A METHOD FOR ASSESSING THE FULL COSTS AND BENEFITS OF GROUNDWATER REMEDIATION

摘要

Economic analysis can be used to compare the real overall costs of pollution, including private costs (to the problem holder) and external costs (to society), and the benefits accruing from remediation and the avoidance of future damages. Overall decisions on the required level of remediation can thus be made with an understanding of the full economic ramifications, including the wider implications for the environment and society as a whole. Recognizing the need to include economic concerns in groundwater remediation decision making, the UK Environment Agency have recently published a research document which provides a method for assessing groundwater remediation alternatives. This framework is linked directly to existing UK guidance on risk assessment for contaminated sites. The method involves an iterative screening approach, starting with high level analysis of the costs and benefits of remedial objective options and the technical approaches which are best suited for reaching those objectives. The benefits analysis includes both private benefits, and if possible wider external benefits (often described as the value of damage averted by taking action). Valuation of external benefits of remediation is not straightforward, and can include the value of damaged resources, option values, and intrinsic worth (existence and bequest values). Often, only partial monetization of some benefits can be practically achieved. However, benefits can be compared with expected annualized costs for achieving overall specific remedial objectives, allowing a preliminary identification of the economically optimal objective. The framework provides a tool with which firms and regulators can negotiate a position that balances their respective concerns (social optimum against private optimum). Once the remedial objective has been set, and with it the most economically attractive approach, technology selection becomes merely a least-cost analysis. In many cases, the hidden costs of certain remedial objectives and approaches are revealed. This framework is applied to the problem of a contaminated manufactured gas plant (MGP) in the United Kingdom. The site was used for coal gas production from the turn of the last century until the late 1950's. Deep migration of coal tar NAPL into the fractured bedrock aquifer underlying the site has resulted in a significant dissolved phase plume. Risk analysis was used to identify and prioritize pollutant linkages, and the impacts on receptors were then quantified and monetized. A variety of remedial objectives are evaluated, and cost-benefit analyses conducted, using notional least-cost solutions, and partially monetized private and social benefits. The results show the variability in benefit-cost ratio which can occur when comparing widely differing remedial objectives, and the economic implications associated with the use of passive techniques such as natural attenuation.