Concept Prioritization

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