Some cities try to address the problem by treating stormwater. Unfortunately, not every roadway is surrounded by storm sewers, and eliminating contaminants at the endpoint is often costly. A common cleaning task performed in many cities, however, helps contain contaminants at their source.

Sweep Those Streets!

Street sweeping, in one form or another, has long been a basic city maintenance task. The earliest street sweepers were just that: Using shovels and simple household brooms, workers collected the debris in wheeled push- or horse-drawn carts and transported the trash to the local city dump. Until the advent of the automobile, however, most of the trash was made up of paper, various refuse, leaves, and horse droppings. 

In the early 20th century, mechanical sweepers were invented. For example, the Elgin Sweeper Company, headquartered in Elgin, IL, delivered its first motorized sweeper to Boise, ID, in 1914. Although many improvements have been made over the years, mechanical broom-type sweepers still comprise about 90% of the street sweepers currently in use in the United States.

While sweeping's primary task was once to eliminate unsightly, unsanitary trash from streets, today—with such governmental regulations as National Pollutant Discharge Elimination System (NPDES)—sweepers are expected to collect particles less than 10 microns in diameter (PM10). Considering that a human hair is 40-120 microns in diameter, some freshly swept streets might be cleaner than the homes situated around them.

Sweepers Making the PM10 Grade

Whether mechanical, regenerative air, or vacuum filter style, many of today's sweeper models have been certified as being able to clean to PM10 standards.

Mechanical. With variations, this process usually removes debris by sweeping material onto a conveyor system, which then transports it into a debris hopper. PM10-certified mechanical sweepers include Elgin's Pelican and Eagle and Tennant's Centurion.

Regenerative Air. In this process, the sweeper blows air onto the road surface, raising fine particles and sediments, which are then vacuumed up. PM10-certified regenerative air sweepers include Elgin's Crosswind J, Schwarze's A-series, and Tymco's 210 and 600 models.

Vacuum Filter. These sweepers combine a mechanical process with a vacuum to capture small particles they stir up. PM10-certified vacuum filter sweepers include Elgin's GeoVac and Schwarze's EV-2.

With many systems meeting PM10 standards, price and personal preference are the primary selection criteria for most users. No definitive independent studies have yet been staged to determine "the best" sweeping system. Anecdotal data has also been inconclusive. "The City of Milwaukee did a test a few years back, comparing vacuum versus mechanical," says Jim Weedman of Wisconsin's Bruce Municipal Equipment, which sells Elgin sweepers. "According to their test, neither proved to be better at getting particulates out."

Hopper Size, Speed, and Other Parameters

Although continually improved, Elgin's mechanical/broom, three-wheel Pelican model is a direct descendant of the company's 1914 design. With its smaller (3.5-yd.³) hopper capacity, the machine must be unloaded more frequently than some models, but its front high dump hopper allows for single-lane dumping (minimizing traffic interruption) into a dump truck that precedes it. The Pelican has a 20-mph travel speed, which could delay traffic behind it. This also shortens its per-day use, as its driver needs to allow more time to return to the garage by the end of his shift.

Elgin added more than a fourth wheel when it developed its mechanical/broom Eagle model. In addition to a larger (4.5-yd.³) hopper, the Eagle also has a travel speed of 55 mph. To keep the air clean while cleaning the streets, the Eagle can also be powered by two alternative fuels: compressed natural gas (CNG) and liquefied petroleum gas. 

A "pure vacuum street sweeper," Elgin's GeoVac offers a large, 8-yd.³ hopper and can take its operator back to the shop at 55 mph. The model also boasts high pickup efficiency and low noise emissions.

Elgin's Crosswind J regenerative air sweeper offers an 8-yd.³ hopper and a 55-mph travel speed. With its trailing side-arm brooms, this giant of the line also features a 12-ft. maximum sweeping path (the Pelican and Eagle offer 10 ft.; the GeoVac offers 8.5 ft.).

Schwarze's A4000, A7000, and A8000 regenerative air sweepers position themselves as less expensive to operate and maintain than mechanical broom sweepers. They also posit being more environmentally friendly because of their regenerative air design. Hopper sizes vary: The A4000 carries a 4.3-yd.³ hopper, the A8000 a 5.8-yd.³ hopper, and the A7000 a 8.4-yd.³ hopper.

Schwarze claims its EV-2 model is the "cleanest" machine, with the ability to pick up particulates of 2.5 microns and scrub up to 900,000 ft.²/hr. of air, down to the same 2.5-micron level. Only 6 ft. tall, the EV-2 features a 4.25-yd.³ hopper capacity and can be used to sweep indoors as well as out.

Introduced just this spring, Tennant's five-speed automatic Centurion mechanical/broom sweeper has one-button operation and a sweeping efficiency that reduces need for multiple passes by 50%. Centurion's debris management system also eliminates the dust clouds often associated with brush street sweepers. Perhaps because of its Minneapolis location, Tennant created the Centurion as a dry sweeper. Because the unit doesn't use water, it can be used in below-zero (Fahrenheit) temperatures–a common occurrence during Minnesota's winters.

Cutaway View of the Centurion

Another "weather-sensitive" feature to note is Tennant's StreetSmart System, a load-sensing hydraulic technology that matches brush speed, brush pattern, and conveyor speed to the application, which allows operators to manage sweeper functions from inside the toasty-warm cab.

Waco, TX–based Tymco offers the PM10-certified regenerative air models 210 and 600. The model 210, which is aimed at parking-lot as well as street cleaning, touts 50% more sweeping ability at reduced rpms, for more power at less cost. The 210 also offers a hand hose for cleaning hard-to-reach places. 

Tymco's top-of-the-line model 600 can sweep a wide swath, depending on which components are used. The pickup head covers 87 in.; adding one gutter broom takes coverage to 110 in.; and using two gutter brooms, the 600 will clean a path 142 in. wide. The debris collected from this path settles in the 6-yd.³ hopper, and with its four-speed automatic transmission, the 600 doesn't take forever to return to the garage at end of shift. Cities facing air-quality regulations as well can choose the CNG model over the diesel.

"San Francisco has recently purchased some of our units that run on alternative fuels," notes Tymco Marketing Manager Bobby Johnson. "As for aiding in stormwater practices, San Antonio uses 25 to 30 of our sweepers for that task."

Street Sweeping in West Palm Beach

Although his model 600 Tymcos are not PM10-certified, Pete Spatara, assistant director of public utilities for West Palm Beach, FL, is nevertheless happy with the machines' performance.

"They suit Florida–the flat land, the sandy soil," Spatara says. "We leased four Tymco 600s five or six years ago, and we've had no engine repairs. The machines still seem to be running well. Just the part that hits the streets wears out, and you have to maintain them. The Tymcos certainly outdid the machines they replaced."

West Palm Beach does quite a bit of sweeping too. "The city contains about 1,342 miles of road, which we sweep every week," Spatara says. "Tuesday through Saturday we run four routes, sweeping streets with curbs and gutters. Roads with swales we sweep only every other week. Sweeping helps with our NPDES permit; we turn this in as being a factor, getting brake dust, et cetera, off the street."

Rain or shine, the sweeping goes on. "West Palm collects garbage twice a week and yardwaste once a week. The day after your yardwaste pickup, your street is swept. I set up the routing to follow the yardwaste cranes–this keeps the streets cleaner. Rain has nothing to do with our schedule; we keep going, even though sometimes rain turns to flooding. We'll also sometimes do an extra sweeping after a flooding rain," Spatara explains.

West Palm Beach citizens also need to play their part in keeping the streets clean.

"City inspectors watch where dirt erodes into street; they also try to keep people from putting yardwaste and garbage out on wrong days. We also keep a lookout for illegal dumping," Spatara maintains.

The only problem Spatara experiences with his Tymco machines is the streets' fault, he notes. "Citizens don't mind the sweeping, but we get complaints if the sweepers don't work well, and we have some problems. We're trying to be a livable city, and we are putting in traffic-calming items, such as speed bumps, and having a terrible time with sweeping around them. We talked to Tymco, and when we replace our 600s, we'll be buying smaller sweepers, ones with a smaller truck body and turning radius, hoping that will help this problem. The traffic-calming items are a problem, but it's what the residents want."

As its name would suggest, the material West Palm Beach sweeps up contains a lot of palm tree debris; however, sand and automotive detritus are also in the mix. "We bring it into our complex, dump it onto a cement slab, then take it to the landfill where our dump tickets are marked ‘sweeper debris,' and it goes in a certain area," Spatara explains.

A Painless Operation in Aiken

With 25,000 people living within its 15 mi.², Aiken, SC, located about 17 mi. from Augusta, GA, needs only one sweeper to keep itself clean: a Tymco 600. "We've had it about three years; it's the best one we've ever had," says Assistant Public Works Director Kenny Cook. 

"We sweep primarily in our downtown area every week, and the major thoroughfares or entrances to the city every other week," he goes on. "I'd say our weekly cleaning covers about 10 miles. We don't sweep residential, except on request. We ask residents to keep their areas clean. About 50% of our streets are curbed; older neighborhoods don't have curb and gutter."

Aiken is currently working on its NPDES Phase II permit. "We have some requirements we have to meet, and we have a committee just getting into the rules now," Cook says. "Right now we're getting into the educational part of it, inspections and so on, to make sure no contaminants are getting into water sources. We're not close to a large body of water; the streams we draw water from are well out into the country. In the next year we will get into NPDES in a big way. It may change our street-sweeping program—that's certainly a possibility."

Cook credits the town's "very good solid waste division" for doing its part to keep Aiken clean and in compliance. "On a weekly basis we pick up almost everything, except hazardous waste," Cook reports. "We do recycle paint and motor oil, which also helps. Yardwaste is composted. In fact, we had the first curbside recycling in South Carolina, and the first composting operation. We sell our compost—it's considered professional grade—for $100 per 5-cubic-yard load. And since our growing season is nine months out of the year, we can make a lot of compost!"

Aiken also gives its runoff some treatment. "We've made some manmade wetlands. In one of the main ones, water that comes off the highway goes into a sedimentation pond," Cook explains. "Then the water goes over a spillway into a pond with plants that absorb metals. From there, it goes over another spillway, into another sedimentation pond. In the final pond—the water's so clean, there's fish in it."

Overall, Aiken residents have no complaints about the street-sweeping operation. "If we come in too early in the morning, people say we wake them, so now we do it at 7 a.m.," Cook says. "And yet it's not that noisy; I think our Tymco 600 has the sound-deadening unit on it."

Sound Sweeping Ideas

Sound is, of course, one of the major hurdles for street sweeping. The "best" time to sweep is when few vehicles are on the roads; however, that's usually between midnight and 6 a.m., the hours when cities are their most quiet and residents are sleeping. Most sweeper manufacturers have addressed the sound problem. Elgin's GeoVac touts low noise levels both for the operator in the cab and those hearing it from the street. Schwarze says its WhisperWheel's fan system reduces noise by more than 70%.

Ambient noise is relative; even during peak traffic hours, Aiken is considerably less noisy than, say, Chicago at the same time. (Considering its smaller population, Aiken's rush hour might well be quieter than Chicago's overnights.) Americans are also becoming more sensitive to noise pollution, and many cities have long-standing noise ordinances on the books, with new ones added each year.

The chance for a sleep disturbance also varies from person to person and sound to sound. An urbanite might sleep through police sirens until they stop right in front of his house, while a rural resident might bolt awake immediately at first hearing. By the same token, city dwellers on camping trips often complain about the constant chirp of crickets or the "deafening silence."

So what's "too loud"? According to the National Institute for Occupational Safety, maximum allowable exposure to 85 decibels (dBA) is eight hours. For 110 dBA, maximum exposure time is just 1 minute and 29 seconds. Noise levels above 140 dBA can cause hearing damage after just one exposure. Decibel increases and decreases are exponential. A 5-dBA noise reduction is about 30% quieter.

Tymco has toned down its sweepers' noise levels as well. During "heavy sweeping" mode, the standard Tymco model 210 runs at about 81 dBA; at "normal sweeping" mode, the sound drops to about 78 dBA. With the Sound Reduction Engineering package, however, heavy sweeping marks at about 71 dBA, and normal sweeping at about 68 dBA. (Noise level, measured at 50 ft., was performed during a stationary test.)

Quiet or not, however, sweepers can be an important tool in meeting NPDES requirements. Incorporating regularly scheduled street sweeping with a comprehensive stormwater program is a sound solution.