CORRELATION BETWEEN HYDROLOGICAL, GEOCHEMICAL AND MICROBIOLOGICAL PROCESSES IN GROUNDWATER-STREAM WATER MIXING ZONE Heejung Kim, Seong-Sun Lee, Yunjung Hyun, Kang-Kun Lee School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea ABSTRACT Stream water and groundwater can affect each other by sharing a hyporheic zone to degrade or improve the water quality. Hyporheic zone is the area where mixing and exchange of surface and groundwater occurs due to large chemical and hydraulic gradients. For the remediation of the contaminated groundwater, the natural attenuation by controlling the environmental factors has recently been studied widely. This study is focused on the characterization of the factors effective to the natural attenuation in hyporheic zones. In this study, vertical flow exchange (hyporheic flow) rates between stream and groundwater were estimated based on vertical hydraulic gradients measured at mini-piezometers of various depths. To investigate the biological natural attenuation potential, biological analyses using Cloning methods were performed in this study. In addition, partial correlation analysis between vertical flow exchange, nitrate concentration and microbial activity was roughly estimated. The featured correlation shows that there were significant effects of vertical exchange flux, nitrate concentration and microbial activity on the biogeochemical processes and natural attenuation of the site. Quantitative evaluation of the natural attenuation potential is greatly dependent on the accuracy of characterization of the hyporheic zone dimension and groundwater – surface water mixing rate. 1. Introduction  Site characteristics and hydrogeology Fig.1. Conceptual model of the groundwater recharge and discharge with hyporheic flow along a single stream (adapted from Riparian Areas) 2. Materials and Methods Fig.1. Location of the study site, and the layout of the monitoring wells and the piezometers. The location of the waste water treatment is also shown Fig.2. Functions of (a) comparative overview of the monthly rainfall and temperature (values for the 2007/2008/2009 period correspond to weather station, location of Munsan, (b) monitoring period temperature, Direct DNA extraction from soil samples Cloning*Sequencing PCR  PCR amplication of 16S rRNA gene and Cloning experiments 3. Results Bi-variate Plot of physico-chemical properties Partial correlations and associated statistics between flux, cell, can nitrate concentrations in study site 1. Hyporheic water flux shows seasonal variation and high water flux enlarges aerobic condition in hyporheic zone. 2. Microbial densities are influenced by concentration of contaminants and direction of hyporheic water flow. 3. Partial correlation analysis showed that cell density and concentration of nitrate are closely related with Flux. 4. Biogeochemical function of a hyporheic zone is predictable from examination of interaction among microbial activity, concentration of nitrate, and vertical exchange flux. 4. Conclusion This research was financially supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(grant number ). 5. Acknowledgement AUG SEP NOV AUG SEP NOV AUG SEP NOV Darcian Velocity (m/day) A clear seasonal difference in Darcian velocity at the hyporheic zone.