Northern Guam Lens (Lens) is the primary fresh water resource on Guam. A plethora of research has been conducted upon the Lens; generally, this research has focused on aquifer processes that occur at a monthly or annual time scale. The focus of this paper is analysis of data that was collected, in a collaborative effort between the Guam Environmental Protection Agency, the United States Geological Survey, and the Water and Environmental Research Institute of the Western Pacific at the University of Guam, between May 25, 2004 and February 20, 2005, at a finer time-scale. This paper will demonstrate how climatic stimuli affect the water table and salt - fresh water interface differently depending on the time-scales considered. Presented herein, are time series of measurements that describe the upper and lower Lens boundaries, climatic variables, and an analysis of the cumulative effects of these variables on lens geometry.

The results of the study clearly show that temporal variability in climatic conditions affected the distribution of both fresh water and salt water within the Lens. Large rapid fluctuations in the water table result from the onset and cessation of large rain events; whereas, more moderate rainfall result in a gradual rise of the water table during the early portion of the wet season. To the greatest extent the salt -fresh water interface was depressed during the study period. This was the result of the combined affects of a water table elevation fluctuation and sea level elevation decline. Large, short-term storm events tend to influence the upper portion of the salt - fresh water interface. Longer-term changes in the water table and sea level elevation influenced the entire salt - fresh water interface.