Option 1- Maximum use of Green Infrastructure: The sample development project shown here includes two typical medium-density residential buildings with associated parking spaces. Green infrastructure is implemented throughout the site to the maximum extent practicable. This sample project represents a green approach to stormwater management and includes rain gardens to manage runoff from the roof areas and some of the parking area, pervious asphalt pavement, pervious concrete paver sidewalk areas and an underground stormwater detention/retention system. Click here to view this side-by-side example.
Option 2 – Minimal use of Green Infrastructure: The sample development project shown here includes the same two typical medium-density residential buildings and associated parking spaces as option 1. This approach uses an underground stormwater detention/retention system with a manufactured treatment device to meet regulatory requirements. Click here to view this side-by-side example.
The estimated costs included in the summary tables are only provided for the design elements that differ between the green and gray scenarios. For example, no building costs or underground piping costs were included as these items were assumed to be the same for both approaches. Capital cost assumptions included the following:
- No additional cost was added for a blue roof versus the cost of a conventional roof.
- Porous pavement cost was calculated as the difference between porous pavement and standard impervious asphalt.
- Pervious paver cost was calculated as the difference between pervious pavers and standard concrete.
- Rain garden cost was calculated as special soil media, additional landscaping, and underdrains and was calculated as the difference between rain gardens and basic landscaping with trees and mulch.
- Underground detention/retention facility cost was calculated as the difference in size between the gray and green infrastructure approaches and includes a manufactured treatment device for water quality control for the gray approach.