Texas Administrative Code › Title 30 - ENVIRONMENTAL QUALITY › Part 1 - TEXAS COMMISSION ON ENVIRONMENTAL QUALITY › Chapter 334 - UNDERGROUND AND ABOVEGROUND STORAGE TANKS › Subchapter G - TARGET CONCENTRATION CRITERIA › Section 334.203 - Risk-Based Criteria for Establishing Target Concentrations

Current through Reg. 49, No. 28; July 12, 2024
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.