Reports of a noxious odor in a Clearlake neighborhood on Wednesday afternoon led to the discovery of a naturally occurring release of gases including hydrogen sulfide, as Lake County News has reported.
The Lake County Air Quality Management District (LCAQMD) conducted initial testing of air samples at a site located in a vacant lot where the gas was observed to be venting from a hole in the soil.
Calpine Corp. environmental staff provided additional laboratory testing of the vent gases, according to the report from Lake County's Environmental Health and Public Health departments.
Testing revealed the presence of hydrogen sulfide at levels capable of causing adverse health effects, officials said.
In addition to LCAQMD, Lake County Fire Protection District, city of Clearlake Police Department and Public Works Department, and Lake County Health Services all responded to the site.
Many residents of the neighborhood in Clearlake are familiar with the periodic venting of geothermal gases, the report stated.
The noticeable increase is the consequence of saturation of the soil by recent heavy rains, causing gases that are normally present in low concentrations in the soil to collect in pockets and release to the surface through any available channel. This concentration of the gases can be seen as a bubbling in the soil and can be detected as a rotten-egg or skunky odor.
The gases are comprised of a mixture that includes hydrogen sulfide, carbon dioxide and methane.
Hydrogen sulfide is known to produce a range of harmful health effects depending on its concentration and the duration of exposure. In addition, venting of the gases to an enclosed space can be dangerous by displacing oxygen necessary for breathing.
Responders to the Clearlake incident near Robinson Avenue and Division Street conducted air sampling at the site of the initially discovered vent. Hydrogen sulfide levels were found to be significantly elevated at the source, with levels that would be expected to cause eye and respiratory tract irritation and potentially more serious effects with prolonged exposure over hours.
Temporary measures were taken to reduce the release by covering the site with plastic sheeting, which reduced the hydrogen sulfide levels in the immediate area to less than half of the initial measurements. Levels taken at the closest home, approximately 60 feet from the site were only 1 percent to 2 percent of the original level at the source.
Residents in the immediate vicinity of the gas release were notified and advised to consider precautionary evacuation on a voluntary basis.
With assistance from the American Red Cross, one family was housed in a local hotel, officials reported.
Additional air sampling over a wider area, including Burns Elementary School, was conducted early Thursday morning. There were no detectable levels of hydrogen sulfide at the school.
A Public Health advisory also was distributed to residents in the areas impacted by the geothermal gas release.
Since hydrogen sulfide gas can produce symptoms, the health advisory encouraged residents of the affected neighborhood with recent, unexplained onset of irritation of the eyes, nose or throat, difficulty breathing or worsened asthma, headaches, poor attention span or poor memory to see their doctor for evaluation.
Young children and people with existing medical conditions are generally considered more susceptible to the adverse effects of this type of exposure. Staying away from the source of exposure is the recommended prevention and treatment.
As of mid-day Thursday, air samples from approximately 50 feet away from the geothermal vent showed essentially little to no detectable levels of hydrogen sulfide. Although levels may fluctuate slightly, these findings provide reassurance that significant exposure can be avoided by simply staying at least 50 feet away from the vent site, reducing the level of concern for households in the area.
Later in the day, with the assistance of Calpine engineers, a filtering device was installed to filter the escaping gas.
Following installation of the device, the filtered air showed no detectable hydrogen sulfide. This device will remain in place as long as necessary and will continue to be monitored by appropriate agencies.
With the filtering device in place, concerns about exposure of neighborhood residents largely subsided, but responders remain at the scene and are currently reassessing some leakage of gas that has been detected adjacent to the filtering device, officials reported.
Multiple agencies continue to monitor the area and, though the initial vent area has been capped, additional vents may be present.
Additional measures may be necessary if significant vents or large areas of gas release occur.
This seasonal release of naturally occurring gases is a temporary situation that is expected to resolve once the soil is no longer saturated with water, according to the report.
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