Chester Engineers

Alum creek large diameter sewer assessment case study

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Courtesy of Chester Engineers

The Challenge

The City of Columbus, like many municipalities, must make hard decisions on where to spend their limited capital improvement dollars. In tight economic conditions, a municipality’s decision to monitor, rehabilitate, or replace their assets is not cut and dry. Deferred maintenance of non-critical assets in one department may give other departments the monetary resources to address serious problems with their facilities.

The Interdisciplinary Approach

Chester Engineers is working with the City of Columbus to assist in the rehabilitation planning of approximately 50,000 linear feet of 42 to 78 inch trunk sewers. The primary goal is to recommend the most efficient capital expenditure strategy by completing a Business Case Evaluation of several rehabilitation scenarios. The Business Case approach allows subjective issues such as social impacts to be compared with objective issues such as construction costs.

Chester Engineers worked with RedZone Robotics to collect CCTV with sonar data and reviewed the overall condition of the sewer.

Many times, decisions are made to rehabilitate a sewer based on the segment in worst condition. Unfortunately, taking this approach does not identify segments to be repaired if all sewers are in poor condition. To address this, we considered sewers that had a high likelihood of failure as well as sewers with a high consequence of failure – many times located near highways, bodies of water, or in high density urban areas.

Alternatives such as replacement, sliplining, CIPP, spot lining, gunite spot repairs, etc. were evaluated and the alternative with the lowest net present life cycle cost was selected. The lowest life cycle cost was not the same as the alternative with the lowest installation cost. For example, covering exposed rebar with gunite or shotcrete may cost less than lining, but the risk costs for doing “patch” repairs went up significantly for these options.

The Sustainable Result

Utilizing a Business Case approach allowed Chester Engineers to objectively evaluate and recommend the right capital expenditure strategy for the Alum Creek Trunk sewer. This approach ensures that decisions are made in a manner that looks beyond a single project and helps the City effectively utilize capital improvement dollars on the their most critical assets. In addition, the establishment of a systematic approach allows Chester to quickly and efficiently evaluate future projects for the City of Columbus.

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