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The work covered by this section consists of the construction, maintenance, and removal of physical barriers placed in ditches, diversions, drainage turnouts, or swales to reduce water velocity and trap sediment.
The quantity of silt basin type-A devices to be constructed will be affected by the actual conditions which occur during the construction of the project. The quantity of type-A silt basins may be increased, decreased, or eliminated entirely at the direction of the Engineer. Such variations in quantity will not be considered as alterations in the details of construction or a change in the character of the work.
All materials shall meet the following requirements:
Perforated C.S. pipe tee riser Section 320
Sediment Control Stone Section 1005
Silt basin type-A devices shall be constructed as shown on the plans. The silt basin type-A basins shall be constructed at the locations shown on the plans and at other locations directed by the Engineer.
The Contractor shall construct earth dikes and overflow spillways, and install outfall pipe, perforated tee-riser sections, trash racks, and anti-flotation devices in silt basins where shown on the plans or as directed by the Engineer. The Contractor may use either anti-flotation method shown on the plans.
The earth dikes shall be constructed with 2:1 side slopes with material suitable for and meeting roadway embankment specifications. The height of earth dikes shall not exceed 12 feet. Excavation may be required to provide minimum surface area and/or minimum storage volume area measured below the top of the principal spillway (top of the riser pipe).
The silt basin type-A perforated C.S. pipe tee riser shall be installed as specified on the plans and as directed by the Engineer. The Contractor shall install 3/8 inch holes on 3 inch centers on the riser pipe and face the riser pipe with sediment control stone. The riser pipe shall have a trash rack and an anti-floatation device.
An overflow spillway, constructed on natural ground, shall be provided to control runoff that exceeds the riser capacity. The Contractor shall line the overflow spillway with Erosion Control Stone Class B when directed by the Engineer and/or as specified on the plans.
Upon installation of silt basin type-A, the embankment and surrounding areas shall be stabilized with vegetation.
1637-4 MAINTENANCE AND REMOVAL.
Silt basin Type-A shall be cleaned out when sediment volume reaches 50% of the storage volume and when so directed by the Engineer in accordance with Section 1630. To facilitate determination of maintenance cleanout requirement a marker should be placed in the basin indicating the 50% volume level.
Unless otherwise directed by the Engineer, silt basin type-A devices shall be removed as the project nears completion, or at such time the Engineer deems the device to be no longer useful. The actual time of removal shall be as directed by the Engineer. Upon removal, the Contractor shall dress the area to give a pleasing appearance, and shall seed and mulch the area in accordance with Section 1660.
Measurement for excavation will be made in accordance with Section 1630.
The quantity of perforated C.S. pipe tee risers to be paid for will be the actual number of tee risers which have been installed and accepted.
Payment for excavation will be made in accordance with Section 1630 of the Standard Specifications.
Payment for the outfall pipe will be made in accordance with Section 320 of the Standard Specifications.
Payment for the Sediment Control Stone and Erosion Control Stone Class B will be made in accordance with Section 1610 of the Standard Specifications.
The quantity of perforated C.S. pipe tee risers measured as provided for above will be paid for at the contract unit price each for ____ x ____ x ____ Perforated C.S. Pipe Tee Riser, ____ Thick.
No separate payment will be made for furnishing and installing the trash rack and for installing the anti-flotation device as payment at the contract unit price each for the item of ____ x ____ x ____ Perforated C.S. Pipe Tee Riser ___ Thick will be full compensation for such work.
The above prices and payments will be full compensation for all work covered by this section including but not limited to excavation, shaping of the basins or ditches, cleaning out and maintaining the basins or ditches, disposal of all materials, and backfilling. Paymentwill not be made for any work performed under this section that is solely for the convenience of the Contractor or that is made necessary due to negligence of the Contractor.
Payment will be made under:
Silt Excavation Cubic Yard
Sediment Control Stone Ton
___ x ___ x ___ Perforated C.S. Pipe Tee Riser ____ Thick Each