The Clean Water Act (CWA) employs three general types of standards:
technology-based standards, ambient or water quality-based standards,
and in the case of a small number of toxic compounds, health-based
The CWA employs four technology-based water pollution control
standards. "Best practicable control technology currently available"
(BPT) sets uniform, industry-wide effluent standards that approximate
the average amount of control achieved from existing technology in the
specific industry. BPT sets the initial national floor applicable to all
existing industrial sources of water pollution. "Best available
technology economically achievable" (BAT) applies primarily to certain
toxic pollutants, 33 U.S.C. sec. 1317, nonconventional pollutants, 33
U.S.C. sec. 1311(b)(2)(F), and thermal pollution, 33 U.S.C. sec. 1326.
"Best conventional pollutant control technology" (BCT), which is
essentially the best available technology modified to reflect only those
technologies where the benefits of pollution control are greater than
the costs, applies to certain "conventional pollutants, including
biochemical oxygen demand (BOD), total suspended solids (TSS), fecal
coliform, and pH. "Best available demonstrated control technology"
(BACT) forms the basis for new source performance standards (NSPS). BACT
incorporates the "greatest degree of effluent reduction achievable,"
which is set according to different categories of industrial and
agricultural activities. 33 U.S.C. sec. 1316.
Water Quality-Based Standards.
Ambient, water quality-based standards may also form the basis for a
federal water permit. Water quality-based standards are imposed when the
technology-based standards are not expected to provide sufficient
protection for local water quality, given local water conditions and
uses. States must classify all state waters according to specific uses
and then set an ambient water quality standard to protect that use. Once
the standard is set, the total maximum daily load (TMDL) of a particular
pollutant is set at a level that will not violate the standard. The TMDL
is then translated into specific numerical limits in particular permits.
The states identify the uses, set the water quality standards, and
determine how to allocate the TMDL among different users. The federal
role is limited to reviewing the standards or developing replacement
standards for states that fail to meet minimum federal requirements. 33
U.S.C. sec. 1313; 40 C.F.R. pt. 131. EPA also retains, but has rarely
used, the authority to impose more stringent water quality limitations
if necessary to meet the national goal of fishable and swimmable waters.
Where the BAT standard is not sufficient to achieve an "ample margin of
safety" in protecting the environment and public health from certain
toxic pollutants, EPA has the authority to issue toxic pollutant
effluent standards. 33 U.S.C. sec. 1317. In setting these standards, the
agency has no authority to consider economic factors. Toxic pollutant
effluent standards have been set for six chemicals: aldrin, DDT and
related compounds, endrin, toxaphene, benzidine, and polychlorinated
biphenyls. 40 C.F.R. pt. 129.
States have the explicit right to enact any water quality standard or
limitation that is more stringent than those required by federal
statute. 33 U.S.C. sec. 1370. Most states have enacted separate state
water pollution control laws and regulations. The states also take the
lead role in setting water quality-based standards, which from the basis
for both federal National Pollutant Discharge Elimination System (NPDES)
and state permits. The states must also be given an opportunity to
review any federal NPDES permit before it is issued. If the proposed
NPDES permit does not meet state standards, it cannot be issued. 33
U.S.C. sec. 1341.
From Summary of Enviromental Law in the United States - CEC
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