Underground Ponding Narrative 2-26-09
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UNDERGROUNDPONDING NARRATIVE
The above-ground bio-retention basin has a total live storage (100-year event) of approximately
25,500 cf. An underground system would require a volume equal to or greater than this storage.
Attached is a design schematic for an underground storage system called CHAMBERMaxx. This
system, having a footpriht of approximately 82 feet by 143 feet, has a total storage (chambers and
rock bed) approximately equal to the required storage.
From previous experience with other projects, and from discussions with Contech, an
approximate "installed" cost for underground systems is $5-6 per cubic foot of storage. For this
storage volume, this equates to $125,000 to $150,000.
Not included in this estimate is an underdrain system and a pre-treatment system (e.g.
ecoSTORM).
CITY OF CHANHASSEN
. RECEIVED
FER 2 6 2009
CHANHASSEN PLANNING Dr:PT
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