Best Management Practices (BMPs): Performance

Range of Best Management Practice Percent Removal Efficiency

BMP Type	TSS	Nitrogen	Phosphorus	Pathogens	Metals
Dry Detention Basins	30-65	15-45	15-45	<30	15-45
Retention Basins	50-80	30-65	30-65	<30	50-80
Constructed Wetlands	50-80	< 30	15-45	<30	50-80
Infiltration Basins	50-80	50-80	50-80	65-100	50-80
Infiltration Trenches/Dry Wells	50-80	50-80	15-45	65-100	50-80
Porous Pavement	65-100	65-100	30-65	65-100	65-100
Grassed Swales	30-65	15-45	15-45	<30	15-45
Vegetated Filter Strips	50-80	50-80	50-80	<30	30-65
Surface Sand Filters	50-80	< 30	50-80	<30	50-80
Other Media Filters	65- 100	15-45	<30	<30	50-80

It must be stressed that these data represent typical ranges of performance. For both "soft" BMP's, as well as traditional stormwater treatment methods, many factors will affect performance, and, in some cases, there have been reported negative performances, or actual contribution of pollutants to the effluent stream. The reasons for this can vary from improper design, to natural fluctuations in water chemistry, to even the overloading of an organic pollutant which can destroy beneficial microbial communities which are required for optimal BMP function. Additionally, issues of maintenance can factor into the system's performance, and the latter concerns should be considered carefully when choosing any method of stormwater treatment.

By way of full disclosure, the U.S. EPA has written the following:

"The use of BMPs to control storm water runoff and discharges where none previously existed will ultimately result in a change in pollutant loadings, and there are indications that in the aggregate BMPs will improve water quality. The actual manner in which the loadings reductions are achieved will depend on the BMPs selected, which will determine the associated costs. The physical-chemical properties of receiving streams and consequent linkages to biologic/ecologic responses in the aquatic environment, and human responses and values associated with these changes will determine the benefits."

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Last modified October 16 2009 09:57 AM