I am working on a project in Germany that is using multiple buffer strips to remove TSS from runoff before it reaches a small drainage channel. Rain water from the roof of the building is collected in a cistern for toilet flushing. Rainwater falling on the asphalt parking (2% slope) area flows (sheet flow) across a 10 ft long grass buffer strip (1% slope) and then across a 70 ft long forested (large pine trees, small other trees, underbrush) buffer strip (3% slope) before reaching a small drainage channel. Because of the dual buffer strip combined with the relatively low slopes and long distance to the drainage channel, I think that the actual TSS removal is higher than the default 65% taken from the EPA’s Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters manual. I think that the TSS removal of the bufferstrip should be closer to the 80-90% range but I do not have a local resource or a good equation to use that would justify this. Is there a way to claim greater TSS removal efficiency than the default 65% removal efficiency for my case that would be acceptable to GBCI reviewers?
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Amy Rider
Sustainability ManagerKEMA Services
161 thumbs up
April 25, 2011 - 2:30 pm
Rich,
I would agree that, based on your description of the system, you are achieving higher TSS removal rates. While a local resource that shows higher TSS removal rates will always make your case stronger don't forget about the magnification effect of using multiple BMPs in series.
Remember that while not a perfect indicator of removal efficiency, you can assume that each of the filter strips is removing a percentage of the TSS present, for a combined removal efficiency for all of the water that passes through both filter strips. Assuming the first removes 65% of the TSS and the second removes 65% of what remains the combined efficiency should be 87% (65% + 35% x 65%).
Don't forget to also give yourself credit for the rainwater that is captured and reused.
Richard Gifaldi (Team Leader)
Sustainability ManagerUSACE Europe District
4 thumbs up
May 6, 2011 - 6:06 am
Thank you Amy. I'll try the combination approach. Much appreciated.
Rich
Juan Robles
Senior Architect, AIA, LEED AP BD+CRoblesArq Architecture and Planning
17 thumbs up
June 10, 2011 - 3:38 pm
May I include native landscape restored as a BMP? What would be the average TS removal?
Can you explain in detail the combined removal efficiency?