Hydrological appraisal of radioactive waste disposal site at PINSTECH

Hydrological investigation of Radioactive Waste Disposal Site at PINSTECH was carried out to check the effectiveness of the existing monitoring wells, identify the locations for new wells and suggest design of the wells for proper monitoring. For this purpose, five piezometers were installed. Soil samples of depth profiles were analyzed for grain size distribution. The soil texture is dominantly silty clay with minor fractions of fine sand and gravel. The strata do not vary significantly along the depth profiles. The hydraulic conductivity is extremely low. Therefore, the groundwater regime can be considered as an aquitard which is very suitable for disposal of wastes. From the data of piezometers/monitoring wells, Water-table contour maps and groundwater flow nets were prepared. These maps show that the existing monitoring wells are insufficient for surveillance of the site. Four additional wells are needed for more affective check of possible migration of radionuclides. Using the information on flow nets (hydraulic gradient, groundwater flow direction), proper locations of proposed additional monitoring wells have been selected and design of the wells (casing dia., depth, open area, slit size of the filter and grain size of gravel shroud etc.) has been suggested. (author)