Abstract
The authors conducted the study to clarify the role of aquitard on nitrate in groundwater in Tsukuba upland and the slope. The groundwater flow pattern was primarily horizontal in the sand and gravel layer and vertical (downward) through the underlying aquitard with dark greenish gray color. Groundwater in the sand and gravel layer contained nitrate of 0.350-1.150mM and in the aquitard with dark greenish gray color did below 0.015mM. The groundwater flow pattern and the simple chemical mass balance showed that biochemical barrier such as denitrification led to the decrease of NO3- concentration in the silt and clay layer with dark greenish gray color of the slope. On the other hand, in the upland, the results of the measurement of electrical conductivity in groundwater and the observation of water level indicated that the clay layer with dark greenish gray color filled the role of hydraulic barrier.
