Hello Michael,
I'm currently working for a utility that serves a population of ~30k. I'm fairly new to the industry but here are our general methods:
Q: What ratio of renewal vs. full replacement do you typically see in your program?
A: I would say we largely prefer renewal. The majority of our system is ca 1960s and newer with mostly clay and pvc where most of the issues can be resolved by a week or two worth of trenchless work. Sometimes we set out on larger projects to relocate a main that is in a bad location (ie highway r/w or backlot) when we feel it is a better long-term decision.
Q: How much of your gravity system has undergone condition assessment (e.g., % inspected per year or total inspected to date)?
A: We inspect our wastewater basins on a rotation. I don't know how much is inspected per year, but we have a fairly good idea of the condition of certain areas through ongoing maintenance activities.
Q: Do you more often perform full manhole‑to‑manhole replacement, or do you rely heavily on trenchless methods such as spot lining, point repairs, manhole‑to‑manhole lining, or pipe bursting?
A: When we do rehab work, we mostly consider trenchless methods since it is less intrusive. We have done a large rehab project in recent years that employed all of the previously mentioned trenchless methods based on a study of our collection system. For general maintenance that our crews perform, we recently started doing point repair work for the smaller issues in the system.
Q: What defect thresholds or decision criteria push you from trenchless rehabilitation to full replacement?
A: The biggest decision criteria as previously mentioned is the location of the main. If the main is located in a highway r/w, we will heavily consider moving it to avoid safety issues for both our crews and contractors that have to perform work on the main. It also saves a lot of time that is spent adjusting manhole rims during the routine overlay projects. Other times a main may be moved when it is a part of a long range plan to alter the collection system in some way.
Q: How often do you upsize structurally deficient segments, and what typically drives that decision?
A: Not very often. In our last rehab project a few years ago we did upsize some segments based on recommendations from a sewer study that was conducted. The growth of my city is also somewhat limited in this aspect due to zoning restrictions, so this hasn't created the issue of some mains becoming undersized.
Hope this helps.
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Will Gander EI, M.ASCE
Civil Engineer
Beech Grove AR
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Original Message:
Sent: 03-13-2026 11:27 AM
From: Michael Tran
Subject: Gravity Sewer Renewal & Replacement Programs
Hi everyone,
I'm looking to compare gravity sewer renewal and replacement practices across different utilities, and I'd really appreciate any insights from your programs.
A few specific questions:
What ratio of renewal vs. full replacement do you typically see in your program?
How much of your gravity system has undergone condition assessment (e.g., % inspected per year or total inspected to date)?
Do you more often perform full manhole‑to‑manhole replacement, or do you rely heavily on trenchless methods such as spot lining, point repairs, manhole‑to‑manhole lining, or pipe bursting?
What defect thresholds or decision criteria push you from trenchless rehabilitation to full replacement?
How often do you upsize structurally deficient segments, and what typically drives that decision?
Thanks in advance for any feedback-large or small. It's all helpful. I'm cross-posting this on a few forums as well.
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Michael Tran P.E., M.ASCE
San Francisco Public Utilities Commission
San Francisco CA
(415)695-7372
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