Night Flow Isolation Night flow Isolation is an important tool used in sewer evaluations to measure possible infiltration in the sewer lines. The objective of this task is to isolate sewer line segments and measure the suspected infiltration. Crew members perform this task in the sewer system during early morning hours, between midnight and 5:00 a.m. theoretically, at this time the sewer flows should be virtually zero. Usually, the test evaluates isolated sewer lines of approximately 1000 feet. The line segments tested must have all upstream lines plugged or isolated with other tests. These isolated lines with significant flows during the early morning hours are most likely to have significant infiltration. All inspection reports will be entered into a database. A binder with hard copies of the inspection reports including photos will be submitted to the engineer. All photographs will also be delivered in electronic format. The database and photographs will meet City requirements. A volumetric calibrated weir is a portable flow measuring device used to measure infiltration in newly installed and existing sewer lines. The volumetric weir is basically a compound weir that incorporates the advantage of a 90°V notch for measuring small infiltration flows where accuracy is imperative. It measures from 57 gallons per 24 hours to 3700 gallons per 24 hours, which is the range of normal sewer line Acceptance Test Requirements. The rectangular section is capable of measuring in gallons per day up to 35% of pipe capacity. Volumetric weirs are able to measure flow in 6", 8", 10", 12", 14", and 15" pipe. Adaptors for 18", 21", 24", 27", 30", 36", 42" and 48" pipe are used in conjunction with a 15" weir. All night flow isolation procedures will be performed in accordance with the specification provided by the City.