SEWERAGE SYSTEM

Satus of Existing Sewerage System.

It was in the year 1880 when existing sewerage system was laid for a population of 16,000. sewage is carried through CI pipes of various sizes ranging from 100mm to 225 mm dia.  The total length of sewer lines, leading to 5 existing disposal sites namely Lalpani, Kasumpti, North Disposal, Snowdon and Summer Hill is 49564 m.  Unsewered areas are being served through as many as 52 Pail Depots.

Area Served by Sewer Network.

The existing sewerage network caters to needs of Central Shimla Chotta Shimla, Brockhurst, Khalini, Nabha Estate, Phagli, Tuti Kandi, Chakkar, Boileauganj, Summer Hill, Annandale, Kaithu and Bharari.

Municipal Sewer Bye-laws.

The Municipal Corporation (formulated during British regime) only permitted sewage from water closets (WC) seat into Sewer lines.  The Sullage was allowed to flow in drains, channelized for the purpose.  It was in the year 1936, that the sullage was permitted to enter the sewage system.

Existing System.

Century old Sewerage system has functioned satisfactorily.  Particular arrangements made in the system take care of the demands of hilly terrain.  The alignment of sewer line involve steep gradients which generate abnormally high velocities and twisting contours which necessitate the provision of numerous bends.  The disposal of excreta from the unsewered are made through Pail Deports connected to Sewerage network.

Sewerage Disposal Works.

Population of Shimla township, being scattered on different ridges, STP and disposal units have been provided at five different locations as under.

Lal Pani Disposal

Snowdon Disposal

North Disposal

Kasumpti Disposal.

Summer Hill Disposl.

Sewer lines laid in the Recent Past.

Certain areas have been provided with new sewer lines in the recent past.  All the lines have been accounted for in the design and no provision of sewer lines has been made in the estimate in place of these recently laid lines,.  The length of these lines is 694 m for 150mm dia and 4459 m for 100 diameter gives the details.

EXISTING STP WORKS

All the five existing STP works were constructed for the population of only 16,000 and consist of simple detention tanks.  The present sewage load is beyond the capacity of these tanks.  Moreover, with the extension of the urbanizable limits, the locations of the disposal points need to be taken beyond these limits at suitable locations for proper and safe disposal.

At present, no treatment of sewage is taking place at any of the disposal points and raw sewage is flowing near the disposal points resulting in heavy pollution, spoiling the environment and may pose a serious health hazard at the disposal point and downstream.

At several places, (the already worn-out and inadequate to cater to the either present population) the branch and trunk sewers are broken and sewage is not even reaching the disposal points thereby causing insanitary conditions. The environment is being subjected to a high level of threat.

AREAS LACKING SEWER NETWORK.

Many new areas along the present Municipal boundaries have been included in the Shimla urbanizable area, but underground sewage network has not been extended so far.  Such areas are Wild Flower Hall, Kasumpti, parts of Sanjauli, Totu, Jutogh, Tara Devi, Shogi and other adjoining areas that now falling under the urbanisable boundaries are without sewerage system.

LOCATION OF DISPOSAL WORKS.

Various parts of the town are located on different terraces and on different hill spurs.  The alignment of sewer lines and the setting of disposal works is therefore dictated by the topographic conditions of the town.  Due to hill terrain it is not possible to carry the waste water of the entire town to one place.  In the existing system, there are five disposal points located below different hill spurs.  Now with the extension of the urbanisable limits and inclusion of several new hill spurs as well as new areas of adjoining suburbs like Mashobra, Kukri, Jutogh etc. 14 new disposal points with STP’s has been proposed in the Sewerage Improvement Scheme of I&PH Department.  These are proposed keeping in mind the topography of the town.  The problem of ground water infiltration into sewers is absent in the project area as the ground water table is very low due to hilly terrain and nowhere in the sewer network ground water table is likely to be encountered.  The existing natural nallah/ Channelized drains take care of storm water, therefore only sewage and sullage constitute the total volume of sewer generated.

SEWERAGE CHARACTERISTICS.

Raw Sewage.

The quality of raw sewage is primarily domestic in nature as no industries are located in Shimla Urbanizable areas.  Therefore, the BOD of raw sewage has been assumed as 250 mg/I.  The standard of effluents as prescribed under Indian Standard 4764, “Tolerance Limits for Effluent Discharged into Inland Surface Waters, is given in the Appendix # 1.7.

Sewage Temperature.

Minimum Temperature of sewage during January 23rd to 25th, 1996 (winter period) observed by I.J. Raju & Associates at the existing disposal sites are given in Table # 39.

The other parameters that relate to the sewage effluents like Biochemical oxygen demand and Total Suspended Solids are assumed.  The assumption made is more than the tolerable limits prescribed by Government of India (cf. Appendix).

Sewage system is an essential urban utility and forms an integral part of physical planning. Sewerage system for Shimla was designed for a population of 18000 persons in 1880. The system continued for around 100 years without any augmentation. Population in the intervening period has increased to about 1,50,000. As a result, system has become grossly inadequate. Therefore, due to excess load certain portions have led to frequent leakages, causing environmental hazards and air pollution. The State Government has now taken steps to modernise the system to manage the city sewage and sullage efficiently for congenial environment of Shimla city. This milestone dream has been fulfilled by the financial patronage of OPEC and State Govt. Therefore, the city has now systematic and properly designed sewerage system and most areas are covered with necessary sewerage networks..