppt

Model Results

Modeling Results Evaluation Points Internal External (Breach & River)

Modeling Results - Salinity

70-foot Breach Modeling Results - Salinity Maximum Salinity – after 6 days

70-foot Breach Modeling Results - Salinity after 8 days

70-foot Breach Modeling Results - Salinity after 28 days

70-foot Breach Modeling Results - Salinity after 42 days

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

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

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

2-D Modeling 70’ Breach Maximum Salinity Difference (ppt) Max. Salinity Duration Location C: Outside Breach Max. Hourly10 Once a day for three days Max. Tidally Averaged 46 days Location B: Outside Mudflat Max. Hourly2 Once a day for two days Max. Tidally Averaged <2- Location A: Napa River Max. Hourly<2- Max. Tidally Averaged <2- 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

Questions?

Input Data - Flow Flow Data Typical ( )

Input Data - Tidal Tidal Data Typical per Historical Means