Water quality from SWM pond

[waterguy]

Good Day,

I'm working on a project in which a stormwater management pond is being utilized for both quantity (100 year) and quality control. Quality control is based on "Level 1" criteria (most stringent in the Province of Ontario). However, a concern has been raised by an ecologist working for the reviewing agency with respect to gas/oils (from parking lot runoff) that might spill out and over the pond during severe events (like the 100 year storm will happen every day !!).

My Question: Has anybody ever had to address such a problem as this ? Is there any data available that might relate the removal of oils and petroleum products to the type of vegetation that is in the pond ? The stormwater pond that has been proposed will be built with a forebay as well as a 1.0m deep permanent pool. I don't see what else can be done with respect to oils that might be floating on the ponds surface. Perhaps some sort of filtration device on the overflow weir of the pond ?? Any thoughts on this would be greatly appreciated.

Regards,

John

 

[DPB]

One approach is to remove any oil and gas from the parking lot prior to release to the pond. Several proprietary oil and grease separator devices are available on the market. StormCeptor is one, CDS Technologies is another. These devices either use detention time or vortex separation to accomplish this task. The benefit of these devices is that oil and grease (as well as heavy metals) are separated from the from the stormwater runoff before entering the pond. Hazardous wastes are contained within the separators and easiliy collected for disposal. A non-proprietary oil and grease separator may also be designed and constructed upstream of the pond headworks.

 

[MarkRay]

Yes, there are oil/water separation devices that can be used to separate floating pertroleum products from flowing inputs of water. They are concrete or fiberglass construction and are fitted in-line with piped storm waterr. It would be preferable to install one upstream of the pond unless you would rather deal with only the peak flows coming out of the pond. In either case, they can be retrofitted to a variety of uses. Just get on the internet and you should have several choices. Good luck.

 

[MarkRay]

Yes, there are oil/water separation devices that can be used to separate floating pertroleum products from flowing inputs of water. They are concrete or fiberglass construction and are fitted in-line with piped storm water. It would be preferable to install one upstream of the pond unless you would rather deal with only the peak flows coming out of the pond. In either case, they can be retrofitted to a variety of uses. Just get on the internet and you should have several choices. Good luck.

 

[ejrandall]

Prince Georges County in Maryland has done much work to develop standards for bioretention as a method to lessen the impact of development. It is a constructed area to provide infiltration and oil/grit separation adjacent to areas of sheet flow (like a parking lot) which will receive the runoff and entrap the contaminants. Vegetation (trees, shrubs and groundcover) which are tolerant of the toxins are planted in the bioretention area.

Try this URL:

http://www.goprincegeorgescounty.com/government/der/ppd/pgcounty/pdf/bioplant2.doc

There are some particular constraints regarding width, depth, and soils which affect the applicability of bioretention, but I find it an elegant solution for water quality where it can be applied.


A simpler mechanical solution to separate volatiles may be to attach a sheet metal baffle to your outlet control structure (assuming a riser-type OCS). It is essentially a 3-sided box enclosing the discharge orifice(s) of the structure. It requires some additional depth of your pond below the discharge invert. The sheet metal extends from below the discharge invert to the elevation of your emergncy overflow, with approximately a foot or so of clearance to the OCS. It works by forcing the design discharge of the rising pool to be drawn from below the free water surface. Any volatiles float on the surface of the water, and are withheld in the pond, allowing UV breakdown, or removal by regular maintenance.

Hope these help.