Comments on: Sustainable Sites 6.2 – Stormwater Design – Quality Control

By: Graham Bryant

Graham Bryant — Fri, 20 Nov 2009 19:37:44 +0000

The wording should be to treat the first inch of runoff. This means that the first inch of runoff per storm is treated which over the entire year (storm every 3 days or so) equates to treating 90% of the annual rainfall. This occurs since most storms (i.e. 90%)are smaller than 1 inch in size.

By: Tom

Tom — Mon, 25 May 2009 22:52:31 +0000

Gail,

An example of “disconnection of imperviousness” would be to have roof downspouts discharge onto to green surfaces where the runoff will naturally filter into the soil and vegetation. Inhis manner the downspouts are disconnected from the site storm sewer system.

My undersanding of a manhole treatment device would be something like a sand filter system.

Hope that helps. If not let me know and I will try to clarify.

By: Gail

Gail — Mon, 25 May 2009 11:19:23 +0000

Hi,
wonder if you could explain the following from the ref guide-

Under SS6.2 Stormwater Design Quality Control
what is ‘Disconnection of imperviousness’
what is a ‘manhole treatment device’
Thanks
Gail

By: Wes

Wes — Tue, 24 Feb 2009 19:21:29 +0000

Yes it is backwards, careful those not referencing the LEED manual: “Use alternative surfaces (e.g., vegetated roofs, pervious pavement or grid pavers) and nonstructural techniques (e.g., rain gardens, vegetated swales, disconnection of imperviousness, rainwater recycling) to reduce imperviousness and promote infiltration, thereby reducing pollutant loading.

The natural/mech treatment systems are correct.

By: sally

sally — Tue, 16 Dec 2008 22:34:27 +0000

very helpful but you have Alt surfaces and non-structural elements BACKWARD.

By: Laura

Laura — Thu, 04 Dec 2008 18:54:58 +0000

this site seems to elucidate things better.
http://www.stormwatercenter.net/Manual_Builder/Sizing_Criteria/Water%20quality/Options%20for%20Water%20Quality%20Volumes.htm

Though it perplexes me that the LEED manual would be so unclear.

By: Larry

Larry — Thu, 04 Dec 2008 12:43:39 +0000

My feeling on this – without digging – is that the 1″ might be expected during a typical “rain-event” in the types of climates listed, respectively. I live in a humid climate (OK) and 1″ of rain is a fairly common event. Yes, it rains more on occasion. We need to consider also if this is a function of time (24Hr?).

By: Laura

Laura — Thu, 04 Dec 2008 01:40:46 +0000

I second the question posted by John regarding how 90% of 40 is 1. Are they considering runoff as something different than the annual rainfall?

By: Shane

Shane — Thu, 13 Nov 2008 01:02:56 +0000

It appears you used the same intention criteria from 6.1. The intention for 6.2 worded slightly different…the main difference having focus on elimintating sources of contaminants, and removing polltants from stormwater:

Reduce or eliminate water pollution by reducing impervious cover, incresing onsight infiltration, eliminating sources of contaniminants, and removing pollutants from stormwater runoff

By: John

John — Wed, 12 Nov 2008 20:53:29 +0000

The ref. guide gives you equivilent amounts of of water treatment required for the different watershed types. But i am confused. If you are supposed to treat 90% of runoff in a Humid Watershed site (which receives at least 40 inches per year) how is that equivalent to treating just 1 inch of run off. 90% of 40 inches of rainfall is not 1 inch. Can someone please explain this to me.

By: Amanda

Amanda — Tue, 04 Nov 2008 02:54:22 +0000

Pat, great site, very helpful! However, if I’m reading this correctly, under implementation, you have alternative surfaces and non-structural surfaces listed backwards (at least according to the 3rd edition).