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