Septic Drainfield Trench Length

Required absorption area and trench linear feet from design daily flow and the application rate set by your local code.

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Formula and source

Required absorption area = design_daily_flow_gpd / application_rate_gpd_per_ft². Trench feet = required_area / trench_width_ft.

U.S. EPA Onsite Wastewater Treatment Systems Manual (EPA/625/R-00/008) by name; per-state and per-county application rates set by local code (not bundled).

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Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.