Practical application of groundwater recharge

Many groundwater recharge applications (Pyne 1995) can be easily identified; however, for simplicity, only the basic applications are briefly described here (Anderbouhr & Perez-Paricio

Table 10. Groundwater recharge uses of reclaimed water

Type of use

Specific use

Observations

Groundwater recharge

Direct recharge

Potable quality if treated for domestic uses

Pre-potable if other source

Indirect recharge

Through soil formations

Modified from Brissaud et al. (2005).

Modified from Brissaud et al. (2005).

1999). More than one of the possibilities mentioned can be true for the same application site.

Aquifer water levels recovery. This is by far the most typical cause of groundwater recharge: if the extraction patterns or the natural losses caused by human activities (e.g. river beds channelling, water abstractions, civil works) overwhelm natural recharge, the solution is supplying additional water flows to the aquifer.

Minimization of seawater intrusion. Injection-extraction barriers or just injection are used. As a consequence, the freshwater level can increase and the seawater-freshwater front can become stabilized.

Reclaimed water storage. The aquifer can be used for storage of reclaimed water or as a management facility to deal with uneven demands.

Storage facility for tap water. This function is usually performed for additional storage of tap water near the site of production and use. Although it is not fully accepted, the capacity of the aquifer to be used for advanced treatment to reclaimed water should not be forgotten.

Fighting against subsidence in areas where excess groundwater extraction is common.

Improvement of water quality by passage through the aquifer. Two possibilities are indicated: (1) when the quality of groundwater is defective (e.g. brackish) reclaimed water can improve the quality; and (2) the water which enters the aquifer receives additional treatment.

Tap water generation. This is usually performed when trying to improve 'natural' water that has been polluted. Several experiences have been described around the north of Europe (Paris, Dortmund, The Netherlands) and near Toulouse (south of France).

Wastewater reclamation. As described, natural systems can improve the quality of reclaimed wastewater.

Environmental improvements. The negative impacts of dams can be reduced, while not affecting the natural water bodies.

Technical and real-time problems

If water of a different quality from that existing in the aquifer is introduced, technical problems can appear arise, which are mainly related to the following.

Clogging by reduction of the surface infiltration capacity. Chemical, physical and biological problems appear. There are five main processes affecting the permeability on the surface: suspended solid retention; bacterial and algal growth; chemical precipitation; gas formation; and settled material compaction.

Pathogen presence. When viruses and bacteria enter the aquifer, a negative impact is produced, although there is discussion on the real origin of such organisms. There is a relationship between the hydraulic residence time and the elimination of micro-organisms in the aquifer; it means that long residence times favour the decontamination of water.

Organic matter and chemicals. The elimination of organic matter and chemicals in the aquifers is complicated and difficult, due to the lack of oxygen present. Reduction is mainly performed during passage through the vadose zone and not in the aquifer.

Social problems

Groundwater recharge needs to be accepted by society, which means that an adequate effort must be performed by the authorities to make the practice understandable to people. It is recommended that pilot studies are developed and demonstration facilities used before undertaking a full-scale procedure.

Tools for public acceptance are available to contribute to the success of the practice. Full and adequate planning should be prepared and implemented.

The economy of any project is paramount to guarantee the success, as well as adequate legislation to be followed by the managers of the facility.

Environmental problems

The definition of environmental problems associated with groundwater recharge using reclaimed water can be described using the environmental impact assessment tools. First of all, it is necessary to state that the distinction between 'environmental impact' and 'change in an environmental attribute' is that changes in the attributes provide an indication of changes in the environment. In a sense, the set of attributes must provide a model for the prediction of all impacts. The steps in determining environmental impact are: (1) identification of impacts on attributes; (2) measurement of impacts on attributes; and (3) aggregation of impacts on attributes to reflect impact on the environment.

The conditions for estimating environmental impact are measurement of attributes with (positive scenarios) and without (zero scenario) the project or activity under consideration at a given point in time. Consideration of the potential for impact if no action is taken, that is, maintaining the status quo, is called the 'no-action alternative' (the zero scenario, in other words).

While 'affected environment' describes the condition of the environment when the action is proposed to take place, the environment will not remain static over time. If a hypothetical 'proposed action' were implemented, the impact would be the degree of change over time if the action were taken, compared to the condition of the environment over the same span of time if the action were not taken. It should be noted that the impact would not be the proposed action over time compared to the ambient environment prior to the point of action.

For other alternatives, the comparison can be to the impacts of the proposed action or all alternatives can be compared to the no-action alternative. Both approaches are used; the only caution is to be consistent throughout the analysis and explain clearly which approach is used.

A difficulty is that data for a 'with activity' and 'without activity' projection of impacts are difficult to obtain, and results are difficult to verify.

In respect to the practical application, environmental impacts of recharge must be related to soil, water, air, flora and fauna, and partly to social, cultural and economic impacts. It should be noted that impacts can be positive or negative with respect to the environment. In Table 11 there is a description of both types of impact.

Control needs

Due to the fact that groundwater recharge is identified as being more hazardous than other reclaimed water uses (e.g. agricultural irrigation), there is the need to strictly control the whole procedure. There are two types of control: analytical, related to the quality of water that will enter into the aquifer formation; and legal, the control of the later uses of the recharged water (recovered water).

It is also necessary to establish differences, with respect to the degree of risk, between direct and indirect recharge. Direct recharge (i.e. making the water enter directly into the aquifer) generates more hazards than indirect recharge (passage through the soil and subsoil). There are usually rules and regulations on this (see above).

Apart from the controls stated in the regulations, the HACCP approach indicates the points where it is essential to perform controls (e.g. the effluent from the reclamation facility, the point of application or the point of recovery of the recharged water).

Apart from the pure controls, marked by rules and regulations, there is the need to establish the periodicity of sampling procedures. This can be stated by the standards or by good reuse practices. This control has a cost that must be fully considered when making economic calculations on groundwater recharge.

Table 12 shows a sampling pattern suggested by a draft version for a Spanish decree on reuse.

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