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The respondents added that the studies related to site specific assessment of seismicity, testing of fill materials for determining dynamic properties and detailed dynamic analysis, were carried out independently by two agencies; that they are the Department of Earthquake Engineering, University of Roorkee, and Hydro Project Institute (HPI), Moscow; that the result of their studies indicated that earth and rockfill type dams as chosen for Tehri are the safest man-made structures in earthquake prone zones due to their large inertia, high damping and high flexibility; that the dam fill material is being compacted to concrete like density, which provides high strength while retaining the flexibility; that relatively flat slopes have been adopted for up-stream and down stream of the dam, which are flatter than the slopes provided in some recent high dams built/ planned in regions of similar high seismicity; that, therefore, the Tehri Dam is a fail-safe structure and the design has been found safe against the worst earthquake scenario of the area, even when very conservative and severe seismic parameters were assumed for these tests. A high level Committee under the Chairmanship of Director General, Geological Survey of India, which consists members from Central Water Commission; Director, National Geophysical Research Institute; Head of Department of Earthquake Engineering, University of Roorkee, and Dr. V.K. Gaur, the then Secretary, Department of Ocean Development was also constituted to examine issues concerning safety of the dam. The Committee in its report established that even in the worst scenario of possible occurrence of a large magnitude earthquake of 8+ in richter scale with the probable location at a depth of 15 km below the dam site, the same would be safe. They concluded that dam design is safe and added that all danger arising out of the seismicity have been taken note of and taken care of in the planning of Tehri Dam project.

From the documents before us, it could be gathered that the Government also referred the matter to Seismic Expert, Prof. Jai Krishna who was the former President of International Academy of Earthquake Engineering and also Vice- Chancellor of the University of Roorkee. He examined the matter and opined that "the proposed dam section for the Tehri Project is safe from the point of view of seismicity of the region" and "since conservatism has entered at almost every step of decision making, the overall factor of safety of the dam is high enough to eliminate any risk from earthquake of the future." The next Expert Group that consisted of the Director General, Geological Survey of India, made a report on 25.7.1991 and recommended that the reports of the High Level Committee and the review given by Prof. Jai Krishna should be accepted. The seismic stability of the dam was further got tested through the Hydro Project Institute, Moscow, against actual acceleogram of the Gazli earthquake for the maximum vertical acceleration of 1.36g and horizontal acceleration of 0.72g both acting simultaneously and the dam design was again found to be safe. Even though the design of the dam had been earlier independently checked by two separate agencies, it was again examined and it was found that the project appears to be safe. Subsequently, during the pendency of this petition, in order to allay fears expressed in certain quarters, the Government of India in June 1996 appointed a Group of Five Experts to examine the relevant scientific and technical reports and other information relating to safety of the Tehri Dam and make its recommendations to the Government for consideration. In the selection of the experts Shri Sandra Bahuguna, who has been spearheading the movement against the construction of the Tehri Dam, was also associated and he recommended the inclusion of two engineers apart from the three seismologist. Thus the names of all the five Experts were suggested by Shri Bahuguna. The Group of Five Experts, after a detailed discussion on the various issues related to the seismic safety of the Tehri Dam, concluded that a comprehensive appraisal of the seismic safety of the dam required completion of the two key exercises by employing recent advances in conceptual and computational capabilities and they are, (i) quantitative estimation of seismic hazard at all the Tehri Dam site, and (ii) evaluation of the performance of the Tehri Dam as currently designed, if it was exposed to the estimated seismic hazard at the site. Accordingly, the Group of Experts got conducted the necessary exercises at their own decided parameters and methods. The Group also considered the International Commission on Large Dams Guidelines on Earthquake Analysis Procedure for Dams and Seismicity and Dam Design. Based on these materials the Group of Experts finally submitted the report on 18.2.1998. They concluded that the "present design of the Dam is expected to be structurally safe to withstand the maximum credible earthquake during the economic performance life of the dam-reservoir system." The Group of Experts was unanimous in their recommendation as stated above. However, as a matter of abundant caution, four Experts suggested (i) 3-D Non-Linear analysis of the Dam to evaluate its performance against the maximum credible earthquake and (ii) a simulated dam break analysis to ensure that in the unlikely event of an uncontrolled release of water, the consequences are minimum, be conducted. There was difference of opinion between the four Experts and the Fifth Expert only on the need to undertake these two additional studies as a matter of abundant caution. The Government of India, after receipt of the report of the Group of Experts, examined the further recommendation of the four out of five Experts in consultation with the Central Water Commission, which is a technical body of the Government and nodal agency in the country for planning and design of River Valley Projects who in turn referred the report of the Expert Group together with the need for carrying out the work recommended by way of abundant caution to the National Committee on Seismic Design Parameters which is a standing technical committee and it furnished its views. In addition, plethora of material has been placed by way of various text books and studies carried out by other agencies. We think that it is neither feasible nor proper for us to delve into these details. The Government of India, after considering the views thereof, finally decided that there was no necessity to undertake the work recommended further by the Four Experts by way of abundant caution and clearance to the project was given.

In the present case, we are not concerned with the polluting industry which is being established. What is being constructed is a large dam. The dam is neither a nuclear establishment nor a polluting industry. The construction of a dam undoubtedly would result in a change of environment but it will not be correct to presume that the construction of a large dam like the Sardar Sarovar will result in an ecological disaster. India has an experience of over 40 years in the construction of dams. The experience does not show that construction of a large dam is not cost-effective or leads to ecological or environmental degradation. On the contrary there has been ecological upgradation with the construction of large dams. What is the impact on environment with the construction of a dam is well known in India and, therefore, the decision in A.P. Pollution Control Board case will have no application in the present case." [at pp. 727-728] Aspects Related to Conditional Clearance Before adverting to other issues, certain aspects pertaining to the preservation of ecology and development have to be noticed. In Vellore Citizens Welfare Forum v. Union of India, [1996] 5 SCC 647, and in M C Mehta v. Union of India, [2002] 4 SCC 356, it was observed that the balance between environmental protection and developmental activities could only be maintained by strictly following the principle of' sustainable development.' This is a development strategy that caters the needs of the present without negotiating the ability of upcoming generations to satisfy their needs. The strict observance of sustainable development will put us on a path that ensures development while protecting the environment, a path that works for all peoples and for all generations. It is a guarantee to the present and a bequeath to the future. All environmental related developmental activities should benefit more people while maintaining the environmental balance. This could be ensured only by the strict adherence of sustainable development without which life of coming generations will be in jeopardy.

4. Measures to prevent and minimise impact on health.

5. Safeguards against ill effects to the seismicity.

6. Ways of saving translocated wild plants and animals.

7. Proving alternative fules to project labour and ladders for migrant fish to cross over the dam.

The Tehri Dam Project has obtaind a clearance and a major portion of the dam has already been constructed. The catchment area has not been filled with water as the two diversion channels having gates have not been closed for filling the dam. This is the right stage when there is necessity of close monitoring, evaluation and reappraisal of work to ascertain compliance of the conditions and check adverse impact on environment as also ensure rehabilitation of the people displaced from the dam area and the old Tehri town. In the instant case, the Corpration claims that it has fulfilled the conditions pari passu with the engineering works. This high claim is with the admission that the time Schedule in the condition of clearance has not been kept up. This is the proper stage when a thorough assessment by a team of experts in relevant branches is required to be undertaken for ascertaining whether the conditions of clearance have been fulfilled pari passu with the engineering works. If this is not done before the dam is allowed to be filled, adverse impact caused on environment would be irreversible and would not be compensated because of the severe scale of the ecological intervention. The mistake that might have been done in the past with regard to other similar large and small dams should not be allowed to be repeated in the Tehri Dam Project which is different from other dam Projects in plains. Tehri dam being located in the Himalayas the adverse environmental impact would both be up-stream and down-stream. Meticulous care and precaution, therefore, is required to be taken for a dam which is being constructed on a high altitude area posing threat to downstream population. If the safety aspects are not fully taken care of and the command area treatment is not done to the desired level or standard, the consequence may be catastrophic and beyond repair.