Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. of
Sub-Agency 0011 - Water Quality
Chapter 17 - STORAGE TANKS
Part J - ENVIRONMENTAL RESTORATION STANDARDS FOR LEAKING STORAGE TANK REMEDIATION ACTIONS
Section 17-42 - Vapor Hazards Evaluation
Current through September 21, 2024
(a) Petroleum and/or hazardous substance vapors in either soil, vadose zone, or groundwater resulting from a storage tank release and that has caused, or has 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 accomplished using a properly calibrated and operating combustible gas meter. Explosive atmosphere action levels for volatile substances are defined as 25% of the substance lower explosive limit (LEL).
When an explosive action level is exceeded, immediate measures shall be taken to reduce the explosive environment below the action level. The immediate action system will be operated and/or maintained until such time as a soil and/or groundwater restoration action(s) has eliminated the explosive atmosphere, or the immediate action system is not required to maintain the environment below the explosive atmosphere action level. Atmospheric monitoring shall be required for any immediate action system.
(b) After remediation or immediate response, soil or groundwater contamination caused by a storage tank release shall not contain any contaminant concentration which causes a release of vapors to the vadose zone or atmosphere which could present a human health hazard in an indoor structure or confined space where people or animals may work or live and receive an exposure.
Chemical substance airborne concentrations in occupational environments are regulated by Chapter 7, Occupational Health and Environmental Control, General Rules and Regulations, Wyoming Occupational Health and Safety Division, Department of Employment, for protection of employees in a work place.
Hazardous substance indoor air quality action levels will be calculated using the following equations.
where;
IAAL = Indoor Air Action Level, µg/m3.
RISK = Cancer risk ( 1 x 10-6).
RfD = Inhalation Reference dose ; chemical specific.
CPFi = Inhalation Cancer Potency Factor; chemical specific.
ABW = Average body weight (70 kg).
UCF = Unit conversion factor (1,000 //g/mg).
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 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 is not listed in these references, the administrator will 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 will be implemented to eliminate the airborne health hazard to the applicable airborne occupational or indoor air quality action level. Immediate action will continue until the airborne concentration(s) is below those levels specified in this section.
