Replacement of complete filter media of Rapid Sand Gravity Filter at

Amount

Supplying and stacking of filter media of graded gravel (pebbles) of sizes of density of above 1600 Kg/cum to be used as filter media shall be hard, durable, preferably rounded stone, free from clay, sand, loam and organic impurities of any kind, having average specific gravity of not less than 2.5, water absorption not more than 0.50% and conforming to IS: 8419 (Part-I) - 1977 and reaffirmed 2010 as per the direction of Engineer-in-charge at site.

Graded Gravel of size 40 mm to 60 mm

Graded Gravel of size 20 mm to 40 mm

Graded Gravel of size 10 mm and down graded

Laying of filter media of graded gravel (pebbles) of sizes to be used as filter media shall be hard, durable, preferably rounded stone, free from clay, sand, loam and organic impurities of any kind, having average specific gravity of not less than 2.5, water absorption not more than 0.50% and conforming to IS: 8419 (Part-I) - 1977 and reaffirmed 2010 asper the direction of Engineer-in-charge at site.

Graded Gravel of size 40 mm to 60 mm

Graded Gravel of size 20 mm to 40 mm

Graded Gravel of size 10 mm and down graded

Supplying and stacking of silica sand, dry, clean, washed of all impurities like vegetation, lime pieces etc. as per IS: 8419 (Part-I) - 1977 and reaffirmed 2010 as per the direction of Engineer-in-charge.

The shape, size and quality shall satisfy the following norms: a) Filter sand shall consists of hard, durable grains of silica, shall be of resistant quartz or quartzite and free from clay, fine particles, soft grains and dirt of every description. b) Effective size shall be 0.40 to 0.70 mm. c) Uniformity coefficient D60/D10 shall not be more than 1.70 nor less than 1.30. d) Ignition loss shall not be more than 0.70% by weight. e) Soluble fraction in HCl shall not exceed 5% by weight. f) The minimum silica content in sand shall be 90% g) Shall have an averge specific gravity of not less than 2.50 h) Wearing loss shall not exceed 3%

Laying of silica sand in layers of 15 cm thick for a total thickness of 70 cm complete in filter bed as per the direction of Engineer-in-charge.

Removing of old filter media from filter bed, segregating as per graded sizes, acid washing, cleaning, screening & stacking of serviceable materials etc. Complete as per direction of Engineer-in-charge.

Graded gravel of sizes and silica sand.