| (3) Aquatic life. The establishment of numerical criteria
for aquatic life is highly dependent on desired use, sensitivities
of aquatic communities, and local physical and chemical characteristics.
Six subcategories of aquatic life use are established. They include
minimal, limited, intermediate, high, and exceptional aquatic life
and oyster waters. Aquatic life use subcategories designated for segments
listed in Appendix A of §307.10 of this title recognize the natural
variability of aquatic community requirements and local environmental
conditions.
(A) Dissolved oxygen.
(i) The characteristics and associated dissolved oxygen
criteria for limited, intermediate, high, and exceptional aquatic
life use subcategories are indicated in Table 3 of this clause. This
table also includes dissolved oxygen criteria for a minimal aquatic
life use subcategory that applies to intermittent streams without
perennial pools as indicated in §307.4(h)(4) of this title.
Attached Graphic
(ii) Critical low-flow values associated with the bedslopes
and dissolved oxygen criteria in Table 4 of this clause apply to streams
that have limited, intermediate, high, or exceptional aquatic life
uses and to streams that are specifically listed in Appendix A or
D of §307.10 of this title. The critical low-flow values in Table
4 of this clause apply to streams in Texas that are east of a line
defined by Interstate Highways 35 and 35W from the Red River to the
community of Moore in Frio County, and by US Highway 57 from the community
of Moore to the Rio Grande. Table 4 of this clause does not apply
where specifically superseded by the equation that is listed in footnote
3 in the Cypress Creek Basin in Appendix A and in footnote 1 in Appendix
D of §307.10 of this title. The critical low-flow values in Table
4 of this clause (at the appropriate stream bedslope) are utilized
as headwater flows when the flows are larger than applicable seven-day,
two-year low-flows in order to determine discharge effluent limits
necessary to achieve dissolved oxygen criteria. For streams that have
bedslopes less than the minimum bedslopes in Table 4 of this clause,
the flows listed for the minimum bedslope of 0.1 meters per kilometer
(m/km) are applicable. For streams that have bedslopes greater than
the maximum bedslope in Table 4 of this clause, the flows listed for
the maximum bedslope of 2.4 m/km are applicable. The required effluent
limits are those necessary to achieve each level of dissolved oxygen
(as defined in Table 3 of clause (i) of this subparagraph) at or below
an assigned, designated, or presumed aquatic life use. Presumed aquatic
life uses must be in accordance with those required by §307.4(h)
of this title. The critical low-flow values in Table 4 of this clause
do not apply to tidal streams.
Attached Graphic
(iii) The critical low-flow values in Table 4 of clause
(ii) of this subparagraph for limited, intermediate, high, and exceptional
aquatic life uses are based upon data from the commission's least
impacted stream study (Texas Aquatic Ecoregion Project). Results of
this study indicate a strong dependent relationship for average summertime
background dissolved oxygen concentrations and several hydrologic
and physical stream characteristics - particularly bedslope (stream
gradient) and stream flow. The critical low-flow values in Table 4
of clause (ii) of this subparagraph are derived from a multiple regression
equation for the eastern portion of Texas as defined in clause (ii)
of this subparagraph. Further explanation of the development of the
regression equation and its application are contained in the standards
implementation procedures as amended.
(iv) The critical low-flow values in Table 4 of clause
(ii) of this subparagraph may be adjusted based on site-specific data
relating dissolved oxygen concentrations to factors such as flow,
temperature, or hydraulic conditions in accordance with the standards
implementation procedures as amended. Site-specific, critical low-flow
values require approval by the commission. The EPA must review any
site-specific, critical low-flow values that could affect permits
or other regulatory actions that are subject to approval by EPA. Critical
low-flow values that have been determined for particular streams are
listed in the standards implementation procedures.
(B) Oyster waters.
(i) A 1,000 foot buffer zone, measured from the shoreline
at ordinary high tide, is established for all bay and gulf waters
except those contained in river or coastal basins as defined in §307.2
of this title (relating to Description of Standards). Recreational
criteria for indicator bacteria, as specified in §307.7(b)(1)
of this title (relating to Site-Specific Uses and Criteria), are applicable
within buffer zones.
(ii) The criteria for median fecal coliform concentration
in bay and gulf waters, exclusive of buffer zones, are 14 colonies
per 100 mL with not more than 10% of all samples exceeding 43 colonies
per 100 mL.
(iii) Oyster waters should be maintained so that concentrations
of toxic materials do not cause edible species of clams, oysters,
and mussels to exceed accepted guidelines for the protection of public
health. Guidelines are provided by the United States Food and Drug
Administration Action Levels for molluscan shellfish, but additional
information related to human health protection may also be considered
in determining acceptable toxic concentrations.
(4) Additional criteria.
(A) Chemical parameters. Site-specific criteria for
chloride, sulfate, and total dissolved solids are established as averages
over an annual period for either a single sampling point or multiple
sampling points.
(B) pH. Site-specific numerical criteria for pH are
established as absolute minima and maxima.
(C) Temperature. Site-specific temperature criteria
are established as absolute maxima.
(D) Toxic materials. Criteria for toxic materials are
established in §307.6 of this title (relating to Toxic Materials).
(E) Nutrient criteria. Numeric and narrative criteria
to preclude excessive growth of aquatic vegetation are intended to
protect multiple uses such as primary, secondary, and noncontact recreation,
aquatic life, and public water supplies. Nutrient numeric criteria
for specific reservoirs, expressed as concentrations of chlorophyll
a in water, are listed in Appendix F of §307.10 of this title.
(5) Additional uses. Other basic uses, such as navigation,
agricultural water supply, industrial water supply, seagrass propagation,
and wetland water quality functions must be maintained and protected
for all water in the state where these uses can be achieved.
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| Source Note: The provisions of this §307.7 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 TexReg 1450; amended to be effective March 1, 2018, 43 TexReg 1102; amended to be effective September 29, 2022, 47 TexReg 6216 |
