PT-2: Permeable Pavement

Post by SteveM Aug 27th, 2010
at 4:48 pm

Addressing more NPS BG comments:

Most studies involving low impact development (LID) strategies (many include permeable pavements) have found the life cycle cost to build and maintain such systems to be equal to or less than an equivalent traditional system. I would also say that stormwater systems in rural areas (ditches and the like) area already quite close to an LID solution.

I agree that not every contractor will be able to build a porous pavement. But many will and more are getting proficient at it all the time. In fact, there is a certification offered by the National Ready Mix Concrete Association (NRMCA) for contractors so you can be confident that a certified contractor can do the job you ask.

Permeable pavements work on uncompacted subgrades in many applications. I would not recommend one for a mainline Interstate highway but they do well in parking lots and residential applications.

Post by SteveM Aug 27th, 2010
at 4:43 pm

Addressing BG comments:

Overall, I agree. Permeable pavements are probably not the best expenditure of NPS dollars give what you have laid out. My recommendation would be to not pursue this credit. I think that's one of the neat things about Greenroads is that you don't HAVE to do anything. As an organization you can make this system context sensitive by choosing the items you wish to pursue that are most in line with your strategic goals and direction. The middle of page 8 in the GR Manual talks about how GR can be sensitive to your organization's needs better than I just did there.

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
Documentation seems excessive.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
General Comment: An urban municipality may benefit from permeable pavements, but I doubt the Park Service would (other than the more traditional methods and usages (paths, driveways) noted above. Permeable pavements may work well to provide storm water detention for large parking areas in non-freezing part of the country. Permeable pavements used for Park Roads don’t seem to me to be able to provide proper benefits when placed against their costs. Very little positive benefit can be provided to groundwater or runoff quality when compared to high construction and maintenance costs.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
General comments on this Section: A benefit of permeable pavements seems to be groundwater infiltration and recharge, reducing groundwater pollution, etc. Looking at some numbers is beneficial: Sequoia/Kings Canyon NP in California is about 0.07% paved with regular good old asphalt pavement. Less than 1.1% of Petersburg National Battlefield is paved. Much of the water that hits the paved surfaces in these Parks runs off the road; very little is concentrated in pipes and then discharged. Many Parks are similar to these in percentage of pavement and runoff characteristics. What groundwater benefit would be realized by adding costs for permeable pavements?
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
2
Clog Prevention Maintenance seems very excessive, especially “Vacuum pavement twice a year” and “Immediately clean any soil deposited on pavement” - most likely by vacuuming. (Funny how the enviros don’t mention the air-quality impacts of having another piece of machinery to vacuum the road.)
NPG-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
SECTION 8
Bullet items list “provides local flood control” and “reduces need for traditional stormwater infrastructure which may reduce the overall project cost” [my italics] as reasons to use permeable pavements. Local flood control can be controlled in a number of ways, and “traditional stormwater infrastructure” such as culvert pipes and catch basins aren’t that expensive to begin with. They are probably much cheaper to install and maintain than a permeable HMA road.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
SECTION 2
Design Elements (15 items) seem very excessive, and can do nothing but add costs – geotextiles, perforated pipe network, etc., in addition to what appears to be restrictive design criteria – can’t use on roads over 5%, place infiltration beds (another design detail and cost) on upland soil, when possible.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
SECTION 5-6
There are other “permeable” surfaces which make sense for use in National Parks: brick or paver sidewalks or driveways, or turf reinforced with geogrid for paths or driveways. I have used (with success) a 3/4-inch gravel and topsoil/grass seed mix that is good for maintenance access (less visually obtrusive) and overflow parking areas. These are structurally sound, drain water very well, and maintenance-free. The water also goes into the groundwater system, which is one of the considerations in this Section.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2 SECTION 2
Vacuuming – does this mean that each Park that used permeable pavement would have to buy and maintain a special piece of equipment to maintain the permeable roads?
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

SECTION 2
Costs, I understand, are high, as subgrade treatments, porous base, and porous pavements are all needed, and I’m sure not every contractor or batch plant is familiar with the products, workmanship, and quirks involved. Maintenance costs also seem as though they would be high, and if maintenance was not performed on a regular schedule, the whole thing – including the pipe network below the road – would clog up, and either become unusable, or just another non-permeable road.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-2
SECTION 2
I am not familiar with permeable pavements or their performance. I am skeptical of the references made to the placement of permeable pavements on uncompacted subgrades.
NPS-BG