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*A layer of geotextile is usually then used to prevent migration of fines into the underdrain/reservoir space.
*A layer of geotextile is usually then used to prevent migration of fines into the underdrain/reservoir space.
A pair of small wells are recommended to inspect and periodically flush accumulated sediment from the underdrain pipe.
A pair of small wells are recommended to inspect and periodically flush accumulated sediment from the underdrain pipe.
==Maintenance and inspection==
**Well(s), of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.
**Where a horizontal underdrain is being installed, an upstream and a downstream well should be coupled to the underdrain pipe. The pair of wells can then be used to flush out the length of underdrain if required.
==Material specifications==
==Material specifications==