July-August 2007

The Art of Testing

Putting stormwater, erosion, and sediment control BMPs through their paces

There are those who would argue that the science of keeping stormwater runoff free of sediment, dirt, and pollution is boring, like eating dry toast without butter.

These people have never met Jett McFalls.

True, his name is cool, but that’s not the only interesting thing about McFalls. He’s the manager of the Hydraulics, Sedimentation, and Erosion Control Laboratory operated by the Texas Transportation Institute and Texas Department of Transportation. This means that he oversees a 19-acre funhouse of flumes, indoor waterfalls, and greenhouses.

McFalls isn’t running a waterpark. His facility, and all the equipment in it, exists to make sure that officials with the Texas Department of Transportation use erosion and sediment control products that actually work.

So McFalls and his fellow engineers pour gallons of simulated rainwater over erosion control blankets to make sure they hug the soil even in fierce storm conditions. They send raging rivers of water down a 30-foot channel flume and dare liner materials to stay not only in place but also in one piece. They stretch, bend, and crush sediment and erosion control products to make sure they can take whatever punishment nature can give them.

Does that sound like a dry-toast kind of job?

“Oh, we do have fun here,” McFalls says. “We are doing a job, an important one, but at the same time this is a fun place to work. People always say that erosion control is not an interesting topic, not an exciting topic to study. Well, they’ve never been here.”

McFalls isn’t alone. Labs designed to test stormwater and erosion control products dot the country. Some, like McFalls’s lab, work mainly for one state, testing materials; then, if the products pass, they get put on the state’s list of approved best management practices (BMPs). Others run tests not associated with state agencies, trying to discover, for instance, if wattles filled with recycled palm fronds perform as well as those filled with straw or other materials. (By the way, according to preliminary data from the San Diego State University Soil Erosion Research Laboratory, they do just fine.)

The research labs are an important element of the stormwater and erosion control industries. They provide key information about how different products work and in what environments and situations they work best. And they do this without the bias that a manufacturer, no matter how scrupulous, has when testing its own products.

But how do these labs operate? What equipment do they use? What tests do they put products through? And how do they decide what gets tested?

Stormwater decided to find out. To do so, we spoke with the researchers at four of the busiest testing labs in the country. What’d we find? The testing industry is a fascinating one, and one that deserves a little press now and again.

Photo: Jett McFalls

Test beds under a rainfall simulator. Clay and sand soils are tested.

Paving the Way for Palms
The engineers at the San Diego State University Soil Erosion Research Laboratory are busy. The lab tests sediment and erosion control products for local, county, state, and federal agencies. The engineers also test products for private companies who are either developing new ways of keeping stormwater runoff clean or are preparing to go to market with a product.

There is never a shortage of work here.

“We have two things going on here all the time: research and development,” says Ed Beighley, co-director of the laboratory. “We are always trying to get a better understanding of how the different devices work. When we work for private companies, they will have a particular product and they want to know how well it works. We’ll run the tests and then give them the data and tell them how well their products performed under our conditions.”

To do this, the laboratory relies on a tilting soil bed, portable overhead rainfall simulators, and a water treatment and storage system. The soil bed is 3 meters wide and 10 meters long, occupying a total of 323 square feet. The bed can accommodate soil up to a foot deep.

When testing products, the researchers here compare them to a bare soil run. This allows them to determine how well the particular sediment or erosion control device performs against a soil bed that is graced with no BMPs. The engineers then know how much runoff and sediment displacement they’d get with no stormwater products in place.

They then test again, this time with the BMPs installed, and make a comparison. This gives a picture of how specific stormwater products perform in certain conditions during a certain type of rainfall.

Photo: Jett McFalls

Testing in an outdoor flume

City officials in San Diego often turn to the laboratory, which recently tested wattles filled with recycled palm fronds. The goal? To see if the fronds are as effective a filler material as are the more traditional ones such as straw.

The lab’s engineers finished testing the palm fronds in September of last year. That doesn’t mean the project, though, is complete. Beighley and others with the lab are still conducting their own independent research. Beighley is also preparing the lab’s results for publication.

The results are important for the city. San Diego, after all, has no shortage of palm fronds.

“Palm fronds are abundant here, and they are a product that no one uses,” Beighley says. “They have to go to the landfills. But if we could find a use for them, if we could use them in wattles, that would be a good solution of what to do with these products.”

The testing process lasted about nine months, Beighley says. The lab tested the palm-frond-filled wattles much the same way it tests other stormwater and erosion control materials, comparing against a bare soil bed with no BMPs installed. The results were solid. The palm fronds worked just as well as any other wattle material, Beighley says.

The lab is now testing the palm fronds to see how they work for blanket-type settings. Lab researchers are in the middle of these new tests, mixing the palm fronds with other materials to see how effective they are in preventing sediment in water runoff. The tests will probably continue through mid- or late 2007, Beighley says.

Testing the Separators
St. Anthony Falls Laboratory, run by the University of Minnesota, is a rarity: It’s the only fluid-mechanics laboratory that uses a natural waterfall as its primary source of water. It’s situated on an island in the Mississippi River.

But most unusual of all might be the research that the lab tackles. The dozen University of Minnesota faculty members who work at the lab conduct both applied and basic research. Currently, the lab is running more than $1 million worth of projects with state agencies, testing different stormwater BMPs.

The lab is currently testing the effectiveness of a variety of underground hydrodynamic separation devices in removing suspended sediments and other pollutants.

“We realized that there are many who are building these devices,” says Omid Mohseni, associate director of applied research with St. Anthony Falls. “But no one knows how they really perform. They only way to evaluate them is through monitoring, and there are a lot of problems with monitoring.”

The biggest problem with monitoring, Mohseni says, is that most observers only monitor a system’s performance for one year or, at the most, two summers. The underground separator may for this limited time period perform extremely well or do a terrible job, depending on the amount of rainfall an area sees during these months. Thus, underground separators rarely receive an accurate portrayal of how they perform during specific types of rainfall conditions. This is important: The devices may work well in one area that sees a certain amount of rainfall—and a certain number of severe storms—in a given year but fail in another area that suffers from significantly higher rainfall.

Municipal officials also generally rely on automatic samplers to monitor their underground devices. This is a mistake, Mohseni says, because such samplers are not designed to analyze suspended sediments. Automatic samplers work well only for dissolved materials, he says.

Researchers at St. Anthony Falls decided that it was time to put the popular underground hydrodynamic separators to the test. The lab would test four of the most commonly used separators, but the tests wouldn’t be run in simulated laboratory conditions. Instead, researchers would go out into the field, testing separators that were currently operating in municipalities in the Minneapolis–St. Paul area.

To do this, researchers mapped 150 of the underground devices from the different manufacturers that were currently in use in the Twin Cities area. In the end, the lab found four different brands of separators to test, in four different locations. Researchers chose separators that were located close to fire hydrants that had sufficiently powerful water flows.

Lab officials also made sure that their researchers would be able to run their field tests safely. That meant not testing separators that would require testing crews to stand alongside heavy traffic. It also meant not testing devices located in the middle of busy streets.

In the summer of 2006, crews from the laboratory subjected the underground separators to 12 different water-flow tests, using the water from nearby fire hydrants to conduct their work. Researchers fed known amounts of sediments into the underground separators and then analyzed just how much of these sediments the separators removed.

Researchers subjected the devices to a wide variety of water-flow levels to see how they handle heavier and lighter rainfalls. They also fed varying sediment sizes—80 microns to 400 microns—into the devices.

The results? Not surprisingly, they depend on the severity of the water flow and the size of the sediments fed into the devices. If the sediment was heavy and the flow rate slow, the devices were able to remove 100% of the sediment particles, Mohseni says. But as the flow’s force increased and the sediment size dropped, the effectiveness of the underground separators dropped, too, he says.

Photo: Jett McFalls

Testing at Texas’s Hydraulics, Sedimentation, and Erosion Control Lab

Researchers at St. Anthony Falls were preparing their final analysis of the data as this article was being written. Their final report will include a series of performance curves for the four separators that show how each performed depending on flow rates and sediment size.

“Our testing is probably the most robust done on these devices,” Mohseni says. “Now different agencies can use the data we produce for evaluating these four products, no matter where they are being installed. In Washington or Vermont or down in Louisiana, anywhere they go, these results will be valuable. The only thing they need to know is what kind of sediment size they have in their stormwater runoff. If they don’t have that piece of information, then these performance curves will not be that valuable. They’ll have to assume something. They’ll have to assume what they think the sediment size will be instead of knowing exactly what it is.”

The Need for Testing
James Mailloux, engineer with Holden, MA–based Alden Research Laboratory, is a busy man.

Photo: Jett McFalls

A typical test flow

Then again, so are all the researchers at Alden, the oldest continuously operating hydraulic laboratory in the United States. This lab never has any shortage of stormwater-treatment devices to test.

This is no surprise. Alden is one of the most respected, and largest, hydraulic labs in the country. The Alden campus occupies 32 acres of hilly land, though Mailloux does much of his work in a 70- by 120-foot building designated exclusively for stormwater-related testing. A 5-foot-deep sump at one end holds 50,000 gallons of water.

A 50-horsepower vertical pump produces the water flow that Mailloux and his fellow researchers rely on to test separator units, filter units, or whatever other product they happen to be analyzing. A second 50-horespower pump sits alongside the first, just in case they need an even more powerful flow of water.

Of course, this is just the start of the equipment that Alden relies on to test sediment removal products. Mailloux has five calibrated flow meters at his disposal, ranging from the 2-inch to the 12-inch variety.

“Depending on what we are testing, what size unit, and what size flow we need that day, we select one of these meters to run the flow through,” Mailloux says. “We then have full documentation of the flow, averaged every five seconds, during the duration of the test. It gives us an excellent record of what the flow was during the entire test. We get all types of useful information.”

Researchers then inject sediment into the flow. Alden uses both a flurry system and a dry-injection system, though researchers here typically reserve the dry-injection method for testing larger sediment control devices.

The tests Alden runs are important, Mailloux says, in part because manufacturers are constantly developing new products to treat stormwater runoff. As federal regulations regarding sediment control become more stringent, these products have to do a better job than ever at removing sediment, oil, trash, and debris from water runoff.

Without independent testing labs such as Alden, government agencies and local municipalities would have to rely too much on test results provided by the manufacturers themselves. Not all manufacturers test their products using the same test parameters, and some potential buyers trust third-party testing over the manufacturers’ own results.

Photo: Jett McFalls

Vegetated flume test trays in the greenhouse

The goal at Alden, Mailloux says, is to establish accurate removal rates for the sediment control devices that its researchers test. That way, municipalities can install those devices that have been proven to work well under the type of actual weather conditions that they’d be expected to face in the field.

Most of Alden’s testing requests come directly from the companies that manufacture stormwater-related devices. “They come to us and ask if we can write a proposal to test to a specific protocol, whether it be for Washington state or New Jersey,” Mailloux says. “We’ll find out what is required by that particular municipality, write a proposal to do the work, and, if they decide they want to go ahead, we’ll work up a schedule.”

Mailloux, though, doesn’t want to know ahead of testing what specific results—as far as sediment removal goes—his clients want to achieve.

“I don’t want to know anything about what the clients expect,” Mailloux says. “I don’t want to go into testing with any predetermined ideas. I don’t want to be biased on what I can expect to see. Then we can run the tests and, after we’re done testing, get feedback from the manufacturer.”

Sometimes testing will prove that a manufacturer was dead accurate in its predictions of how a particular product will work. Other times, the results may surprise a company. Perhaps the product removed even greater levels of sediment at more powerful flows than the manufacturers expected.

Other times the surprise isn’t as pleasant: The product may perform less ably than its makers anticipated.

“But we don’t like to have the information on what the clients expect,” Mailloux says. “I don’t want that at all before we start running our tests.”

Those who run the independent testing labs across the country feel the same way. It’s important not to perform a test with biases—even unconscious ones. It helps no one, after all, to give a product a better performance evaluation than it deserves.

It’s not just highway department officials, contractors, builders, and municipal officials who rely on the labs for impartial product evaluation. The labs are sort of the Consumer Reports of the stormwater industry. Manufacturers, too, then, rely on the labs to help them develop the best products they can.

It is these products that work the best that will attract the most attention, and most business, from clients.

“We’ve been at this since 1990,” says McFalls in Texas. “I think we’ll be running these tests for a long time.”