Paleoclimate Signals and Groundwater Age Distributions From 39 Public Water Works in the Netherlands; Insights From Noble Gases and Carbon, Hydrogen and Oxygen Isotope Tracers. Issue 7 (16th July 2021)

• Record Type: Journal Article
• Authors: Broers, Hans Peter; Sültenfuß, Jürgen; Aeschbach, Werner; Kersting, Arne; Menkovich, Armin; de Weert, Jasperien; Castelijns, Jeroen
• Is Part Of: Water resources research. Volume 57:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-16
• Subjects: public supply wells -- groundwater age -- age distribution -- travel time distribution -- noble gases -- noble gas temperature -- graben structure -- tritium‐helium -- 4‐helium -- carbon‐14 -- 3He/4He ratio; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2020WR029058
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Knowing the age distribution of water abstracted from public water supply wells helps to ensure customer trust in drinking water sources and underpin predictions of water quality evolution. We sampled the mixed water of 39 large public supply well fields for major ion chemistry, 3 H, 3 He, 18 O, 2 H, 14 CDIC, 13 CDIC and noble gases and determined the Noble Gas Temperature (NGT). We used a discrete travel time distribution model to quantify the age distributions using 3 H, 4 He, 14 C apparent age and NGT as the 4 distinctive tracers. Helium‐4 and NGT provided information on the older part of the age distributions and showed that the 14 C apparent ages are often the result of mixing of waters ranging between 2, 000 and 35, 000 years old, instead of being discrete ages with a limited variance as previously assumed. The results reveal a large range of age distributions, comprising vulnerable well fields with >60% young water (<100 years) and well fields with >30% paleo groundwater (>25, 000 years) and all forms of intermediate distributions. The age distributions match the hydrogeological setting; well fields with age distributions skewed towards older ages appear in the Roer Valley Graben structure, where fluvial and marine aquitards and sealed faults provide protection from recent recharge. Waters from this graben exhibit paleoclimate signals, with a clear relation between NGT (range 3.2–9.3 °C), 4 He (up to 3.3 × 10 −6 ccSTP/g) and δ 18 O (range −8.5‰ to −5.9‰VSMOW ). Moreover, 3 He/ 4 He ratios of these graben waters suggest a certain influx of He from mantle origin. Key Points: Thirty nine well fields show diverging patterns of isotopes and noble gases revealing different vulnerability and resilience under contaminant stress Multiple age tracers can constrain the age distribution of mixed water from public supply well fields using a discrete groundwater age model The combined age distribution of the total of 0.2 km 3 annually abstracted water for public drinking water estimates: 9% is of recent origin, 56% is of Holocene age and 35% of Pleistocene age, with the percentage of the last paleo‐fraction increasing in time