New Stormwater Management and Sediment Control Requirements for Montgomery County

Date: August 4, 2010

On July 27, 2010, the Montgomery County Council passed a bill that revised the County's stormwater management and sediment control code. The stated purpose of the new ordinance is to bring local stormwater management practices - for development and redevelopment projects - into compliance with the Maryland Stormwater Management Act of 2007 ("the Act").1 The bill also incorporates the 2000 Maryland Stormwater Design Manual into the County Code. The ordinance is effective immediately.

Consistent with the terms and goals of the Act, the ordinance requires developers to use Environmental Site Design ("ESD") to reduce stream channel erosion, pollution, sedimentation and siltation. ESD is defined in the ordinance to include non-structural techniques "and better site planning to mimic natural hydrologic runoff characteristics and minimize the impact of development on water resources." Developers and redevelopers must use ESD practices to maintain 100% of the average annual groundwater recharge for the development site. The ordinance requires that applicants demonstrate that ESD has been "implemented to the maximum extent practicable," before structural best practices can be included in the stormwater management plan, such that all reasonable opportunities for using ESD planning techniques and treatment practices are "exhausted." Only when such a showing has been made, and only when "absolutely necessary," may structural techniques be employed to meet stormwater control requirements.

The ordinance and the Act instruct that developers must conserve natural drainage patterns, minimize impervious surfaces, and incorporate into their plans the use of green roofs, pervious pavement and other alternative surfaces.

Before the County Planning Board may approve a subdivision preliminary plan, the developer must submit a stormwater management and sediment control "concept" plan. No site plans will be approved by the Board without a stormwater management plan, which must also address sediment control. Plans must contain detailed information concerning the natural features and drainage patters, hydrologic calculations of ESD and unified sizing criteria for each point of discharge from the site, as well as hydraulic calculations for each ESD practice and each structural management measure used. The ordinance contains additional requirements site drawings, as well. The amendment requires that developers must obtain easements from adjacent property owners if the management plan involves redirection of runoff to that owner's property.

The ordinance includes a grandfathering provision, which permits the Director of the Department of Permitting Services to issue waivers of the requirements of the ordinance to applicants whose development received preliminary approval from the Department of Permitting Services prior to May 4, 2010. Such waivers expire on May 4, 2013, unless the project has received final approval by May 4, 2013. In that case, the waiver may be extended to May 4, 2017. Waivers may be extended under particular circumstances described in the ordinance. The ordinance also permits waivers of the on-site stormwater management requirement, if ESD is employed to the maximum extent practicable. According to the ordinance, "the standard [maximum extent practicable] is met when channel stability is maintained, predevelopment groundwater recharge is replicated, nonpoint source pollution is minimized, and structural stormwater management practices are used only if absolutely necessary."

1. "Redevelopment," under the ordinance, means "[a]ny construction, alteration or improvement that: (a) equals or exceeds 5,000 square feet of land disturbance; and (b) is performed on a site where the existing land use is commercial, industrial, institutional or multifamily residential and the existing imperviousness is greater than 40%."