Washington State Department of Ecology

Best Management Practices (BMPs) for Management and Disposal of Street Wastes

Street Waste Management Practices

Historic Practices

Catch basins were originally installed in sewer systems to collect suspended solids which tended to settle in low gradient pipes and cause clogs, backups, and overflows. Cleaning was done on regular basis after storms and street washing as part of regular maintenance and for odor control (horse dropping were originally a major constituent) (King County, 1994). Cleaning of the catch basins was with hand tools until the 1920's when mechanical systems began to be developed. The majority of wastes collected was solids and disposal was not a major problem.

Current Practices

Collection

Current street waste collection practices range from emergency response to clogged pipes, to cleanup of visual problems (litter) and hazardous materials, to regular preventative maintenance. Recent efforts to reduce discharges to surface water of pollutants from stormwater has increased both the number of catchment structures used and the frequency of cleaning. Reported catch basin cleaning frequency varies from twice a year to once every five years (Herrera, 1991). However, private operators report that half of their business is response to emergency flooding and clients only want the problem be cleaned.

Catch basins can be cleaned out by hand, but a eductor truck (commonly referred to using the brand name Vactor) is more commonly used. The eductor truck uses hydrodynamic pressure and a vacuum, to loosen and removes solids and standing liquids (typically liquid remaining in the sump of the stormwater facility from preceding precipitation events) from a catch basin or other stormwater facility. The waste is carried in a tank mounted on the truck and the entire load is dumped at a central site. This system has a problem in that it creates a large amount of liquid in comparison with solids. The liquids are difficult to transport and places to properly dump the liquids are difficult to find.

Street sweepers are used to remove litter, debris, and fines from street and parking lot surfaces. Street sweeping systems vary from mechanical broom sweepers, to vacuum/brooms, to regenerative air systems. Street sweeping is good method and necessary method for removing litter and other coarse street waste. However, its usefulness is limited by access, slope, and wet weather and difficulties in removing the finer and more contaminated particles. Better removal of the finer particles may be accomplished using regenerative air systems in conjunction with the broom or broom/vacuum systems.

Disposal

Complex waste disposal regulations, costly analytical methods, limited contaminant toxicology data, liquid intensive collection methods, liability consideration, and cost restraints make disposal of street wastes a major problem today. The major purpose of this document is to outline ways of street waste treatment, disposal and reuse that are economic, preserve resources, and protect human health and the environment.

Current street waste disposal and utilization practices are extremely varied. Solid disposal and/or use varies from landfill disposal, asphalt and concrete manufacture, hazardous waste treatment, reuse, fill and dumping in pits. Some of these methods are not appropriate.

Liquid disposal is also varied. For example, some communities decant liquids into sumps to separate liquids from the solids. Liquids settle anywhere from two hours to overnight. Liquids overflow into the sanitary sewer when more liquids are added and solids are removed about every other day. At other locations; solids and liquids are dumped into a holding bay where liquids run off, drain into settling tanks and then are discharged into the sanitary sewer. Unfortunately, dumping in pits and letting the liquid run off is also used for liquid and solid disposal.

Quantity of Waste Generated

 Maintenance of the stormwater facilities and street and parking lot surfaces generates a substantial quantity of solid and liquid street waste. The amount collected depends on the drainage features, maintenance frequency, operator practices, method, and surrounding land use.

Solids

A maintenance crew using a five cubic yard eductor truck can typically clean 25, type 1 catch basins and 6 manholes per day, decant liquids 6 times per day, and dump solids twice per day. In eight months, two trucks (5 and 10 cubic yard ) removed 145 cubic cubic yards of solids from 745 type 1 catch basins and 115 manholes (source??).

The Thurston County regional decant facility received 340 cubic yards of catch basin solids from Olympia, Lacey, Tumwater, and Thurston County government in 1994 (Meyer, 1995). A survey by Snohomish County Department of Public Works (1994) estimated government agency street grit collection for the Snohomish County area at 4,540 tons (3,500 cubic yards). The Snohomish County survey also shows the extreme variations in the amount of street waste collected in a year in that the Everett estimate was 12 pounds per resident while the Edmonds estimate was 75 pounds per resident.

In Alameda County, California, the amount of street sweepings collected per mile ranged from 1.4 to 2.0 cubic yards (Alameda County, 1993).

Liquids

The amount of liquids collected is dependent on weather, equipment used, operator practices, and stormwater facility type and condition.

Eductor truck operators typically decant liquids in the field before going to special site to dump solids. With less water, trucks are safer to operate, load limit problems less, and more solids can be hauled. The average truck decants three times a day with approximately 1200 gallons per decant (Herrera, 1991). Liquids are decanted back into the cleaned catch basin, storm sewer, sanitary sewer, or into surface water.

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