Numerical model of the behavior of chlorinated ethenes in a fractured, karstic limestone aquifer

Characterizing the transport and degradation of chlorinated ethenes in fractured aquifers, as well as the assessment of cleanup times, poses an extreme technical challenge. In the presented study, a method to analyze reactive transport and reductive dechlorination of chlorinated solvents in fractured aquifers is developed. A rough-walled parallel-plate model of nonlinear flow behavior is coupled with random-walk particle tracking, incorporating particle exchange between the mobile and stagnant zones, adsorption processes, and reductive dechlorination reaction pathways. The developed methodology, considering reductive dechlorination processes in a Lagrangian framework, is able to simulate the motion of particles affected by first-order network reactions, so that particles move according to their chemical state, affecting physical transport processes (advection, dispersion, mass-transfer exchange between mobile and stagnant zones). The developed model is applied to a case study of groundwater contamination in the industrial area of Bari and Modugno (Italy), where the limestone aquifer has a fractured, karstic nature. The steady-state distribution of the contamination by chlorinated ethenes from a source at a hot spot is obtained and compared with the observed scenario of contamination, in order to estimate the plausible transport and degradation processes and the mass loading at source. The study represents a valuable tool in deciding the role of natural attenuation as a treatment option, where the natural attenuation capacity of groundwater can be integrated with engineering methods in order to obtain site remediation.