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Southern California Agency's Sweeper Certification Test Answers Some Questions, Raises More

AQMD by Ranger Kidwell-Ross

As of January 1, 2000, all sweepers purchased for regular municipal routes in four California counties - Los Angeles, Orange, Riverside and San Bernadino - had to be 'Rule 1186 Certified' by the South Coast Air Quality Management District (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 set out to develop a test that would provide guidelines to municipalities so they could purchase sweepers that were more environmentally sound.

Material picked up by the wet scrubber was collected into bins and allowed to settle.

To develop a testing protocol, including a 'street dirt surrogate,' sweeper speed during testing, 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 will 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. Perhaps predictably, given that most of the sweeper manufacturers seem reluctant to produce sweepers that are more environmentally viable, the committee procedure was drawn out long enough to have the SCAQMD's original January 1, 1999 purchase deadline extended by a year. According to SCAQMD officials, the time frame was also extended in order to finish the protocol and testing, and to allow sufficient time for local governments to prepare for the new requirements.

The final 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. The tunnel was approximately 240 feet long, 15 feet wide and 14.5 feet high. About halfway down the tunnel, a metal 2x4 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. The rationale behind including the paint pigment was that it is composed of approximately 1/3 PM-10 material, which would bring the combined mixture to the 3% PM-10 composition normal for street dirt. A total of 38 pounds of the combined material was placed over 200 feet of the tunnel's pavement surface by utilizing two Scott-brand fertilizer spreaders.

Fifteen sweeper models, built by a total of six manufacturers, took part in the test. Prior to the sweeping portion of the test, each sweeper was powered up as though it was sweeping and then run through the already clean tunnel. This allowed researchers, supplied under contract with the University of California at Riverside's Center for Environmental Research and Technology (CE-CERT), to measure the amount of engine exhaust emitted by each machine prior to the actual sweeping portion of the test. The intent of the 'pre-run' was to enable researchers to calculate the particulates emitted by the drive engine of the sweepers. Then, the plan was to take the engine exhaust out of the final equation, in order to derive a more accurate reading on the fine dust particles generated by the sweeping operation itself. Ultimately, according to researchers, that portion of the data was unable to be used, so the final results included the amount of particulates emitted by the drive engines as well as those produced by the actual sweeping.

Before conducting its actual test runs, each sweeper was 'preconditioned' by having it pick up approximately 3/4 cubic yard of washed sand that had been spread out on a nearby parking lot. Finally, each sweeper model entered into the test was allowed 3 monitored sweeping runs. During these runs, measurements were taken to determine how much dust was produced by each sweeper. After each test run, the speed bump was removed and the entire track cleaned with a walk-behind wet scrubber. All the material picked up by the scrubber was poured into a tub and allowed to settle overnight. The next morning the liquid was decanted, and the settled residue dried and weighed. This represented the amount of material not picked up by each sweeper during each run.

Although the sheer number of sweepers evaluated makes this one of the most comprehensive tests of sweepers conducted to date, several potentially serious flaws seemed to exist in terms of how the proceedings were conducted. For example, American Sweeper had requested that an independent monitor from the industry be onsite during all runs, to confirm that each sweeper manufacturer complied with the protocol. Our concern stemmed from the reports we had received after a similar test conducted by CE-CERT several years ago. At the time, informants had told us that one or more manufacturers had cleaned their filters prior to each test pass. We also knew that at least one sweeper had used only one gutter broom during its test, while some others had used two.

In response, SCAQMD agreed to have one of its own representatives there during the testing process. However, on at least two days of testing, there was no one there from SCAQMD monitoring the activity. This omission gave the appearance of opening the testing process up to potential abuse. For example, sweeper operators were instructed to pick up the 'pretest loading' at the parking lot; however, no one watched to see if this was done or not. Likewise, I was told that in at least several instances no one ever checked to see if the test sweepers actually had the same configuration as the manufacturer had pre-submitted on paper for its machines.

Of greater concern, however, is that the results of this test may be construed to imply that, if Rule 1186 Certified, a sweeper has proven itself to be efficient at the pickup of small-micron material. Julia Lester, PM-10 Program Supervisor for SCAQMD, agrees that it does not.

"As part of a comprehensive air pollution reduction program," explains Lester, "the purpose of the testing was to obtain an objective measure of a sweeper's ability to remove typical street loadings and [to measure] the amount of PM-10 [fugitive dust] generated during the sweeping process.Vehicular entrainment of paved road dust is the largest source of primary PM-10 in the geographical region under our jurisdiction. SQAQMD began the program with a Phase 1 preliminary trial intended to determine if the testing protocol would work in practice. The Phase 1 results did show that the protocol was effective; however, several minor testing parameters were refined because of lessons learned.Subsequently, the contractor, University of California at Riverside, initiated Phase 2 and evaluated the manufacturer-supplied sweepers.

"Because this was the first comprehensive evaluation of sweepers for these two criteria using this protocol, our agency had no predetermined concept of acceptable thresholds for pickup efficiency and PM-10 entrainment. Moreover, if the data had suggested there was little variability among the equipment evaluated, this information would have had to been forwarded to other decision makers. As it turned out, there was a clear delineation between the equipment tested, both in terms of pickup efficiency and PM-10 entrainment.

"Specifically, the test results indicated that a natural break exists between data clustered above 80 percent pickup efficiency and data below 70 percent pickup efficiency. In terms of PM-10 entrainment, the data showed that the average emission rate for equipment proposed to be certified was approximately one-third the emission rate of equipment above the threshold.Based on these results, the data supported the concept that equipment is available to remove dust on paved roads, thereby reducing vehicular entrainment, without generating significant PM-10 emissions in the process. It should be noted, however, that this test procedure and proposed certification limits were developed for SCAQMD Rule 1186 requirements only, and may not be indicative of other street sweeping goals, e.g., non-point stormwater programs."

Schwarze Industries' EV2 sweeper is shown during a test run, with the air filter collection machinery in the foreground.

Unfortunately, the 80% threshold level for passing this test means it would be possible for a sweeper to leave all 3% of the PM-10 paint pigment on the ground and still become Rule 1186 Certified. Exhaustive testing by Roger Sutherland of Pacific Water Resources [see side-bar entitled "Recent SCAQMD Test Ignores PM-10 Efficiency Issue"] and others, has shown that regenerative air sweepers stop picking up material at around 63 microns (a human hair is about 70 microns wide). And, most all of the sweepers tested will have used water for dust suppression, a technique that has been proven to leave a highly concentrated pollution slurry of PM-10 material behind in the cracks of the pavement. For that reason, the implications for the SCAQMD test, in terms of stormwater runoff pollution - which is the primary concern in most areas of the US - are minimal. Although the complete results were not available at press time, Ms. Lester revealed that 7 of the 15 sweepers tested had passed the SCAQMD certification thresholds.

It is also disappointing that SCAQMD has decided not to release the rankings, or relative test results, of any of the sweepers tested. Rather, they have adopted a simple pass/fail designation. As a result, those sweepers that 'pass' toward the bottom echelon of the test results will be flaunting the same certification document, for example, as the Schwarze EV-series sweepers that have been independently tested and proven PM-10 efficient a number of times. That fact is not going to help the decision making of those who truly have a pavement-based, small-micron problem to solve. However, the SCAQMD certification process will probably keep some of the worst dust-producing sweepers in the industry out of contention.

Still, a test of this scope could have brought the industry so much more. Again, we call for a true national testing procedure to show what really can be done by state-of-the-art sweepers to address the increasing problem the US is facing with its non-point source pollution runoff, in addition to our nation's fugitive dust issues. We need a test that is national in scope, sanctioned by the EPA or similar agency, and that is not part of a preformed political agenda. Until then, there will be little incentive for all the sweeper manufacturers to get involved in building machines that truly address the Clean Water Act and Clean Air Act issues that are so quickly threatening the quality of our nation's water and air.

For a copy of the SCAQMD testing procedures and protocol, as well as the final results, Julia Lester requests that you contact her associate, Mike Laybourn, at (909) 396-3066, or via email sent to You can also see the particulars of the testing procedure by viewing the pdf file of the protocol we have archived online.


SCAQMD Test Ignores PM-10 Efficiency Issue

by Roger Sutherland

I am writing to voice my concerns regarding the perception the sweeper-buying public may have about the study conducted by California's South Coast Air Quality Management District (SCAQMD). I believe my assessment will accurately reflect the concerns of all of us who have been researching the effectiveness of street sweeping equipment and its ability to reduce stormwater pollution and, at the same time, not create a fugitive dust problem.

The initial idea of SCAQMD's Rule 1186 was, in part, to develop a selection process to designate which sweepers would be 'PM-10 Certified' for use in the southern California region. In a recent meeting of SCAQMD, the term 'Rule 1186 Certified' replaced the previous designation. However, in many people's minds, a certification by that agency may still imply that a sweeper has the ability to pick up and contain 10-micron material. Unfortunately, based upon the testing protocol that was employed, such an implication is absolutely not realistic. That's because nowhere in the final test procedure is any relationship shown between a sweeper's pickup performance and particle size.

This creates a tremendous concern on my part. Here's why: We know, on the average, that only about 3% of the dirt accumulation on a typical street surface is of the size of 10 microns or less (a human hair is about 70 microns wide). Yet, that seemingly tiny amount of small-micron material may well account for up to 50% of the most toxic pollution load on the street. In the recent SCAQMD tests, also about 3% of the total mass of 'street dirt surrogate' material put down was 10 microns or less in size. However, since the SCAQMD chose, after reviewing the test data, to say a sweeper was compliant if it had a pickup performance of as little as 80%, then a so-called 'Rule 1186 Certified' sweeper may well have literally picked up zero 10-micron material and yet still be approved through the agency.

My understanding of the advent of the SCAQMD's Rule 1186 is that it was an attempt to force communities to buy sweepers that were PM-10 efficient. Minimizing dust output while sweeping is part of that equation, as is the ability to pick up material at the 10-micron level - along with larger material. However, my concern is that any layperson looking at the study results will think that any or all of the sweeper models the SCAQMD is calling Rule 1186 Certified are efficient at not creating a fugitive dust problem and at picking up 10-micron material in the process.

As far as I'm concerned, that's a joke, and it needs to be exposed for what it is. Based upon the protocol of the SCAQMD tests, and since the actual data for each of the tested machines hasn't been released, 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 find out 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 95-to-97%, then you can legitimately say that the machine most likely picked up a significant portion of the 10-micron material from the test track - and that it's probably 'PM-10 efficient.' Otherwise, you just can't.

The only way to be able to determine a given sweeper's level of PM-10 efficiency with the pass/fail set at the 80% pickup amount would have been if the protocol included wet-sieving of the material left on the pavement after each run. That's the only way we could have gotten an understanding about the particle size distribution of the mass that remained after sweeping.


The other item in this particular test that I find of real concern is the use of a metal 2x4 halfway down the test track. I have no idea why that was included. It's certainly not representative of a speed bump, or it would have been rounded. My bet is that most all of the accumulation that was left by the top echelon sweepers - or by all of them, probably - was left right at the 2x4.

The 2x4 should not have been there. It was never discussed during the extensive consultations I provided on my own time with the SAE's three-man subcommittee [this consisted of one representative each from Schwarze Industries, Tennant and Tymco]. We talked at length about the layout of the track, about the dirt surrogate material that could be used and what its particle size distribution should be, about sensible ways the dirt surrogate could be put down, what weight of total material should be used per test run and more. At no time was there any discussion about the use of a 2x4-type barrier.

In a test like this, good pavement conditions need to be simulated. The sweepers should not be penalized because of poor surface conditions. When a bump like that is included, all of the machines are challenged to pick up the material at the edges of it. As far as I'm concerned, the inclusion of the metal 2x4 in the middle of the tunnel makes the test results even less meaningful.

There's a lot at stake in terms of particular sweeper models being certified as compliant for the southern California marketplace, and I'm sure it's a very political process. The SCAQMD can and will do whatever they want in terms of where they want to draw the line in their own certification process. However, as I'm sure they would agree, this test can in no way be construed as a conclusion about which sweeper models are now able to pick up 10-micron material effectively. That's quite clear.

Also, my understanding is that, as it stands now, the SCAQMD has decided not to release the data, even to other researchers such as myself who have been doing sweeper studies for over 20 years. Releasing the complete data, including the information that tags the pickup ability of each of the participating sweepers, is the only way other researchers around the US and the world will be able to improve in the future upon this recent SCAQMD testing process.

Roger Sutherland is president of Pacific Water Resources, and a nationally recognized industry observer and consultant on sweeping, as it relates to stormwater runoff pollution. You may reach him by calling 503-671-9709, extension 24, or by sending email to


This article is reprinted from American Sweeper magazine, Volume 7 Number 2, 1999.

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