STRUCTURAL MEASURES: CONSTRUCTION, OPERATION, AND MAINTENANCE - Low Impact Development and Sustainable Stormwater Management - page 167

in pervious pavement placement. An impervious water stop should be placed
along infiltration bed edges where pervious pavement meets standard impervious
pavements.
15. Control of sediment is critical. Rigorous installation and maintenance of
erosion and sediment control measures are required to prevent sediment deposi-
tion on the pavement surface or within the stone bed. Nonwoven geotextile may
be folded over the edge of the pavement until the site is stabilized. The designer
should consider the site placement of pervious pavement carefully to reduce the
likelihood of sediment deposition. Surface sediment should be removed by a
vacuum sweeper and not power-washed into the underlying bed.
16. Infiltration beds may be placed on a slope (Figure 8-1) by benching or ter-
racing parking bays. Orienting parking bays along existing contours will reduce
site disturbance and cut-and-fill requirements. If infiltration beds are to be ter-
raced, earthen berms should be left in place between the various terraces to
maximize storage and infiltration throughout the system.
17. The underlying infiltration bed is typically 12 to 36 in. deep and consists
of clean, uniformly graded aggregate with approximately 40% void space
(Figure 8-2). AASHTO No.3, which ranges from 1.5 to 2.5 in. in gradation, is
often used. Depending on local aggregate availability, both larger and smaller
aggregate has been used. The critical requirements are that the aggregate be
uniformly graded, clean washed, and result in a significant void content. The
depth of the bed is a function of stormwater storage requirements, site grading,
and anticipated loading. Infiltration beds are typically sized to mitigate the
increased runoff volume from the more frequent storm events.
18. While most pervious pavement installations are underlain by an aggre-
gate bed, alternative subsurface storage products may also be employed. These
Figure 8-1 Infiltration bed system on a slope. (Courtesy of SKB Site Design.)