FROM: James D. Herberg, General Manager
Originator: Riaz Moinuddin, Director of Operations & Maintenance
SUBJECT:
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SONAR INSPECTION OF LARGE-DIAMETER SEWERS AND SIPHONS
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GENERAL MANAGER'S RECOMMENDATION
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RECOMMENDATION: Recommend to the Board of Directors to:
A. Approve a General Services Contract to Pipe and Plant Solutions, Inc. to provide Sonar Inspection Services, Specification No. S-2022-1327, for a total amount not to exceed $344,949; and
B. Approve a contingency of $34,495 (10%).
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BACKGROUND
Orange County Sanitation District (OC San) maintains more that 350 miles of gravity sewer pipes in its service area which are cleaned on a scheduled basis consistent with OC San's Sewer System Management Plan (SSMP). Line segments range in size from 8 inches to 120 inches. Depending on the pipe size and historical issues, cleaning frequencies have been developed and range from every 4 weeks to once every 5 years.
For smaller diameter pipes ranging from 8 inches to 18 inches, cleaning is conducted primarily through hydraulic flushing and vacuuming using a combination sewer cleaning vehicle. For medium diameter pipes ranging from 21 inches to 42 inches, pipes are cleaned mechanically using a cable tethered tire to act as a moving hydraulic scouring plug. Pipes greater than 42 inches are generally designed to be "self cleaning" by creating internal flow velocities that scour potential sediment. These pipes require special cleaning techniques such as flow diversions to increase flow velocity, specialized hydraulic cleaning systems, or human entry depending on the specific situation.
In 2020, a hydraulic analysis of large-diameter sewers and inverted siphons was performed to verify these sewers maintained adequate scour velocity in current flow conditions. At the same time, large diameter lines with known or suspected low flow velocities were inspected with a sonar device for pipe defects or sediment buildup b...
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