Use of Strontium Isotopes to Identify Buried Water Main Leakage Into Groundwater in a Highly Urbanized Coastal Area

Previous studies indicate that the local aquifer systems in the Mid-Levels, a highly urbanized coastal area in Hong Kong, have commonly been affected by leakage from water mains. The identification of leakage locations was done by conventional water quality parameters including major and trace elements. However, these parameters may lead to ambiguous results and fail to identify leakage locations especially where the leakage is from drinking water mains because the chemical composition of drinking water is similar to that of natural groundwater. In this study, natural groundwater, seepage in the developed spaces, leakage from water mains, and parent aquifer materials were measured for strontium isotope (87Sr/86Sr) compositions to explore the feasibility of using these ratios to better constrain the seepage sources. The results show that the 87Sr/86Sr ratios of natural groundwater and leakage from water mains are distinctly different and thus, they can provide additional information on the sources of seepage in developed spaces. A classification system based on the aqueous 87Sr/86Sr ratio is proposed for seepage source identification.