This drawing offers a recommended layout and specifications for installation of the ADS Retention-Detention system for drainage.

The drawing shows the nominal pipe diameter as related to minimum and maximum depths, embedment limits, typical side walls, pipe cover depth under traffic and not under traffic, pipe fittings under traffic and not under traffic, fittings cover depth and bedding depth.

References in the drawing to Class I or II materials are per ASTM D2321 “Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity Flow Applications".

All references to AASHTO material specifications are per AASHTO M43 and M145 gradations.

Retention and detention systems shall be installed in accordance with ASTM D2321, latest edition and the manufacturer's published installation guidelines. Measures should be taken to prevent the migration of native fines into the backfill material, when required, see ASTM D2321.

Geotextile filter fabric may be used as specified by the engineer to prevent the migration of fines from the native soil into the selected backfill material. Suitable bedding material should be Class I or II. The contractor shall provide documentation for material specification to the engineer.

Suitable backfill material should be Class I or II in the pipe zone extending not less than 6" (152 mm) above the crown of the pipe. All backfill materials shall be installed as required in ASTM D2321, latest edition. If a different fill is used in zones b and c, filter fabric may be used as specified by the engineer.

Additional cover may be required to prevent floatation. For traffic applications, minimum cover is measured from top of pipe to bottom of flexible pavement or to top of rigid pavement. Maximum fill height is limited to 8 ft (2.4 m) over fittings for typical system installations. please note these limits apply to all fittings within systems limits, and not just manifold fittings.

This drawing provides information on acceptable fill materials for the ADS Retention-Detention System Installation.