PACKAGE : I Bid Document VOLUME : II - Public Health Engineering

21.16 Filter media and charging.
The Contractor shall supply the filter media for the works and shall submit with his
tender details of the source from which he proposes to draw his supplies of filter
sand and verify that sufficient tities of satisfactory filter sand can be obtained,
necked, stored on site and the filter shells charged in accordance with his work
programme, within two months of the date of acceptance of tender, the contractor
shall submit to the Engineer two-20 kg. Representative samples of the filter sand
(and also a sample of supporting media) one of which will be tested. When the sand
is found to be conforming to the above requirements and also with requirements of
the Contractor, which he shall submit with his tender, the second sample shall be
retained by the Engineer and the Contractor will then be given permission to place
an order for his supplies. Prior to packing, all filter sand shall be washed, heat dried
and sieved to confirm the specified grading and be tested. Separate test certificates
(in triplicate) shall be provided to the Engineer for each 20 cubic meter of media to
be supplied. Packing shall be in suitable approved double or triple bags to protect
the media from spillage or contamination. Any sand or media delivered loose or
found to be split or in open bags shall be rejected on site. Storage on site shall be
only in an approved, pre-designed area, well drained and free of mud and silt.
Following installation and satisfactory testing of all the filter floors and when the
Engineer is satisfied that installations floors and when the Engineer is satisfied that
the installations are complete, the Contractor will be given written permission to
commence filling the filters. The Contractor will set out and indicate the method of
filling the media in his tender submission and specification. Filter media shall be
carefully placed and not charged by dropping, dumping, machine handling or any
other method which in the opinion of the Engineer will be detrimental to the floor
media nozzles /drains of sealant. In each filter, two adjacent halves shall - be
charged simultaneously. Following the initial charging the filters shall be washed by
the Contractor. Filter beds, designed for expansion during cleaning, shall be
skimmed prior to disinfection and the commissioning of the works.
21.17 Expansion of sand bed.
Properly designed sand expansion gauge shall be provided to accurately determine
the correct percent of sand expansion and the proper washing cycle for each filter
bed. The sand should expand to about 130-150 percent of its undisturbed volume
during back wash. The pressure at which the wash water is applied is about 5 mt
head of water as measured in under drains.
DTS : Detailed Tender Specification. Page 251