water quality considerations for integrating desalinated ... · •nikolay voutchkov water globe...

Brent Alspach, PE, BCEEDirector of Applied Research

Arcadis

Carlsbad, CA

Water Quality Considerations for

Integrating Desalinated Seawater from the

Carlsbad SWRO Plant into

Existing Regional Supplies

February 8, 2018

Brent Alspach, PE, BCEEDirector of Applied Research

Arcadis

Carlsbad, CA

February 8, 2018

Case Study of the City of Carlsbad and

Surrounding Areas’ Experience with Integrating

Desalinated Seawater Supply

in Municipal Distribution Systems

WERF-15-06

Case Study of the City of Carlsbad and

Surrounding Areas’ Experience with Integrating

Desalinated Seawater Supply

in Municipal Distribution Systems

5© SCMA

Acknowledgements

Research Team

• Brent Alspach, PI Arcadis

• Greg Imamura Arcadis

• Chris Hill Arcadis

• Dr. Jerry Speitel U. of Texas

Water Research Foundation

• Kristan VandenHeuvel, PM

6© SCMA

Acknowledgements

Project Advisory Committee

• Wendy Chambers Carlsbad Municipal Water District

• Dr. Robert Cheng Coachella Valley Water District

• Dr. Christine Owen Tampa Bay Water1

• Nikolay Voutchkov Water Globe Consulting

• Justin Pickard Water Systems Consulting2

1 Formerly of Tampa Bay Water

2 Formerly of West Basin Municipal Water District

7© SCMA

Acknowledgements

Partner Agencies

Carlsbad Municipal Water District

City of San Diego

Helix Water District

Olivenhain Municipal Water District

Otay Water District

Poseidon Water

Rincon del Diablo Municipal Water District

San Diego County Water Authority

Sweetwater Authority

Vallecitos Water District

8© SCMA

SDCWA Service Area

WERF-15-06 Partner Agencies

Carlsbad SWRO Plant

50 MGD

(Poseidon Water)

Twin Oaks Valley WTP

100 MGD

(SDCWA)

9© SCMA

SDCWA Service Area


• Member Agencies that have

their own surface water

treatment plants typically

purchase raw water exclusively.

• Member Agencies that do not

have surface water treatment

plants purchase treated water

exclusively.

Agencies that purchase treated

water will sometimes receive

100% SWRO water.

10© SCMA

Flow Analysis: Key Points

• SWRO water constitutes a significant percentage of

treated water purchased by SDCWA

Member Agencies.

• The % contribution of SWRO water can vary widely.

• Member Agencies that purchase treated water may

receive 100% SWRO water.

SWRO water will have a significant influence

on blended water quality.

11© SCMA

Concentrate &

Salinity Management

Session, Part 1

12© SCMA

Concentrate &

Salinity Management

Session, Part 1

13© SCMA

Preliminary Data

14© SCMA

Carlsbad SWRO Plant

15© SCMA

0

5

10

15

20

25

30

35

Tem

pe

ratu

re(°

C)

Temperature

16© SCMA

0

100

200

300

400

500

600

700

TDS,

Co

nd

uct

ivit

y(m

g/L,

µS/

cm)

TDS Conductivity

TDS & Conductivity

17© SCMA

0

100

200

300

400

500

600

700

TDS,

Co

nd

uct

ivit

y(m

g/L,

µS/

cm)

TDS Conductivity TDS (MWD/Skinner)

TDS & Conductivity

18© SCMA

0

20

40

60

80

100

120

Ch

lori

de

(mg/

L)Chloride

19© SCMA

0

5

10

15

20

25

30

0

20

40

60

80

100

120

Tem

pe

ratu

re(°

C)

Ch

lori

de

(mg/

L)

Chloride

Temperature

Chloride & Temperature

0

5

10

15

20

25

30

0

20

40

60

80

100

120

Tem

pe

ratu

re(°

C)

Ch

lori

de

(mg/

L)

Chloride Temperature

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30

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20

40

60

80

100

120

Tem

pe

ratu

re(°

C)

Ch

lori

de

(mg/

L)

Chloride Chloride (MWD/Skinner) Temperature

Chloride & Temperature: SWRO vs. MWD

21© SCMA

0

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Tem

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ratu

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Ch

lori

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(mg/

L)



80 mg/L desirable for avocados*

100 mg/L tolerable for avocados*

* Escondido Growers for Agricultural Preservation (EGAP)

22© SCMA

0

5

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30

0

20

40

60

80

100

120

Tem

pe

ratu

re(°

C)

Ch

lori

de

(mg/

L)



80 mg/L desirable for avocados*

100 mg/L tolerable for avocados*

Thresholds exceeded during

the summer when irrigation peaks

* Escondido Growers for Agricultural Preservation (EGAP)

23© SCMA

Boron

24© SCMA

About Boron

Reference PointBoron

Conc.Notes

Seawater ~ 4.5 mg/L

California Standard 1 mg/L

SWRO Permeate varies Best case rejection: 80-90% (ideal)

Carlsbad WPA

Limits

“Central

Tendency”0.75 mg/L Acceptable in ≤ 50% of samples

“Extreme” 1.0 mg/L Acceptable in ≤ 5% of samples

What You Need to Know

• Poorly rejected by RO membranes

• Adverse impact on irrigated plants

25© SCMA

Boron and Irrigated Plants

Cash Crop Value1 Rank1 % of Total1

Ornamental trees and shrubs $425M 1 23%

Indoor flowering plants $329M 2 18%

Avocados $198M 4 11%

Lemons $80M 6 4%

Local Impact

• San Diego area economy has a significant agriculture component

• Many valuable crops are among the most boron-sensitive, with

adverse effects from concentrations in the 1-2 mg/L range

1 2013 Crop Statistics and Annual Report. County of San Diego Dept. of Agriculture, Weights, and Measures

26© SCMA

Boron and Irrigated Plants

Cash Crop Value1 Rank1 % of Total1

Ornamental trees and shrubs $425M 1 23%

Indoor flowering plants $329M 2 18%

Avocados $198M 4 11%

Lemons $80M 6 4%

Local Impact

• San Diego area economy has a significant agriculture component

• Many valuable crops are among the most boron-sensitive, with

adverse effects from concentrations in the 1-2 mg/L range

1 2013 Crop Statistics and Annual Report. County of San Diego Dept. of Agriculture, Weights, and Measures

Boron is a potential

concern for 56% of the

region’s cash crop.

27© SCMA

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Bo

ron

(mg/

L)Boron

28© SCMA

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Bo

ron

(mg/

L)Boron

29© SCMA

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5

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30

35

0

0.1

0.2

0.3

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0.5

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1

Tem

pe

ratu

re(°

C)

Bo

ron

(mg/

L)

BoronTemperature

Boron

30© SCMA

Sodium Adsorption Ratio (SAR)

31© SCMA

Sodium Adsorption Ratio (SAR)

What You Need to Know

• Quantifies the suitability of irrigated water relative to sodium

• Lower values are desirable

• Many boron-sensitive plants are also susceptible to sodium effects

][][2

1

][

22

MgCa

NaSAR

Carlsbad SWRO Requirements

• [Ca] > 40 mg/L in 10% of samples

• No specification for [Mg] or [Na]

32© SCMA

0

20

40

60

80

100

120

140

160

180

200

Cal

ciu

m, M

agn

esi

um

, Har

dn

ess

(mg/

L -C

aCO

₃, m

g/L,

mg/

L -C

aCO

₃)

CalciumMagnesiumHardness

Calcium, Magnesium, & Hardness

33© SCMA

0

20

40

60

80

100

120

140

160

180

200

Cal

ciu

m, M

agn

esi

um

, Har

dn

ess

(mg/

L -C

aCO

₃, m

g/L,

mg/

L -C

aCO

₃)



Not all outliers

are of interest.

34© SCMA

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20

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200

Cal

ciu

m, M

agn

esi

um

, Har

dn

ess

(mg/

L -C

aCO

₃, m

g/L,

mg/

L -C

aCO

₃)



WERF-15-06 objectives are not:

• Optimization

• Troubleshooting

• Compliance

35© SCMA

0

10

20

30

40

50

60

70

80

90

Cal

ciu

m(m

g/L)

Calcium Calcium (MWD/Skinner)

Calcium: SWRO vs. MWD

41© SCMA

SDCWA Service Area


• Member Agencies that have

their own surface water

treatment plants typically

purchase raw water exclusively.

• Member Agencies that do not

have surface water treatment

plants purchase treated water

exclusively.

Agencies that purchase treated

water will sometimes receive

100% SWRO water.

Salinity reversal induced

by SWRO blending

benefits agencies that

purchase treated water.

43© SCMA

0

5

10

15

20

25

30

35

Tem

pe

ratu

re(°

C)

SWRO Plant Effluent TOVWTP After Blending Otay Intake

Temperature

44© SCMA

0%

20%

40%

60%

80%

100%

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400

500

600

700

800

900

Pe

rce

nt

De

salin

ate

d S

eaw

ater

TDS

(mg/

L)

SWRO Plant Effluent Otay Intake MWD/Skinner % Desal (7-Day Avg)

TDS

45© SCMA

0%

20%

40%

60%

80%

100%

0

100

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800

900

Pe

rce

nt

De

salin

ate

d S

eaw

ater

TDS

(mg/

L)

SWRO Plant Effluent Otay Intake % Desal (7-Day Avg)

TDS

TDS Influences:

• % SWRO water

• Temperature

47© SCMA

• Water temperature can affect the ability of a SWRO process

to achieve finished water quality objectives.

• The components of salinity are also important:

− Chloride

− Boron

− Calcium, magnesium, sodium (via SAR)

• The use of SWRO as a means of salinity management may

not benefit an entire service area evenly.

• Salinity reversal can have unintended benefits

(e.g., demand reduction)

Key Points

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