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 July 13, 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.
(i)
Carcinogens:
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(ii)
Non-carcinogens:
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where;
IAAL
= Indoor Air Action Level,
µ
g/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.