HW-4: Danube bank infiltration - due: 3/4/08
- download the Excel 97 file DanubeGw3H3He.xls
which contains the relevant measured data and constants
- a map of the area of investigation:
1) (10p) He, Ne data
- plot Ne versus 4He concentration for the groundwater
data
and
for water in solubility equilibrium with the atmosphere
- determine slope of the additional component, what conclusion can
you
draw
from this regarding the He and Ne components present?
- what is your best rough estimate of the temperature at which the
water
equilibrated with the atmosphere?
Observed Ne and He data plot to the right of concentrations calculated
using solubility data (Fig).
The slope of the additional component (excess air) is very close to
atmospheric air (3.5). There is no evidence for the presence of
radiogenic 4He. If you extrapolate the observations
to the solubility equilibrium line, you get a temperature of
about 8 or 9oC (Fig).
2) (10p)
Groundwater 3H/3He data
- write out the balance equation for 3He, 4He,
and
Ne
- calculate the tritiogenic 3He (3Hetrit)
- convert 3Hetrit from ccSTP/g into TU
- calculate the 3H/3He age
- plot 3H and 3H+3Hetrit
versus
distance from the Danube; where do the peaks occur?
- plot 3H/3He age versus distance from the
Danube
(mark
shallow and deep wells by different symbols)
- determine horizontal flow velocity
The total 4He is just the sum of He in solubility
equilibrium and excess air 4He, the same for Ne, 3He
contains a tritiogenic component in addition. Tritiogenic 3He can then
be calculated using equation 4 in the dovument linked below.
If plotted as a function of distance from the Danube, you obtain the
following (Fig).
The peaks occur 13-14km from the Danube. The flow velocity ranges from
500 to 800 m/y depending on well depth (Fig).
3) (10 p)
Compare groundwater data with 3H in precipitation
and Danube River
- plot 3H in precipitation and Danube River water
as a
timeseries
- can you explain the differences between the two time series?
- plot 3H+3Hetrit as a function
of 3H/3He
age, and 3H in precipitation and Danube River water in one
timeseries
plot (groundwater sampling date: 5/1993)
- what does this plot tell you?
A comparison of 3H in precipitation and in Danube River
water shows that there is a delay between the two, likely caused by
temporary storage of rain in the subsurface before it reaches the river
(Fig)
Most groundwater data points plot very closely on the river 3H
curve (Fig), at least
for your ages, providing a consistent check for the method. There are
deviations for higher groundwater ages, likely caused by
mixing/dispersion in the aquifer.
For background on how to do all this, see: basics
of 3H/3He dating