There are a few additional design considerations that will need to be taken into account when preparing a Stormwater Pollution Prevention Plan for Residential Subdivisions, particularly those developing subdivisions.
Residential Subdivision Guidance
Residential Disturbance Formula
Amount of Disturbance = 2[Max Restricted Building Size][Number of Lots] + Right of Way Areas
*Max Restricted Building Size = Maximum
Disturbed Area per Lot (Acres)
Residential Note for Plans
The site is not to be mass-graded. Only 2 times the footprint is to be cleared as the lots are developed. The assumed disturbance on each lot is _____ sq. ft."
One of those considerations that will affect the stormwater management plan of a Residential Subdivision Projects is the decision if the subdivision is to be mass graded or not. If the decision is made for the site not to be mass graded the following steps must be implemented while developing the SWPPP:
- Determine the Disturbed Area based off the Residential Disturbance Formula provided in the Residential Subdivision Guidance to the right.
- Include a note on the plans that states the site is not to be mass graded and the amount of disturbance allotted for each lot. (See Residential Guidance)
- Provide a Residential Lot Detail that illustrates how much of the lot may be disturbed in addition to the placement of BMPs.
Developers may decide that they do not wish to include any of the residential lot's disturbed area in their NPDES Permit Coverage when deciding to not mass grade the site. In this case, the Max Restricted Building Sizevalue would be Zero (0) in the above Residential Disturbance Formula and each individual lot would have to apply for NPDES coverage under a separate permit number but part of a Larger Common Plan (LCP) .
Larger Common Plan (LCP)
A Larger Common Plan (LCP) is "broadly defined as any announcement or piece of documentation (including a sign, public notice or hearing, sales pitch, advertisement, drawing, permit application, zoning request, computer design, etc.) or physical demarcation (including boundary signs, lot stakes, surveyor markings, etc.) indicating construction activities may occur on a specific plot."
63 Federal Register No. 128, July 6, 1998, p. 36491
For example, if master calculations have been prepared and/or submitted for an entire site, then all phases and parcels at that site would be considered part of an LCP. If the site is part of a subdivision, industrial park, commercial park, etc., then it is considered to be part of an LCP.
Any land-disturbing activities, including clearing, grading or excavating, on any site considered part of a Larger Common Plan, based on the definition above, would be required to obtain coverage under the NPDES Construction General Permit even if the land-disturbing activities resulted in a disturbed area of less than one (1) acre.