The following manufactured treatment devices (MTDs) have obtained interim approval by the Virginia Department of Environmental Quality and are listed on Virginia Stormwater BMP Clearinghouse as propriety best management practices (BMPs). In accordance with PFM § 6-0402.3B, manufactured BMPs may be used to meet the water quality control requirements of Stormwater Management Ordinance Article 4, subject to review and approval by the Director of Land Development Services (Director). Compliance with the total phosphorus (TP) reduction requirements should be demonstrated by manually inserting the Clearinghouse-assigned TP removal efficiency into the drainage area tab in the Virginia Runoff Reduction Method spreadsheet.
Subject to the limitations and conditions listed below, the Director has approved the following MTDs for use in Fairfax County:
- Aqua-Swirl® Stormwater Treatment System
- Continuous Deflective Separator® (CDS)
- Downstream Defender®
- First Defense®
- Stormceptor® OSR
- Stormceptor® STC
- Stormwater Quality Unit
- Terre Kleen™ Hydrodynamic Separator
- The Vortechs® System
- Dual Vortex Separator
- Baysaver BarracudaTM
- SciCLONE® Separator
- Aqua-Filter™ Stormwater Filtration System
- StormTech® Isolator Row
- Up-Flo Filter® with CPZ media
- The Stormwater Management StormFilter® with ZPG media
- BayFilterTM Stormwater Cartridge System
- Filterra Bioretention Systems
- Jellyfish® Filter
- Modular Wetland System Linear (MWS-Linear)
- Perk Filter
- The Stormwater Management StormFilter® with Phosphosorb media
- FocalPoint High Performance Modular Biofiltration System (HPMBS)
- StormKeeper™ Sediment Strip
- StormKleener™ Filter Cartridge System
- Kraken™ Filter
The use of the above devices is subject to the following:
- Each MTD must comply with PFM § 6-1321, and shall be privately maintained. A private maintenance agreement must be executed prior to plan approval.
- Pursuant to the PFM § 6-1321.2A, individual manufactured BMPs will have different site constraints and limitations and must be feasible and appropriate for use on a specific site. In accordance with the PFM § 6-0402.5, the Director may preclude the use of any BMP otherwise allowed, or require more stringent conditions upon its use, for a specific land-disturbing activity based on a review of the stormwater management plan and project site conditions provided such limitations are based on site-specific concerns.
- The manufacturer or manufacturer's representative shall verify, in the form of a letter or certification on the plan, that the size and proposed configuration of the MTD meets the manufacturer's sizing, design, and installation requirements for the product. The plan shall also include the manufacturer's installation requirements and maintenance recommendations, noting the intervals and methods for inspections and routine maintenance.
- Any MTD that is sized using a flow-based method shall be designed to treat the water quality peak flow rate calculated using the Modified CN method. The design procedure can be found in Chapter 11 of the Virginia Stormwater Management Handbook (July 2013) in Section 11.5.3. In no case shall the treatment capacity be less than the minimum required by Chapter 124 of the County Code or an instantaneous flow rate of 0.7 cfs per acre, irrespective of the land cover. Sizing computations must be included on the plan.
- Any MTD that includes an underground storage chamber used to attenuate peak discharges, when located in residential areas, shall be subject to the same restrictions as underground detention in residential areas per the PFM § 6-0303.6.