Napa Plant Site Desalting Modeling Summary

November 10, 2009

Overview

1. Background2. Approach to Salt Removal3. Breach Concept4. 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

BackgroundApproach 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 LayerMudflat Weir

High Saline Layer

Dissolutiontons/day

Tidal Exchange Two layers exist within Site

MudflatBreach

• 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

Beds Salt Mass (tons)

B1+B2 16,000

B3 32,000

Unit 3 32,000

Crystallizers 240,000

Total 320,000 Unit 3

B-2

B-3

B-1

-

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

8/16/2000 8/26/2000 9/5/2000 9/15/2000 9/25/2000 10/5/2000 10/15/2000

Date

Dis

solu

tion

Rat

e (to

n/da

y)

Rate of Salt DissolutionB-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 (1999-2005)

Seasonal Variability of 20 ppt

Average Salinity Readings at Mare Island Causeway Station

Input Data - Salinity

Daily Variability of 5 ppt

Model Results

Location B: Napa River Outside Mudflat

Location A: Napa River Upstream

Location C: Outside Primary Breach

Notch

CCBB22 CCBB11

CCBB77

CCBB44

CCBB33

CCBB66 CCBB55

CCBB88 CCBB99 UUnniitt 33

BB--33

BB--22

Modeling ResultsEvaluation Points

Internal

External (Breach & River)

Modeling Results - Salinity

Location B: Napa River Outside Mudflat

Location A: Napa River Upstream

Location C: Outside Primary Breach

Notch

CCBB22 CCBB11

CCBB77

CCBB44

CCBB33

CCBB66 CCBB55

CCBB88 CCBB99 UUnniitt 33

BB--33

BB--22

PaletteAbove 30

29 - 3028 - 2927 - 2826 - 2725 - 2624 - 2523 - 2422 - 2321 - 2220 - 2119 - 2018 - 1917 - 1816 - 17

Below 16Undefined Value

8/22/2000 2:00:00 AM, Time step: 146, Layer: 0

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Salt

70-foot Breach

Modeling Results - SalinityMaximum Salinity – after 6 days

PaletteAbove 30

29 - 3028 - 2927 - 2826 - 2725 - 2624 - 2523 - 2422 - 2321 - 2220 - 2119 - 2018 - 1917 - 1816 - 17

Below 16Undefined Value

8/22/2000 2:00:00 AM, Time step: 146, Layer: 0

20 40 60 80 100 120 140 160 180(Grid spacing 20 meter)

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Salt

70-foot Breach

Modeling Results - Salinityafter 8 days

PaletteAbove 30

29 - 3028 - 2927 - 2826 - 2725 - 2624 - 2523 - 2422 - 2321 - 2220 - 2119 - 2018 - 1917 - 1816 - 17

Below 16Undefined Value

8/22/2000 2:00:00 AM, Time step: 146, Layer: 0

20 40 60 80 100 120 140 160 180(Grid spacing 20 meter)

480

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Salt

70-foot Breach

Modeling Results - Salinityafter 28 days

PaletteAbove 30

29 - 3028 - 2927 - 2826 - 2725 - 2624 - 2523 - 2422 - 2321 - 2220 - 2119 - 2018 - 1917 - 1816 - 17

Below 16Undefined Value

8/22/2000 2:00:00 AM, Time step: 146, Layer: 0

20 40 60 80 100 120 140 160 180(Grid spacing 20 meter)

480

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510

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Salt

70-foot Breach

Modeling Results - Salinity after 42 days

Location B: Napa River Outside Mudflat

Location A: Napa River Upstream

Location C: Outside Primary Breach

Notch

CCBB22 CCBB11

CCBB77

CCBB44

CCBB33

CCBB66 CCBB55

CCBB88 CCBB99 UUnniitt 33

BB--33

BB--22

Loc. A

Loc. C

Loc. B

Modeling Results – Location C

Location B: Napa River Outside Mudflat

Location A: Napa River Upstream

Location C: Outside Primary Breach

Notch

CCBB22 CCBB11

CCBB77

CCBB44

CCBB33

CCBB66 CCBB55

CCBB88 CCBB99 UUnniitt 33

BB--33

BB--22

Loc. A

Loc. C

Loc. B

Modeling Results – Location B

Location B: Napa River Outside Mudflat

Location A: Napa River Upstream

Location C: Outside Primary Breach

Notch

CCBB22 CCBB11

CCBB77

CCBB44

CCBB33

CCBB66 CCBB55

CCBB88 CCBB99 UUnniitt 33

BB--33

BB--22

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. Hourly 10 Once a day for three days

Max. Tidally Averaged 4 6 days

Location B: Outside Mudflat

Max. Hourly 2 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 (1999-2005)

Input Data - Tidal

Tidal Data Typical per Historical Means