MPRWA DEIR Review 3 Brine Disposal

8/21/2019 MPRWA DEIR Review 3 Brine Disposal

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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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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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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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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

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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 …

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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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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

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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)

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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)

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Potential Weaknesses

Existing ports are horizontal which is not optimal for

negatively-buoyant discharges

Consider retrofit with inclined ports if additional dilution is

required

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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

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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

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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

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Far Field Approach


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)

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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

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Appendix D1, page 8


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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

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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)

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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)

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Sediment oxygen demand

Entrainment of dissolved oxygen


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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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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

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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?

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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)

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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)

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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

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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

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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

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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?

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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

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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

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Recommended Minor Edits

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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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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.

MPRWA DEIR Review 3 Brine Disposal

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