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In reply refer to: DEPARTMENT OF THE INTERIOR Technical Letter GEOLOGICAL SURVEY Long Shot-lA Federal Center, Denver, Colorado 80225 TECHNICAL LETTER: LONG SHOT-1A HYDROLOGY OF THE LONG SHOT SITE, AMCHITKA ISLAND, IK ILASSIRCATION RETAINED CLASSIFICATION CHANGED TO:. _
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In reply refer to: DEPARTMENT OF THE INTERIOR Federal Center, Denver, Colorado 80225 HYDROLOGY OF THE LONG SHOT SITE, AMCHITKA ISLAND, ALASKA--AN ADDENDUM This report is a revision and an addendum to the hydrology section e4 of U.S. Geological Survey Technical Letter Long Shot-1. Further analysis of the hydrologic data obtained from test holes, a more realistic estimate of the residual tritium available from the proposed shot, and consideration of dilution of radioactivity to near background in sea water require this revision and addition. MOVEMENT OF GROUND WATER The ground-water system is assumed as before to consist of a network of interconnected fractures, A ground-water divide is assumed to occur near the center of the island and recharge to occur uniformly over the island. A comparison of the head distribution in a model of a uniformly permeable fresh water system to that measured in test hole EH-5 suggests that the zone between 2,175 and 2,574 feet (the zone of the andesite sill) is more permeable than the bulk of the ground-water system. The approximate permeability of this lower zone is 0.03 foot per day. This value for permeability is taken as the maximum limit for the permeability of the system as a whole.
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Using 0.03 foot per day for the average permeability, an approximate head distribution derived from the flow net, and an assumed effective porosity of 0.001, the travel time under natural conditions for ground water to move from the proposed shot point to the discharge area on the ocean floor is calculated to be about 40 years. If the effective porosity were about 1 percent, the travel time would be about 400 years. The more conservative value for travel time from a hazard viewpoint, i.e., 40 years, will be used in computation of transport of radionuclides, although 400 years certainly is not unreasonable. MOVEMENT OF RADIONUCLIDES Although at this time the type of proposed nuclear device to be used is not definitely known, the residual tritium available from the explosion is estimated to be about 3 X 10^ curies. If the yield of the device is about 100 Kt it should produce a cavity volume (Re = 200 feet) of about 9 X 10 cc. Assuming that the tritium will combine to form water and will be dispersed uniformly through the water contained in the chimney (volume of water equals cavity volume), then the initial concentration of tritium will be about 3 X 10"^ curies per cc, or about 3 X 102 times MPC (AEG Manual, 1963) for the population at large. If the chimney should extend to the surface, the initial concentration of tritium will be somewhat larger because of the reduced volume of voids in the chimney rubble; formation of a chimney to the surface is not expected to occur (R. F. Beers, Inc., 1965),
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Using a travel time of 40 years for ground water to move to the ocean from the shot point and assuming no dispersion of tritium in the ground-water system, tritiated water contained about 3 X 10“® curies per cc would emerge on the ocean floor beginning in about 40 years. The discharge rate for this contaminated water, estimating a zone about 1,000 feet wide, would be about 200 ft^ per day, a revised decreased estimate from the initially estimated 500 ft per day because of the decreased permeability value. Dilution of this contaminated water in about 6,000 ft^ of sea water daily would bring the concentration of tritium down to 10“” curies per cc. This volume of sea water required daily would seem to be easily available. Further dilution of the tritiated water may be required if the limited Test Ban Treaty is considered. The present concentration of tritium in sea water ranges between 4 and 10 tritium/^ankama, 1963) (1 tritium unit is about 3.3 p curies per liter). If it is assumed that an increase in concentration of 10 tritium units is the threshold of a detectable increase, then the estimated yield of 200 ft^ of tritiated water daily requires dilution in about 2 X 10® ft® of sea water daily within a 3-mile limit of the shore. If it is assumed that tidal currents would cause effective mixing 2 miles out from the shore, then in a strip 1,000 feet wide and 2 miles long (at a distance of 2 miles, the depth of water is about 200 feet in this locality) the volume of water available for mixing is about 10^ ft®. With this volume available for mixing, the average daily
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transfer of sea water parallel to the shore would need to be about 200 feet. No measurement of ocean currents are known to have been made along the north shore of Amchitka Island but westward flowing currents along the south side of the island and northward flowing currents around the ends of the island have a speed of 1 to 2 miles a day (Dodimead, Favorite, Hirano, 1962). From these data it is reasonable to infer an average transfer of water amounting to 200 feet a day, but measurements need to be made to confirm this notion. ■ Considering the preliminary statements together with the revised treatment of some aspects of the hydrologic conditions and movement of radionuclides, it is concluded that: (1) No contamination of surface waters will result from the Long Shot event. (2) , Fission products of concern in ground-water contamination probably will be confined to the rubble in the chimney and adjacent (3) Tritium in estimated concentrations ranging between 10“^ and 10"® curies per cc may be expected in the fresh ground-water system at depth along a path about 1,000 feet wide extending from the shot point to the sea. Tritiated water will begin to emerge on the ocean floor at the rate of 200 ft^ per day in about 40 years.
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The maximum concentration of tritium should occur within a few years period and thereafter diminish at rate. The area of emergence is estimated to be about 1,000 feet long (parallel to shore) and within 2,000 feet of the shore. Dilution of this tritiated water in sea water to concentrations of at least 10“^ curies per cc are confidently predicted. Further dilution to 10 tritium units per liter within 3 miles of the coast is a reasonable prediction, but measurements of ocean currents are needed to bolster this prediction.
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Roland F. Beers, Inc., 1965, Final evaluation of feasibility, Project Long Shot; Alexandria, Virginia. of the Subarctic Pacific Region in Salmon of the North Pacific Ocean: Bull. 13, International North Pacific Fisheries Comm., Rankama, Kalerno, 196-3, Progress in Isotope Geology: Interscience Publishers, a division of John Wiley and Sons, London, England. U.S. Atomic Energy Commission, 1963, Standards for Radiation Protection: Chapter 0524, jm AEG Manual.