llydrological Sciences-Journal-des Sciences Hydrologiques, 45(1) February 2000 ]_47

Sustainable groundwater management of the stressed Coastal aquifer in the Gaza region

ABRAHAM J. MELLOUL Hydrological Service, PO Box 6381, Jerusalem 91063, Israel

MARTIN L. COLLIN Hydrological Service, PO Box 57081, Tel Aviv 61570, Israel

Abstract This study proposes an empirical approach that can lead to the sustainable management of groundwater resources. This approach enables a comprehensive understanding of an aquifer, delineates distinct hydrological scenarios, and recom­mends a set of operational activities for each sub-region of the aquifer. The paper focuses on the Coastal aquifer of the Gaza Strip region which has been divided into three sub-regions. The southern sub-region (WSW) is classified as scenario "+a2", which indicates that it can be used as a multi-annual groundwater reservoir. The northern sub-region (NW-E) is designated scenario "~a2", where the recommended operational measures include injection of freshwater in wells and cleaning of the surface environment. The third sub-region (CSE), is classified as scenario "-b2", which requires severe management measures to correct both a negative hydrological and environmental situation. The approach also involves on-going monitoring of the aquifer, and can be considered as an empirical tool to provide preliminary guidelines for long-term groundwater management.

Une approche empirique pour la gestion à long terme des eaux souterraines: Le cas de l'aquifère côtier surexploité de la région de Gaza Résumé Cette étude propose une approche empirique aboutissant à des recommandations opérationnelles pour une gestion optimale à long terme des ressources en eaux de l'aquifère. La méthode développée consiste en une représentation des principaux scénarios éco-hydrologiques qui caractérisent les eaux souterraines et leur environnement. Pour simplifier le problème, un scénario des activités opérationnelles adéquates a été attribué à chacune des sous-régions de la région étudiée. Au titre de l'application, l'aquifère côtier de la Bande de Gaza a été divisé en trois sous-régions présentant des situations éco-hydrologiques différentes, chacune d'entre elles ayant des recommandations particulières. Le scénario "+a2" , dans lequel l'aquifère peut être utilisé comme réservoir opérationnel interannuel d'eaux souterraines a été choisi pour la sous-région sud (WSW). Le scénario "-a2", dans lequel les mesures recommandées consistent principalement à injecter les eaux potables directement dans les puits tout en diminuant les sources de pollution du milieu environnant a été choisi pour la sous-région nord (NW-E) et le scénario "-b2", dans lequel les situations écologique et hydrologique sont critiques et où de sévères mesures de contrôle des sources de pollution et de la gestion des eaux souterraines doivent être envisagées, a été choisi pour la sous-région centrale (CSE). Pour conclure, cette approche empirique qui implique une amélioration du réseau de puits d'observation, peut être considérée comme un outil de gestion qui met en relief les traits essentiels et les directives préliminaires nécessaires à la gestion à long terme des eaux souterraines.

INTRODUCTION

Rapid population growth and poorly planned agricultural and industrial land use near urban and coastal areas have often led to inappropriate building development and

Open for discussion until 1 August 2000

148 Abraham J. Melloul & Martin L. Collin

general hydro-ecological imbalances. The soil and vadose zone have often been disturbed by channels, or short-cut pathways, which significantly increase percolation rates from the ground surface to the water table, and reduce the time of arrival at the aquifer of pollutants applied at the surface (Lerner, 1997). In arid zones such processes may be enhanced (Goldenberg et al, 1997; Zoller et al, 1998).

Groundwater has gained increasing attention as a source of water supply owing to its relatively low susceptibility to pollution in comparison to surface water, and its relatively large storage capacity. However, in the absence of water resource manage­ment based upon sustainability, overexploitation of groundwater resources can exceed their natural potential, so lowering groundwater levels. In confined aquifer layers, especially where recharge is weak, this can lead to deterioration of the aquifer matrix, involving subsidence of aquifer layers (Castany, 1982; Zammouri & Besbes, 1994). In coastal phreatic and semi-phreatic aquifers, overexploitation along the seashore will draw saline water from the sea into the aquifers. Inland, radial hydraulic gradients may develop creating internal circulations which increase the salinity and pollution of major portions of these aquifers (Goldenberg & Melloul, 1994a). Thus, uncontrolled land-use activities, and overexploitation can lead to deterioration of groundwater quality and quantity (US EPA, 1990; Ford et al, 1992; Heatwole et al, 1992; Hrkal, 1992; Cox et al, 1996; Howard et al, 1996). This results in an increasing gap between the supply available and the demand for drinking water, the continuation of which reduces the scope for feasible solutions and the time for implementation of remedial activities.

Therefore, long-term planning of land use and groundwater management are required to ensure a sustainable groundwater resource and maintain the water supply required for future human and life-nurturing utilization, whilst enabling maximal demographic, commercial, and industrial development.

Enlightened management must consider the wider hydrological significance of an aquifer and present environmental characteristics vis à vis acceptable groundwater table levels and groundwater quality standards (US EPA, 1990; Fiirst, 1995; Schultz & Hornbogen, 1995; Smithers & Walker, 1995). Use of appropriate guidelines can result in planning which minimizes short-term adverse impact, while providing long-term strategies controlling pollution sources and groundwater resources management with the appropriate regulations and enforcement to enable on-going sustainable aquifer utilization (Schultz & Hornbogen, 1995).

This study focuses on the Coastal aquifer of the Gaza region, which is particularly stressed. The empirical approach attempts to achieve a better understanding of the various components of the aquifer, its groundwater properties, and the environment influencing it. A scheme was used to classify each sub-region of the aquifer according to its hydrology and environmental conditions, so enabling recommendations of measures for maintaining sustainable levels of high-quality groundwater.

METHODOLOGY

Decision making for sustainable water resource management necessitates clear insight into the hydrogeology and the environmental situation of the aquifer, as well as an accurate grasp of the economic, political and social milieu. This study focuses only upon the former. The main steps of this methodology consist of taking a conceptual

An empirical approach to sustainable groundwater management 149

view of the aquifer, assessing its hydrology and the environmental pressures on it at a local scale, determining which of a set of hydrological scenarios it fits and, thus, the operational measures to recommend for sustainable groundwater resource management. The flow chart (Fig. 1) illustrates the three basic stages of this process: the development of a multi-disciplinary databank, the assessment and integration of the available information leading to assigning hydrological scenarios, and so recommendation of operational activities.

Multi-disciplinary databank

Figure 1 summarizes the types of data to be included in the databank.

Assessment and integration of data

The aquifer and its environment Geographical and geological considerations include use of data derived from geological maps and cross-sections. These enable assessment of the relative vulnerability of groundwater resources to pollution in light of the characteristics of the unsaturated zone and the degree of aquifer confinement (US EPA, 1985; Van Stempvoort et al, 1993; Secunda et al, 1996).

Hydrological assessment determines the groundwater resource potential and quality relative to desired values or mandatory standards. Environmental assessment focuses upon the degree to which stress from pollution sites results in a positive (low pollution) or negative (high pollution) scenario.

Overview of the aquifer The geological and geographical information is integrated with the hydrological assessments to develop a comprehensive understanding of the aquifer. Its degree of confinement, dimensions and geometry, and its actual situation relative to desirable water table and groundwater quality standards are considered. This stage enables the division of aquifers into operational sub-regions for definition of their hydrological scenarios (Fig. 1).

Delineating hydrological scenarios The third substage integrates the comprehensive, hydrogeological perspective of an aquifer with its environmental assessment. The combination of hydrological and environmental considerations for each sub-region are based upon groundwater levels and water quality, in the context of the positive or negative environmental situation at the ground surface (E+/-), as shown in Fig. 2.

The hydrological situation is characterized by the actual water table level (Ha), relative to the desired level (Hj), which is likely to be the level in this portion of the aquifer during the initial stages of aquifer exploitation, or that corresponding to an optimal steady-state situation indicated by aquifer modelling and simulation (Melloul & Bachmat, 1975). Groundwater quality (GQa) may be expressed by a variety of chemical, physical and biological parameters, as each relates to desired drinking water standards (GQd). In this study, only chloride and nitrate levels have been used. The environmental situation (E) is assessed by such parameters as the density of pumping wells, human population, the number of sewage ponds and waste disposal sites per

150 Abraham J. Melloul & Martin L. Collin

km , etc. The environmental situation of an area can be considered positive (E+), or negative (E-), depending whether the area is relatively free of, or suffers from, pollution.

Eight possible hydrological scenarios are illustrated schematically in Fig. 2. Four involve a positive environment (E+), and four a negative environment (E-). For each

1. Multi-disciplinary data bank

X Geology & geography: Soils Lithology Stratigraphy Aquifer geometry Vadose zone Topography Drainage basins

_̂ _

Hvdrology: Depth to water table Direction of groundwater

flow Conductivity Groundwater quality Groundwater quantity Early warning signals

of contamination and water depletion

Rainfall recharge

Environment: Potential pollution sites:

industry solid waste sanitary treatment oil spillage & drainage agriculture:

pesticides, herbicides irrigation with treated

effluents

Assessment and mtegiation of data

Geology & geography Vulnerability assessment of

unsaturated zone: Drastic, Electre, etc.

Degree of confinement

Hvdiology Groundwater potential: hydrological ratings

vis-a-vis desired ratings (HJd, GQa) of saturated zone

Envnonment Positive or negative

ecological ratings: E+/E-

Global uev, ot the aquifer and its division in

sub-iegions or units of works

r 3. Recommended operational activities

Fig. 1 Flow-chart of procedure leading to decision making for sustainable water resources management.

An empirical approach to sustainable groundwater management 151

environmental situation, scenarios al and a2 indicate that groundwater quality in the sub-region meets water standards (GQa > GQa), and scenarios bl and b2 indicate that groundwater quality in the sub-region is lower than desired water standards (GQa < GQd). These scenarios are further subdivided on the basis of head or water table levels (Ha). These may be either equal to, or exceed a desirable level (HJ) in scenarios al and bl , or be below this level, as in scenarios a2 and b2 (Fig. 2).

Recommended operational activities for each scenario

After determining the scenario of a sub-region, the third stage (Fig. 1) recommends activities which may have relatively immediate as well as long-term beneficial impacts upon the aquifer. Figure 2 indicates various activities recommended for each scenario. In the short term, this may include activities such as: pumping (P); recharge (R); maintenance of the status quo (M); treatment of effluents, groundwater or the environment (Et); or environmental land-use prohibitions (Ep). Long-term approaches could necessitate new regulations to maintain the environment (Em), hydrological research (Hr) or drilling of new wells mainly to enable exploration of deeper layers (Wd).

Recommendations for a positive environment (E+) In a positive environment, land-use guidelines and prohibitions should be implemented to maintain and protect the favourable conditions at the ground surface. Where groundwater levels and groundwater quality in the sub-region exceed desired values (scenario +al represents

a

b

a

b

E+

GQa > GQd

GQa < GQd

E-

GQa > GQd

GQa < GQd

1

Ha > Hd

Pd, Wd, Ep, M

Po.n.t. Hr, W d *

Ha > Hd

Pd, Hr, Ep, Wd

D C M •o . t i t p , t , n r

2

Ha < Hd

Pd,n, Ep, M, Rsw

fo .n i '"'r, 'M.s.w

Ha < Hd

Pd,n, Hr, EPit, Rw

EP i t , Rt,w> H r

E: environment at the ground surface (anthropogenic input); +: positive situation; - : negative situation; GQ: groundwater quality; H: water table level; a: actual situation in the study area; d: desired situation (water level, water quality standard and environment); *: ideal situation.

Recommended measures P = pumping; Pd: for drinking; P,: for treatment; Pn: only if necessary. R = Recharge; Rs: surface; Rw: well; Rt: after treatment (desalinization etc.). M = Maintaining the current situation. Ep = Environmental land-use prohibitions. E, = Environmental treatment. Hr = Hydrological research. Wd = Well drilling.

Fig. 2 Hydrological scenarios and recommended measures.

152 Abraham J. Melloul & Martin L. Collin

the ideal case), these conditions need to be maintained while freely pumping for drinking water. The aquifer can thus be used both for abstraction and as an on-going long-term groundwater reservoir to which recharge with freshwater either at the surface, or directly into wells, may be envisaged. Scenario +a2 differs from scenario +al in that pumping of water for drinking purposes might have to be restricted due to low water table levels. Simultaneous recharge of freshwater is thus recommended to improve the situation from +a2 to +al.

Scenarios +bl and +b2 occur where groundwater quality is below the desired water standards. For scenario +bl, recommendations include pumping water for subsequent treatment to bring it to drinking water standards. For scenario +b2, additional freshwater could be recharged either directly into wells or at the ground surface. Such fresh water could include desalinated seawater or brackish aquifer water, rainfall drainage, or imported water.

Recommendations for a negative environment (E-) Where environmental conditions are negative, emphasis should be placed upon improving the unfavourable conditions, especially those directly surrounding the area of abstraction (Fig. 2). For scenario - a l , abstraction for drinking water can be carried out, very carefully and under close monitoring, until the early warning signs of groundwater contamination appear. In the case of -a2, higher quality water can be recharged directly into wells, for short periods, to maximize the potential abstractable groundwater.

In scenario - b l , water may only be abstracted if the demand for the water is critical. Abstraction must be very careful in order to mitigate any adverse impact upon neighbouring areas. In scenario -b2, severe measures must be taken. These may include high level treatment of water, and if necessary, imposition of environmental quarantine measures to prevent pollution spreading to neighbouring areas of the aquifer where abstractable water remains.

APPLICATION TO THE GAZA COASTAL AQUIFER

The Gaza region is a prime example of an aquifer suffering from over-abstraction and under stress due to land-use planning and management. It is a typical case study for implementing an approach for sustainability management.

Hydrological and environmental assessment of the Gaza region

The Gaza region is located in the southwestern portion of Israel's Coastal aquifer (Fig. 3). The aquifer is granular, composed of layers of dune sand, sandstone, calcareous sandstone, and silt, with intercalated clay and loam lenses. The clays which separate the aquifer into sub-aquifers are thicker near the coast, thinning out towards its eastern edge, ~5 km from the sea (Fig. 4). The aquifer lies over a base of marine clays and shales of Neogene age (Fink, 1970; Galai, 1973; Melloul & Bachmat, 1975; Tolmach, 1991).

Abstraction estimates for the Coastal aquifer in the Gaza region are based on data from about 1800 wells, an average of seven wells per km2, a high density compared to the northern portions of Israel's Coastal aquifer, where the average is half that (Fig. 3).

An empirical approach to sustainable groundwater management 153

r V Israel!

Gsi» Strip Segton^/ f)

Fig. 3 Location map of the Gaza strip region and its sub-regions.

Most exploitation is limited to the upper sub-aquifers. Exploitation of the aquifer's eastern region is relatively small (Melloul & Bibas, 1992; Israel Hydrological Service, 1989). Between 1970 and 1992, 70-100 x 106 m3 year"1 of water was pumped in the Gaza region. The recommended abstraction rate (as noted in Melloul & Bachmat, 1975) is -55 x 106 m3 year"1. Over the last twenty years, the extent of over-abstraction has decreased slightly. This is due to new methods of irrigation (changes from canal to drip and sprinkler irrigation), and a reduction in the number of wells pumped because of increased groundwater salinity levels and management decisions encouraging use of groundwater for drinking purposes at the expense of irrigation usage.

Despite this, groundwater quality in the area continues to deteriorate, as shown by changes in nitrate and chloride levels and other parameters (Table 1). Pollution sites, over-use of pesticides and fertilizers, the cesspools used as reservoirs for agricultural irrigation, insufficient control of industrial and domestic land use and a lack of effective effluent treatment facilities (Fig. 3) all have a significant impact on groundwater quality (Melloul & Bibas 1992; Juanico et al, 1992; Goldenberg, 1992; Magaritz et al, 1992).

Near the coast, overexploitation has led to seawater intrusion, increasing the salinity of the groundwater and reducing the storage capacity of the aquifer. This situation, and the utilization of the groundwater resources beyond the potential renewal

154 Abraham J. Melloul & Martin L. Collin

Fig. 4 Hydrogeological cross-section of Coastal aquifer in the Gaza Strip region.

Table 1 Means and trends of selected hydrological parameters in the Gaza Strip aquifer between 1970 and 1993.

Parameter Water table* Chlorides*

Nitrates

Surfactants

Mean range level

1.50-2.00 (m) 400-610 (mgF1) 25-383 (mg l"1)

0.1-2.5 (MBAS)

Trend 1970-1993

-0.06 (m year"1) 6 (mg T1 year"1)

No. of observations

24 36

388

3

* Based upon representative well data for the period 1970-1993. T Based upon data for the period 1988-1990. * Anionic surfactants data (from Juanico et ai, 1992).

capacity of the aquifer, have resulted in a general environmental malaise and a significant reduction in available drinking water in the Gaza Strip region (Melloul & Collin, 1994).

Following the transition to Palestinian Autonomous government, increase in water consumption and changes in land use are expected to exert additional stress upon the groundwater resources (Palestinian Water Authority, 1996). The groundwater quality problem is thus likely to be exacerbated rather than reduced. An improved comprehensive and detailed understanding of the aquifer is thus necessary to improve its management (Figs 3 and 4, Table 1).

The aquifer and its sub-regions

A conceptual model of the aquifer indicates that freshwater along the aquifer's western border is bounded by seawater, and that its base is underlain by subterranean water of salinity higher than seawater. Along the eastern and southeastern borders, fresh groundwater is in contact with saline groundwater (1000-2000 mg l"1 chloride) of the Eocene aquifer (Fink, 1970; Melloul & Bachmat, 1975). In inland areas, pollution from ground surface land use puts the aquifer's remaining freshwater at risk.

Based upon these geographical and hydrological data, and the conceptual model of the aquifer, the Gaza Coastal aquifer has been divided into three sub-regions (Fig. 3).

An empirical approach to sustainable groundwater management 155

The northern area (NW-E) located between hydrological strips 98-100 and within columns 0-5; the central southeastern area (CSE) located between hydrological strips 87-98 and within columns 0-7, and between strips 81-86 and within columns 2-7; and the western-southwestern area (WSW) located between hydrological strips 81-86 and columns 0-1 (Fig. 3).

The environment and hydrology of each sub-region is summarized in Table 2. In this study, chlorides are used to represent salinity problems and nitrates to indicate pollution by agriculture and domestic usage. Drinking water standards stipulate an hydraulic gradient of about l%o in water table levels—a head of around 1 m per km from the seashore. The desired groundwater quality values are 250 mg l"1 for chlorides and 70 mg 1"' for nitrates, that is levels higher than internationally accepted standards (WHO, 1993). Parameters such as the number of pollution sites (Fig. 3) and the density of wells and population (Table 2) were included in the assessment of these areas, smaller values indicating a more positive environment.

Table 2 Data regarding sub-regions of Gaza's Coastal aquifer involved in this study until 1993.

Sub-region of Environmental situation of the sub-region: Groundwater Groundwater quality: Gaza region A r e a Density of Urban population levels above or a N03

(km2) wells density below desirable (rngF1) (ragf1) (wells/km2) (inhabitants/km2) level* (m)

North: NW-E 64 8 1800 0(1 to-2)

Central and 265 10 2000 0.5 (-0.2 to 5) southeastern: CSE West 36 4 500 0 (-1 to 0.2) southwest: WSW * average (range given in parentheses).

The NW-E sub-region In the NW-E sub-region the water quality is very close to the permissible limits for drinking water. Water tables are lower than the desired natural levels of the 1930s, before intensive pumping began. Environmental stress on the aquifer can be seen in the high abstraction rate and the urban population density.

The WSW sub-region This sub-region is located mostly along the coast of the southern portion of the Gaza Strip (Fig. 3). This aquifer contains freshwater of relatively good quality. Chloride and nitrate levels are mainly below permissible drinking water standards. Water table levels of around 0 m (a.s.l.) are below desired levels. Environmental stress is low to moderate, as expressed by both lower abstraction and urban population density.

The CSE sub-region The groundwater in this sub-region is very saline, with mean chloride levels of around 700 mg T1 (range 300-1000). Average nitrate values are similar to those of the NW-E area, and within permissible limits for drinking water. Water table levels of around 0.5 m (a.s.l.) are lower than desired. The degree of environmental stress is apparent in the very high abstraction and urban population densities.

150 90 (50-300) (60-200) 700 90 (300-1000) (50-300)

150 70 (50-300) (30-200)

156 Abraham J. Melloul & Martin L. Collin

Scenarios and recommended operational activities for each sub-region

As shown in Table 2, the larger central and southeastern portion of the Gaza aquifer (CSE), and the northern area (NW-E) are characterized by a high stress, or negative environment scenario. Only in the WSW sub-region is the scenario characterized as a minimally stressed, and consequently a positive environment. To simplify the process and presentation, only one scenario has been attributed to each sub-region. Use of Fig. 2 in conjunction with the data in Table 2 enables delineation of major scenarios with appropriate optimal management activities (indicated inside the boxes of Fig. 2) to typify each sub-region or portion of the aquifer as follows.

NW-E sub-region (-a2) Here, key management activities consist of abstraction for subsequent treatment, including dilution with fresh imported (or desalinized) water. Recharge should be carried out by injection of treated water directly into the aquifer by wells. In addition, research is required to enable management decision making as to the emplacement of abstraction and/or recharge wells. Management activities should include land-use controls, prohibitions, and remedial measures to alleviate pollutant sources by means of clean water legislation and enforcement.

WSW sub-region (+a2) The key management activities proposed are operational measures to improve the situation from scenario +a2 to +al (the ideal scenario for maintaining continuous pumping for drinking water). Stringent environmental land-use guidelines and prohibitions should be implemented. Thus, the aquifer should be recharged with freshwater, by well injection and also from the surface. The objective is to give high priority to measures for mitigating pollution from land use, and through increased recharge to raise groundwater levels. This would enable use of the sub-region as a multi-seasonal underground reservoir for water storage during droughts. Intervention is important because, once an aquifer deteriorates, as noted at Superfund sites in the USA, remediation is excessively expensive, very complex, and sometimes impossible to realize (Travis & Doty, 1990; Goldenberg & Melloul, 1994b).

CSE sub-region (-b2) The recommended management activities include most of those advised for the previous case. In addition, hydrological and land-use constraints must be applied, to reduce adverse impacts upon surrounding sub-regions. However, due to the severity of the situation of some portions of this sub-region, stringent environmental measures such as high level treatment, desalinization, and even quaran­tine of some portions may be considered to mitigate the environmental conditions and their potential effect upon groundwater.

For more detailed operational measures more specific scenarios must be delineated. This can be done only by use of additional data and sophisticated models to reduce the sub-region into smaller work units.

DISCUSSION AND CONCLUSIONS

Management strategies

The study area involves a phreatic coastal aquifer, which can be considered as a lens of freshwater impinged upon laterally by sea water, and/or salty brines and/or brackish

An empirical approach to sustainable groundwater management 157

water, and from above by pollutants percolating from anthropogenic sites. This lens of fresh groundwater must supply water for the continuing development of agriculture, allowing for pollution sources and the increasing demand for additional drinking and domestic water (Palestinian Water Authority, 1996). The comprehensive view of the aquifer indicates the need for more careful and rational management activities which may include stringent environmental guidelines, as well as appropriate legislation, regulations and enforcement.

Based upon this approach, it appears that high priority management activities should be implemented in the CSE sub-region to mitigate and prevent the spread of contamination from this area to surrounding ones. However, owing to the importance of preserving, and maintaining groundwater storage for times of drought and for the future needs of the area's population, the WSW sub-region, characterized by a positive scenario, must be considered as the highest priority. Stringent measures must be applied to maintain it not only for supplying water resources for present drinking needs, but so that this portion of the aquifer can operate as a multi-annual and seasonal operational underground reservoir. This can be accomplished by injecting water, using wells and surface application, to replenish supplies and to prevent saline up-coning and mitigate adverse trends to safeguard the reservoir for future needs. Additional fresh­water is needed urgently to augment and maintain reserves. This can be achieved by importing water from non-conventional sources, such as desalinized sea and brackish water, importing freshwater from abroad, etc. In addition, the monitoring network must be improved, to enable recognition of, and mitigation of the early signals of aquifer contamination.

Aquifer management should correspond closely to the existing field situation. In the case of the Gaza region of the Coastal aquifer, abstraction mainly involves the uppermost layers of the aquifer (around 10 m below the water table), whilst in deeper layers, more saline water may be present. Therefore, management activities ought to be conducted carefully so that pumping of the upper sub-aquifer layer of the aquifer will not lead to up-coning of saline layers from below. Long-term management decision­making should examine both the lower and deep sub-aquifers, delineate areas where freshwater remains, and improve field monitoring and other management activities.

Measures for future improvement

Improved management requires further development of the multi-disciplinary databank to facilitate the decision-making process outlined in Fig. 1.

The importance of a clean environment must be recognized. Varied surface environmental conditions call for different water management approaches, even when groundwater conditions are similar. Where anthropogenic input to the ground surface is still relatively inoffensive, ground surface recharge and abstraction of freshwater are both possible without damaging the nature and the carrying capacity of the unsaturated zone. However, where high levels of pollutants percolate from the ground surface, the unsaturated zone becomes contaminated, and possibilities of remediation are restricted within a normal budget (Travis & Doty, 1990). "Pump and treat" is then an adequate solution for recharging freshwater and treated water directly into wells for maximal benefit.

158 Abraham J. Melloul & Martin L. Collin

It is recommended that a denser monitoring network should be installed to allow early identification of the warning signals of contaminant spread into the adjacent aquifer area. This is especially critical where polluted water is in close proximity to areas having high quality drinking water resources, and where the aquifer can still be utilized as a multi-annual reservoir for groundwater storage.

If the situation reaches a critical stage, the process of rehabilitation of aquifers becomes more complex, expensive, and not always efficient. Then, an order of groundwater management priorities is necessary to attain rapidly feasible solutions. Priority management measures should lead to operations which rectify problematic situations for each unit work area, in accordance with their scenario classification. Interaction between disciplines and between neighbouring aquifer sectors can mitigate adverse trends as early as possible, before deterioration of the aquifer and neighbouring sectors causes remediation to become practically impossible.

To operate more efficiently, the surface area of each work unit should be reduced. This can lead to more focused operations, enabling a more logical prioritization to flow smoothly from one stage to the other towards sustainable development.

A necessary condition of sustainable groundwater development is linked with the education and quality of life of the local population. Where quality of life and education levels are high, full understanding and agreement of society with respect to present and future objectives would be required as regards individual and societal needs, the desirability of a clean environment, as well as the advantages of industrial and commercial development of a region, country, etc. Where the quality of life is low, individuals and small population groups are passive. In this case, only government initiatives towards education, legislation, and enforcement may prove necessary to effect long-term environmental measures for sustainable management.

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Received 5 January 1998; accepted 16 September 1999