Frequently Asked Questions (FAQ)

Question:
Are BMPs effective?


ANSWER:
The EPA, in its published Storm Water Technology Fact Sheets, cites the applicability, advantages and disadvantages of various nonproprietary BMPs, including vegetated swales, sand filters, bioretention, infiltration drainfields, infiltration trenches, porous pavement, wetlands, vegetative covers, and wet detention ponds.

"Effectiveness" of proprietary BMPs has typically been reported (usually by the manufacturer) as the percent removal of suspended solids. If reported accurately, percent removal of suspended solids is a useful parameter for evaluating erosion control BMPs. Useful reporting would include particle grain size, information regarding grab or composite samples, and whether or not the testing was conducted in a lab or in the field under storm conditions.

However, because there are other constituents of concern regarding stormwater quality besides suspended solids, there is little information available to date to evaluate proprietary BMPs for uses other than erosion control. Therefore, removal of suspended solids must be viewed as a surrogate for other constituents of concern. For example, with proper study, a correlation might be made between removal of particulate metals and removal of suspended solids, since certain pollutants are know to adhere to sediment. To date, however, there are few such studies. Besides percent removal, because pollutant concentrations of influent stormwater can vary greatly, another useful parameter would be outflow vs. inflow concentration.


Links:
  EPA Post-Construction BMP Fact Sheets

  ASCE/USEPA National Stormwater BMP Database

  CASQA BMP Handbooks

  Low Impact Development Center Design Tools

  Caltrans BMP Retrofit Pilot Program--Final Report
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