Flow Measurement is Crucial to Preventing Overload

Flow measurement is a missing link in computing why septic systems may fail. Do we really know the flow entering a septic tank? Do we really know a way to justify when a septic system is in a state of hydraulic overload? Daily flow can exceed the design capacity of the system, resulting in frequent sewer backups or puddling of sewage onto the ground surface.

Is the guess of daily sewage flow based on an engineer prescription or a value based on the number of bedrooms, seats, etc.? Septic codes in each state adopt a value for daily sewage flow. However, the value is different from state to state. Two state agencies may disagree on the same estimated value. Is the value accurate enough to constitute reasoning or could a misdiagnosis of the estimated sewage flow affect system design? A poorly designed system can lead to premature failure.

The only real solution is this: water usage records have been an acceptable way to calculate average daily flow where septic systems have been repaired. Using this method may hint if hydraulic overloading has occurred and if this condition is an ongoing issue in system performance. At present, this can only be calculated by subtracting the water used for filling the swimming pool or for irrigating the yard from the mass flow.

When a building served by an onsite septic system is not connected to a metered water system, verification of above normal flow cannot be proved unless the flow can be metered. If in-line flowmeters are used on drinking water systems, they should also be available for private water systems serving a residence or business. Using such a flowmeter would register the mass flow used. The mass flow includes the usage from showers, baths, toilet flushes, tooth brushing, dishwashing, laundry, and other indoor uses. Lawn watering and other outdoor uses are also considered into the mass flow equation. As one septic tank contractor commented, “There would be no basis for an argument from the homeowner about water usage anymore.”

Let’s take that thought to the next level. Can we specifically measure sewage flow in a gravity sewer line? Infiltration, inflow, and exfiltration can affect sewage flow. Often, these conditions are not considered when a septic system is sized. When there is a break in the sewer line, or if the sewer clean out cap is missing, this can affect the flow entering a septic tank. So, do we really know the sewage flow of any system?

The flow of a single waste stream should be able to be measured without comparing the mass flow from water used for filling the swimming pool or for irrigating the yard.

Being able to meter sewage flow would be a benefit to septic utility groups and septic tank contractors that service onsite management programs. Metered sewage flow should not burden a mandated regulation upon every system in use. The idea would be to offer a way to monitor those septic systems where hydraulic overloading is suspected. Alternative measures to conserve water could be addressed in those cases to prevent the occurrence of system overuse. The system user should be advised that flow measurement can benefit the overall management of system performance. Bottom line: homeowners should be able to monitor daily sewage flow accurately.

Story by Albert Royster

Albert Royster is an Environmental Specialist with Volusia County Health Department, Deland, FL. For more information or to learn solutions to measuring flow, contact Albert at Doctorseptic@cfl.rr.com.

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