System-Wide Sewer Rehabilitation – Efficiency in Design
Abstract:Large, system-wide sewer system rehabilitation programs can take years to move from planning projects (inspection and condition assessment) to actual design contracts. Because of that lengthy process and the dynamic nature of infrastructure asset deterioration, the design engineer is often faced with decisions as to what previous inspection data can be used for the design and what additional inspection is needed to complete the design. By recognizing these challenges early on, there are approaches to design that make the most efficient use of time and budget on these large-scale projects.
The Northeast Ohio Regional Sewer District (NEORSD) provides wastewater conveyance and treatment for 61 municipalities in the Greater Cleveland metropolitan area. In the late 1990s, the District conducted a comprehensive interceptor inspection and condition assessment program incorporating every interceptor and dry weather outlet in the three District combined sewer service areas totaling approximately 1.2 million feet of sewer. Following this work, the District conducted a series of interceptor rehabilitation design projects based on their findings. The rehabilitation work was bid under seven different construction contracts as follows:
2 – Spot Repair Contracts (Totaling 6.2 million)
2 – Sewer Lining and Replacement Contracts (totaling 25.3 million)
2 – Sewer Cleaning Contracts (Totaling 4.3 million)
1 — Manhole Rehabilitation Contract (Totaling 1.3 million)
Design has been completed on all seven interceptor rehabilitation contracts over the period of 2001 through 2009. Construction has been completed on six of the seven projects. The final construction contract began in February 2010 and is scheduled to be completed in August 2011.
The inspection and evaluation program identified pipes and manholes needing rehabilitation. Due to project packaging (by work type and service area), and incorporating rehabilitation projects into a crowded capital improvement plan, the timing of the rehabilitation work stretched over a number of years. By the time some of the design projects were initiated, the original inspection data was up to 12 years old. All sewer reaches identified for lining or replacement were re-inspected as part of the design contract to ensure that design is based on current information. However, the lining and replacement only accounted for approximately 112 reaches. There were more than 980 sites identified for cleaning, spot repairs, or manhole rehabilitation. Because it was not practical or cost effective to re-inspect all of these reaches or manholes, much or, in some cases, all of the data included in the construction documents had to be based on the historic information for condition, location, access, and rehabilitation recommendations. Due to the inherent changing nature of this information, the challenge faced was how to effectively verify the design data and reduce potential contract change orders.
When evaluating whether to rely on previous inspection data or conduct additional inspection activities there are several issues that need to be considered:
Will you conduct any re-inspection as part of design?
If so, how much will you re-inspect?
How will you decide which reaches to re-inspect and which to use the historical data?
What are the implications of using old data?
Is there a more efficient and effective way to spend your design money to verify this information for design?
How do you interpret and incorporate historical inspection and condition assessment data from various sources?
What is the critical information that needs to be included in the design documents?
This paper will focus on how NEORSD approached the answers to all of these questions and ways to incorporate the lessons learned on better approaching data verification during design. This methodology was developed and refined over the course of the eight-year rehabilitation design program and will provide guidance for determining the most efficient use of available design investigation budget for other system-wide improvement projects.
In 2009, the District began design for rehabilitation of their combined sewer overflow (CSO) system which also is based on historical inspection data up to 12 years old. The methodology developed during the interceptor design program has also been implemented for the design of the three CSO rehabilitation projects estimated at 29 million in construction cost. Design of the cleaning, spot repair, and manhole rehabilitation contract was completed in August 2010. The results and additional lessons learned from the design investigation phase of this project also will be discussed.
Document Type: Research Article
Publication date: 2011-01-01
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