11831 AIRPORT RD WHOLE SITE FILE 2020-01-21

• Treatment media retention time shall be at least 3 minutes. Downward flow filters are not acceptable alternatives. • Treatment media thickness shall be at least 19 inches from inlet to outlet. • Treatment media loading rate on the media shall not exceed 1.1 gallons per minute per square foot surface area. • Plant support media shall be made of a 3 inch thick moisture retention cells that are inert and contain no chemicals or fertilizers. The plant support media shall not be made of organic material and shall have an internal void ratio of 80 percent. Biofiltration Catch Basin Biofiltration catch basin for bioretention and filtration of stormwater shall use physical, chemical and biological mechanisms of soil, plant and microbe complex to remove pollutants typically found in urban stormwater runoff. The treatment system shall be a fully equipped, pre- constructed, drop-in-place unit designed for applications in the urban landscape to treat contaminated runoff from impervious surfaces. The dealer or manufacturer shall furnish to the Contractor all required engineering assistance required to place all bioretention filtration structure components in accordance with the approved drawings and these specifications. Each unit shall consist of a precast concrete container together with an underdrain system, filter media, plant material, and appropriate tree grate where applicable. Plant materials shall comply with the type and size required by the approved drawings and shall be alive and free of obvious signs of disease or shall be replaced. Bioretention filtration structure media shall be certified using approved procedures to meet or exceed the following performance criteria. • The filter media shall achieve a minimum infiltration rate equivalent to 80 inches per hour. • The bioretention filtration structure system shall remove an average of 80% total suspended solids and a minimum of 50% total phosphorous (tp) and shall have passed field monitoring and testing as per TARP and TAPE testing protocols, as reviewed, approved and certified by a third party accredited consulting firm or state agency. Concrete for precast unit shall conform to the following: • The wall thickness shall not be less than 5". In all cases, the wall thickness shall be no less than the minimum thickness required to meet loading requirements of the application. • The precast concrete unit shall be cured by an approved method. The unit shall not be shipped until the concrete has attained 85% of its design compressive strength. • The connections shall be provided to accept pipes of the specified size(s) and material(s). • The base and sides must be of monolithic construction. No cold joints will be permitted. Underdrain shall be SDR-35 PVC Pipe meeting the requirements of Section 9-05.12(1) of the specifications. Tree grate shall be standard grate as provided by Manufacturer with unit. Swift Green Line—Corridor Stations Special Provisions SP95 May 2017