Launch Slideshow

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Low-impact inflow/infiltration investigation

Low-impact inflow/infiltration investigation

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    Six Micromonitors placed throughout 4.7 miles of sanitary sewer showed significant inflow and infiltration was limited to two of six sub-basins. As a result, Clayton County Water Authority managers limited investigative efforts to homes only within those areas. Photo: Stantec

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    A Micromonitor is ready to be installed. An early concept for the device was developed by David Saylor, president of Indiana's South Haven Utilities Water Works. Photos: Stantec

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    Close-up of a Micromonitor inside a controlled flow flume. Measurements of the level and flow under controlled conditions develop the low-flow rating curve for the weir as a primary device before it's installed in a sewer pipe.

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    Stantec Consulting Services Inc. engineers demonstrate a Micromonitor installation.


WHAT'S A ‘MICROMONITOR'?

Measure flows down to 1.0 gpm without a confined space permit.

Standard monitoring equipment can be unreliable in very-low-flow situations because debris sometimes obstructs the equipment, leading to inaccurate measurements.

Designed and developed by Stantec Consulting Services Inc., Micromonitors are fabricated fiberglass weir inserts installed behind standard area-velocity probes. The weir insert has a defined rating curve. At very low levels the weir is used as a primary device. If flow exceeds the limit of the weir's rating curve, the continuity equation is used to calculate the flow from the level-velocity data. The addition of the weir conditions the flow over the probe to prevent obstruction by debris, enabling the Micromonitor to measure flows down to 1.0 gallons per minute (gpm) — generally in low-flow sewer segments like those with only a few houses.

The device is installed with a street-level insertion tool, eliminating issues related to Occupational Safety & Health Administration confined space entry (CSE) requirements. Thus the Micromonitors efficiently adapt existing equipment and open up a new approach for pinpointing inflow and infiltration in upstream segments.

Without the need for permitted installation, rapid deployment is the hallmark of the micromonitoring approach. One person can remove Micromonitors from at least eight sites, download the data, change the batteries, recalibrate the meter, and install Micromonitors in eight new sites in one workday.

In-house micromonitoring can easily reduce costs to a couple hundred dollars per point measured, much less expensive than regional flow monitoring to find out how the entire collection system's performing. The process also identifies areas with the worst inflow and infiltration, limiting further investigation via intrusive techniques to only the homes in those areas.