Here is some helpful information from Rich Simcich of Agresource Inc:
When designing a bio-retention an architect or engineer must
calculate the volume of water the basin must filter for a 50-100 year
storm. The square footage, depth of the media, and soil physical
properties must be considered. Agresource will meet any specification
for raingarden or Bio-retention soils but provide our own bio-retention
media that works well in New England. See attached analysis.
It
consists of 50% uniform coarse sand, 20% sandy loam and 30% leaf
compost. The proportions are put together and mixed with a mechanical
mixer which will produce a media that will infiltrate greater than 2
inches per hour and contain 2.5% to 6% organic matter. The choice of
sand is the key. The fines fraction of the media, particle that pass
.15mm sieve, must be less than 20% to reduce compaction and increase
infiltration. The organic matter content in the soil is important to
nourish plants and break down hydrocarbons commonly found in storm water
runoff. Too much compost can reduce hydraulic conductivity. There is a
balance of particle distribution or soil texture and organic matter
content.
Bio-retention
basins that drain too quickly will not remove contaminates they were
design to remove and will not support plant life during dry summer
months. If you have any question please call me to discuss.
Click here for specification manual
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