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Fine-Tuning Street Cleaning

Source: Stormwater
Author: Don Talend
Published: May 16th, 2012

San Angelo, TX, home of the Concho River that flows through the downtown area and three lakes, is a lot like many cities that sprang up along the banks of a river. Stormwater runoff affects the viability of drinking water and the ecosystem not only of San Angelo, but also of several communities located downstream. The Texas Commission on Environmental Quality (TCEQ) lists the North Concho River on its 2010 303(d) list for a water-quality impairment and cites water-quality concerns for high levels of bacteria and depressed dissolved oxygen (DO). As part of its stormwater quality permit issued in August 2007, the city was required to submit a National Pollutant Discharge Elimination System (NPDES) Phase II stormwater management program by February 2008, with full implementation by August 2012.

Cities such as San Angelo are finding that cleaning streets of oils, grit, trash, and other pollutants is a much more cost-effective way of keeping these materials out of stormwater before it reaches rivers, lakes, and streams than is cleaning out storm drains and catch basins on a regular basis.

San Angelo, population 93,200, has about 1,100 curb miles of streets and more than 70,000 feet of city-owned open storm drains. The city’s acquisition of five Tymco Model 600 regenerative air sweepers from August 2010 through December 2011 has been a major part of its initiative to get the river off of the list of impaired water bodies by creating a cleaner stormwater environment before runoff enters these structures instead of cleaning large quantities of pollutants from the structures periodically. Although bacteria and DO levels are not directly affected by street sweeping, they are indirectly connected because the debris and pollutants picked up by street sweepers contain elements such as dead vegetation that grow bacteria and other organisms that use up much of the oxygen in the river.

The city is divided into six districts, each of which is cleaned several times a year—except for both sides of the river in the downtown area, which is cleaned every morning before traffic picks up. “It’s an aesthetic issue, but also, street sweepers pick up a lot of material off of the street,” says Clinton Bailey, city engineer. He adds that clean streets make the downtown area more of a potential tourist attraction, so the city purchased a smaller Tymco 600 sweeper that is dedicated to this area.

Street cleaning is not a new concept to the city; prior to 2010, three sweeper-type machines were in use. “With regenerative [sweepers], you have a vacuum system,” says Doug Kirkham, the city’s stormwater superintendent. “With the regular broom system, we were finding that we were sweeping and doing some good, but we were not able to vacuum up the small particles that are embedded into the streets. We found that we were stirring up the dirt and getting some of it, but a lot of it was turning into dust particles and spreading into the air.” Kirkham estimates that, prior to the purchase of the Tymco regenerative air sweepers, the city was picking up 200 to 250 tons of pollutants from the streets per month. Since the purchases, the city has begun tracking the total weight of pollutants and is now picking up 400 to 450 tons per month.

Art Gonzales, stormwater inspector for the city, reports that the new machines are making a difference in terms of effectiveness. “I think they do a really good job of picking up smaller particles,” he says. One option that the operator relies on is the machine’s Broom Assist Head, which loosens dirt before removing it from the surface by using an extra broom installed within the sweeper head that works in conjunction with a blast of air from the blast orifice. When necessary, operators also use the gutter brooms to loosen fine dirt particles that get packed down in the curb line, Gonzalez adds.

When the stormwater management plan was implemented, the city cleaned out the storm drains and made necessary repairs. Then the street cleaning program was implemented. “We’ve gone back in and looked at these storm drains and it’s amazing, the difference from what they were to what they are now,” says Kirkham, noting that no regular maintenance was performed on the storm drains before the stormwater management plan was implemented. “I can’t give all of the credit to the sweepers because some of those storm drains have probably been in the ground for 40 years and there has never been any maintenance on them. Now we’ve gone in and cleaned them out, and we’re finding that they’re staying clean. We’re keeping the debris off of the streets, and then when we are blessed with the rain, the storm drains are flowing; we don’t have debris caught in them.”

Kirkham reports that the public does not seem to mind the fact that the street sweepers occasionally clean the pavement. “The response is excellent, I would say. People appreciate the service. We added a stormwater management fee to the water bill, so we have to be out there in the public eye and let them see what we’re doing.” Currently, however, the cleaning schedule is not determined far enough in advance that residents can be given notice to move their vehicles.

Besides picking up significantly greater quantities of pollutants so that they do not wind up in storm drains, Bailey says, the street cleaning program has had a major impact on reducing stormwater pollution. “Street sweeping is one of those things that has a direct effect on stormwater quality. We can see the results in the quality of the runoff that we’re seeing pass our monitoring stations.”

The city worked with the Upper Colorado River Authority (UCRA) and shaped its stormwater management program around reducing high readings bacteria and total suspended solids and low of dissolved oxygen levels that were impacting the Concho River and Upper Colorado river basins several years ago, Bailey recalls. “A major difference between our program, as a Phase II city, and other ones around the state is that we are actively sampling and analyzing stormwater runoff in tributaries to our rivers throughout San Angelo. We’re doing that to establish background data for three main purposes. First, we want to identify what the real problems are. Then, we plan to build a model so we can build BMPs, detention ponds, gabion structures, things like that to prevent this pollution. Third, this will guide us to reduce the overall effort and dollars it takes to manage the entire system.”

The assessment of the stormwater management fee is allowing the city to address the high pollution readings, Bailey points out. As the stormwater program evolves, plenty of opportunities exist to reduce pollutants in the stormwater cost effectively, he adds. “The city council is not interested in taxing our citizens any more than they have to. This stormwater management fee came right after a big water rate increase, so it really wasn’t very popular. We won’t be gaining any popularity by telling the council that we need more sweepers to do a better job—we’ll gain more popularity by telling them that we can do more with less, so we’re taking a very strategic, calculated approach to gathering this data.”

A big part of this comprehensive initiative to acquire data for the purpose of optimizing maintenance scheduling, assets, and labor is the use of geospatial technology: Eagle Eye GPS for automatic vehicle location and ESRI geographic information system (GIS) software. The city recently installed GPS devices on its street sweepers to locate them practically in real time and develop optimal scheduling based on the average duration of various tasks performed during a shift. The GPS pings the antennas mounted on the sweepers every three seconds when the sweeper heads are in contact with the pavement, recording time stamps and locations, but the system does not collect signals when the sweepers are dumping. The GIS contains these data points and time stamps.

New scheduling would likely have a sweeper first clean the streets closest to the riverfront as soon as conditions allow following a storm event, for example. Based on these data, the city has already set up some routes that utilize intermediary dumping sites rather than having the sweepers go back to the city landfill, which is up to 15 miles away from some parts of the city.

“We’re really trying to streamline our processes here so that we can go to the city council and say that with what they’ve given us, this is how much we’ve been able to improve what we’re doing,” says Bailey of a comprehensive study that began in early 2011. “At this level, this is how we’re impacting water quality based on sampling results. We feel like we can do the same job we’re doing now with three sweepers once we get the operation streamlined. Or, maybe we can reduce the stormwater utility fee by 10% for everyone by streamlining our processes. We’re trying to do more with less.”

The technology also aids community relations’ efforts. By tracking the time and date when a given street was last cleaned, the city can show neighborhood residents evidence of its maintenance efforts. If residents make claims of vehicle damage, the data also can be used to show whether a sweeper was in the location of that vehicle. Making determinations like these without the aid of geospatial technology would be time-consuming and not a good use of workers’ time.

“One of the things we’re trying to do on the GIS side of it is implement something where we could track activity and have a history, so that at the end of the year if a council member wanted to know how many times a sweeper was in their district, we could have information in the GIS to show them that we’ve been there five times,” says Mike Smith, GIS manager for the city, adding that the city is looking at storing historical data for more than 12 months.

The reports compiled by the GIS are giving the city a detailed picture of the resources needed to execute its stormwater management program. “We’re getting to the point where we’re picking up a little less every month,” notes Bailey. “Along with determining paths of least resistance for the sweepers, we’re making sure that we’re utilizing the street sweepers a full eight hours a day and that there’s not a lot of dead time driving from location to location. We’re really trying to narrow down and present to the council that we really don’t need this many sweepers or we really don’t need to sweep once a quarter or once every two months to be effective.”

Tim Wolff, stormwater engineer for the city, says that enough data have been collected to date that it is possible to schedule the sweepers with great precision. “The street sweeper operators are told to slow down a little bit to let the machine pick everything up more effectively whenever they encounter heavily dirtied roads,” he says. “Before, if you asked them where the streets were dirtiest on a given day, they would have to try to remember. Well, with these data, you have cold, hard facts as to where the street sweepers slowed down, and if they only stripped five streets before they had to go and dump. You can actually see where the dirty areas are and where we need to focus more heavily. You can also rearrange your dump sites to make them more efficient for those areas so that the sweepers are not tracking all the way across town to dump.”

Bailey and Kirkham plan to present to the city council as soon as late 2012 a recommendation on the optimal resources necessary to continue managing the program. The severe drought that plagued much of the state in the summer of 2011 has limited the amount of data that would be needed to make the recommendation. That has not stopped the city’s Engineering Services Department from teaming up with Texas Institute for Applied Environmental Research instructors and Ph.D. students at Tarleton State University in Stephenville to begin develop a predictive stormwater quality model tied to the street cleaning data.

The study is roughly coinciding with an $11 million first phase of a river beautification project, and Bailey says the hope is that the TCEQ has removed the river from its list by the time the project is completed. As efforts to clean up the river continue, public education will have an increasing impact on water quality, Wolff adds. The city is working with the UCRA to educate children on everyday practices that help keep pollutants out of stormwater, such as refraining from blowing leaves or broadcasting fertilizer into the street.

“It’s raining a little more often and we’re keeping our fingers crossed that it continues,” says Bailey. “Every time it does, we’re building more and more data, and we’re able to see what the true issues are. It’s just a matter of time and rainfall events.”

Solids Reduced by Half

Although its NPDES Phase II permit requirements are different from those of San Angelo, the city of Tacoma, WA, is also using street cleaning as a key element of its stormwater management program. Also similar is Tacoma’s comprehensive approach to stormwater management; According to Hugh Messer, assistant division manager of Environmental Services, Maintenance Division, Environmental Services has been monitoring outfall areas and cleaning drainage areas for the outfall areas over the past several years. All told, Tacoma has 25,000 catch basins servicing 33,500 acres.

In 2006, Environmental Services took over the city’s street cleaning program from the Public Works Streets and Grounds Division and purchased four Tymco 500X regenerative air sweepers between 2007 and 2009. Previously, the streets were cleaned using mechanical brooms and, according to Messer, the focus was on maintenance, such as preparing pavement for overlays. Now, the focus is on keeping pollutants out of catch basins.

Messer reports that of the city’s $22 million annual stormwater management budget, the Maintenance Division budgets about $7 million—a portion of which is the street sweeping budget. The sweepers are paid for out of capital funds at about $210,000 each, so the city does not incur rental or lease costs during the equipment life cycle. Each machine is a scheduled for an eight-year life cycle before replacement is considered. Tacoma spends about $400,000 on personnel, $200,000 on maintenance and operation of the four sweepers, and $130,000 on disposal of swept debris.

The high-dump profile of the 500X sweepers makes them a good fit for the way that his department does things, Messer says. Sometimes, when remote areas are swept, a dump truck will be dispatched so that no haul time for dumping is necessary. All told, sweeping productivity has taken a quantum leap with this practice: Messer estimates that in the first year that his department took over sweeping, just under 5,200 miles of streets were cleaned. In 2011, about 17,000 miles of streets were cleaned with the assistance of dump trucks. Additionally, the new machines have much more uptime than the old mechanical sweepers, which had to be disassembled twice a year to fix the assembly bearings, Messer recalls. He estimates that the previously used machines were in operation 50 to 60% of the time, while the new machines are in operation 85 to 90% of the time, and the cost to operate the newer machines is about half that of the old ones.

Since the Maintenance Division began cleaning all of the catch basins every three years and took over street cleaning, crews have report reduced volumes of material found in catch basins, Messer says. The streets are cleaner and the department has received appreciative feedback from the public. This outcome is largely due to the new sweepers: Messer reports that they pick up fine particles that other sweepers do not—reducing mud that otherwise would be constantly present in the wet climate—and they also pick up leaves effectively. Although the city does not have a leaf collection program, areas with a high concentration of deciduous trees are prioritized for street sweeping from November through January, according to Messer.

In addition to street sweeping, a focus on source control is having a major impact, Messer says. Private parking lots, such as those at stores and gas stations, are inspected to ensure that appropriate BMPs are in place, and if street sweeping and maintenance crews find grease or oil spills, filtering BMPs are put in place to manage the sources.

According to Messer, the goal of Environmental Services is to clean every street in the city—which is divided into seven areas for this purpose—twice a year. Arterials are swept monthly, business districts once a week, and the industrial areas every six weeks. Because various parts of the city have limits on parking, notifications are sent out to residents informing them that their street will be cleaned on a given day. When vehicles are parked on a street to be cleaned, the machine goes around them; the program currently does not fine residents for not moving their vehicles.

The amount of total solids entering Commencement Bay via the Foss Waterway, a major saltwater basin that connects the city with the bay, has been reduced by more than half since Environmental Services began to focus on cleaning storm drains and took over street sweeping in 2007, according to Rick Fuller, a scientist with Environmental Services. Fuller reports that Environmental Services has monitored several locations in outfall points and the bay itself and recorded statistically significant reductions in heavy metal deposits in both sediment and whole water. The city has not yet conducted a specific study of the impact of street cleaning by itself. A new eductor decant facility completed in April 2012 is equipped to allow analysis of where various pollutants end up.

Like San Angelo, Tacoma is relying on GPS and GIS in its stormwater management program, albeit for a different application. Among other data, the system tracks miles swept as the sweeper head contacts the pavement. Also, sweeper operators can press a button in their Zonar Systems GPS-equipped machines when they see a catch basin that requires maintenance, an act that locates the structure. The next step is creating a maintenance work order. “That helps us to do the inspection, to verify what’s been cleaned and not cleaned, and also gives us follow-up documentation,” says Messer. Operators can make several different inputs that show up in the city’s GIS, including dirty catch basins, which catch basins have “fish labels” indicating that they flow to the local watershed, and even low-hanging branches that require trimming.

Tacoma’s streets have been plotted onto its Web-based GovME (Government Made Easy) GIS. If Environmental Services gets a complaint from a resident that the street has not been cleaned in a long time, he can look up the street on the GIS and access historical records of cleanings. “There’s a whole myriad of uses that we’ve found through the system; it allows us to pull up data for tracking what we’re doing with the sweeping program,” says Messer.

Managing Snow-Melt-Driven Runoff

The town of Vail, CO, is smaller than San Angelo or Tacoma, but its high population density and location give the town considerable potential to impact local watersheds with polluted stormwater. Most Americans think of arguably the most famous ski resort in the country when they hear the town’s name, but the tourist community also has some characteristics that create plenty of concerns about stormwater pollution: its location in a very narrow valley among the Rocky Mountains, seasonal spikes in population as a tourist community, and the need to use large volumes of bulk materials to aid vehicle traction in snow and ice during much of the year.

The long, narrow resort town has more than 700 stormwater inlets that capture snowmelt and stormwater flows. As a skiing paradise, Vail usually gets significant snowfall, but this can make driving and walking treacherous, so the town does its best to improve traction. “Since we’re in the Rocky Mountains and we’re in a ski area, we get a lot of snow, so there’s a lot of aggregate put down the road and sand, salt, and volcanic cinders,” says Todd Scholl, fleet manager with the town of Vail. “A big issue around here is keeping the cinders out of the waterways—Gore Creek runs right down to the valley here. We’re trying to keep the snowmelt out of the waterways; it migrates through all of the various channels into the creek. So we try to remove the material before it’s washed down into the various waterways and catch basins, even culverts, before it goes to the creek.”

The town has always swept its streets in an attempt to keep these materials out of the storm inlets but has improved the effectiveness of its street cleaning since it purchased an Elgin Sweeper Megawind vacuum sweeper in 2010. “The other machines that we used to clean the catch basins weren’t as effective,” recalls Scholl. “We’re at an 8,200-foot elevation, so being able to generate enough vacuum at this altitude to pick things up is an issue for us. The Megawind, hence its name, is very good at picking out rocks and whatever else is down in the catch basins, better than anything else we’ve tried before.”

One could consider the mountains surrounding the valley as a giant nonpoint source, Scholl indicates. “We’re in a narrow valley with pretty good-sized mountains on either side. Anything we put down typically ends up in the waterways. We get a lot of storms here and we put down a lot of aggregate—anti-skid material—and even in the winter, when the weather allows, we’re out there picking it up and trying to keep it off of the shoulder. For one thing, it’s an eyesore, and we’re a resort community. We keep it off of the road but also out of the waterways.” The majority of the streets are asphalt, but some pedestrian walkways use pavers. Scholl acknowledges that using the Megawind on these pavements probably hastens the need to replace the sand in the joints.

The town’s street cleaning schedule is highly weather dependent. During the winter, cleaning is done whenever conditions allow. In the spring, it is typical for street cleaning to be done 10 hours a day, seven days a week to get the majority of pollutants picked up before all of the snow melts.

“We only have a certain amount of time in a day, and that’s why we thought the Megawind really fit in well here, because it does more with the time we have available to clean the catch basins,” says Scholl. “We felt that this machine was the most cost-effective way to do that.”

Scholl said anecdotal evidence indicates the effectiveness of street cleaning in Vail. The most conspicuous signs of fewer pollutants are less dust in the air and cleaner-looking streets. “It’s one of those things that is hard to quantify, but if you don’t do it, you’ll notice more air pollution from kicking up all of that dust,” he says.

The public does not appear to mind the street cleaning, according to Scholl. “The only annoyance with street cleaning would be the inconvenience of having a street sweeper in your driving lane,” contends Scholl. “Also, the sweepers are fairly large and aren’t quiet, and they have an effect on pedestrian areas, so we have time constraints—we can’t clean the streets at four o’clock in the morning. But, for the most part, people are happy to see that we are doing it.”

Author’s Bio: Don Talend specializes in covering sustainability, technology, and innovation.