Reliability of hydraulic performance and cost estimates of barrier-supported pump-and-treat systems in heterogeneous aquifers

Addressing the need for cost-effective long-term groundwater remediation methods, pump-and-treat systems, supported by means of additional impermeable barriers, are proposed as a reasonable alternative to standard pump-and-treat systems. Compared to only pumping, the barriers yield a reduction of the pumping rate required to establish a certain capture zone. This paper presents the results of a comparative analysis of the hydraulic performance of both systems in heterogeneous aquifers and, based on that, an economic evaluation. Taking into account the fact that the description of heterogeneous aquifers is inevitably uncertain, the hydraulic analysis is based on Monte Carlo simulations which incorporate the reliability (probability of failure) of the specific pump-and-treat system. The reliability trade-offs obtained show that considerably less water has to be pumped (and treated) if an additional impermeable barrier is implemented. This joint economic evaluation reveals, however, that due to the additional costs for barrier installation, a barrier-supported pump-and-treat system is only advantageous if the unit costs for pumping and on-site treatment exceed a certain limit, which again depends on the degree of aquifer heterogeneity.