1639SPECIAL STILLING BASIN

Coir Fiber Baffle will be measured and paid in accordance with Article 1640 -4. Payment will be made under: Pay Item Pay Unit Stilling Basins Cubic Yard

SPECIAL STILLING BASIN -1 DESCRIPTION Furnish, plac e and remov e special stilling basins as directed by the Engineer . The special stilling basin can be used to filter pumped water during construction of drilled piers, footing excavation or culvert construction. The special stilling basin can be used for sediment storage at the outlet of temporary slope drain pipes. -2 MATERIALS Refer to Division 10. Item Section Geotextile for Drainage, Type 2 1056 Sediment Control Stone, Standard Size No. 5 or 57 1005 Use geotextile and sediment control stone that is clean and without debris. Use a special stilling basin that is a water permeable geotextile bag that traps sand, silt and fines as sediment -laden water is pumped into it, or as runoff flows into it through the temporary slope drain pipe(s). Provide special stilling basin of a bag constructed to a minimum size of 10 f eet x 15 feet made from a nonwoven geotextile . Provide a sewn -in 8 inches (maximum) spout for receiving pump discharge. Sew the bag seams with a double needle machine using a high strength thread. The seams shall have a minimum wide width strength of 60 lb s. per inch in accordance with ASTM D4884. Construct the bag with a geo textile stabilized to provide resistance to UV degradation meeting Table 1639- 1. TABLE 1639 -1 GEOTEXTILE PROPERTIES Property Minimum Requirement Test Method Weight 8.0 oz/yd ASTM D3776 Grab tensile 200.0 lb ASTM D4632 Puncture 520 lb ASTM D6241 Flow rate 80.0 gal/min/sf ASTM D4491 UV Resistance 70.0% ASTM D4355 -3 CONSTRUCTION METHODS Install the special stilling basin(s), geotextile and stone in accordance with the plans and as directed by the Engineer . Place t he special stilling basin(s) on level ground. Construct the special stilling basin(s) such that it is portable and can be used adjacent to each drilled pier, footing and/or culvert, as required by the project commitments. T emporary slope drain pipe(s) or pump discharge hoses will be attached to the special stilling basin(s) to divert runoff or pumped effluent directly into the s pecial stilling basin(s). The special stilling basin may be cut to allow slope drain pipe to be inserted if needed and tied off tightly. The remaining sleeve or spout of the bag, if present, may be used to connect more than one special stilling basin in series as directed by the Engineer . If not used in this manner, the sleeve shall be tied off tightly to allow the bag to contain the effluent and force it to filter through the sides