Street Sweeping 101
Using street sweepers to improve water and air quality
Since its inception in the early 1900s, mechanized street sweeping has been used to remove what might be termed “cosmetic” or “political” debris from roadways and other paved surfaces. Conventional wisdom has always dictated that if a street looked clean, it was clean. Today however, this reason for sweeping is undergoing significant reappraisal. That is because study after study dating back to the 1970s (Sartor and Boyd 1972; Pitt and Amy 1973; Pitt 1979; Revitt and Ellis 1980; Biggins and Harrison 1980; Pitt and Sutherland 1982; Pitt and Shawley 1982; Pitt 1985; Pitt and McLean 1986; HDR 1993; Sansalone et al. 1998; Sansalone and Tribouillard 1999; Hubbell, Roth, and Clark 2001; Tetra Tech 2001; Townsend et al. 2002; and PWR 2004) have constantly shown that up to 50% of heavy metals and other pollutants of great concern like nutrients and toxics are attached to street dirt particles too small for most mechanical brush sweepers currently being used to effectively remove. Even though a street may look clean after being swept, there still may be a significant loading depending on the sweeper model used and the operational characteristics employed by the driver. But in spite of this overwhelming evidence, a controversy continues to rage over the actual particle pickup effectiveness of modern day sweepers and whether that effectiveness translates into a real reduction in the mass of pollutants being washed from urban streets and transported downstream by stormwater and entering receiving waters (Sutherland 2009a).
In addition, extremely small-micron particles are seen to pose a significant air-quality concern. According to EPA estimates, about 30,000 people in the United States die each year as a result of pollutants attached to extremely small-micron particles, and about 1,000,000 more sustain serious lung impairment.
Important Aspects of a Water- and Air-Quality-Focused Street Sweeping Program
The important aspects of a street sweeping program designed to focus on the maximum reduction of pollutants traditionally found in urban stormwater runoff and particulate material (PM) that fouls urban air quality will now be discussed. As part of this discussion, we will also describe the various types of street sweepers readily available in the marketplace today, along with a brief description of their ability to address water- and air-quality problems.
Pavement conditions are known to significantly affect the pickup performance of street cleaners (Sartor and Boyd 1972). Street sweepers have considerable difficulty effectively picking up particulate material from streets whose pavements are classified as poor, because this usually means lots of surface cracks and deep depressions where dirt can accumulate. The uneven surfaces that accompany poor pavement conditions make it difficult for the sweepers to operate effectively, especially the newer air machine that will be described later. Research has shown that when sweeping poor-pavement-condition streets, a large portion of the material removed could be the street pavement itself. For a community to realize the benefits of better street sweeping pickup performance, proper pavement maintenance activities are needed to maintain a minimum pavement condition rating of “fair” with a preference for “good” throughout the community. In addition, all cracks should be sealed on a regular and ongoing basis.
Barriers such as street curbs or New Jersey median barriers are known to have a significant effect on both the accumulation of “street dirt” and the ability of street cleaners to effectively pick up the accumulated material. A recent study in Madison, WI, showed that during most of the year, 75% of the sediment and associated pollutant captured through sweeping were found within 3 feet of the curb face (USGS 2007). A study in San Jose, CA, found that on monitored residential asphalt streets in fair to good condition with medium to light parking densities, approximately 58 to 73% of the street dirt accumulation was located within 2 feet of the curb (Pitt 1979). Street dirt monitoring throughout six cities at bus stops where no parking was allowed found that 90% of the solids were located within 1 foot of the curb (Sartor and Boyd 1972). So the focus of the good street sweeping program should be on streets and roadways that are curbed or have other barriers like New Jersey barriers. Other uncurbed streets could be swept on occasion, perhaps in response to a windstorm where a significant amount of vegetative debris has accumulated.
Parked car interference can have a significant negative effect on the ability of street sweepers to pick up accumulated particulate material. Since it is reasonable to assume that all street dirt accumulation essentially occurs within the width of a parked car, access to the curb is denied for the entire length of the parked cars along with the additional distance it takes for the sweeper to maneuver around parked cars. The most skilled sweeper operators can minimize this additional interference to a distance of approximately the length of a single car on both sides of one or more parked cars. So a good program minimizes parked car interference by sweeping at night in commercial or industrial areas and during the day for residential areas. It also uses and enforces residential parking restrictions where they are warranted.
Forward speed of a street cleaner while sweeping will significantly affect its ability to pick up particulate material. Everything else considered equal, the pickup effectiveness increases as the forward speed decreases (Sartor and Boyd 1972). The optimum average forward sweeping speed is approximately 5 miles per hour. This is good balance for the tradeoff between pickup performance effectiveness and the need to sweep a reasonable length of streets in a given day. A good program realizes that there will be a range of, say, 3 to 7 miles per hour while sweeping that will occur daily. This allows the operator to adjust speed in response to conditions that are encountered. A good sweeping program uses continuous-recording GPS devices on the sweepers that allow management to both monitor and document the actual forward sweeping speeds being used.
Fugitive dust losses are the important linkage between those sweeping programs that have a positive impact on air quality and those that do not. The use of water spray during sweeping operations to reduce fugitive dust losses is quite typical. However, this practice has been shown to reduce street dirt pickup, especially for the smallest particulate fractions of the accumulated street dirt that are very contaminated with pollutants. It is clear that the selection of the type of street sweeper matters for both pickup performance and the fugitive dust losses that might occur.
Types of Sweepers
There are four general types of sweepers: mechanical broom, vacuum, regenerative air, and high-efficiency (which the author originally defined in 1997). Each type has its advantages and disadvantages.
Mechanical Broom Sweepers. Mechanical broom sweeping technology may be likened to cleaning with a broom and a dustpan. For decades, this was the only type of sweeper available for use by cities, counties, and other agencies. Even with the advent and continual improvements in the other types of sweepers (to be described later), mechanical broom sweepers remain as the primary type of machine in use today. Typically, these machines have a main broom that runs transversely—from one side of the sweeper to the other—such that the broom bristles contact the paved surface the full width of the sweeper unit. Collected debris is swept onto some type of a conveyor for transfer to a containment hopper.
Mechanical broom machines are usually outfitted with gutter brooms. Gutter brooms are relatively small (i.e., typically 36 to 50 inches in width, or 1 to 1.5 meters) and located to the left, right, or both sides of the sweeper. They are primarily used to transfer debris from the gutter line into the path of the sweeper. Even though mechanical sweepers are usually outfitted with a series of water spray nozzles to suppress fugitive dust losses, they still tend to create a substantial amount of dust in dry weather. The use of water during sweeping transforms the accumulated street dirt into a mud-like substance whose removal becomes more difficult. Recent sweeper pickup performance studies have shown that the mechanical sweeper model tested with the use of water increased the remaining mass of material by 124% when compared to the same sweeper operated without the use of water (Sutherland 2009b).
In recent times, it has been recognized that modern air sweepers (discussed below) have many advantages over mechanical broom sweepers for general road sweeping usage. One reason is that most mechanical sweepers only give the illusion of leaving a clean pavement surface. Although large debris is removed by mechanical broom sweepers, most are ineffective at removing small particles on the order of 60 microns and smaller. Studies have even shown that, from an environmental standpoint, some mechanical broom sweepers may actually have a negative effect on the amount of stormwater runoff pollution (Pitt 1979). This is because the action of the broom tends to break larger particles down into smaller ones, creating more small-micron particles than there were to start with. And, whenever debris pickup is via an elevator rather than involving any type of air/suction action, a large amount of these small particles are left on the pavement’s surface. Broom sweepers remain the standard for sweeping extremely heavy or packed-down material, and for sweeping deicing sand in cold-climate regions. However, most mechanical sweepers are a poor choice for sweeping programs designed to improve water and air quality.
It must be noted that this discussion relates to the great majority of broom sweepers in use throughout the country. The author does know of one broom sweeper that has been engineered to provide greater pickup efficiencies for smaller-micron particles. The characteristics of this specific model have dramatically increased the pickup performance expected of most mechanical machines and will be described later in the High-Efficiency Sweeper section.
Vacuum Sweepers. Vacuum sweepers may be compared to a household vacuum system. An engine powers a fan, which creates a vacuum and therefore suction. Typically, there is a suction inlet on one side of the sweeping head, and the “used” air is constantly exhausted during the sweeping process. These machines employ some type of broom system to brush debris toward the vacuum opening in the head. These brooms are called windrow brooms. Vacuum machines usually have gutter brooms, as do most sweepers of all types.
Part of the impetus for the advent of vacuum sweepers was the recognition that the majority of debris, especially the heavy debris, is collected within 36 inches of the curb line. Vacuum sweepers are designed to do an effective job of cleaning within this area. Some vacuum sweeper models are designed to remove only material accumulated within 36 inches (1 meter) of the gutter itself and employ only gutter brooms to brush debris toward the vacuum opening in the head.
In areas where cleaning the entire lane width via air is considered paramount, vacuum sweepers are probably not as effective as the regenerative air sweeping technology (discussed below). Another disadvantage of vacuum sweepers is that the windrow broom tends to fill pavement irregularities with debris that can’t be removed since this windrow area is not being vacuumed.
Even though vacuum type sweepers typically use water-based dust suppression systems, traditional vacuum sweepers exhaust a high level of particulates into the atmosphere on a continual basis. While they seem to do a generally better job than brush sweepers in removing and retaining these small particles, the level of the emissions of fine particles can still be significant if fugitive dust losses are not controlled.
Regenerative Air Sweepers. Generally speaking, regenerative air systems are more environmentally friendly than are vacuum or mechanical broom sweepers. There are several factors that contribute to this. Regenerative air sweepers employ a closed-loop “cyclonic effect” to clean. They are similar to vacuum sweepers in that there is a similar vacuum inlet located on one side of the sweeping head. Unlike vacuum machines, however, regenerative air sweepers constantly recirculate (regenerate) their air supply internally. To accomplish this, the recirculating air is blasted into the sweeping head on the side opposite the pickup, or inlet, tube. Essentially, the air “blasts” down onto the pavement on one side of the head, travels across the width of the head (gathering debris with it as it goes), and then travels up the pickup hose on the other side with the debris. Manufacturers design their sweeping heads so as to swirl the air, so it will retain the collected debris within the airstream as it moves from the blast to the intake side of the head.
Like any other sweeper type, regenerative air machines can be equipped with gutter brooms to brush material accumulated against the curb into the path of the sweeper. Regenerative air models, like any other type of sweeper designed to clean the entire lane, can be equipped with gutter brooms on both sides of the machine. This affords the operator the opportunity to effectively sweep both sides of a one-way street without creating a traffic hazard.
Regenerative air technology has become widely seen as having a number of advantages: cleaning a wider path, removing small particles better, and limiting the amount of dust-laden air that is exhausted back into the atmosphere. Since these machines “air-blast” the pavement across the entire width of the sweeping head, regenerative air sweepers tend to do a better job of cleaning over the entire pavement surface covered and are recognized for this capability.
Although some air is lost by the regeneration process due to unevenness of the pavement, which allows air to escape from under the sweeping head’s rubber flaps, the amount of exhausted pollutant-laden air is typically much less than that from a vacuum sweeper. Because of this, and the fact that regenerative-based machines also tend to pick up the small-micron particles across the entire sweeping head, regenerative air sweepers are generally considered a better choice for those programs designed to improve both water and air quality. All standard regenerative air sweepers (excluding high-efficiency models discussed in the next section) have the means to introduce water into the vacuum intake on the curb side to help knock down the dust in the hopper. In addition, many believe the blast-and-pickup cycle of these machines also makes them more capable of picking up heavy debris, because the blast is better able to dislodge heavier materials and get them into the airflow. Because it has fewer moving parts, none of which touches the pavement, a regenerative air machine is less expensive to maintain that a mechanical brush sweeper.
However, it should be noted that some vacuum sweepers have been able to remove concrete chunks up to 8 inches in size as part of bridge deck reconstruction, for example. In addition, pure vacuum machines have been shown to be the best choice in rejuvenating plugged porous pavement, and the stronger the airflow, the better the results. Today’s air machines that include regenerative air and vacuum sweepers are able to supplant mechanical broom sweepers for all but the most challenging applications. Several air machine models are now available with fugitive dust controls, and these will be discussed in the next section.
High-Efficiency Sweepers. This is a relatively new technology that employs various fugitive dust loss controls and includes a variety of different types of machines such as vacuum, regenerative air, and one known mechanical broom machine, for example, to efficiently remove accumulated PM and associated organic material. The key to the current definition of a high-efficiency sweeper is that these machines not only remove a high level of accumulated material of all sizes (but especially small-micron material less than 60 microns), but also are designed to control fugitive dust losses. This means they are designed to exhaust no visible fugitive dust, and most are designed to sweep without water. Not having to deal with water is a huge plus in terms of time savings and fuel savings, because water is heavy and adds to the machine’s weight that has to be transported.
The term high-efficiency sweeper was first coined by the author in 1997 to describe a brand-new vacuum sweeping technology that employed a sophisticated filtration system for dust containment in combination with the use of both main and gutter brooms (Sutherland and Jelen 1997). This high-efficiency vacuum sweeper (which is no longer in production) was developed by Enviro Whirl Technologies of Centralia, IL, in 1995 and later acquired by Schwarze Industries of Huntsville, AL, in 1999. The EV-series machines that Schwarze built and marketed based on the original Enviro Whirl design employed a unique self-cleaning filtration system that can filter “dust” and exhaust only PM less than 2.5 microns. Fugitive dust control was not available at that time by any other sweeper in the nation. And because the EV-series fan operated only in filtered air with no debris or dust coming in contact with the blades, the manufacturer could provide a lifetime guarantee for the fan, which was unheard of at the time.
Tests showed that the pickup ability of the EV-series’s sweeping technology surpassed even that of the regenerative air sweepers that were available at the time (Sutherland and Jelen 1997). Because the EV used no water for dust suppression, and because it cleaned to a very-small-micron level, these machines were ideal for any application where dangerous or toxic materials were present. This included usage in industrial and manufacturing settings where material needed to be recycled, reused, or securely contained and disposed of after pickup.
Unfortunately, the EV machines were much more expensive to purchase, and the relatively unknown cost of maintenance remained a concern. But, more importantly, because they were mounted onto a tractor chassis rather than a truck chassis, their top non-sweeping speed of about 25 miles per hour was seen as a disadvantage in the municipal sweeping marketplace, especially for large cities. Schwarze no longer produces the EV machines, and their only established market was as an industrial sweeper for exclusive use on industrial sites where toxic and/or hazardous materials needed to be cleaned up and/or recycled. Historically, that’s where the vast majority of the limited EV-series sales actually occurred.
However, the invention of the Enviro Whirl sweeper and its subsequent testing led to the author’s realization (through sediment-transport-based stormwater quality modeling) that this new high-efficiency sweeping technology coupled with optimal sweeping practices would result in significant reductions in both PM and associated pollutants found in stormwater (Sutherland, Jelen, and Minton 1998). The purchase of this technology in 1999 by Schwarze Industries, a major sweeper manufacturer, signaled to the power sweeping industry that air-filtration systems needed to control fugitive dust losses and allow machines to sweep dry was the way of the future. Two other companies have subsequently developed and released several sweeper models that vie for the coveted label of high-efficiency machine.
Elgin Sweeper Company of Elgin, IL, developed a patented dust suppression system with a powerful vacuum fan to create an airstream; main and side broom skirting for dust capture; and a long-life, low-maintenance filter between the hopper and the vacuum fan.
These components together create a highly effective method for controlling fugitive dust generation that usually occurs during sweeping. This dust suppression system is also available for Elgin’s mechanical sweeper called the Eagle. In addition, Elgin recently released another fugitive dust control system that is available on its regenerative air model called the Crosswind NX. Real-world pickup performance testing of the waterless Eagle and the Crosswind NX conducted by Pacific Water Resources Inc. in July 2008 verified that these sweepers provided excellent overall pickup, including small-micron particles, and did not create any observable fugitive dust losses (PWR 2008). These are the underlying requirements for classification as a high-efficiency sweeper.
Tymco of Waco, TX, is another street sweeper manufacturer that has developed a dust suppression system, available on two of its sweeper models, which should qualify these models as high-efficiency machines. Tymco prides itself as the originator of regenerative air sweeping technology, the only type of sweepers the company manufactures. Two of the Tymco sweeper models, DST-4 and DST-6, currently have a dust control system. The system is a multi-pass cylindrical centrifugal dust separator to provide for maximum particulate separation. The small amount of air that is diverted from the regenerative air system to achieve the dustless effect is filtered through Tymco’s patented DST system. The DST system filters 90% of the diverted air through a pre-cleaner. The remaining 10% is filtered through cartridge filters. An intermittent air pulse cleans these filters automatically.
Schwarze Industries recently introduced a new waterless regenerative air sweeper called the DXR that employs a fugitive dust loss control technology that should qualify it as a high-efficiency machine. Schwarze describes the DXR sweeper as a heavy-duty, chassis-mounted, dustless regenerative air sweeper with an 8-cubic-yard hopper, whose basic design has over 20 years of successful operation. The DXR sweeper’s dust containment chamber is integral to the hopper and utilizes a series of cartridge filters that filter 100% of the air prior to insertion into the blower. Schwarze claims this design reduces overall wear to key components, including the blower fan and sweeping head, while providing dust control in the most extreme conditions. The sweeping head is also equipped with a suction side skid nozzle to further prevent dust from becoming airborne. The sweeping head suction tube has suction hoses that are connected to the shrouded gutter brooms to provide additional dry dust control.
Street Sweeper Pickup Performance Monitoring
Dr. Robert Pitt was the first to conduct monitoring activities designed to estimate overall street cleaner pickup performance for stormwater quality improvements. This occurred as part of his EPA-funded San Jose, CA, study (Pitt 1979). His sampling technique was used in many early street sweeper testing efforts including the Castro Valley, CA, study (Pitt and Shawley 1982); the Reno, NV, study (Pitt and Sutherland 1982); the Bellevue, WA, Nationwide Urban Runoff Program (NURP) (Pitt and Bissonnette 1984); and the Toronto, Canada, Humber River study (Pitt and McLean 1986), just to name a few. This monitoring technique is still very popular, as it was recently used in several different street sweeping pilot studies undertaken in Baltimore, MD (CWP 2008), Madison, WI (USGS 2007), and Seattle, WA (SPU 2009).
The technique involves street dirt collection throughout of a given study area by driving around with a mobile sampling setup, stopping frequently along each block, and randomly sampling at a number of locations. The procedure involves the use of an industrial vacuum cleaner with a stainless steel canister powered by a gas-powered electric generator. The sample collector randomly selects a location along the curb and vacuums up a sample of street dirt found lying anywhere from the curb to the centerline of the street. By keeping track of the total number of vacuum wand pulls obtained before the vacuum canister is emptied, the length of curb randomly sampled can be computed and used in the calculation of street dirt loading, usually expressed as pounds per curbed mile. Depending on when this sampling occurs, it constitutes either a “before sweeping” or an “after sweeping” sample.
The pros for this random monitoring technique is that it is easy to implement and does not require any direct coordination with the street sweeper operator other than knowing that you sampled the day before or the day after a sweeping occurred. Many researchers like the technique because its random nature seems to fit the random nature of stormwater itself. This technique works well if the objective is to establish average street dirt loading throughout a study area. However, as a technique for measuring the pickup performance of a specific street cleaner operation, it has some serious drawbacks.
The testing procedure usually requires that the “before sweeping” sampling be conducted a day or two before the actual street sweeping occurs. To determine the amount of material left behind, an “after sweeping” sampling is usually conducted a day or two after the street sweeping occurred. To compute the pickup performance of the sweeper, the before and after street dirt loadings obtained from these sampling are computed and used to establish a pickup percentage.
The obvious problem is that a many hours lapse between these two samplings, and a lot could happen to affect these loads. So one really doesn’t know exactly what the street dirt loadings were immediately before and immediately after the actual sweeping. In addition, nothing is known about the street cleaning operation actually used. For example, forward sweeping speed, which is a very important variable, is usually not known. If the speed of the sweeper is not known, then the pickup results are of very limited value, because changes can’t be specified to help improve pickup performance.
Parked cars are another obvious problem. If parking restrictions have not been imposed or enforced, then random sampling will include areas that have not even been swept; estimated pickup performance suffers because parked cars prevented access to the curb where the pollutants are located. This kind of uncontrolled variability has led to very poor pickup performance estimates that are inappropriately attributed to the machine that was used.
Controlled Sweeper Pickup Performance Testing
Accurate measurement of street sweeper pickup performance requires the establishment of a specific test area of a known length and a known initial loading. A street cleaning operation with forward sweeping speeds timed and performance observed is conducted, followed immediately by an after sweeping sampling to determine what was left behind. The author pioneered this type of performance testing back in the mid-1990s for two major reasons. First was the need to obtain particle-size-specific pickup performance parameters required for the accurate simulation of stormwater pollutant load reduction from street cleaning operations (Sutherland and Jelen 1997). Second, it is the most accurate test, needed in the never-ending search for more efficient sweeper models currently available from the various sweeper manufacturers. For more information on controlled street sweeper testing protocols please refer to Sutherland 2009a.
SCAQMD Sweeper Pickup Performance Tests
Perhaps the best-known controlled pickup performance test is the PM-10 Certification test developed by the South Coast Air Quality Management District (SCAQMD) in 1999. As of January 1, 2000, sweepers purchased for regular municipal routes in four California counties, Los Angeles, Orange, Riverside, and San Bernardino, must be “Rule 1186 Certified” by the SCAQMD. The agency’s Rule 1186 is designed, among other things, to reduce the level of dust produced by sweepers and ensure they have an adequate collection efficiency. The agency wanted to develop a test that would provide guidelines to municipalities so they could purchase sweepers that were more environmentally sound.
To develop a testing protocol, including a “street dirt surrogate,” testing speed, and other procedures, SCAQMD initially convened the sweeper subcommittee of the Society of Automotive Engineers (SAE). This subcommittee is composed primarily of engineering-oriented employees of sweeper manufacturers. Although the parent SAE organization eventually decided that SAE would not certify the sweeper test protocol, after a series of subcommittee meetings the guidelines for what the SCAQMD initially called a “PM-10 Sweeper Certification Test” were hammered out.
The eventual protocol called for each participating sweeper being tested to be operated at 5 miles per hour down the length of a tunnel at the California Speedway. About halfway down the length, a metal 2-by-4 was placed diagonally to simulate a speed bump. The test material consisted of, by weight, 90% washed sand and 10% Georgia paint pigment, a composition that had been agreed upon by SCAQMD and the SAE subcommittee. For complete information on the test please refer to Kidwell-Ross 1999.
Although it was a good first attempt at conducting independent, unbiased, and realistic controlled pickup performance tests, there were and still are several serious problems with the test that the author first pointed out in 1999 (Sutherland 1999). The initial idea of SCAQMD’s Rule 1186 was, in part, to develop a testing process to be able to clearly designate which sweepers would be PM-10 certified for use in the southern California region. In most people’s minds, a certification by the SCAQMD would mean that a “compliant sweeper” has the ability to pick up and contain a significant quantity of this 10-micron material. Unfortunately, based upon the testing protocol that was developed, such an assumption is not realistic. That is because nowhere in the final test procedure is there any measurement of the particle size of the removed material.
We know that, on average, only about 3% of the dirt accumulation on a typical street surface is 10 microns or less (a human hair is about 70 microns wide). Yet that seemingly tiny amount of small-micron material can account for a considerable amount of the most toxic pollutants on the street. In the SCAQMD test, about 3% of the total mass of dirt surrogate material put down was 10 microns or less in size. However, the SCAQMD chose, after reviewing the test data, to call a sweeper “compliant” if it had a pickup performance of as little as 80%.
This means a so-called compliant sweeper may well have literally picked up zero 10-micron material and still have been certified through the agency. And because the SCAQMD does not release the actual data for each of the tested machines, it is impossible to determine what, if any, amount of PM-10 material any sweeper in the test was actually able to pick up. The only way to infer this result would be to go back and look at the individual results of each sweeper tested. If the data for a given machine shows that it picked up 90 to 97% of the initial material, then we could legitimately say that the machine most likely picked up a significant portion of the 10-micron material from the test track, and so is probably “PM-10 efficient.” Otherwise, we simply can’t say for sure that is the case.
Closing Remarks
A great deal of controversy currently surrounds the question of how much of the pollution generally found in urban stormwater runoff can be reduced by street sweeping practices (Sutherland 2009b). That controversy is liable to always be present given the multitude of variables that can affect the answer to this question. This article has focused on the important aspects of a sweeping program that matter greatly if the program’s underlying objective is to improve a community’s stormwater and air quality. Some of these items are politically challenging and costly to implement, like pavement maintenance to create better street conditions or imposing effective parking restrictions. But one thing is quite clear. The ability of a street sweeping program to effectively reduce stormwater and air pollution starts with the equipment that is being used.
One extremely important question that a potential sweeper buyer should always be asking is: Provided the sweeper can get to the curb where most of the pollutants are found and it is being operated at a reasonable forward speed, how much of the accumulated loading that it encounters will it remove?
I n 1997, the author called for accurate street sweeper pickup performance testing by an independent third party using realistic loadings and operational characteristics on a measured, curbed test track with at least fair pavement conditions (Sutherland 1997). What was envisioned then and still now is an independent Consumer Reports–type of document of all available street sweeping models. This fair and unbiased information could be used by stormwater and public works personnel throughout the nation for either acquisition purposes or for the development of specifications for contract street sweeping services. This type of data is vital for stormwater, air-quality, and public works personnel to change the focus of their sweeping programs from not only the removal of “cosmetic” debris, but also the effective removal of containments that continue to pollute our nation’s air and water. Isn’t it time that the USEPA or perhaps another independent third party found the resources needed to make this dream a reality?
Author’s Bio: Roger C. Sutherland, P.E., is a senior water resources engineer with AMEC Earth & Environmental in Tigard, OR.
