Structure Modifications

The Scope of work is for the construction of two detention basin retrofits (retrofits) located approximately 2-miles apart (by road) in Blue Ash and Sycamore Township, Hamilton County, Ohio. Both retrofits will involve installation of modifications to the existing outflow structures, and one of the retrofits will also involve installation of new rock structures. The scope of services associated with Retrofit 1 include: 1. installing a flow restrictor plate, onto the outside surface of the existing outlet control structure, covering the 12-inch diameter orifice as specified in the plans developed by SS; 2. expanding the existing 2.5-inch diameter orifice, located on the existing outlet control structure, to a 12-inch by 3-inch window orifice as specified in the plans developed by SS; 3. expand the size of an existing window orifice with an additional 18-inch by 3-inch window to the top portion of the existing window as specified in the plans developed by SS; and 4. replacing/modifying the water quality underdrain and aggregate rock layer as specified in the plans developed by SS. This involves 1) excavating, cleaning, and/or entirely replacing the aggregate to ensure it is free of sediment, organics, and other build up (aggregate not reused must be removed from the site), 2) excavating, cleaning, removing potential restrictions (e.g. a potentially clogged filter fabric?), and/or entirely replacing the 4” perforated underdrain, 3) grading to remove potential sediment build up and accommodate the new pipe section and relocated underdrain/aggregate, 4) installing two new sections of 10-feet of schedule 40 4” PVC pipe (one section unperforated with joint to connect to a perforated section per the drawings, and 5) installing the cleaned/new underdrain/aggregate at a relocated position as specified in the plans developed by SS. Retrofit 2 refers to work to be conducted within the Michelman Chemicals, Inc. detention basin located adjacent to Shell Road at 9080 Shell Road, Blue Ash, Ohio 45236. The scope of services associated with Retrofit 2 include: 1. replacing an existing flow restrictor plate covering the outflow pipe inside the existing outlet control structure, with a new flow restrictor plate as specified in the plans developed by SS; and 2. placing aggregate rock on the existing concrete channel, below the outfalls and down to the drain grate, and placing additional aggregate rock around the drain grate to form a rock check dam ring as specified in the plans developed by Sustainable Streams, LLC. Care must be taken to avoid rock installation work during wet conditions that could lead to rutting and compaction within or around the detention basin. Additionally, to minimize disturbance within the detention basin, rock installation work must be limited, as much as practical, to the area in the immediate vicinity of the concrete channel and outflow structure. Coordinating timing of rock installation with our native vegetation installation contractor may be required if fall planting is perused. Contractors with appropriate experience are encouraged to submit proposals for the native plant restoration work in addition to submitting bids for the structural modifications work.

Division 03 -	Concrete, Precast Concrete.
Division 33 -	Utilities, Storm Drainage Utilities, Storm Utility Drainage Piping, Storm Utility Water Drains, Storm Drainage Structures.