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Finale! Top 10 Items to Remember for Treatment Credit Compliance

This article covers important information on treatment crediting, alternative compliance, compliance units, RSA requirements, and more. It also highlights key concepts such as ATA#1, NNI, RIS, the 50% Rule, site design principles, and volumetric runoff coefficients.

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Finale! Top 10 Items to Remember for Treatment Credit Compliance

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  1. Finale! – Top 10 Items to Remember • What are the two types of Treatment “Crediting?” • Alternative Compliance • Compliance Units. • When is an RSA required? • When there are stream crossings in project limits, • Project NNI of 1-acre or more, and • NNI in a TDA. Brown and Caldwell

  2. Finale! – Top 10 Items to Remember • When is ATA#1 generated? • Additional Treatment Area #1 is area that must be treated due to partial or complete removal of an existing Treatment BMP. • When the contributing drainage area is removed or modified. • What areas are excluded from NNI and RIS? • Per Table 4-1 of PPDG. • Impervious areas related to utility replacement, intersection of bridges, tunnels, sidewalks, pedestrian facilities, bike lanes, and impervious footprint of DPP or T-BMPs. • RIS areas that are already treated by existing T-BMP. Brown and Caldwell

  3. Finale! – Top 10 Items to Remember • Treatment is required when RIS exceeds? • 1-acre for highway project. • 5,000 SF for a non-highway project. • What is the 50% Rule? • When NNI divided by Total Post Project Impervious Area exceeds 50%. • The entire impervious area minus the NNI becomes ATA#2, or ATA#2 = Total Post Project Impervious – (NNI+RIS+ATA#1) Brown and Caldwell

  4. Finale! – Top 10 Items to Remember • What are the seven site design principles? • Conserve natural areas, • Minimize the impervious area, • Minimize disturbances to natural drainages, • Design pervious area to receive impervious runoff taking into consideration soil conditions, slope, and other factors. • Implement landscape and soil-based BMPs, where feasible. • Use climate-appropriate landscaping to minimize irrigation and runoff. • Comply with MWELO. Brown and Caldwell

  5. Finale! – Top 10 Items to Remember • When can compositing of the volumetric runoff coefficients (Rv) be used? • When 50% or more of impervious surfaces drain to pervious areas. • Sheet flow conditions exist from impervious to pervious. • What does the PCTA represent? • Post Construction Treatment Area, which is the treatment compliance standard. • If the PCTA balance is greater than or equal to “0,” then compliance has been met. If the PCTA balance is a negative value, then additional treatment is needed. Brown and Caldwell

  6. Finale! – Top 10 Items to Remember • When can a short form SWDR be used for a project? • Less than 1-acre of DSA; • Disturbs more than 1-acres, but is less than 5-acres and qualifies for the Rainfall Erosivity waiver; • Not required to implement Treatment; and • Does not impact an existing Treatment BMP. • The District SW Coord. gives an exception. Time to Take the Post Exam! Brown and Caldwell

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