§ 22-4. Environmental site design; Structural practices.

(a) In general.

(1) In designing stormwater management measures, the following must be used, either alone or in combination:

(i) environmental site design techniques and practices; and

(ii) structural practices.

(2) The applicant must demonstrate that environmental site design has been implemented to the maximum extent practicable before the use of a structural best management practice or alternative practice may be considered in developing the stormwater management plan.

(3) Stormwater management measures, their selection, basic design criteria, methodologies, and construction specifications:

(i) must comply with the State's Design Manual and the City's Design Guidelines; and

(ii) are subject to approval of the Department and the State Water Management Administration.

(4) Environmental site design techniques and practices and structural stormwater management measures used to satisfy the minimum control requirements of § 22-3 of this subtitle:

(i) must have easements, as described in § 25-1(b)(1) of this Division II, recorded in the land records of Baltimore City;

(ii) must have a recorded inspection and maintenance agreement, as described in § 27-3 of this Division II; and

(iii) may not be altered without the Department's prior approval.

(b) Environmental site design planning techniques and practices.

(1) The following planning techniques must be applied according to the State's Design Manual to satisfy the applicable minimum control requirements of § 22-3 of this subtitle:

(i) preserving and protecting natural resources;

(ii) conserving natural drainage patterns;

(iii) minimizing impervious area;

(iv) reducing runoff volume;

(v) using environmental site design practices to maintain 100% of the annual predevelopment groundwater recharge volume;

(vi) using green roofs, permeable pavement, reinforced turf, and other alternative surfaces;

(vii) limiting soil disturbance, mass grading, and compaction;

(viii) clustering development; and

(ix) other practices approved by the Department.

(2) The following environmental site design treatment practices must be designed according to the State's Design Manual and the City's Design Guidelines to satisfy the applicable minimum control requirements established in § 22-3 of this subtitle:

(i) disconnection of rooftop runoff;

(ii) disconnection of non-rooftop runoff;

(iii) sheetflow to conservation areas;

(iv) rainwater harvesting;

(v) submerged gravel wetlands;

(vi) landscape infiltration;

(vii) infiltration berms;

(viii) dry wells;

(ix) micro-bioretention;

(x) rain gardens;

(xi) swales;

(xii) enhanced filters; and

(xiii) other practices approved by the Department.

(3) The use of environmental site design planning techniques and treatment practices may not conflict with existing State or local laws, ordinances, regulations, or policies.

(1) The following structural stormwater management practices must be designed to satisfy the applicable minimum control requirements of § 22-3 of this subtitle.

(i) stormwater management ponds;

(ii) stormwater management wetlands;

(iii) stormwater management infiltration;

(iv) stormwater management filtering systems;

(v) stormwater management open channel systems; and

(vi) other practices provided in the State's Design Manual.

(2) In selecting structural practices, consideration must be given to the performance criteria specified in the State's Design Manual for:

(i) general feasibility;

(ii) conveyance;

(iii) pretreatment;

(iv) treatment and geometry;

(v) environment and landscaping; and

(vi) maintenance.

(3) Structural practices must accommodate the unique hydrologic or geologic regions of the site.

(d) Alternative practices.

(1) Alternative structural and nonstructural stormwater management practices may be used for new development water quality control if they:

(i) meet the performance criteria established in the State's Design Manual; and

(ii) are approved by the State Water Management Administration.

(2) Practices used for redevelopment projects must be approved by the Department.

(e) Impact analysis.

(1) For the purposes of modifying the minimum control requirements or design criteria, the applicant must submit to the Department an analysis of the impacts of stormwater flows downstream in the watershed.

(2) The analysis must include the hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications of the proposed development upon a dam, highway, structure, or natural point of restricted streamflow.

(3) The point of investigation is to be established, with the Department's concurrence, downstream of the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility.