Current through Register Vol. 63, No. 3, March 1, 2024
This rule describes the requirements for developing risk-based
concentrations for use in establishing remediation levels in corrective action
plans under OAR
340-122-0250.
(1) A conceptual model must be developed for
the site describing how exposure to contaminants is reasonably likely to occur.
(a) The conceptual site model must be based
on, at a minimum:
(A) The magnitude and areal
and vertical extent of soil and groundwater contamination;
(B) The concentration of applicable
contaminants of concern in each contaminated medium;
(C) The likelihood for exposure to occur,
given the concentration, location, and mobility of the contaminants in
conjunction with factors such as local climate, geology, and hydrogeology;
and
(D) Information on current and
reasonably likely future land and water uses in the area of potential
impact.
(b) Subject to
site-specific conditions, the following exposure pathways must be considered in
the conceptual site model:
(A) Direct contact
with contaminated soils resulting in exposure due to a combination of dermal
contact, soil ingestion, vapor inhalation, and particulate
inhalation;
(B) Leaching from soils
to underlying groundwater with subsequent groundwater ingestion;
(C) Volatilization from soils to outdoor air
and subsequent inhalation;
(D)
Volatilization from soils to indoor air and subsequent inhalation;
(E) Ingestion or other exposure to
contaminated groundwater;
(F)
Volatilization from groundwater to outdoor air and subsequent inhalation;
and
(G) Volatilization from
groundwater to indoor air and subsequent inhalation.
(c) Subject to site-specific conditions, the
following exposure scenarios must be considered in the conceptual site model:
(A) Exposure to adults and children as
typified by single-family residential living conditions;
(B) Exposure to adults as typified by
industrial or commercial working conditions; and
(C) Exposure to adults whose occupation
requires increased direct contact with soil as typified by a trench
worker.
(d) Depending on
conditions found at the site, the Department may require the evaluation of
additional exposure pathways and scenarios.
(2) Risk-based concentrations must be
developed for contaminants of concern identified during the site
characterization or other site investigation activities, including total
petroleum hydrocarbons (TPH) when appropriate, for exposure pathways and
scenarios identified in the conceptual site model.
(a) The Department shall develop and
maintain, in accordance with OAR
340-122-0252, a
table of generic risk-based concentrations that may be used for this purpose;
or
(b) A responsible person may
calculate site-specific risk-based concentrations by employing contaminant
fate, transport, and exposure models.
(A)
Sources of models and default exposure parameters include:
(i) Applicable Department of Environmental
Quality generic remedy guidance documents developed pursuant to OAR
340-122-0252;
(ii) ASTM Standard Guide for Risk-Based
Corrective Action Applied at Petroleum Release Sites (ASTM E
1739-95); and
(iii) US EPA
Risk Assessment Guidance for Superfund.
(B) The Department may approve the use of
other models if they are deemed appropriate for the proposed task.
(C) A responsible person may propose, subject
to the Department's approval, the use of site-specific exposure parameters in
place of default exposure parameters.
(3) Risk-based concentrations for protection
of the environment must be developed if contamination poses a potential risk
exceeding the acceptable risk levels for ecological receptors. Unless the
Department determines that screening is required for threatened and endangered
species, screening for potential ecological impact is not required if:
(a) Contaminated soils are only present at a
depth greater than 3 feet below ground surface, or, if present at a shallower
depth, such soils cover an area no greater than 0.125 acre;
(b) Surface water has not been affected by
the release;
(c) Contaminated
groundwater does not and is not reasonably likely to discharge to surface
waters or otherwise reach the surface in a manner that might result in contact
with ecological receptors; and
(d)
Contaminated groundwater does not and is not reasonably likely to come into
contact with aquatic sediments.
Publications: Publications referenced in this rule are
available from the agency.
Stat. Auth.: ORS 465.400 & ORS 466.746
Stats. Implemented: ORS 465.200 - ORS 465.455 & ORS
466.706 - ORS 466.835
