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NSF 240

2017 Edition, January 21, 2017

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Drainfield Trench Product Sizing for Gravity Dispersal Onsite Wastewater Treatment and Dispersal Systems

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Product Details:

  • Revision: 2017 Edition, January 21, 2017
  • Published Date: January 21, 2017
  • Status: Active, Most Current
  • Document Language: English
  • Published By: NSF International (NSF)
  • Page Count: 34
  • ANSI Approved: Yes
  • DoD Adopted: No

Description / Abstract:

This Standard provides a methodology to compare, assess and document product sizing criteria for alternative or proprietary products with respect to conventional coarse aggregate used in onsite wastewater dispersal drainfields, based on comparative hydraulic performance.

The comparative treatment performance of alternative products compared to performance of conventional systems is not within the scope of this Standard.


The purpose of this Standard is to establish minimum material, design, construction, and performance requirements for comparing gravity dispersal drainfield products based on hydraulic performance used in place of conventional coarse aggregate within onsite wastewater treatment and dispersal systems. This Standard also specifies the minimum literature that manufacturers shall supply to authorized representatives. Two alternate protocols for establishing the sizing relationship are provided.

Long term acceptance rate (LTAR)

In 4, the long term acceptance rate (LTAR) of gravity dispersal drainfield products using alternatives is compared to conventional coarse aggregate trench media. Bottom area sizing and infiltration rate comparisons are based on test center data collected using multiple product and control trench cells under accelerated hydraulic loading conditions. Independent variables that may affect hydraulic infiltration shall be controlled.

Field performance assessment (FPA)

Field Performance Assessment (FPA) methodology evaluates relative failure rate studies of systems constructed using alternatives to conventional natural coarse aggregate. This methodology compares drainfields’ bottom area (footprint) with respect to the system’s hydraulic performance (hydraulic failure) to arrive at a suitable bottom area relationship. Manufacturers of general use products, as defined in 3, which include technologies in use for 10 or more years, may apply for certification under this Standard, including a statement of the bottom area relationship.