annexures - Indian Institute of Technology Roorkee

Guidelines for preparation of reports Under NRCP / NGRBAb) Actual Water Quality Of The River5.4 QUANTITY OF WASTE WATERFor sewers, a 30-year design perspective is proposed. Actual flows measured through fieldinvestigations should be projected for this period. Similarly for STPs and pumping stations,flows should be projected taking into consideration population of the respective design period.The figure arrived at, following the method given in paragraph 4.9, should be adopted if there isdiscrepancy between the two projections.There should be permanent arrangement for measuring discharge in drains.5.5 SEWAGE QUALITY FOR STP DESIGNPast experience indicates that normative values of parameters like BOD and SS have been takenfor influent sewage despite actual quality characteristics having been established through fieldinvestigations. Such considerations result in over design of STPs with higher cost implications.This must be avoided and actual influent quality with an appropriate mark up only beconsidered for design purposes. For adopting BOD levels above 150 mg/l, proper justificationmust be provided.Parameters for the quality of wastewater (Values of BOD and SS) shall be adopted on the basisof actual quality of wastewater incoming at STPs / sewage pumping stations under O&M in thetown / other towns in the vicinity, under similar situation. Such laboratory reports shall formpart of DPR.5.6 SEWERSLayouts of sewerage mains or sub-mains should be prepared maintaining minimum depths andshortest flow distances with laterals proposed in the DPRs. Gravity flows must be preferred overpumping mains as far as possible to minimize pumping costs.a) Sewers shall be designed crown meeting crown. Drops shall be avoided at junction points.b) The plans should show basic details such as GLs, contours, major drains, their points ofoutfall, diameter and invert levels of sewers provided, specially at junction points.c) Layout of trunk sewer should be properly highlighted and be shown bold on the plans andthe design chart.d) Type of subsoil strata up to sewer invert level, subsoil water table data and type of roadsurface over the proposed sewer alignments shall be mentioned in the L-section of theproposed sewer.e) Wherever it is not possible to generate self-cleansing velocity, flushing of sewer linesshould be carried out at regular intervals. The requirement and number of flushing vansavailable with the O&M agency may be reviewed and provision for the same, if required,may be made in the estimate to be submitted.f) Suitable bedding should be provided below sewers to safeguard them against possiblesettlement, as per the guide lines suggested in the Manual on Sewerage & SewageTreatment of CPHEEO.g) Soil investigation and test bores should be carried out at suitable intervals along the43