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Inflow and Infiltration (I & I) Annual Reports
What is an Inflow & Infiltration annual report?
Every year, City staff or their consultants write an Inflow & Infiltration program annual report describing the highlights of what was accomplished over the course of the outgoing fiscal year. The City’s fiscal year runs from the first day of July through the last day of June every year. It is for financial reporting and budgeting purposes.
The annual report summarizes the I&I projects that were in design or in construction, progress made on the City’s Lateral Program, annual flow monitoring, and pipe testing data collected over the year.
Summary of 2022-2023 Annual Report
WORK ACCOMPLISHED IN 2022-2023
Lateral Policy Development
The project team worked with the city to develop and refine a private property lateral policy to enable the program to address infiltration and inflow deficiencies within private property. Rehabilitation of private laterals was incorporated into every design package initiated this year and will continue being incorporated going forward.
Basin Condition Assessment
CCTV video footage for approximately 79,000 linear feet of sewer mainline was collected and reviewed. The team prepared a database of the conditions filmed to then categorize the types of repairs needed, prepare a cost estimate and create a prioritized list of the segments that need to be designed.
An additional 55,000 linear feet of CCTV in Basins 5, 5A, and 5B is in progress.
Design Services
1. Linn Basin SS I&I Rehabilitation 1 CI 23-001 – Design 90% complete
Pilot project that consists of 11,000 linear feet of mainline sewer pipe and associated public side laterals within Basin 8 (Linn). This will need CIPP rehabilitation with some spot repair and open excavation lateral replacement.
2. Linn Basin SS I&I Rehabilitation 2 CI 23-002 – Design 90% complete
The second design package within Basin 8 (Linn) consists of 1,800 linear feet of mainline sewer pipe, manhole replacement and associated public side laterals. This will address some high priority maintenance concerns that will require full replacement with open trench or pipe bursting methods.
4. Rivercrest SS I&I Rehabilitation 4 CI 23-009 – Final Review
FLOW MONITORING GENERAL SUMMARY
Flow Monitoring and Analysis
At the outset of this project the City modified the boundaries for all of the sanitary sewer basins throughout the system. Basins 5 and 12 were divided into five separate basins (now Basins 5, 5A, 5B, 12, and 12A). As a result, flow data for all basins needed to be updated. New baseline flows were obtained for basins 5/5A/5B, and the baselines were refreshed for basins 8 and 12 (12A was not monitored separately).
Flow meters were installed and monitored flows at 4 sites (Basins 5B, 8, 10 and 12) from March 20, 2023 to May 8, 2023. The meters captured flows during a significant storm event on April 10th with a 1.16 inch 24-hour rainfall depth.
New flow data has been collected and used to recalibrate the hydraulic model (last updated over 10 years ago). The model will be calibrated with parameters to the April 10th storm event, and the model will be run with a new prediction of 5-year flows and distribution of I/I throughout the 4 priority basins.
Summary of 2023-2024 Annual Report
WORK ACCOMPLISHED IN 2023-2024
In its second full year, the Oregon City I&I Rehabilitation Program is continuing to investigate, design, and construct projects that will reduce Inflow and Infiltration (I & I) into the Oregon City sewer system and into the Water Environmental Services (WES) Tri-City Wastewater Treatment Plant. This program focuses on six sewer basins determined to have the most I&I issues.
The engineering design for several basin rehabilitation projects are nearing completion. Construction is completed on one basin package and the manhole sealing program. Two more basin rehabilitation packages will start construction after July 1, 2024. At the end of the 2024 calendar year, 4.7 miles of sewer mainline and 4.4 miles of private laterals will be rehabilitated.
I&I Rehabilitation Program effectiveness is measured by flow monitoring the amount of water in the sewer system. A low I&I system should have roughly the same amount of water flowing in the mainline pipes regardless of rainfall amounts in the area. A yearly flow monitoring and analysis in the target basins will determine program effectiveness. This year’s monitoring showed reductions in flow with only partial basin rehabilitation and manhole sealing completed (Linn Basin).
Looking ahead to 2024-25, the design of three new area packages and the construction of four packages are planned.
REHABILITATION HIGHLIGHTS
(through June 2024)
- 42% of Program pipes investigated
- 9% of sewer mainline rehabilitated
- 91 laterals replaced
- 95 manholes rehabilitated
Construction complete
The first lateral construction project, Linn Basin Sewer I&I Rehab Project 1 (Linn 1), which started construction in December 2023 was completed in June 2024. The construction of Linn 1 provided a chance to refine the I&I Reduction Program specifications and communication protocols. The Program Manager worked with the City, the Contractor, and public works staff to find solutions to issues noted during bidding and construction.
Private Laterals
Improving private side sewer laterals is critical to effective I&I reductions. As such, the I&I Reduction Program includes a strong effort to obtain Rights of Entry (ROEs) from private property owners to facilitate the investigation, design, and construction of private side lateral improvements. This year the project increased ROE response from 80% to 95% by having construction contractors engage with neighbors while onsite.
Testing completed this year
- CCTV for 100,000 feet of mainline sewer.
- Almost 18,000 feet of mainline sewer reviewed.
- Smoke testing on 135,000 linear feet of mainlines with 206 manholes.
Smoke testing found 159 potential sources of I&I:
- 27 Cleanouts
- 26 Ground leaks
- 24 Storm catch basins
- 44 Illicit connections
- 5 Stand pipes
- 33 Miscellaneous defects
A majority of the issues were found in the McLoughlin Basin.
REHABILITATION DESIGN AND CONSTRUCTION PROJECTS UNDERWAY
There are 10 design projects in progress this year, including:
1. Linn Basin SS I&I Rehabilitation 1 CI 23-001 – Construction complete
2. Linn Basin SS I&I Rehabilitation 2 CI 23-002 – At 90% Design
3. Molalla Ave. SS I&I Rehabilitation CI 23-013 – Bidding
4. Rivercrest SS I&I Rehabilitation 4 CI 23-009 – Final Review
5. Newell Basin SS I&I Rehabilitation 1 CI 23-012 – In Scoping
6. Linn Basin SS I&I Rehabilitation 3 CI 23-003 – In Scoping
7. McLoughlin SS I&I Rehabilitation 2 No CI Number – Investigation
8. Center St/Catch Basin Disconnect CI 23-005 – At 30% Design
9. McLoughlin SS I&I Rehabilitation 1 CI 24-005 – Investigation
10. Manhole Rehabilitation CI 23-011 – Construction complete
FLOW MONITORING
Flow monitoring efforts for FY 23-24 were focused on gathering pre-construction flow data to set a baseline for measurement of post-construction flow data and determination of I&I reduction. The I&I Reduction Program is intended to prioritize areas with the highest I&I, so the four basins selected for flow monitoring are located in high I&I areas – the Newell, Linn, Rivercrest, and Warner Parrott Basins.
The Linn Basin is the first basin that was monitored before and after rehabilitation work – winter 2024 monitoring took place after completion of approximately 50% of Linn I&I Rehab Project 1. Work in the Linn Basin included mainline sewer rehabilitation and lateral rehabilitation covering approximately ¼ of the basin. Based on observations of peak flow rates from 2023 and 2024 there are indications that the rehabilitation work reduced I&I in the basin.
summary of 2024-2025 annual report
In its third year, (5-year program) the Oregon City I&I Rehabilitation Program continues to investigate, design, and construct projects that will reduce Inflow and Infiltration (I & I) into the Oregon City sewer system and into the Water Environmental Services (WES) Tri-City Wastewater Treatment Plant.
Extensive CCTV and smoke testing efforts were conducted this year, and flow monitoring in each of the City’s identified I&I basins indicates program success.
Contractor-led outreach during construction raised Right of Entry responses from private property owners from 80% to 95% (to allow lateral repairs and investigations on private property).
Oregon City won the 2025 Large City Award of the Year for the I&I Rehabilitation Program through the League of Oregon Cities.
PROJECT DELIVERY
The I&I program focused on creating data-driven, holistic projects to ensure prioritized areas received complete rehabilitation before moving to the next zone, while coordinating efforts with other City programs to avoid duplicative work. Projects addressed critical factors like geohazard planning, cultural resource investigations, historic property preservation, and easement/Right of Way (ROW) acquisitions.
WORK ACCOMPLISHED THIS YEAR
This year, the program moved three projects into construction and has two more with nearly final designs. These projects include rehabilitation of nearly 15,000 linear feet of sanitary sewer main, 475 sanitary sewer laterals, and more than 120 sanitary sewer manholes.
Two projects were completed: Linn Basin SS I&I Rehabilitation 1 CI 23-001 and Molalla Ave. SS I&I Rehabilitation CI 23-013.
Three new design projects are scheduled for construction in 2025-2026, five are scheduled for various stages of design, and as many as four additional projects are underway based on ongoing investigation efforts.
REHABILITATION HIGHLIGHTS
(Through June 2025)
- 60% of Program pipes investigated
- 13% of sewer mainline rehabilitated
- 51% of lateral rehabilitated/Laterals inspected
- 100 manholes rehabilitated
- 391 Right-of-Entry forms approved
TESTING AND EVALUATION COMPLETED THIS YEAR
- 18,000 lineal feet of mainline sewers evaluated from CCTV inspections, smoke testing, and dye testing results.
- Smoke testing on 152,370 linear feet of mainlines, identified 34 sources of inflow with most coming from degraded manholes.
REHABILITATION DESIGN AND CONSTRUCTION PROJECTS UNDERWAY
8 projects are currently in progress, on the spectrum of design to construction:
- Newell Basin SS I&I Rehabilitation 1 CI 23-012 – Beginning design
- Linn Basin SS I&I Rehabilitation 2 CI 23-002 – Moving into construction
- Linn Basin SS I&I Rehabilitation 3 CI 23-003 – Moving into construction
- Linn Basin SS I&I Rehabilitation 4 – Moving into construction
- McLoughlin SS I&I Rehabilitation 2 No CI Number – Moving into construction
- McLoughlin SS I&I Rehabilitation 1 CI 24-005 – Moving into construction
- Manhole Rehabilitation CI 24-012 – Construction
- Rivercrest SS I&I Rehabilitation 4 CI 23-009 – Construction
FLOW MONITORING
Flow monitoring plays a crucial role in measuring progress toward reducing infiltration and inflow in Oregon City’s sanitary sewer system. Since I&I is influenced by precipitation and winter water tables, peak flows during the winter season strain sewer infrastructure. The program tracks wet weather flow before and after construction and conducts annual monitoring to reach its ultimate goal of a 65% reduction in I&I peak flows.
In FY 24-25, a revision of the City’s flow model was prepared. The “2024 Flow Monitoring Report” summarizes the modeling results and analysis of collected flow data. An update of this model including FY 24-25 flow data will be prepared in the Fall of 2025 to give a more detailed analysis of basin flow results. The model will update peak flow projections in each basin during 5-year and 10-year storm events. This information will be critical to determine progress towards the I&I reduction goals.
Flow modeling and data analysis from FY 23-24 show encouraging results in the one post-construction basin area that was monitored. Updates in the coming year will include post-construction results in several basins and will hopefully provide further evidence of program success.
A BRIEF OVERVIEW OF THE FISCAL YEAR 2024-2025 FINDINGS:
- Newell Basin was monitored for the first time during the wet season of 24-25, at the same time as construction of the Molalla Ave project. There has been an initial indication of peak flow reduction, with more analysis needed.
- Linn Basin 2024 peak sewer flows indicate the I&I repairs completed as part of project 1 successfully removed some amount of I&I from the system.
- Rivercrest Basin has had ongoing construction since the end of 2024, and monitoring was completed during this construction. This year’s flow monitoring was completed before the construction on private laterals was completed.
- Warner Parrot Basin has not seen consistent flow data since the program’s inception, and flow monitoring conducted in FY 24-25 using a new permanent flow measuring device will hopefully help establish true baseline flow results for the basin. No construction has yet occurred in this basin.
- South End Basin was a late addition to the program, and the presence of newer infrastructure in the basin has led to low prioritization of work there. Most of the basin flows through the Parrish Rd pump station, so flow monitoring was conducted there to establish baseline flows for the basin. Initial results indicate pump station flows do not correlate strongly with rainfall events, and I&I in the basin may be minimal.
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