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are many five to ten year and older installations that have never been
maintained and continue to function well.
Bioswales
Maintenance of the bioswales includes inspections to ensure that the amended
topsoil is not clogged, inspection of the outlet control, and vegetative
management. Specific maintenance activities are described in Appendix 2.
Inspections should occur twice annually and after large rainfall events as
indicated. Each inspection of the entire system should not require more than
approximately four man-hours.
Clogging of outlet structures is not expected to occur since stormwater entering
the system must pass through bioswale amended topsoil or through permeable
paving for most all events. However, should clogging occur, the orifices may be
cleared by simply sweeping away the obstruction.
Clogging of the amended topsoil within the rain gardens and bioswales is not
expected to occur provided the vegetation is maintained in a vigorous
condition. Should clogging occur, it is unlikely that the entire bioswale will clog
but more likely that isolated locations will clog. The cost to remove and replace
clogged amended topsoil should not exceed $1 per square foot for small areas.
Replacement for large areas (i.e., the entire bioswale) should not exceed $0.25
to $0.50 per square foot. These costs do not include replacement of vegetation.
Green Roofs
Very little maintenance is required for green roofs except vegetative
maintenance to control weeds. The sedums used to vegetate the green roof are
very drought tolerant and will go dormant under extreme dry conditions.
However, the roof can be irrigated if desired to prevent dormancy and improve
aesthetics during dry periods.
Summary
The Villa Park police station Urban BMP demonstration project utilizes advanced
runoff management techniques that minimize generation of runoff and associated
urban pollutants using green roof and permeable paving technology. Runoff that
does occur is directed to biofiltration swales that filter the runoff and provide
temporary storage for infiltration and runoff rate control.
The system was designed to restore pre-development hydrologic conditions as well
as water quality while also meeting local stormwater flood control standards. The
system has been estimated to remove 90% to 97% of urban runoff pollutants and
reduce runoff volumes to less than produced by a typical park area (the expected
equivalent curve number for the site is approximately 61), despite 65% coverage by
surfaces normally considered to be impervious (roofs, parking, and walks). Runoff
volumes are being monitored to verify the hydrologic analysis and to assist local
designers and regulators in designing and evaluating these systems.