When an on-site stormwater disposal system installation requires an excavation deeper than 5 feet (1524 mm), the sides of the excavation shall be protected and maintained in accordance with Section 3304.4 of the New York City Building Code.
Where the installation of an on-site stormwater disposal system requires the installation of a sand column, measures shall be taken to ensure the sand column is installed without contamination by impervious materials.
The department reserves the right to require a 24-hour test to verify the absorption of water in the installed on-site stormwater disposal system prior to final approval.