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When Pervious Pavement Penetrated the Market

In the early days of pervious installations, the importance of maintenance was rarely mentioned.  Back in the day, I listened to a host of experts on the subject showing their pervious installations and forgetting the important discussion of maintenance once installed. The Pacific Northwest was especially aggressive with the new technology because their interest was focused on protecting Puget Sound in a very rainy environment.  

Even there, rarely did you hear the word maintenance in APWA and other stormwater conferences.  A hard, paved surface was treated as a hard, paved surface.  Not surprisingly, BMP for hard surfaces were generally not changed.  The cleaning process for pervious pavement practice for years had been and continued to be conventional mechanical street sweeping, or brush type sweeping enhanced with vacuum or regenerative air retrieval systems.  

Improved Pervious Percolation Performance Through Appropriate Maintenance.

The unique conditions in the Pacific Northwest, however, lent itself to a tattle tale visual cue that new techniques were needed to maintain the new pervious surfaces to best effect.  Accumulated dirt and organic material filtered out by the pervious surface provides an excellent growing medium for moss.  

In the Northwest, when pervious sidewalks and parking lots became green and slick when wet, it was the pervious installations crying out for help.  Dirt and organics filtered out by pervious in other parts of the country just do not have the climatic advantage of that in the Northwest, so the pervious surface cannot so loudly cry out for help – and improved maintenance practices. 

Subtle and Not-So-Subtle Views of Clogged Pervious

Street View. Note lack of surface texture in upper left area of photo. “The filter was full.” Lower right shows the pervious after one pass of MCV emptying the filter

Macro parking lot view. Can’t miss this cry for help in the Pacific Northwest. (Im)permeable concrete being made permeable again. Path made by single pass of MCV.

While both the areas pictured had been swept traditionally on a regular basis, neither of them had any meaningful percolation rate prior to proper treatment to bring back the original functionality.

Keeping Pervious Effective Cost Effectively

It is a FACT that sooner or later your pervious pavement will clog and be less effective than when it was new. All sites have their own characteristics.  Identify the sources of the debris and dirt that are migrating into your pervious:

• Trees and nearby or overhanging vegetation;
  • Particularly seasonally in spring (budding) and fall (shedding).
• Run-on from nearby unpaved areas, especially nearby bare slopes
• Road traffic 
  • This is also a large source of hazardous pollutants that will transport via stormwater.
• Road sand / cinders. (!)
• Piling plowed snow, with dirt and debris with it, on a pervious surface
• Designed inflows from larger areas to the pervious receiving area
• The landscaper that dumps his truck load of topsoil or mulch directly on the pervious for his momentary convenience.  (!)  — you know I am not kidding, right?
• Airborne dust and particulates
• (Coastal) Bird excrement. (!)

Totally covered and clogged pervious sidewalk downhill from, and adjacent to, an untended bare slope. Photo from fall, 2020 during percolation recovery operation. Yes, it was brought back to a useful life.

The fact is that while effective recovery and periodic maintenance require high pressure wash applied with simultaneous vacuum, conventional sweeping has a role to play in extending the periods between deep, sub-surface cleaning with high pressure water and simultaneous vacuum recovery.  

The most cost effective, long-term maintenance for your pervious surfaces will consist of a judicious, well-thought-out program using both methods.  A deeper dive into balancing these two cleaning methods is provided in Triverus’ Pavement Maintenance Cleaning Guide.

Through contract service work for municipalities that are still expanding their use of pervious pavement, Triverus has experience with a large number of variable pervious pavement applications and conditions. 90% of our contract service work has been aimed at recovering percolation rates of clogged pervious asphalt and pervious concrete, while only about 10% could be categorized as maintenance of pervious pavement. 

Municipal satisfaction with percolation recovery results is now leading more and more often to contracts for pervious maintenance work or vehicle procurement by the municipalities themselves to establish consistent pervious pavement maintenance programs.  This trend is enhanced where state or Federal assistance is available (e.g. Washington State) to assist local procurement of pressure wash /simultaneous vacuum type equipment. 

Want to talk more about methodology through email or a site visit by Triverus? Get in touch with us today.

The simple, but unhelpful, answer to this question is, “maybe.” There are multiple factors that can influence how pervious surfaces handle stormwater. Among criteria to consider are the soil beneath, the flow of water, and the traffic the surface experiences.

What type of soil substrate do you have?

The first criteria are the characteristics of the soil at your intended installation point. Installing a pervious surface above an impermeable substrate will not work. However, if your substrate is penetrable, then you can take advantage of that fact by allowing stormwater to reach the substrate.

As an example, a major East Coast City selected a sub-division to test the effectiveness of pervious surfaces in controlling stormwater outflows.

• First, they spent over a year collecting data on the amount of stormwater that was flowing out of the subdivision and entering the neighboring environmentally challenged bay
• Second, because the residential streets are crowned and relatively narrow, the city engineers opted for 4-ft wide precast pervious concrete blocks lining the edges of the streets.
• Third, after the installation of the pervious blocks, they continued to collect data on stormwater outflows from the area.

The data showed that stormwater outflows from the study area were reduced by 60%.

Based on these excellent results, the city is continuing to expand its installed base of pervious surfaces in other areas of the city.

Precast pervious concrete blocks installed on crowned street in East Coast city. The crowned conventional impervious roadway delivers the stormwater to the pervious surface for processing.

Stormwater and Solids

The stormwater issue is not just about the water itself, but what stormwater run-off carries with it.  You don’t really see it because we are so used to it, but traffic bearing paved surfaces are filthy. Paved surfaces have a coating of tire residue (including copper and the tire preservative 6PPD that has been proven to decimate salmon in the Northwest), hydrocarbons from our cars, pulverized organic matter, dirt (both fine and coarse), and so on.

Just look at your local white shiny crosswalks if you want to see the amount of dirt and residue that covers our city streets.  A lot of this stuff is adhered to the surface of the pavement.  It is stuck.  It tends to become unstuck when it rains.

Typical crosswalk, except the brighter black and white area in the rear has been pressure washed to remove adhered solids.

How Does Traditional Street Cleaning Work?

Think of the stuck cheese and dried marinara sauce on your pizza plates when you save the clean up for the morning after your party. How do you make cleaning up easier? You soak the plates in water.

Streets go through the same process.  Paved surfaces become a storage area for adhered solids, heavy metals and pollutants.  The conventional street sweeper, with or without vacuum or regenerative air, moves anything that is loose, including dixie cups, cigarette butts, and dust.

Much of that dust escapes into the air only to settle on nearby cars and back onto the just-swept street.  All those adhered solids are still there when it rains the next time. The rainwater loosens many of these solids, and into the storm drain and out to the river or bay they go. This is not a good time for the EPA to show up at your outflow with its sampling equipment, test kit and a copy of your stormwater plan and commitments.

How Do Pervious Surfaces Work With Stormwater?

If we catch and redirect the rainwater from conventional hard surfaces into and through the pervious surface, we will also accumulate the solids and pollutants without letting them flow to the storm sewer and on to the river or bay.  A pervious installation is a giant water filter, letting the water flow back to the aquifers below the surface while the pollutants are collected in the upper levels of the voids of the pavement for cleanup and disposal.

Can a Traditional Street Sweeper Clean Pervious Surfaces?

A conventional street sweeper with or without vacuum does not exert enough energy on the paved surface to break the adhered material free, nor can it apply effective amounts of energy into the pavement voids where the rain loosened solids have collected for us.  Conventional sweeping will extend the original functionality of a pervious surface, but inevitably, enough solids collect to reduce and eventually eliminate stormwater percolation.  A hygienically applied high pressure spray and recovery is required to finish the job and to keep pervious surfaces functioning.

Contact Triverus to set up a demonstration of how Triverus technology can recover your pervious flow rates at your location. 

A Mobile Cleaning, Recovery, and Recycling System Helps with Runway Cleaning and Gets Naval Aircraft Carriers and Municipal Parking Lots into Shipshape. 

A Navy aircraft carrier idles in the middle of the ocean, readiness compromised by foreign object debris (FOD) across its flight deck. Debris and hard particles have built up from aircraft and ground-support activity. Even something as routine as moving planes from the hangar deck to the flight deck can spread debris or spill grease and jet fuel. Given that jet engines have powerful intakes that can suck up debris, the risk of damage to aircraft engines becomes too significant to allow takeoffs and landings. Even a bit of spilled grease or fuel can be dangerous if aircraft slip into each other on the rolling deck of a carrier on high seas.

In order to get the carrier fully operational, the Navy calls on Triverus, a Palmer, Alaska-based small business that has produced advanced cleaning technology since 2001. Triverus ships their five-ton Mobile Cleaning Reclaim Recycle System (MCRRS, pronounced “McChris”) to the vessel overnight. MCRRS immediately starts runway cleaning on the deck using water-jet technology, integrated air recovery, and waste-water recycling. Within a short time, the flight deck is spotless, and the ship certified as mission ready.

Read the full article

Before Triverus MCV Cleaning — Water Running Off       After Triverus MCV Cleaning — Water infiltrating

In the summer of 2019, the University of New Hampshire Stormwater Center invited Triverus to their campus in Durham, NH, to determine the effectiveness of the Triverus Municipal Cleaning Vehicle (MCV) in pervious pavement cleaning and restoring percolation rates. UNH has several generations of pervious pavements, each installed when major changes or advancements in pavement design or installation occurred.  While each plot is still in use, predictably, percolation rates deteriorated over time.  By the summer of 2019, all their pervious paved surfaces were non-functional.  Over the period of a week, the MCV performed trial pervious pavement cleanings on five such plots. Every treated test plot showed restoration of acceptable percolation rates, even after up to 15 years of non-functionality.  UNHSC published a full review of the process and results of testing in the parking lot of their Alumni Center. Read the study here.

PALMER, Alaska (KTUU) — Technology pioneered in an Anchorage garage and produced in Palmer is making its way onto Navy aircraft carriers.

Since the early 2000s, Triverus has been working on a porous pavement maintenance machine that efficiently cleans flight decks and removes everything from grease and oil to debris.

“That can get sucked into jet engines and destroy planes awfully quickly, so what the Navy does right now is what’s called a FOD walk where they just send sailors out to one end of the carrier and they literally walk multiple times a day and just stare at the flight deck and pick things up,” Triverus manufacturing manager Nathan Green said.

The current methods used to clean flight decks inhibit the Navy’s ability to respond immediately when aircraft need to be deployed.

Triverus won a contract from the Navy to build 43 mobile recycling cleaning system MCRRS vehicles. Each machine costs $850,000.

It works by using pressurized water, magnets and a vacuum to remove debris from the flight deck. The debris is then filtered out and the water recycled.”

Click here for the full KTUU article

With its large 60 inch deck and high-efficiency technology, the Triverus MCV Vehicle is unmatched in achieving regulatory compliance through the removal or containment of restricted materials. The Minneapolis-St. Paul International Airport was able to save over $4 million, have 111% faster results than manual cleaning, and retained 95% water recovery and reuse. In addition, the new MCV vehicles allowed crews to clean the same 500-space area in two days, rather than seven.  Click here to read more!

“While some may say there are no large manufacturing export markets in Alaska, one Palmer business is proving otherwise.”

Click here to read more in the Mat-Su Valley Frontiersman!

Photo Credit: Mat-Su Valley Frontiersman