Plainfield, NJ Environmental Rules: Stormwater Management (2026)

Article XII of Chapter 17 of the Plainfield Municipal Code, Stormwater Management, was amended in its entirety on 9-9-2024 by Ord. No. MC 2024-48. Section 17:12-1 covers non-major development, and § 17:12-2 and its subsections cover major development.

Under § 17:12-1, all development must have a stormwater management plan consisting of, but not limited to, inlets, manholes and pipes where necessary for proper surface drainage. The system must carry off or store stormwater and natural surface runoff that originates within the property and beyond the tract boundaries. Where possible, runoff must leave the site in the same watershed in which it originated, and must not overload existing drainage systems, create flooding or increase predevelopment erosion of adjacent lands.

The peak rate of runoff during and after development cannot exceed the predevelopment peak rate. Development upstream of known areas of problem flooding must reduce the peak rate below the predeveloped rate. Where the upstream tributary drainage area exceeds fifty (50) acres, the NJDEP Technical Manual for Stream Encroachment standards in N.J.A.C. 7:13-2.8 govern. The increase in runoff volume must be minimized, using measures such as infiltration pits, dry wells, infiltration trenches and sheet flow through vegetated areas.

Calculation methods are set out: the rational method for areas up to twenty (20) acres, with a minimum time of concentration of five (5) minutes, and hydrograph analysis (TR55) for larger areas. Collection systems must handle a storm frequency of once in ten (10) years on rural, local and minor collector streets, and once in twenty-five (25) years for secondary arterial and major collector streets and all open channels. No storm drain pipe may be smaller than fifteen (15) inches in diameter, closed conduit velocities run from two (2) to ten (10) feet per second, and inlets are spaced so surface water does not flow more than five hundred (500) feet.