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

Filter outlets shall be located in the inspection chamber and they shall discharge
into a common filtered water collection pipe /channel.
The filter structure shall have an adequate depth to provide 2.0 m water over sand
"The filtration work shall be designed for a water column of 2.0 in above the top of
sand bed to dislodge / discourage air binding and to ensure reasonable length of
filter runs.
Depth of sand bed shall be 0.75 m supported over gravel media of 0.60 m depth as
below.
21.14 Filter feed beds.
Range in Size mm Range in depth Cm
65 - 38 20
38 - 20 12
20 - 12 12
12 - 5 8
5 - 2 8
Total Depth 60 Cm
Inlet flows to the filters shall evenly be distributed along the length of the filter
battery through reinforced concrete settled water common influent channel, with a
suitable arrangement of submerged in-flows to enable the in-coming flows to be
automatically divided between the filters going to be used, and to allow for common
variable level of water on the filters beds going to be used. The feed channels shall
be appropriately dimensioned to keep turbulence and velocities with in the required
limits which shall not in any case exceed 0.6m /sec. Channels and associated
chamber floors shall be given slope towards the drains and drainage valves. They, if
necessary, shall be fitted with steps or step irons for internal access.
21.15 Filter sand.
Filter sand shall be free of clay, mica, shale, dirt, loam, organic impurities, and
water soluble and manganese. The weight loss on contact with 2N hydrochloric acid
shall be less than 2% after 24 hours. The specific gravity of the sand shall be
between 2.55 to 2.65.
DTS : Detailed Tender Specification. Page 250