Proposed 2025 Street Sweeper Testing Collaboration with AQMD

Key Considerations for Potential AQMD Involvement in Street Sweeper Testing

This summer a Sea Grant/NOAA street sweeper test will be held to gauge the effectiveness of street sweepers in capturing microplastics and other pollutants. Members of that process contacted the South Coast Air Quality Management District (AQMD) management team with an intent to showcase the value of that agency leading an effort to include air quality monitoring in the upcoming testing process.

What you will read, below, highlights the potential role and benefits that would be derived if AQMD participated in, and/or assisted in, carrying out the 2025 testing. Ideally, the AQMD's Rule 1186 would become updated as a result of the test results.

The topic of the air and water quality capabilities of mechanical broom vs. regenerative air and vacuum sweepers is also the topic of the linked podcast. The information, which is generated by the NotebookLM podcast team, also discusses the emerging importance of removing microplastics from the air and runoff stream, as well as the importance of updating the only nationally-touted sweeper test in existence, which is the test the South Coast Air Quality Management District conducted over a quarter-century ago.

1. Project Overview and Objectives:

Focus on the NOAA Grant for Street Sweeper Testing in Summer of 2025: The core project, led by Jill Murray (City of Santa Barbara) with support from Roger Sutherland (Water Resources Consulting Engineer) and Ranger Kidwell-Ross (WorldSweeper.com), is funded by a Sea Grant/NOAA grant. The primary goal is to demonstrate the efficacy of street sweeping in capturing microplastics from urban runoff.

Scope Expansion to Air Quality: The current project has limited resources for comprehensive testing. There is a strong desire to expand the scope to include robust air quality monitoring during sweeper testing. This would address a critical gap in current understanding and testing methodologies. Another goal is to increase the number of sweepers that can be tested in 2025.

"If we had more resources, we could expand our testing," said Roger Sutherland. "We believe it would be extremely valuable to test every street class make and model that wants to compete not just in the Southern California market – but anywhere in America. All of the manufacturers could see how their technology is doing in terms of its ability to pass the challenges of the testing process."

Addressing Limitations of Current Testing: Existing street sweeper certification tests, particularly AQMD's Rule 1186 (established to regulate sweepers starting with model year 2000), are seen as flawed by some experts. The primarily focus of the test – now over a quarter-century old – was on overall pickup efficiency capture and the associated dust generation. It included a relatively limited understanding of fine particle, PM-10 pickup. As examples, as explained below it allowed a potentially high level of PM10s staying on the ground and included zero information on microplastics. The latter is becoming increasingly important.

In addition, as far as is known, every sweeper that tested pre-2000 passed the test, i.e., all air and broom-based street sweepers in the test.

The 80% threshold level for passing that test, which contained only 10% of PM-10s (paint pigment) meant it would be possible for a sweeper to leave all of the PM-10 paint pigment on the ground and still become Rule 1186 Certified. Nowhere in the final test procedure is any relationship shown between a sweeper's pickup performance and particle size. That now has greater importance since it has been learned that up to 60% of the pollutant load on a street can come from the (typically) less than 20% of material on the ground that's 250-microns or smaller.

Microplastic Focus: The upcoming testing project aims to fill a knowledge gap regarding the effectiveness of street sweeping in removing microplastics, which are defined as particles 5000 microns or less. Current academic understanding, influencing state water quality strategies, often lumps microplastics with fine inorganic particles, suggesting sweepers are not effective. This project seeks empirical data to validate or refute this.

"The academic side has really focused on a couple of studies that have shown that street sweeping – especially mechanical broom sweepers – isn't as effective for, or can't be demonstrated to be as effective for, the small particles," said Jill Murray. "To date, microplastics have been dumped right into that. Our stance is to be outcome neutral. We're testing to see how effective street sweeping is as a potential interception tool."

2. Key Issues and Concerns:

Fugitive Dust from Broom Sweepers: Mechanical broom sweepers are believed to create more fine particulate matter by breaking down larger debris and loosening the deposition layer on streets, making these fines more susceptible to becoming airborne and/or washing into stormwater systems.

The abrasive action of a mechanical broom tends to break larger debris into smaller particles. They also loosen the packed-down deposition layer of street dirt. This combination – absent any vacuum action – can create and leave more fine particulate matter behind.

With a broom sweeper, you're just brushing the surface, which loosens the deposition layer. No question that some of it goes up the conveyor belt, but that's the only pickup capability. There's no air/suction aspect at all. Unfortunately, as any remaining small particles settle back down, they are much more available to air flow or water flow during whatever next event happens in either one of those areas.

Effectiveness of Air Sweepers: Regenerative air and vacuum sweepers are generally considered to be more effective at removing fine particulate matter, including particles under 60 microns. Although we are not making our own judgments until we see what the testing results are, it seems at this point that regenerative air and vacuum street sweepers are the best choice when small-micron removal is desired, in addition to removal of other general street dirt. Smaller micron material, if left behind, can more easily entrain into the air as dust, as well as become wash-off during stormwater events.

Limitations of Rule 1186: The current AQMD certification test, resulting in its Rule 1186, is over a quarter-century old. Today it can be criticized for:

• Not directly measuring PM-10 or fine particle pickup efficiency.
• Using a pass/fail system without releasing detailed performance data, hindering informed decision-making.
• Potentially allowing sweepers with poor fine particle pickup to be certified.
• Using a test protocol (including a speed bump and wet scrubbing) that may not accurately reflect real-world conditions and introduces potential errors.
• Lacking a mechanism for manufacturers to retest and improve their equipment based on a tiered performance standard (e.g., bronze, silver, gold).
• Many of the sweeper models tested 25 years ago are no long in production. As a result, many of the current models are Rule 1186-Compliant only as a result of being 'grandfathered in.'

Today's Need for Improved Standards and Consumer Information: There is a recognized need for a more comprehensive and replicable testing standard that provides data on pickup efficiency across various particle sizes, including microplastics, as well as measures fugitive dust emissions during operations. This information would empower municipalities to make more informed purchasing decisions.

"What we need in this country – and really throughout the world – is something like a Consumer Reports for street sweeper equipment," said Ranger Kidwell-Ross. "That would provide data for municipal managers and stormwater officials alike to view so they can have a better idea of the capabilities of the various makes and models of street sweepers in the marketplace."

Cost and Adoption Challenges: While air sweepers are often preferred for water quality, broom sweepers are perceived to be better at picking up larger debris. However, the long-term costs associated with stormwater treatment due to ineffective fine particle removal by broom sweepers may outweigh these initial savings in some instances.

3. Involvement and Potential Benefits Proposed to AQMD:

Financial Support: The project currently has limited funding and seeks financial assistance from AQMD to expand testing to a larger number of street sweeper models (aiming for testing 10 additional sweepers at an estimated $5,000 per sweeper).

Technical Expertise and Participation: AQMD's involvement in the testing process, including input on the test simulant to better assess air quality impacts as well as active participation in data collection and analysis, is highly desired. Kidwell-Ross added that if AQMD can be involved, the organization's input as to what might be added to the simulant so that it really tests the air quality side of it would be a big plus. Ideal would not just be support financially. AQMD's active participation in the testing, including whatever analysis for that aspect of the test would be big additions, as well.

Air Quality Monitoring: A key aspect of AQMD's potential contribution is incorporating robust air quality monitoring during the sweeper tests. This would provide crucial data on the fugitive dust generated by different sweeper technologies. Ideal AQMD's involvement would include testing the 'background air concentration;' then, the test would include sampling the air downstream so as to figure out how much of a concentration increase is likely created by each sweeper during sweeping operations.

Increased Credibility and Impact: AQMD's involvement would lend significant credibility to the test results, potentially leading to greater adoption of effective sweeping practices and technologies. Ideally AQMD would get involved AND certify the results as Rule 1186 compliant. "If we are able to report that AQMD got involved, not just that we negotiated its involvement," said Jill Murray, "it would add tremendous credibility to what it is we're trying to accomplish."

Potential for Rule 1186 Updates: The project proponents hope that the data generated from this more comprehensive testing, with AQMD's involvement, could provide the scientific basis for future amendments or updates to Rule 1186, leading to more effective, updated, certification standards.

National and International Influence: Improved testing standards and data on sweeper performance could have implications beyond Southern California, influencing purchasing decisions and environmental regulations nationwide and even internationally. "Having air quality being one of the things that stormwater professionals can look at, along with the pickup data of the material, allows this testing to really make an impact on air quality around the country in addition to providing stormwater pollutant runoff data.

4. Next Steps and Timeline:

Testing Timeline: The proposed testing is scheduled to begin around July 14th and could last for one-to-three weeks, depending on funding and number of sweeper manufacturers participating.

Further Discussions: AQMD management has been asked to express the Agency's interest by April 30th; after that, if AQMD is to be involved then further meetings will be necessary to detail the scope of AQMD's participation, including technical aspects of air monitoring, funding contributions, and data sharing.

5. Example Considerations for AQMD:

• Aligning participation with current Rule 1186 and potential future amendments.
• Balancing support for this project with existing certification processes and resource allocation.
• Including the technical requirements and costs associated with incorporating air quality monitoring into the proposed testing protocol.
• Evaluating the potential benefits of updated testing standards for air quality management in Southern California.
• Considering the potential for how this collaboration could inform national best practices and standards in regard to street sweeper performance.

Conclusion:

The proposed project offers a valuable opportunity for AQMD to contribute to a more comprehensive understanding of street sweeper effectiveness in addressing both water quality (including microplastics) and air quality (fugitive dust) concerns. Participation in this testing initiative could provide critical data to inform future regulations, enhance AQMD's credibility in environmental stewardship, and potentially lead to significant improvements in both air and water quality in the region and beyond.

To contact Roger Sutherland, the co-creator of the upcoming testing, send email to sutherland.roger1@gmail.com. For more information on the qualifications Sutherland brings to the testing process, you may view his current Vita at this link.

To reach Ranger Kidwell-Ross, you may reach him at editor@ worldsweeper.com. To view his sweeping industry experience use this link.

If you have questions or comments about this article, please let us know. If appropriate, we will append them to the article.

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