Concept Prioritization

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Concept BMP Prioritization – NPDES Permit

December 16, 2009

Universal Low Impact Development (LID) Features (Can be used independently of soil type, high groundwater, and ground contamination and should be considered for all projects)

  • Green Roofs
  • Cisterns – above ground (below ground maybe effected by groundwater and contamination, but may be feasible in some cases)
  • Tree Canopy – credit
  • Vegetated Area – evapotranspiration credit

Priority 1: Volume Based Low Impact Development (LID) BMPs

With no subdrains (achieves volume capture)

(typically to be used in A and B type soils, may be used in other conditions using amended soils, bypass inlet for high flow required)

  • Raingardens (bioretention areas) – with no subdrains
  • Permeable (porous) Pavement – with storage volume and no subdrains
  • Vegetated Buffer Strip – achieving volume capture/evapotranspiration
  • Vegetated Swale (bioretention swales) – with engineered soil and no subdrains
  • Constructed Wetlands – with no subdrains

Priority 1A: Other Low Impact Development (LID) BMPs

With no subdrains (achieves volume capture)

(typically to be used in A and B type soils, may be used in other conditions using amended soils, bypass inlet for high flow required)

  • Raingardens (bioretention areas) – with no subdrains
  • Permeable (porous) Pavement – with storage volume and no subdrains
  • Vegetated Buffer Strip – achieving volume capture/evapotranspiration
  • Vegetated Swale (bioretention swales) – with engineered soil and no subdrains
  • Constructed Wetlands – with no subdrains

Priority 1A: Other Low Impact Development (LID) BMPs

With no subdrains (achieves volume capture)

(typically to be used in A and B type soils, may be used in other conditions using amended soils, bypass inlet for high flow required)

  • Infiltration trench/ basin – with no subdrains
  • Drywell- with no subdrains

Priority 2: Low Impact Development (LID) BMPs

With subsurface drains above the capture volume (achieves volume capture) (typically to be used in C and D type soils, bypass inlet for high flow required)

  • Raingardens (bioretention areas) – with subsurface drains above the capture volume
  • Vegetated Swales – with engineered soil and subsurface drains above the capture volume
  • Permeable Pavement – with storage volume and subsurface drains above the capture volume
  • Constructed Wetlands – with subsurface drains above the capture volume
  • Wet Ponds – with subsurface drains above the capture volume

Priority 3: Partial Low Impact Development (LID) BMPs

With subdrains (does not achieves volume capture and may require mitigation) (typically to be used in C and D type soils, bypass inlet for high flow required)

  • Includes all of Priority 1, 1A, and 2 with an impermeable liner and/or subdrain

Priority 4: Modular/Property LID Units

(does not achieves volume capture and may require mitigation) (bypass inlet for high flow required)

  • Tree Filter Units (tree boxes) – landscape based treatment
  • Modular Bioretention Units – landscape based treatment

Priority 5: Structural Treatment

(To be done in conjunction with an in-lieu LID fee, offset project, or as part of a LID treatment train or suite)

  • Chambered Separator Units
  • Centrifugal Separator Units
  • Trash Excluders
  • Filter Inserts

Priority 6: Offset Program

Other: Impervious Detention-Hydromodification Control

  • Underground Detention Vault
  • Underground Chambered Detention
  • Above Ground Detention Pond
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