Bioretention systems with an internal storage reservoir shall comply with the following:

1. (a) The system shall be designed in accordance with the “Standard Detail, Bioretention ISR Stormwater System” in the “UNH Stormwater Center Hybrid Bioretention Template”, February 2020, available as noted in Appendix B, with the additional requirements in (b) though (g), below;

2. (b) Pretreatment as described in Env-Wq 1508.12 through Env-Wq 1508.16 shall be provided if

   stormwater, other than roof runoff, will be discharged to the practice;

3. (c) If a sediment forebay is used to meet (b), above, it shall be designed to contain 25% of the WQV and otherwise meet the criteria specified in Env-Wq 1508.12;
4. (d) The volume above the filter material shall be equal to or greater than 100% of the WQV;
5. (e) The filter media shall consist of one of the mixtures specified in Env-Wq 1508.08(k)(4);
6. (f) The system, excluding the saturated zone but including any sediment forebays, shall be designed to completely drain within 72 hours; and

7. (g) If iron filings are proposed, the following shall apply:

   1. (1) The iron filings shall be well mixed with the filter material and mixing an installation shall be observed by a professional engineer to ensure proper mixing and installation of the iron filings;
   2. (2) Iron filings shall not be mixed into the top 4" of the filter material; and
   3. (3) The iron filings shall be sized in accordance with Appendix D of the United States Army Corps of Engineers Engineering Manual EM-1110-2-1913, April 2020, available as noted in Appendix B, such that the iron filings are sized as a filter for the bioretention soil mix filter material.

Source. #13758, eff 9-28-23; ss by #14472, eff 1-19-26, EXPIRES: 1-19-36