| (39) Method detection limit--The minimum concentration
of a substance that can be measured and reported with 99% confidence
that the analyte concentration is distinguishable from the method
blank results and is determined from analysis of a sample in a given
matrix containing the analyte. The method detection limit is estimated
in accordance with 40 Code of Federal Regulations Part 136, Appendix
B.
(40) Minimum analytical level--The lowest concentration
that a particular substance can be quantitatively measured with a
defined accuracy and precision level using approved analytical methods.
The minimum analytical level is not the published method detection
limit for a United States Environmental Protection Agency-approved
analytical method that is based on laboratory analysis of the substance
in reagent (distilled) water. The minimum analytical level is based
on analyses of the analyte in the matrix of concern (e.g., wastewater
effluents). The commission establishes general minimum analytical
levels that are applicable when information on matrix-specific minimum
analytical levels is unavailable.
(41) Mixing zone--The area contiguous to a permitted
discharge where mixing with receiving waters takes place and where
specified criteria, as listed in §307.8(b)(1) of this title (relating
to Application of Standards), can be exceeded. Acute toxicity to aquatic
organisms is not allowed in a mixing zone, and chronic toxicity to
aquatic organisms is not allowed beyond a mixing zone.
(42) Noncontact recreation--Activities that do not
involve a significant risk of water ingestion, such as those with
limited body contact incidental to shoreline activity, including birding,
hiking, and biking. Noncontact recreation use may also be assigned
where primary and secondary contact recreation activities should not
occur because of unsafe conditions, such as ship and barge traffic.
(43) Nonpersistent--Describes a toxic substance that
readily degrades in the aquatic environment, exhibits a half-life
of less than 60 days, and does not have a tendency to accumulate in
organisms.
(44) Nutrient criteria--Numeric and narrative criteria
that are established to protect surface waters from excessive growth
of aquatic vegetation. Nutrient numeric criteria for reservoirs are
expressed in terms of chlorophyll a concentration
per unit volume as a measure of phytoplankton density.
(45) Nutrient--A chemical constituent, most commonly
a form of nitrogen or phosphorus, that in excess can contribute to
the undesirable growth of aquatic vegetation and impact uses as defined
in this title.
(46) Oyster waters--Waters producing edible species
of clams, oysters, or mussels.
(47) Persistent--Describes a toxic substance that is
not readily degraded and exhibits a half-life of 60 days or more in
an aquatic environment.
(48) Pollution--The alteration of the physical, thermal,
chemical, or biological quality of, or the contamination of, any water
in the state that renders the water harmful, detrimental, or injurious
to humans, animal life, vegetation, or property or to the public health,
safety, or welfare, or impairs the usefulness or the public enjoyment
of the water for any lawful or reasonable purpose.
(49) Point source--Any discernible, confined and discrete
conveyance, including but not limited to any pipe, ditch, channel,
tunnel, conduit, well, discrete fissure, container, rolling stock,
concentrated animal feeding operation, or vessel or other floating
craft, from which pollutants or wastes are or may be discharged into
or adjacent to any water in the state.
(50) Presumed use--A use that is assigned to generic
categories of water bodies (such as perennial streams). Presumed uses
are superseded by designated uses for individual water bodies in Appendix
A, D, or G of §307.10 of this title (relating to Appendices A
- G).
(51) Primary contact recreation 1--Activities that
are presumed to involve a significant risk of ingestion of water (e.g.,
wading by children, swimming, water skiing, diving, tubing, surfing,
handfishing as defined by Texas Parks and Wildlife Code, §66.115,
and the following whitewater activities: kayaking, canoeing, and rafting).
(52) Primary contact recreation 2--Water recreation
activities, such as wading by children, swimming, water skiing, diving,
tubing, surfing, handfishing as defined by Texas Parks and Wildlife
Code, §66.115, and whitewater kayaking, canoeing, and rafting,
that involve a significant risk of ingestion of water but that occur
less frequently than for primary contact recreation 1 due to:
(A) physical characteristics of the water body; or
(B) limited public access.
(53) Protection zone--Any area within the watershed
of a sole-source surface drinking water supply that is:
(A) within two miles of the normal pool elevation of
a body of surface water that is a sole-source surface drinking water
supply;
(B) within two miles of that part of a perennial stream
that is:
(i) a tributary of a sole-source surface drinking water
supply; and
(ii) within three linear miles upstream of the normal
pool elevation of a sole-source surface drinking water supply; or
(C) within two miles of that part of a stream that
is a sole-source surface drinking water supply, extending three linear
miles upstream from the water supply intake (Texas Water Code, §26.0286).
(54) Public drinking water supply--A water body designated
to provide water to a public water system as defined in Chapter 290
of this title (relating to Public Drinking Water).
(55) Saltwater--A coastal water that has a measurable
elevation change due to normal tides. In the absence of tidal information,
saltwater is generally considered to be a coastal water that typically
has a salinity of two parts per thousand or greater in a significant
portion of the water column.
(56) Salinity--The total dissolved solids in water
after all carbonates have been converted to oxides, all bromide and
iodide have been replaced by chloride, and all organic matter has
been oxidized. For most purposes, salinity is considered equivalent
to total dissolved salt content. Salinity is usually expressed in
parts per thousand.
(57) Seagrass propagation--A water-quality-related
existing use that applies to saltwater with significant stands of
submerged seagrass.
(58) Secondary contact recreation 1--Activities that
commonly occur but have limited body contact incidental to shoreline
activity (e.g. fishing, canoeing, kayaking, rafting, and motor boating).
These activities are presumed to pose a less significant risk of water
ingestion than primary contact recreation 1 or 2 but more than secondary
contact recreation 2.
(59) Secondary contact recreation 2--Activities with
limited body contact incidental to shoreline activity (e.g. fishing,
canoeing, kayaking, rafting, and motor boating) that are presumed
to pose a less significant risk of water ingestion than secondary
contact recreation 1. These activities occur less frequently than
secondary contact recreation 1 due to physical characteristics of
the water body or limited public access.
(60) Segment--A water body or portion of a water body
that is individually defined and classified in Appendices A and C
of §307.10 of this title (relating to Appendices A - G) in the
Texas Surface Water Quality Standards. A segment is intended to have
relatively homogeneous chemical, physical, and hydrological characteristics.
A segment provides a basic unit for assigning site-specific standards
and for applying water quality management programs of the agency.
Classified segments may include streams, rivers, bays, estuaries,
wetlands, lakes, or reservoirs.
(61) Settleable solids--The volume or weight of material
that settles out of a water sample in a specified period of time.
(62) Seven-day, two-year low-flow (7Q2)--The lowest
average stream flow for seven consecutive days with a recurrence interval
of two years, as statistically determined from historical data. As
specified in §307.8 of this title, some water quality standards
do not apply at stream flows that are less than the 7Q2 flow.
(63) Shellfish--Clams, oysters, mussels, crabs, crayfish,
lobsters, and shrimp.
(64) Sole-source surface drinking water supply--A body
of surface water that is identified as a public water supply in rules
adopted by the commission under Texas Water Code, §26.023 and
is the sole source of supply of a public water supply system, exclusive
of emergency water connections (Texas Water Code, §26.0286).
(65) Standard Methods for the Examination of Water
and Wastewater--A document describing sampling and analytical procedures
that is published by the American Public Health Association, American
Water Works Association, and Water Environment Federation. The most
recent edition of this document is to be followed whenever its use
is specified by this chapter.
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