GROUNDWATER MODEL FOR MANAGEMENT AND REMEDIATION OF A HIGHLY POLLUTED AQUIFER (ORGANO-CHLORINE COMPOUNDS) IN AN URBAN AREA, USING RADIOACTIVE TRACERS (~(131)I) FOR HYDRODYNAMIC PARAMETERS AND DISPERSIVITY MEASUREMENTS

摘要

The paper presents the methodology and results of a flow transport model (organo-chlorine compounds, mainly trichloroethylene, TCE). Pollution was discovered in 1989 and has been widely monitored in a medium sized Italian industrial town. It involved the contamination of areas where several wells of the municipal water system were located. The monitoring data showed that the source of the pollution was in the industrial part of the town, where a chemical plant is located. The breakdown responsible for the pollution was identified (industrial sewage pipeline damaged) so that the TCE mass lost in the aquifer (from 1988 to 1992) was accurately evaluated (252.3 kg). A numerical model was realized with the following aims:(1) to simulate the polluted area evolution (up to 2020), with and without remediation systems;(2) to define which other public wells would be reached by the contaminant from and to calculate the concentration versus time curves in these wells; (3) to define the maximum extension of the contaminated area in order to drill new wells as alternative sources of supply for the polluted area; (4) to define wellhead protection areas and the location of monitoring wells around public exploitation wells. Aquifer parameters were mainly evaluated using the radioactive tracer ~(131)I, by means of dilution point tests (single well method) and multiwell tests. The main results of the simulations were as follows: (1) the contaminant front will reach the public wells supplying the southeast part of the town and the concentration will be over potability limits (μg/L) in about five years; (2) the benefit of any remediation system (reasonable from the cost point of view) is appreciable but only partial, since the pollution is very widespread; (3) the leaky confined aquifer pollution is mainly due to the over-exploitation of the aquifer, causing strong depression of the piezometric surface (several metres below phreatic level) increasing leakage from the highly polluted phreatic aquifer.