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Low Impact Development
Regulated Projects must provide a Stormwater Control Plan that describes and illustrates the exclusive use of Low Impact Development (LID) measures. Provision C.3.c of the Municipal Regional Stormwater NPDES Permit requires each Regulated Project to treat 100% of a project’s stormwater runoff with LID treatment measures as of December 1, 2011. 

LID measures include:
  • preserving existing open space areas and reducing the amount of impervious surfaces (Site Design); 
  • preventing stormwater runoff from coming into contact with pollutants (Source Control); 
  • removing pollutants from stormwater runoff (Treatment); and 
  • retaining or detaining runoff (Hydromodification). 

LID Treatment Measures include:
  • Infiltration; 
  • Evaportranspiration; and 
  • Biotreatment. 

Infiltration is the preferred method. Biotreatment is only permitted if Infiltration and/or Harvest and Use are infeasible. There is no separate evapotranspiration treatment measure because this process occurs naturally in infiltration, harvest and use, and biotreatment.

The standards for determining if infiltration is feasible or infeasible are based on a report by Geosyntec Consultants: BASMAA Harvest and Use, Infiltration and Evapotranspiration Feasibility/Infeasibility Criteria Report. The process to determine which Treatment Measure is appropriate to use is described under Application Requirements. 

For more information about these using these techniques, refer to the C.3 Stormwater Handbook.