Field Verification of Manufactured BMPs Subject to Rainfall-Runoff Loadings

Field-testing of unit operations and processes (nominally called BMPs) requires critical planning and implementation through all steps of the verification process from initial watershed selection through defensible statements of BMP behavior based on field verification results. The desired goals and outcomes must be known and designed into the entire verification process. A continual evaluation, quality assurance and feedback protocol must be part of the testing protocol. What are the basic component categories of a well-designed and defensible field-testing protocol? In general, while watershed processes can be categorized and modeled, each watershed is different and unique with respect to BMP loadings of hydrologic, chemical, biological and particulate matter (PM) quantities. We must recognize these challenges and collect sufficient representative data so that the role of such uniqueness can be quantified for the specific BMP or BMPs tested. These challenges are significant because at this time there are very disparate methodologies of PM protocols mat range from gravimetric index tests such as the traditional total suspended solids (TSS) method adopted from wastewater treatment evaluations, or the more recent suspended sediment concentration (SSC) method, index tests such as turbidity testing, to more fundamental methods of particle size distributions (PSDs). Each index method provides an indication of BMP performance with respect to PM; however a more fundamental, transferable and defensible methodology includes PSD and turbidity testing that is combined with a representative gravimetric index test for PM. The committee is envisioning developing a multi-tiered approach to field testing predicated on the intended utilization and rigor required for the defensible and transferable application of BMP performance results. This committee is focused on manufactured BMP separation of PM. It should be recognized that the entire gradation of PM should be representatively characterized for a BMP, in particular the suspended fraction because of the mobility and acute bio-availability of this finer fraction.