1. ALDERWOOD WATER AND
WASTEWATER DISTRICT
OUTFALL UPGRADE
Seattle University Senior Design Team CEE 16.7
Kristin Ramey, Isabella Schwartz, Abbie Lorensen, Larissa
Grundell
2. Science and Engineering Project Center
College of Science and Engineering
Seattle University
Faculty Advisor: Dr. Michael Marsolek
Sponsor: Alderwood Water and Wastewater District
4. Useful Terms
Outfall: The pipe that conveys treated effluent from
the wastewater treatment plant to the Puget Sound
Diffuser: The last section of pipe that has openings to
distribute effluent into the surrounding water body
5.
6. 3,100 ft - 18” Ductile
Iron
1,300 ft - 18” Reinforced
Concrete
80’
Diffuser
4” Portholes
1972 – CAS
Facility
2013 – MBR Facility
7. Project Motivation
Structural Condition
Internal condition unknown
External inspections show signs
of corrosion
Pipe Capacity
Expanding Service Area
Corrosion of pipe to flange weld at 12
o’clock position on outfall pipe.
12. Condition Assessment
External Dive Inspection
Determine condition of submerged concrete pipe and diffuser
Results:
Flanged end of diffuser in "poor" condition with heavy corrosion
Indicates a new diffuser should be included in all design options
Internal Camera Inspection
On hold
14. Hydraulic Modeling
Purpose:
Determine capacity of the outfall
Approach:
Use PCSWMM to model dynamic outfall hydraulics
Storm Water Management Model
Constructed by the EPA
Use as-built information to construct model
Input wet weather flow data from December 2015
Apply peaking factor
25. Hand Calculations
𝒉 𝒅𝒊𝒇𝒇𝒖𝒔𝒆𝒓
Flow equally distributed at maximum capacity
Conservation of mass at each port
Ports modeled as expansions
ℎ = 𝑘
𝑉2
2𝑔
Friction losses between ports
27. Capacity Conclusions
Hydraulic modeling capacity = 11.1 MGD
Hand calculations capacity = 11 MGD
Corroborates modeling results
11 MGD capacity is less than the projected 15.8 MGD
Design options need to account for flow attenuation
30. Detention Vault Design
Purpose:
Flow attenuation is required
Approach:
Conservation of mass
Inflow – modified wet weather time series
Outflow – 10 MGD (conservative)
Q=10 MGD
Q=10 MGD
Q=15.8 MGD
30,000 gallons
31. Detention Vault Design
Constrained by
Max Plan Dimensions: 100ft X 45ft
Pipe diameter of surrounding pipe network: 24in
Design Plan Dimensions: 45ft X 15ft
Detention Vault Plan View
Vault
34. Pipe Replacement
Purpose:
Condition assessment shows concrete is deteriorating
Hydraulic analysis indicates insufficient capacity
Approach:
Partial Replacement
Replace concrete portion with 24”
pipe
Alleviate structural concerns
Compatible with future upgrades
Full Replacement
Replace entire system with 24” pipe
Alleviate structural concerns
Improves capacity
35. Pipe Replacement - Capacity Calculations
Same procedure as existing capacity hand calculations
𝑧 =
𝑉2
2𝑔
+
𝜌 𝑎
𝜌 𝑒
𝑧 𝑆𝐿 − 𝑧1 + 𝑧1 + ℎ 𝑓 + ℎ 𝑚 + ℎ 𝑑𝑖𝑓𝑓𝑢𝑠𝑒𝑟
New Qmax = 20 MGD
Z
WWTP
36. Pipe Replacement - Material Selection
Ductile Iron Portion
Replace with 24” DIP
Concrete Portion
Replace with 24” HDPE
Advantages Disadvantages
Corrosion resistance
Relies on surroundings for
rigidity
Fatigue Resistance Floats
Extended service life
Larger pipes require
heavier/thicker walls
Flexibility
Difficult to verify field joint
39. Diffuser Design - Mixing Zone Analysis
Purpose:
Scope of the project includes a diffuser design
Department of Ecology (DOE) requires a mixing zone analysis to receive
an NPDES permit
Approach:
Performed analysis on current diffuser
Used the same process for new diffuser design
40. Diffuser Design - Mixing Zone Analysis
Steps
Wastefield plume
Profile Section
1. Determine mixing zone regions
Define acute and chronic zones boundaries as prescribed by the DOE
Permit Writer’s Manual
2. Calculate dilution factors
3. Calculate pollutant concentrations at mixing zone boundaries
4. Ensure this meets pollutant regulations
41. Acute Mixing Zone
• 26.4 ft.
• Aquatic criteria
considered
Chronic Mixing Zone
• 264.4 ft.
• Aquatic criteria
considered
• Human health criteria
considered for:
• Carcinogenic
pollutants
• Non-carcinogenic
pollutants
Plan View
42. Diffuser Design - Dilution Calculations
Input
Ambient water specifications
current velocity and direction
ambient water density
Discharge characteristics
flow rates
effluent density
diffuser depth
port size
port spacing
Visual Plumes will calculate the dilution ratio of the effluent to
the water at specific distances from the diffuser
43. Diffuser Design - Pollutant Concentrations
Divide effluent pollutant concentration by DF to get diluted
concentration at boundary
Compare against regulation value
Example:
Pollutant: Zinc
Effluent concentration = 820 µg/L
DF (Acute, Aquatic Life Criteria ) = 32
Diluted Concentration=
820 µg/L
32
= 25.6 µg/L
Regulation (Acute, Aquatic) = 90 µg/L
25.6 µg/L < 90 µg/L
PASS
44. Diffuser Design - Diffuser Selection
Replaces open port diffuser with duckbill diffuser
Duckbill valve remains closed under low flow preventing
seawater intrusion and sediment buildup
Duckbill Valve Profile
View
45. Diffuser Design - Plume Depth
Considerations
To protect shellfish the plume boundary should be below -70 ft.
MLLW
-70 ft
-115 ft
57. Diffuser Design - Dilution Calculations
At 26.4 ft.
the DF is 45
Dilution with Acute Zone, Aquatic Life Criteria
Centerline
dilutionAverage
dilution
Editor's Notes
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Picture from
http://discoverycwa.org/Columbia_River_Outfall_Project.html
Need a zoomed out map for WEFTEC – probably improve these screenshots
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20 miles north of Seattle
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Outfall has design capacity of 13.2
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Current and future Qmax
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Define PCSWMM: used for x made by EPA, private model company that…
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Arrows, zoom in on red box
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Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
KR
Arrows on the plan view, where the outfall is
Add zoom out view from report
KR
Include map (profile) of concrete section, show what part of the pipe we are focused on (context for audience)
This material is most commonly used now
KR
𝑉 2 2𝑔 , ℎ 𝑓 , and ℎ 𝑚 changed due to the increased diameter.
Determined ℎ 𝑑𝑖𝑓𝑓𝑢𝑠𝑒𝑟 using empirical formulas and charts reported in the Journal of Hydraulic Engineering for duckbill diffusers.
Concrete portion offshore
KR
Simplification- saying anchors support 80%
0.8 is a correction factor due to float in place
IS
Average dilution over the wastefield plume
The aquatic life criteria is based on the time of exposure that the organisms are being exposed to a certain pollutant concentration.
Human health criteria is based off of daily exposures, ingestion rate, and cancer risk for carcinogenic chemicals.
The design flow, current speed, and density stratification must be chosen from the conditions set by the DOE Permit Writer’s Manual, Appendix C
Mention that I calibrated with hand calculations, showed agreement
That concludes option 1, option 1 includes (Reiterate option 1), now we will talk about option 2
“It is best practice to ensure that the plume boundary is 70 feet below the water surface in order to protect shellfish habitats.”
Geoduck, hard-shell clam, and Dungeness crab reside within the mixing zones of our outfall.
In order to ensure plume depth below 70 ft. with 8 portholes at 12 ft. spacing the diffuser needs to be at a depth of 115 ft. which means extending pipe 120 ft.
IS
Summarize option 2, replace concrete…. Same as option 1, extended outfall deeper to protect shellfish
Next Option is.
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Outfall has design capacity of 13.2
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Outfall has design capacity of 13.2
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Outfall has design capacity of 13.2
LG
Show one detail cost, for each option we included material cost and construction costs
Figure out which costs are the right ones
LG
Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
LG
Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
LG
LG
Add picture
Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
Based on the inspection, hydraulic modeling, and results of literature review the team chose 3options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
Based on the inspection, hydraulic modeling, and results of literature review the team chose 4 options to bring to 30% design
Conceptual level drawings
Bulk cost estimations
Justification of each design option
Option 1: Least Expensive since not replacing onshore section or extending diffuser
Option 2: Better effluent mixing due to extending diffuser
What about this research affects the design
Animation where one row pops up, or just have one row
