WAC 173-340-708
Human health risk assessment procedures. (1) Purpose. This section defines the risk assessment
framework that shall be used to establish cleanup levels, and
remediation levels using a quantitative risk assessment, under
this chapter. As used in this section, cleanup levels and
remediation levels means the human health risk assessment
component of these levels. This chapter defines certain
default values and methods to be used in calculating cleanup
levels and remediation levels. This section allows varying
from these default values and methods under certain
circumstances. When deciding whether to approve alternate
values and methods the department shall ensure that the use of
alternative values and methods will not significantly delay
site cleanups.
(2) Selection of indicator hazardous substances.
When defining cleanup requirements at a site that is
contaminated with a large number of hazardous substances, the
department may eliminate from consideration those hazardous
substances that contribute a small percentage of the overall
threat to human health and the environment. The remaining
hazardous substances shall serve as indicator hazardous
substances for purposes of defining site cleanup requirements.
See WAC 173-340-703 for additional information on establishing
indicator hazardous substances.
(3) Reasonable maximum exposure.
(a) Cleanup levels and remediation levels shall be based
on estimates of current and future resource uses and
reasonable maximum exposures expected to occur under both
current and potential future site use conditions, as specified
further in this chapter.
(b) The reasonable maximum exposure is defined as the
highest exposure that is reasonably expected to occur at a
site under current and potential future site use. WAC 173-340-720 through 173-340-760 define the reasonable maximum
exposures for groundwater, surface water, soil, and air. These reasonable maximum exposures will apply to most sites
where individuals or groups of individuals are or could be
exposed to hazardous substances. For example, the reasonable
maximum exposure for most groundwater is defined as exposure
to hazardous substances in drinking water and other domestic
uses.
(c) Persons performing cleanup actions under this chapter
may use the evaluation criteria in WAC 173-340-720 through173-340-760
, where allowed in those sections, to demonstrate
that the reasonable maximum exposure scenarios specified in
those sections are not appropriate for cleanup levels for a
particular site. For example, the criteria in WAC 173-340-720(2) could be used to demonstrate that the
reasonable maximum exposure for groundwater beneath a site
does not need to be based on drinking water use. The use of
an alternate exposure scenario shall be documented by the
person performing the cleanup action. Documentation for the
use of alternate exposure scenarios under this provision shall
be based on the results of investigations performed in
accordance with WAC 173-340-350.
(d) Persons performing cleanup actions under this chapter
may also use alternate reasonable maximum exposure scenarios
to help assess the protectiveness to human health of a cleanup
action alternative that incorporates remediation levels and
uses engineered controls and/or institutional controls to
limit exposure to the contamination remaining on the site.
(i) An alternate reasonable maximum exposure scenario
shall reflect the highest exposure that is reasonably expected
to occur under current and potential future site conditions
considering, among other appropriate factors, the potential
for institutional controls to fail and the extent of the time
period of failure under these scenarios and the land uses at
the site.
(ii) Land uses other than residential and industrial,
such as agricultural, recreational, and commercial, shall not
be used as the basis for a reasonable maximum exposure
scenario for the purpose of establishing a cleanup level. However, these land uses may be used as a basis for an
alternate reasonable maximum exposure scenario for the purpose
of assessing the protectiveness of a remedy. For example, if
a cap (with appropriate institutional controls) is the
proposed cleanup action at a commercial site, the reasonable
maximum exposure scenario for assessing the protectiveness of
the cap with regard to direct soil contact could be changed
from a child living on the site to a construction or
maintenance worker and child trespasser scenario.
(iii) The department expects that in evaluating the
protectiveness of a remedy with regard to the soil direct
contact pathway, many types of commercial sites may, where
appropriate, qualify for alternative exposure scenarios under
this provision since contaminated soil at these sites is
typically characterized by a cover of buildings, pavement, and
landscaped areas. Examples of these types of sites include:
(A) Commercial properties in a location removed from
single family homes, duplexes or subdivided individual lots;
(B) Private and public recreational facilities where
access to these facilities is physically controlled (e.g., a
private golf course to which access is restricted by fencing);
(C) Urban residential sites (e.g., upper-story
residential units over ground floor commercial businesses);
(D) Offices, restaurants, and other facilities primarily
devoted to support administrative functions of a
commercial/industrial nature (e.g., an employee credit union
or cafeteria in a large office or industrial complex).
(e) A conceptual site model may be used to identify when
individuals or groups of individuals may be exposed to
hazardous substances through more than one exposure pathway. For example, a person may be exposed to hazardous substances
from a site by drinking contaminated groundwater, eating
contaminated fish, and breathing contaminated air. At sites
where the same individuals or groups of individuals are or
could be consistently exposed through more than one pathway,
the reasonable maximum exposure shall represent the total
exposure through all of those pathways. At such sites, the
cleanup levels and remediation levels derived for individual
pathways under WAC 173-340-720 through 173-340-760 and WAC 173-340-350 through 173-340-390 shall be adjusted downward to
take into account multiple exposure pathways.
(4) Cleanup levels for individual hazardous substances. Cleanup levels for individual hazardous substances will
generally be based on a combination of requirements in
applicable state and federal laws and risk assessment.
(5) Multiple hazardous substances.
(a) Cleanup levels for individual hazardous substances
established under Methods B and C and remediation levels shall
be adjusted downward to take into account exposure to multiple
hazardous substances. This adjustment needs to be made only
if, without this adjustment, the hazard index would exceed one
(1) or the total excess cancer risk would exceed one in one
hundred thousand (1 x 10-5).
(b) Adverse effects resulting from exposure to two or
more hazardous substances with similar types of toxic response
are assumed to be additive unless scientific evidence is
available to demonstrate otherwise. Cancer risks resulting
from exposure to two or more carcinogens are assumed to be
additive unless scientific evidence is available to
demonstrate otherwise.
(c) For noncarcinogens, for purposes of establishing
cleanup levels under Methods B and C, and for remediation
levels, the health threats resulting from exposure to two or
more hazardous substances with similar types of toxic response
may be apportioned between those hazardous substances in any
combination as long as the hazard index does not exceed one
(1).
(d) For carcinogens, for purposes of establishing cleanup
levels under Methods B and C, and for remediation levels, the
cancer risks resulting from exposure to multiple hazardous
substances may be apportioned between hazardous substances in
any combination as long as the total excess cancer risk does
not exceed one in one hundred thousand (1 x 10-5).
(e) The department may require biological testing to
assess the potential interactive effects associated with
chemical mixtures.
(f) When making adjustments to cleanup levels and
remediation levels for multiple hazardous substances, the
concentration for individual hazardous substances shall not be
adjusted downward to less than the practical quantitation
limit or natural background.
(6) Multiple pathways of exposure.
(a) Estimated doses of individual hazardous substances
resulting from more than one pathway of exposure are assumed
to be additive unless scientific evidence is available to
demonstrate otherwise.
(b) Cleanup levels and remediation levels based on one
pathway of exposure shall be adjusted downward to take into
account exposures from more than one exposure pathway. The
number of exposure pathways considered at a given site shall
be based on the reasonable maximum exposure scenario as
defined in WAC 173-340-708(3). This adjustment needs to be
made only if exposure through multiple pathways is likely to
occur at a site and, without the adjustment, the hazard index
would exceed one (1) or the total excess cancer risk would
exceed one in one hundred thousand (1 x 10-5).
(c) For noncarcinogens, for purposes of establishing
cleanup levels under Methods B and C, and remediation levels,
the health threats associated with exposure via multiple
pathways may be apportioned between exposure pathways in any
combination as long as the hazard index does not exceed one
(1).
(d) For carcinogens, for purposes of establishing cleanup
levels under Methods B and C, and for remediation levels, the
cancer risks associated with exposure via multiple pathways
may be apportioned between exposure pathways in any
combination as long as the total excess cancer risk does not
exceed one in one hundred thousand (1 x 10-5).
(e) When making adjustments to cleanup levels and
remediation levels for multiple pathways of exposure, the
concentration for individual hazardous substances shall not be
adjusted downward to less than the practical quantitation
limit or natural background.
(7) Reference doses.
(a) The chronic reference dose/reference concentration
and the developmental reference dose/reference concentration
shall be used to establish cleanup levels and remediation
levels under this chapter. Cleanup levels and remediation
levels shall be established using the value which results in
the most protective concentration.
(b) Inhalation reference doses/reference concentrations
shall be used in WAC 173-340-750. Where the inhalation
reference dose/reference concentration is reported as a
concentration in air, that value shall be converted to a
corresponding inhaled intake (mg/kg-day) using a human body
weight of 70 kg and an inhalation rate of 20 m3/day, and take
into account, where available, the respiratory deposition and
absorption characteristics of the gases and inhaled particles.
(c) A subchronic reference dose/reference concentration
may be used to evaluate potential noncarcinogenic effects
resulting from exposure to hazardous substances over short
periods of time. This value may be used in place of the
chronic reference dose/reference concentration where it can be
demonstrated that a particular hazardous substance will
degrade to negligible concentrations during the exposure
period.
(d) For purposes of establishing cleanup levels and
remediation levels for hazardous substances under this
chapter, a reference dose/reference concentration established
by the United States Environmental Protection Agency and
available through the "integrated risk information system"
(IRIS) data base shall be used. If a reference dose/reference
concentration is not available through the IRIS data base, a
reference dose/reference concentration from the U.S. EPA
Health Effects Assessment Summary Table ("HEAST") data base
or, if more appropriate, the National Center for Environmental
Assessment ("NCEA") shall be used.
(e) If a reference dose/reference concentration is
available through IRIS, HEAST, or the NCEA, it shall be used
unless the department determines that there is clear and
convincing scientific data which demonstrates that the use of
this value is inappropriate.
(f) If a reference dose/reference concentration for a
hazardous substance including petroleum fractions and
petroleum constituents is not available through IRIS, HEAST or
the NCEA or is demonstrated to be inappropriate under (e) of
this subsection and the department determines that development
of a reference dose/reference concentration is necessary for
the hazardous substance at the site, then a reference
dose/reference concentration shall be established on a
case-by-case basis. When establishing a reference dose on a
case-by-case basis, the methods described in "Reference Dose
(RfD): Description and Use in Health Risk Assessment:
Background Document 1A", USEPA, March 15, 1993, shall be used.
(g) In estimating a reference dose/reference
concentration for a hazardous substance under (e) or (f) of
this subsection, the department shall, as appropriate, consult
with the science advisory board, the department of health, and
the United States Environmental Protection Agency and may, as
appropriate, consult with other qualified persons. Scientific
data supporting such a change shall be subject to the
requirements under WAC 173-340-702 (14), (15) and (16). Once
the department has established a reference dose/reference
concentration for a hazardous substance under this provision,
the department is not required to consult again for the same
hazardous substance.
(h) Where a reference dose/reference concentration other
than those established under (d) or (g) of this subsection is
used to establish a cleanup level or remediation level at
individual sites, the department shall summarize the
scientific rationale for the use of those values in the
cleanup action plan. The department shall provide the
opportunity for public review and comment on this value in
accordance with the requirements of WAC 173-340-380 and 173-340-600.
(8) Carcinogenic potency factor.
(a) For purposes of establishing cleanup levels and
remediation levels for hazardous substances under this
chapter, a carcinogenic potency factor established by the
United States Environmental Protection Agency and available
through the IRIS data base shall be used. If a carcinogenic
potency factor is not available from the IRIS data base, a
carcinogenic potency factor from HEAST or, if more
appropriate, from the NCEA shall be used.
(b) If a carcinogenic potency factor is available from
the IRIS, HEAST or the NCEA, it shall be used unless the
department determines that there is clear and convincing
scientific data which demonstrates that the use of this value
is inappropriate.
(c) If a carcinogenic potency factor is not available
through IRIS, HEAST or the NCEA or is demonstrated to be
inappropriate under (b) of this subsection and the department
determines that development of a cancer potency factor is
necessary for the hazardous substance at the site, then one of
the following methods shall be used to establish a
carcinogenic potency factor:
(i) The carcinogenic potency factor may be derived from
appropriate human epidemiology data on a case-by-case basis;
or
(ii) The carcinogenic potency factor may be derived from
animal bioassay data using the following procedures:
(A) All carcinogenicity bioassays shall be reviewed and
data of appropriate quality shall be used for establishing the
carcinogenic potency factor.
(B) The linearized multistage extrapolation model shall
be used to estimate the slope of the dose-response curve
unless the department determines that there is clear and
convincing scientific data which demonstrates that the use of
an alternate extrapolation model is more appropriate;
(C) All doses shall be adjusted to give an average daily
dose over the study duration; and
(D) An interspecies scaling factor shall be used to take
into account differences between animals and humans. For oral
carcinogenic toxicity values this scaling factor shall be
based on the assumption that milligrams per surface area is an
equivalent dose between species unless the department
determines there is clear and convincing scientific data which
demonstrates that an alternate procedure is more appropriate. The slope of the dose response curve for the test species
shall be multiplied by this scaling factor in order to obtain
the carcinogenic potency factor, except where such scaling
factors are incorporated into the extrapolation model under
(B) of this subsection. The procedure to derive a human
equivalent concentration of inhaled particles and gases shall
take into account, where available, the respiratory deposition
and absorption characteristics of the gases and inhaled
particles. Where adequate pharmacokinetic and metabolism
studies are available, data from these studies may be used to
adjust the interspecies scaling factor.
(d) Mixtures of dioxins and furans. When establishing
and determining compliance with cleanup levels and remediation
levels for mixtures of chlorinated dibenzo-p-dioxins (dioxins)
and/or chlorinated dibenzofurans (furans), the following
procedures shall be used:
(i) Assessing as single hazardous substance. When
establishing and determining compliance with cleanup levels
and remediation levels, including when determining compliance
with the excess cancer risk requirements in this chapter,
mixtures of dioxins and/or furans shall be considered a single
hazardous substance.
(ii) Establishing cleanup levels and remediation levels.
The cleanup levels and remediation levels established for
2,3,7,8 tetrachloro dibenzo-p-dioxin (2,3,7,8-TCDD) shall be
used, respectively, as the cleanup levels and remediation
levels for mixtures of dioxins and/or furans.
(iii) Determining compliance with cleanup levels and
remediation levels. When determining compliance with the
cleanup levels and remediation levels established for mixtures
of dioxins and/or furans, the following procedures shall be
used:
(A) Calculate the total toxic equivalent concentration of
2,3,7,8-TCDD for each sample of the mixture. The total toxic
equivalent concentration shall be calculated using the
following method, unless the department determines that there
is clear and convincing scientific data which demonstrates
that the use of this method is inappropriate:
(I) Analyze samples from the medium of concern to
determine the concentration of each dioxin and furan congener
listed in Table 708-1;
(II) For each sample analyzed, multiply the measured
concentration of each congener in the sample by its
corresponding toxicity equivalency factor (TEF) in Table 708-1
to obtain the toxic equivalent concentration of 2,3,7,8-TCDD
for that congener; and
(III) For each sample analyzed, add together the toxic
equivalent concentrations of all the congeners within the
sample to obtain the total toxic equivalent concentration of
2,3,7,8-TCDD for that sample.
(B) After calculating the total toxic equivalent
concentration of each sample of the mixture, use the
applicable compliance monitoring requirements in WAC 173-340-720 through 173-340-760 to determine whether the total
toxic equivalent concentrations of the samples comply with the
cleanup level or remediation level for the mixture at the
applicable point of compliance.
(iv) Protecting the quality of other media. When
establishing cleanup levels and remediation levels for
mixtures of dioxins and/or furans in a medium of concern that
are based on protection of another medium (the receiving
medium) (e.g., soil levels protective of groundwater quality),
the following procedures shall be used:
(A) The cleanup level or remediation level for
2,3,7,8-TCDD in the receiving medium shall be used,
respectively, as the cleanup level or remediation level for
the receiving medium.
(B) When determining the concentrations in the medium of
concern that will achieve the cleanup level or remediation
level in the receiving medium, the congener-specific physical
and chemical properties shall be considered during that
assessment.
(e) Mixtures of carcinogenic PAHs. When establishing and
determining compliance with cleanup levels and remediation
levels for mixtures of carcinogenic polycyclic aromatic
hydrocarbons (carcinogenic PAHs), the following procedures
shall be used:
(i) Assessing as single hazardous substance. When
establishing and determining compliance with cleanup levels
and remediation levels, including when determining compliance
with the excess cancer risk requirements in this chapter,
mixtures of carcinogenic PAHs shall be considered a single
hazardous substance.
(ii) Establishing cleanup levels and remediation levels.
The cleanup levels and remediation levels established for
benzo(a)pyrene shall be used, respectively, as the cleanup
levels and remediation levels for mixtures of carcinogenic
PAHs.
(iii) Determining compliance with cleanup levels and
remediation levels. When determining compliance with cleanup
levels and remediation levels established for mixtures of
carcinogenic PAHs, the following procedures shall be used:
(A) Calculate the total toxic equivalent concentration of
benzo (a) pyrene for each sample of the mixture. The total
toxic equivalent concentration shall be calculated using the
following method, unless the department determines that there
is clear and convincing scientific data which demonstrates
that the use of this method is inappropriate:
(I) Analyze samples from the medium of concern to
determine the concentration of each carcinogenic PAH listed in
Table 708-2 and, for those carcinogenic PAHs required by the
department under WAC 173-340-708 (8)(e)(iv), in Table 708-3;
(II) For each sample analyzed, multiply the measured
concentration of each carcinogenic PAH in the sample by its
corresponding toxicity equivalency factor (TEF) in Tables
708-2 and 708-3 to obtain the toxic equivalent concentration
of benzo(a)pyrene for that carcinogenic PAH; and
(III) For each sample analyzed, add together the toxic
equivalent concentrations of all the carcinogenic PAHs within
the sample to obtain the total toxic equivalent concentration
of benzo(a)pyrene for that sample.
(B) After calculating the total toxic equivalent
concentration of each sample of the mixture, use the
applicable compliance monitoring requirements in WAC 173-340-720 through 173-340-760 to determine whether the total
toxic equivalent concentrations of the samples comply with the
cleanup level or remediation level for the mixture at the
applicable point of compliance.
(iv) Protecting the quality of other media. When
establishing cleanup levels and remediation levels for
mixtures of carcinogenic PAHs in a medium of concern that are
based on protection of another medium (the receiving medium)
(e.g., soil levels protective of groundwater quality), the
following procedures shall be used:
(A) The cleanup level or remediation level for
benzo(a)pyrene in the receiving medium shall be used,
respectively, as the cleanup level or remediation level for
the receiving medium.
(B) When determining the concentrations in the medium of
concern that will achieve the cleanup level or remediation
level in the receiving medium, the carcinogenic PAH-specific
physical and chemical properties shall be considered during
that assessment.
(v) When using this methodology, at a minimum, the
compounds in Table 708-2 shall be analyzed for and included in
the calculations. The department may require additional
compounds in Table 708-3 to be included in the methodology
should site testing data or information from other comparable
sites or waste types indicate the additional compounds are
potentially present at the site. NOTE: Many of the
polycyclic aromatic hydrocarbons in Table 708-3 are found
primarily in air emissions from combustion sources and may not
be present in the soil or water at contaminated sites. Users
should consult with the department for information on the need
to test for these additional compounds.
(f) PCB mixtures. When establishing and determining
compliance with cleanup levels and remediation levels for
polychlorinated biphenyls (PCBs) mixtures, the following
procedures shall be used:
(i) Assessing as single hazardous substance. When
establishing and determining compliance with cleanup levels
and remediation levels, including when determining compliance
with the excess cancer risk requirements in this chapter, PCB
mixtures shall be considered a single hazardous substance.
(ii) Establishing cleanup levels and remediation levels.
When establishing cleanup levels and remediation levels under
Methods B and C for PCB mixtures, the following procedures
shall be used unless the department determines that there is
clear and convincing scientific data which demonstrates that
the use of these methods is inappropriate:
(A) Assume the PCB mixture is equally potent and use the
appropriate carcinogenic potency factor provided for under WAC 173-340-708 (8)(a) through (c) for the entire mixture; or
(B) Use the toxicity equivalency factors for the
dioxin-like PCBs congeners in Table 708-4 and procedures
approved by the department. When using toxicity equivalency
factors, the department may require that the health effects
posed by the dioxin-like PCB congeners and nondioxin-like PCB
congeners be considered in the evaluation.
(iii) Determining compliance with cleanup levels and
remediation levels. When determining compliance with cleanup
levels and remediation levels established for PCB mixtures,
the following procedures shall be used:
(A) Analyze compliance monitoring samples for a total PCB
concentration and use the applicable compliance monitoring
requirements in WAC 173-340-720 through 173-340-760 to
determine whether the total PCB concentrations of the samples
complies with the cleanup level or remediation level for the
mixture at the applicable point of compliance; or
(B) When using toxicity equivalency factors to determine
compliance with cleanup or remediation levels for PCB
mixtures, use procedures approved by the department.
(g) In estimating a carcinogenic potency factor for a
hazardous substance under (c) of this subsection, or approving
the use of a toxicity equivalency factor other than that
established under (d), (e) or (f) of this subsection, the
department shall, as appropriate, consult with the science
advisory board, the department of health, and the United
States Environmental Protection Agency and may, as
appropriate, consult with other qualified persons. Scientific
data supporting such a change shall be subject to the
requirements under WAC 173-340-702 (14), (15) and (16). Once
the department has established a carcinogenic potency factor
or approved an alternative toxicity equivalency factor for a
hazardous substance under this provision, the department is
not required to consult again for the same hazardous
substance.
(h) Where a carcinogenic potency factor other than that
established under (a) of this subsection or a toxicity
equivalency factor other than that established under (d), (e)
or (f) of this subsection is used to establish cleanup levels
or remediation levels at individual sites, the department
shall summarize the scientific rationale for the use of that
value in the cleanup action plan. The department shall
provide the opportunity for public review and comment on this
value in accordance with the requirements of WAC 173-340-380
and 173-340-600.
(9) Bioconcentration factors.
(a) For purposes of establishing cleanup levels and
remediation levels for a hazardous substance under WAC 173-340-730, a bioconcentration factor established by the
United States Environmental Protection Agency and used to
establish the ambient water quality criterion for that
substance under section 304 of the Clean Water Act shall be
used. These values shall be used unless the department
determines that there is adequate scientific data which
demonstrates that the use of an alternate value is more
appropriate. If the department determines that a
bioconcentration factor is appropriate for a specific
hazardous substance and no such factor has been established by
USEPA, then other appropriate EPA documents, literature
sources or empirical information may be used to determine a
bioconcentration factor.
(b) When using a bioconcentration factor other than that
used to establish the ambient water quality criterion, the
department shall, as appropriate, consult with the science
advisory board, the department of health, and the United
States Environmental Protection Agency. Scientific data
supporting such a value shall be subject to the requirements
under WAC 173-340-702 (14), (15) and (16). Once the
department has established a bioconcentration factor for a
hazardous substance under this provision, the department is
not required to consult again for the same hazardous
substance.
(c) Where a bioconcentration factor other than that
established under (a) of this subsection is used to establish
cleanup levels or remediation levels at individual sites, the
department shall summarize the scientific rationale for the
use of that factor in the draft cleanup action plan. The
department shall provide the opportunity for public review and
comment on the value in accordance with the requirements of
WAC 173-340-380 and 173-340-600.
(10) Exposure parameters.
(a) As a matter of policy, the department has defined in
WAC 173-340-720 through 173-340-760 the default values for
exposure parameters to be used when establishing cleanup
levels and remediation levels under this chapter. Except as
provided for in (b) and (c) of this subsection and in WAC 173-340-720 through 173-340-760, these default values shall
not be changed for individual hazardous substances or sites.
(b) Exposure parameters that are primarily a function of
the exposed population characteristics (such as body weight
and lifetime) and those that are primarily a function of human
behavior that cannot be controlled through an engineered or
institutional control (such as: Fish consumption rate; soil
ingestion rate; drinking water ingestion rate; and breathing
rate) are not expected to vary on a site-by-site basis. The
default values for these exposure parameters shall not be
changed when calculating cleanup levels except when necessary
to establish a more stringent cleanup level to protect human
health. For remediation levels the default values for these
exposure parameters may only be changed when an alternate
reasonable maximum exposure scenario is used, as provided for
in WAC 173-340-708 (3)(d), that reflects a different exposed
population such as using an adult instead of a child exposure
scenario. Other exposure parameters may be changed only as
follows:
(i) For calculation of cleanup levels, the types of
exposure parameters that may be changed are those that are:
(A) Primarily a function of reliably measurable
characteristics of the hazardous substance, soil, hydrologic
or hydrogeologic conditions at the site; and
(B) Not dependent on the success of engineered controls
or institutional controls for controlling exposure of persons
to the hazardous substances at the site.
The default values for these exposure parameters may be
changed where there is adequate scientific data to demonstrate
that use of an alternative or additional value would be more
appropriate for the conditions present at the site. Examples
of exposure parameters for which the default values may be
changed under this provision are as follows: Contaminant
leaching and transport variables (such as the soil organic
carbon content, aquifer permeability and soil sorption
coefficient); inhalation correction factor; fish
bioconcentration factor; soil gastrointestinal absorption
fraction; and inhalation absorption percentage.
(ii) For calculation of remediation levels, in addition
to the exposure parameters that may be changed under (b)(i) of
this subsection, the types of exposure parameters that may be
changed from the default values are those where a
demonstration can be made that the proposed cleanup action
uses engineered controls and/or institutional controls that
can be successfully relied on, for the reasonably foreseeable
future, to control contaminant mobility and/or exposure to the
contamination remaining on the site. In general, exposure
parameters that may be changed under this provision are those
that define the exposure frequency, exposure duration and
exposure time. The default values for these exposure
parameters may be changed where there is adequate scientific
data to demonstrate that use of an alternative or additional
value would be more appropriate for the conditions present at
the site. Examples of exposure parameters for which the
default value may be changed under this provision are as
follows: Infiltration rate; frequency of soil contact;
duration of soil exposure; duration of drinking water
exposure; duration of air exposure; drinking water fraction;
and fish diet fraction.
(c) When the modifications provided for in (b) of this
subsection result in significantly higher values for cleanup
levels or remediation levels than would be calculated using
the default values for exposure parameters, the risk from
other potentially relevant pathways of exposure shall be
addressed under the procedures provided for in WAC 173-340-720
through 173-340-760. For exposure pathways and parameters for
which default values are not specified in this chapter, the
framework provided for by this subsection, along with the
quality of information requirements in WAC 173-340-702, shall
be used to establish appropriate or additional assumptions for
these parameters and pathways.
(d) Where the department approves the use of exposure
parameters other than those established under WAC 173-340-720
through 173-340-760 to establish cleanup levels or remediation
levels at individual sites, the department shall summarize the
scientific rationale for the use of those parameters in the
cleanup action plan. The department shall provide the
opportunity for public review and comment on those values in
accordance with the requirements of WAC 173-340-380 and 173-340-600. Scientific data supporting such a change shall
be subject to the requirements under WAC 173-340-702 (14),
(15) and (16).
(11) Probabilistic risk assessment. Probabilistic risk
assessment methods may be used under this chapter only on an
informational basis for evaluating alternative remedies. Such
methods shall not be used to replace cleanup standards and
remediation levels derived using deterministic methods under
this chapter until the department has adopted rules describing
adequate technical protocols and policies for the use of
probabilistic risk assessment under this chapter.
[Statutory Authority: RCW 70.105D.030(2). 07-21-065 (Order
06-10), § 173-340-708, filed 10/12/07, effective 11/12/07. Statutory Authority: Chapter 70.105D RCW. 01-05-024 (Order
97-09A), § 173-340-708, filed 2/12/01, effective 8/15/01;
91-04-019, § 173-340-708, filed 1/28/91, effective 2/28/91.]