Low Impact Development (LID) Project

Permeable Surfaces

September 17, 2003

Purpose

The purpose of this memo is to summarize the design, construction, and maintenance concepts associated with permeable (porous or pervious) surfaces.  Attached separately are preliminary drawings, special provisions to standard specifications, and a list of pay items.  The Permeable Surface concepts discussed in this memo include: Permeable Concrete, Permeable Asphalt, Paving or Lattice Stone, and Geo-Cells.

Environmental Overview

Permeable (porous or pervious) surfaces can be applied to parking lots, pedestrian/bike paths, traffic islands, and sidewalks and may be considered for the outside portion of roadway shoulders.  Permeable surfaces allow stormwater to pass through and infiltrate the soil below, thereby reducing the rate and volume of runoff associated with conventional surfacing and can foster groundwater recharge.  If necessary, permeable surface designs may include a media filtration sub-layer for calculated water quality treatment (such as a sand or an amended soil).

Permeable LID Pavement Surfaces

The permeable concrete or asphalt pavement surface is an open-graded mix that is placed in a manner that results in a high degree of interstitial spaces within the cemented aggregate.  This allows for a high degree of infiltration of water through the pavement.  The pavement may be permeable concrete, permeable asphalt, or manuf