The document discusses permeable paving surfaces and their ability to recreate natural water attenuation by allowing water to soak into the ground. It explains how development has increased impervious surfaces, preventing groundwater recharge. Under Maryland's Stormwater Management Act of 2007, new development and redevelopment projects must implement Environmental Site Design to a minimum standard to treat the first inch of rainfall runoff. This can include permeable paving surfaces designed to meet stormwater management and traffic load requirements simultaneously. Precast permeable concrete panels provide an alternative to poured-in-place surfaces that allow for easy year-round installation and replacement of sections.

1. March 22, 2016
By Marshall Davidson, P.E.
Howard County Department of Public Works
Transportation & Special Projects Division

2. In a completely natural environment (Open Country), rain, sleet and snow would fall
onto open land, soak into the ground and then gradually make its way through the soils
and sub-soils towards a local stream or river, recharging natural aquifers en route. As
land is developed, runoff is directed to channels and impervious areas (which prevent
recharge of groundwater) are connected to storm drains, curb and gutters that by-pass
this natural process, denying the ground the chance to recharge and soak up much of
that water. Permeable paving surfaces attempt to re-create the natural attenuation by
allowing the ground to absorb, store, and gradually release collected water.

3.  Maryland's Stormwater Management Act
 “The “Stormwater Management Act of 2007” (Act)
became effective on October 1, 2007. Prior to this Act,
environmental site design (ESD), was encouraged through
a series of credits found in Maryland’s Stormwater Design
Manual. The Act requires that ESD, through the use of
nonstructural best management practices and other better
site design techniques, be implemented to the maximum
extent practicable.”
 Source:

4.  Under the Stormwater Management Act of 2007, for all new development
and redevelopment - Businesses and Homeowners need to implement
Environmental Site Design! At a minimum to treat the first 1” of rainfall.
 Maryland Stormwater Design Manual , Volumes I and II
(October 2000, Revised May 2009)
 The Design Manual is the official guide for stormwater management
principles, methods, and practices in Maryland. The Design Manual was
originally published in October 2000, and was later revised in May 2009 to
meet the goals of the 2007 Act. Chapter 5 of the Design Manual was
revised in 2009 and covers ESD. (The manual may be downloaded from
MDE’s website).

9. Constraints: (cont.)

13. Concrete Pavers on stone subgrade

14. The sub-base layer is intended to
act as a reservoir, to provide
storage for collected surface water
and to release it to the natural
environment at a controlled rate.
The simplest model involves water
accumulating within the sub-base
from where it slowly seeps into the
ground beneath.

15. Partial Infiltration System - The position of the 'overflow pipe' can be
established to suit local conditions. The higher up the sub-base it is
placed, the greater will be the quantity of water stored before overflow
conditions occur. There are designs that place the overflow pipe at the
bottom of the sub-base layer: these designs often involve a relatively free-
draining sub-grade and the overflow pipe is provided to remove any
excess water that does not escape to the sub-grade fairly quickly.

17.  DESIGN: Two factors determine the design thickness of
pervious pavements: the hydraulic properties, such as
permeability and volume of voids, and the mechanical
properties, such as strength and stiffness. Pervious concrete used
in pavement systems must be designed to support the intended
traffic load and the site-specific stormwater management goal.
The designer selects the appropriate material properties, the
appropriate pavement thickness, and other characteristics needed
to meet the hydrological requirements and anticipated traffic
loads simultaneously.

18. Pervious concrete, lacks the fine aggregates
(stones) of conventional concrete giving it a
unique surface texture. It has an appearance
similar to that of a Rice-Krispie treat. The
exposed course aggregates of pervious concrete
allow for drainage.

19. Placement of pervious concrete

20. What is it?
Precast under controlled conditions — reproducible strength and flow characteristics
Porous sections are removable and reusable - sections can be easily replaced
Reduced life cycle costs vs. poured-in-place porous
Applications
Green Infrastructure - provides runoff reduction
Parking lots, driveways, sidewalks, gutter lines, etc.
Can be cost-effectively retrofitted into existing sites
Easy Installation
Slabs arrive on site pre-cured - traffic ready immediately
Installs year-round in any type of weather
Lightweight, can be placed by most small equipment

23. Panels stored on site. Panel being lowered into place

24. Subgrade installation
Lowering the panels onto
the subgrade

28. THANK YOU FOR YOUR
ATTENTION
Marshall Davidson, P.E.
Howard County Department of Public Works
Transportation & Special Projects Division