A. 
The minimum control requirements established in this section and the Design Manual are as follows:
(1) 
The planning techniques, nonstructural practices, and design methods specified in the Design Manual be used to implement ESD to the MEP. The use of ESD planning techniques and treatment systems must be exhausted before any structural BMP is implemented. Stormwater management plans for development projects subject to this chapter shall be designed using ESD sizing criteria, recharge volume, water quality volume, and channel protection storage volume criteria according to the Design Manual. The MEP standard is met when channel stability is maintained, predevelopment groundwater recharge is replicated without causing damage or unduly endangering the water quality of the underlying aquifer, nonpoint source pollution is minimized, and structural stormwater management practices are used only if determined to be absolutely necessary.
(2) 
Control of the two-year and ten-year frequency storm event is required according to the Design Manual and all subsequent revisions unless the City Engineer determines that additional stormwater management is necessary because historical flooding problems exist downstream.
(3) 
The extreme flood volume calculated for the one-hundred-year frequency storm event shall be used as sizing criteria if so directed by the City Engineer. However, this requirement may be waived if the owner/developer demonstrates that implementing the extreme flood volume will actually cause detrimental impacts downstream. As a minimum, any structural BMPs proposed shall convey the runoff for the one-hundred-year storm event through the BMP structure without causing unacceptable damage and/or flooding to the subject property or surrounding properties. Undeveloped off-site areas contributing runoff to the point of study, if not under the direct control of the owner/developer performing the analysis, shall be treated as being developed in accordance with the zoning designation for those lands for the one-hundred-year analysis.
(4) 
The City Engineer may require more than the minimum control requirements specified in this chapter if hydrologic or topographic conditions warrant, or if flooding, stream channel erosion, or water quality problems exist downstream from a proposed project. The extent of a downstream area that is subject to the requirements stated herein will vary depending upon the location, and will be established with the concurrence of the City Engineer.
B. 
Alternate minimum control requirements may be adopted subject to Administration approval. The Administration shall require a demonstration that alternative requirements will implement ESD to the MEP and control flood damages, accelerated stream erosion, water quality, and sedimentation. Comprehensive watershed studies may also be required.
C. 
Stormwater management and development plans, where applicable, shall be consistent with adopted and approved watershed management plans or flood management plans as approved by the Maryland Department of the Environment in accordance with the Flood Hazard Management Act of 1976.[1]
[1]
Editor's Note: See § 5-809 et seq. of the Environment Article of the Annotated Code of Maryland.
D. 
Should, in the opinion of the City Engineer, downstream deficiencies require stormwater management criteria in excess of the minimums identified in this chapter, the City Engineer may direct or the owner/developer may elect to correct the noted deficiencies in order the obtain relief from the more stringent criteria. However, nothing in this section shall be considered as waiving the need for a development to comply with the minimum requirements identified in this chapter.
The ESD planning techniques and practices and structural stormwater management measures established in this chapter and the Design Manual shall be used, either alone or in combination in a stormwater management plan. A developer shall demonstrate that ESD has been implemented to the MEP before the use of a structural BMP is considered in developing the stormwater management plan.
A. 
ESD planning techniques and practices.
(1) 
The following planning techniques shall be applied according to the Design Manual to satisfy the applicable minimum control requirements established in § 213-11 of this chapter:
(a) 
Preserving and protecting natural resources;
(b) 
Conserving natural drainage patterns;
(c) 
Minimizing impervious area;
(d) 
Reducing runoff volume;
(e) 
Using small-scale ESD practices to maintain 100% of the annual predevelopment groundwater recharge volume, subject to the limitations for stormwater management and infiltration practices in Karst areas as defined in Appendix D.2 of the Design Manual;
(f) 
Using green roofs, permeable pavement, reinforced turf, and other alternative surfaces, subject to the restrictions listed in Subsection A(2) below;
(g) 
Limiting soil disturbance, mass grading, and compaction;
(h) 
Clustering development; and
(i) 
Any practices approved by the Administration.
(2) 
The following ESD treatment practices shall be designed according to the Design Manual to satisfy the applicable minimum control requirements established in § 213-11 of this chapter. However, for any proposed practice that relies upon infiltration to discharge stormwater from the site, the owner/developer must demonstrate to the City Engineer's satisfaction that such infiltration can be accomplished without causing damage to existing or proposed structures and features, and with minimal degradation to the aquifer underlying the site.
(a) 
Disconnection of rooftop runoff;
(b) 
Disconnection of non-rooftop runoff;
(c) 
Sheetflow to conservation areas;
(d) 
Rainwater harvesting;
(e) 
Submerged gravel wetlands;
(f) 
Landscape infiltration;
(g) 
Infiltration berms;
(h) 
Micro-bioretention;
(i) 
Rain gardens;
(j) 
Swales;
(k) 
Enhanced filters; and
(l) 
Any practices approved by the Administration.
(3) 
The use of ESD planning techniques and treatment practices specified in this section shall not conflict with existing state law or local ordinances, regulations, or policies. The City shall modify planning and zoning ordinances and public works codes to eliminate any impediments to implementing ESD to the MEP according to the Design Manual.
B. 
Structural stormwater management measures.
(1) 
The following structural stormwater management practices shall be designed according to the Design Manual to satisfy the applicable minimum control requirements established in § 213-11 of this chapter:
(a) 
Stormwater management ponds;
(b) 
Stormwater management wetlands;
(c) 
Stormwater management infiltration, subject to the approval of the City Engineer, and taking into consideration the issues identified in Subsection B(3) below;
(d) 
Stormwater management filtering systems incorporating underdrains, unless the underdrain requirement is waived by the City Engineer; and
(e) 
Stormwater management open channel systems.
(2) 
The performance criteria specified in the Design Manual with regard to general feasibility, conveyance, pretreatment, treatment and geometry, environment and landscaping, and maintenance shall be considered when selecting structural stormwater management practices.
(3) 
Structural stormwater management practices shall be selected to accommodate the unique hydrologic or geologic regions of the state. When selecting structural BMPs, special attention is directed to the existence of Karst geology within Washington County, and the influence these areas have on acceptable means for stormwater management. Refer to the Design Manual for specific guidelines.
(4) 
The design engineer and the owner/developer are responsible for considering safety and access to all proposed facilities. The Design Manual includes several possible design safety considerations. Measures to be considered may include fencing, slope benching, flattened side slopes, access roads, etc. Permanent pools greater than two feet in depth, or structures with one-hundred-year ponding depths greater than four feet, shall incorporate appropriate safety measures, approved by the City Engineer.
C. 
ESD planning techniques and treatment practices and structural stormwater management measures used to satisfy the minimum requirements in § 213-11 of this chapter must be recorded in the land records of Washington County and remain unaltered by subsequent property owners. Prior approval from the City Engineer shall be obtained before any stormwater management practice is altered.
D. 
Alternative ESD planning techniques and treatment practices and structural stormwater measures may be used for new development runoff control if they meet the performance criteria established in the Design Manual and all subsequent revisions, and are approved by the City Engineer and the Administration. Practices used for redevelopment projects shall be approved by the City Engineer.
The basic design criteria, methodologies, and construction specifications, subject to the approval of the City Engineer and the Administration, shall be those of the Design Manual.