![](media/image1.png){width="5.874305555555556in"
height="1.2916666666666667in"}

# Measurement of Seafloor Radioactivity at the Farallon Islands Radioactive Waste Dump Site, California

By D.G. Jones^1^, P.D. Roberts^1^, J. Limburg^2^, H. Karl^3^, J.L.
Chin^3^,W.C. Shanks^4^,

R. Hall^5^, and D. Howard^6^

**Open-File Report 01-62**

2001

Any use of trade, firm, or product names is for descriptive purposes
only and does not imply endorsement by the U.S. Government.

**U.S. Department of the Interior**

**U.S. Geological Survey**

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

^1^British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

^2^Kernfysisch Versneller Instituut, Zernikelaan 25, 9747AA Groningen,
The Netherlands

^3^U.S. Geological Survey, Menlo Park, CA 94025

^4^U.S. Geological Survey, Denver, CO 80225

^5^U.S. Environmental Protection Agency, San Francisco, CA 94105

^6^Gulf of the Farallones National Marine Sanctuary, San Francisco, CA
94129

# Introduction

Between 1946 and 1970, approximately 47,800 55-gallon drums, concrete
blocks, and other containers of low-level radioactive waste were
reportedly dumped offshore of San Francisco Bay. Three sites on the
continental shelf and slope adjacent to the Farallon Islands were
designated for the disposal of the waste (Jose*ph et a*l., 1971; NOAA,
1990; Noshk*in et a*l., 1978; Waldichuk, 1960). According to the
records, approximately 150 drums were deposited in a water depth of
about 90 m, 3,600 in a water depth of about 900 m, and 44,000 in a
nominal water depth of 1,800 m. These sites are referred to here as the
90-m, 900-m, and 1,800-m sites, although the actual water depths at and
around each site vary from the nominal values.

In reality, many of the drums were probably not disposed of at the
specific sites. It is more likely that they litter a 1,400-km2 area of
sea floor, the Farallon Island Radioactive Waste Dump (Noshk*in et a*l.,
1978), defined by the irregular polygon on figure. 1.

Excluding tritium, an estimated total of some 540 TBq (14,500 Ci) of
thorium, uranium, transuranic, and other activation products, and mixed
fission products were disposed of at the three locations (Jose*ph et
a*l., 1971; Waldichuk, 1960). The precise amounts of individual
radionuclides are not known. In addition to radioactive wastes, other
wastes, including phenols, cyanides, mercury, beryllium and other heavy
metals, dredge spoils, explosives, and garbage were also dumped in and
around the area (NOAA, 1990).

Much of the Farallon Island Radioactive Waste Dump lies within the
boundaries of the Gulf of the Farallones National Marine Sanctuary,
which was designated in 1981 (fig. 1). In 1990, the U.S. Geological
Survey (USGS) and the Gulf of the Farallones National Marine Sanctuary
jointly surveyed part of the Farallon Island Radioactive Waste Dump with
a sidescan-sonar system. The result of this survey (Ka*rl et a*l.,
1994), following subsequent computer enhancement of the data to assist
in the identification of barrels, was the mapping of barrel locations
over an area of 125 km^2^. The identification of the barrels was
verified during the initial survey using an underwater camera/video and
subsequently using the manned Navy submersible *Sea Cliff* and the
unmanned Advanced Tethered Vehicle. Visual observations showed the
barrels to be in all states of preservation, ranging from completely
intact to completely disintegrated.

The Gulf of the Farallones and adjacent areas support a major commercial
fishery. The area is also used extensively for sport fishing (NOAA,
1990). Fears of radioactive contamination have previously had an adverse
impact on the fishery (E. Ueber, personal communication).

Discussions between the USGS and the British Geological Survey (BGS) led
to a proposal to carry out a radioactivity survey of parts of the
Farallon Islands Radioactive Waste Dump Site (fig. 1). This was done
using the proven BGS towed seabed spectrometer (EEL) system (e.g.,
Jones, 1994; Mill*er et a*l., 1977), modified to operate in deeper water
(Deep Tow EEL). The main aim was to obtain regional-scale information on
sea floor radioactivity levels for parts of the site, particularly with
reference to USGS mapping of barrel locations using sidescan sonar data
(Ka*rl et a*l., 1994). Previous radioactivity measurements had been
restricted to the analyses of samples of water, sediments and biota
(Dyer, 1976; Noshk*in et a*l., 1978; PneumoDynamics Corporation, 1961;
Schell and Sugai, 1980; Suchan*ek et a*l., 1996). In the case of the
sediments, only a relatively small number of sites had been sampled,
although some samples were collected from areas adjacent to barrels
using submersibles (Dyer, 1976; Schell and Sugai, 1980).

The survey was carried out in April-May 1998 on the NOAA ship *McArthur*
and involved interagency collaboration between the BGS, USGS, U.S.
Environmental Protection Agency, National Oceanographic and Atmospheric
Administration, and Gulf of the Farallones National Marine Sanctuary.
Work was concentrated on the shallower parts of the site where
commercial fishing occurs and where locations of barrels had been
mapped.

![](media/image2.png){width="6.0in"
height="7.059027777777778in"}**Figure 1.** Farallon Islands Radioactive
Waste Dump Site: Location map showing 90-, 900- and 1800m sites. Insets
A-D show the areas covered by Figures 4-7, respectively.

# Seabed gamma-ray spectrometry

The BGS EEL system (Jones, 1994; Mill*er et a*l., 1977) was developed
for continental shelf use and has mostly been operated at depths less
than 200 m, although it was used briefly at 600 m. Significant
modifications were made to the system for the Farallon survey to cope
with the much greater depths involved. This entailed uprating the
pressure vessel that houses the detector to a 3,000-m capability,
switching to digital data transmission to allow signal transmission
through 6,000 m of cable, and completely updating the control
electronics and data logging software. In addition, extra sensors were
added to the seabed probe (c.f. de Meij*er et a*l., 1997) to give
pressure (=depth), temperature, and noise (=roughness) information (fig.
2). A 'saddleback' monitor was used to measure the strain on the towing
cable to ensure that this stayed within safe working limits. This also
incorporated a cable counter to keep track of the length of cable
deployed.

![](media/image3.png){width="5.998611111111111in"
height="4.439583333333333in"}

**Figure 2.** Schematic diagram of Deep Tow EEL system.

The detecting probe of the EEL is towed on the sea floor, protected
inside a 30-m length of PVC hose (fig. 3). The gamma-ray detector used
for the survey was a bismuth germanate (BGO) scintillation detector.
When gamma rays interact with the detector, flashes of light
(scintillations) are emitted. These are converted to voltage pulses and
amplified and then sorted by pulse height. The intensity of the
scintillations and the pulse height are proportional to the energy of
the gamma rays. Hence the detector can measure the full gamma-ray
spectrum, enabling contributions from natural and artificial
radioactivity to be identified and quantified. The equipment measures
the gamma emitters in the surficial sea floor material to an effective
maximum depth of about 30 cm.

The length of towing cable is altered, using a remote control, to
maintain the probe on the seabed as the water depth changes or to
accommodate changes in the speed of the survey vessel. A clear reduction
in signal is seen if the probe loses contact with the sea bed. This is
apparent in both the gamma-ray data and the sound signal and enables the
detector, as far as possible, to be kept on the sea floor.

Although originally developed for geological mapping and mineral
exploration (e.g., de Meij*er et a*l., 1997; Jon*es et a*l., 1988a;
Ring*is et a*l., 1993), the equipment has subsequently been used for a
variety of environmental surveys. These include the mapping of
artificial radionuclides discharged from the Sellafield nuclear plant in
the Irish Sea (Jon*es et a*l., 1988b; Mill*er et a*l., 1982).

![](media/image4.jpeg){width="5.847222222222222in"
height="5.790972222222222in"}

**Figure 3.** EEL method diagram.

# Survey operations

The EEL was successfully deployed on the survey to a depth of 1,500 m.
Sets of lines were towed at both the 90-m and 900-m sites. Additional
shorter tows were made through known barrel clusters at the 900-m site
and lines extended from the 900-m site into deeper water adjacent to the
1,800-m site (see figure 1 for index map to areas covered). Bottom
sediment samples were also collected. These related both to the EEL
towing and to clusters of barrels, identified from the USGS sidescan
data, in areas deemed to be too rugged for bottom towing.

The survey was planned so that work proceeded from shallow to deeper
water; i.e., towing conditions for the EEL became progressively more
hazardous. The aim was to maximise the likelihood of successful data
collection.

Approximately 90 line-km of EEL data were towed on seven parallel
traverses at the 90-m site, and nine sediment samples were collected
with a Van Veen grab (fig. 4). The lines were oriented NW-SE,
perpendicular to the direction of the swell, primarily because the ship
could not maintain other headings in the prevailing sea conditions.
Towing in the shallow water and predominately smooth seafloor conditions
was relatively straightforward.

**Figure 4.** Survey lines and sample locations at 90-m site (e.g.,
∆20). Contours show depths (m) below mean sea level.

A further set of seven NW-SE lines, totalling some 60 line-km, was
surveyed at the 900-m site (fig. 5). These were sited mainly on a broad
spur between two submarine canyons, where seafloor

**Figure 5**. Survey lines and sample locations at 900-m site (e.g.,
∆15). Contours show depths (m) below mean sea level

gradients were not too extreme. Two short traverses (about. 5.5 line-km)
were made through known barrel clusters (fig. 6). Six sediment samples
were collected with the grab related to lines towed at the900-m site as
well as a further 10 samples in the vicinity of barrel clusters that
were not towed with the EEL (fig. 5).

**Figure 6.** Survey lines and sample locations (e.g. ∆12) at the
'Cluster' site. Contours show depths (m) below mean sea level.

Two lines (about 18 line-km) were run from the 900-m site into deeper
water adjacent to the 1,800-m site (fig. 7). These were run roughly
perpendicular to the main 900-m traverses, in improved sea conditions,
and reached a maximum depth of 1,500 m.

Grab sampling was restricted, by the length of cable available on the
ship's sampling winch, to a maximum water depth of about 1,200 m. Thus
no samples were collected from the deeper parts of the area surveyed
with the EEL.

The EEL radiometric data were collected continuously over 5-s intervals
with the full gamma-ray spectrum being displayed on the logging screen
over the previous 10 minutes and integrated over the entire

**Figure 7.** 1 Survey lines at 1,800-m site. Contours show depths (m)
below mean sea level.line. At the typical towing speed of approximately
2 knots (3.6 kmh^-1^), a 5-s interval represents the coverage of about 5
m of seabed.

line. At the typical towing speed of approximately 2 knots (3.6
kmh^-1^), a 5-s interval represents the coverage of about 5m of seabed.

# Laboratory analyses

The gamma-emitting radionuclides in the sediment samples were analysed
(in BGS and USGS laboratories) using high-resolution gamma spectrometry
in low background counting facilities. The two sets of data are
generally in good agreement. The BGS results are summarised in table 1.
The Am and Pu content of a selection of samples was also investigated at
BGS by alpha spectrometry, following extraction and concentration, as
outlined in Jones *et al*. (1999). The results are summarised in table
2.

Grain size analysis of the sediments (summarised in table 3) was carried
out at the USGS facility in Menlo Park. Coarse fractions were separated
by wet sieving, intermediate fractions by using Rapid Settling Analysis
in settling tubes, and fine fractions by using a Micromeritics SediGraph
5100 particle-size analyser.

The general geochemistry of the samples was undertaken at USGS Denver by
ICP-MS following an acid digestion (see Briggs and Meier, 1999 for
details). This had the dual purpose of providing background geochemical
information on the sediments and their variability and of assessing
whether any nonradioactive contaminants were present. The results are
given in table 4.

Quality Assurance/Quality Control of the laboratory determinations was
ensured by the use of international standards or other accredited
reference materials and by analyzing duplicate samples and blanks. The
laboratories of the BGS and USGS also took part in interlaboratory
comparison exercises.

<table>
<colgroup>
<col style="width: 9%" />
<col style="width: 9%" />
<col style="width: 5%" />
<col style="width: 0%" />
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
</colgroup>
<tbody>
<tr class="odd">
<td><strong>Site</strong></td>
<td><strong>Sample<br />
No.</strong></td>
<td colspan="2"><strong><sup>241</sup>Am</strong></td>
<td><h2 id="am-error"><sup>241</sup>Am Error</h2></td>
<td><strong><sup>137</sup>Cs</strong></td>
<td><strong><sup>137</sup>Cs<br />
Error</strong></td>
<td><strong><sup>40</sup>K</strong></td>
<td><strong><sup>40</sup>K<br />
Error</strong></td>
<td><strong>U(<sup>214</sup>Bi)</strong></td>
<td><strong>U<br />
Error</strong></td>
<td><strong>Th(<sup>208</sup>Tl)<br />
</strong></td>
<td><strong>Th<br />
Error</strong></td>
</tr>
<tr class="even">
<td>Cluster'</td>
<td>A1A</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>0.8</td>
<td>0.4</td>
<td>581.6</td>
<td>11.2</td>
<td>44.5</td>
<td>1.3</td>
<td>27.6</td>
<td>1.5</td>
</tr>
<tr class="odd">
<td></td>
<td>B1</td>
<td>3.5</td>
<td colspan="2">0.6</td>
<td>1.9</td>
<td>0.8</td>
<td>582.1</td>
<td>16.4</td>
<td>49.5</td>
<td>2.0</td>
<td>24.9</td>
<td>2.1</td>
</tr>
<tr class="even">
<td></td>
<td>10A</td>
<td>1.2</td>
<td colspan="2">0.3</td>
<td>0.9</td>
<td>0.3</td>
<td>578.8</td>
<td>13.9</td>
<td>24.1</td>
<td>1.4</td>
<td>20.2</td>
<td>1.7</td>
</tr>
<tr class="odd">
<td></td>
<td>5</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>4.2</td>
<td>0.8</td>
<td>578.8</td>
<td>16.5</td>
<td>42.5</td>
<td>1.9</td>
<td>27.9</td>
<td>2.3</td>
</tr>
<tr class="even">
<td></td>
<td>6</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.8</td>
<td>0.8</td>
<td>560.2</td>
<td>15.5</td>
<td>43.7</td>
<td>1.9</td>
<td>24.8</td>
<td>2.2</td>
</tr>
<tr class="odd">
<td></td>
<td>7</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>2.6</td>
<td>0.7</td>
<td>567.5</td>
<td>15.3</td>
<td>44.6</td>
<td>1.7</td>
<td>24.4</td>
<td>2.0</td>
</tr>
<tr class="even">
<td></td>
<td>8</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>591.0</td>
<td>19.8</td>
<td>42.7</td>
<td>2.5</td>
<td>21.6</td>
<td>3.2</td>
</tr>
<tr class="odd">
<td></td>
<td>9</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>3.8</td>
<td>0.8</td>
<td>571.1</td>
<td>17.5</td>
<td>43.4</td>
<td>2.0</td>
<td>21.3</td>
<td>2.3</td>
</tr>
<tr class="even">
<td></td>
<td>11</td>
<td>2.5</td>
<td colspan="2">0.4</td>
<td>1.7</td>
<td>0.4</td>
<td>612.3</td>
<td>12.7</td>
<td>36.2</td>
<td>1.4</td>
<td>26.5</td>
<td>1.5</td>
</tr>
<tr class="odd">
<td></td>
<td>12</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>2.6</td>
<td>0.7</td>
<td>578.8</td>
<td>14.7</td>
<td>43.4</td>
<td>1.6</td>
<td>21.6</td>
<td>2.0</td>
</tr>
<tr class="even">
<td></td>
<td>13</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>2.6</td>
<td>0.7</td>
<td>579.2</td>
<td>14.9</td>
<td>42.3</td>
<td>1.8</td>
<td>23.4</td>
<td>1.9</td>
</tr>
<tr class="odd">
<td></td>
<td>14</td>
<td>2.6</td>
<td colspan="2">0.4</td>
<td>3.5</td>
<td>0.4</td>
<td>574.6</td>
<td>10.4</td>
<td>46.4</td>
<td>1.3</td>
<td>21.9</td>
<td>1.3</td>
</tr>
<tr class="even">
<td>900m</td>
<td>15</td>
<td>&lt;1.0</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>616.4</td>
<td>12.9</td>
<td>17.7</td>
<td>1.2</td>
<td>11.8</td>
<td>1.6</td>
</tr>
<tr class="odd">
<td></td>
<td>16</td>
<td>&lt;1.0</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>574.7</td>
<td>12.4</td>
<td>21.2</td>
<td>1.2</td>
<td>15.4</td>
<td>1.5</td>
</tr>
<tr class="even">
<td></td>
<td>17</td>
<td>&lt;1.0</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>584.4</td>
<td>13.4</td>
<td>24.2</td>
<td>1.3</td>
<td>22.0</td>
<td>1.6</td>
</tr>
<tr class="odd">
<td></td>
<td>18</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.5</td>
<td>0.3</td>
<td>543.6</td>
<td>13.4</td>
<td>36.4</td>
<td>1.6</td>
<td>23.2</td>
<td>2.0</td>
</tr>
<tr class="even">
<td>90m</td>
<td>19</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.3</td>
<td>0.3</td>
<td>522.0</td>
<td>7.9</td>
<td>29.6</td>
<td>1.1</td>
<td>29.8</td>
<td>1.0</td>
</tr>
<tr class="odd">
<td></td>
<td>20</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.0</td>
<td>0.5</td>
<td>451.0</td>
<td>10.9</td>
<td>18.7</td>
<td>1.0</td>
<td>16.4</td>
<td>1.2</td>
</tr>
<tr class="even">
<td></td>
<td>21</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.2</td>
<td>0.4</td>
<td>482.0</td>
<td>8.5</td>
<td>18.2</td>
<td>0.8</td>
<td>18.1</td>
<td>1.1</td>
</tr>
<tr class="odd">
<td></td>
<td>22</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>420.0</td>
<td>10.3</td>
<td>8.2</td>
<td>1.0</td>
<td>21.2</td>
<td>1.3</td>
</tr>
<tr class="even">
<td></td>
<td>23</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>&lt;0.5</td>
<td></td>
<td>193.0</td>
<td>6.4</td>
<td>3.8</td>
<td>0.8</td>
<td>6.1</td>
<td>0.9</td>
</tr>
<tr class="odd">
<td></td>
<td>24</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>2.1</td>
<td>0.4</td>
<td>466.0</td>
<td>10.9</td>
<td>16.4</td>
<td>1.1</td>
<td>15.6</td>
<td>1.2</td>
</tr>
<tr class="even">
<td></td>
<td>25</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.9</td>
<td>0.4</td>
<td>480.0</td>
<td>11.9</td>
<td>18.4</td>
<td>1.0</td>
<td>17.1</td>
<td>1.3</td>
</tr>
<tr class="odd">
<td></td>
<td>26</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.3</td>
<td>0.3</td>
<td>506.0</td>
<td>7.6</td>
<td>21.3</td>
<td>0.7</td>
<td>21.9</td>
<td>0.8</td>
</tr>
<tr class="even">
<td></td>
<td>27</td>
<td>&lt;0.5</td>
<td colspan="2"></td>
<td>1.0</td>
<td>0.3</td>
<td>476.0</td>
<td>10.8</td>
<td>18.7</td>
<td>1.0</td>
<td>17.3</td>
<td>1.3</td>
</tr>
</tbody>
</table>

**Table 1.** Radionuclide data for sediment samples (in Bqkg^-1^) by
gamma-ray spectrometry at BGS (errors are 1 σ counting errors)

**Table 2.** Radionuclide data for sediment samples (in Bqkg^-1^) by
alpha spectrometry at BGS (errors are 1 σ counting errors)

<table>
<colgroup>
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 14%" />
<col style="width: 11%" />
<col style="width: 7%" />
<col style="width: 9%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td><h2 id="site">Site</h2></td>
<td><strong>Field No.</strong></td>
<td><strong>Longitude</strong></td>
<td><strong>Latitude</strong></td>
<td><strong>Depth (m)</strong></td>
<td><strong><sup>239/240</sup>Pu<br />
</strong></td>
<td><strong><sup>239/240</sup>Pu<br />
error</strong></td>
<td><strong><sup>238</sup>Pu<br />
</strong></td>
<td><strong><sup>238</sup>Pu<br />
error</strong></td>
<td><strong><sup>241</sup>Am<br />
</strong></td>
<td><strong><sup>241</sup>Am<br />
error</strong></td>
</tr>
<tr class="even">
<td>Cluster'</td>
<td>A1A</td>
<td>-123.14352</td>
<td>37.62143</td>
<td>1450</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>B1</td>
<td>-123.14588</td>
<td>37.62096</td>
<td>1150</td>
<td>2.6</td>
<td>0.1</td>
<td>&lt;0.1</td>
<td></td>
<td>1.8</td>
<td>0.2</td>
</tr>
<tr class="even">
<td></td>
<td>10A</td>
<td>-123.15921</td>
<td>37.62384</td>
<td>1100</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>5</td>
<td>-123.14562</td>
<td>37.62943</td>
<td>1100</td>
<td>3.1</td>
<td>0.2</td>
<td>0.3</td>
<td>0.07</td>
<td>2</td>
<td>0.07</td>
</tr>
<tr class="even">
<td></td>
<td>6</td>
<td>-123.15510</td>
<td>37.62925</td>
<td>1100</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>7</td>
<td>-123.14967</td>
<td>37.62427</td>
<td>1150</td>
<td>2.8</td>
<td>0.2</td>
<td>&lt;0.1</td>
<td></td>
<td>1.2</td>
<td>0.9</td>
</tr>
<tr class="even">
<td></td>
<td>8</td>
<td>-123.15765</td>
<td>37.61577</td>
<td>1180</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>9</td>
<td>-123.14616</td>
<td>37.61723</td>
<td>1150</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>11</td>
<td>-123.14038</td>
<td>37.62593</td>
<td>1060</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>12</td>
<td>-123.14868</td>
<td>37.61915</td>
<td>1150</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>13</td>
<td>-123.15097</td>
<td>37.62163</td>
<td>1150</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>14</td>
<td>-123.15897</td>
<td>37.61677</td>
<td>1120</td>
<td>2.1</td>
<td>0.1</td>
<td>&lt;0.1</td>
<td></td>
<td>&lt;0.1</td>
<td></td>
</tr>
<tr class="even">
<td>900m</td>
<td>15</td>
<td>-123.17923</td>
<td>37.64832</td>
<td>1050</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>16</td>
<td>-123.18697</td>
<td>37.63455</td>
<td>1015</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>17</td>
<td>-123.20768</td>
<td>37.64116</td>
<td>1080</td>
<td>0.8</td>
<td>0.04</td>
<td>&lt;0.1</td>
<td></td>
<td>&lt;0.1</td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>18</td>
<td>-123.18455</td>
<td>37.61825</td>
<td>1100</td>
<td>1.1</td>
<td>0.06</td>
<td>&lt;0.1</td>
<td></td>
<td>&lt;0.1</td>
<td></td>
</tr>
<tr class="even">
<td>90m</td>
<td>19</td>
<td>-123.00136</td>
<td>37.60260</td>
<td>136</td>
<td>0.6</td>
<td>0.04</td>
<td>&lt;0.1</td>
<td></td>
<td>&lt;0.1</td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>20</td>
<td>-123.00207</td>
<td>37.62037</td>
<td>118</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>21</td>
<td>-123.01758</td>
<td>37.62567</td>
<td>123</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>22</td>
<td>-122.99587</td>
<td>37.66318</td>
<td>73</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>23</td>
<td>-122.98837</td>
<td>37.67187</td>
<td>58</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>24</td>
<td>-122.96485</td>
<td>37.64437</td>
<td>91</td>
<td>0.8</td>
<td>0.05</td>
<td>&lt;0.1</td>
<td></td>
<td>0.2</td>
<td>0.04</td>
</tr>
<tr class="even">
<td></td>
<td>25</td>
<td>-122.96890</td>
<td>37.59508</td>
<td>114</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>26</td>
<td>-122.98218</td>
<td>37.56576</td>
<td>131</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td>27</td>
<td>-122.90722</td>
<td>37.57253</td>
<td>100</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>

**Table 3.** Summary of grain size data for sediment samples (data
produced by sieving, settling tubes, and SediGraph at USGS)

<table style="width:100%;">
<colgroup>
<col style="width: 7%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 5%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 3%" />
</colgroup>
<tbody>
<tr class="odd">
<td><h3 id="sample">Sample</h3></td>
<td><strong>Al</strong></td>
<td><strong>Ca</strong></td>
<td><strong>Fe</strong></td>
<td><strong>K</strong></td>
<td><strong>Mg</strong></td>
<td><strong>Na</strong></td>
<td><strong>Ag</strong></td>
<td><strong>As</strong></td>
<td><strong>Ba</strong></td>
<td><strong>Be</strong></td>
<td><strong>Bi</strong></td>
<td><strong>Cd</strong></td>
<td><strong>Ce</strong></td>
<td><strong>Co</strong></td>
<td><strong>Cr</strong></td>
<td><strong>Cu</strong></td>
<td><strong>Dy</strong></td>
<td><strong>Er</strong></td>
<td><strong>Eu</strong></td>
<td><strong>Ga</strong></td>
<td><strong>Gd</strong></td>
<td><strong>Ge</strong></td>
<td><strong>Ho</strong></td>
<td><strong>La</strong></td>
</tr>
<tr class="even">
<td></td>
<td>%</td>
<td>%</td>
<td>%</td>
<td>%</td>
<td>%</td>
<td>%</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
</tr>
<tr class="odd">
<td>A1A</td>
<td>7.2</td>
<td>1.9</td>
<td>3.5</td>
<td>1.6</td>
<td>1.8</td>
<td>2</td>
<td>0.26</td>
<td>7.4</td>
<td>590</td>
<td>1.5</td>
<td>0.2</td>
<td>1</td>
<td>46</td>
<td>10</td>
<td>150</td>
<td>30</td>
<td>4.4</td>
<td>2.7</td>
<td>0.96</td>
<td>17</td>
<td>4.2</td>
<td>1.1</td>
<td>0.88</td>
<td>26</td>
</tr>
<tr class="even">
<td>B1</td>
<td>7.2</td>
<td>1.8</td>
<td>3.7</td>
<td>1.6</td>
<td>1.7</td>
<td>1.7</td>
<td>0.36</td>
<td>7.5</td>
<td>680</td>
<td>1.4</td>
<td>0.1</td>
<td>1</td>
<td>55</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.9</td>
<td>2.6</td>
<td>0.99</td>
<td>17</td>
<td>4.2</td>
<td>1.3</td>
<td>0.89</td>
<td>29</td>
</tr>
<tr class="odd">
<td>10A</td>
<td>6.4</td>
<td>1.3</td>
<td>6.2</td>
<td>1.8</td>
<td>1.6</td>
<td>1.9</td>
<td>0.27</td>
<td>6.9</td>
<td>560</td>
<td>1.6</td>
<td>&lt; 0.05</td>
<td>0.7</td>
<td>35</td>
<td>8.4</td>
<td>140</td>
<td>20</td>
<td>2.9</td>
<td>1.9</td>
<td>0.8</td>
<td>14</td>
<td>3</td>
<td>1.9</td>
<td>0.62</td>
<td>17</td>
</tr>
<tr class="even">
<td>5</td>
<td>7.6</td>
<td>1.7</td>
<td>3.7</td>
<td>1.7</td>
<td>2</td>
<td>2.2</td>
<td>0.36</td>
<td>7.5</td>
<td>610</td>
<td>1.5</td>
<td>0.1</td>
<td>1</td>
<td>49</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.9</td>
<td>2.6</td>
<td>0.98</td>
<td>17</td>
<td>4.2</td>
<td>1.2</td>
<td>0.89</td>
<td>24</td>
</tr>
<tr class="odd">
<td>6</td>
<td>7.1</td>
<td>2.8</td>
<td>3.4</td>
<td>1.5</td>
<td>1.8</td>
<td>2.2</td>
<td>0.36</td>
<td>8</td>
<td>580</td>
<td>1.2</td>
<td>0.1</td>
<td>1</td>
<td>45</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.9</td>
<td>2.3</td>
<td>0.96</td>
<td>15</td>
<td>4</td>
<td>1.1</td>
<td>0.81</td>
<td>23</td>
</tr>
<tr class="even">
<td>7</td>
<td>7.8</td>
<td>1.8</td>
<td>3.6</td>
<td>1.6</td>
<td>2</td>
<td>2</td>
<td>0.35</td>
<td>7.4</td>
<td>560</td>
<td>1.4</td>
<td>0.1</td>
<td>1.1</td>
<td>42</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.7</td>
<td>2.4</td>
<td>0.93</td>
<td>17</td>
<td>3.8</td>
<td>1</td>
<td>0.8</td>
<td>22</td>
</tr>
<tr class="odd">
<td>8</td>
<td>7.3</td>
<td>1.9</td>
<td>3.7</td>
<td>1.6</td>
<td>1.9</td>
<td>1.8</td>
<td>0.4</td>
<td>7.3</td>
<td>670</td>
<td>1.4</td>
<td>0.1</td>
<td>1</td>
<td>47</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>4.3</td>
<td>2.7</td>
<td>0.99</td>
<td>17</td>
<td>4</td>
<td>1.2</td>
<td>0.92</td>
<td>25</td>
</tr>
<tr class="even">
<td>9</td>
<td>7.3</td>
<td>1.9</td>
<td>3.6</td>
<td>1.6</td>
<td>1.8</td>
<td>2.2</td>
<td>0.4</td>
<td>7.9</td>
<td>570</td>
<td>1.2</td>
<td>0.1</td>
<td>1</td>
<td>45</td>
<td>11</td>
<td>150</td>
<td>31</td>
<td>4.2</td>
<td>2.7</td>
<td>0.97</td>
<td>16</td>
<td>4</td>
<td>1.2</td>
<td>0.84</td>
<td>23</td>
</tr>
<tr class="odd">
<td>11</td>
<td>7.8</td>
<td>1.6</td>
<td>3.7</td>
<td>1.6</td>
<td>1.9</td>
<td>2</td>
<td>0.23</td>
<td>7</td>
<td>580</td>
<td>1.3</td>
<td>0.1</td>
<td>1</td>
<td>48</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.9</td>
<td>2.4</td>
<td>0.98</td>
<td>17</td>
<td>4</td>
<td>1.3</td>
<td>0.8</td>
<td>24</td>
</tr>
<tr class="even">
<td>12</td>
<td>7.3</td>
<td>2.1</td>
<td>3.6</td>
<td>1.8</td>
<td>1.7</td>
<td>2.3</td>
<td>0.31</td>
<td>8</td>
<td>610</td>
<td>1.3</td>
<td>0.09</td>
<td>1.1</td>
<td>46</td>
<td>11</td>
<td>150</td>
<td>30</td>
<td>3.9</td>
<td>2.5</td>
<td>1</td>
<td>17</td>
<td>4.3</td>
<td>1.2</td>
<td>0.84</td>
<td>25</td>
</tr>
<tr class="odd">
<td>13</td>
<td>7</td>
<td>1.9</td>
<td>3.6</td>
<td>1.8</td>
<td>1.8</td>
<td>2.3</td>
<td>0.29</td>
<td>8.3</td>
<td>620</td>
<td>1.2</td>
<td>0.08</td>
<td>1.2</td>
<td>45</td>
<td>11</td>
<td>140</td>
<td>30</td>
<td>3.6</td>
<td>2.5</td>
<td>0.88</td>
<td>16</td>
<td>3.7</td>
<td>1.2</td>
<td>0.86</td>
<td>24</td>
</tr>
<tr class="even">
<td>14</td>
<td>7.4</td>
<td>2.1</td>
<td>3.8</td>
<td>1.6</td>
<td>2</td>
<td>2.1</td>
<td>0.35</td>
<td>7.8</td>
<td>680</td>
<td>1.3</td>
<td>0.1</td>
<td>0.8</td>
<td>46</td>
<td>11</td>
<td>160</td>
<td>31</td>
<td>4</td>
<td>2.5</td>
<td>0.97</td>
<td>17</td>
<td>4.2</td>
<td>1.2</td>
<td>0.91</td>
<td>28</td>
</tr>
<tr class="odd">
<td>15</td>
<td>5.1</td>
<td>1.1</td>
<td>9.1</td>
<td>2</td>
<td>1.7</td>
<td>1.9</td>
<td>0.28</td>
<td>7</td>
<td>430</td>
<td>2.2</td>
<td>&lt; 0.05</td>
<td>0.3</td>
<td>31</td>
<td>6.8</td>
<td>160</td>
<td>20</td>
<td>2.7</td>
<td>1.6</td>
<td>0.6</td>
<td>12</td>
<td>2.7</td>
<td>2.4</td>
<td>0.53</td>
<td>15</td>
</tr>
<tr class="even">
<td>16</td>
<td>7.2</td>
<td>1.6</td>
<td>4.2</td>
<td>1.8</td>
<td>1.5</td>
<td>2.1</td>
<td>0.18</td>
<td>5.6</td>
<td>580</td>
<td>1.2</td>
<td>0.06</td>
<td>0.5</td>
<td>42</td>
<td>9</td>
<td>150</td>
<td>20</td>
<td>3.7</td>
<td>2.2</td>
<td>0.93</td>
<td>15</td>
<td>3.8</td>
<td>1.5</td>
<td>0.81</td>
<td>21</td>
</tr>
<tr class="odd">
<td>17</td>
<td>7.6</td>
<td>1.5</td>
<td>4.8</td>
<td>1.9</td>
<td>1.8</td>
<td>2.2</td>
<td>0.17</td>
<td>7.1</td>
<td>640</td>
<td>1.5</td>
<td>0.06</td>
<td>0.5</td>
<td>50</td>
<td>11</td>
<td>160</td>
<td>20</td>
<td>3.8</td>
<td>2.6</td>
<td>1</td>
<td>17</td>
<td>4</td>
<td>1.6</td>
<td>0.81</td>
<td>26</td>
</tr>
<tr class="even">
<td>18</td>
<td>7.9</td>
<td>2</td>
<td>3.7</td>
<td>1.8</td>
<td>1.8</td>
<td>2</td>
<td>0.19</td>
<td>7</td>
<td>680</td>
<td>1.4</td>
<td>0.07</td>
<td>1.3</td>
<td>43</td>
<td>11</td>
<td>140</td>
<td>20</td>
<td>4</td>
<td>2.4</td>
<td>1</td>
<td>18</td>
<td>3.8</td>
<td>1.3</td>
<td>0.85</td>
<td>21</td>
</tr>
<tr class="odd">
<td>19</td>
<td>7.2</td>
<td>2.8</td>
<td>3</td>
<td>1.7</td>
<td>1.4</td>
<td>2.2</td>
<td>0.14</td>
<td>6.7</td>
<td>600</td>
<td>1.4</td>
<td>&lt; 0.05</td>
<td>0.8</td>
<td>55</td>
<td>12</td>
<td>120</td>
<td>8</td>
<td>4</td>
<td>2.7</td>
<td>1.1</td>
<td>13</td>
<td>4.7</td>
<td>0.9</td>
<td>0.93</td>
<td>27</td>
</tr>
<tr class="even">
<td>20</td>
<td>7.4</td>
<td>1.9</td>
<td>2.7</td>
<td>1.6</td>
<td>1.4</td>
<td>2.4</td>
<td>0.08</td>
<td>6.1</td>
<td>640</td>
<td>1</td>
<td>&lt; 0.05</td>
<td>3.6</td>
<td>44</td>
<td>8.3</td>
<td>130</td>
<td>10</td>
<td>3.4</td>
<td>2.2</td>
<td>1</td>
<td>14</td>
<td>3.5</td>
<td>1.1</td>
<td>0.76</td>
<td>20</td>
</tr>
<tr class="odd">
<td>21</td>
<td>7.6</td>
<td>1.9</td>
<td>2.8</td>
<td>1.6</td>
<td>1.4</td>
<td>2.3</td>
<td>0.05</td>
<td>5.8</td>
<td>590</td>
<td>1.3</td>
<td>&lt; 0.05</td>
<td>3</td>
<td>41</td>
<td>8.6</td>
<td>130</td>
<td>10</td>
<td>3.7</td>
<td>2.4</td>
<td>0.97</td>
<td>13</td>
<td>3.9</td>
<td>1.1</td>
<td>0.77</td>
<td>22</td>
</tr>
<tr class="even">
<td>22</td>
<td>5.8</td>
<td>13</td>
<td>1.1</td>
<td>1.1</td>
<td>0.43</td>
<td>2.5</td>
<td>0.02</td>
<td>5</td>
<td>710</td>
<td>1</td>
<td>&lt; 0.05</td>
<td>0.1</td>
<td>62</td>
<td>1.4</td>
<td>17</td>
<td>3</td>
<td>2</td>
<td>1.1</td>
<td>0.73</td>
<td>10</td>
<td>2.5</td>
<td>0.5</td>
<td>0.42</td>
<td>32</td>
</tr>
<tr class="odd">
<td>23</td>
<td>1.4</td>
<td>32</td>
<td>0.71</td>
<td>0.36</td>
<td>0.48</td>
<td>0.98</td>
<td>&lt;0.02</td>
<td>6.1</td>
<td>240</td>
<td>0.3</td>
<td>&lt; 0.05</td>
<td>0.2</td>
<td>15</td>
<td>0.5</td>
<td>9</td>
<td>&lt;3</td>
<td>0.98</td>
<td>0.58</td>
<td>0.25</td>
<td>2.7</td>
<td>1.1</td>
<td>0.1</td>
<td>0.21</td>
<td>8.7</td>
</tr>
<tr class="even">
<td>24</td>
<td>6.8</td>
<td>1.5</td>
<td>2.6</td>
<td>1.5</td>
<td>1.2</td>
<td>2.2</td>
<td>&lt;0.02</td>
<td>6</td>
<td>670</td>
<td>1.5</td>
<td>&lt; 0.05</td>
<td>3.2</td>
<td>39</td>
<td>7.2</td>
<td>120</td>
<td>10</td>
<td>3</td>
<td>2</td>
<td>0.88</td>
<td>13</td>
<td>3.3</td>
<td>1</td>
<td>0.69</td>
<td>19</td>
</tr>
<tr class="odd">
<td>25</td>
<td>7.6</td>
<td>2</td>
<td>3.1</td>
<td>1.6</td>
<td>1.5</td>
<td>2.4</td>
<td>&lt;0.02</td>
<td>5.7</td>
<td>660</td>
<td>1.3</td>
<td>&lt; 0.05</td>
<td>3.6</td>
<td>45</td>
<td>9.5</td>
<td>140</td>
<td>10</td>
<td>3.6</td>
<td>2.3</td>
<td>1</td>
<td>14</td>
<td>3.9</td>
<td>1</td>
<td>0.77</td>
<td>22</td>
</tr>
<tr class="even">
<td>26</td>
<td>7.7</td>
<td>2.4</td>
<td>3.2</td>
<td>1.8</td>
<td>1.6</td>
<td>2.1</td>
<td>&lt;0.02</td>
<td>6</td>
<td>600</td>
<td>1.4</td>
<td>&lt; 0.05</td>
<td>2.5</td>
<td>56</td>
<td>11</td>
<td>140</td>
<td>10</td>
<td>4</td>
<td>2.6</td>
<td>1.2</td>
<td>15</td>
<td>4.3</td>
<td>1.1</td>
<td>0.88</td>
<td>28</td>
</tr>
<tr class="odd">
<td>27</td>
<td>7.2</td>
<td>2.1</td>
<td>2.9</td>
<td>1.7</td>
<td>1.4</td>
<td>2.3</td>
<td>&lt;0.02</td>
<td>5.1</td>
<td>580</td>
<td>1.1</td>
<td>&lt; 0.05</td>
<td>1.8</td>
<td>44</td>
<td>10</td>
<td>140</td>
<td>9</td>
<td>3.5</td>
<td>2.2</td>
<td>0.93</td>
<td>14</td>
<td>3.7</td>
<td>1</td>
<td>0.78</td>
<td>22</td>
</tr>
</tbody>
</table>

**Table 4.** Summary of geochemical data for sediment samples (analyses
by ICP-MS after acid digestion at USGS Denver)

**Table 4** (continued). Summary of geochemical data for sediment
samples (analyses by ICP-MS after acid digestion at USGS Denver)

<table style="width:100%;">
<colgroup>
<col style="width: 5%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 3%" />
<col style="width: 3%" />
<col style="width: 4%" />
<col style="width: 4%" />
<col style="width: 4%" />
</colgroup>
<tbody>
<tr class="odd">
<td><h4 id="sample-1">Sample</h4></td>
<td><strong>Li</strong></td>
<td><strong>Mn</strong></td>
<td><strong>Mo</strong></td>
<td><strong>Nd</strong></td>
<td><strong>Ni</strong></td>
<td><strong>Pb</strong></td>
<td><strong>Pr</strong></td>
<td><strong>Rb</strong></td>
<td><strong>Sb</strong></td>
<td><strong>Se</strong></td>
<td><strong>Sm</strong></td>
<td><strong>Sn</strong></td>
<td><strong>Sr</strong></td>
<td><strong>Tb</strong></td>
<td><strong>Th</strong></td>
<td><strong>Tl</strong></td>
<td><strong>Tm</strong></td>
<td><strong>U</strong></td>
<td><strong>V</strong></td>
<td><strong>W</strong></td>
<td><strong>Yb</strong></td>
<td><strong>Zn</strong></td>
</tr>
<tr class="even">
<td></td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
<td>ppm</td>
</tr>
<tr class="odd">
<td>A1A</td>
<td>43</td>
<td>350</td>
<td>1.9</td>
<td>22</td>
<td>81</td>
<td>17</td>
<td>5.5</td>
<td>78</td>
<td>0.5</td>
<td>1</td>
<td>3.9</td>
<td>12</td>
<td>210</td>
<td>0.68</td>
<td>7.6</td>
<td>0.6</td>
<td>0.39</td>
<td>3.6</td>
<td>120</td>
<td>1.5</td>
<td>2.7</td>
<td>92</td>
</tr>
<tr class="even">
<td>B1</td>
<td>43</td>
<td>370</td>
<td>1.6</td>
<td>22</td>
<td>79</td>
<td>13</td>
<td>5.6</td>
<td>78</td>
<td>0.4</td>
<td>1</td>
<td>4</td>
<td>14</td>
<td>220</td>
<td>0.7</td>
<td>7</td>
<td>0.5</td>
<td>0.36</td>
<td>3.5</td>
<td>120</td>
<td>1.3</td>
<td>2.7</td>
<td>94</td>
</tr>
<tr class="odd">
<td>10A</td>
<td>29</td>
<td>300</td>
<td>0.7</td>
<td>15</td>
<td>57</td>
<td>8.5</td>
<td>3.8</td>
<td>72</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3</td>
<td>4</td>
<td>190</td>
<td>0.5</td>
<td>4.6</td>
<td>0.4</td>
<td>0.26</td>
<td>1.8</td>
<td>90</td>
<td>0.7</td>
<td>1.8</td>
<td>76</td>
</tr>
<tr class="even">
<td>5</td>
<td>44</td>
<td>360</td>
<td>1.8</td>
<td>20</td>
<td>80</td>
<td>13</td>
<td>5.5</td>
<td>81</td>
<td>0.4</td>
<td>1</td>
<td>3.6</td>
<td>13</td>
<td>200</td>
<td>0.65</td>
<td>7.4</td>
<td>0.5</td>
<td>0.33</td>
<td>3.6</td>
<td>120</td>
<td>1.2</td>
<td>2.4</td>
<td>95</td>
</tr>
<tr class="odd">
<td>6</td>
<td>40</td>
<td>360</td>
<td>2.3</td>
<td>20</td>
<td>80</td>
<td>13</td>
<td>4.9</td>
<td>74</td>
<td>&lt;0.3</td>
<td>1</td>
<td>3.8</td>
<td>12</td>
<td>240</td>
<td>0.65</td>
<td>6.9</td>
<td>0.5</td>
<td>0.32</td>
<td>3.3</td>
<td>120</td>
<td>1</td>
<td>2.3</td>
<td>93</td>
</tr>
<tr class="even">
<td>7</td>
<td>40</td>
<td>340</td>
<td>2.3</td>
<td>20</td>
<td>78</td>
<td>14</td>
<td>5.1</td>
<td>76</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.8</td>
<td>13</td>
<td>210</td>
<td>0.62</td>
<td>6.4</td>
<td>0.5</td>
<td>0.35</td>
<td>3.2</td>
<td>120</td>
<td>1.1</td>
<td>2.4</td>
<td>92</td>
</tr>
<tr class="odd">
<td>8</td>
<td>44</td>
<td>360</td>
<td>1.6</td>
<td>20</td>
<td>82</td>
<td>13</td>
<td>5.2</td>
<td>80</td>
<td>&lt;0.3</td>
<td>1</td>
<td>3.7</td>
<td>9.5</td>
<td>200</td>
<td>0.64</td>
<td>7.1</td>
<td>0.5</td>
<td>0.36</td>
<td>3.4</td>
<td>120</td>
<td>1.2</td>
<td>2.6</td>
<td>99</td>
</tr>
<tr class="even">
<td>9</td>
<td>41</td>
<td>350</td>
<td>2.4</td>
<td>20</td>
<td>78</td>
<td>14</td>
<td>5.2</td>
<td>79</td>
<td>0.3</td>
<td>1</td>
<td>3.8</td>
<td>13</td>
<td>220</td>
<td>0.67</td>
<td>7.1</td>
<td>0.5</td>
<td>0.34</td>
<td>3.3</td>
<td>120</td>
<td>1.2</td>
<td>2.5</td>
<td>94</td>
</tr>
<tr class="odd">
<td>11</td>
<td>43</td>
<td>360</td>
<td>1.8</td>
<td>21</td>
<td>82</td>
<td>12</td>
<td>5</td>
<td>75</td>
<td>0.3</td>
<td>1</td>
<td>3.7</td>
<td>13</td>
<td>200</td>
<td>0.66</td>
<td>6.5</td>
<td>0.5</td>
<td>0.35</td>
<td>2.9</td>
<td>120</td>
<td>1.1</td>
<td>2.6</td>
<td>96</td>
</tr>
<tr class="even">
<td>12</td>
<td>40</td>
<td>380</td>
<td>1.9</td>
<td>21</td>
<td>79</td>
<td>14</td>
<td>5.2</td>
<td>77</td>
<td>&lt;0.3</td>
<td>1</td>
<td>4</td>
<td>14</td>
<td>240</td>
<td>0.65</td>
<td>7.2</td>
<td>0.5</td>
<td>0.34</td>
<td>3</td>
<td>130</td>
<td>1.1</td>
<td>2.6</td>
<td>98</td>
</tr>
<tr class="odd">
<td>13</td>
<td>42</td>
<td>380</td>
<td>2</td>
<td>18</td>
<td>80</td>
<td>13</td>
<td>4.9</td>
<td>75</td>
<td>1.3</td>
<td>1</td>
<td>3.4</td>
<td>31</td>
<td>220</td>
<td>0.63</td>
<td>6.8</td>
<td>0.5</td>
<td>0.33</td>
<td>3</td>
<td>120</td>
<td>1</td>
<td>2.3</td>
<td>91</td>
</tr>
<tr class="even">
<td>14</td>
<td>44</td>
<td>360</td>
<td>2.6</td>
<td>20</td>
<td>81</td>
<td>12</td>
<td>5.2</td>
<td>79</td>
<td>0.3</td>
<td>1</td>
<td>4</td>
<td>12</td>
<td>210</td>
<td>0.65</td>
<td>7.4</td>
<td>0.5</td>
<td>0.38</td>
<td>3.6</td>
<td>120</td>
<td>1.2</td>
<td>2.8</td>
<td>110</td>
</tr>
<tr class="odd">
<td>15</td>
<td>25</td>
<td>240</td>
<td>0.5</td>
<td>13</td>
<td>45</td>
<td>7.9</td>
<td>3.2</td>
<td>80</td>
<td>0.3</td>
<td>&lt; 1</td>
<td>2.6</td>
<td>3</td>
<td>190</td>
<td>0.38</td>
<td>3.9</td>
<td>0.3</td>
<td>0.22</td>
<td>1.6</td>
<td>81</td>
<td>0.4</td>
<td>1.4</td>
<td>79</td>
</tr>
<tr class="even">
<td>16</td>
<td>30</td>
<td>340</td>
<td>0.6</td>
<td>19</td>
<td>58</td>
<td>10</td>
<td>4.5</td>
<td>71</td>
<td>0.4</td>
<td>&lt; 1</td>
<td>3.4</td>
<td>3</td>
<td>240</td>
<td>0.58</td>
<td>5.4</td>
<td>0.4</td>
<td>0.33</td>
<td>2.2</td>
<td>93</td>
<td>0.7</td>
<td>2.2</td>
<td>66</td>
</tr>
<tr class="odd">
<td>17</td>
<td>36</td>
<td>380</td>
<td>0.7</td>
<td>20</td>
<td>67</td>
<td>10</td>
<td>5.1</td>
<td>83</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.7</td>
<td>2</td>
<td>240</td>
<td>0.64</td>
<td>7.4</td>
<td>0.4</td>
<td>0.36</td>
<td>2.4</td>
<td>110</td>
<td>0.8</td>
<td>2.4</td>
<td>77</td>
</tr>
<tr class="even">
<td>18</td>
<td>41</td>
<td>360</td>
<td>1.4</td>
<td>21</td>
<td>75</td>
<td>15</td>
<td>5.2</td>
<td>78</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>4</td>
<td>12</td>
<td>230</td>
<td>0.65</td>
<td>6.9</td>
<td>0.5</td>
<td>0.32</td>
<td>3.1</td>
<td>120</td>
<td>1.6</td>
<td>2.4</td>
<td>92</td>
</tr>
<tr class="odd">
<td>19</td>
<td>20</td>
<td>440</td>
<td>0.6</td>
<td>26</td>
<td>44</td>
<td>12</td>
<td>6.1</td>
<td>48</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>4.5</td>
<td>2</td>
<td>270</td>
<td>0.7</td>
<td>9</td>
<td>0.4</td>
<td>0.33</td>
<td>2.4</td>
<td>96</td>
<td>0.8</td>
<td>2.3</td>
<td>44</td>
</tr>
<tr class="even">
<td>20</td>
<td>26</td>
<td>380</td>
<td>0.6</td>
<td>17</td>
<td>43</td>
<td>9.4</td>
<td>4.4</td>
<td>55</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.4</td>
<td>4</td>
<td>260</td>
<td>0.6</td>
<td>8.9</td>
<td>0.5</td>
<td>0.29</td>
<td>2.5</td>
<td>84</td>
<td>0.6</td>
<td>2.2</td>
<td>53</td>
</tr>
<tr class="odd">
<td>21</td>
<td>25</td>
<td>360</td>
<td>0.6</td>
<td>20</td>
<td>48</td>
<td>10</td>
<td>4.7</td>
<td>54</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.5</td>
<td>2</td>
<td>240</td>
<td>0.58</td>
<td>5.5</td>
<td>0.5</td>
<td>0.33</td>
<td>2</td>
<td>84</td>
<td>0.6</td>
<td>2.3</td>
<td>55</td>
</tr>
<tr class="even">
<td>22</td>
<td>8.4</td>
<td>140</td>
<td>0.2</td>
<td>21</td>
<td>2</td>
<td>6.3</td>
<td>5.7</td>
<td>34</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>2.9</td>
<td>0.8</td>
<td>1100</td>
<td>0.38</td>
<td>5.8</td>
<td>0.3</td>
<td>0.16</td>
<td>0.77</td>
<td>24</td>
<td>&lt; 0.1</td>
<td>0.98</td>
<td>20</td>
</tr>
<tr class="odd">
<td>23</td>
<td>4.1</td>
<td>91</td>
<td>0.1</td>
<td>6.8</td>
<td>&lt;0.1</td>
<td>4.7</td>
<td>1.7</td>
<td>11</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>0.99</td>
<td>&lt; 0.5</td>
<td>2300</td>
<td>0.16</td>
<td>1.1</td>
<td>&lt;0.1</td>
<td>0.068</td>
<td>0.63</td>
<td>13</td>
<td>&lt; 0.1</td>
<td>0.5</td>
<td>7</td>
</tr>
<tr class="even">
<td>24</td>
<td>27</td>
<td>300</td>
<td>0.5</td>
<td>17</td>
<td>41</td>
<td>8.9</td>
<td>4.2</td>
<td>56</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.1</td>
<td>2</td>
<td>260</td>
<td>0.53</td>
<td>4.7</td>
<td>0.6</td>
<td>0.26</td>
<td>1.9</td>
<td>83</td>
<td>0.5</td>
<td>1.9</td>
<td>55</td>
</tr>
<tr class="odd">
<td>25</td>
<td>28</td>
<td>440</td>
<td>0.7</td>
<td>20</td>
<td>52</td>
<td>9.4</td>
<td>4.7</td>
<td>64</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.6</td>
<td>2</td>
<td>280</td>
<td>0.66</td>
<td>6.3</td>
<td>0.5</td>
<td>0.3</td>
<td>2</td>
<td>99</td>
<td>1.1</td>
<td>2.4</td>
<td>58</td>
</tr>
<tr class="even">
<td>26</td>
<td>24</td>
<td>450</td>
<td>0.6</td>
<td>25</td>
<td>48</td>
<td>11</td>
<td>6.1</td>
<td>62</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>4.5</td>
<td>2</td>
<td>280</td>
<td>0.68</td>
<td>6.7</td>
<td>0.5</td>
<td>0.34</td>
<td>2.1</td>
<td>93</td>
<td>0.6</td>
<td>2.4</td>
<td>55</td>
</tr>
<tr class="odd">
<td>27</td>
<td>26</td>
<td>380</td>
<td>0.5</td>
<td>20</td>
<td>50</td>
<td>9.7</td>
<td>4.8</td>
<td>54</td>
<td>&lt;0.3</td>
<td>&lt; 1</td>
<td>3.7</td>
<td>2</td>
<td>260</td>
<td>0.6</td>
<td>5.5</td>
<td>0.4</td>
<td>0.32</td>
<td>1.8</td>
<td>90</td>
<td>0.6</td>
<td>2.2</td>
<td>51</td>
</tr>
<tr class="even">
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>

# Results and discussion

## Seabed gamma spectrometry

The EEL data were converted in real time into approximate sea floor
concentrations of radionuclides. This was done by comparing each 5-s
gamma-ray spectrum to standard spectra for K, U, Th, and Cs (Hendri*ks
et a*l., 2001). The standard spectra were obtained from measurements
made with the detector in a tank of water on each of a set of
calibration pads. The K, U, and Th pads are concrete blocks containing
known amounts of K, U, and Th. A fourth, background, pad is a plain
concrete block with no added radioactive material. The Cs pad consists
of a wooden box containing fine sand from the Irish Sea contaminated by
^137^Cs from the authorised discharges of the Sellafield nuclear plant.

Examination of the EEL data during the survey suggested only very low
seabed levels of gamma-emitting artificial radionuclides such as
^137^Cs; no obvious ^137^Cs peaks were noticed in the sea bed gamma-ray
spectra (e.g., fig. 8). The variations seen in sea floor radioactivity
were in natural isotopes (of K and the U and Th decay series)
attributable to geological features. These are most obvious at the 90-m
site where features seen on sidescan sonar records (fig. 9) have a
distinctive response in the radiometric and other EEL data (fig. 10).

**Figure 8.** Typical seabed gamma-ray spectrum from the survey.
Horizontal axis = gamma-ray energy (MeV), vertical axis = counts. The
red vertical lines indicate the positions of the ^137^Cs (0.66MeV),
^40^K (1.46MeV), ^214^Bi (U)(1.76MeV), and ^208^Tl (Th) (2.62MeV) lines

Line 90_3 (fig 10a) shows a generally uniform total gamma signal over a
smooth sediment-covered sea floor. Two small upstanding features on the
seabed (seen on the pressure trace and as high noise features)
correspond to gravel waves seen clearly on the sidescan mosaic (fig. 9).
These do not show any major difference in total count compared to the
surrounding finer grained sediments.

In contrast, the rough areas of sea floor on Line 90_7 (fig. 10b), which
are apparent on the sound and pressure traces, have a markedly higher
total count signal than their surroundings. These features match rock
outcrops seen on the sidescan image (fig. 9) and are probably (from
their radiometric signature) granitic, an interpretation consistent with
their proximity to the granite ridge of the Farallon Islands (NOAA,
1990). Line 90_7 also shows a change in sediment type along its length.
The left hand end of the

**Figure 9.** Sidescan mosaic for 90-m area.

segment of line depicted in figure 10b shows a general total count base
level of about 100 counts per second between the outcrops. This is
consistent with siliciclastic sediments. In contrast, the right hand end
of the line shows sediments with a total count of only around 50 counts
per second. These were interpreted as shelly sands, and this was
confirmed by sampling.

**Figure. 10A.** Examples of geological variation of gamma spectrometer
data. Line 90_3 (complete line).

**Figure. 10B**. Examples of geological variation of gamma spectrometer
data. Line 90_7 (N end of line approximately N of sample site 24, fig.
10) .

After the survey, the gamma-ray spectra were postprocessed to optimise
the sea floor data for individual radionuclides. Particular attention
was given to the ^137^Cs data. Initially this was done for each 5-s
gamma-ray spectrum, but this produced very noisy Cs results owing to the
very low levels present. A second stage of the postprocessing was
therefore undertaken. This involved integrating the data over longer
periods of time to try to obtain more reliable ^137^Cs values. Data were
compared for one test line (900_7) on the basis of spectra integrated
over 5-s, 50-s, 150-s and 500-s periods (corresponding to approximately
5, 50, 150, and 500 m of seabed towed). When the integration period was
extended to 500 s, variations along the test line showed a coherent
structure and the highest values occurred where the line came closest to
the known highest concentrations of barrels on the sea floor (fig. 11).
This suggested that meaningful data might be extracted over 500-s
periods.

The postprocessing was therefore re-run using 500-s integration, on the
basis of moving averages along each line, to assess whether there was a
geographical coherence to the ^137^Cs values. One data file had become
corrupted (line 900_6) and was not available for postprocessing.

The 500-s data for the 900-m site data appear to show a coherent
pattern, with the connection of relatively high and low values between
survey lines (fig. 12). This suggests some confidence can be placed in
the data. However, the levels of ^137^Cs present must be regarded as
being close to the detection limit of the system, even for 500-s
counting periods, and the data should be treated with caution.

**Figure 12.** ^137^Cs data for 900-m site. Typical uncertainties (1σ)
are about 15 percent.

. ![](media/image5.wmf) **Figure 11.** ^137^Cs data integrated over 5,
50, 150 and 500 s. Each record number represents one 5s count covering
about 5m of seabed.

A background was removed, initially, from the full postprocessed
dataset. This was designed to remove the effects of seawater and the
detector itself. Seawater contains some 50 Bq/l of ^40^K, and the
detector has a small amount of ^207^Bi, which mainly affects the U and
^137^Cs data (because of the proximity of the 570 keV ^207^Bi peak to
the 662 keV ^137^Cs peak and the 609 keV ^214^Bi peak). However,
background removal caused a relative increase in the Cs values, compared
with those obtained with no background subtraction. The ^137^Cs
concentrations from nonbackground corrected data are closer to those
obtained by sample analysis (table 1). Also, the statistical fit of the
spectra with the standard spectra is, paradoxically, better when no
background is used. This may reflect the different operating conditions
under which the standard spectra had to be collected under, owing to
lack of time, compared with the background data. The latter were
gathered under survey conditions, whereas the standard spectra were
obtained using the same detector, but a different cable and electronics.

As the background correction largely causes a uniform shift in the final
^137^Cs and other radionuclide concentrations, it does not affect
significantly the relative values. In order to keep the ^137^Cs figures
(and those for other radionuclides) closer to the more accurate sample
analyses, the data are presented without background removal (figs.
12-23).

The postprocessed seabed data show some correspondence between higher
seabed ^137^Cs concentrations and proximity to the known locations of
barrels at the 900-m and cluster sites (figs. 12 and 13). There are also
relatively high values where no barrels have been located. This might be
expected to occur where barrels are too degraded to produce a detectable
sidescan response. It should be noted that the total number of targets
identified using sidescan data represents only a small proportion of the
total number of barrels reportedly disposed of at the 900-m site.

**Figure 13.** ^137^Cs data for Cluster site. Typical uncertainties (1σ)
about 15 percent.

There are also relatively low ^137^Cs levels around some barrel
clusters. This again is to be expected; the barrels could be intact, or
at least have not suffered leakage, or there may not be any Cs present
in those barrels.

Overall, the data indicate very low ^137^Cs contents across the survey
area. There are no suggestions of any significant regional scale
contamination of the sediments by ^137^Cs, nor of any localised
concentrations of this radionuclide.

The postprocessed 500-s ^137^Cs data for the 90m site are also
apparently quite coherent. The 90-m ^137^Cs values are lower overall
than the 900m and cluster data (figs. 12-14), which fits with the lower
concentrations of ^137^Cs observed in sample analyses (table 1).
Similarly low levels were seen on the two 1,800-m lines (fig. 15).
Higher levels of ^137^Cs at the 90-m site appear to be very localised.
There is no real correlation between the Cs data at the 90-m site and
those for K, U, and Th, making the data difficult to interpret in terms
of seabed geology (figs. 14 and 16-19).

**Figure 14.** ^137^Cs data for 90-m site. Typical uncertainties (1σ)
about 15 percent

## Laboratory analysis

Subsequent laboratory sample analysis has confirmed the low levels of
^137^Cs (\<5 Bqkg^-1^) (table 1). The data are consistent with
concentrations less than 10 Bqkg^-1^ ^137^Cs reported from earlier
studies (Dyer, 1976; NOAA, 1990; Noshk*in et a*l., 1978; Schell and
Sugai, 1980). Gamma-ray spectrometry indicated that similarly low levels
of ^241^Am may be present in a few samples. This was confirmed by alpha
spectrometry of a selected number of samples (table 2). The latter
analysis reveals detectable ^241^Am, in four of the eight samples
selected, at levels below 2 Bqkg^-1^. Plutonium isotopes were also
detected; ^239,240^Pu in all eight

**Figure 15.** ^137^Cs data for 1800-m site. Typical uncertainties (1σ)
about 15 percent.

samples at similarly low levels to ^241^Am (no greater than 3 Bqkg^-1^)
and ^238^Pu only in sample 5. Again, these results are in line with
previous work with ^239+240^Pu concentrations up to 5 Bqkg^-1^ being
reported (Noshk*in et a*l., 1978; Schell and Sugai, 1980), whilst Dyer
(1976) found slightly higher levels, in some samples, up to 20 Bqkg^-1^
and ^238^Pu contents of up to 5 Bqkg^-1^.

These concentrations are well below the natural background levels of
^40^K (typically 400-600 Bqkg^-1^) and generally below the
concentrations of U(^214^Bi) and Th(^208^Tl), which mostly range from
15-50 and 15-30 Bqkg^-1^ respectively. Whether the sediments are
contaminated in excess of what would be expected from nuclear weapons
fallout has been a matter of some controversy (NOAA, 1990). What is
clear is that the concentrations of ^137^Cs, ^241^Am, and Pu isotopes
are considerably lower than levels encountered in Irish Sea sediments
(e.g., Jon*es et a*l., 1999; Kersh*aw et a*l., 1999). These reach maxima
2 or 3 orders of magnitude higher than those observed from the
Farallons, but they do not give rise to doses in excess of annual
limits, either through direct exposure or through the food chain (e.g.
FSA/SEPA, 2000).

^137^Cs was detected in all the 90-m samples except for two with very
high shell contents (Nos. 22 and 23). Three of the 900-m site samples
had no detectable ^137^Cs. Slightly higher (albeit still very low)
levels of ^137^Cs occur in samples taken near known barrels, and some of
these have detectable ^241^Am. Away from the 'cluster' locations,
^241^Am was only detected in one sample (from the 90-m site) at an
extremely low level (0.2 Bqkg^-1^) by α spectrometry. Similarly, Pu
contents of the sediment samples are higher in the vicinity of known
barrels than elsewhere in the 900-m site or the 90-m site. The
differences in Cs, Am, and Pu levels between the 'cluster' samples and
other locations could be due to inputs of radioactivity from the waste
in the barrels or the result of differential input/uptake of fallout
radionuclides.

Barrel leakage is indicated by the coincidence of higher values of Cs,
Am, and Pu with the barrel clusters and the generally similar levels of
natural radioactivity in the samples, regardless of Cs and Am content.
It is further supported by the poor condition of at least some barrels.
There have been differing interpretations made of previous sample
analyses, but most authors conclude that there has been some input

**Figure 16.** Total count data for 90-m site (counts.s^-1^). Typical
uncertainties (1σ) better than 1 percent.

to the sediments from the barrels (NOAA, 1990; Schell and Sugai, 1980).
If barrel leakage has occurred, then there are no indications, in the
present data, of any significant enhancement of radionuclide levels on a
regional scale in the areas surveyed.

Alternative explanations are that the variations are due to differences
in fallout radionuclide input or uptake. The latter could be influenced
by differences in sedimentation rate, with fallout particles being more
efficiently scavenged from the water column or, conversely, diluted by
higher rates of sediment buildup.

Sample data do indicate clear differences between the shallow water
sediments at the 90-m site and those from the much deeper 900-m site
(fig. 24; tables 1-4). The 900-m site has finer grained sediments (figs.
25 and 26); mud contents at the 90-m site are less than 40% with clay
contents below about 10%, whereas mud contents at the 900-m site are
mostly above 30%, ranging up to over 90%, and clay contents are in the
range of 10-40%. The main geochemical differences between the two areas
lie in higher Fe and Mg values at the 900-m site, along with a range of
trace elements, including As, Cr, Cu, Ge, Li, Mo, Ni, Pb, Rb, Sn, U, V,
W, and Zn (Fig. 24; Table 4). Levels of Al and K are broadly comparable.
This suggests a different mix of clay minerals at the sites with Fe and
Mg-rich species (e.g., smectite), with a great affinity for many trace
elements, being more important in deeper water. An increase in smectite
with increasing water depth has been noted in mineralogical studies of
the area (Boo*th et a*l., 1989; Griggs and Hein, 1980).

**Figure 17.** K data for the 90-m site. Typical uncertainties (1σ)
better than 2 percent.

There is, however, no obvious relationship between ^137^Cs content and
the grain size of the sediments (Figs. 25 and 26), or their
geochemistry. Thus the data do not support the preferential uptake of
^137^Cs in the 'cluster' area owing to an increased sorption capacity
for Cs of the sediments. Geochemicallyand texturally the 'cluster' site
is very similar to the remainder of the 900-m site (fig. 24; tables 3
and 4). This suggests that the slightly higher contents of radionuclides
in the vicinity of known barrels are most likely due to leakage from the
barrels. However, the differences in radionuclide contents between the
90-m and 900-m sites could in part be due to the increased sorption
capacity of the deeper water, relatively smectite-rich sediments. An
increase in radionuclide retention capacity of the deeper sediments was
suggested by the data of Booth et al. (1989).

U and Th concentrations in the bottom sediments are all well within
normal ranges for sediments (Wedepohl, 1978) in both the EEL and the
sample data (figs. 18, 19, 22-24 and tables 1 and 4). Levels of U are
higher in the deeper water sediments, reflecting the greater proportion
of finer material, but Th values are broadly similar across the whole
survey area. As for Cs, there is no clear-cut relationship between U or
Th content and known barrel locations. Some higher Th and/or U areas
coincide with barrels, but other barrel locations are associated with
lower Th and/or U. Since the levels of U and Th do not differ from
natural background values, there is no need to invoke an input from the
barrels to explain the distribution. However, the generally higher
contents of U and Th in the sediments from the cluster site, when
compared with elsewhere in the 900-m site, may indicate a slight
enhancement due to input from the barrels. U and Th

**Figure 18.** U data for the 90-m site. Typical uncertainties (1σ)
better than 25 percent.

are listed as being present in the wastes disposed at the Farallon
Islands Radioactive Waste Dump (NOAA, 1990; Noshk*in et a*l., 1978).

Geochemical analyses of the sediment samples do not indicate any
significant enhancement of other contaminants such as heavy metals or Be
(fig. 24; table 4). Sn is the only element reported at levels that are
appreciably above those expected for average fine-grained sediments or
rocks (Turekian and Wedepohl, 1961). Concentrations of Sn are
approximately twice the average shale levels (of 6 ppm) in most samples
from the cluster site, and one from the 900-m site, with a maximum of 31
ppm in sample 13. Since Hg and organic contaminants were not measured in
the samples, it is not possible to comment on the impact, if any, of the
disposal of other types of waste in the area.

# Conclusions

Both in situ measurements and laboratory analyses of sediment samples
indicate only very low levels of artificial radionuclides in the
surveyed areas of the Farallon Dump Site. Concentrations of ^137^Cs,
^241^Am, ^239+240^Pu and ^238^Pu, in the sediments are all below 10
Bqkg^-1^. These are significantly lower than natural background levels
of K, U, and Th. They are also well below concentrations encountered in
Irish Sea sediments, which arise from authorised discharges of waste
from the Sellafield nuclear reprocessing plant. There appears to be some
indication of leakage of radionuclides from the barrels of waste, but
this only

**Figure 19.** Th data for the 90-m site. Typical uncertainties (1σ)
better than 5 percent.

seems to have raised radionuclide levels slightly in the sediments in
the vicinity of the barrels. There is no evidence for significant
regional-scale contamination as a result of the dumping in the areas
surveyed.

Levels of natural radionuclides are well within the normal range for sea
floor sediments, although there could have been some input of U and Th
from the barrels.

It should be borne in mind, however, that, at this stage, no data have
been obtained for large areas of the dump site. In particular the 1800m
site, where the majority of the barrels are believed to have been
dumped, remains virtually unstudied, in terms of both the radionuclide
content of the sediments and the actual locations of the barrels. To
date barrel locations have only been mapped in 15% of the dump area, and
radionuclide concentrations examined in only about 10% of the site. On
the other hand, the areas studied are those in the shallower waters of
the 90-m and 900-m sites most accessible to man.

This study, along with the earlier USGS work, shows the value of
interagency co-operation and the merit of being able to target
measurements and sampling on the basis of knowledge of barrel locations.
This integrated approach could be extended to the deeper parts of this
site and applied in other areas, such as Boston Harbour, the Kara Sea,
and Beauforts Dyke in the Irish Sea. The data obtained by this type of
study enable informed decisions to be made regarding the environmental
quality and management of the ocean.

# Acknowledgments

We are grateful to M.H. Strutt, D.K. Talbot, M P Rainey and J.R. Davis,
of the BGS for logistical support, sample analysis, data processing and
presentation. The assistance of the USGS Marine Facility staff (S.
Wallace, D. Hogg, L. Kooker, F. Payne and others) is acknowledged with
thanks. Navigational support was provided by M. Hamer and G. Dunhill of
the USGS and radiological safety support by C. Petullo, L. Karr and S.
Faller of EPA. The work would not have been possible without the help of
the officers and crew of the NOAA ship *McArthur* and the co-operation
of the Gulf of the Farallones National Marine Sanctuary.

**Figure 20.** Total count data for the 900-m site (counts.s^-1^).
Typical uncertainties (1σ) better than 1 percent.

**Figure 21.** K data for the 900-m site. Typical uncertainties (1σ)
better than 2 percent.

**Figure 22.** U data for the 900-m site. Typical uncertainties (1σ)
better than 25 percent.

**Figure 23.** The data for the 900-m site. Typical uncertainties (1σ)
better than 5 percent.

![](media/image6.wmf)**Figure 24A**. Multielement geochemical plots for
sediment samples. All samples.

> ![](media/image7.wmf)**Figure 24B**. Multielement geochemical plots
> for sediment samples. Two shelly samples (22, 23) omitted.

![](media/image8.wmf)**Figure 25.** Relationship of ^137^Cs to mud
content of sediments samples.

**Figure 26**. Relationship of ^137^![](media/image9.wmf)Cs to clay
content of sediments samples.

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