Ask the average citizen about “street sweeping,” and chances are she’ll say, “It cleans up the trash people toss out of their cars.” This is, of course, true, and what most people notice. Minutes after Los Angeles’ 2013 Golden Dragon Parade ended, pedestrians quickly returned to Chinatown’s sidewalks as street cleaners whisked along the parade route, collecting the numerous piles of paper confetti and Mylar streamers shot from and to the crowds.
However, street sweeping does much more, and not only citizens, but also their municipalities, need to realize what’s actually on the streets, and what that debris can do to local waterways, and, perhaps, residents’ health.
Roger Sutherland, P.E., principal water resources engineer with AMEC Environment and Infrastructure in Portland, OR, who’s slated to give a talk on street cleaning at StormCon 2013 in August, points out that “aesthetic” definition is causing problems for America’s cities as well as its rivers and streams. “What I call “˜street dirt’ is composed of heavy metals and other pollutants–items that may be killing fish when they get into waterways via stormwater runoff. Ironically, some cities are trying to solve the problem by using media filters for stormwater treatment, when effective street cleaning could lessen much of that problem at about one-fourth the cost, based on a pound of sediment removed from the stormwater.”
To Sweep, Perchance to Clean?
To begin with, Sutherland thinks a simple name change would offer a better understanding of what the process entails. “I prefer to call it street cleaning. The connotation of “˜sweeping’ is “˜sweeping under the carpet.’ “˜Cleaning’ is something useful–a job well done.”
Street “sweeping” has likely been performed for centuries–of course, before the advent of automobiles, much of that cleaning entailed horse manure. However, the cleaning vehicles we see today had their start around the turn of the 20th century. Many cities across America purchased them, but their effectiveness was somewhat limited.
“I can’t tell you how many American cities sweep and how many don’t,” says Sutherland. “It’s a situation where a number of communities swept streets for years and years. As far back as 1969, “˜street dirt,’ the material accumulating mainly in the gutters, was identified as a source of water contamination. In 1972, in the first USEPA publication ever on stormwater [Sartor and Boyd 1972], street dirt was named as the primary source of contamination, in terms of mass.”
The contamination was identified, so one would think street sweeping was desperately needed. “And yet,” he says, “what happened was, EPA did a study of the effectiveness of best management practices needed to remove stormwater that involved 30 American cities–the Nationwide Urban Runoff Program, between 1980 and 1982, at a cost of about $30 million. EPA looked at studies and technology, and concluded sweeping was “˜ineffective in the ability to reduce pollutant concentrations found in stormwater.’ This was a death knoll for street sweeping for America.
“If a community was trying to cut costs, street sweeping was one of the first items to go,” he continues. “EPA’s evaluation was correct when it was made; 1980 machines were not very effective at picking up sediment, especially the finer material that contains a higher proportion of the contaminates. But now we have really lost sight of how smart people, mechanical engineers, have improved the technology in street sweeping.”
Street Tech: The Next Generation
Sutherland gives an overview of street cleaners on the market today. “Mechanical machines, which use a main broom and conveyor belt to pick up material–the only ones being used at the time of that 1980s EPA study–have been around at least 100 years. Their design hasn’t changed that much, although impressive improvements have been made, such as the broom design and speed, and the conveyor belt speed and alignment, which carries particulates to the hopper. The mechanical machines are still the most popular–perhaps 90% of those in operation? During my next webinar I’ll have to ask the attendees for a “˜show of hands’ on the type of machines they use.
“There are also regenerative air street cleaners. In one motion, the machine blows air down on the pavement to dislodge material, and then the air is immediately vacuumed into the hopper,” he adds. “Some of these machines can stir up lots of dust, because most do not filter the return airflow.
“Vacuum machines are just that, and they can be very effective. Manufacturers have strived to increase the fan speed and create a greater vacuum. But sediment in the return airflow limits their ability to do just that. Perhaps Dyson should be working on this?” jokes Sutherland.
“All of these machines can, and some have been designed to, capture fugitive dust and basically filter it in some way,” he says. “Each of the major manufacturers has one or more sweeper models that do just that. In fact, I believe that only these machines should be viewed as “˜high-efficiency cleaners,’ a term I coined in 1997. Certainly, all street cleaners are more efficient than what was tested in the 1980s. Some can actually change the color of the pavement, and there’s no dust.”
Picking up the contaminants is, after all, the objective. “If you’re just “˜sweeping,’ you’re blowing it away,” he says. “True, that contaminated material has less chance to get into stormwater, because you’ve blown it onto nearby grassy areas, where it can infiltrate through the soil. Of course, though, this irritates people, and it looks awful, going down the street in a cloud of dust–and it’s not good for anyone breathing in that stuff.”
Beautiful Downtown Burbank–and Glendale
In Burbank and Glendale, CA, Sutherland’s firm and Larry Walker Associates of Santa Monica, CA, have been studying the potential effectiveness of enhanced street cleaning programs in removing heavy metals from stormwater runoff. “We’re getting down to the heart of the issue. Are cities cleaning streets merely for the cosmetic or aesthetic value, or to reduce the concentration of contaminants found in the runoff? Our work is a quest to get them to recognize the pollution-reduction benefits of street cleaning. And these two cities sweep a lot–I don’t know many in southern California that don’t have a program. However, some don’t understand the value of that program; even though they sweep, the focus is on aesthetics. If one concentrates too much on the “˜big stuff,’ everything else will suffer; you may not be picking up the contamination material.”
Studies such as this are being driven by total maximum daily loads (TMDLs) for various waterways. “Heavy metals–cadmium, copper, lead, zinc–are specific pollutants of interest in Burbank and Glendale, since they’re included as part of the Los Angeles River TMDL,” says Sutherland. “The study we did was just the first step; maybe next year they will move to the next step.
“We put together a street dirt sampling program that monitored the accumulated material both before and after sweeping, for three separate sweeping events, spread over a three-month period in late winter and early spring,” he adds. “Interestingly, to my knowledge, this is the first time anyone had sampled street dirt in southern California. We need to learn more about street dirt–its accumulation over time, its particle size distribution–but most importantly, we need to learn more about the pollutants that are in it, and their association with these particle size groups. If we focus on the pollutants by particle size group, we can understand how effective the different cleaning processes are.”
Using Google Earth and Street View, Sutherland’s team selected 10 different areas, five in each city. “We selected typical land-use areas: single-family residential, commercial, major arterials, and industrial areas. We started the data collection program, knowing the cities were not going to stop cleaning; one sweeps weekly, the other, every two weeks. So the data collection program was designed to determine the pickup effectiveness of these cleaning programs. Unfortunately, not being able to stop the cleaning program made it difficult to see much accumulation there would have been if cleaning had not occurred.”
Effective street cleaning starts with empty streets. As debris tends to settle in the gutters, one must clean along the curb, and having to swerve around parked cars greatly hinders the cleaning procedure, because a minimum of three car lengths of curb line would be missed for every parked car. Sutherland knows the average citizen recognizes a huge “hassle factor” with the process. “I started my career in the 1970s, living in a busy residential area in northern Chicago, near the lake, where signs were posted: “˜Street sweeping every other Tuesday from 8 a.m. to 5 p.m. No parking during that time,’ so I understand there’s a human impact to this. One time I didn’t move my car and it was towed,” he chuckles. “How can we make these restrictions more effective, and enforce them, realizing that people with busy lives are dealing with this? Maybe a city should offer an e-mail reminder.”
To find what’s occurring in his field of study, Sutherland uses a Google alert feature which lets him know daily when the terms “street cleaning” and “street sweeping” appear in postings throughout the world. “There’s a tremendous amount of chatter out there–people are upset about sweeping. “˜So I moved my car and they didn’t sweep’ is a recurring complaint. Perhaps people would be more compliant if they knew more about street cleaning, and how important it is in the battle to reduce pollutants in stormwater. Public education on this topic is needed.”
Educating the public might be accomplished by shifting street cleaning’s “image” from “a tidy city” to “averting health problems.” Sutherland wonders, “Do we breathe any of this dust that’s being swept up? Yes, street cleaning removes possible pollutants from stormwater, but it also could help keep them out of the airshed. Machines that embrace filtering airflow with pickup are particularly effective in reducing pollutants in the air, such as PM10 particulate matter. If you’re filtering to about 2.5 microns, you’re doing a good job. All major street sweeper manufacturers have a machine or two that have been fitted with this type of advanced technology. These are the true high-efficiency cleaners that every city should work towards obtaining.”
Sometimes the street pavement can be part of the problem: “Want to improve water quality? Maintain the condition of street pavements to “˜good’ if at all possible, since “˜poor’ condition streets contribute to the pollutant load when the asphalt and concrete break down,” he says.
Getting stuck in traffic behind a street cleaner will take less of one’s time these days. “It had been thought that to be effective, street cleaners had to sweep fairly slow–five or six miles per hour. However, studies in Burbank, Glendale, and elsewhere have shown that today’s cleaners can sweep at twice that speed–10 miles per hour or so–and do the job well. Of course, an experienced driver who wants to do a good job will slow down if he encounters an atypical, higher accumulation.”
Water: Part of the Problem
Dry street cleaning captures the pollutants before rains can transport them someplace else, such as down a drain, which makes them even more of a hazard. “A few years ago, I read research, done in Hamilton, ON, in which the team went around the city, especially its industrial areas, and picked up street dirt [Irvine et al. 2009],” says Sutherland. “Their data went beyond the particle size distribution and chemical analysis, such as total pollutant mass, as I and others have done. They also looked at the bioavailability or solubility of the metals in much greater detail. They identified four different categories of metals’ bioavailability, from “˜readily available,’ once the material is wetted, to “˜potentially available,’ under certain environmental conditions that may not often be met. As an example, copper’s bottom line: The bioavailability of the accumulated street dirt ranged between 21% and 73%, depending upon land use and contact time. It’s ironic–humans can drink a certain amount of cadmium, copper, zinc, and so on. If toxicity levels were based on human consumption, the levels would be higher, but these metals are very bad for fish, so toxicity levels are much lower.”
When soluble metals do get into stormwater, is there any way to get them out? “For passive stormwater treatment, some argue the most effective way to reduce soluble metal pollution is to use media filters with the appropriate media,” he says. “However, that’s very expensive–costing up to perhaps $20 per pound of sediment that contains metals removed from the stormwater. On the other hand, by street cleaning, I can pick up these metals and contain them for about three to five dollars per pound of sediment removed from the stormwater. That’s why we need street cleaning–it’s good for the environment, and better for municipal budgets.”
Although the composition of street dirt is now better known, 30 years ago Sutherland confused labs with his samples. “When I first collected street dirt in the 1980s and got back the results, the testing lab asked “˜What mine is that sample from?’ When I told them the sample was southeast Portland street dirt, they said “˜What? We found almost every single metal known to man, except gold and silver.'” Sutherland chuckles, “Heck, if there was gold and silver in it, everyone would be cleaning the streets.”
Yet, after 40 years of stormwater data collection, there’s still not much known about the source of this road pollution “street dirt.” “We still don’t understand all of it, and most communities don’t know anything about this material. Gary Minton, author of Stormwater Treatment: Biological, Chemical, and Engineering Principles, wrote an article calling stormwater sampling “˜a fool’s errand,’ because you can take a grab sample of stormwater, but it tells you nothing about the pollution’s source and what you can actually do about controlling those sources [Minton 2009]. We have asked “˜How did these metals get into stormwater?’ and the answer is “˜Via the street dirt.’ From some California work, we learned the street dirt was related to buying cheaper automobile brakes from Asia. No one seemed to care that these imported brakes were very high in copper, which is very toxic to fish and highly soluble. Just by stopping that purchasing practice we were able to reduce copper in street dirt, which in turn reduced the concentration of soluble copper in stormwater. Thankfully, lead is one of the least soluble metals in water, because when we had leaded gasoline, there was an order of magnitude higher concentration of lead in street dirt–and, as a result, in the stormwater. More studies on the original source of contaminants found in street dirt would be very helpful in identifying other “˜common sense’ sustainable practices that can be implemented.
“Our own behaviors can have an impact,” he continues. “Something as elemental as leaves, which are full of nutrients–communities that don’t have an aggressive leaf pickup program are missing the boat. Since street dirt contains many toxic contaminants in high concentrations, we should be very focused: How can we get that stuff before the rain does, or even before the street dirt does?”
Cash-strapped municipalities likely need lots of data, and yeah, there’s an app for that. “I have a computer model I’ve developed over my lifetime, which can play the “˜what if’ game–“˜What if we would sweep this often over this area, how much could we contain, and what would be the impact on stormwater?’ I ran the model for Livonia, MI, in 2000, when it was only sweeping four times a year. The model estimated that optimized street cleaning practices–with parking restrictions and regenerative air street cleaners–performed every other week would reduce total suspended solids as much as 65%. There would also be significant reductions in other pollutants.”
Perhaps a grassroots campaign–getting citizens to buy into the process–would drive more cities to clean streets. “The key is getting people focused on the end result: “˜We should clean streets to save salmon, or other fisheries.’ Of course, then, comes the question: Where does the funding come from? It has to be found somewhere, as new regulations will soon be in place. When we recognize what various municipal separate storm sewer systems communities could do, they’ll see the big picture. Cities need to work with their communities, to obtain dedicated sources of funding, such as stormwater fees, which are not new taxes, but a recognition that we have a problem that’s threatening the quality of our waterways, and we must act. I’ve been paying a monthly residential four- to five-dollar stormwater fee in Portland since 1990. By the same token, if stormwater utilities are not subsidizing good street cleaning practices, they must at least have an influence on those decisions.”
Areas that still think of street cleaning as “appearance” are likely wasting money. “The amount of effort some spend sweeping downtown every day is ridiculous. For one thing, that’s high labor costs–albeit deserved, as street cleaner operators should be well educated, because they’re the first line of defense against stormwater pollution. You want aesthetics? Then hire some teens, give them push brooms and buckets on wheels, to collect the trash and debris every work day in the downtown area, and you’ll save money, as well as create employment for kids who should learn how to work hard. There are trash TMDLs in California, so trash pickup could be a reasonable objective in these cases. However, trash is usually inert, from a chemical standpoint. There’s no reason to street-clean with expensive machines every day; we monitored areas that were swept daily, and the amount of accumulation was under 100 pounds per curb mile, versus 300 to 600 pounds per curb mile everywhere else.”
Water: Part of the Solution?
What’s on the horizon for street cleaning? “There’s another technology I’ve teased people with–I’m amazed it doesn’t yet exist here–called “˜captive hydrology.’ Their term, not mine,” says Sutherland. “Think of it as a “˜carpet cleaner for pavement,’ a machine with both clean- and dirty-water tanks. Rotary arms with nozzles on the end blow water down on the pavement; the back end of the machine features a powerful vacuum and a squeegee that sucks up the water and the debris it contains. We used this technology as part of the work I did in Israel in 2000 through 2004; I’d never seen it before then. We were cleaning some paved areas outside a cement factory–phenomenal amounts of accumulated dust, until we cleaned. After delivering its passengers to a nearby attraction, a tour bus rolled up, and the driver asked, “˜Is it OK to park on the clean, brand-new pavement?’ This machine’s power is remarkable; it can be used to scarify pavement, or remove paint. Right now, this technology is being used in the UK, Germany, Israel, and the Netherlands. However, it’s expensive, and I was concerned that it didn’t have a gutter broom, so accumulated street dirt, against a barrier like a curb, would be missed.
So I thought, wouldn’t that be great if someone added gutter brooms, to throw the accumulated material into the machine’s path? Well, last December, someone sent me a link for a Turkish manufacturer I didn’t know that’s essentially combined the pressure-washer technology with adjustable, responsive, dual gutter brooms.”
Despite the costs, “pressure washing” streets might be a great solution–providing the water’s removed–especially for a question that’s yet to be answered: What are the health effects of street dirt pollutants once they become airborne? “That’s a good question,” Sutherland concludes. “How much illness, how many deaths a year could be linked to breathing street dust?”
Small Town, Big Ideas
The town of Zebulon, NC, population 4,500, might be small in size, but big on ideas for keeping streets and streams clean.
“For us, sweeping is a big part in meeting our stormwater management program goals,” says director of public works Chris Ray. “We’re trying to prevent debris and catch it before it enters the stormwater system. Along with our sweeping program, we and stormwater superintendent Tony Rose promote stormwater education: mainly, telling people to not put stuff into storm drains. We talk at schools and public events, such as Zebulon Festival on the Lawn and Zebulon Business Expo, on the importance of keeping debris or other foreign objects out of the storm drainage systems. Our in-person efforts are reinforced by the work done by our volunteer stormwater stenciling program.”
To make street cleaning as effective as possible, Zebulon recently purchased a Schwarze A7000 street sweeper. “Buying this machine and putting the informative “˜wrap’ on it was a significant investment for our small town, considering our typical stormwater budget is $151,000 a year,” says Ray. “It cost us $170,000 to purchase the sweeper, which includes highway use taxes and tags, and to install the vehicle wrap, which was designed by Looking Glass Communications and installed by Capital City Signs, both of Raleigh, NC. The wrap ties in with the brochures, fliers, and t-shirts we give to the public. Since the sweeper goes down roads at two to five miles per hour, it’s like a moving billboard down the street.”
A state program allowed Zebulon to get a good deal on the machine. “Price is always an issue; we “˜piggybacked’ a purchase from the city of Lexington. North Carolina has a purchasing listserv where you can post questions. Our staff learned Lexington had recently publicly bid for a street sweeper. We requested and reviewed its specifications and decided the specs met Zebulon’s needs, and the price Lexington quoted was within our budget limitations. We advertised our bid process, and the vendor, Carolina Environmental Systems, extended us the same price as Lexington.
“Being in a small town requires wearing many different hats; developing bid purchases is time consuming,” he continues. “If we find a town that’s already done that, and it meets our requirements, then it’s a winning solution to allow you accomplish the purchase and to invest your time in other tasks. We still bring in other vendors for demos and field testing to ensure the machine meets our needs. We review the ease of maintenance, and evaluate operator feedback on performance and ease of operation, as well as discuss with other owners their experience with the machine.”
Because it benefitted more than one department, the Schwarze machine’s cost was shared by Zebulon’s streets and stormwater capital budgets. “Thirty-five percent of the total stormwater budget was the truck, with a goal of it giving us 12 to 15 years of service, with proper preventative maintenance,” explains Ray. “Two town employees are assigned to the sweeper full-time, but all public works employees are trained on it.” The dedicated drivers become diagnosticians: “The crew that’s on the sweeper all the time can tell by noise or vibration if something is wrong with it. They can stop and fix it before it suffers significant damage. We do most preventive maintenance on it here in our shop, run by our sanitation and fleet maintenance superintendent Dale Matthews. Major overhauls we have to outsource.”
Ray says the city is pleased with the Schwarze machine. “We have found the machine is highly efficient on larger debris, but also on PM10 fines, which are known to contain a high percentage of heavy metals and other pollutants. The Schwarze A7000 can pick that up. We keep records on the amount of miles and debris picked up in a typical month. We then know that’s not entering the stormwater system. The sweeper is proven to get the obvious debris on the street surface, plus the small particulates hidden within pavement cracks and voids. In our small town, we average collecting approximately 28 to 30 cubic yards of debris, or one-and-a-half tandem dump truck loads of debris per month. We feel this is significant.”
The street sweeping schedule varies. “Residential areas are swept once a month,” he explains. “Major thoroughfares are swept 26 times a year. The downtown area is cleaned weekly. Before we got the Schwarze A7000, we struggled in residential areas during autumn leaf fall, but this machine has no problem with them. We’re responsible for 19 miles of the town’s maintained streets, plus another six miles of NCDOT roadway in town, for an approximate total of 25 miles of street sweeping.”
Zebulon citizens seem happy. “We’ve heard very positive remarks thus far,” he says. “Sometimes, if residents haven’t seen the sweeper in a while, they call and ask us to send it to their neighborhoods. This is the second sweeper we’ve had; the last one was bought in 1997. We’re very impressed with the product performance, and have excellent past experience and service with Carolina Environmental Systems.”
