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Street and Municipal Sweeping:

Street Sweeping and Stormdrain Cleanout Study: Chesapeake Bay Area

Study released and posted at in September, 2008

In 2005, the Center for Watershed Protection collaborated with a number of agencies and set out to quantify the pollutant reduction that can be achieved by street sweeping and storm drain cleanouts. This research study had three phases: a literature review, a survey and a monitoring program. All of the information was used to provide locally-derived pollutant removal reductions for street sweeping and storm drain cleanout practices for Chesapeake Bay communities. CWP Logo

This research project report provides information to support pollutant removal efficiencies for street sweeping and storm drain cleanout practices for Phase I and II communities in the Chesapeake Bay watershed.

Information and data was gathered for this project through a comprehensive literature review, a basin-wide municipal survey of existing street sweeping and storm drain cleanout practices, and an intensive field monitoring program within two study catchments located in Watershed 263 in Baltimore, MD and additional sites in Baltimore County.

Street sweeping and storm drain cleanout practices rank among the oldest practices used by communities for a variety of purposes to provide a clean and healthy environment, and more recently to comply with National Pollutant Discharge Elimination System stormwater permits. The ability for these practices to achieve pollutant reductions is uncertain given current research findings.

Only a few street sweeping studies provide sufficient data to statistically determine the impact of street sweeping and storm drain cleanouts on water quality and to quantify their improvements. The ability to quantify pollutant loading reductions from street sweeping is challenging given the range and variability of factors that impact its performance, such as the street sweeping technology, frequency and conditions of operation in addition to catchment characteristics. Fewer studies are available to evaluate the pollutant reduction capabilities due to storm drain inlet or catch basin cleanouts.

A multi-faceted monitoring study was completed to provide locally-derived pollutant removal reductions for street sweeping and storm drain cleanout practices. The monitoring program including water quality and flow, bedload, first flush, precipitation, source area street particulate matter, and storm drain inlet accumulation and chemical characterization.

A 'before-and after' study design was used based on the inability to find a suitable control catchment to implement a paired watershed study design. An insufficient number of samples were collected given the conditions experienced during the study period to statistically detect differences in the street sweeping treatment on water quality.

Monitoring efforts, however, did reveal key findings to determine factors contributing to the effectiveness of street sweeping and storm drain cleanout practices such as the particle size distribution of the street particulate matter picked-up by sweeping and its chemical composition, along with the significance of leaf litter and other organic material in storm drains and its contributions to pollutant loadings.

To synthesize the diverse research findings from this and other studies, a conceptual model was developed to provide pollutant removal efficiencies for TS, TN and TP for street sweeping and storm drain cleanout practices. The conceptual model is defined by a set of bounding conditions and assumptions that were made based on the literature, survey findings and monitoring data collected as part of the project.

Click here to download the Final Report: Deriving Reliable Pollutant Removal Rates for Municipal Street Sweeping and Storm Drain Cleanout Programs in the Chesapeake Bay Basin.

The Report information also includes two technical memorandums. The first, 'Research in Support of an Interim Pollutant Removal Rate for Street Sweeping and Storm Drain Cleanout Activities,' is organized into eight major sections, which are summarized below.

1. Background and History of Street Sweeping - This section presents a brief overview of the street sweeping research from the NURP studies in the late 1970s and early 1980s to more recent studies. The background section highlights the shift in research methods to study the effectiveness of street sweeping and how it may affect water quality.

2. Conceptual Model to Define Pollutant Removal Rate -- This section outlines a conceptual model that organizes the existing research to help define interim pollutant removal rates for select nutrients on street sweeping and storm drain cleanout practices.

3. Characterization of Street Dirt -- Streets are one of many source areas for pollutants within urban watersheds. This section summarizes key characteristics of street dirt/particulate matter with a focus on sediments, nutrients and metals. The section reviews the sources and accumulation rates of street dirt and its physical and chemical characterization.

4. Characterization of Storm Drain Inlet Behavior -- This section summarizes the quality of trapped sediment in storm drain inlets and catch basins, and reviews the physical and chemical characteristics of trapped material.

5. Street Sweeper Performance --This section summarizes the key factors that affects overall street sweeper performance, and evaluates pollutant removal for street sweeping based on sweeping frequency, technology and sweeping conditions.

6. Storm Drain Cleanout Performance -- This section reviews the available research on the potential for storm drain and catch basin cleanouts to reduce stormwater pollutants.

7. Interim Pollutant Removal Efficiencies -- This section outlines the detailed assumptions to derive pollutant removal rates for TSS, TN and TP over a range of street sweeping frequencies and catch basin cleanouts.

8. Application of Project Monitoring Effort - This section illustrates how monitoring data from this research project will be used to adjust the interim removal rates to derive final values. The section indicates how stormwater monitoring data in test catchments and sampling of street dirt and catch basins will be applied to the conceptual model to provide more accurate pollutant removal rates.

Click here to download the literature survey memorandum, entitled: Research in Support of an Interim Pollutant Removal Rate for Street Sweeping and Storm Drain Cleanout Activities.

Technical Memorandum Two: Research in Support of an Interim Pollutant Removal Rate for Street Sweeping and Storm Drain Cleanout Activities

1. The Center for Watershed Protection surveyed twenty MS4s in the Chesapeake Bay watershed about their street sweeping and storm drain cleanout practices. Collectively, these communities represent nearly half of the urban population in the Chesapeake Bay watershed. Only one community did not have a street sweeping program. All communities surveyed had a storm drain cleanout program.

2. Chesapeake Bay MS4 street sweeping and storm drain cleanout programs are exceedingly diverse in their size and scope. Cumulatively, Chesapeake Bay MS4 programs are spending as much as $13 million/year on these programs.

3. Chesapeake Bay communities sweep at least 70% of the public streets in their community on an annual basis. 85% of communities sweep more frequently than once per year. However, only a small subset of communities are sweeping frequently enough (e.g. biweekly or more) to realize a potential water quality benefit as outlined in Technical Memo 1.

4. Most Chesapeake Bay communities maintain several thousand miles of streets. Street sweeping frequency is often related to street land use or street type. For example, streets located in commercial or central business districts tend to be swept more frequently than local residential streets. Additional street sweeping is commonly scheduled for Spring cleanup of streets from the previous winter de-icing practices.

5. Pollutant reduction is not a primary factor driving Chesapeake Bay MS4s to sweep streets or cleanout storm drains, inlets or catchbasins. The purpose of street sweeping and storm drain cleanouts is based on maintaining aesthetics and responding to public demand. Only one community reported that nutrients were a target pollutant for street sweeping. This may reflect that fact that minimal monitoring has been completed within the Bay to determine the effectiveness of these practices with respect to improving stormwater quality.

6. Respondents noted several factors that reduce the effectiveness of street sweeping programs, including parked cars and inadequate budgets. Ineffective technology was not stated as a problem, although only 27% of the communities use the more efficient street sweeping technology (i.e., regenerative air, vacuum). Conversely, more modern equipment such as vacuum-based technology is used in the majority of the communities to cleanout storm drains.

7. Communities that use a stormwater utility fee or other stormwater tax typically have larger street sweeping budgets.

8. Storm drains, inlets and catchbasins within the Bay are infrequently cleaned out. 75% percent of Phase I and Phase II communities cleanout their storm drains every two years or less, either as part of a regular cleanout program or based on complaints or clogging

9. Assuming this research study is able to confirm the value of street sweeping as a nutrient reduction BMP, most Chesapeake Bay MS4s would need to greatly increase the frequency of sweeping or target specific areas of street dirt accumulation in order to see potential water quality improvements.

10. At this time, with a few local exceptions, storm drain cleanouts cannot be considered a nutrient reduction BMP given the small percentage of storm drains, inlets or catch basins that are cleaned out, the infrequency of cleaning, and the absence of a database to track and maintain cleanout records.

Click here to download memorandum #2, entitled: Research in Support of an Interim Pollutant Removal Rate for Street Sweeping and Storm Drain Cleanout Activities.

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