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DRAFT
Review of Brine Disposal System
DEIR, Monterey Desal Project
DRAFT Presentation to Monterey
Peninsula Regional Water Authority
23 June 2015
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DRAFT
Outline
Brine Disposal System Overview
Critical Issues
Near Field Approach
Semi-Empirical Analysis Conservative assumptions
Potential weaknesses
Far Field Approach
Conservative assumptions
Potential weaknesses
Results and Mitigation
Conclusions
Recommendations
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DRAFT
Brine Disposal System
3
Monterey Regional Water Pollution Control Agency’s
(MRWPCA) ocean outfall and diffuser (existing)
Diffuser
1,100 ft long 90 – 110 ft deep
172 ports total
130 ports open
8 ft port spacing
Alternating sides
Horizontal discharge
3.5 to 4 ft above
sea floor Source: Appendix D2
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DRAFT
Brine Disposal System
4
Buoyancy
Wastewater floats
High dilution
Brine sinks
Lower dilution
Blend can do either
wastewater
brine
Source: modified from Appendix D2
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DRAFT
Discharge Composition
5
Source: Modified from Appendix D4
eosyntec C
consultants
Tab
le
ode
led fl
ow
scenari
s
fo r
the
PWSP
RTP
design capa city witho
ut
Desai B
ne
9 6 0 1
2
Desa i Brine wi
th
no
seco
n
da
ry efflue
nt
13 98 0 1
3
Desa
i Brinewi
th
l
ow seco
nd
ary
e
ffl
uent
2 13 98 0 1
4 Desa i Brinewith highsecondary effluent b 19 68 13 98 0 1
Table M ode led fl
ow
scenari sfor the Vari
ant pr
oject
D
esa
i B
ri
neonly
8
99
0 1
2
Desai Brine wi
th
high
seco
ndary effluent b
19 68 8 99 0 1
3
D
esa
i B
ri
ne with
GWR
Concentra
te
and
15 9 8 99 0 94° 0 1
high secondary effluent
4
Desai Brine with GWR oncentrate and
8
99
0 94c
0 1
no
seco
ndary effluent
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DRAFT
Terminology
6
Source: Abessi & Roberts (2014)
Near Field Far Field
Source: Jenkins and Wasyl (2009).
Dominated by jets
Short time and length
scales
Seconds to minutes
Feet to tens of feet
Dominated by ocean processes
Long time and length scales
Hours to days
Hundreds of feet to miles
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Critical Issues
Near Field (mixing due to jet/plume velocity/buoyancy)
Achieving targets at edge of “brine mixing zone” (defined as
the lesser of the zone of initial dilution (ZID) and 100 m)
Change in salinity < 2.0 ppt (SWRCB March 2015
recommendation)
Concentrations for numerous constituents as per 2012
California Ocean Plan
Edge of ZID governs (ZID within 100 m)
Critical case is when plume sinks
7
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Critical Issues
Far Field (mixing due to ambient ocean currents)
Hypoxic: low dissolved oxygen concentration
Density currents
Pooling due to bathymetry
8
May 5, 2015 Draft Final Desalination
Amendment to the Ocean Plan
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Near Field Approach
Rising positively-buoyant plume
When volume of blended wastewater is large enough plume
will rise
Analyzed using Visual Plumes (VP)
Well accepted for rising (buoyant) plumes
Used appropriate ambient salinity and temperature conditions
Assumed zero ambient cross-flow (conservative assumption)
Large dilution (≥ 68) at edge of ZID is achieved
Salinity and Ocean Plan objectives easily met
9
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Near Field Approach
Sinking negatively-buoyant plume
Considered two approaches:
Visual Plumes (VP)
VP is well-validated for rising plumes
Less validation for sinking plumes (especially for horizontaldischarge)
Compelling evidence that dilution from VP is substantially under-
estimated for negatively-buoyant discharges (Palomar et al., 2012)
CORMIX, CORJET, and JetLag also substantially underestimate
Dilution results from VP were not used
Semi-empirical analysis
Based on analysis by Kikkert et al., (2007) and Fischer et al., (1979)
Approach is reasonable …
10
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Semi-Empirical Analysis (Near Field)
Plume trajectory based on
analysis by Kikkert et al. (2007)
Well validated by experiments
Dilution based upon analysis
for non-buoyant jet (Fischer et
al., 1979) using plume length
calculated along trajectory
Fischer approach is reasonable due to flat trajectory
[vertical distance (3.5 feet)
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Semi-Empirical Analysis (Near Field)
Conservative assumptions
Dilution calculation assumed round jet, whereas jet is oval
shaped
Oval shape has higher area to volume ratio and will achieve
more dilution than circular shape
Assumed minimum height above sea-floor of 3.5 feet (only
19 ports have height of 3.5 feet, most ports have height
nearer to 4 feet)
Larger height will allow for longer travel distance and moredilution
12
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Semi-Empirical Analysis (Near Field)
Conservative assumptions
The dilution at the impact point was used in the analysis.
However, the near-field continues beyond the impact point
(the flow and mixing are still dominated by jet processes)
and additional dilution will occur within the near field (i.e.,the ZID is larger than assumed)
“the increase in dilution
from the impact point to
the end of the near field
is approximately 60%for nonmerged jets”
(inclined jets,
Abessi & Roberts, 2014)
13
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Semi-Empirical Analysis (Near Field)
Potential Weaknesses
Analysis used in DEIR to assess merging of jets is ad-hoc
Volume of water entrained in 10 seconds was compared to
volume of water available per port
Merging of jets will reduce dilution
Recommend replacing analysis in EIR with improved Port
Spacing Analysis by Geosyntec (provided on Slide 16)
Coanda effect is not addressed in DEIR
Coanda effect is the tendency for a jet to deviate towards andattach to near surfaces (in this case the sea-floor)
Coanda attachment would reduce dilution
Recommend including new Coanda Analysis by Geosyntec in
EIR (provided on Slide 17)
14
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Semi-Empirical Analysis (Near Field)
Potential Weaknesses
Existing ports are horizontal which is not optimal for
negatively-buoyant discharges
Consider retrofit with inclined ports if additional dilution is
required
15
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Port Spacing Analysis
Based on experiments Abessi & Roberts (2014)
recommend the following to avoid merging of jets;
s >~2.d.F
where s = spacing, d = port diameter, and F = densimetric
Froude number
d = 1.86 inches (Appendix D2, Table 3)
F ≈ 26 (Appendix D1, Table 5)
→ s > ~ 8 ft
Port spacing on diffuser is 16 ft (alternating sides)
Jets will not merge
Same conclusion as in DEIR, but this analysis is more robust
16
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Coanda Analysis
Based on experiments Shao & Law (2011) recommend
the following minimum clearance above the sea-floor to
prevent Coanda attachment;
z0 > 0.12 (π/4)0.25 d.F = 0.11 d.F
where, d = port diameter, and F = densimetric Froudenumber
d = 1.86 inches (Appendix D2, Table 3)
F ≈ 26 (Appendix D1, Table 5)
→ z0 > ~ 0.5 ft
Ports are 3.5 ft above sea-floor
Coanda attachment will not occur
Include this analysis in EIR
17
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Far Field Approach
Uses regional ocean model (ROM) to extract time-series
of horizontal velocities (u and v) at diffuser location
Examines different seasonal patterns
Oceanic, Davidson, Upwelling
Assumes the velocity field (u,v) is spatially homogeneous
Generally conservative assumption
Neglects local variations in bathymetry
Bathymetry in vicinity of brine plume is generally flat (no
depressions or ridges) and sloping to sea
Brine plume does not extend to Monterey Canyon
Diffuser structure may act as a ridge to trap brine locally
Solves 2-D advection-diffusion
18
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Far Field Approach
Conservative assumptions
Neglects vertical mixing
Mixing and dilution underestimated away from the diffuser
Stability was examined via computing Richardson number
Uses low-end lateral diffusion coefficient
1.37 m2/s (versus 2 m2/s measured by Ledwell et al., (1998))
Neglects wave action
Waves provide additional mixing
Neglects gravity current
Gravity current would tend to move brine away from diffuser
more quickly (down-slope)
19
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Far Field Potential Weaknesses
Present analysis is “dated”
Modern approach would use full 3D model including density
effects and spatially varying velocity field
However, present analysis is generally conservative
3D model will likely result in additional dilution
Neglects gravity currents
Unlikely to affect conclusions, since bathymetry is generally
flat in vicinity of diffuser
Brine plume does not reach Monterey Canyon
20
Appendix D1, page 8
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Far Field Potential Weaknesses
Brine particles are only tracked for 48 hours
Simulation period is 90 days
What happens to particle after 48 hours?
If particle simply disappears then will the extent of the plume be
underestimated?
Unlikely to affect conclusions, since exceedances are
governed by near field
21
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DRAFT
Far Field Potential Weaknesses
Local trapping of brine by diffuser structure was not fully
addressed
Trapping is minimized by aligning diffuser structure with
slope (perpendicular to shore)
Recommend adding discussion of this issue consideringcurrent directions (from ROM) with respect to diffuser
alignment and tidal reversals
Potential for hypoxia was not addressed Recommend including Hypoxia Analysis by Geosyntec in
EIR (provided on Slides 23-25)
22
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DRAFT
Hypoxia Analysis
Potential for hypoxia can be addressed using simple
mass balance approach;
Estimate oxygen demand from sediments
Estimate oxygen supplied by brine plume (including entrained
flow)
23
Sediment oxygen demand
Entrainment of dissolved oxygen
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DRAFT
Hypoxia Analysis
Sediment oxygen demand (SOD) in Monterey Bay
5.0 to 13.5 mmol/m2/day (Berelson et al., 2003)
0.16 to 0.43 g/m2/day
Areal extent of plume
~3,000 ft x 1,500 ft = 4,500,000 ft2
~420,000 m2
Mass flux consumed;
70 to 180 kg/day
24
Figure 4.3-5
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DRAFT
Hypoxia Analysis
Brine flow rate = 13.98 MGD
Dilution > 15
Entrained flow > 15 x 13.98 = 210 MGD = 9.2 m3/s
Ambient dissolved oxygen concentration > 7 mg/L lower limit of Ocean Plan
Mass flux supplied;
> 5,600 kg/day
Oxygen supplied by entrained flow > 30 times greater
than oxygen consumed by sediments
Hypoxia unlikely
25
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DRAFT
Results and Monitoring
Results of analyses indicate some exceedances of
Ocean Plan criteria at edge of ZID are possible for
certain constituents;
Copper, Ammonia, Chlordane, DDT, PCBs, TCDD
Equivalents, Toxaphene
Depends upon Project versus Variant and on flow blends
Monitoring program may indicate no exceedances
Many conservative assumptions in analysis
Drawing source water through sand/sediments will likely
remove some PCBs
Will this cause a build up of PCBs in sediments?
26
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DRAFT
Mitigation Measures
Proposed Mitigation Measure 4.3-4
Additional pre-treatment of source water
Treatment of discharge
Temporary storage and release of brine
3 million gallon brine storage basin
Store 5 to 8 hours of flow
Can pulsing achieve necessary dilutions?
Recommend conducting additional near-field analysis to
demonstrate (if necessary)
Consider retrofit of diffuser to add inclined ports
60o – 65o is optimal for negatively-buoyant
Need to also consider buoyant cases (trade-off)
27
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DRAFT
Brine Disposal System - Conclusions
Brine disposal governed by near field
Concentrations at ZID
DEIR used two methodologies for near field Visual Plumes for rising discharges
Semi-empirical analyses for sinking discharges
Trajectory for sinking plume from Kikkert et al., (2007)
Dilution for sinking plume estimated using method for non-
buoyant jet (Fischer et al., 1979)
28
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DRAFT
Brine Disposal System - Conclusions
Near field analyses make reasonable and conservative
assumptions
Round jets (instead of oval)
Minimum height of port above sea-floor of 3.5 feet ZID defined as jet impact point and not end of near field
29
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DRAFT
Brine Disposal System - Conclusions
Near field analysis of merging jets was ad-hoc New analysis by Geosyntec indicates jets will not merge
Near field analysis of Coanda attachment was not
included
Analysis by Geosyntec indicates Coanda attachment will not
occur
Near field analysis was not performed to demonstrate
extent of increased dilution due to pulsing
Mitigation measure 4.3-4
30
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DRAFT
Brine Disposal System - Conclusions
Far field analyses makes conservative assumptions
No vertical mixing of brine
Low-end estimate for horizontal diffusivity
Neglects wave action
No density current*
Far field method is “dated”
3D simulations including density currents could be used 3D simulations would likely result in more dilution
Flat bathymetry in the vicinity of the diffuser and conservative
assumptions
31
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DRAFT
Brine Disposal System - Conclusions
Potential for hypoxia not discussed
Analysis by Geosyntec indicates hypoxia is unlikely
Brine trapping by diffuser structure not analyzed Minimized by aligning diffuser structure with slope
(perpendicular to shore)
Brine particles are only tracked for 48 hours
What happens to particle after 48 hours?
32
Brine Disposal System
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DRAFT
Brine Disposal System -
Recommendations
Include the following analyses provided by Geosyntec
Port merging
Coanda effect
Hypoxia
Address/discuss potential for build up of PCBs in
sediments surrounding intakes
Conduct additional near field analysis to estimate
additional dilution achievable by pulsing brine discharge
Consider retrofit of diffuser ports with inclined angles to
achieve more dilution if necessary
33
Brine Disposal System
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DRAFT
Brine Disposal System -
Recommendations
Add discussion of potential for diffuser structure to trap
brine
Consider current directions (from ROM) and bathymetry
slope with respect to diffuser alignment and tidal reversals
Consider using 3D far field model
Will likely result in additional dilution
Will better address potential for brine trapping by diffuser
structure
Add discussion of the effect of only tracking brine
particles for 48 hours
34
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DRAFT
Recommended Minor Edits
35
Issue Descr ipt ion Page Comments / RecommendationsIncorrect
interpretation
of SWRCB
2012a
SWRCB 2012a states that increase
in salinity should be limited to < 5%
of background, corresponding to 1.7
ppt in California waters. The DEIR
then rounds this to 2.0 ppt, but this
is an incorrect interpretation of the
2012 document (i.e., it should be 1.7
ppt).
4.3-27 The phrase, “(rounded to 2.0 ppt)” should be
removed from the EIR. Note that SWRCB 2015
refers directly to 2.0 ppt (it does not refer to 5% or
1.7 ppt). That is, 2.0 ppt is the correct target per
SWRCB 2015, but not per SCWRCB 2012a.
Different
number of
ports
The correct number of open ports
(130) is first mentioned in Section
4.3. This is late in the report to
mention the change (from 120) and
surprises the reader.
4.3-72 The incorrect number of ports should be mentioned
earlier in the EIR, including in the Executive
Summary. It should also be re-iterated that using
130 instead of 120 provides additional dilution (as
demonstrated in Addendum to Appendix D4).
Misleading
statement
overstates theextent of the
plume
The DEIR states, “where the plume
extended from near the Monterey
Submarine Canyon rim to the centerof the southern half of Monterey
Bay”. This statement overstates the
extent of the plume, and is perhaps
mistakenly based on the inset figure.
4.3-88 Revise wording to better indicate that the plume
extent is several miles from the Monterey Submarine
Canyon rim.
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DRAFT
Recommended Minor Edits
36
Issue Descr ipt ion Page Comments / RecommendationsUnnecessary
footnote in
table
See Comments / Recommendations Table
4.3-11
Footnote ‘a’ should be removed and the column
header changed from “Average Dilution” to
“Centerline Dilution”.
Equation for
centerline
dilution not
provided
Equation (7) presented in Appendix
D2 is for average dilution, whereas
calculations provide centerline
dilution (which is ~1.4 times lower
(Fischer et al., 1979)).
App D2,
pages 10
and C-13
EIR should be modified to include the relation
between average and centerline dilution.
Apparent
discrepancy in
port and
duckbill size
4 inch duckbill valves are specified,
but the port size is given as 2 inch.
App D2 This discrepancy should be corrected or explained.
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References
1. Abessi & Roberts (2014), Multiport Diffusers for Dense Discharges, J. Hydraul. Eng. 04014032-1.
2. Berelson, McManus, Coale, Johnson, Burdige, Kilgore, Colodner, Chavez, Kuleda, Boucher
(2003), A time series of benthic flux measurements from Monterey Bay, CA, Continental Shelf
Research 23 (2003) 457-481.
3. Fischer, List, Koh, Imberger, Brooks (1979), “Mixing in Inland and Coastal Waters”, Academic
Press
4. Jenkins & Wasyl (2009), Current Analysis for Receiving Water of the Santa Cruz SeawaterDesalination Project, submitted to City of Santa Cruz, 49 pp + app.
5. Kikkert, Davidson, Nokes (2007), Inclined Negatively Buoyant Discharges, J. Hydraul. Eng.
2007.133:545-554.
6. Ledwell, Watson, Law, Law, (1998), Mixing of a tracer in the pycnocline, Journal of Geophysical
Research, 103(C10), 21499-21529.
7. Palomar, Lara, Losada (2012), Near field brine discharge modeling part 2: Validation of
commercial tools, Desalination 290 (2012) 28-42.
8. Shao & Law (2011), Boundary impingement and attachment of horizontal offset dense jets,
Journal of Hydro-environment Research 5 (2011) 15-24.