From the 2022 NYC Building Code:
1705.27 Private on-site storm water disposal systems and detention facilities.
Storm water detention and retention systems required to comply with Section 1114 of the New York City Plumbing Code, and roof detention facilities shall be inspected for compliance with the provisions of this section.
1705.27.1 Subsurface investigation special inspection.
Soil borings, test pits and soil percolation testing shall be subject to the special inspection requirements of this section.
1705.27.1.1Soil borings and test pits.
Prior to the approval of construction documents, soil borings and test pits shall be performed in accordance with the provisions of Section 1114.2.1 of the New York City Plumbing Code. Soil borings and test pits shall be performed under the supervision of a special inspector. The results of the soil borings and test pits shall be filed on forms provided by the department.
1705.27.1.2 Soil percolation tests.
Prior to the approval of construction documents, soil percolation tests shall be performed in accordance with the provisions of Section 1114.2.2 of the New York City Plumbing Code at the site of a proposed on-site stormwater drainage and detention facility installation to determine the suitability of the soil and site. Such test shall be performed under the supervision of a special inspector. The results of the percolation tests shall be filed on forms provided by the department, stating the suitability of the site and the capacity of the subsoil for the proposed use. The registered design professional of record for the dry-well system shall be notified immediately if the results of the percolation test demonstrate that the system may not function as designed.
1705.27.2 Installation special inspection.
Private on-site stormwater disposal systems and detention facilities shall be inspected for conformance with the approved construction documents. Minor variations, based on actual site conditions, shall be acceptable at the discretion of the registered design professional of record. Verification shall include:
Materials of construction.
Compliance of bedding, per Section 306 of the New York City Plumbing Code of pipe and facilities.
Placement and installation of fill materials.
Volume of drywell and detention facilities.
Installation of volume flow control devices.
Workmanship and quality of installation.
Overall conformance with the approved construction documents.
Detention tanks, and roofs used for stormwater detention, shall be filled with water to demonstrate water tightness for a 2-hour duration or as specified by the registered design professional or the manufacturer’s specifications.