Post on 15-Apr-2017
ALDERWOOD WATER AND WASTEWATER DISTRICT
OUTFALL UPGRADESeattle University Senior Design Team CEE 16.7
Kristin Ramey, Isabella Schwartz, Abbie Lorensen, Larissa Grundell
Science and Engineering Project Center
College of Science and Engineering
Seattle University Faculty Advisor: Dr. Michael Marsolek
Sponsor: Alderwood Water and Wastewater District
Acknowledgments
Thank you!
Useful TermsOutfall: 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
3,100 ft - 18” Ductile Iron
1,300 ft - 18” Reinforced Concrete
80’Diffuser
4” Portholes 1972 – CAS Facility
2013 – MBR Facility
Project MotivationStructural 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.
Project Motivation
Q= 8.7 MGD
Q=15.8 MGD
Design Approach
Preliminary Assessment Condition Assessment Hydraulic Analysis
Design Selection Design Considerations
Detention Vault Design Pipe Replacement Mixing Zone Analysis
Cost & Decision
Condition AssessmentHydraulic Analysis
Preliminary Assessment
Condition AssessmentHydraulic Analysis
Preliminary Assessment
Condition AssessmentExternal Dive Inspection
Determine condition of submerged concrete pipe and diffuser Results:
Flanged end of diffuser in "poor" condition with heavy corrosionIndicates a new diffuser should be included in all design options
Internal Camera Inspection On hold
Condition AssessmentHydraulic Analysis
Preliminary Assessment
Hydraulic ModelingPurpose:
Determine capacity of the outfallApproach:
Use PCSWMM to model dynamic outfall hydraulicsStorm Water Management ModelConstructed by the EPA
Use as-built information to construct model Input wet weather flow data from December 2015 Apply peaking factor
Hydraulic Modeling
JunctionConduit
Hydraulic Modeling
Max Flow = 11.1 MGD
Hydraulic Modeling
Hand CalculationsPurpose:
Verify capacity determined in PCSWMM modeling.Approach:
Determine the maximum allowable flow rate given the fixed changed in elevation available. WWTP
ZZ=169’
Hand Calculations
Velocity Head
Ambient /Effluent Density Difference
Hand Calculations
Datum
Hand Calculations
Friction Losses
Hand Calculations
Minor
Losses
Hand Calculations
Horizontal bends from As-builts Radius of curvature to determine K from tabulated values
BendRadius of Curvatur
eK
1 48 0.35 1.48’ 0.52’2 37.3 0.35 1.48’ 0.52’3 7.26 0.25 1.48’ 0.37’4 7.16 0.25 1.48’ 0.37’5 3.87 0.16 1.48’ 0.24’6 16.26 0.35 1.48’ 0.52’7 14.67 0.32 1.48’ 0.47’8 14.67 0.32 1.48’ 0.47’Total 3.48’
Hand Calculations
E
Hand Calculations
Flow equally distributed at maximum capacity Conservation of mass at each port Ports modeled as expansions
Friction losses between ports
Hand Calculations
Z=169ft Iterating with V=Q/A
Z
WWTP
Capacity ConclusionsHydraulic modeling capacity = 11.1 MGDHand calculations capacity = 11 MGD
Corroborates modeling results11 MGD capacity is less than the projected 15.8 MGD
Design options need to account for flow attenuation
Option 3Full
Replacement
Extend Diffuser
Design SelectionOption
1Partial Replacemen
tDetention
VaultShallow Diffuser
Option 2Partial
Replacement
Detention Vault
Extend Diffuser
Detention VaultPipe Replacement Mixing Zone Analysis
Design Considerations
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
Detention Vault DesignConstrained 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
Detention Vault Profile Section
Detention Vault DesignConstrained by:
Allowable depth 22 ft.Design depth 10ft
Detention VaultPipe Replacement Mixing Zone Analysis
Design Considerations
Pipe Replacement Purpose:
Condition assessment shows concrete is deteriorating Hydraulic analysis indicates insufficient capacity
Approach:
Partial ReplacementReplace concrete portion with 24” pipeAlleviate structural concernsCompatible with future upgrades
Full ReplacementReplace entire system with 24” pipeAlleviate structural concernsImproves capacity
Pipe Replacement - Capacity Calculations
Same procedure as existing capacity hand calculations
New Qmax = 20 MGD
Z
WWTP
Pipe Replacement - Material SelectionDuctile Iron Portion
Replace with 24” DIPConcrete Portion
Replace with 24” HDPE
Advantages DisadvantagesCorrosion resistance Relies on surroundings for
rigidityFatigue Resistance FloatsExtended service life Larger pipes require
heavier/thicker wallsFlexibility Difficult to verify field joint
quality
Pipe Replacement - Anchor DesignAnchor Design:
Calculated Weight = 2120 lbs/Anchor
Anchor Detail – Dimensions determined from weight requirement
Detention VaultPipe Replacement Mixing Zone Analysis
Design Considerations
Diffuser Design - Mixing Zone AnalysisPurpose:
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
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 factors3. Calculate pollutant concentrations at mixing zone
boundaries4. Ensure this meets pollutant regulations
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
Diffuser Design - Dilution Calculations Input
Ambient water specificationscurrent velocity and directionambient water density
Discharge characteristicsflow rateseffluent densitydiffuser depthport sizeport spacing
Visual Plumes will calculate the dilution ratio of the effluent to the water at specific distances from the diffuser
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= Regulation (Acute, Aquatic) = 90 < 90 PASS
Diffuser Design - Diffuser SelectionReplaces open port diffuser with duckbill diffuserDuckbill valve remains closed under low flow preventing
seawater intrusion and sediment buildup
Duckbill Valve Profile View
Diffuser Design - Plume Depth Considerations
To protect shellfish the plume boundary should be below -70 ft. MLLW
-70 ft
-115 ft
PROPOSED SYSTEM DESIGNS
Replace with 24” HDPE
Option 1
Replace with 24” HDPE
Option 2
Upsize to 24”
Option 3
Cost Estimate
Option 3
Better Effluent Mixing
Longest Potential Lifespan
Most Expensive
Option SummaryOption
1Least
Expensive
Option 2
Better Effluent Mixing
Option 3
Better Effluent Mixing
Longest Potential Lifespan
Most Expensive
Option SummaryOption
1Least
Expensive
Option 2
Better Effluent Mixing
Option 3
Better Effluent Mixing
Longest Potential Lifespan
Most Expensive
Option SummaryOption
1Least
Expensive
Option 2
Better Effluent Mixing
ConclusionRecommendation: Option 3 Highest score in matrix
Longest lifecycleMinimal O&MMinimal Impacts over lifespan
AWWD Response Incorporated Option 3 design into plant assessment project
Option 3Full
Replacement
Extend Diffuser
QUESTIONS?
Diffuser Design - Dilution Calculations
At 26.4 ft. the DF is 45
Dilution with Acute Zone, Aquatic Life Criteria
Centerline dilutionAverage
dilution