Tracers for long residence times He, (Rn), 40Ar

Noble gases in groundwater solubility equilibrium => He, Ne, Ar, Kr, Xe excess air => He, Ne, Ar, Kr, Xe 3H => 3He, T1/2=12.43y U, Th (a) decay series => 4He 6Li(n,a)3H => 3He Mantel sources => 3He, 4He 40K => 40Ar U fission => 136Xe, 134Xe, 132Xe, 86Kr 226Ra => 222Rn

Release mechanisms, 4He, 222Rn (etc) 222Rn halflife: 3.8 days use of Rn as measure of U, Th concentrations depends very much on grain size useful tracer for discharge of groundwater into surface waters Torgersen, 1980

Non-atmospheric noble gases in groundwater Isotope ~1% increase in liquid phase 222Rn <day 4He 100y 40Ar 5·106y 86Kr 6 ·1010y 131Xe 2 ·1010y 132Xe 3 ·109y 134Xe 9 ·108y 136Xe 7 ·108y * (assume in situ production, only local accumulation, complete release)

He in groundwater 4He Concentration 3He/4He (ccSTP/g) Solubility equilibrium: ~4.6•10-8 1.360 •10-6 Excess air: 0….5 •10-8 1.384 •10-6 Crustal He: up to 10-1 10-9….10-7 U, Th => a => 4He 6Li(n,a)3H => 3He Mantel He: up to 10-5 1.2•10-5 primordial He: - 4•10-4 Tritium: - 

Mantle He R/Ra: He isotope ratio relative to the atmosphere

He balance He excess:

Separation of the components

Crustal (‘radiogenic’) in situ production A: 4He accumulation rate in water CU, CTh: concentrations in solid phase in mg/g N, neff: porosity, effective (flushed) porosity L: release factor Typical rate: 5*10-12 ccSTPg-1

Great Artesian Basin Torgersen & Clarke, 1985 Torgersen & Ivey, 1985

Model:

He excess, Namibia He excess (ccSTP/g) C age (years) 0 10 2 10 4 10 2 10 -5 4 10 6 10 8 10 1 10 -4 1.2 10 1.4 10 10000 20000 30000 40000 He excess (ccSTP/g) 14 C age (years) He excess, Namibia

Great Hungarian Plain Stute et al., 1992

Great Hungarian Plain

4He accumulation model U, Th => a => 4He

Great Hungarian Plain

Great Hungarian Plain

Great Hungarian Plain

Great Hungarian Plain Peclet number:

Sturgeon Falls, Ontario Solomon et al., 1996

Solomon et al., 1996

Presence of crustal Helium! Release rate 300x in situ production Source is non equilibrium diffusion out of sediments Solomon et al., 1996

The paradox of gw age Bethge and Johnson, 2002