State of water environmental issues
Groundwater is emerging as a large and generally untapped resource. However, there is very little monitoring of groundwater quality in Lao PDR, even though it is the main source of rural water supply. The study made by the Interim Mekong Committee (1986) observed that the country is divided into two geological areas: the Annamian Strata occupying most of northern and eastern part of the country and the Indosinian sediments mainly along the Mekong. There are three different aquifer systems:
- The Annamian aquifers occur randomly. These are local systems that discharge locally to the river or its tributaries. As local flow systems, they are not part of the regional flow system and will not carry pollution into the regional groundwater system. The potential water supply from groundwater in the northern part of the country is considerable in view of the high amount of recharge available. Water quality should be reasonably good and for the most part potable but will be iron rich. Yields up to 5 liters/sec can generally be anticipated.
- The Indosinian group of aquifers, which have regional flow, includes rock of the Indonisian Moyennes and Superieures and is relatively young. They are mostly freshwater sediments, although there are horizons of brackish water, and one major zone of saline water. Yields of 12-24 liters/sec can be developed.
- The alluvial aquifers associated with the sedimentary deposits of the Mekong River are not rated highly as aquifers.
Limestone in the Central Lao PDR is strictly Annamian in age, but its location places it logically in the Indosinian flow system. It has been described as having enormous groundwater resources.
To date the only regional assessment of groundwater potential is the on-going study of groundwater in the Provinces of Champassack and Saravane funded by JICA. There are, however, studies and use of groundwater at specific locations for urban water supply purposes, and several hundreds of wells have been drilled throughout the country mainly for rural supply but also for a few cottage and small-scale industries. Information relating to drilled wells for rural water supply generally includes a location sketch, depth of the wells, type of pump and ground water level. Geological logging and yields tests are only occasionally undertaken. The information of drilled wells for rural water supply is kept at the offices of the Provincial Rural Water Supply Center. In most cases, the depth of the rural water supply wells in lowland areas varies from 30 to 45 meters and the yields varies from about 1 liter/sec to less than 5 liters/sec.
The groundwater is and will probably remain the main source of potential rural and small town water supply, especially in lowland areas located far from the surface water sources such as the southern and western parts of Champassack Province, the hinterlands of the Senbangfay, Sebanghieng and Sedone valley. Anecdotal evidence suggests that poor sanitation and sewerage facilitiesare contributing towards the contamination of surface and groundwater.