Groundwater contamination from waste management sites: The interaction between risk‐based engineering design and regulatory policy: 1. Methodology

This paper puts in place a risk‐cost‐benefit analysis for waste management facilities that explicitly recognizes the adversarial relationship that exists in a regulated market economy between the owner/operator of a waste management facility and the government regulatory agency under whose terms the facility must be licensed. The risk‐cost‐benefit analysis is set up from the perspective of the owner/operator. It can be used directly by the owner/operator to assess alternative design strategies. It can also be used by the regulatory agency to assess alternative regulatory policy, but only in an indirect manner, by examining the response of an owner/operator to the stimuli of various policies. The objective function is couched in terms of a discounted stream of benefits, costs, and risks over an engineering time horizon. Benefits are in the form of revenues for services provided; costs are those of construction and operation of the facility. Risk is defined as the cost associated with the probability of failure, with failure defined as the occurrence of a groundwater contamination event that violates the licensing requirements established for the facility. Failure requires a breach of the containment structure and contaminant migration through the hydrogeological environment to a compliance surface. The probability of failure can be estimated on the basis of reliability theory for the breach of containment and with a Monte‐Carlo finite‐element simulation for the advective contaminant transport. In the hydrogeological environment the hydraulic conductivity values are defined stochastically. The probability of failure is reduced by the presence of a monitoring network operated by the owner/operator and located between the source and the regulatory compliance surface. The level of reduction in the probability of failure depends on the probability of detection of the monitoring network, which can be calculated from the stochastic contaminant transport simulations. While the framework is quite general, the development in this paper is specifically suited for a landfill in which the primary design feature is one or more synthetic liners in parallel. Contamination is brought about by the release of a single, inorganic nonradioactive species into a saturated, high‐permeability, advective, steady state horizontal flow system which can be analyzed with a two‐dimensional analysis. It is possible to carry out sensitivity analyses for a wide variety of influences on this system, including landfill size, liner design, hydrogeological parameters, amount of exploration, extent of monitoring network, nature of remedial schemes, economic factors, and regulatory policy.