| (9) Numerical criteria for bioconcentratable pollutants
are derived in accordance with the general procedures in the EPA guidance
document entitled Assessment and Control of Bioconcentratable Contaminants
in Surface Water (March 1991). The commission may develop discharge
permit limits in accordance with the provisions of this section.
(10) Numerical human health criteria are expressed
as total recoverable concentrations for nonmetals and selenium and
as dissolved concentrations for other metals and metalloids.
(11) Additional site-specific factors may indicate
that the numerical human health criteria listed in Table 2 of paragraph
(1) of this subsection are inappropriate for a particular water body.
These factors are applied as a site-specific standards modification
in accordance with §307.2(d) of this title. The application of
site-specific criteria must not impair an existing, attainable, presumed,
or designated use or affect human health. Factors that may justify
a temporary variance or site-specific standards amendment include
the following:
(A) background concentrations of specific toxics of
concern in receiving waters, sediment, or indigenous biota;
(B) persistence and degradation rate of specific toxic
materials;
(C) synergistic or antagonistic interactions of toxic
substances with other toxic or nontoxic materials;
(D) technological or economic limits of treatability
for specific toxic materials;
(E) bioavailability of specific toxic substances of
concern;
(F) local water chemistry and other site-specific conditions
that may alter the bioconcentration, bioaccumulation, or toxicity
of specific toxic substances;
(G) site-specific differences in the bioaccumulation
responses of indigenous, edible aquatic organisms to specific toxic
materials;
(H) local differences in consumption patterns of fish
and shellfish or drinking water, but only if any changes in assumed
consumption rates are protective of the local population that frequently
consumes fish, shellfish, or drinking water from a particular water
body; and
(I) new information concerning the toxicity of a particular
substance.
(e) Total toxicity.
(1) Total (whole-effluent) toxicity of permitted discharges,
as determined from biomonitoring of effluent samples at appropriate
dilutions, must be sufficiently controlled to preclude acute total
toxicity in all water in the state with the exception of small ZIDs
at discharge points and at extremely low streamflow conditions (one-fourth
of critical low-flow conditions) in accordance with §307.8 of
this title. Acute total toxicity levels may be exceeded in a ZID,
but there must be no significant lethality to aquatic organisms that
move through a ZID, and the sizes of ZIDs are limited in accordance
with §307.8 of this title. Chronic total toxicity, as determined
from biomonitoring of effluent samples at appropriate dilutions, must
be sufficiently controlled to preclude chronic toxicity in all water
in the state with an existing or designated aquatic life use of limited
or greater except in mixing zones at discharge points and at flows
less than critical low-flows, in accordance with §307.8 of this
title. Chronic toxicity levels may be exceeded in a mixing zone, but
there must be no significant sublethal toxicity to aquatic organisms
that move through the mixing zone.
(2) General provisions for controlling total toxicity.
(A) Dischargers whose effluent has a significant potential
for exerting toxicity in receiving waters as described in the Procedures
to Implement the Texas Surface Water Quality Standards (RG-194) as
amended are required to conduct whole effluent toxicity biomonitoring
at appropriate dilutions.
(B) In addition to the other requirements of this section,
the effluent of discharges to water in the state must not be acutely
toxic to sensitive species of aquatic life, as demonstrated by effluent
toxicity tests. Toxicity testing for this purpose is conducted on
samples of 100% effluent, and the criterion for acute toxicity is
mortality of 50% or more of the test organisms after 24 hours of exposure.
This provision does not apply to mortality that is a result of an
excess, deficiency, or imbalance of dissolved inorganic salts (such
as sodium, calcium, potassium, chloride, or carbonate) that are in
the effluent and are not listed in Table 1 of subsection (c)(1) of
this section or that are in source waters.
(C) The latest revisions of the following EPA publications
provide methods for appropriate biomonitoring procedures: Methods
for Measuring the Acute Toxicity of Effluents and Receiving Waters
to Freshwater and Marine Organisms, Short-term Methods for Estimating
the Chronic Toxicity of Effluents and Receiving Waters to Freshwater
Organisms, Short-term Methods for Estimating the Chronic Toxicity
of Effluents and Receiving Waters to Marine and Estuarine Organisms,
and the Technical Support Document for Water Quality-based Toxics
Control. The use of other procedures approved by the agency and the
EPA is also acceptable. Toxicity tests must be conducted using representative,
sensitive aquatic organisms as approved by the agency, and any such
testing must adequately determine if toxicity standards are being
attained.
(D) If toxicity biomonitoring results indicate that
a discharge is not sufficiently controlled to preclude acute or chronic
toxicity as described in this subsection, then the permittee will
be required to eliminate sources of toxicity and may be required to
conduct a toxicity reduction evaluation (TRE) in accordance with the
permitting procedures of the commission. In accordance with the standards
implementation procedures (RG-194), permits are amended to include
appropriate provisions to eliminate toxicity. Such provisions may
include total toxicity limits, chemical-specific limits, best management
practices, or other actions (such as moving a discharge location)
designed to reduce or eliminate toxicity. Where sufficient to attain
and maintain applicable numeric and narrative state water quality
standards, a chemical-specific limit, best management practices, or
other actions designed to reduce or eliminate toxicity rather than
a total toxicity limit may be established in the permit. Where conditions
may be necessary to prevent or reduce effluent toxicity, permits must
include a reasonable schedule for achieving compliance with such additional
conditions.
(E) Discharge permit limits based on total toxicity
may be established in consideration of site-specific factors, but
the application of such factors must not result in impairment of an
existing, attainable, presumed, or designated use. These factors are
applied as a site-specific standards modification in accordance with
§307.2(d) of this title. A demonstration that uses are protected
may consist of additional effluent toxicity testing, instream monitoring
requirements, or other necessary information as determined by the
agency. Factors that may justify a temporary variance or site-specific
standards amendment include the following:
(i) background toxicity of receiving waters;
(ii) persistence and degradation rate of principal
toxic materials that are contributing to the total toxicity of the
discharge;
(iii) site-specific variables that may alter the impact
of toxicity in the discharge;
(iv) indigenous aquatic organisms that may have different
levels of sensitivity than the species used for total toxicity testing;
and
(v) technological, economic, or legal limits of treatability
or control for specific toxic material.
|
| Source Note: The provisions of this §307.6 adopted to be effective July 10, 1991, 16 TexReg 3400; amended to be effective July 13, 1995, 20 TexReg 4701; amended to be effective August 17, 2000, 25 TexReg 7722; amended to be effective July 22, 2010, 35 TexReg 6294; amended to be effective March 6, 2014, 39 TexReg1450; amended to be effective March 1, 2018, 43 TexReg 1102; amended to be effective September 29, 2022, 47 TexReg 6216 |
