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"BMPs employed at new development in the State of Maryland are now required to meet a performance standard under the recently issued CZARA Coastal Zone 6217(g) management measures guidance (US EPA, 1993). The specific management measures read "After construction is completed and the site is permanently stabilized, reduce the average annual total suspended solid (TSS) loadings by 80% percent...on an average annual basis."The link:https://www.waterboards.ca.gov/rwqcb2/water_issues/programs/stormwater/muni/nrdc/appnd_d5.pdfFrom the New Jersey Stormwater Best Practices Manual, Chapter 4, "According to these Rules, a "major development" project that creates at least 0.25 acres of new or additional impervious surface must include stormwater management measures that reduce the average annual total suspended solids (TSS) load in the development site's post-construction runoff by 80 percent. This 80 percent requirement has been based, in part, upon Section 6217(g) of the 1990 Coastal Zone Management Act Reauthorization Amendments as enforced by the U.S. Environmental Protection Agency."The link:http://www.nj.gov/dep/stormwater/bmp_manual/NJ_SWBMP_4%20print.pdfSo you can see the 80% criterion evolved from the 1993 guidance issued to implement the 1990 CZARA and was based on performance data for public domain systems like dry and wet ponds, wetlands, filters, infiltration and marshes. The 80% TSS removal CZARA guideline (EPA 1993) was based on the removal efficiencies for storm water control practices such as constructed wetlands, wet ponds and infiltration basins reported by Schueler (1992). But note Maryland is one of the "leaders" with the Bay, so I would submit it is likely a lot of agencies have copied from them at this point.
Note I think the most overlooked thing to the 80% TSS removal is a definition of particle size distribution, or what TSS, basketballs? The TARP and TAPE programs attempted to define some of this better. Not to mention, Schueler (1997) subsequently found that the systems above do not achieve the 80% TSS removal guideline and EPA (August 1999) reported that these systems achieve only 50-80% removal of TSS.Hope that is interesting.