Groundwater field pumping out and tracer injection test had been carried out at Nghiem Xuyen commune, Thuong Tin district, Hanoi where salinized and fresh groundwater boundary exist in the Pleistocene aquifer. The test was executed with pumping out rate of 9l/sec and tracer injection rate of 0.7l/sec of water with the salt concentration of 5g/l. The interpretation and analysis of the groundwater solute transport parameters by the field pumping out and tracer injection test is a rather complicated and delicate task due to the variability of the temporal boundary conditions. The test results have shown that although the tracer injection time is rather long (up to 60 hours), the tracer breakthrough curve of the tracer concentration of the pumped out water has its very specific characteristic shape, however with some variation due to the test invisible variability of conditions. The results of the parameter identification based on the method of least squares have given effective porosity of 0.32 and longitudinal dispersivity of 2.5m (which give the hydrodynamic dispersion of from D=250m 2 /day right outside the pumping well screen to D=18m 2 /day right outside the injection well screen). The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119, which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.0355 (while 1 is the worse and 0 is the best). The results have also shown that the maximal tracer concentration right outside the pumping out well screen is 6.1 times greater than the tracer concentration of the pumped out water. The distortion flow coefficient αW (the ratio between the flow rate through the injection well section without its presence) and the groundwater flow into the tracer injection well is from 18.66 (at the early testing time) to 10.76 (at the later testing time).

hoạch và Điều tra Tài nguyên nước miền Bắc 3 Cục Quản lý Tài nguyên nước 4 Trường Đại học Khoa học tự nhiên-Đại học Quốc gia Hà Nội 5 Trung tâm Chất lượng và Bảo vệ Tài nguyên nước

Co To is an island of the Co To district in Quang Ninh province with an area of about 18 km2. Average rainfall on the island is 1,738.8 mm/yr, evaporation is 925 mm/yr. On the island, there are some small streams but they are temporary flow in the rainy season, there is not any natural lakes. There are 2 aquifers. The Quaternary aquifer (q) is distributed in a low terrain with area of about 9 km2, thin thickness and saline water is in about half of the area, so it does not make sense for water supply. The fissured aquifer of the ocdovic-silua (o-s) formation is distributed in the high terrain with an area of about 9 km2, this is low potential water layer. The flow rate in the boreholes in the fractured zone due to tectonic activity can be 1–1.5 l/s, it can satisfy small-scale water supply. Potential groundwater reserve of Co To island is 6,472 m3/day, exploitable reserve is 1941 m3/day, exploited reserve level at C1 range is 1,144 m3/day. This can satisfy the water demand for the living of people on the island today. Small-scale groundwater exploitation in the island has just been beginning, but it has the prospect of replication and at the same time there must be reasonable measures to protect and develop water resources to ensure sustainable development and meet the larger water requirements in the future.