If background concentrations of a constituent are higher
than the protection standards presented in this Section, cleanup shall be
completed to the background level. Cleanup shall only be completed for
constituents from an eligible storage tank system.
(a)
Surface Water. Storage
Tank Program remediation actions shall protect surface water quality to the
standards contained in Chapter 1, Wyoming Water Quality Rules and Regulations,
Quality Standards for Wyoming Surface Waters.
(b)
Groundwater. Storage
Tank Program remediation actions shall:
(i)
Protect Class I, II, III, IV(a), IV(b) or Special A groundwater quality to the
most stringent of the:
(A) Federal primary
MCL contained in 40 CFR
141, as referenced in Section 2;
(B) Water quality standards contained in this
Section when there is no federal MCL for a substance; or
(C) Groundwater quality standards found in
Chapter 8, Wyoming Water Quality Rules and Regulations, Quality Standards for
Wyoming Groundwaters.
(ii) Protect Class VI groundwater to the
groundwater quality standards found in Chapter 8, Wyoming Water Quality Rules
and Regulations, Quality Standards for Wyoming Groundwaters.
(c)
Eligible Sources.
Groundwater remediation shall address contaminants that originated
from an eligible storage tank system. Remediation of constituents that are
naturally occurring or are from sources other than an eligible storage tank
system shall not be completed, except as incidental and necessary to the
remediation of the eligible contaminants.
(d)
Free Product. Whenever
any free-phase liquid layer of a regulated substance is encountered in
groundwater or floating on the groundwater surface with a thickness in excess
of 0.05 inches, restoration shall begin as soon as possible to remove the
regulated substance(s) and prevent contaminant migration into previously
uncontaminated areas.
(e)
Drinking Water Equivalent Levels. If an MCL does not exist and
there is no standard for a constituent in either Chapter 1 or 8, Wyoming Water
Quality Rules and Regulations, the following procedures shall be used to
calculate a state Drinking Water Equivalent Level (DWEL). Calculations shall be
based on chronic exposure.
(i)
Non-carcinogenic substances:
Equation 1:
Click
here to view image
(ii) Carcinogenic substances:
Equation 2:
Click
here to view image
where:
| DWEL = |
Drinking water equivalent level,
mg/L. |
| RISK = |
Cancer risk for drinking water, (1
x 10-6). |
| ABW = |
Average adult body weight over
exposure period (70 kg). |
| CPFo = |
Oral cancer
potency factor (mg/kg-day)-1; chemical specific.
|
| RfDo = |
Oral
reference dose (mg/kg-day); chemical specific. |
| DWI = |
Adult drinking water intake, 2
L/day. |
| AB = |
Gastrointestinal absorption rate
(1.0). |
| LIFE = |
Lifetime (70 years). |
| DUR = |
Duration of exposure (30 years).
|
| FOE = |
Frequency of exposure, (350 days/365
days = 0.96). |
| HQ = |
Hazard quotient (1). |
Values for oral toxicological reference doses
(RfDo) and/or cancer potency factors
(CPFo) shall be obtained from current data in the U.S.
Environmental Protection Agency's (EPA) Integrated Risk Information System
(IRIS), the EPA Health Effects Assessment Summary Tables (HEAST) toxicity data
sources, or the EPA Region IX Preliminary Remediation Goals Data Base. If an
oral reference dose or cancer potency factor is not listed in the above
database sources, the administrator shall determine a state DWEL using the
latest available toxicological data.
(f)
Multiple Standards. When
more than one standard exists in Section 39 for any constituent, the most
stringent standard shall be used.
