020-1 Wyo. Code R. §§ 1-42 - Vapor Hazards Evaluation

(a) Petroleum and/or hazardous substance vapors in soil, the vadose zone, or groundwater resulting from a storage tank release and that have caused, or have a potential to cause, an explosive atmosphere in a private residence, business, or other occupied structure, or in a confined space such as utility conduits, sewer mains, etc., shall be evaluated and remediated according to this Section. Monitoring for explosive atmosphere action levels shall be completed using a properly calibrated and operating combustible gas meter. Explosive atmosphere action levels for volatile substances are defined as 25% of the substance's lower explosive limit (LEL).

(b) When an explosive action level is exceeded, immediate measures shall be taken to reduce the explosive environment to below the action level. If a mechanical remediation system capable of mitigating vapors is installed, it shall be operated and maintained until, at a minimum, the explosive atmosphere has been eliminated. Atmospheric monitoring shall continue until the explosive atmosphere has been eliminated.

(c) Contamination may not remain in soil or groundwater if the contamination could cause a release of vapors to receptors in an indoor structure or confined space at levels that present a human health hazard.

(d) Chemical substance airborne concentrations in occupational environments are regulated by the Wyoming Occupational Health and Safety Division, Department of Employment, for protection of employees in a work place.

(e) Hazardous substance indoor air quality action levels shall be calculated using the following equations:

(i) Carcinogens:

Equation 15:

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(ii) Non-carcinogens: Equation 16:

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where:

IAAL =	Indoor Air Action Level,//g/m3.
RISK =	Cancer risk (1 x 10-6).
RfDi=	Inhalation Reference Dose; chemical specific.
CPFi=	Inhalation Cancer Potency Factor; chemical specific.
ABW =	Average body weight (70 kg).
UCF =	Unit conversion factor (1,000 Wmg).
BR =	Indoor breathing rate (15 m3/day).
ABS =	Absorption percentage (100%).
HQ =	Hazard quotient (1).
LIFE =	Lifetime exposure (70 years).
DUR =	Duration of exposure (30 years).

Values for inhalation toxicological reference doses (RfDi) and/or cancer potency factors (CPFi) shall be obtained from current data in the U.S. Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS), the Health Effects Assessment Summary Tables (HEAST), or the EPA Region IX Preliminary Remediation Goals Data Base. Where toxicological data are not listed in these references, the administrator shall establish the appropriate airborne concentration standard.

When an airborne concentration is confirmed in any building that equals or exceeds calculated concentrations and the source of the contaminant airborne concentration is known to be associated with a leaking storage tank release, immediate action shall be implemented. Action shall be taken to eliminate the airborne health hazard to the applicable airborne occupational or indoor air quality action level. Immediate action shall continue until the airborne concentration(s) is below those levels specified in this Section.

Notes

020-1 Wyo. Code R. §§ 1-42

Adopted, Eff. 6/29/2018.