| (a) Definitions. The following words and terms, when
used in this chapter, have the defined meanings, unless the context
clearly indicates otherwise.
(1) Acute toxicity--Toxicity that exerts a stimulus
severe enough to rapidly induce an effect. The duration of exposure
applicable to acute toxicity is typically 96 hours or less. Tests
of total toxicity normally use lethality as the measure of acute impacts.
(Direct thermal impacts are excluded from definitions of toxicity.)
(2) Ambient--Refers to the existing water quality in
a particular water body.
(3) Aquatic vegetation--Refers to aquatic organisms,
i.e., plant life, found in the water and includes phytoplankton; algae,
both attached and floating; and vascular and nonvascular plants, both
rooted and floating.
(4) Attainable use--A use that can be reasonably achieved
by a water body in accordance with its physical, biological, and chemical
characteristics whether it is currently meeting that use or not. Guidelines
for the determination and review of attainable uses are provided in
the standards implementation procedures. The designated use, existing
use, or presumed use of a water body may not necessarily be the attainable
use.
(5) Background--Refers to the water quality in a particular
water body that would occur if that water body were relatively unaffected
by human activities.
(6) Bedslope--Stream gradient, or the extent of the
drop in elevation encountered as the stream flows downhill. One measure
of bedslope is the elevation decline in meters over the stream distance
in kilometers.
(7) Best management practices--Schedules of activities,
maintenance procedures, and other management practices to prevent
or reduce the pollution of water in the state from point and nonpoint
sources, to the maximum extent practicable. Best management practices
also include treatment requirements, operating procedures, and practices
to control plant site runoff, spillage or leaks, sludge or waste disposal,
or drainage from raw material storage.
(8) Bioaccumulative--Describes a chemical that is taken
up by aquatic organisms from water directly or through the consumption
of food containing the chemical.
(9) Bioaccumulation factor--A unitless value describing
the degree to which a chemical can be concentrated in the tissues
of an organism in the aquatic environment and that is absorbed through
all routes of exposure, including the food chain. The bioaccumulation
factor is the ratio of the concentration of a chemical in the tissue
of an aquatic organism to the concentration of the chemical dissolved
in ambient water at the site of sampling.
(10) Bioconcentration factor--A unitless value describing
the degree to which a chemical can be concentrated in the tissues
of an organism in the aquatic environment and that is absorbed directly
from the water. The bioconcentration factor is the ratio of a chemical's
concentration in the tissue of an organism compared to that chemical's
average concentration in the surrounding water.
(11) Biological integrity--The species composition,
diversity, and functional organization of a community of organisms
in an environment relatively unaffected by pollution.
(12) Biotic ligand model--A metal bioavailability model
that uses receiving water body characteristics to develop site-specific
water quality criteria.
(13) Chronic toxicity--Toxicity that continues for
a long-term period after exposure to toxic substances. Chronic exposure
produces sub-lethal effects, such as growth impairment and reduced
reproductive success, but it may also produce lethality. The duration
of exposure applicable to the most common chronic toxicity test is
seven days or more.
(14) Classified--Refers to a water body that is listed
and described in Appendices A and C of §307.10 of this title
(relating to Appendices A - G). Site-specific uses and criteria for
classified water bodies are listed in Appendix A of §307.10 of
this title.
(15) Coastal recreation waters--Marine coastal waters
including oceans, coastal estuaries, and bays designated as primary
contact recreation. Waters upstream of an unimpaired natural connection
to the open sea or tidal inland waters are not considered coastal
recreation waters (e.g., tidal rivers or streams).
(16) Commission--Texas Commission on Environmental
Quality.
(17) Criteria--Water quality conditions that are to
be met in order to support and protect desired uses, i.e., existing,
designated, attainable, and presumed uses.
(18) Critical low-flow--Low-flow condition that consists
of the seven-day, two-year low-flow or the alternative low-flows for
spring-fed streams as discussed in §307.8(a)(2) of this title
(relating to Application of Standards) and below which some standards
do not apply.
(19) Designated use--A use that is assigned to specific
water bodies in Appendix A, D, or G of §307.10 of this title
(relating to Appendices A - G). Typical uses that may be designated
for specific water bodies include domestic water supply, categories
of aquatic life use, recreation categories, and aquifer protection.
(20) Discharge permit--A permit issued by the state
or a federal agency to discharge treated effluent or cooling water
into waters of the state.
(21) Dry weather flows--Sustained or typical dry, warm-weather
flows between rainfall events, excluding unusual antecedent conditions
of drought or wet weather.
(22) EC50 --The concentration
of a toxicant that produces an adverse effect on 50% of the organisms
tested in a specified time period.
(23) E. coli--Escherichia
coli, a subgroup of fecal coliform bacteria that is present
in the intestinal tracts and feces of warm-blooded animals. It is
used as an indicator of the potential presence of pathogens.
(24) Effluent--Wastewater discharged from any point
source prior to entering a water body.
(25) Enterococci--A subgroup of fecal streptococci
bacteria (mainly Streptococcus faecalis and Streptococcus faecium that is present in
the intestinal tracts and feces of warm-blooded animals. It is used
as an indicator of the potential presence of pathogens.
(26) Epilimnion--The upper mixed layer of a lake (including
impoundments, ponds, and reservoirs).
(27) Existing use--A use that is currently being supported
by a specific water body or that was attained on or after November
28, 1975.
(28) Fecal coliform--A portion of the coliform bacteria
group that is present in the intestinal tracts and feces of warm-blooded
animals; heat tolerant bacteria from other sources can sometimes be
included. It is used as an indicator of the potential presence of
pathogens.
(29) Freshwaters--Inland waters that exhibit no measurable
elevation changes due to normal tides.
(30) Halocline--A vertical gradient in salinity under
conditions of density stratification that is usually recognized as
the point where salinity exhibits the greatest difference in the vertical
direction.
(31) Harmonic mean flow--A measure of mean flow in
a water course that is calculated by summing the reciprocals of the
individual flow measurements, dividing this sum by the number of measurements,
and then calculating the reciprocal of the resulting number.
(32) Incidental fishery--A level of fishery that applies
to water bodies that are not considered to have a sustainable fishery
but do have an aquatic life use of limited, intermediate, high, or
exceptional.
(33) Industrial cooling impoundment--An impoundment
that is owned or operated by, or in conjunction with, the water rights
permittee, and that is designed and constructed for the primary purpose
of reducing the temperature and removing heat from an industrial effluent.
(34) Industrial cooling water area--A designated area
associated with a permitted wastewater discharge where numerical temperature
criteria are not applicable in accordance with conditions and requirements
specified in §307.4(f) of this title (relating to General Criteria)
and §307.8(b) of this title (relating to Application of Standards).
(35) Intermittent stream--A stream that has a period
of zero flow for at least one week during most years. Where flow records
are available, a stream with a seven-day, two-year low-flow of less
than 0.1 cubic feet per second is considered intermittent.
(36) Intermittent stream with perennial pools--An intermittent
stream that maintains persistent pools even when flow in the stream
is less than 0.1 cubic feet per second.
(37) LC50 --The concentration
of a toxicant that is lethal (fatal) to 50% of the organisms tested
in a specified time period.
(38) Main pool station--A monitoring station that is
located in the main body of a reservoir near the dam and not located
in a cove or in the riverine portion or transition zone of a reservoir.
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