in
cistern
cisterns.
water
subsequently
Contamination of
increased,
with
larger
the water supplies with
increases
resuspended
in
certain
particulates
cannot account for the increases in concentrations detected, but there are two
other possibilities.
The
first
requires
an assumption
cisterns was contaminated.
were
used
with
radionuclides
cement
that material
used
to construct
the
This is possible because local aggregate and water
to
manufacture
The
1376,
with
exchange
or
other
any
water
less of
levels decrease with use,
When water
saturating the cistern walls.
cisterns.
could
mixture
the
in
incorporated
the
the interior surface area of the cistern is’ in direct contact with the water.
As
a
the
result,
volume
less
of
1376,
water
in
the
cistern
result,
cistern
the
is
radionuclide
full
and
and
dilutes
lower activity water and
concentrations
there
is
no
the
rain
increases
concentration
of
A continuous use of water shortens the
radionuclides in the residual water.
contact time between this
New
the matrix.
from
is mobilized
further
decrease
use
for
As
the cistern walls.
as
observed.
the
water,
When
a
the
radionuclides
continuously exchange between the cistern walls and the water.
A second possible cause
is
that concentrations of radionuclides
in
the
water will decrease as a result of dilution with lower activity rainwater and
Heavy demands on the
increase if the standing water is allowed to evaporate.
cistern water between 1975 and 1977 reduced the inventory of available water.
Rainfall continuously replenished part of the cistern supply and diluted the
residual
radionuclide
During
concentrations.
this
1376,
their lowest level since 1975.
in
an
increased
and
90.
in
the
in
By September 1978,
cistern water approached those expected in wet deposition.
the average concentrations of
concentrations
period,
water
were
reduced
to
When water usage ceased, evaporation resulted
radionuclide
concentration.
Some
lower
concentration
rainwater diluted the radionuclide concentration of the cistern water, but the
rate
of
the
dilutant
input
was
not
equivalent
to
the
evaporation
Evaporation rates for standing bodies of water have been measured at
and
average
0.5 cm/d. 16
With
this
assumption,
Table 2 can be explained by a process of dilution,
concentration
use,
and
rate.
Bikini
changes
in
evaporation.
We
are currently investigating the importance of these processes and how they may
alter future radionuclide concentrations in atoll cistern water.
13