Brent Alspach, PE, BCEE Director 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
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
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
WERF-15-06 Partner Agencies
• 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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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 Chloride (MWD/Skinner) Temperature
Chloride & Temperature: SWRO vs. MWD
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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 Chloride (MWD/Skinner) Temperature
Chloride & Temperature: SWRO vs. MWD
80 mg/L desirable for avocados*
100 mg/L tolerable for avocados*
* Escondido Growers for Agricultural Preservation (EGAP)
22© 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 Chloride (MWD/Skinner) Temperature
Chloride & Temperature: SWRO vs. MWD
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
0
5
10
15
20
25
30
35
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
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)
CalciumMagnesiumHardness
Calcium, Magnesium, & Hardness
Not all outliers
are of interest.
34© 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
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
36© SCMA
0
5
10
15
20
25
30
Mag
ne
siu
m(m
g/L)
Magnesium Magnesium (MWD/Skinner)
Magnesium: SWRO vs. MWD
37© SCMA
0
20
40
60
80
100
120
Sod
ium
(mg/
L)
Sodium Sodium (MWD/Skinner)
Sodium: SWRO vs. MWD
38© SCMA
0
1
2
3
4
5
6
7
8
9
10
SAR
SAR SAR (MWD/Skinner)
SAR: SWRO vs. MWD
39© SCMA
Concentrate &
Salinity Management
Session, Part 1
40© SCMA
Concentrate &
Salinity Reversal
Session, Part 1
But not uniformly across the region
41© SCMA
SDCWA Service Area
WERF-15-06 Partner Agencies
• 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.
42© SCMA
San Diego County
Water Authority
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%
0
100
200
300
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
200
300
400
500
600
700
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
46© SCMA
Key Points
…from this brief presentation
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