STRUCTURAL MEASURES: CONSTRUCTION, OPERATION, AND MAINTENANCE - Low Impact Development and Sustainable Stormwater Management - page 173

cleaned off the pavement immediately to prevent further clogging of the pores.
Furthermore, if any bare spots or eroded areas are observed within the planted
areas, they should be replanted and/or stabilized at once. Planted areas should be
inspected on a semiannual basis. All trash and other litter that is observed during
these inspections should be removed.
Superficial dirt does not necessarily clog the pavement voids, but dirt that is
ground in repeatedly by tires can lead to clogging. Therefore, trucks or other
heavy vehicles should be prevented from tracking or spilling dirt onto the pave-
ment. Furthermore, all construction or hazardous materials carriers should be
prohibited from entering a pervious pavement lot. Descriptive signage is recom-
mended to maintain institutional memory of pervious pavement.
Vacuuming
Pervious pavement should be cleaned with a vacuum sweeper on a biannual
basis. Acceptable types of vacuum sweepers include the Elgin Whirlwind and
the Allianz Model 650. Although much less effective than “pure” vacuum sweep-
ers, regenerative air sweepers (e.g., Tymco Model 210, Schwarze 348, Victory)
are sometimes used. These units contain a blower system that generates a high-
velocity air column, which forces the air against the pavement at an angle,
creating a “peeling” or “knifing” effect. The high-volume air blast loosens the
debris from the pavement surface, then transports it across the width of the sweep-
ing head and lifts it into the containment hopper via a suction tube. Thus, sediment
and debris are loosened from the pavement and sucked into the unit. Simple
broom sweepers are not recommended for pervious pavement maintenance.
If the pavement surface has become clogged significantly, such that rou-
tine vacuum sweeping does not restore permeability, a more intensive level of
treatment may be required. Recent studies have revealed the usefulness of wash-
ing pervious pavements with clean, low-pressure water, followed by immediate
vacuuming. Combinations of washing and vacuuming techniques have proved
effective in cleaning both organic and sandy clogging. Research in Florida found
that a “power head cone nozzle” that “concentrated the water in a narrowly
rotating cone” worked best. ( Note: If the pressure of the washing nozzle is too
great, contaminants may be driven farther into the pervious surface.) Maintenance
crews are encouraged to determine the most effective strategy of cleaning their
pervious pavement installations.
For smaller installations such as sidewalks, plazas, or small parking lots, walk-
behind vacuum units may prove most effective. Although these units can be loud
and somewhat deleterious to the operator due to the lack of dust suppression, they
are also relatively easy to operate and inexpensive. Examples of acceptable walk-
behind units, such as Billy Goat models, the Tennant 5700 industrial-strength
scrubber, and sidewalk class vacuum sweepers (e.g., Nilfisk, Advance, Hako),
are available. If walk-behind units are used, it is recommended that the scrub
pressure be kept relatively low. The dirtiest areas may need to be power-washed
after scrubbing to get out deeply ground-in dirt.