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(a) An applicant must use the ESD planning techniques and practices and structural stormwater management measures established in this Article and the Design Manual, either alone or in combination, in a stormwater management plan. An applicant must demonstrate that environmental site design has been implemented to the maximum extent practicable before a structural best management practice is included in a stormwater management plan.
(b) ESD planning techniques and practices.
(1) An applicant must apply the following planning techniques according to the Design Manual to satisfy the on-site stormwater management requirements of Section 19-24:
(A) preserve and protect natural resources;
(B) conserve natural drainage patterns;
(C) minimize impervious area;
(D) reduce runoff volume;
(E) use ESD practices to maintain 100% of the average annual pre- development groundwater recharge volume for the site;
(F) use green roofs, permeable pavement, reinforced turf, and other alternative surfaces;
(G) limit soil disturbance, mass grading, and compaction;
(H) cluster development; and
(I) any practice approved by the Administration.
(2) An applicant must design the following ESD treatment practices according to the Design Manual to satisfy the on-site stormwater management requirements of Section 19-24:
(A) disconnection of rooftop runoff;
(B) disconnection of nonrooftop runoff;
(C) sheetflow to conservation areas;
(D) rainwater harvesting;
(E) submerged gravel wetlands;
(F) landscape infiltration;
(G) infiltration berms;
(H) dry wells;
(J) rain gardens;
(L) enhanced filters; and
(M) any practice approved by the Administration.
(3) The use of ESD planning techniques and treatment practices specified in this Section must not conflict with existing State or County laws.
(c) Structural stormwater management practices.
(1) An applicant must design the following structural stormwater management practices according to the Design Manual to satisfy the on-site stormwater management requriements of Section 19-24:
(A) stormwater management ponds;
(B) stormwater management wetlands;
(C) stormwater management infiltration;
(D) stormwater management filtering systems; and
(E) stormwater management open channel systems.
(2) An applicant must consider the performance criteria specified in the Design Manual with regard to general feasibility, conveyance, pretreatment, treatment and geometry, environment and landscaping, and maintenance when selecting structural stormwater management practices.
(3) An applicant must select structural stormwater management practices to accommodate the unique hydrologic or geologic region of the County where the property to be developed is located.
(d) An applicant may use an alternative ESD planning technique or treatment practice or structural stormwater management measure for new development runoff control if it meets the performance criteria established in the Design Manual and is approved by the Administration. Any practice used for a redevelopment project must be approved by the Department.
(e) Before modifying the on-site stormwater control requirements or design criteria, the applicant must submit to the Department an analysis of the impacts of stormwater flows downstream in the watershed. The analysis must include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications of the proposed development on a dam, highway, structure, or natural point of restricted streamflow, established with the Department’s concurrence, downstream from the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility. (2010 L.M.C., ch. 34, § 1.)