nememeeenpwneene
ea
gas
é
inCz ani’fae
Rainfall produces only smal} amounts of fresh groundwater on the large
islands of Bikini and Eneu, and probably no potable groundwater on the smaller
islands.
Rainfall drains quickly through the soil and accumulates in a roughly
“lens-shaped" body of fresh water floating on the more dense salt water. Most
of the fresh groundwater is very rapidly mixed with the underlying salt water
by wave and tidal activity, leaving only a very thin Fresh layer, generally in
the central portion of the island (Figure g).
Development of potable groundwater in Bikini Atoll is limited by two
-factors: chemical quality and radiological quality.
In terms of chemical
quality, salinity is most important, with chloride content normally being the
limiting constituent.
In the United States the standard for chloride content
in drinking water is set at 250 mg/1 (for Bikini groundwater this is approxi-
mately equivalent to 0.45 ppt total salinity), but a higher standard has been
set by TTPI of 400 mg/1 Cl for drinking water (for Bikini groundwater this is
approximately equivalent to 0.75 ppt total -salinity).
In terms of radiological
quality the most important constituents in Bikini groundwater are 90s; and
oa
In the United States (oresumably the same standards wil] be applied
© Bikini) the limiting concentrations of 90s, and 137c¢. are 10-and
200 pCi/l, respectively. When both nuclides are present the standard for each
is reduced proportionally.
Groundwater chemical and radiological quality data collected from wells on
Bikini and Eneu Islands by Lawrence Livermore Laboratory since 1975 are
summarized in Figure 9 and Table 2. As can be seen from these data, a very
smal } body of marginally potable (from a salinity standpoint) groundwater.
exists in the south-central part of Bikini Island in the vicinity of wells HFH2
and HFH7.
All Cl and total salinity data collected from these two wells during
the period 1975-79 meet United States drinking water standards. However,
salinity measurements made by two of the Committee members (Peterson and
Robison) on May 10-11, 1984, after nearly two years of very low rainfall show
,
Cl and total salinity levels of the freshest water sampled (well HFH7) to be
approximately triple the limits set in the United States for potable water, and
about double those of TTPI (see Table 2).
Water salinity data collected by the
United States Geological Survey in April and-May 1972 generally confirm these
1984 results. These data raise a serious question about the availability of
potable groundwater on Bikini Island during times when it would be needed most,
that is during periods of drought.
This question may be moot, however, because
as can be seen in Table 2, the concentration of both 90s, and 137¢.5 in
Bikini groundwater exceed drinking water standards.
From both a chemical and a radiological standpoint the groundwater picture
on Eneu looks much more promising than on Bikini. As can be seen in Table 2
and Figure 9 a moderately-sized body of potable groundwater exists in the
central part of the island near the runway. All samples collected from wells
FWR 4, 5, 6, and 7.during the period 1975-84 yielded water that meets TTP]
standards for potability.
In fact, groundwater collected from FWR 4 on May 12,
1984 contained only 23.2 mg/1 C1, an extremely low value considering the long
period of drought conditions preceding this sampling. Furthermore, an 8-hour
pump test run on well FWR 4 on May 13, 1984, during which time about 82,000
liters (21,500 gallons) of water were pumped from the well, produced virtually
no increase in water salinity, thus further substantiating the existence of a
significant fresh groundwater lens.
The very freshness of this groundwater
undoubtedly is due to extensive runoff from the runway, and hence this general
region would be a good place for groundwater development.
I009bb
A-5