Except as otherwise expressly provided in this Division II, no person may develop any land unless:
the project is a single-lot residential construction that establishes stormwater management measures in accordance with a standard stormwater management plan prepared in accordance with the City’s Design Guidelines and approved by the Department; or
the person:establishes stormwater management measures that control or manage runoff
from the development; and
incorporates those measures into phased stormwater management plans approved by the Department.
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These stormwater management measures must:
meet the requirements of the State’s Design Manual, this Division II, and the City’s Design Guidelines; and
be constructed according to:an approved plan for new development; or
the policies stated in <cite data-path="|7|§23-7">§ 23-7 of this Division II</cite> for redevelopment.
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The minimum control requirements for these management measures are as provided in this section and the State’s Design Manual.
The criteria in the State’s Design Manual for environmental site design to the maximum extent practicable and the use of environmental site design planning techniques and treatment practices must be exhausted before any structural best management practice or alternative practice is implemented.
Stormwater management plans for development projects subject to this Division II must be designed using environmental site design sizing criteria, recharge volume, water quality volume, and channel protection storage volume criteria according to the State’s Design Manual. The maximum-extent-practicable standard is met when channel stability is maintained, predevelopment groundwater recharge is replicated, nonpoint source pollution is minimized, and structural stormwater management practices or alternative practices are used only if determined to be absolutely necessary.
Runoff from the 10-year frequency storm event must be controlled in accordance with the State’s Design Manual if the Department determines that additional stormwater management is necessary because historical flooding problems exist and downstream floodplain development and conveyance system design cannot be controlled.
The Department may require more than the minimum control requirements of the State’s Design Manual if:hydrologic or topographic conditions warrant; or
flooding, stream channel erosion, or water quality problems exist downstream from a proposed project.
With the approval of the State Water Management Administration, the Department may adopt alternative minimum control requirements that will:implement environmental site design to the maximum extent practicable; and
control flood damages, accelerated stream erosion, water quality, and sedimentation.
Where applicable, stormwater management and development plans must be consistent with watershed management plans and flood management plans approved by the State Water Management Administration under the Flood Hazard Management Act of 1976.
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In designing stormwater management measures, the following must be used, either alone or in combination:environmental site design techniques and practices; and
structural practices.
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.
Stormwater management measures, their selection, basic design criteria, methodologies, and construction specifications:must comply with the State’s Design Manual and the City’s Design Guidelines; and
are subject to approval of the Department and the State Water Management Administration.
Environmental site design techniques and practices and structural stormwater management measures used to satisfy the minimum control requirements of <cite data-path="|7|§22-3">§ 22-3 of this subtitle</cite>:must have easements, as described in <cite data-path="|7|§25-1|(b)|(1)">§ 25-1(b)(1) of this Division II</cite>, recorded in the land records of Baltimore City;
must have a recorded inspection and maintenance agreement, as described in <cite data-path="|7|§27-3">§ 27-3 of this Division II</cite>; and
may not be altered without the Department’s prior approval.
The following planning techniques must be applied according to the State’s Design Manual to satisfy the applicable minimum control requirements of <cite data-path="|7|§22-3">§ 22-3 of this subtitle</cite>:preserving and protecting natural resources;
conserving natural drainage patterns;
minimizing impervious area;
reducing runoff volume;
using environmental site design practices to maintain 100% of the annual predevelopment groundwater recharge volume;
using green roofs, permeable pavement, reinforced turf, and other alternative surfaces;
limiting soil disturbance, mass grading, and compaction;
clustering development; and
other practices approved by the Department.
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 <cite data-path="|7|§22-3">§ 22-3 of this subtitle</cite>:disconnection of rooftop runoff;
disconnection of non-rooftop runoff;
sheetflow to conservation areas;
rainwater harvesting;
submerged gravel wetlands;
landscape infiltration;
infiltration berms;
dry wells;
micro-bioretention;
rain gardens;
swales;
enhanced filters; and
other practices approved by the Department.
The use of environmental site design planning techniques and treatment practices may not conflict with existing State or local laws, ordinances, regulations, or policies.
The following structural stormwater management practices must be designed to satisfy the applicable minimum control requirements of <cite data-path="|7|§22-3">§ 22-3 of this subtitle</cite>.stormwater management ponds;
stormwater management wetlands;
stormwater management infiltration;
stormwater management filtering systems;
stormwater management open channel systems; and
other practices provided in the State’s Design Manual.
In selecting structural practices, consideration must be given to the performance criteria specified in the State’s Design Manual for:general feasibility;
conveyance;
pretreatment;
treatment and geometry;
environment and landscaping; and
maintenance.
Structural practices must accommodate the unique hydrologic or geologic regions of the site.
Alternative structural and nonstructural stormwater management practices may be used for new development water quality control if they:meet the performance criteria established in the State’s Design Manual; and
are approved by the State Water Management Administration.
Practices used for redevelopment projects must be approved by the Department.
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.
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.
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.
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For any proposed development, the applicant must submit phased stormwater management plans to the Department for review and approval.
At a minimum, plans must be submitted for the concept, site development, and final stormwater management construction phases of project design.
Each plan must:include the minimum content specified in <cite data-path="|7|§22-3">§ 22-3 {“Minimum control requirements”} of this subtitle</cite>; and
meet the requirements of the State’s Design Manual, the City’s Design Guidelines, and <cite data-path="|7|§22-4">§ 22-4 {“Environmental site design; Structural practices”} of this subtitle</cite>.
The applicant must submit a concept plan that provides sufficient information for an initial assessment of the proposed project and whether stormwater management can be provided according to <cite data-path="|7|§22-4">§ 22-4 {“Environmental site design; Structural practices”} of this subtitle</cite> and the State’s Design Manual.
Plans submitted for concept approval must include the following, minimum information:a map that shows, at a scale specified by the Department:site location;
existing natural features;
water and other sensitive resources;
topography; and
natural drainage patterns;
the anticipated location of all:impervious areas;
buildings;
roadways;
parking;
sidewalks;
utilities; and
other site improvements;
the location of:the proposed limit of disturbance;
erodible soils;
steep slopes; and
areas to be protected during construction;
preliminary estimates of:stormwater management requirements;
the selection and location of environmental site design practices to be used; and
the location of all points of discharge from the site;
a narrative that supports the concept design and describes how environmental site design will be implemented to the maximum extent practicable; and
any other information the Department requires.
After approval of the concept plan, the applicant must submit, unless exempted by the Department, at the Department’s discretion, site development plans that reflect comments received during the previous review phase.
Plans submitted for site development approval must be of sufficient detail to allow site development to be reviewed.
These plans must include the following, minimum information:all information provided during the concept plan review phase;
final site layout, including:exact impervious area locations and acreages;
proposed topography;
delineated drainage areas at all points of discharge from the site; and
stormwater volume computations for environmental site design practices and quantity control structures;
a narrative that:supports the site development design;
describes how environmental site design will be used to meet the minimum control requirements; and
justifies any proposed structural stormwater management or alternative practice measure; and
any other information the Department requires.
After site development approval, the applicant must submit final stormwater management plans that reflect the comments received during the previous review phase.
Stormwater management plans submitted for final approval must be in the form of construction drawings, in sufficient detail to allow all approvals and permits to be issued, and accompanied by a report that includes sufficient information to evaluate the effectiveness of the proposed runoff control design.
The plan must be accompanied by an application for any waiver or variance sought under Subtitle 23 or Subtitle 24.
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The report submitted for final stormwater management plan approval must contain the following, minimum information:
a brief narrative description of the project;
geotechnical investigations, including soil maps, borings, site specific recommendations, and any additional information necessary to evaluate the final stormwater management design;
descriptions of all water courses, impoundments, and wetlands on or adjacent to the site or into which stormwater directly flows;
drainage area maps that show pre- development and post-development runoff flow path segmentation and land use;
hydrologic computations of the applicable environmental site design and unified sizing criteria, according to the State’s Design Manual, for all points of discharge from the site;
hydraulic computations for all environmental site design practices and structural stormwater management measures to be used;
structural computations;
volume sizing computations, according to the State’s Design Manual, that support the final stormwater management design; and
any other information that the Department requires.
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The construction drawings submitted for final stormwater management plan approval must include the following:a vicinity map;
a topography survey that shows existing and proposed contours, including the area necessary to determine downstream analysis for proposed stormwater management facilities;
any proposed improvements, including the location of buildings or other structures, impervious surfaces, storm drainage facilities, and all grading;
the location of existing and proposed structures and utilities;
any easements and rights-of-way;
the delineation, if applicable, of:the 100-year floodplain; and
any on-site wetlands;
structural and construction details, including representative cross sections, for all components of:the proposed drainage system or systems; and
stormwater management facilities;
all necessary construction specifications;
a sequence of construction;
data for:total site area;
disturbed area;
new impervious area; and
total impervious area;
a table that shows the environmental site design and unified sizing criteria volumes required by the State’s Design Manual;
a table of materials to be used for stormwater management facility planting;
all soil boring logs and locations;
a maintenance inspection and maintenance activity schedule;
a proposed construction and inspection schedule;
an as-built certification signature block, to be executed after the project is completed; and
any other information that the Department requires.
The applicant must certify on the drawings that all grading, drainage, construction, and development will be done in strict accordance with the approved plan.
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The design of all stormwater management plans must be prepared by a professional engineer, professional land surveyor, or landscape architect licensed in the State.
If stormwater best management practices require a dam safety permit from the Maryland Department of the Environment or small pond approval from the City, the plan must be prepared by a professional engineer licensed in the State.
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If a stormwater management plan involves directing some or all runoff from the site, the applicant is responsible for obtaining from adjacent property owners any needed easements or property interests for water flow.
Approval of a stormwater management plan does not create or affect any right to direct runoff onto adjacent property without that property owner’s permission.
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The Department must perform a comprehensive review of the plans for each phase of site design to determine compliance with this Division II.
For each plan phase, coordinated comments will be provided that reflect input from all appropriate agencies, including Planning, Zoning, and Public Works.
At each phase of project design, comments from the Department and other appropriate agencies must be addressed by the applicant and approval received before subsequent submissions.
In approving a plan, the Department may impose any conditions that it considers necessary or appropriate to:ensure compliance with this Division II; and
preserve the public health and safety.
After the Department has completed its comprehensive review for each phase of site design, the Department must notify the applicant of:the Department’s approval of the plan;
the Department’s disapproval of the plan, together with:the reasons for disapproval; and
any modifications that the Department requires for approval; or
if no decision has yet been made:the status of the review process; and
the anticipated date of completion.
A stormwater management plan is not valid until the plan has been endorsed and dated by the Department.
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