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[[File:Selbig graph.png|400px|thumb|alt=graph of P removal with street sweeping|<font size=3>Research conducted by Bill Selbig (USGS) shows that streets, when cleaned of leaf litter prior to a storm, can significantly decrease phosphorus loads in stormwater runoff ([https://www.usgs.gov/centers/umid-water/science/using-leaf-collection-and-street-cleaning-reduce-nutrients-urban?qt-science_center_objects=0#qt-science_center_objects Link to study])</font size>]] | [[File:Selbig graph.png|400px|thumb|alt=graph of P removal with street sweeping|<font size=3>Research conducted by Bill Selbig (USGS) shows that streets, when cleaned of leaf litter prior to a storm, can significantly decrease phosphorus loads in stormwater runoff ([https://www.usgs.gov/centers/umid-water/science/using-leaf-collection-and-street-cleaning-reduce-nutrients-urban?qt-science_center_objects=0#qt-science_center_objects Link to study])</font size>]] | ||
− | Roadways accumulate debris and material such as sediment, vegetation, vehicle debris/waste, industrial emission particle deposition, and litter. Harmful pollutants which accumulate on roadways, parking lots, and pavement include metals, organics, nutrients, and particulate matter, which street sweeping helps remove. The effectiveness of street sweeping for removing specific pollutants depends on the timing and methods of sweeping, including season, frequency of sweeping, timing relative to runoff events, type of sweeper(s), sweeping practices such as speed of sweeper and vehicle parking, and the characteristics of the surface being swept (land use, surface roughness, etc.). Below is a qualitative summary focused on pollutant and sweeper type. | + | Roadways accumulate debris and material such as sediment, vegetation, vehicle debris/waste, industrial emission particle deposition, and litter. Harmful pollutants which accumulate on roadways, parking lots, and pavement include metals, organics, nutrients, and particulate matter, which street sweeping helps remove. The effectiveness of street sweeping for removing specific pollutants depends on the timing and methods of sweeping, including season, frequency of sweeping, timing relative to runoff events, type of sweeper(s), sweeping practices such as speed of sweeper and vehicle parking, and the characteristics of the surface being swept (land use, surface roughness, etc.). Recommended sweeping practices for water quality purposes can be found on the page called [[Recommended street sweeping practices for water quality purposes]]. Links to other information on street sweeping, including case studies and credit calculations and calculators can be found on the page called [[Street sweeping]]. |
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+ | Below is a qualitative summary focused on pollutant and sweeper type. | ||
*Nutrients (phosphorus and nitrogen): In areas with annual leaf drop from trees, nutrient removal is greatest at the time of leaf drop. Some additional benefit occurs with spring sweeping during seed drop. Sweeping at other times of the year provides limited benefit. For more information on phosphorus, see [[Event mean concentrations of total and dissolved phosphorus in stormwater runoff]]. | *Nutrients (phosphorus and nitrogen): In areas with annual leaf drop from trees, nutrient removal is greatest at the time of leaf drop. Some additional benefit occurs with spring sweeping during seed drop. Sweeping at other times of the year provides limited benefit. For more information on phosphorus, see [[Event mean concentrations of total and dissolved phosphorus in stormwater runoff]]. | ||
*Sediment and metals: Sediment removal as discussed here does not include coarse organic sediments, which would be included in the discussion for nutrients. Removal of metals is strongly correlated with sediment removal for most metals. In areas where sweeping cannot be done during winter, sediment removal is greatest immediately following snowmelt, or during snowmelt if streets can be accessed. Sediment buildup increases with length of time between runoff events. Sediment and metal concentrations are typically greatest in industrial and major transportation areas. Sediment associated with first flush is a greater concern in small watersheds with highly connected impervious surfaces. Focused sweeping should occur in areas where there is a significant amount of construction activity. For more information on sediment see [[Event mean concentrations of total suspended solids in stormwater runoff]]. | *Sediment and metals: Sediment removal as discussed here does not include coarse organic sediments, which would be included in the discussion for nutrients. Removal of metals is strongly correlated with sediment removal for most metals. In areas where sweeping cannot be done during winter, sediment removal is greatest immediately following snowmelt, or during snowmelt if streets can be accessed. Sediment buildup increases with length of time between runoff events. Sediment and metal concentrations are typically greatest in industrial and major transportation areas. Sediment associated with first flush is a greater concern in small watersheds with highly connected impervious surfaces. Focused sweeping should occur in areas where there is a significant amount of construction activity. For more information on sediment see [[Event mean concentrations of total suspended solids in stormwater runoff]]. |
Overview, water quality benefits, and other co-benefits of street sweeping
This page provides an overview of street sweeping and a discussion of water quality benefits and co-benefits of street sweeping.
Street sweeping (also called street cleaning) refers to removal of sediment, litter, or other accumulated substances on roadways, particularly in urban and suburban areas. Street sweeping does not include removal of large quantities of leaves brought to the street/verge for removal, large debris or bulky items; removal of these items is typically handled by large vacuum leaf collectors or dump trucks, respectively.
Historically, street sweeping was conducted manually by a sanitation worker with a broom or shovel to remove animal waste from horse-drawn vehicles and other detritus on roadways. Mechanical sweepers such as broom systems attached to horse carts came about in the mid-1800s, and in the early 1900s street cleaning wagons sprayed water onto roadways to wash away debris. Motor-driven street sweeping vehicles were patented in the US in 1917.
Modern street sweeping has improved efficiency of debris removal from roadways dramatically. The focus of street sweeping was simple large “cosmetic” debris removal until the 1970s when concerns about water quality arose. In the decades following, improvements in street sweeping technology focused more on the removal and collection of coarse sand particle-sized street dirt, and smaller particles which contribute to instream sediment and nutrient pollution when swept off of or washed into waterways. Even when a street was cleaned of large refuse, the amount of tiny particulate matter that could not be effectively removed manually remained to wash-off into waterways following precipitation. Pollutants in stormwater runoff have long been recognized as contributors to aquatic habitat degradation, nuisance algal growth, low dissolved oxygen and toxicity in receiving water bodies . More recently, there has been a focus on street sweeping to remove the organic matter produced by street trees (leaves, seeds, flowers, etc), which can contribute significant amounts of phosphorus to runoff, especially in the fall during leaf drop. Particulate matter (air) also poses significant air-quality concerns when entrained in the air due to wind.
Roadways accumulate debris and material such as sediment, vegetation, vehicle debris/waste, industrial emission particle deposition, and litter. Harmful pollutants which accumulate on roadways, parking lots, and pavement include metals, organics, nutrients, and particulate matter, which street sweeping helps remove. The effectiveness of street sweeping for removing specific pollutants depends on the timing and methods of sweeping, including season, frequency of sweeping, timing relative to runoff events, type of sweeper(s), sweeping practices such as speed of sweeper and vehicle parking, and the characteristics of the surface being swept (land use, surface roughness, etc.). Recommended sweeping practices for water quality purposes can be found on the page called Recommended street sweeping practices for water quality purposes. Links to other information on street sweeping, including case studies and credit calculations and calculators can be found on the page called Street sweeping.
Below is a qualitative summary focused on pollutant and sweeper type.
For more information on stormwater and pollutants in stormwater, link here.
Street sweeping provides several benefits in addition to water quality improvement. The most cited co-benefits include improved appearances (aesthetics), improved roadway safety, potential reduction in flooding associated with clogging of stormwater conveyance systems, and reduced air pollution. Many key benefits associated with street sweeping have cumulative impacts as well. For example, increased removal of fine particulate matter can reduce the sediment load to downstream BMPs, extending the life of these practices which provide improved water quality further downstream.
Cost and maintenance information for street sweeping for water quality
Information on cost and maintenance for implementing a street sweeping program is variable. This is due to several factors, including but not limited to equipment cost and maintenance, frequency of sweeping, operator skills, and disposal methods.
Data compiled from the case studies in this manual are illustrated in the adjacent table. The median cost per curb mile is $94 while the mean cost is $487, showing the wide variation in cost information. The cost information provided by the cities typically does not include equipment costs but typically does include disposal costs.
Three cities from the case studies (Mankato, St. Cloud, Roseville) reported information on mass or volume of material collected. We used the Street Sweeping Phosphorus Credit Calculator to estimate cost per pound of phosphorus removed. We used the wet mass method and calculated values for fall and for the remainder of the year.
The City of Prior Lake and University of Minnesota researchers conducted an intensive study of street sweeping in Prior Lake (Kalinosky et l., 2014). This study included a literature review of other sweeping studies. Cost per mile swept was computed on a monthly basis and ranged from $20-29 per mile. This is similar to the cost data reported by Mankato and St. Cloud, which were the two best documented case studies. Cost effectiveness of sweeping was $41-lb-P in October, less than $100/lb-P during March, April, October, and November, and $400-600/lb-P in the summer months. While tree canopy and cost effectiveness were correlated, other factors such as particle size of solids affected the cost effectiveness of sweeping.
A discussion of cost consideration can be found at this link.
City | Annual cost ($) | Curb miles swept | Cost per curb mile |
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Lakeville | 246000 | 1200 | 205 |
Mankato | 400000 | 11814 | 34 |
Rochester | 80000 | 11000 | 7 |
St. Cloud | 70000 | 1825 | 38 |
Bloomington | 850000 | 342 | 2485 |
Fridley | 225000 | 1500 | 150 |
Costs typically do not include sweeper replacement cost |
There is considerable variability in cost effectiveness of different stormwater practices. Some studies show street sweeping to be ineffective for phosphorus removal compared to other practices, while other studies indicate sweeping is highly cost effective. A challenge in comparing studies is gaining access to specific information for each practice. In the case of street sweeping, for example, studies comparing sweeping to other practices rarely provide information about the sweeping practice, such as time of year, type of sweeper, and frequency of sweeping. Another challenge is studies do not contain the same set of bmps, and street sweeping is often not included in these studies. Another concern is that some studies favor specific bmps and therefore the data presented are questionable.
We conducted a cursory review of the literature to get a range of information on cost effectiveness for stormwater practices, including street sweeping.