The 2013 stormwater management manual is a current reflection of the most recent stormwater management design in washington dc regulations that are in place as a result of the EPA issuing their permit that DOEE had to meet. Since then, DOEE has sent out two errata, one in 2014 and another in 2017, and they seem to be reissuing one, which will be final in the summer of 2019.
This week I have attended several informative meetings about how these changes will affect the development team, engineers/designers and the environmental community.
Development Community
For the development community, one change that stood out was that before it was required to retain at least 50% of the stormwater on site, however, after finalization of these new rules, it will depend on where the project is. For example, if a site is in the municipal separate storm sewer system (MS4), then yes, you will still need to retain at least 50% on site. However, if your project is within some areas of the Combined storm sewer (CSS) then, you won’t HAVE to retain anything on site… not even there if there a vehicle access area…. But you will still need to buy credits, and only from a property that is located within the MS4. So while this sounds great, especially in a downtown area, where most of the CSS is, one credit is about $1.75/gallon at the lowest, and a project that would generate stormwater management will require at least 3,000 gallons. Another thing to look at is that green area ratio (GAR) will still need to be met for these projects within the CSS area unless granted an exemption… with that said, some stormwater management might as well be done.
Civil Design/Engineering Community
For the design community, it was all good news! I cannot wait for the updated regulations for the BMP’s be implemented! Things that stood out to me where the green roof, infiltration and permeable pavement changes.
Green Roofs: During this meeting, it was made clear that for the green roofs, the CDA can be more than just the actual green roof, despite what the manual and many reviewers may say! On top of that, the systems will be able to accept side drainage if the green roof system uses Rockwool. Whoo! That was exciting!
Infiltration: Another thing was that we would no longer be using the infiltration rate to determine how the water will move down to the aquifer (or nowhere)… now we will be using Ksat. For those that know nothing about Ksat or forgot since college, if infiltration rate was a theme, then Ksat would be the category within it. Infiltration rate shows the speed at which water travels during any given moment in time through the ground, regardless of the soil’s saturation. However, the Ksat is when the soil has become completely saturated, and the infiltration rate is pretty constant. THIS makes the most sense. But within this the biggest positive would be thanks to NOAA, we can use their information as civil engineers to let the developers know if a Geotech report would be needed, as opposed to a “maybe?” We can also be more precise as engineers when determining ideal locations for BMPs and providing the geotechnical engineers a more certain area to survey.
Permeable Pavement: The final was that permeable pavement retention requirement went from 4.5ft3/100sf to almost 5ft3/100sf… it is not much… but it is something, in the right direction!… Ha!
Environmental Community
Finally! For the environmental community. They have 2 major concerns, one was that the current regulations are not enough, especially considering climate change and the other was that the cost for stormwater management dc is not sustainable for the little guy.
Regulations not enough: It is interesting; I use to think the same thing that the current regulations were not enough… but with GAR requirement, and the efforts of the city to have as many street trees, this takes into account the extreme rainfall event. Another thing is that the extreme rainfall event is more of a grey infrastructure issue, so if we increase this requirement, we will also have to increase the size of all the grey infrastructure, which would cost DC Water,
the residents and taxpayers of DC, billions!
The little guy: The idea of a developer has a weird rap, we view them as powerful rich guys with their own tv shows with slogans like “you’re fired!” But there are developers that took a risk by putting their home as collateral or their may be a small church. I have at least three projects that were designed three years ago, one a church, but they cannot afford to construct, they even end up losing the property as a result. The cost of stormwater management adds a substantial burden to projects, for smaller developers. Even the choice to buy credits is not enough of an option for those people that do not have the means. While there is relief for affordable housing, this relief is limited to affordable housing as of now.
– Gladys Sera, Phd, PMP, PE
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