Application corner: Sewage districts case is resolved

May 3, 2023
The final installment of a multi-part series that examined a case involving flow measurement disputes, two sewage districts and a water treatment plant.

February's article showed that a superior flowmeter was installed in series with each of two billing flowmeters as a result of a legal dispute regarding the second sewage district’s billing for treating sewage from the first sewage district. Measurements clearly showed that the billing flowmeter measured significantly higher than the superior flowmeter. However, a court ruling allowed the second sewage district to continue operating the billing flowmeters “as is.”

Some years later, the sewage flow measured by one of these two flowmeters that had been measuring approximately 50% higher than a superior flowmeter in series suddenly dropped approximately 70% and remained low for a few days. The drop in flow and its resultant revenue loss was so extreme that the lawyers and engineers from both districts were asked to attend a joint inspection of the installation.

Physical observation revealed that the second district had replaced the flowmeter and changed its transmitter technology to measure level at the correct location in the flowmeter primary element. In addition, the steel piping immediately upstream of the flowmeter was replaced with fiberglass reinforced pipe that had a considerably smaller inside diameter than that of the existing pipe it replaced, which made the sewage drop into the flowmeter instead of flowing straight into the flowmeter.

Faced with a loss of revenue, the second sewage district re-installed the fiberglass reinforced pipe with steel pipe a few days later. This action stands in stark contrast to the second sewage district’s lack of interest in correcting the previous installation that had been overbilling the first sewage district for years. After making these changes, the billing flowmeter measured less than 10% higher than the first district’s superior flowmeter — much less than the approximately 50% measured prior to the change. 

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