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Power Sweepers Remove Stormwater Pollutants

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From the Road Manager section of the March 2007 issue of 'Better Roads Magazine'

by Ranger Kidwell-Ross, editor of

Designers of sweeping programs need to learn about the relatively inexpensive role sweeping has in removing pollutants from the runoff stream. Street cleaning has the broadest potential for reducing stormwater pollution in the urban environment. That's because half of all the rain that falls on impervious surfaces connected to urban stormwater collection systems is falling on pavement.

In the past five years, updated sweeper designs that are much more efficient at picking up accumulated contaminants have entered the market. Yet, many jurisdictions that are now imposing stormwater runoff taxes and spending high dollars in an attempt to reduce their runoff pollution have, at the same time, cut back on their sweeping efforts. The only rational reason can be that they lack knowledge about the positive, relatively cost-effective impact a well-planned environmental sweeping program now can attain.

CWA Requirements

Wherever Clean Water Act compliance is required, sweeping program designers need to learn about the role newer sweepers can have in removing pollutants from the runoff stream.

Closeup This close-up shot shows how a sweeper picks up leaves before they enter stormwater drains.

Studies confirm the real-world pickup efficiency of today's broom sweepers is probably only between 20 and 35%. Despite this fact, mechanical broom sweepers continue to be the leading type used by municipalities in the United States. As municipalities struggle to reduce non-point source pollutants and meet the Best Management Practices requirements of Phase I and II, newer technologies of regenerative air and vacuum sweeper models are clearly a better choice. These have both been shown to raise pickup efficiencies into the 60 to 90% and above range.

A study of structural BMPs by the California Department of Transportation indicates the cost per pound of pollutant removed (as Total Suspended Solids) runs $10 to $60, not including land costs. In contrast, sweeping industry studies by well-known researcher, Roger Sutherland, of Oregon-based Pacific Water Resources, indicate that newer mechanical broom sweepers reduce TSS in stormwater at a cost of $5 to $10 per pound. Regenerative air and vacuum-assisted sweepers offer an even higher level of efficiency, removing TSS at a cost of $2 to $5 per pound.

Sutherland's company has also developed modeling software that uses historic rainfall data, which in most locales spans over 50 years, to accurately predict sweeping efficiencies for watersheds. This has aided a number of municipalities in determining relative pickup volume at given sweeping frequency intervals without having to conduct costly studies of their own.

Sutherland's Livonia, Michigan, study found the optimal frequency (during the nine months when sweeping can occur in snowbelt areas) for residential areas was about once every three weeks. Every two weeks is typically reasonable for higher-density residential and general commercial. In major traffic areas, like arterials, optimal sweeping was determined to be once per week. Optimal frequency depends, however, upon accumulation of the contaminated material typically called street dirt.

Monitoring accumulation can be of great value, as well as determining the chemical component of what is collecting on given roadways. Not only can a correctly designed sweeping program remove a significant amount of targeted chemicals; correct sweeping also has a positive impact on the gross pollutants that contribute sediment, silt, and organic debris to streams and other waterways.

TYMCO 500X A Tymco 500X gets set to remove debris that might otherwise pollute water.

Another efficiency sweeping offers is that it prolongs the operational efficiency of structural-based devices, as well as reduces the ongoing maintenance they require. Although by no means a silver bullet, widespread agreement is developing that sweeping should begin taking a more central role in stormwater runoff plans.

Charging Off Costs

Well-informed NPDES managers, aware of how cost-effective sweeping is when compared to infrastructure-based solutions, are now making an increase in air sweeping frequency a foundation of their stormwater runoff plans. The problem they're faced with is that, even in the face of the EPA mandates, their budgets are still largely based on the frequency of sweeping needed to provide a pleasing aesthetic value and, to a lesser extent, keep storm drains flowing.

Because of sweeping's now-demonstrated lower-cost-per-pound of pollutant removal, jurisdictions under Phase I or II mandates clearly should develop an optimal sweeping frequency designed to minimize the overall cost of meeting their non-point pollutant reduction goals.

Only by comparing sweeping to end-of-the-pipe solutions, like sedimentation tanks and filters, grassy swales, detention ponds, and all the other infrastructure-based solutions now emerging, can the most cost-effective mix of sweeping and other technologies be attained.

Elgin Eagle sweeperAn Elgin Eagle sweeper picks up leaves along a curb.

Once an optimal, least overall cost for achieving TMDL limits (or attainment of other goals) has been established for a given watershed, the next question is figuring out how to pay for that mixture of solutions. Some cities are now including the sweeping department within the overall budget for stormwater runoff reduction. That way, if a stormwater utility fee is being collected through NPDES mandates, the cost of sweepers and sweeping can be funded as a component.

Key Points

Here are the main points to consider when trying to assess how sweeping should fit into an overall NPDES pollution reduction plan:

• Answer the question "Why are we sweeping?" Is it just for cosmetic/aesthetic reasons, or are there water quality aspects to consider? If the answer includes water quality, then collaborate with your stormwater people to examine your current program. As you redefine your budget allocations, you'll also want to put a larger value on the small-micron pickup effectiveness of the sweeper you choose. In addition, evaluate both the sweeping frequency and the conditions under which sweepers will be used.

• If your target is water quality goals, forget about sweeping areas without curb-and-gutter, since there will be no appreciable accumulation.

• Review sweeping studies available, most of which are available at Use the information, especially results from geographical areas similar to the one you're in, to make future sweeper purchase decisions that maximize the potential for solving both water and air pollution problems in your particular area.

• If you truly want a sweeper that will make a difference, do not simply rely on the well-known certification process for sweepers that was designed and conducted by a California agency, the South Coast Air Quality Management District. SCAQMD's PM10 Certification is now widely used by manufacturers to tout that the machines in their product line are effective environmental sweepers. The fact is that, over time, sweeper manufacturers have been able to find a way to certify virtually all makes and models of street sweepers. Over 50 models including almost every type and configuration of street sweeper on the market have gained certification via compliance with the brief SCAQMD test, rendering any given machine's compliance essentially meaningless.

• Probably the single biggest factor driving street sweeping effectiveness is removal of vehicles on sweeping days. This is vitally important: a single car represents three spaces that can't be swept, since the sweeper operator must swing out around a car and then can't get back to the curbline until well past each parked vehicle. Develop and print brochures on the topic, and find innovative ways to distribute the information. For example, send the information out in city billing envelopes, put them onto your Web site as .pdf files, and provide them to environmental groups for distribution.

Many cities are now using the Internet creatively in this regard. Consider developing an e-mail signup Web site location that automatically reminds citizens to move their cars prior to sweeping days. Once in place, fines from vehicle citations will create an income stream that may even pay for a major portion of the sweeping program.

• Also consider contracting out sweeping services, which can often provide significant cost and service advantages. In England, statutes require that cities bid in-house sweeping against contractors every few years. This tends to keep municipal operations more efficient. Some larger U.K. municipalities even bid on providing sweeping to smaller cities nearby.

• Some innovative U.S. sweeper dealers are now offering cradle-to-grave sweeper purchases, another standard practice in Europe. With these arrangements, the cost is actually a monthly payment that includes all standard repair items and upkeep for the pre-agreed life of the sweeper and chassis, usually five years. This type of arrangement provides municipalities with the advantage of a predictable, steady budget item.

• Another way to potentially save money when using a contractor is to issue computerized fuel cards for the municipal contract. When the city pays the tab for fuel, fuel excise taxes are refundable.

• Remove disposal costs from your sweeping bids. Because future cost increases in this area are an unknown, experienced sweeping contractors typically realize they must overbid to account for unforeseen tipping fee increases that may not ever occur. Plus, when the contractor pays for disposal, there is actually a disincentive to doing a great job; the more material that is removed from the roadway, the less money the contractor makes.

• Be sure to test sweepers according to your particular requirements. If leaves are your biggest problem, then finalize your sweeper purchase in the fall when you can compare the current sweeper models on their ability to pick them up. If snow (i.e., sand and cinders cleanup) is the central issue, then test under those conditions. I've seen cities in all parts of the country test sweepers by putting an impossible amount of material down in some municipal parking area and then eyeballing which sweeper appears to leave behind the smallest pile. This methodology is especially senseless when choosing a sweeper for environmental reasons.

• If you're in the snowbelt, investigate the new crop of waterless sweepers designed to let you sweep all year.

• A number of sweeper models can also be operated on compressed natural gas or other diesel alternatives. However, since by 2010 the emissions of diesel engines will be cleaner than the current CNG engines, most CNG conversion companies have already exited the marketplace. Further, CNG appears to only be widely accepted in Southern California where it's mandated. Paradoxically, the mandate has actually eliminated the ability to sell some high-efficiency sweeper models since they are unable to use the limited number of CNG options available.

• Is most of the material within 3 feet of the curbline? One of the current models of vacuum sweepers offers a side-shift sweeping head that allows it to employ suction right up next to the curb.

• Need to find ways to get more bang for your buck? You may be able to work creatively with sweeping contractors in other ways than hiring them to sweep. These may include sweeper repair and assistance with sweeper selection.

• Establishing a debris-screening and/or composting program can save over 50% on disposal costs. If one of your local sweeping contractors operates a debris-screening program, the company may have enough capacity to add city debris to its existing operation.

• If your city is small, investigate sharing a sweeper and its usage with one or more neighboring districts. Some smaller California cities have found value in combining budgets to fund a stormwater-runoff compliance official in charge of keeping up with the information needed to assure each of the cities stays compliant.

• Some cities have found other ways for their sweepers to pull double duty. The City of Palmdale, California uses a video camera system that's mounted on the dash of its sweepers. Drivers are trained to look for problem areas and the system makes it easy to create a report flag on the video. Since the sweeper is traversing most areas of a city, it can be an inexpensive way to spot graffiti, signs down, lights out, curbs needing repair, overhanging trees, pothole problems, and so on. The system also documents exactly when sweeping occurred at any particular location.

• Both sweeping personnel and citizens need to be educated about the latest in industry findings. Educate your sweeping managers, as well as rank-and-file sweeper operators, about why a different sweeping frequency, type of sweeper, or switching to air-based technology now makes more sense. Doing so can even have positive implications for how well any new sweepers will be operated and maintained.

• Another way to reduce overall sweeping costs is to switch to one of the variety of high-dumping sweepers that are now available. These are designed to dump into dump trucks or roll-off containers, instead of using the sweeper for transport to a disposal facility. This keeps the relatively more expensive sweeper on the job, as well as keeps small-micron material from escaping due to double handling.

• In order to make your sweeping program more efficient, upgrade part of your road system, especially in runoff non-attainment areas. Steep curb cuts and potholes degrade performance of all types of sweepers, but more so regenerative air and, to some extent, vacuum sweepers.

EPA Phase I permits now need to prove they are achieving BMP results, and Phase II permits will soon need to do the same. Before you spend significant dollars on retro-fitting and other relatively expensive infrastructure-based projects, learn how sweeping your streets with today's new technology is able to address runoff pollution on the order of 100 to 1,000% more cost-effectively.

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