water quality question

[Surcharged]

I have been designing traditional detention ponds for years but am new to the water quality aspects of it. I understand that I must provide a water quality volume. Can I count the permanent pool as part of the water quality volume? Or at least a portion?

 

[newnickname]

My experience has been to address WQv before it enters the detention pond, or I account for it partially in the sediment forebay while the remainder is accounted for in my detention volume.

 

[jgailla]

I am in north Florida. Local regulations typically allow treatement volume in the wet detention pond, i.e. no pre-treatment. The permanent pool volume is not part of the treatment volume, as permanent pool is not available for storm storage. If we need 10 ac-ft of treatment, we would provide 10 ac-ft of volume between the normal water level and the outfall weir elevation. For a 10-acre pond with normal water level at EL 10, the lowest we could set the weir elevation is EL 11 (not counting side slopes).
Different areas can have much different rules. Miami, for instance, does not allow any treatment in wet ponds. All stormwater quality treatment must take place before discharge into a wet pond.

 

[TerryScan]

Surcharged,

Water Quality requirements can vary greatly from one jurisdiction to another. What are the requirements where you are located?

 

[Surcharged]

there are no requirements. very vague. we are just supposed to do it. so it really is up to us. i just want to do it right. It seems as if the permanent pool if made large enough can treat portions of the storm by displacement. (ie the treated water is displaced during a storm leaving the new storm water in the permanent pool. this water is then treated and leaves when the next storm comes. researching on internet I found a New York State manual that says that you can use up to 100% of the permanent pool.

 

[newnickname]

The permanent pool is, well, permanent unless infiltration or exfiltration takes place. The WQv must be accounted for above the permanent pool.