higher than the California air quality standard. To prove that this response was Mineralized emissions from cooling towers Utility companies realize that the Statewide Air Pollution Research Center at the University will inevitably be associated with geothermal energy production) can kill off nearby vegetation as it escapes from the cooling towers. At the Geysers, the Pacific Gas and Electric Companyhas observed the death of more and moreplants in deposition zones downwind from its powerstations. However, the affected area is of trivial size com- the rule rather than the exception, of California, Riverside, screened many crop and tree species under laboratory conditions to determine - their relative sensitivity to hydrogen sulfide. Later, we used GROW1, an LLNL-developed computer simulation of the mechanisms of biochemical transformation of sulfur and energy allocation in plants, to show that the observed heavily mineralized water (which pared to the land area (approx- imately 5% of the total) required for roads and well heads. We have measured mineral deposition by positioning potted barley plants and passive aerosol collectors downwind from The ozone—is present). Hydrogen sul- Geysers power plants. Boron fide is thus only a problem from the showed up in the barley and native point of view of odor. The Califor: plants and in animals. At 100m nia air quality standard has a more downwind, deposition was than adequate margin to protect primarily a result of the drift of livegetation, even when ozone is quid aerosols (reflected in high flux also present. rates onto leaf tissue and the ground). However, at 1200 m and physiological responses do not indicate a substantial toss of growth for any reasonable, worst-case geothermal emission scenario (even when urban smog—i.e., beyond, we observed higher deposition of cooling tower minerals than would be expected from liquid aerosol transport. Thus, dry transport and deposition mechanisms must also be operative. We observedsignificant increasesin the levels of minerals in runoff water collected at the confluence of streams draining the area. Figure 3 shows boron and sulfate concentrations attributed to deposition on watersheds surrounding The Geysers. Although aquatic ecosystemsat The Geysers may well be adapted to these relatively minor increases, it is important that this mode of transport (and the ultimate fate of the minera! material chronically deposited) be investigated because of the possibility of serious effects over a period of decades. This potential problem has only recently been recognized. Summary Concem about hydrogen sulfide has been a substantial institutional impediment to the development of geothermal resources. However, our research showsthatits actual impact on ecosystems is minor. Conversely, the long-range transport of minerals from cooling towers has been largely ignored, but it appears to be worthy of further investigation. Key words: boron; geothermal energy; geother- mal power plants; hydrogen sulfides. Notes and references 1. See “Portable Instrumentation for Environmental Field Studies,” in the September 1980 Energy and Technology Reuieu (UCRL-52000-80-9), pp. 36-41. 26