(a) New development.
(1) ESD requirements. The planning techniques, nonstructural practices, and design methods specified in the Design Manual shall be used to implement ESD to the MEP. The use of ESD planning techniques and treatment practices shall be exhausted before any structural best management practice (BMP) is implemented. The approved structural stormwater management measures are listed in COMAR 26.17.02.08C and the County Procedures Manual. All stormwater management plans must be designed using the ESD sizing criteria, recharge volume, water quality volume, and stream channel protection storage volume criteria according to the Design Manual.
(2) MEP standard. The MEP standard is met when channel stability is maintained, predevelopment groundwater recharge is replicated, nonpoint source pollution is minimized, and regenerative step pool conveyance systems are employed to the extent possible on all public stormwater systems. Structural management practices may be used only if determined to be absolutely necessary.
(3) Overbank flood protection. Overbank flood protection (Qp) is required as specified in the County Procedures Manual.
(4) Extreme flood volume. Extreme flood volume (Qf) is required as specified in the County Procedures Manual.
(b) Redevelopment.
(1) Unless otherwise specified in an approved watershed management plan, the minimum control requirements for redevelopment are:
(i) reduction of existing impervious area by at least 50% within the limits of disturbance according to the Design Manual;
(ii) implementation of ESD to the MEP to provide water quality treatment for at least 50% of the existing impervious area within the limits of disturbance; and
(iii) use of a combination of (i) and (ii) for at least 50% of the existing site impervious area.
(2) Alternative stormwater management measures may be used to meet the requirements of this title if it can be satisfactorily demonstrated to the Department that impervious area reduction has been maximized and ESD has been implemented to the MEP. Alternative stormwater management measures include but are not limited to:
(i) use of an onsite structural BMP;
(ii) use of an offsite structural BMP to provide water quality for an area equal to or greater than 50% of the existing impervious area; and
(iii) use of a combination of impervious area reduction, ESD implementation, and onsite or offsite structural BMP for an area equal to or greater than 50% of the existing site impervious area within the limits of disturbance.
(3) If it can be demonstrated to the Department that all attempts to reduce impervious area, implement ESD to the MEP, and use alternative measures described in paragraph (2) above have been exhausted, then the following alternatives may be considered:
(i) watershed or stream restoration;
(ii) retrofitting an existing stormwater management facility, including existing BMP upgrades, filtering practices, and offsite ESD implementation;
(iii) a combination of ESD and an onsite or offsite structural BMP;
(iv) payment of a fee-in-lieu;
(v) a partial modification of the treatment requirements if ESD is not practicable;
(vi) using design criteria based on watershed management plans prepared by the County; or
(vii) implementing stormwater management practices to provide water quality control for 50% of the existing impervious area.
(4) The Department may consider the prioritization of alternatives in § 16-4-202(b)(3) after determining that it is not practicable to meet the 2009 regulatory requirements using ESD. In deciding what alternatives may be required, the Department may consider factors including, but not limited to:
(i) whether the project is in an area targeted for development incentives such as a Priority Funding Area, a designated Transit Oriented Development Area, or a designated Base Realignment and Closure Revitalization and Incentive Zone;
(ii) whether the project is necessary to accommodate growth consistent with comprehensive plans; or
(iii) whether bonding and financing have already been secured based on an approved development plan.
(5) Stormwater management shall be addressed according to the new development requirements in the Design Manual for any net increase in impervious area.
(Bill No. 58-10; Bill No. 74-11; Bill No. 65-17)