Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity Flow Applications.”

Reference Note 2 states: All retention and detention systems shall be installed in accordance with ASTM D2321.

Reference Note 3 states: Measures should be taken to prevent migration of native fines into the backfill material.

Reference Note 4 indicates: Use a filter fabric such as a geotextile fabric as specified by an engineer to prevent the migration of fines from the native soil into the select backfill material.

Reference note 5 covers the foundation. If the trench is unstable, the contractor should excavate to a predetermined depth and replace it with suitable material. A design engineer can call for the trench bottom to be stabilized using a geotextile material.

This drawing includes a table for reference to support the drawing. The table provides values for the nominal diameter, the nominal O.D., typical spacing “S”, nominal spacing “C”, the typical side wall “X”, non-traffic “H” height, and traffic “H” height.

Other notes cover information about suitable bedding materials, initial backfill requirements and the necessary minimum cover. Refer to the drawing for more specific details.