8-Attachment D-Sewer ComprehensivePlan 2008.pdf

City of Oak Harbor Comprehensive Sewer Plan

DECEMBER 2008

CITYOF b QD~Y~JJ.~t1N9J

COMPREHENSIVE SEWER PLAN

DECEMBER 2008

Prepared for:

City of Oak Harbor

865 SE Barrington Dri ve Oak Harbor, WA 98277

Prepared by:

TETRA TECH/KCM

1420 Fifth Avenue, Suite 600

Seattle, Washington 98 101-3941

(206) 883-9300

In association with:

Katy Isaksen and Associates P.O. Box 30008

Seattle, WA 98113-2008

(206) 706-8893

Project #3530009

Cover Photo: Oak Harbor Area Aerial Photos from lslu11d Counry Public Works Departmenr Website (http://www.islandc01111ty.11e1/PublicWorks/DigitalPhotos/11wmap.htm)

Memo Date: 12/18/2008

To: File

Cc:

From: Eric Johnston, PE, City Engineer ~-C::::~ - ----· RE: Council Approval of Sewer Plan ~'- - · ·~

At the August 8, 2007 City Council meeting the City Council approved the draft City of Oak Harbor Comprehensive Sewer Plan.

The motion for approval included a requirement to include a general statement related to the Oak Harbor with the final version. Specifically the motion stated, " To approve the 2006 City of Oak Harbor Comprehensive sewer plan with a general statement to be added referencing the Puget Sound Partnership and Island County being named as one of the counties for ongoing State efforts." This memo is the required general statement.

The Puget Sound Partnership Action Agenda published in December 2008 includes a number of action areas for cleanup of Puget Sound. Priority action area C "Reduce sources of water pollution" specifically identifies the Whidbey Basin as a target area for reducing pollutants generated by on site treatment systems and municipal wastewater treatment plants. The Oak Harbor wastewater treatment plants discharge to Oak Harbor Bay and to Crescent Harbor Bay both of which lie within the Whidbey Basin Action Area.

The City of Oak Harbor Sewer Plan identifies the need for additional treatment capacity beginning in 2017, depending on growth rates. However, in approving the sewer plan the City Council was clear that nothing bared the City from proceeding with projects for additional capacity early than 2017. The Council was clear that there may be funding opportunities through the Puget Sound Partnership efforts to assist the City in increasing wastewater treatment capacity functions while meeting the stated priorities of the Action Plan to reduce pollutants discharged to the Whidbey Basin Action Area and that the City should pursue those funding opportunities.

C:\JJocLITlenls and Settings\ejohnston\Desktop\sewer cover !tr.doc 1

City of Oak Harbor Comprehensive Sewer Plan

TABLE OF CONTENTS

Title Page No.

Table of Contents ........................................................................................................................... i List of Tables......................................................................................................................................... v List of Figures ....................................................................................................................................... vi

Acknowledgments ...................................................................................................................... viii

Executive Summary Background ...................................................................................................................................... ES-1

Study Area ................................................................................................................................. ES-1 Land Use .................................................................................................................................... ES-1 Population .................................................................................................................................. ES-1

Existing Wastewater System ............................................................................................................ ES-3 Treatment Facilities ................................................................................................................... ES-3 Collection Facilities ................................................................................................................... ES-5

Potential System Improvements ....................................................................................................... ES-5 Collection System ...................................................................................................................... ES-5 Treatment Facilities ................................................................................................................... ES-7

Chapter 1. Introduction Purpose ................................................................................................................................................1-1 Authorization.......................................................................................................................................1-1 Scope ...................................................................................................................................................1-1 Related Studies ....................................................................................................................................1-2 Wastewater System Ownership and Operation ...................................................................................1-2

Chapter 2. Background Study Area...........................................................................................................................................2-1 Topography .........................................................................................................................................2-1 Climate ................................................................................................................................................2-1 Surface Waters ....................................................................................................................................2-2 Groundwater........................................................................................................................................2-2 Geology ...............................................................................................................................................2-2 Water Supply.......................................................................................................................................2-3 Other Wastewater Facilities ................................................................................................................2-3

Chapter 3. Land Use and Population Planning Areas ....................................................................................................................................3-1 Land Use..............................................................................................................................................3-1

Existing Land Use.........................................................................................................................3-1 Future Land Use............................................................................................................................3-2

Population............................................................................................................................................3-3

Chapter 4. Permits, Requirements, and Regulations Federal Regulations.............................................................................................................................4-1

Federal Water Quality Acts ..........................................................................................................4-1 Federal Effluent Limitations .........................................................................................................4-1 i

…TABLE OF CONTENTS

Federal Standards for Use or Disposal of Sludge .........................................................................4-2 EPA Reliability Criteria................................................................................................................4-4 National Environmental Protection Act........................................................................................4-4 Clean Air Act ................................................................................................................................4-4 Historical and Archaeological Sites..............................................................................................4-4 Floodplains and Wetlands.............................................................................................................4-7 Agricultural Lands ........................................................................................................................4-7 Coastal Zone Management ...........................................................................................................4-8 Fish and Wildlife Protection .........................................................................................................4-8 Endangered Species Act ...............................................................................................................4-8 Magnuson-Stevens Fishery Conservation and Management Act .................................................4-8 United States Navy Seaplane Lagoon Lease Agreement..............................................................4-8

State Policies and Regulations.............................................................................................................4-9 Water Quality Standards for Surface Waters ................................................................................4-9 Department of Natural Resources Aquatic Lands Outfall Easement..........................................4-12 NPDES Wastewater Permit ........................................................................................................4-12 NPDES Stormwater Permit.........................................................................................................4-14 Washington State Standards for Use and Disposal of Sludge.....................................................4-14 Washington Department of Ecology Criteria for Sewage Works Design...................................4-14 Standards for Water Reclamation ...............................................................................................4-15 Department of Health On-Site Sewage Requirements................................................................4-15 Joint Aquatics Resources Permit ................................................................................................4-16 State Environmental Policy Act..................................................................................................4-16 State Environmental Review Process; Department of Ecology Documentation ........................4-16 Office of Archaeology and Historic Preservation Approval.......................................................4-17

Local Policies ....................................................................................................................................4-17 City Sewer Regulations...............................................................................................................4-17 SEPA Review .............................................................................................................................4-18 Shoreline Management ...............................................................................................................4-18 Stormwater Regulations..............................................................................................................4-18 Critical Areas Regulations ..........................................................................................................4-19 Local Building Codes and Permits .............................................................................................4-19 County Requirements for Archeological Sites............................................................................4-19 Northwest Clean Air Agency......................................................................................................4-19 Uniform Fire Code......................................................................................................................4-19 Development Standards ..............................................................................................................4-20

Chapter 5. Collection System Design Criteria and Flows Design Criteria ....................................................................................................................................5-1 Projected Base Flows ..........................................................................................................................5-2

Residential Unit Flow ...................................................................................................................5-3 Commercial Unit Flow .................................................................................................................5-3 School Unit Flow ..........................................................................................................................5-4 Base Flow Peaking Factors...........................................................................................................5-4

Infiltration and Inflow .........................................................................................................................5-4 New Sewers ..................................................................................................................................5-4 Existing Sewers.............................................................................................................................5-5 I/I Assessment Based on EPA Criteria .........................................................................................5-7

Summary .............................................................................................................................................5-7

Chapter 6. Collection System Description History of System Development .........................................................................................................6-1 ii

On-Site Sewer Systems .......................................................................................................................6-1 Gravity Sewers ....................................................................................................................................6-2 Pumped Systems..................................................................................................................................6-2

Lift Station No. 1, Taftson Street..................................................................................................6-2 Lift Station No. 2, NE 9th Avenue ...............................................................................................6-3 Lift Station No. 3, NE 7th Avenue ...............................................................................................6-3 Lift Station No. 4, Crosby Road ...................................................................................................6-3 Lift Station No. 5, Cabot Street ....................................................................................................6-3 Lift Station No. 6, East Pioneer Way............................................................................................6-4 Lift Station No. 7, Golf Course.....................................................................................................6-4 Lift Station No. 8, Capital Street ..................................................................................................6-4 Lift Station No. 9, East Park .........................................................................................................6-4 Lift Station No. 10, Harbor Terrace..............................................................................................6-5 RBC Diversion Pump Station .......................................................................................................6-5 Marina Grinder Stations................................................................................................................6-6 Reliability Summary .....................................................................................................................6-7

Chapter 7. Collection System Analysis Analysis of Existing System Capacity ................................................................................................7-1

Model Loading..............................................................................................................................7-1 Model Scenarios ...........................................................................................................................7-2

System Expansion ...............................................................................................................................7-2 System Expansion Area A—Scenic Heights ................................................................................7-3 System Expansion Area B—Swantown Road and Fort Nugent Avenue......................................7-3 System Expansion Area C—Crosby Road....................................................................................7-6 System Expansion Area D—Heller Road to Goldie Road ...........................................................7-6 System Expansion Area E—Crescent Harbor ..............................................................................7-9

Analysis of Future System Capacity ...................................................................................................7-9 Capacity Analysis Approach.........................................................................................................7-9 Capacity Analysis Results...........................................................................................................7-11

Upgrades for Future System Capacity...............................................................................................7-12 Criteria for Upgrading.................................................................................................................7-12 Upgrade Alternative 1—One Diversion Pump Station...............................................................7-13 Upgrade Alternative 2—Two Diversion Pump Stations.............................................................7-15 Comparison of Alternative 1 and Alternative 2 ..........................................................................7-17 Conclusion ..................................................................................................................................7-18

Other System Improvements .............................................................................................................7-18

Chapter 8. Wastewater Treatment Alternatives Existing Treatment Facilities...............................................................................................................8-1

RBC Plant .....................................................................................................................................8-1 Seaplane Lagoon Plant..................................................................................................................8-4

Wastewater Flows and Loads............................................................................................................8-10 Historical Flows..........................................................................................................................8-10 Historical BOD Loads.................................................................................................................8-11 Historical TSS Loads ..................................................................................................................8-12 Projected Flows and Loads .........................................................................................................8-13 Flow and Load Conclusions........................................................................................................8-13

Effluent Disposal ...............................................................................................................................8-16 Effluent Discharge Limits...........................................................................................................8-17

Treatment Plant Alternatives.............................................................................................................8-17 Treatment Plant Design Conditions ............................................................................................8-17 iii

Treatment Alternatives................................................................................................................8-18 Treatment Plant Conclusions ......................................................................................................8-23

Chapter 9. Recommended Improvements Collection System Improvements........................................................................................................9-1

System Expansion.........................................................................................................................9-1 Existing System Upgrades ............................................................................................................9-1 Operation and Maintenance ..........................................................................................................9-1 Emergency Response Plan............................................................................................................9-2

Wastewater Treatment Plant Improvements........................................................................................9-3 Capital Improvements...................................................................................................................9-3 Treatment Plant O&M Requirements ...........................................................................................9-4

Implementation Schedule ....................................................................................................................9-5

Chapter 10. Financing Analysis Current Sewer Funding .....................................................................................................................10-1 Outstanding Sewer Debt....................................................................................................................10-1 Current Sewer Rates and Charges .....................................................................................................10-2 Capital Program Funding Methods ...................................................................................................10-3 Alternative Capital Program Funding Scenarios ...............................................................................10-5

Annual O&M Changes ...............................................................................................................10-6 Escalated Project Costs ...............................................................................................................10-7

Appendices A. Navy Seaplane Base Lease Agreement

B. DNR Aquatic Lands Outfall Easement

C. NPDES Permit

D. WAC 173-221

E. SEPA Checklist

F. City of Oak Harbor Sanitary Sewer Design Standards

G. Modeling Input Data and Results

H. Potential Collection System Improvements Cost Estimation Data

I. Cost Model

J. RBC Plant Data iv

LIST OF TABLES

No. Title Page No.

ES-1 Existing Land Use in the City Proper............................................................................................ ES-2 ES-2 Existing and Projected Future Population..................................................................................... ES-3 ES-3 Projected Raw Wastewater Flows and Loads through 2025......................................................... ES-4 ES-4 Summary of Recommended Collection System Improvements.................................................... ES-8 ES-5 Estimated Capital Costs for Recommended Wastewater Treatment Improvements................... ES-10

3-1 Existing Land Use in the City Proper ..............................................................................................3-2 3-2 Existing and Projected Future Population........................................................................................3-4

4-1 Ceiling Concentrations for Metals in Land-Applied Sludge............................................................4-3 4-2 Metal Concentration Limits for Bulk Sewage Sludge Land Application.........................................4-3 4-3 Summary of EPA Design Criteria for System and Component Reliability .....................................4-5 4-4 Washington State Freshwater Water Quality Criteria (WAC 173-201A)......................................4-10 4-5 Washington State Marine Water Quality Criteria (Excellent Quality Aquatic Life Uses;

Shellfish Harvest)...........................................................................................................................4-11 4-6 NPDES Permit Limits ....................................................................................................................4-13 4-7 Reliability Class System in the Orange Book ................................................................................4-15

5-1 Minimum Slopes for a Selection of Sewer Pipe Diameters .............................................................5-2 5-2 Allowable Residential Development Densities................................................................................5-3 5-3 Projected Wastewater Unit Flows for Planning Purposes................................................................5-8

6-1 Lift Station and Pump Station Summary .........................................................................................6-2

7-1 Peak-Hour Flows at RBC Diversion Pump Station .......................................................................7-13 7-2 Peak-Hour Flows at Diversion Pump Stations...............................................................................7-15

8-1 NPDES Permit Limits for RBC Plant Outfall..................................................................................8-3 8-2 NPDES Permit Limits for Seaplane Lagoon Plant Outfall ..............................................................8-6 8-3 Criteria for Projecting Raw Wastewater Flows and Loads for the City Outside the Seaplane Base for 2006 through 2025............................................................................................8-14 8-4 Criteria for Projecting Raw Wastewater Flows and Loads for the Seaplane Base for 2006 through 2025....................................................................................................................8-14 8-5 Projected Raw Wastewater Flows and Loads Through 2025.........................................................8-14 8-6 Estimated Capital Costs for Treatment Plant Alternatives.............................................................8-22 8-7 Qualitative Summary of Secondary Process Alternatives..............................................................8-23

9-1 Summary of Recommended Collection System Improvements ......................................................9-2 9-2 Estimated Capital Costs for Recommended Wastewater Treatment Improvements........................9-4 9-3 Proposed Implementation Schedule for Recommended Improvements ................... Follows page 9-6

10-1 Monthly Sewer Rates .....................................................................................................................10-2 10-2 Sewer Connection Fees ..................................................................................................................10-3 10-3 Funding Sources for Capital Improvements...................................................................................10-6 10-4 Escalated Costs to Year of Construction........................................................................................10-7 10-5 Debt Repayment if Bonds Sold for all 6-year CIP.........................................................................10-8 10-6 Collection System Expansion per ERU .........................................................................................10-8 10-7 Approximate System Development Charge...................................................................................10-9 10-8 Estimated Cumulative Reserve ......................................................................................................10-9 10-9 Capital Funding Plan....................................................................................................................10-10 v

LIST OF FIGURES

No. Title Page No.

ES-1 City of Oak Harbor and Vicinity................................................................................................... ES-2 ES-2 Recommended Collection System Improvements ........................................................................ ES-9 ES-3 Recommended Treatment Plant Improvements .......................................................................... ES-10

2-1 Vicinity Map ............................................................................................................. Follows page 2-2 2-2 Oak Harbor Study Area and Topography ................................................................. Follows page 2-2 2-3 Oak Harbor Surface Waters and Critical Areas ........................................................ Follows page 2-2 2-4 Water System Facilities....................................................................................................................2-4

3-1 Oak Harbor Land Use ............................................................................................... Follows page 3-2 3-2 Oak Harbor Zoning ................................................................................................... Follows page 3-2

5-1 Ratio of Peak-Hour Flow to Design Average Flow .........................................................................5-5 5-2 Daily total Flow vs. Daily Rainfall, January 1999 to October 2005................................................5-6 5-3 30-Day rolling Average Total Flow vs. 30-Day Rolling Average Rainfall, January 1999 to October 2005....................................................................................................................................5-6

6-1 Existing Wastewater Collection System ................................................................... Follows page 6-2

7-1 Collection System Model Coverage.......................................................................... Follows page 7-2 7-2 2005 Capacity Analysis Results................................................................................ Follows page 7-2 7-3 System Expansion Area A: Scenic Heights ....................................................................................7-4 7-4 System Expansion Area B: Swantown Road and Fort Nugent Avenue..........................................7-5 7-5 System Expansion Area C: Crosby Road........................................................................................7-7 7-6 System Expansion Area D: Heller Road to Goldie Road................................................................7-8 7-7 System Expansion Area E: Crescent Harbor Road .......................................................................7-10 7-8 Assumed Future Development for 2011 and 2025.................................................. Follows page 7-10 7-9 Alternative 1: 2011 Capacity Analysis Results...................................................... Follows page 7-10 7-10 Alternative 1: 2025 Capacity Analysis Results...................................................... Follows page 7-10 7-11 Alternative 1: Long-Term Growth Capacity Analysis Results .............................. Follows page 7-10 7-12 Alternative 2: 2011 Capacity Analysis Results...................................................... Follows page 7-10 7-13 Alternative 2: 2025 Capacity Analysis Results...................................................... Follows page 7-10 7-14 Alternative 2: Long-Term Growth Capacity Analysis Results .............................. Follows page 7-10 7-15 Alternative 1 Improvement Projects ....................................................................... Follows page 7-14 7-16 Alternative 2 Improvement Projects ....................................................................... Follows page 7-18 7-17 Comparison of Cumulative Net Present Costs ...............................................................................7-19

8-1 RBC WWTP Process Flow Schematic ............................................................................................8-2 8-2 Existing Lagoon Treatment Plant Site .............................................................................................8-5 8-3 Historical Monthly Average Effluent CBOD Data ..........................................................................8-7 8-4 Historical Monthly Average Effluent TSS Data ..............................................................................8-8 8-5 Historical Monthly Average Effluent Fecal Coliform Concentrations ............................................8-8 8-6 Historical Daily Effluent pH, Alkalinity and Soda Ash Dose..........................................................8-9 8-7 Daily Wastewater Flow..................................................................................................................8-10 8-8 Average Daily Wastewater Flow ...................................................................................................8-11 8-9 Daily BOD5 Load...........................................................................................................................8-11 8-10 Average Daily BOD5 Load ............................................................................................................8-12 8-11 Daily TSS Load..............................................................................................................................8-12 8-12 Annual Daily TSS Loads ...............................................................................................................8-13 vi vii

8-13 Average Flow Projection and Treatment Capacity ........................................................................8-15 8-14 Average BOD5 Projection and Treatment Capacity.......................................................................8-15 8-15 Average TSS Projection and Treatment Capacity..........................................................................8-16 8-16 Treatment Plant Improvement Alternatives 1 and 2 ......................................................................8-19 8-17 Treatment Plant Improvement Alternative 3..................................................................................8-20 8-18 Treatment Plant Improvement Alternative 4..................................................................................8-21

9-1 Recommended Capital Improvement Projects.......................................................... Follows page 9-2

ACKNOWLEDGMENTS

Cathy Rosen—Public Works Director

Eric Johnston—City Engineer

Larry Benfield—Former City Engineer

Brad Gluth—Engineer

Steve Bebee—Field Supervisor

Bob Jarski—Operations Manager

Rob Kelley—Lead Wastewater Operator

Jason Daley—Lead Wastewater Collections Specialist

Doug Merriman – Finance Director

Steve Powers – Development Services Director

Larry Cort—Senior Planner

David Kane—Associate Planner viii

EXECUTIVE SUMMARY

This Comprehensive Sewer Plan for the City of Oak Harbor updates the City’s previously prepared Comprehensive Sewerage Plan (URS Greiner, 1997). The Washington State Growth Management Act requires the City to provide sanitary services for the anticipated growth in population that may occur during the 20 year planning period. This planning effort responds to existing system needs and the needs associated with the population increase anticipated by the City of Oak Harbor. The updates in this document address the City’s sewer conveyance system and treatment needs through the planning period that extends to 2025.

BACKGROUND

Study Area The City of Oak Harbor is near the northern end of Whidbey Island on Oak Harbor and Crescent Harbor.

The eastern portion of the City is the U.S. Navy’s Seaplane Base, which is one of two bases that make up Naval Air Station Whidbey Island (NAS Whidbey); the other base is Ault Field, which lies to the north of the City. The City covers 9.4 square miles, of which 4.4 square miles is the Navy’s Seaplane Base and 5.0 square miles is in the “City proper”.

The City’s urban growth area (UGA) includes all of the City of Oak Harbor, as well as unincorporated areas to the north, between the City and Ault Field, and to the south and west. The study area for this master plan is all of the UGA, a total of 11.8 square miles. Beyond the UGA lies the Oak Harbor Island County Joint Planning Area (JPA), in which the City of Oak Harbor is likely to expand beyond the 20-year planning horizon. Figure ES-1 shows the city limits, UGA and JPA.

Land Use The predominant land use in the City is residential development, with densities from 3 to 22 dwelling units per acre. Higher densities are located primarily near the center of the City, which features a mix of single-family and multi-family dwellings. Lower density areas, consisting mostly of single-family homes, are located to the east, west and south of the City’s central core. Residential development has been limited in the northern portion of the City, due largely to noise impacts from aircraft operations at Ault Field. A survey conducted for the City’s Comprehensive Plan found that Oak Harbor’s mix of residential, commercial, and industrial uses is generally consistent with that of similar communities in the State of Washington. One exception is in the area of industrial land, for which Oak Harbor’s total is significantly lower than other cities. However, the land use survey did not include UGA lands outside the city limits, and it is likely that the percentage of industrial land will be more in line with that of other communities as industrial land to the north of Oak Harbor is annexed over time. Table ES-1 summarizes existing land uses within the city limits.

Population Table ES-2 summarizes estimates used in this comprehensive plan for current population and future population through the planning period

ES-1

City of Oak Harbor Comprehensive Sewer Plan…

Figure ES-1. City of Oak Harbor and Vicinity

TABLE ES-1.

EXISTING LAND USE IN THE CITY PROPER

Land Use Total Area

(acres) Portion of City Proper Total

Area (%)

Single Family Residential 1,435 45 Multiple Family Residential 540 17 Commercial 420 13 Office 125 4 Industrial 120 4 Public 350 10 Open Space 220 7

Total 3,210 100

ES-2

…EXECUTIVE SUMMARY

TABLE ES-2.

EXISTING AND PROJECTED FUTURE POPULATION

Year Total Navy Seaplane Base City Proper

2000 19,800 4,400 15,400

2005 22,200 4,400 17,800 2011 24,200 4,400 19,800

2025 28,700 4,400 24,300

EXISTING WASTEWATER SYSTEM

Treatment Facilities Treatment Type, Location and Ownership The City owns, operates, and maintains a rotating biological contactor (RBC) treatment plant on SE City Beach Drive, near the City’s central business district. The City operates and maintains, under a lease agreement with the U.S. Navy, a second treatment plant on East Pioneer Avenue, on the Seaplane Base.

The leased plant is an aerated lagoon facility with anaerobic pretreatment.

Flow and Load Capacity The City’s current National Pollutant Discharge Elimination System (NPDES) permit, issued on May 25, 2005, applies to both of the City’s wastewater treatment plants. The NPDES permit establishes the following rated flow and load capacities for the treatment plants:

• RBC Plant rated capacity for wastewater influent

– Average flow for the maximum month = 0.7 million gallons per day (mgd)

– Biochemical oxygen demand (BOD) loading for the maximum month = 2,000 pounds per day (ppd)

• Seaplane Lagoon Plant rated capacity for wastewater influent

– Average flow for the maximum month = 2.5 mgd

– BOD loading for the maximum month = 4,580 ppd

– Total suspended solids (TSS) loading for the maximum month = 5,130 ppd

Table ES-3 summarizes projections for citywide flows and BOD and TSS loads through 2025, the end of the planning period for this comprehensive sewer plan. It is recommended that the City expand the capacity of its treatment facilities for future flows within the 20 year planning period.

ES-3

TABLE ES-3.

PROJECTED RAW WASTEWATER FLOWS AND LOADS THROUGH 2025

2010 2015 2020 2025

Flow (mgd) Average Annual 2.08 2.22 2.36 2.50 Maximum Month 2.91 3.11 3.31 3.51 Maximum Day 5.03 5.34 5.64 5.95

BOD (ppd) Average Annual 4,288 4,584 4,880 5,177 Maximum Month 5,047 5,392 5,738 6,084 Maximum Day 7,447 7,973 8,499 9,026

TSS (ppd) Average Annual 4,305 4,618 4,931 5,243 Maximum Month 6,273 6,733 7,194 7,655 Maximum Day 9,881 10,621 11,361 12,102

Effluent and Sludge Disinfected secondary effluent from the RBC Plant is discharged into Oak Harbor through an 18-inch-diameter corrugated metal outfall. The outfall is 1,160 feet long and terminates with a diffuser section 15 feet below mean lower low water. Disinfected effluent from the lagoon plant is discharged into Crescent Harbor through an 18-inch diameter outfall. The outfall is 3,284 feet long and terminates with a diffuser section 44 feet below mean lower low water. The NPDES permit defines the following effluent limits:

• RBC Plant

– Monthly average effluent CBOD (carbonaceous BOD) = 25 mg/L or less

– TSS = 30 mg/L or less

• Seaplane Lagoon Plant

– Monthly average CBOD = 25 mg/L or less

– TSS = 75 mg/L or less.

In recent years the Seaplane Lagoon Plant has continuously met the NPDES effluent limits, except for once in March 2004. The RBC Plant has continuously met the NPDES effluent limits except for three occasions (June 2005, August 2004 and September 2004):

Digested sludge (biosolids) from the RBC Plant is pumped to the Seaplane Lagoon Plant where it is further stabilized in anaerobic lagoons. Testing conducted in 2002 indicated that the biosolids met all criteria for “exceptional quality” as defined in federal 503 regulations. The biosolids also met the Class B requirement for testing of fecal coliform. The City plans to remove sludge from the anaerobic lagoons at least every two years and apply it as a soil amendment to permitted land application sites.

ES-4

Collection Facilities System Components The gravity collection system serving the City proper consists of approximately 65 miles of PVC, concrete, clay and ductile iron sewer pipe ranging in diameter from 6 to 24 inches. The collection system also includes 10 lift stations and the RBC Diversion Pump Station, with approximately 5 miles of associated ductile iron, PVC and asbestos cement force mains ranging in size from 2-inch to 16-inch.

Wastewater from the City proper flows to the RBC Plant, where it is either treated or pumped to the Seaplane Lagoon Plant by the RBC Diversion Pump Station.

The City owns, operates, and maintains the collection system serving users outside the Navy base and conveying flow to both treatment plants, including the conveyance infrastructure between the RBC Diversion Pump Station and the Seaplane Lagoon Plant, part of which is a 21-inch gravity sewer. The U.S. Navy owns, operates and maintains the collection system serving the Navy base, which conveys flows to the lagoon treatment plant.

System Capacity A capacity analysis of the collection system was undertaken using computer modeling. Existing wastewater flows in the City proper were estimated from unit flows for contributions from residential, and commercial development, schools and other public facilities. Peak hour flows from these sources were obtained by use of a peaking factor. Peak Inflow and infiltration contributions were also included in the model simulations derived from typical areal contribution values related to the age of development.

Out-of-manhole flooding, sewer surcharging, capacity limitation and access restrictions were used as reference criteria for upgrading sewers. No areas of out-of-manhole flooding were identified from the computer modeling using estimated existing flows. The modeling identified peak flows approaching system capacity on some sections of conveyance pipe.

Computer modeling of the system using projected future flows showed greater levels of surcharging in the areas where surcharging is indicated for existing flows. Significant surcharging and out-of-sewer flooding are not predicted for expected flows through the end of the planning period (2025).

It is recommended that a flow monitoring study be implemented early in the planning period to verify flow modeling predictions.

POTENTIAL SYSTEM IMPROVEMENTS

Collection System Existing System Upgrades

The results of the capacity analysis for future flow conditions expected through the end of the planning period (2025) were used to estimate when upgrades to the existing collection system would be required.

Improvement Projects for the 20-Year Planning Period The following specific projects are to be implemented within the 20-year planning period:

• Project 1a(i)—Upgrade the RBC Diversion Pump Station to a capacity of 10 mgd, with an estimated cost of $1.86 million.

ES-5

• Project 1a(ii)—Upgrade the RBC Diversion Pump Station force main. This involves the installation of 7,300 feet of new 28-inch pipe, with an estimated cost of $6.12 million.

• Project 1a(v)—Upgrade the inverted siphon to the Seaplane Lagoon headworks. This involves the installation of 1,700 feet of new 20-inch pipe, with an estimated cost of $1.07 million.

• Project 1b(ii)—Upgrade a portion of the gravity trunk sewer along Heller Street and Whidbey Avenue. This involves the installation of 1,550 feet of new 18-inch pipe, with an estimated cost of $845,000

• Project 1e(i)—Upgrade a portion of the gravity trunk sewer on Ely Street Trunk. This involves the installation of 1,300 feet of new 30-inch pipe and 1,300 feet of new 36-inch pipe, with an estimated cost of $2.11 million.

System Expansion Improvement Projects for the 20-Year Planning Period Expansion of the existing system will be required to support development within the UGA. The following expansion projects were identified as needing to be implemented within the 20-year planning period:

Expansion Area A—Scenic Heights

• Project A1—Install a new 600-gallon-per-minute (gpm) lift station in the southern portion of Expansion Area A, with 2,300 feet of 8-inch force main connecting to an existing trunk sewer, with an estimated cost of $600,000.

• Project A2—Install 3,100 feet of new gravity sewer in Expansion Area A connecting to the proposed new lift station, with an estimated cost of $700,000.

Expansion Area B—Fairway Lane

• Project B1—Install a new 1,700-gpm lift station north of Fairway Lane in Expansion Area B, with 8,500 feet of 12-inch force main and 400 feet of new 18-inch gravity sewer connecting to an existing trunk sewer, with an estimated cost of $3.34 million.

Expansion Area C – Crosby Road

• Project C1—Install a new 850-gpm lift station on Crosby Road in Expansion Area C, with 2,700 feet of 6-inch force main connecting to an existing trunk sewer, with an estimated cost of $1.82 million.

Expansion Area D—Goldie Road Enterprise Area

• Project D1—Install a new 1,400-gpm lift station between Oak Harbor Road and Goldie Road in Expansion Area D, with 1,700 feet of 12-inch force main connecting to an existing trunk sewer, with an estimated cost of $1.86 million.

• Project D2—Install 4,800 feet of new 18-inch gravity sewer along Goldie Road in Expansion Area D, with an estimated cost of $2.62 million.

Miscellaneous Collection System Improvements The following miscellaneous collection system projects that are not associated with capacity deficiencies or system expansion were identified:

• Install data recording and telemetry systems at existing lift stations

• A new standby generator for emergency power at lift stations

ES-6

• A flow monitoring study to verify base flows and quantify infiltration and inflow in the City’s collection system

• A study to assess corrosion in the RBC Plant Diversion Pump Station force main.

Table ES-4 summarizes the resulting recommended collection system improvements and estimated costs.

Figure ES-2 shows the project locations. The recommended improvements are proposed to be implemented in phases as needed. The schedule for implementation should be updated annually. The order of collection and conveyance improvements is coordinated with the recommended treatment plant improvements and assumes that all flows will be pumped from the existing diversion pump station at the RBC plant to the SPB lagoons.

Treatment Facilities A review of the treatment capacity and alternatives is contained in the Wastewater Treatment Facilities Evaluation section of this plan. Based on cost and qualitative considerations, Alternative 3, Activated Sludge, is the recommended alternative for meeting the City’s long term treatment requirements.

However, the conclusions and additional alternatives should be evaluated in more detail when the City prepares a wastewater facility plan to expand the plant in the future. Several miscellaneous improvements, such as a new headworks, lagoon dike protection, and upgrades to chlorination facilities are needed at the SPB lagoon treatment plant.