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This article showcases the challenges faced in the Cayman Islands for the design and installation of a well-field in an aquifer, while preventing the degradation a freshwater lens. In the Cayman Islands, it is typical to abstract the saline water needed for reverse osmosis plants from deep wells and dispose brines into zones that are deeper than the location zones.

In this particular case, the low porosity cap rock of the Cayman Formation isolated effectively the freshwater lens from water circulation in the deeper part of the succession. The well-field abstracted saline water from an open zone below the cap rock of the Cayman Formation at a depth of 45–65 m, and disposed brine at a depth of 62–86 m, where the bottom of the brine disposal zone is highly cavernous.    

The plant became operational in 1998, and production capacity was doubled in 1999. The Lower Valley reverse osmosis plant has been operating successfully without adverse effects on the Lower Valley freshwater lens. This is evident by water quality data obtained from a network of monitoring wells designed to monitor the effects of the plant on the freshwater lens.

Jones, B., van Genderen, H. and van Zanten, T. (n.d.). Wellfield Design for a Reverse Osmosis Plant located over a Fresh Water Lens in Lower Valley, Grand Cayman, Cayman Islands. [online]

Available at:

Link

[Accessed 7 Feb. 2018].

This paper studies the control of seawater intrusion using numerical modelling. A coupled transient density-dependent finite element model was used for modelling seawater intrusion. Also, a new cost-effective method for effectively controlling seawater intrusion in coastal aquifers was presented. This methodology (ADR -Abstraction, Desalination and Recharge) involves abstracting saline water and subsequently desalinating it. This desalinated water is then used for domestic consumption while any excess desalinated water is recharged to the aquifer.

The numerical model was integrated with a genetic algorithm (GA) to simulate different scenarios to control seawater intrusion. The effects that different combinations of abstraction, desalination and recharge have on seawater intrusion were also simulated.

The main objectives of the model were to minimise:

- the total capital and operational costs of the abstraction and recharge wells and

- the salt concentrations in the aquifer.

The results showed that the proposed ADR system performs significantly better than using abstraction or recharge wells alone, as it is the least costly and results in lower salt concentrations in aquifers. From the study, it was found that the cost of the ADR system is about 50% of the abstraction only scenario and 25% of the recharge scenario. This is because the water needed for recharge is provided primarily from the treatment of abstracted saline water. Moreover, excess treated water can be directly used for other purposes. The other aspect of the system’s efficiency is about minimising the total concentration of salinity in the aquifer as it has reduced the total concentration in the system by 15%. This is due to the system’s capability of moving the aquifer transition zone further to the coast.

Numerical modelling and control of seawater intrusion in coastal aquifers. (2013). In: 18th International Conference on Soil Mechanics and Geotechnical Engineering. [online] Available at:

https://pdfs.semanticscholar.org/db85/1041116c39b47a614b8036af9c553118d13b.pdf [Accessed 1 Feb. 2018].

Salt water intrusion is the migration of saltwater into freshwater aquifers under the influence of groundwater development (Freeze and Cherry, 1979). The most detrimental effect of ground water depletion is the lowering of the water table. Saltwater intrusion also has an adverse impact on thee saltwater-freshwater interface. Methods for controlling intrusion vary widely depending on the source of the saline water, the extent of intrusion, local geology, water use and economic factors.

The proposed methodology of this study was to control saltwater intrusion through (ADR) Abstraction, Desalination and Recharge. The proposed methodology takes into account the interactions between the major parameters of an ADR system to control saltwater intrusion. These parameters include: soil/aquifer properties, well locations, well depths, and abstraction and recharge rates. An additional major parameter is the relation between abstraction and recharge rates.  However, this depends on the recovery rate (the rate at which freshwater is rising in a bore) and salinity (the concentration of dissolved salts in seawater) of the abstracted water.

An ADR system is capable of completely preventing saltwater intrusion because it increases the volume of fresh groundwater and decreases the volume of saltwater, while considering economical aspects, environmental impact and sustainable development of water resources.

Payal, Z. (2014). Innovative Method for Saltwater Intrusion Control. INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY, [online] 3(2). Available at:

http://www.ijesrt.com/issues%20pdf%20file/Archives-2014/February-2014/65.pdf [Accessed 31 Jan. 2018].

Nowadays, saline water pollution is increasingly becoming a major global issue, especially in urban coastal areas. Saline water pollution has major impact on human life and livelihood. It´s mainly a result of static fossil water and the dynamics of sea water intrusion. The problem of saline water pollution caused by seawater intrusion has been increasing since the beginning of urban population. The problem of sea water intrusion in the urban coastal area must be anticipated as soon as possible especially in urban areas developed in coastal zones.

In view of this, this review article aims to: (i) analyse the distribution of saline water pollution in the Semarang urban coastal area in Indonesia and (ii) analyse some methods in controlling saline water pollution, especially due to seawater intrusion in urban coastal areas. The strength and weakness of each method were analysed and compared. This analysis involved assessing the impacts that result from applying (a) different pumping patterns, (b) artificial recharge, (c) an extraction barrier, (d) an injection barrier and (e) a subsurface barrier. The best methods were selected on the basis of their possible development in coastal areas of developing countries. The results showed that artificial recharge and extraction barrier are the most applicable methods in the area.

Purnama, S. and Aris Marfai, M. (2011). SALINE WATER POLLUTION IN GROUNDWATER: ISSUES AND ITS CONTROL. Journal of Natural Resources and Development. [online] Available at:

http://jnrd.info/2012/10/10-5027jnrd-v2i0-06/ [Accessed 31 Jan. 2018].

Control of seawater intrusion through a series of injection-extraction wells was studied using a vertically integrated, two-dimensional, sharp interface model. The model is based on the Galerkin weighted-residual technique and has been tested against the existing analytical solutions. The model is then cast in terms of the non-dimensional parameters, and a series of parametric studies are conducted to obtain the characteristic curves for the cases of a seawater extraction barrier alone and its combination with the freshwater injection barrier. These curves could be used to assess the effect of variations in the input parameters on the position of the seawater-freshwater interface toe position.

Mahesha, A. (1996). Control of Seawater Intrusion through Injection-Extraction Well System. Journal of Irrigation and Drainage Engineering, [online] 122(5), pp.314-317. Available at:

Link

[Accessed 31 Jan. 2018]