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Bioretention Areas
- Parking lot island landscaping features adapted to treat stormwater
runoff.
- Surface runoff is directed into shallow, landscaped depressions
with pollutant removal layers.
- Typically, the filtered runoff is collected in a perforated
underdrain and returned to the storm drain system, but the system
can be enhanced for partial exfiltration.
- The system should be sized between 5% and 10% of the impervious
draining area.
- These areas can be designed to hold plowed snow.
Dry Extended Detention Pond
- Vegetated, open channel management practice
- May be an option as a snow storage facility to promote treatment
of plowed snow
- Swale with engineered soil matrix and underdrains to promote
filtration
- Recommended for sites with a minimum drainage of 10 acres
- Least expensive stormwater treatment practice, on a cost per
unit area treated
- Best long-term performance track record (least clogging problems)
Infiltration Trench (narrow and deep)
- Generally applied to sites less than five acres with relatively
high impervious cover
- Soil infiltration rate ranges between 0.5 and 3 inches per hour
- Best applied to drainage areas less than 10 acres
- Soil infiltration rate should range between 0.5 and 3 inches
per hour
- Can be optimized for seasonal operation and to accommodate snow
melt
Note: Design all stormwater detention areas to be "dry" for most
of the year. You should not design stormwater retention areas to
be wet year round, as that may encourage development of wetlands
or breeding areas.
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