Contaminated Sediment and Groundwater Discharge to an Estuarine River and Implications for Regulatory Compliance

摘要

This case study describes a remedial evaluation and feasibility study of a complex groundwater/sediment interaction in a tidal estuary in southern Australia. A detailed hydraulic characterization of the site was undertaken which considered the tidal dynamics. The characterization included the use of a series of transects of multilevel piezometers across the multilayered terrestrial aquifer system and across the remnant intertidal zone. Real-time dynamic water level monitoring was conducted which elucidated the response and interaction of the groundwater system to the tidal elevation. Seepage meters were used to measure the pore water discharge rates and also confirmed the hydraulic head data which inferred pore water discharge on the ebb tide and infiltration of seawater on the rising tide. Stable isotope data independently confirmed the existence of a mixing zone within the intertidal sediments confirming that pore water was largely of marine origin. The data from the field characterization was subsequently used to calibrate a transient numerical groundwater model of the aquifer interaction with the tidal river. The calibrated model was then used to examine the implications of a number of potential remedial scenarios. The preferred remedial scenario was the removal of a 5 m wide zone of contaminated intertidal sediments and contaminated fill. The material would then be replaced with a clean buffer zone to allow for pore water discharge to meet regulatory levels based on the establishment of a suitable mixing zone in the absence of highly leachable contaminated sediments/fill at the site/river boundary.