All these cannot be achieved though project level EIAs alone. Available literature (Therivel et al. 1992, Lee and Walsh 1992, Glassan et al. 1994) suggests greater applicability of strategic environmental assessment (SEA) towards achieving the goals of environmental sustainability. There seems to be a general agreement that SEA is a 'promising' approach to ensure that policy making takes account of sustainability principles (Sadler 1994, Goodland and Sadler 1996, Wood and Djeddour 1992). Sadler (1994) outlined the building blocks of this 'emerging' model (Figure 2.5).

Canter (1996) considered SEA to be analogous with the programmatic EISs (PEISs) practised in USA. Although conceptually SEA may be seen as a tool for achieving sustainable development, the implementation of SEA is fought with both technical and procedural problems (Glasson et al. 1994). Moreover there is a near total absence of institutional arrangements in developing countries to allow SEA studies to be conducted effectively. According to Glasson et al. (1994) the problems of implementing SEA include the following.

* Future development activities showing great temporal and spatial variability leading to great analytical complexity.
* Limited availability of information about existing and proposed future environmental conditions.
* Near absence of information regarding the nature, scale and location of future development proposals.
* A large number of alternatives of diverse characters will have to be considered. This further complicates the assessment process.
* Because of the above problems, public participation becomes difficult and almost meaningless.

The above problems become further complicated because policy making being mostly a political process, the environmental implications of policies, plans and programmes may get lost against the politicians' own interest and the interest of their constituencies.

Apart from the above, perhaps the most significant difficulty in applying SEA towards achieving environmental sustainability goals is that the techniques and methods of SEA are still in the 'evolving' stage. Thus an absence of established method and process pre-empts inclusion of SEA as the primary theme of this study for achieving environmental sustainability.

Attention now, therefore, focuses on EIA in its conventional sense. Cumulative effects assessment (CEA) is a similar sub discipline of EIA which aims at studying the 'impact on the environment which results from the incremental impact of the action when added to other past, present and reasonably foreseeable future actions'. This study recognises CEA as a supplementary tool for informed decision making for environmental sustainability.

2.9 Environmental Impact Assessment and Sustainability at the Project Level
A conventional EIA mainly deals with the possible environmental consequences of a proposed or impending project and its various alternatives rather than how sustainable development objectives are likely to be promoted or impaired by the alternatives under consideration (Mikesell 1994). Any meaningful assessment of a project's compliance of environmental sustainability criteria will require a complete assessment of the role of the project in the context of all other economic activity. Such an assessment, in addition to requiring a huge information beyond the realm of project EIA, will involve macro economic analysis. Questions relating to optimal allocation of the total environmental source and sink capital normally do not fall within the purview of project EIA. However, compatibility of a project with sustainable development objectives can definitely be estimated through EIA studies. It is also possible to incorporate in project EIA the conclusions of an overall economic analysis in its relationship to environmental source and sink functions.

The input rule of environmental sustainability can be largely complied through preservation of productivity and full functioning of the natural resource base. By providing the future generations with the same natural resource capital, this will in part, fulfil the intergenerational equity criterion of environmental sustainability. Sustainability criterion may be applied to conventional project level EIA by measuring the impact of the project on the natural resource base and by including the negative impacts in the cost and the positive impacts in the benefit. All environmental damage costs (e.g., air pollution, water pollution etc.) must be internalised as costs of the project. In addition as suggested by Mikesell (1994), all natural resource depletion, such as extraction of minerals, must also be charged as social costs, while any addition to renewable natural resource stock should be added to the benefits. Apart from the two types of natural resources already discussed, viz., renewable and non-renewable natural resources, a third type - the life support resources may be recognised. Life support resources consist of all levels of the atmosphere, rivers, lakes and oceans, wetlands and ecosystems. While these resources, per se, can seldom be depleted their functions can be greatly impaired, - at times irreversibly, by human actions. Most of the environmental resources are not tradable commodities and hence they defy ready valuation. Environmental economists often argue in favour of valuing such resources in terms of services lost due to impairment of their functions.

Once the valuation problem is solved some ways and means may be devised to assess projects in conformity with environmental sustainability criteria. After the real costs of environmental degradation and natural resource capital depletion are properly calculated and internalised as a project cost component, the polluting and resource capital consuming project will cost more and highly polluting project may simply become unattractive because of high costs involved. Environmental Impact Assessment (EIA) may now reveal the total financial implications involved for the project to meet the environmental sustainability objectives. One of the principal shortcomings of present day EIA is that it does not reveal the full cost of resource depletion and environmental damage and thus the project costs are often under estimated and accordingly more often than not fund shortages are encountered for restoration and reclamation work.

It may be suggested that the environmental damage cost and the exhaustible resource depletion cost be counted separately. While the former may be used for protection, restoration and replacement of renewable resources, the later should be allowed to accrue in a fund so that the interest from the fund may be available to future generations to substitute for the exhausted natural resources. This of course, embraces the weak sustainability assumption that man made and natural resources are substitutable.