NOBLE-GAS RECHARGE TEMPERATURES AND THE EXCESS AIR COMPONENT

The calculation of a groundwater recharge temperature based on the dis solved concentrations of Ne, Ar, Kr and Xe requires a correction for n oble gas supersaturation due to excess air entrainment. This entrainme nt is commonly attributed to the recharge process or to air contaminat ion at the wellhead during sample collection. With the exception of so me local studies, most work has concentrated on interpretation of the recharge temperature or quantification of the radiogenic content for p alaeoclimatic and dating purposes. The magnitude and source of the exc ess air is not directly relevant to these studies and so is often igno red. In this work, excess air Ne and other data have been calculated f rom new and published noble gas data sets for several groundwater syst ems. For younger groundwaters which have been recharged under one broa d climatic regime, the amount of air entrainment increases according t o lithology in the order granites, sandstones and limestones respectiv ely. A negative correlation between precipitation and excess air entra inment is identified in at least one aquifer, and some of the mechanis ms which may influence the entrainment process are discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.