EBOM 2009 SSc6: Stormwater Quantity Control

The carp themselves do not contribute to SSc6 since they are performing a maintenance function unrelated to stormwater quantity control. It probably falls under SSc3, but may go beyond what is standard there.

I suggest reposting your inquiry under SSc3.

Samantha, where is this information requested?

I would say it's a judgment call.

A LEED reviewer requested this. They said that this area is generally sloped and asked us to confirm, but I couldn't find a way to do so, so unfortunately we dropped the credit for the final review.

I don't know if you are still having trouble with the NOAA website, but the HDSC (http://hdsc.nws.noaa.gov/hdsc/pfds/index.html) has data on most states by weather station.

Mechanical filtration can improve the water quality, but doesn't typically reduce the quantity of runoff during the storm event, which this credit requires. Projects typically achieve this credit with one or more strategies for detention (stormwater ponds, cisterns, large planted areas or green roof), infiltration into the ground (pervious paving, drywells, landscaping) or collection and storage of the water for on-site uses such as irrigation or toilet flushing. Hope that helps.

Jae,

Usually, the weather bureau will have information on the means annual rainfall amount, either in inches or mm.

Emily, you need to find opportunities for onsite stormwater mitigation—giving you a plan to compare your preexistingh runoff to.

If it's just a matter of the credit form not showing "1 point documented" you can submit a request to GBCI technical support through the Feedback button in LEED Online. They are pretty quick about fixing small glitches like that.

Generally, when we calculate runoff, we use a runoff coefficient, or in the case of a site with multiple types of surfaces (pavement, grass, gravel, etc.) we calculate the areas of each surface and use a table that provides us with runoff coefficients for each type of surface. Then we develope a combined run-off coefficient value for the site or drainage that can be used with the Rational MethodA formula that can be used for calculating stormwater flow rates. Q = CIA, where C represents a coefficient for physical drainage area, I is the rainfall intensity, and A is area. The method is suitable for watersheds smaller than 300 acres in size.. In the case of storage volume, LEED provides us with an emperical method that essentially calculates the runoff coefficient (Volume of captured runoff) and the "I" stands for the percent of impervious area, as a whole number in the equation. In my opinion, I would rather use a combination of runoff coefficient values and their associated areas to develop a more accurate combined ronoff coefficient volume. This is the same runoff coefficient that is used for the Rational Method. The difference is that you are just calculating a simple volume for storage based on a given rainstorm over an entire area, assuming the surface is impervious, or it isnt, using the LEED storage equation. Runoff coefficients can be easily obtained for various surfaces from the internet.

Steve, I'd say this is highly variable. It would depend a lot on the type and size of gravel, and the characteristics of the sub-base. I think you have the right idea, but obviously that leaves a lot of variability.

I'm sorry, but I don't have suggestions. I have heard other teams complain about trying to find this information in certain countries, but I haven't heard anyone successfully navigate it in these conditions.

There is definitely no guarantee, but I think it is worth responding with an explanation regarding the lack of data and as clear a justification for your methodology as possible. Sometimes showing due diligence is the best you can do and the rest is up to the reviewer.

The credit is asking you to have a stormwater management plan, and surface water would naturally have to be a part of that plan, so I would say that it should be considered.

Prudence, have you reviewd the MPR supplemental guidance? I think you will find your answer in there. Please post back with further thoughts and questions.

I consider a pool the same as a pond or lake. If the pool can contain the rainfall event with no discharge to the sanitary sewer, then the runoff coefficient is essentially zero. If, on the other hand, the rain that falls directly into the pool raises the water level sufficientl6y to overflow into the sanitary sewer, the runoff coefficient is 1.0. Many times the pool will have a bit of freeboard before the water level rises enough to overflow and this will allow you to capture the rainfall, and even make up for some evaporation that would otherwise be made up using potable waterPotable water meets or exceeds EPA's drinking water quality standards and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems.. Much depends on the overflow elevation compared to normal water elevation and the elevation at which makeup water is introduced into the pool to make up for evaporation..

Absolutely, use of captured rainwater for irrigation is a great thing, and contributes to other credits as well.

After thinking about it, it may be 1 or 100% because all water is removed from site, but is it fair to punish those with streams on their property?

I don't know the answer to your question, but I do have a thought—I would say that projects with bodies of water onsite have a particularly high responsibility to manage stormwater effectively, since there is no buffering at all between any runoff from the project, and the water body. I don't think those projects should be "punished" but the credit should be approached with the best of intent. (And I'm sure that is your intent—I simply thought it was important to note.)

It was a major design issue when our building was constructed, we ended up with 2 native planted retention basins, a bank divider to stop runoff and a rainwater collection system that is used to test products we manufacture(water testing) and irrigation.

We feel we did a great job in designing it properly in the beginning, and according to the calculator on LEED Online, so do they. Even if we calculate in the water as 100% runoff we still have 48% which is well above even the 30% requirement for our regional priority.

I just think it's a little strange there is no where to document what to do if you have water on your property. And even so, why make it a detriment to have water on site?

We generally consider bodies of water as having a runoff coefficient of 1.0. The rationale is that any rainfall that falls on a body of water does not infiltrate, and does run off. Now, this may depend on the situation because if the body of water is a pond, and the pond has enough freeboard to contain the rainfall landing on the surface of the water, the rainfall can be 100% contained within the pond and will not run off the site. This has to be considered when you are developing your composite runoff coefficient for the site. However, if the pond is full and the rainfall landing on the pond overflows into a stream or storm drain, then the runoff is 100%, or a runoff coefficient of 1.0. In the case of a stream, the water runs off 100% as it falls on the stream.

The coefficient depends on the kind of pavers.

I would say a "grasscrete" paver with 1/3 vegetation and 2/3 concrete would have a weighted average of 0.66(0.95*2/3 + 0.10*1/3).

Pervious concrete or pavers filled with gravel would be more similar to brick (0.85) in terms of overall permeability.

thanks Amy

I assume you are referring to the two tables on the Credit Form on LEED Online, correct? (the version of the form I am looking at has slightly different wording.)

If so, it is my understanding that table 2.1 is related to volume while table 2.2 is for runoff rate.

James, this is an okay strategy from USGBC's standpoint. To earn SSc6, though, you should focus not on the irrigation system, in my opinion, but in how much stormwater you're capturing from the site, and documenting that.

James,

I'm not sure I totally understand your question, but the 2-year 24 hour design storm is usually shown as either the volume for the entire 24 hour period, or as the average inches per hour over the 24 hour period.

A flat site with grass is a stormwater management facility that according to the credit requirements does need inspection. It could be a pretty simple inspection.

If there were some massive deluge that eroded the grass and led to increased runoff to a local waterway, etc., you would want to be on top of that—so the inspection is that all that frivolous.

I don't see why not. They are really being awarded for separate reasons, and RPc1 is tied to earning the normal threshold, while IDc1 is tied to the exemplary threshold.

I believe these are calculated automaticaly through LEED Online, so you can input the credit documentation and see how it goes—let us know!

In short, you do need to run EBOMEBOM is an acronym for Existing Buildings: Operations & Maintenance, one of the LEED 2009 rating sytems.-specific calculations to earn this credit. I am not an expert on this credit so I can't comment on your chances of earning it, but it does sound like you have a good chance.

Any updates to this? I'm back checking the mitigation percentages and it is close, but not seemingly exact.

I love your new job title, John. What's that about?

According to LEED Online's list of form updates, EBOMEBOM is an acronym for Existing Buildings: Operations & Maintenance, one of the LEED 2009 rating sytems. SSc6 hasn't been updated. So this problem is probably persisting.

Is there a way to include more than one surface type? My site has a mixture of pavement and grass, but I only see a spot for one surface type in the form.

Jordan, just click "Add Row" to get more rows to show up, where you can enter more surface types.

It looks like the form is computing the final percentage correctly. As to the Total Rain and Total Runoff numbers.. not a clue, unless I dig around to check. Any thoughts anyone?

And, Tristan, what happened to my title anyway?

"Chief Mystic in Resident"? How many people can say that? It was something else a few months ago, I recall.

Jordan,

You might try accessing the sample EBOMEBOM is an acronym for Existing Buildings: Operations & Maintenance, one of the LEED 2009 rating sytems. v2008 forms here to learn more about how the calculations work: http://www.usgbc.org/DisplayPage.aspx?CMSPageID=1447

The calculations shouldn't have changed between the 2008 and 2009 versions, though personally I've had trouble with the calcs in the v2009 form working properly. I'm trying to get in touch with GBCI about the issue to see when an updated version of the v2009 form will be released.

Ultimately, you'll need to rely on the calculations embedded within the v2009 forms, so you might want to prioritize getting registered so you can access the right tools.

Dianne,

Some responses:
1. I've seen previously conducted stormwater studies work to document this credit. It kind of depends on what information is included in the report, and whether it can be translated into showing management of at least 15% of the 2-yr, 24-hr volume.
2. In my experience, showing compliance on a campus-wide basis shouldn't be a problem. I'd recommend just making it really clear what the boundary is for the campus included in the stormwater analysis, and that the LEED project boundary falls completely within the larger campus boundary.
3. The form from LEED Online will show you exactly what documentation aspects you do not have to provide if you do an LPE exemption. In generally, the LPE exemption requires that you complete the associated form, and then you get a pass on providing a subset of the usual documentation. Which documentation is excused varies by credit, and the form will show this.

Dianne, the v2009 forms offer a bit of a goose chase, in that you can't see certain things until you click through the associated options on the form. When you are at the SSc6 form page in LEED Online, click on "LEED EB:OM Compliance Path", then "Full Documentation Path", then "Stormwater Calculator".

With any luck, the calculator will magically appear after you do this!

Thank you, thank you, thank you!!

Hi Rashid,

The rainfall event interval only comes into play if you are collecting rainwater in a cistern or other detention facility as part of your stormwater management strategy. If that is the case, you basically need to know the interval between rainfalls so you can figure out if you empty your cistern before the next rains come. If you aren't collecting rainwater, you don't need to worry about this particular aspect of the calculations.

Regarding the average year vs. the 2-year, 24-hour design stormA 2-year, 24-hour design storm is a nationally accepted rate that represents the largest amount of rainfall expected over a 24-hour period during a 2-year interval. The rate is the basis for planning and designing stormwater management facilities and features., in most cases it's appropriate to focus on showing compliance during the 2-year, 24-hour storm, with the idea being that if you can handle that volume on water you'll also be able to deal with the volume of rain that falls during the average year.

Hope this helps.

Thanks Jenny, as you have mentioned it seems like it will be better for us to comply with the 2 year 24 design storm in setting up our rainfall collecting system..

Mark, you have the right general idea. To quote the credit language (shown above):

Implement a stormwater management plan that infiltrates, collects and reuses runoff or evapotranspirates runoff from at least 15% of the precipitation falling on the whole project site both for an average weather year and for the 2-year, 24-hour design stormA 2-year, 24-hour design storm is a nationally accepted rate that represents the largest amount of rainfall expected over a 24-hour period during a 2-year interval. The rate is the basis for planning and designing stormwater management facilities and features..