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

Takeshi Saito,Dang Quoc Thuyet,Toshiko Komatsu,Shigeoki Moritani,Yuji Kohgo,Hirotaka Saito

doi:10.1007/s12665-015-5170-4

Abstract

Abstract 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.

Highlights

As a part of the effort to reduce electricity consumption and CO2 gas emission, the use of ground source heat pump (GSHP) systems for heating and cooling buildings has received a lot of attention recently as they are much more energy efficient than conventional air source heat pump systems (Komatsu 2012)
The water levels in the aquifers C1 and C2 behaved indicating that the two aquifers may be hydrologically connected at some points there is an apparent impermeable silt layer observed between two aquifers at the study site
This study used multivariate statistical techniques to characterize concentrations of 15 elements and standard water quality observed over a year in shallow confined aquifers in Fuchu city, the western suburb of Tokyo Metropolis

Summary

Introduction

As a part of the effort to reduce electricity consumption and CO2 gas emission, the use of ground source heat pump (GSHP) systems for heating and cooling buildings has received a lot of attention recently as they are much more energy efficient than conventional air source heat pump systems (Komatsu 2012). Groundwater hereby is viewed as a water supply resource, and as an effective heat source/sink. Understanding the controls and characteristics of the groundwater quality in areas where GSHP will be installed is essential to ensure sustainable GSHP use and to minimize the effect on subsurface environment from potential temperature changes. It is believed that a large city with ample groundwater, like Tokyo, has high potential for ground source heat 559 Page 2 of 14. The occurrence of trace elements in groundwater in Tokyo has still rarely been reported this has been an issue for a long time in many Asian countries such as Vietnam (Nga 2008), Cambodia (Luu et al 2009; Phan et al 2013), Bangladesh, India, and China (Akai and Anawar 2013)

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