Geothermal Gases-Community Experiences, Perceptions, and Exposures in Northern California

By Chiu, Cindy H.; Lozier, Matthew J. et al. | Journal of Environmental Health, December 2015 | Go to article overview

Geothermal Gases-Community Experiences, Perceptions, and Exposures in Northern California


Chiu, Cindy H., Lozier, Matthew J., Bayleyegn, Tesfaye, Tait, Karen, Barreau, Tracy, Copan, Lori, Roisman, Rachel, Jackson, Rebecca, Smorodinsky, Svetlana, Kreutzer, Richard A., Yip, Fuyuen, Wolkin, Amy, Journal of Environmental Health


Introduction

Lake County, California, is in north central California, north of San Francisco Bay. Lake County sits on tectonic plate conjunctions, generally described as areas where separate slabs of the earth's crust meet. Consequently, Lake County's population--currently at some 64,323 persons--has long been subjected to volcanic activity resulting from plate tectonics, or the movement of these giant slabs (U.S. Census Bureau, 2012; U.S. Geological Survey [USGS], 2004). Plate tectonics make Lake County vulnerable to a variety of environmental hazards, including earthquakes, volcanic eruptions, and geothermal venting. When a complex mixture of geothermal gases vents into the atmosphere from holes in the ground or diffuses through the soil, geothermal venting occurs. Gases such as hydrogen sulfide and methane release into the environment, which at high exposure levels can cause adverse health effects (both) and risk of explosion (methane) (Agency for Toxic Substances and Disease Registry [ATSDR], 2006; Etiope et al., 2006; International Programme on Chemical Safety, 2000a, 2000b; USGS, 2010). Hydrogen sulfide and methane can be summarized as follows:

* Hydrogen sulfide is a toxic gas with a characteristic rotten egg odor detected at 0.0005-0.3 parts per million (ppm), with olfactory fatigue at >100 ppm where continued exposure can temporarily disable the sense of smell (ATSDR, 2006). At 10-20 ppm, exposure can cause irritation to the eyes (World Health Organization [WHO], 2000); higher levels can cause headache, dizziness, and breathing dif ficulty. Exposure to extremely high levels (1,000-2,000 ppm) can result in immediate collapse and death (WHO, 2000).

* Methane is an odorless but highly flammable gas with risk of explosion at 5%-15% in air (International Programme on Chemical Safety, 2000b). At high levels, methane can also cause death through asphyxiation; however, explosion is likely to occur before reaching asphyxiation levels, making explosion risk the primary concern.

Most hydrogen sulfide health effects studies evaluated high-level occupational or accidental release exposures. One example is Poza Rica, Mexico, where in 1950, 22 people died and 320 people were hospitalized (McCabe & Clayton, 1952; National Institute for Occupational Safety and Health, 1977). More recent studies, however, suggest health effects in communities chronically exposed to low environmental hydrogen sulfide levels (Bates, Garrett, Graham, & Read, 1997, 1998; Bates, Garrett, & Shoemack, 2002; Durand & Wilson, 2006; Hansell & Oppenheimer, 2004; Legator, Singleton, Morris, & Philips, 2001). In Rotorua, New Zealand, residents living in an area with hydrogen sulfide levels [greater than or equal to]1 ppm were at increased risk of hospitalization for nervous system and sense organ diseases compared with residents living where hydrogen sulfide exposure levels were <50 parts per billion (ppb) (Bates et al., 2002; Horwell, Patterson, Gamble, & Allen, 2005). Compared with a control community, a Puna, Hawaii, community close to a geothermal plant with periodic releases of hydrogen sulfide ranging from 200 to 500 ppb showed a greater risk of diseases for all body systems, especially for central nervous system and respiratory system disorders (Legator et al., 2001). Other studies have demonstrated adverse health outcomes associated with hydrogen sulfide concentrations in the window between the odor and irritant thresholds (Jaakkola, Vilkka, Marttila, Jappinen, & Haahtela, 1990; Kilburn & Warshaw, 1995; Schiffman & Williams, 2005).

In Lake County's Clearlake area, researchers have identified several geothermal vents. Documentation of geothermal venting and its effects in this area began in the early 1990s, when a home was demolished because of persistent hydrogen sulfide intrusion (ground-level hydrogen sulfide detected at 150 ppm). In 2010, a vent was discovered in Clearlake with high levels of hydrogen sulfide (750-800 ppm) and methane (55%-58% lower explosive limit [LEL]) at the vent surface (Ecology and Environment, 2011). …

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