Current through Register Vol. 39, No. 6, September 16, 2024
(a) A tiered risk
assessment shall be conducted to establish risk-based screening levels or
site-specific target levels for a site.
(b) A site conceptual model shall be
developed including the following elements:
(1) the type and distribution of chemicals of
concern;
(2) the geology and
hydrogeology;
(3) an exposure model
that identifies the receptors, including sensitive subgroups, and the exposure
pathways; and
(4) land use
classification as either residential or non-residential.
(c) Tier 1. A Tier 1 risk assessment is based
on chemical-specific risk-based screening levels. The representative
concentrations of chemicals of concern that exist at a site shall be compared
to these risk-based screening levels for all complete and potentially complete
exposure pathways. If the concentrations exceed the risk-based screening
levels, the Division may require remediation of the site to risk-based
screening levels or the performance of a Tier 2 risk assessment to establish
site-specific target levels. Factors considered by the Division when
determining if remediation or a Tier 2 assessment is warranted shall include:
(1) whether the assumptions on which the
risk-based screening levels are based are representative of the site-specific
conditions;
(2) whether the
site-specific target levels developed under Tier 2 either are likely to be
different than the risk-based screening levels or will modify remediation
activities; or
(3) whether the cost
of remediation to achieve risk-based screening levels will likely be greater
than the cost of further tier evaluation and subsequent remediation.
(d) Tier 2. A Tier 2 assessment
shall allow consideration of site-specific information in order to calculate
site-specific target levels. This information includes the locations of actual
points of exposure and points of demonstration as well as site-specific
geologic, hydrogeologic, and contaminant fate and transport parameters. The
representative concentrations of chemicals of concern that exist at a site
shall be compared to these Tier 2 site-specific target levels for all complete
and potentially complete exposure pathways. If the concentrations exceed the
Tier 2 site-specific target levels, the Division may require remediation of the
site to Tier 2 site-specific target levels or the performance of a Tier 3 risk
assessment to establish alternative site-specific target levels. Factors
considered by the Division when determining if remediation or a Tier 3
assessment is warranted shall include:
(1)
whether the assumptions on which the Tier 2 site-specific target levels are
based are representative of the site-specific conditions;
(2) whether the alternative site-specific
target levels developed under Tier 3 either are likely to be different than the
Tier 2 site-specific target levels or will modify remediation activities;
or
(3) whether the cost of
remediation to achieve Tier 2 site-specific target levels will likely be
greater than the cost of further tier evaluation and subsequent
remediation.
(e) Tier 3.
A Tier 3 risk assessment shall allow consideration of additional site-specific
and toxicological data in order to calculate alternative site-specific target
levels. This data may include alternative, technically defensible toxicity
factors, physical and chemical properties, site-specific exposure factors, and
alternative fate and transport models. The representative concentrations of
chemicals of concern that exist at a site shall be compared to these Tier 3
site-specific target levels for all complete and potentially complete exposure
pathways. If the concentrations exceed the Tier 3 site-specific target levels,
the Division shall consider the results of the Tier 2 and Tier 3 assessments to
determine the site-specific target levels.
(f) The determination of risk-based screening
levels and site-specific target levels shall be based on the following
assumptions and requirements:
(1)
concentrations of chemicals of concern in soil shall not exceed Tier 1
residential risk-based screening levels on land classified as residential land
use. Concentrations in soil may exceed Tier 1 residential risk-based screening
levels on property containing both residential and non-residential land use if
the ground-level uses are non-residential and the potential for exposure to
contaminated soil has been eliminated;
(2) an ecological risk evaluation shall be
conducted to determine the risk to plant and animal receptors and
habitats;
(3) the most recent
versions of the following references, in order of preference, shall be used to
obtain the quantitative toxicity values necessary to calculate risk to
identified receptors:
(A) Integrated Risk
Information System (IRIS);
(B)
provisional peer reviewed toxicity values (PPRTVs); and
(C) published health risk assessment data,
and scientifically valid peer-reviewed published toxicological data;
(4) all current and probable
future use of groundwater shall be protected. If groundwater has been
contaminated or is likely to be contaminated, a point of exposure shall be
established to quantitatively evaluate the groundwater use pathway. The point
of exposure shall be established at the nearest to the source of the following
locations:
(A) closest existing water supply
well;
(B) likely nearest future
location of a water supply well;
(C) hypothetical point of exposure located at
a distance of 500 feet from the downgradient property boundary of the facility
site; or
(D) hypothetical point of
exposure located at a distance of 1000 feet downgradient from the
source;
(5) for
chemicals of concern for which there is a groundwater quality standard in
15A NCAC
02L, concentrations at the point of exposure
shall not exceed the groundwater quality standards as specified in
15A NCAC
02L. For chemicals of concern for which there
are no groundwater quality standards, concentrations at the point of exposure
shall not exceed the risk-based screening levels or site-specific target levels
for these chemicals of concern that assume ingestion based on domestic water
use;
(6) concentrations of
chemicals of concern shall be measured and evaluated at a point of
demonstration well to ensure that concentrations are protective of any point of
exposure;
(7) surface water is
protected. The standards for surface water shall be the water quality standards
in 15A
NCAC 02B.
Authority
G.S.
143-215.104D;
Eff. September 1,
2007;
Readopted Eff. September 1,
2018.
