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Institutional memory on stormwater treatment?

  • 1.  Institutional memory on stormwater treatment?

    Posted 05-01-2018 06:30 PM
    Broadly speaking, many permitting authorities set minimum stormwater quality treatment objectives at 80% TSS long-term average mass removal, or something along those lines. 

    Does anyone know or remember the rationale for the near-ubiquitous 80% TSS removal objective? I have heard somewhere that it was adapted (or adopted) from RCRA, for lack of a better starting place for establishing stormwater quality treatment goals.

    It would be helpful to understand where we came from in order to move forward. We have so much more information available to us now with regard to stormwater quality.

    Elizabeth Fassman-Beck

  • 2.  RE: Institutional memory on stormwater treatment?

    Posted 05-02-2018 10:17 AM
    Edited by Tirza Austin 05-02-2018 10:16 AM

    I believe the 80% comes from the development of the detention basin standards for erosion control. Detention of flowing muddy water is an effective method to cause the water to drop its sediment load.  However, time becomes a factor to drop the smallest soil particles (clay).  I was taught it takes 70 hours of detention to clear sediment laden water of the clay particles. The USDA - Agricultural Research Service may be a source for information on this subject.

    William Heffernan P.E., M.ASCE
    Consulting Engr
    Warren NJ

  • 3.  RE: Institutional memory on stormwater treatment?

    Posted 05-03-2018 10:23 AM

    If that were only the case... the 80% "rule" quickly became the default objective, and BMP/SCMs like extended detention basins, if designed appropriately, were thought to be the solution because they work so well in water and wastewater treatment. By now, we have 30 years' worth of monitoring data that says that is simply not the case. Highly variable loading conditions from storm to storm, dynamic operation conditions (turbulent flow), among a myriad of other factors (including inability to remove the very small particles that often dominate in runoff) really hinder sedimentation. Certainly there are some basins that perform very well, but across the board, evidence simply does not support the 80% objective.... then there's an entire argument (many arguments) around why a %-removal is a poor stand-alone metric for evaluating BMP/SCM performance.

    If interested, there's TONS of information freely available information on all this from the International Stormwater BMP Database (BMP Database
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    BMP Database
    The International Stormwater Best Management Practices (BMP) Database project website features a database of over 600 BMP studies, performance analysis results, tools for use in BMP performance studies, monitoring guidance and other study-related publications. New to the site? Start Here
    View this on Bmpdatabase >

    Elizabeth Fassman-Beck

  • 4.  RE: Institutional memory on stormwater treatment?

    Posted 05-04-2018 10:51 AM
    My reply was to provide a possible starting point for where the 80% originated.  I believe the Erosion Control Standards pre-date the implementation of RCRA and CZARA laws.  These ACTS maybe the point where the 80% became accepted.  I do agree it is time to review and revise the requirement as new approaches and methods have been developed that better address Stormwater treatment.

    William Heffernan P.E., M.ASCE
    Consulting Engr
    Warren NJ

  • 5.  RE: Institutional memory on stormwater treatment?

    Posted 05-02-2018 11:06 AM
    I think it is CZARA. In 1992 EPA adopted the 80% requirement for new development that municipalities in the Coastal Zones of States would need to meet in order to be in compliance with nonpoint source management requirements. See: Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters EPA 840-B-92-002

    Michael Barrett P.E., D.WRE, M.ASCE
    Austin TX

  • 6.  RE: Institutional memory on stormwater treatment?

    Posted 05-02-2018 03:49 PM
    This also was my recollection. I think I heard Rob Roseen give a presentation on the history of the 80% rule and he (or whoever the speaker was) linked it back to the Coastal Zone Act.

    Shirley Clark P.E., D.WRE, M.ASCE
    Penn State Harrisburg
    Middletown PA
    Penn State HarrisburgProfessor

  • 7.  RE: Institutional memory on stormwater treatment?

    Posted 05-02-2018 04:27 PM
    It may have been the result of a compromise between those who originally came up with the standard. Cost to treat vs results.  While the original 80/20 rule (The Pareto principle) deals with peoples time and productivity, I have heard people applying it to other things too. 

    I would be interested in learning the answer too and I am only speculating.

    Gregory Cole P.E., ENV SP, M.ASCE
    Senior Project Manager
    Black Mountain, NC

  • 8.  RE: Institutional memory on stormwater treatment?

    Posted 05-04-2018 10:52 AM
    Edited by Tirza Austin 05-04-2018 10:51 AM
    While maybe not the root source, an early version of LEED included points earned for 80% TSS reduction. This framed the criteria for architects and landscape architects using LEED, correct or not. 

    David Smith Aff.M.ASCE
    Interlocking Concrete Pavement Institute
    Chantilly VA

  • 9.  RE: Institutional memory on stormwater treatment?

    Posted 05-04-2018 11:54 AM
    Edited by Tirza Austin 05-04-2018 11:54 AM
    There may also be a thread connecting these numbers to the diffusion of early "first flush" literature (from sewerage to stormwater).   Some of the literature discussions regarding "how much" of a first flush is needed to represent a true water quality benefit from ff, distinguished 80% of load delivered in the first 20% of flow, as a contrast to so-called first flushes in which, say, 55% of storm load is delivered in first 45% of runoff.  This also connects to John Sansalone's careful work strongly showing the need to capture more runoff volume to reduce TSS (i.e. more than the conventional 1-inch sotmr depth that has been rationalized based on a fuzzy invocation of "first flush").


    Stuart Schwartz A.M.ASCE
    Sr. rsrch Scientist
    University of Maryland Baltimore County
    Baltimore MD

  • 10.  RE: Institutional memory on stormwater treatment?

    Posted 05-04-2018 12:34 PM
    ​I note Appendix D of the 2000 Maryland Stormwater Design Manual prepared by the Center for Watershed Protection and the MDE outlines some of this history.  It may be found at the link below.  In part it states on page 5.1, 

    "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:

    From 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:

    So 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.

    Michael Buechter P.E., D.WRE, M.ASCE
    Program Manager
    Metropolitan St. Louis Sewer District
    Webster Grvs MO

  • 11.  RE: Institutional memory on stormwater treatment?

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    Posted 05-04-2018 12:38 PM
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