Owners and operators shall apply the following risk-based criteria
to evaluate sites and determine target concentrations:
(1) Plan A site evaluation criteria. The owner and operator
should use Plan A established target concentrations to screen sites for closure,
or use the Plan A criteria to establish target concentrations for the purposes
of establishing a corrective action plan in accordance with §334.81 of
this title (relating to Corrective Action Plans), or to evaluate the potential
benefit of further site evaluation under paragraph (2) of this section.
(A) The owner and operator shall consider potential exposure
to receptors through direct and indirect exposure pathways as required by
the agency and determine whether or not such pathways are complete. A pathway
is considered complete if there is a source area, a transport mechanism and
an existing or potential receptor;
(B) For complete pathways, target concentrations shall be calculated
using equations and models, target risk goals, and exposure factors as established
by the agency;
(C) Target concentrations shall be based upon chemical property
information defined by the agency when such information is provided by the
agency;
(D) Target concentrations for indirect or cross-media pathways
shall be based upon default media property assumptions defined by the agency
when site-specific media property information is not available;
(E) Target concentrations shall be based upon residential land
use unless the owner and operator satisfies the requirements of §334.204
of this title (relating to Criteria for Selection of Land Use) to demonstrate
commercial/industrial land use is more appropriate.
(F) The owner and operator shall use equations and models as
required by the agency to calculate target concentrations;
(G) Target air concentrations shall be evaluated when there
is concern of a potential vapor hazard, or known or suspected indoor air exposure
to regulated substances. Regulated substance concentrations in soils and groundwater
are not to generate vapors in soil, air, utilities, or in the atmosphere which
could cause an explosive atmosphere at any surface or subsurface structure.
The presence of free product and associated level of vapors and the presence
of conduits or pathways such as utility conduits, foundation piers, foundation
cracks that may act as a transport pathway should be considered in this determination;
(H) Target surface water concentrations shall be as provided
in the Texas Surface Water Quality Standards of Chapter 307 of this title
(relating to Supplemental Surface Water Quality Standards) and Chapter 319
of this title (relating to General Regulations Incorporated Into Permits).
If those values are not available or appropriate, then federal maximum contaminant
levels (MCLs) promulgated under the federal Safe Drinking Water Act (42 Code
of Federal Regulations §300f, et seq.) shall apply. If MCLs are not available
or appropriate, then the target surface water concentrations are to be based
on reasonable maximum exposure expected to occur through human ingestion of
the water;
(I) Target groundwater concentration criteria:
(i) the actual beneficial use or potential beneficial use of
the affected groundwater shall be considered;
(ii) groundwater with a natural total dissolved solids content
of less than 10,000 mg/l and which is capable of yielding useable quantities
of water to a well or spring shall be considered to have a potential beneficial
use. When no site-specific data is available, the affected groundwater shall
be considered to be potentially useable;
(iii) residential groundwater ingestion shall be the default
exposure pathway unless the owner and operator can show to the satisfaction
of the agency that the documented actual beneficial use of the affected groundwater
is for a use other than drinking water purposes;
(iv) the individual carcinogenic risk must not exceed a range
of 1 X 10-6 to 1 X 10-4
as required by the agency for beneficial use groundwaters. For any
carcinogen, if the federally promulgated MCL is a higher value (less stringent),
then the MCL may be used;
(v) the hazard quotient for non-carcinogens shall not exceed
unity (one) for beneficial use groundwater;
(vi) Only the removal of non-aqueous phase liquid as required
pursuant to §334.79 of this title (relating to Removal of Non-Aqueous
Phase Liquid) and any subsequent monitoring as required by the agency shall
be necessary when the affected groundwater is of no potential beneficial use
provided the owner and operator can document to the satisfaction of the agency
that the dissolved regulated substance concentrations for such groundwater
that is less than 15 feet deep, is protective of potential direct contact
by construction workers; that any explosive vapors, adverse affects to subsurface
utilities, nuisance conditions, discharge of regulated substances to surface
waters at unprotective levels, and plume expansion have been abated and should
not occur in the future. When any of these conditions are not met with only
the removal of non-aqueous phase liquid, then target groundwater concentrations
shall be established by the owner and operator so as to meet these conditions;
(vii) Target groundwater concentrations shall apply throughout
the groundwater plume; and
(viii) If remaining groundwater concentrations will discharge
to a surface water body or other potentially usable aquifer at an unprotective
level, then an additional compliance point shall be established for the point
of discharge. The target groundwater concentration to be applied at the additional
compliance point(s) shall be based on the applicable target concentration
for the receiving water.
(J) Target soil concentration criteria:
(i) ingestion of soils from ground surface to a depth of 15
feet for residential and commercial/industrial land uses unless the owner
and operator can provide documentation to the satisfaction of the agency that
an alternate depth is more appropriate. Fifteen feet in the opinion of the
agency represents a reasonable depth above which soil could be excavated and
brought to the ground surface during construction activities;
(ii) inhalation of volatile and particulate emissions for residential
and commercial/industrial land uses, when the soil from ground surface to
a depth of 15 feet is affected, but not covered with an impermeable surface.
If the owner and operator can provide sufficient evidence that the impermeable
surface will be maintained and will prevent inhalation exposure, then inhalation
from soil contaminants may be dropped from further analysis;
(iii) cross-media affects (e.g., soil leachate to groundwater);
(iv) the target soil concentration shall be the lower concentration
of clauses (i), (ii) or (iii) of this subparagraph;
(v) reasonable maximum exposure expected to occur under both
current and future land use for either residential or commercial/industrial
as appropriate for the site;
(vi) maximum detected concentrations of regulated substances
remaining in place;
(vii) the individual carcinogenic risk shall not exceed 1 X
10-6 for Class A and B carcinogens and 1 X 10-5 for Class C carcinogens; and
(viii) the hazard quotient must not exceed unity (one) for
non-carcinogens;
(K) Target concentrations for soil, air and water shall also
take into account other factors such as vegetation effects, sensitive environmental
receptors, and aesthetic considerations (e.g., stained surface soils) as appropriate
in the final analysis;
(L) The maximum levels of regulated substances remaining in
all affected media shall meet the established target concentrations throughout
the entire extent of affected area unless the owner and operator can demonstrate
to the satisfaction of the agency that such action is technically infeasible
and that public health and the environment are otherwise adequately protected;
(M) The owner and operator shall submit reports in accordance
with a schedule and in a format established by the agency;
(N) The owner and operator or agency may recommend institutional
controls in accordance with §334.205 of this title (relating to Institutional
Control Requirements) to reinforce exposure assumptions; and
(O) Any necessary requirements as established by the agency
to protect public health, safety, and the environment.
(2) Plan B site-evaluation criteria. The owner and operator
may elect to further evaluate a site under Plan B to determine more appropriate
target concentrations for affected media which may be used to justify a closure
recommendation, or for the purposes of establishing a corrective action plan
in accordance with §334.81 of this title.
Cont'd... |
