- A seabed gamma-ray spectrometer belonging to and 

 operated by the British Geological Survey, called the EEL 

 because of its eel-like appearance, was used to measure 

 the radioactivity of the sea floor in the Gulf of the Farallones. 

 As shown in this diagram, the probe, housed in a protective 

 hose (green), is towed along the sea floor. Data are sent 

 up the towing cable to a shipboard computer and recorded 

 continuously. The gamma-ray detector can measure both 

 natural and artificial radioactivity in the top foot or so of 

 sea-floor surface material. 



12314' 12313' 12312' 



12309'W 



3740'N 



3739' 



3738' 



3737' 



3736' 



3735' 



3.5 



2.9 



2.6 



2.3 



2.1 



1.9 I 



1.7 



1.5 



1.3 



1.1 



1.0 



0.8 



0.6 



0.4 



0.2 



0.0 I 

 0.2 

 -0.6 I 

 -0.9 I 

 -1.7 | 



)37 Cs,in 

 Becquerels per 

 kilogram (Bo/kg) 



$5 Sample site 



Waste drum 



Suspected drum 



Drum cluster 



i Distribution of measured cesium-1 37 ( 137 Cs) radioactivity for the survey of the 900-meter dump (see area B on map, 

 next page). This is an example of a plot produced from gamma-ray radioactivity data collected by the EEL in the Gulf of 

 the Farallones. The EEL data from the gulf do not suggest any significant elevation of radionuclide levels on a regional 

 scale. Most of the observed variations in sea-floor radioactivity are due to changes in natural radioactivity and show a 

 good correlation to geological features but almost no correlation to the distribution of low-level radioactive-waste drums. 

 Apparent negative radioactivity values are an artifact of data-processing calculations, combined with the statistical 

 uncertainty inherent in measuring extremely low radioactivity levels. 



Measuring Radioactivity from Waste Drums on the Sea Floor 69 



