Street sweeping and catch basins cleaning removes accumulated sediments, trash, and debris and reduces the amount of pollutants entering our waterbodies. Catch basin cleaning also reduces local flooding. Best Management Practices (BMPs) for street sweeping is a necessary part of the stormwater management plan required by the General Permit for the Discharge of Stormwater from Small Municipal Storm Sewer Systems (MS4 Stormwater Permit).
Street Sweepings and Catch Basin Cleanings Defined:
• Street sweepings are materials such as sand, salt, leaves, broken glass, small pieces of metal, and other litter and debris removed from streets, parking lots and sidewalks in order to prevent these materials from being washed into storm sewers and surface waters, and to improve the appearance and safety of public roadways. Street sweepings are not as clean as virgin earth materials and contain low levels of chemical compounds associated with stormwater runoff.
• Catch basin cleanings are the materials such as sand, silt, leaves, and debris that accumulate in and are removed from catch basins. The material removed from catch basins contains a higher percentage of fine-grained material such as silt and clay. They are usually wet and have higher organic content from decomposing wet leaves than do street sweepings. Catch basin cleanings have higher levels of pollutants than street sweepings. The finer grained sediments in catch basins and other drainage structures adsorb more metals and other pollutants than the coarser sand typically found in street sweepings.
When to Sweep Streets
It is recommended that municipalities conduct street sweeping as soon as possible after snow melt. The longer sand is on the road, the more the coarse sand particles are abraded, rounded and reduced in size. Since the finer particles are more likely to absorb pollutants, prompt sweeping reduces not only the amount of silt levels in catch basins and watercourses but also reduces the amount of pollutants entering surface water bodies.
Prompt spring cleanup also reduces the amount of incidental debris associated with the sand. Prompt pick up before the sand is rounded and abraded also increases the opportunity to reuse the material for road sanding the following winter by blending a portion of the sweepings, after processing, into new street sand.
When To Clean Catch Basins
Municipalities are advised to develop and implement a program to evaluate and clean catch basins and other stormwater structures that accumulate sediment at least once a year, including a provision to identify and prioritize those structures that may require cleaning more than once a year. This task is a required condition of the “pollution prevention/good housekeeping for municipal operations” section in the development of a municipal stormwater management plan as outlined in the MS4 Stormwater Permit.
Late fall is an ideal time to clean basins, after the leaves have fallen and before the first snowfall. Then, another cleaning in the spring is helpful to remove the buildup of sand, leaves, and other debris that accumulated during the winter months. Areas which may contribute to higher pollutant loadings or which discharge to surface waters should be cleaned more frequently.