GROUNDWATER PROTECTION*)

An effort to maintain sustainable development and environmentally sound management of groundwater resources in Indonesia

by : Soetrisno S.

1. Introduction

Groundwater resources have contributed substantially to the clean water supply in Indonesia. Groundwater has been utilized for many centuries, particularly shallow groundwater for domestic purposes. Deep groundwater had begun to be developed since the middle of the 19th century, when a deep well was successfully drilled in 1848 at Fort Prins Hendrik, a fortress in Batavia (presently Jakarta). Since then deep wells have become the means of providing water for many purposes in other parts of Indonesia. At present, groundwater is a major source of water for urban, rural, industrial needs, and in agricultural areas for irrigation.

In the development of the country, the rate of groundwater exploitation has increased enormously. Population growth, increase in the quality of life, and industrial development have led to the rapid increase of groundwater exploitation from private wells in urban areas. For example in 1970 Jakarta consumed less than 10 million m3/year of deep groundwater, which tripled in 1987.

At present about 70 % of the total clean water supply rely on groundwater, whereas industry relies nearly 100 % of its water need on groundwater resources.

On the other hand, increasing groundwater exploitation has already caused negative impacts on the resources itself, both in quality as well as quantity and to the adjacent environment. In coastal areas such as Medan, Jakarta, Semarang, Ujungpandang, and Denpasar, sea water encroachment has led to the deterioration of the groundwater quality, while land subsidence phenomena are recorded in the Jakarta basin. The changing environment as a consequence of rural development has also brought undesirable effects such as deterioration of the groundwater quality.

Realizing the role of groundwater in supporting national development, firm efforts should be taken to conserve this natural resources.

The lowering of the water level both of the shallow and deep groundwater system in Indonesia due to groundwater exploitation is the direct impact, which can be easily observed through observation wells in many groundwater basins. In the nineteen sixties, the static water level of the deep groundwater in many groundwater basins was generally near or above the surface. At present, the above condition has changed, and the water level has dropped far below the ground surface.

The general condition of the water level in 1990 as recorded from several observation wells in areas where groundwater has already been exploited intensively, showed that the groundwater level lies between 20 - 40 m below the surface. Observations in the last ten years showed that the deep groundwater level declined 1 - 3 m/year in most parts of the groundwater basins, such as in Jakarta, Bandung and Semarang. This condition has considerably changed the recharge and discharge situation in many groundwater basins during the natural stage, when discharge quantities did not yet exceed recharge quantities. Recharge from rainfall infiltration replenished the shallow aquifer during the rainy season. When upward leakage from the deeper aquifer system could enter the shallow system.

The actual situation which developed due to overexploitation of the deep groundwater system would be that discharge quantities frequently mostly exceed recharge quantities, resulting in the decline of the groundwater level. The deep groundwater level (piezometric head level) is generally below the phreatic head (shallow groundwater level) of groundwater. Consequently recharge to the deep aquifer system happens also by vertical downward leakage.

The implication of the above situation is that the deep aquifer system is at high risk to pollution from the above system, while the decline of the water level due to overexploitation will change the hydraulic gradient, thus triggering the speedy movement of the pollutants from above to the deeper groundwater system. In coastal areas, such condition has led salt water intrusion into the fresh groundwater system. Land subsidence phenomena are recorded in Jakarta, with rate of subsidence in the range of 23 to 246 mm/year. Over exploitation of groundwater apparently is the major cause of this subsidence.

Contamination of shallow groundwater by domestic waste has been recorded mostly in urban areas, as a result of poor drainage and sewerage. The high content of chlorides of over 500 mg/l and the presence of nitrites indicate that groundwater has been contaminated.

High population density in most of the urban areas, the limited extent of a central sewerage system and inadequate treatment facilities for sewerage water, form a high risk in groundwater contamination due to infiltrating domestic waste water particularly to the shallow system.

In some urban areas, where domestic waste dumping sites are not located in proper places, shallow groundwater has been contaminated.

Groundwater contamination derived from industrial waste mostly affect the shallow aquifer. Most of the industries have no effective treatment plant for their waste, they simply discharge their waste to the surface water bodies, leading to the contamination of the shallow groundwater.

Intensification of agriculture especially in the rice field influence the groundwater quality in particular by excessive fertilizer use and of pesticide residues transported into groundwater. High evapotranspiration from irrigated water may result in increasing salinity of the infiltrating return flow and subsequently to the groundwater.