GROUND WATER VULNERABILITY ASSESSMENT OF THE APARAN AQUIFER, REPUBLIC OF ARMENIA, AND ITS REPRESENTATION IN A 3-D MODEL

摘要

The Aparan confined aquifer feeds the aqueduct supplying Yerevan's drinking water. Hydrogeologically, the terrain consists of an unconfined or water-table aquifer composed of recent alluvial-proluvial sediments, and a confined aquifer composed of Quaternary lacustrine-alluvial sediments. An assessment of the natural and bacteriological vulnerability of these aquifers was made, and a 3D hydrostratigraphic model was constructed. We have conducted the analyses according to depths to water level from land surface and the thickness of poorly permeable soils in the aeration zone. According to this method, the following types of soils have been distinguished in the cross-section of the aeration zone: (1) K = 0.1-0.01 m/day (loamy sand or fractured matrix rocks); (2) K = 0.01-0.001 m/day (loams or relatively confining matrix rocks); and (3) K < 0.001 m/day (clay or confining matrix rocks), where K is permeability (conductance). The quantitative assessment of the unconfined aquifer's vulnerability is being carried out when there is risk of bacteriological infection. This method is based on the downward time-of-travel to the groundwater, during which percolated bacteria or polluted water may reach the water table. The quantitative assessment of the confined aquifer's vulnerability that is nearest to the land surface is carried out on the basis of two parameters: total thickness of the overlaid soils that have slow infiltration rates (m_0) and the interrelation between level of above water-table (H_1) and established level of water of aquifer under study (H_2). A 3-D conceptual hydrostratigraphic model of the study area was constructed. As a result of evaluation, the unconfined aquifer was assessed as highly vulnerable, but the confined aquifer as protected by natural conditions.