Aquifer Recharge (Systems Failure/Outages)

Primary reference(s)

USGS, no date. Aquifers and Groundwater. United States Geological Survey (USGS). Accessed 20 October 2020.

Additional scientific description

Groundwater is a finite but renewable resource. The amount of available groundwater is limited by the porosity and permeability of the aquifer, but it can be renewed by meteoric water or artificial recharge. Aquifers may be unconfined or confined. While the water table in an unconfined aquifer will be in hydraulic continuity with adjacent water courses, a confined aquifer may be isolated from adjacent watercourses by a capping of lower permeability strata. Consequently, meteoric recharge to unconfined aquifers is more direct and generally, depending on the thickness of the unsaturated zone, more rapid than to confined aquifers. Groundwater abstraction via water wells causes a reduction in the water table that is referred to as a cone of depression. Cones of depression are rarely truly cone shaped; the shape being influenced by aquifer permeability, which is rarely isotropic. If groundwater abstraction exceeds recharge, over-abstraction will result in aquifer depletion and potentially outages of supply. Outages can also result from damage to the abstraction well. This could be due to physical damage, for example, pipe fracture or physical blocking by a trapped object, such as a jammed pump. Alternatively, it might occur because of clogging of the permeable part of the well, most likely due to a form of geochemical precipitation. Derogation of supply can also be caused by abstraction from neighbouring parts of an aquifer, either for potable supply or dewatering for mineral extraction or construction. Physical changes to an aquifer and its permeability can be brought about by earthquake activity. More commonly, groundwater infrastructure may be prone to rupture or damage by ground shaking induced by earthquake or volcanic activity (US EPA, 2020).

Groundwater contamination can result from surface or sub-surface contaminants resulting from poor waste management, industry, mining and agriculture. Aquifer vulnerability to contamination reflects the extent of lower permeability materials that cover/ protect the aquifer. Potential contaminants include a very wide range of natural (volcanic) or anthropogenic chemical contaminants, as well as biological contaminants, such as Cryptosporidium (a microscopic parasite; Morris and Foster, 2000) and saline intrusion (USGS, no date).

Metrics and numeric limits

There is no internationally recognised definition of a groundwater aquifer or methods for assessing failure. An example of a metric is the Groundwater Directive 2006/118/EC to meet Article 17 of the European Water Framework (2000) (European Commission Environment, 2020). This states that, the definition of a groundwater body is its capacity to supply 10 m3 of water per day as an average or 50 persons or to support the ecological quality of a surface water body or groundwater dependent terrestrial ecosystem (UKTAG, 2011). Giordano (2009) reported that global groundwater extraction is in excess of 650 km3 per year, with India, the United States, China, Pakistan, Iran, Mexico, and Saudi Arabia collectively accounting for 75% of this total amount.

Examples of drivers, outcomes and risk management

According to Fienen and Arshad (2016) issues include seawater intrusion and groundwater depletion.

• Seawater intrusion has particularly affected groundwater quality in major coastal irrigation regions such as Queensland in Australia, Florida in the United States, the southern Atlantic coastline of Spain, and Lebanon.
• Groundwater depletion has been particularly experienced in southern and central parts of Asia, northern China, the Middle East and North Africa, North America, parts of Australia, and many localised areas in southern Europe.

Groundwater protection requires effective planning and monitoring for resource management with regular reviews and provision for additional resources to meet increasing demand to meet growing demands in the context of population growth, urbanisation and climate change (Bricker et al., 2017). Planning is more effective when supported by groundwater resource mapping (e.g., MacDonald et al., 2012). For zones that are prone to earthquakes, effective planning is required to avoid zones of high susceptibility, or mitigation through engineering, construction material selection and possibly ground improvement (US EPA, 2018).

Some countries, such as the UK define source protection zones that show the risk of contamination from any activities that might cause pollution in the area (Environment Agency, 2018).