Multivariate analysis of trace elements in shallow groundwater in Fuchu in western Tokyo Metropolis, Japan

A rapid increase in the use of ground source heat pump (GSHP) systems for heating and cooling of buildings potentially threatens to harm shallow groundwater quality. As a necessary preliminary step toward evaluating GSHP impact on shallow groundwater quality, this study used multivariate statistical analyses to investigate characteristics of trace elements in groundwater in Fuchu city in western Tokyo Metropolis. Water samples were collected twice a month from two aquifers at 30- and 45-m depths using four observation wells for more than a year. Concentrations of 14 trace elements (Li, B, Al, Cr, Mn, Fe, Ni, Cu, As, Se, Sr, Cd, Sb, and Pb) and Si as well as oxidation–reduction potential (ORP), dissolved oxygen (DO), electrical conductivity (EC), and pH were measured. All elements were under the environmental water quality criteria issued by the Japanese Ministry of the Environment. No clear seasonal trends were observed in the concentrations of 15 elements in groundwater. Principal component analyses showed the element properties were well characterized by three principal components (PC). PC1, which represents the more mobile trace elements in the groundwater, consisted of Li, B, Mn, Fe, As, and Si. PC2 included Al, Ni, Cd, and Sb, and represents ORP-insensitive properties. PC3 consisted of Pb, Cu, and Se, which are less mobile in groundwater. Samples collected from the same aquifer had high similarity in distribution and variation of the trace elements. This study proposes a useful statistical platform for assessing future effects of GSHP systems on shallow groundwater quality.