PREFACEThis report is one of a series documenting the results of the SwedishAmerican cooperative research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and struc tural effects anticipated from the use of a large crystalline rock mass as a geologic repository for nuclear waste. This program has been sponsored by the Swedish Nuclear Power Utilities through the Swedish Nuclear Fuel Supply Company (SKBF), and the U.S. Department of Energy (DOE) through the Lawrence Berkeley Laboratory.The principal investigators are L.B. Nilsson and 0. Degerman for SKBF, and N.G.W. Cook, P.A. Witherspoon, and J.E. Gale for LBL. Other participants will appear as authors of the individual reports.Previous technical reports in this series are listed below. water inflow is appreciable, the result is quite unusual: the radon daughter activity in the water adds considerably to the contribution from the rock, and in fact often dominates the log response.The total gamma activity increases where radon-charged groundwater enters a borehole, and remains at a high level as the water flows along the hole in response to the hydraulic gradient. As a consequence, the gamma log serves as a flow profile, locating zones of water entry (or loss) by an increase (or decrease) in the total gamma activity.A simple model for flow through a thin crack emanating radon at a rate E shows that the radon concentration of water entering a hole is E/xh, where x is the radon decay rate and h the crack aperture, assuming that the flow rate and crack source area are such that an element of water resides within Because of its ability to measure flow at very low rates in open bore holes, the radon method or variants of it deserve further investigation. It is also apparent that the natural radioelement distribution at a potential waste storage site must be carefully determined. Even with good baseline data, it is possible that the naturally-occurring radioactive component in groundwater can change in response to changing hydrological conditions.High levels of radon in subsurface waters can cause high concentrations in air. For health safety purposes, radon levels in air were monitored for a two-year time period. Air samples from the four working drifts almost always registered less than the 0.3 Working Levels required by U.S. mine safety standards. Maintenance of a safe working environment is attributed to the relatively low water infiltration rates, avoicance of ponding, and continual operation of the ventilation system.