integrated coastal zone management project west ... - Iczmpwb.org

187indirectly to the Bay of Bengal and to the Canal besides Digha Bypass. The existing kachhadrains will be lined.230. The technical specifications are as follows:i) Type of drain – Brick built open type surface drainii) Base of drain – PCC 100mm thick to be laid on 1 layer of brick flat solingiii) Side walls – Brick masonry wall varying in thickness from 250 mm to 750 mm to beconstructed with burnt bricks having crushing strength 75 kg./cm 2 , bonded with sandcement mortar in 6:1 proportioniv) Finishing – The external surface and the top surface of the drain section will be finishedwith 20mm thick sand cement plaster in 1:4 proportion to be rendered with 1.6mm thickcement punning.231. So far the attempts to bring the entire city sewage of Digha Township under a STPhave not met with success due to level difficulties arising out of older dunes on which amajor portion of the Old Digha town had developed. During 2007-08 an attempt was madefor a pilot Bioremediation STP behind the Aparajita Cottages which was quite successful inreducing the BOD load and the outfall DO attained a concentration of 6.5 mg./l.232. Two numbers of aeration ditches in series will be created to have sufficient capacityto retain liquid wastes for 3 days with a buffer of 1 day. The outflow from the ditches will bemade to pass in 4 furrows intercepted by mangroveOne Storm W root zones which will actto reduce the septicity of water to the tolerance limit, through root zone absorption.The technical specifications as worked out are given below: Aeration ditches – 2 each of 3000 m 3 capacity Residence time – 3 days plus 1 day buffer Ridges and furrows – 4 each 0.9 m deep and 20 m long Clearing period – every 2 months Plants to be providedAeration pond – water hyacinth or duckweedFurrows – acanthus ilicifolius and sonneratia caseolarisRidges – minjiri (cassia siamea), eucalyptusCost233. The cost estimates are as follows:Rs in Lakhs1. Construction of storm water drains 1461.612. Construction of phyto-remediation of urban sewage system 32.11