ABSTRACT
Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. Subsidence is a global problem and, in the United States, more than 17,000 mi2 have been directly affected by subsidence. The associated costs from flooding and structural damage exceeded an estimated $125 million by 1991.[1] About 60% of the subsidence is attributed to permanent compaction of subsurface sediments caused by the withdrawal of underground fluids-groundwater, oil and gas.[1]
This article will discuss the single largest cause of subsidence-the compaction of susceptible aquifer systems resulting from groundwater pumping for water supply. Thus, the development of groundwater resources has had a major impact on the landscape and the increasing development of land and water resources threatens to exacerbate subsidence problems.[2,3]
MINING GROUNDWATER
The overdraft of susceptible aquifer systems has resulted in regional, permanent subsidence and related ground failures. In the affected alluvial aquifer systems, especially those that include semi-and unconsolidated silt and clay layers (aquitards), long-term groundwater-level declines created a vast one-time release of ‘‘water of compaction’’ from compacting aquitards, which manifests as land subsidence. A largely non-recoverable reduction in the pore volume of the compacted aquitards and of the associated storage capacity accompanied this release of water.
