Detaining the rainwater runoff -an accepted solution?

Are you using the runoff in some way?

You need to actually use the runoff onsite, somehow (infiltration, evapotranspiration, reuse, etc.)

Simply routing it through a BMP and discharging will not meet the intent of the credit. You need to reduce the volume somehow.

Option 1, Path 2 requires you to manage ALL of the volume from the 98th percentile storm. So you can't let anything go.

Now if you look at Option 2, you only need to manage the increase between the pre and post, so this may better suit your project.

Option 2 states manage on-site increase in run-off from natural land cover conditions to post-developed.  So the site must have significant natural areas, correct? I am working on a site where a building is being demolished and a new larger building is being built.  The old building is from 1924 and the site is very urban and small so not a lot of room infiltration of the stormwater.  So is the stormwater that has to be managed the difference between the existing building site and the new - basically the increase in impervious area or does it go back to before 1924?

You need to model the pre-development condition as the site was in it's natural condition....basically before any development occurred.

That's what I thought - Thanks

Is a borehole an accepted solution? Is that considered "on-site" if, at the end of the day, the water is inserted into the aquifer as if it infiltrated naturally?

I think you’re talking about an injection well?

I haven’t heard of anyone trying this before, it’s not really a GI practice though, and you’re still going to need to treat it somehow  

Michael, I just found your reply above. I just returned from some meetings in South Florida where a project team has proposed a deep injection well. What would need to be done from a treatment perspective to get this to work? Even then, do you think that is acceptable as a GI solution? I understand you can't say how GBCI would respond but any tips you can provide are appreciated!

Deep injection wells are new territory for LEED. Treatment regs vary by location, with some requiring the runoff water to be treated to almost drinking water standards. 

Is the well a GI practice? Tough to say, that is something you really need to look at. Are you managing some huge drainage area, is there any holisitc features to the surface practice? The definition of GI is managing runoff at the source, mimicking the natural site hydrology....you need to be able to say with a straight face what you are doing meets that definition.

Michael, this is very helpful, thank you! I'll take this back to our civil team and see how straight their face is when explaining how it mimics the natural site hydrology. :)

Nash, we have the same situation with injection wells for a project in Florida. Would you mind sharing if the GBCI accepted injection wells as a GI practice?

Hi Drew, two of the Miami projects had the injection well approved during the prelim design review (no comments). In both cases, there are some landscaping areas on the roof, in addition to the upper roof and rooftop amenity paving areas (but both zero-lot line), then any collected stormwater from these areas go through an infiltration trench before entering the injection well. We have a third similar project in the area that we will be submitting soon. This one just has some rooftop landscaping but no infiltration trench before the injection well. So we'll see how that goes.

Nash-

Thanks for the update. Appreciate the feedback!

If you are working on a LEED project, for example, achieving the Sustainable Sites credit for managing rainwater runoff (SSc6.1) requires the use of specific strategies and techniques, such as rain gardens, vegetated swales, and permeable paving, to reduce the volume and improve the quality of stormwater runoff.

In terms of the specific questions you asked, evaporation or infiltration is not necessarily required to achieve this credit. However, the goal is typically to manage stormwater runoff in a way that mimics the natural hydrological cycle and reduces the impact on the surrounding environment. This can be achieved through a variety of strategies, including detention systems, as long as they are designed and implemented effectively.

Overall, I recommend consulting the specific requirements and guidelines for the credit you are trying to achieve and working with a qualified professional to ensure that your approach meets the necessary criteria.

Working on a project in Miami-Dade County.  Using injection wells for Rainwater management.  No landscaping on roofs or anything. Would this be acceptable to GBCI reviewers? Retaining 100%.

Hi Joseph,

That's right, as long as your injections well are "on site". The GBCI is being very specific for not using "offsite " infrastructure in order to achieve this credit.

Hello,

Hoping to reopen this discussion. I have a project with a natural stream running through a portion of the site. The civil team has proposed stormwater management system that will route site runnoff to a series of retention ponds, where some natural infiltration and settlement of sediment will occur. The retention pond will also have a feature that slowly releases a portion of the water at a controlled rate into the stream. This seems to be an effort to "mimic natural hydrology". Can anyone confirm if this approach has been accepted on their project? Curious if the broad term "discharge" is intended to only describe municipal stormwater system discharge?

Thanks in advance for any feedback!

I haven't faced such retention pounds are allowed strategy to a water to be discharged to a natural stream according to the country legislation (you can confirm that it's clean enough to be discharged so) - I do not see a problem thta it's not a municipal system. 

All other calculations of "not increased runoff" are also spplicable and you need to show that discharge to the natural stream is not bigger than ... are still applicable to the whole site including the stream (I mean you can't forward the stormwater over the calculated to the onsite stream and say that you are fulfilling the requirements of the credit).