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A Study on the Recovery of Head and the Total Dissolved Solids (TDS) from Long-Term Pressure Depressions in Low Permeable Coastal Aquifers

Studies on the recovery of head and total dissolved solids (TDS) in a coastal aquifer system from long-term pressure depressions because of groundwater abstraction (e.g., pumping) is essential for freshwater protection and seawater-intrusion prevention in coastal areas. A 2D numerical model is applied in this paper to investigate the recovery of head and TDS in terms of long-term behavior considering low permeability media. The spatial behavior of the transition zone (TZ), which was chosen as an indicator, was studied in depth with respect to the participant hydraulic and solute-transport characteristics of the aquifer. The sensitivity of the TZ to different aquifer parameters was evaluated. The hydraulic conductivity and rainfall recharge are the two most sensitive factors that affect the location of the TZ in homogeneous cases, and the spatial structure of the hydraulic conductivity field, namely, the correlation length and variance, largely influences the sensitivity of the TZ. The required time for the complete recovery of head in the heterogeneous cases is much shorter than that in the homogeneous cases, but the TDS recovery takes much more time. When the recovery of head is 90%, low porosity and large specific storage play an important role in the location of the TZ compared to other parameters, except for the hydraulic conductivity and recharge rate. The results of this study are meaningful for coastal-aquifer management and may be instructive in the restoration of coastal areas that have experienced seawater intrusion because of the long-term overexploitation of fresh groundwater.