What is in my “Dirty Pervious Pavement?”

The fact is that the percolation rates of pervious surfaces will decrease over time and finally clog if not properly tended to.  So, what will we 1) pick up when we clean it? And 2) How do we dispose of what we pick up?  

What Makes Pervious Pavement So Dirty?

The top 3/8″ to 1/2″ of pervious surfaces contain lodged organic and inorganic materials. High volumes of fine solids will be suspended in the water used to dislodge the material, which will then be transported back to the recovery tank.  This will include organic and inorganic material. A lot of fine solids will be suspended in the water used to dislodge the material and transport it back to the recovery tank.

The recovered material will include anything and everything that has settled on top of your hard surface, too.  This includes but is not limited to organics, phosphates, heavy metals, oil and gas and tire particulate from car traffic.

What Do I Do With That Stuff?   

Plan to treat the recovered material like you do the debris recovered from your catch basins. 

dirty pervious pavement

Pervious Cleaning at an Amtrak facility. Anything and everything has accumulated in and on this pervious surface.


dirty pervious pavement

Close up view of the Amtrak facility’s pervious asphalt. The pervious surface clogging goo seen on the left (not yet pressure washed) is pollutant rich. Get it out of your storm stream and into your treatment stream.


dirty pervious pavement

Contain and transport the slurry generated by the cleaning process. Best overall results are achieved by means of a high-pressure wash with simultaneous vacuum recovery system as found on the Triverus MCV. Full of fines and pollutants, this material should be hauled to your decant facility for treatment.

What’s the Difference Between Dirt on Pervious Surfaces and Non-Pervious Surfaces?

It stands to reason that both your pervious pavement and your non-pervious pavement will accumulate fine solids and pollutants from ambient sources.  The only difference is that when it rains, the pollutants and solids on a non-pervious surface are not trapped in place like the material that gathers sub-surface in pervious pavements.  

A high-pressure wash system with simultaneous recovery will lift and contain solids and pollutants from any hard surface. A conventional street sweeper only applies enough energy to the surface to move superficial, loose material. Adhered pollutants and those that have moved subsurface into the pervious pavement are beyond the job description of a conventional street sweeper regardless of vacuum recovery or regenerative air. Once wet, fine solids and pollutants will adhere to the surface and can only be moved by a soaking rain or high-pressure water wash.dirty pervious pavement

dirty pervious pavement

High-pressure washing with simultaneous recovery of both pervious and non-pervious surfaces yields the added benefits of enhanced safety as the pavement markings become more visible

Pollutant Recovery from Pervious Pavement and Other Surfaces

For a closer look at what you are pulling from your pervious and non-pervious surfaces, in 2019, the University of New Hampshire Stormwater Center analyzed the material recovered from two pervious surfaces during percolation recovery operations.  The chart below summarizes the analysis of the material recovered in terms of pounds per acre. (note the logarithmic scale). The complete study can be accessed here: University of New Hampshire Stormwater Center Tests Pervious Pavement with Triverus at Durham, NH Campus

dirty pervious pavement

Does the Type of Dirt on a Road Vary By Location?

Depending on your location and application, the mix of material and pollutants recovered will vary.  Cleaning western roadways will yield considerable amounts of copper while the same activity in the East tend not to return as much copper.  Industrial sites or roadways near them will be loaded with more heavy metals contingent on the local industry involved. 

Research has also shown that the tire preservative 6PPD is ubiquitous and deposited on roadways during the tire wear process.  6PPD is setting off alarm bells in the Pacific Northwest with studies linking it to high mortality rates in Coho Salmon.

High-Pressure wash with simultaneous recovery can be a key tool in removing all these pollutants from any hard surface.  Using this cleaning method on pervious pavements has the added benefit of retaining and restoring percolation rates to keep stormwater outflows to a minimum.  

Jumpstart solutions to your pervious maintenance and general pollution problems with Triverus. Get in touch with us today.

How to Prevent Flooding of Pervious Surfaces

“The best tool you can use to verify your pervious pavement is functional . . . . is an umbrella!”  Ever heard that one?  How about, “Why don’t you fix your leaky roof?”  “I have wanted to fix it when the weather is nice, but when the weather is nice, it is not leaking.”  It is the same principle.


Basketball Courts in the Pacific Northwest

“It was pervious when we installed it, anyway.” Although this is an extreme example, this can be a temporary condition while it is raining and for a few hours after. Use an umbrella to inspect pervious pavement.

What Causes Pervious Surfaces to Flood?

Pervious pavement does not clog overnight.  Plugging accelerates during and just after periods of high biological loading.  Although conditions vary across the United States in terms of rainfall, tree cover, and growing season, the general rule applies that spring and fall are the heaviest biological loading periods of the year.

Added to this is the fact that pervious pavement is constantly subject to infiltration by fine solids, dust, and dirt all year long from local and ambient sources.  We can talk about the well-meaning gardener that dumps his mulch and/or topsoil directly on your brand-new pervious surface later.

In the case of the recreational basketball courts pictured above, the percolation rate has deteriorated so badly it was almost nil when this picture was taken.  The inspection and discovery time for a pervious surface in this poor condition is not time-sensitive and can be seen for days after a rain event.

You will probably hear about it from local future NBA stars as well. The environmental benefit from this particular investment has not been realized for many years.  Inspection by umbrella would have helped identify the deteriorating pervious condition and encouraged early and routine maintenance and consistent functioning of this installation.

Materials that Clog Pervious are Transported by Rainfall


Northeastern United States residential street second half of October littered with leaves. Traffic will pulverize the leaves. Crowned conventional pavement delivers rainwater and pulverized leaves to the precast pervious concrete blocks in each gutter. It only took 16 months for this pervious concrete to clog.

From the west coast basketball court, let’s go to an East Coast residential street.  Because gravity is a thing on both coasts, water from grassy areas above the basketball court pictured above adds to the drainage and contaminant load for the pervious pavement.  In the typical residential street pictured, leaf litter is pulverized by car traffic across the entire crowned conventional asphalt surface.  Local residents knew it was failing because they saw the puddles during and directly after each rainstorm.

Pervious Clogs Because it is Doing Its Job

Rainfall effectively delivers the pulverized organic matter and airborne inorganic dust and dirt to the precast porous concrete blocks from the entire width of the street.  Because pervious asphalt and porous concrete are both constructed with voids to let the rainwater pass, gravity deposits these solids in those voids.  This natural process gradually plugs the voids.  Conveniently for us, the bulk of such material is filtered from the water and collected in approximately the top 3/8” of the pervious surface.



Pervious Asphalt Parking Lot in full failure mode. It is raining in this picture, too, but an inspection much later in the day would still show this pervious pavement’s condition.



Same parking lot same day: small demonstration area made functional again with high pressure water and simultaneous vacuum recovery – MCV



Rainwater running down a pervious asphalt street. Two ways to discover this: 1. Drive or walk by with your umbrella while it is raining; 2. Your crew does an ASTM perc test, disrupting traffic, any day of the week.

How To Maintain Your Pervious Surfaces 

  1. Regularly sweep your pervious surfaces with conventional sweeping equipment.  Keep as much organic and inorganic litter off the surfaces as possible.
  2. Inspect your pervious surfaces using an umbrella during rainstorms to note percolation deterioration early.
    1. To learn more and as needed, document the deterioration by means of the conventional ASTM test procedure
  3. Conduct pervious pavement maintenance cleaning regularly as indicated by the results of your observations and tests described in #2. Subsurface pervious cleaning requires a high-pressure wash with simultaneous vacuum recovery (MCV).
  4. Pervious pavement functionality can be restored at sites like the flooded areas shown in this posting.  The recovery or restoration process requires a more intense treatment with the same high-pressure water and simultaneous vacuum recovery that is used for periodic (seasonal or annual) maintenance.


Morals of the story

Don’t pretend your pervious surfaces will not clog over time. Don’t write off your investments in pervious pavements without a fight. See it to believe it.  Get in touch with Triverus for a demonstration on your site.

First MCCRS Aircraft Carrier Surface Cleaning Machine Shipped

 First USN MCCRS Surface Cleaner Machine - Triverus


Palmer manufacturing company Triverus LLC has completed its first of four MCCRS (Mobile Recovery Recycle System) surface cleaning machines for the US Navy. The MCCRS Surface Cleaning Machine uses patented technology to clean and restore the necessary friction on naval carrier flight deck surfaces while dramatically reducing pollution runoff into the ocean.

The MCRRS mobile cleaning system can drastically reduce wastewater generation and disposal footprint compared with the manual labor-intensive SCRUBEX. It uses pressurized water to spray clean surfaces. Material is recovered and a series of solids classification is done to remove solids from the influent and produce process water for continued cleaning.

President/CEO Hans Vogel stated “Our team has worked with the Navy for 10 years in the R&D phase to meet all specifications and create a state of the art hard surface cleaning machine built right here in Palmer Alaska”

The Navy’s long-term plan is for Triverus to build up to 40 machines over the next 6 years, all of which will be made in Palmer according to Vogel. Eric McCallum, an investor, and partner in Triverus points out “ It’s a critical time to show Alaska can export technology and manufacturing, not just natural resources.

Triverus also has a second manufacturing plant in Burlington, Vt. where they make the MCV (Municipal Cleaning Vehicle) a smaller machine tailored for stormwater pollution prevention and high-efficiency cleaning of parking facilities, airports, and industrial applications. Minneapolis International Airport has five MCVs just for cleaning their parking garage.