Mississippi Administrative Code › Title 11 - Mississippi Department of Environmental Quality › Part 6 - Wastewater Pollution Control Regulations › Chapter 2 - Mississippi Commission on Environmental Quality Regulations for Water Quality Criteria For Intrastate, Interstate, And Coastal Waters › Rule 11-6-2.5 - Implementation of Water Quality Criteria

Current through June 25, 2024
According to 40 CFR
131.13
, States
				  may, at their discretion, include in their State standards, policies generally
				  affecting their application and implementation, such as mixing zones, low flows
				  and variances. Such policies are subject to U.S. EPA review and approval. If
				  the State adopts a policy applicable only to Surface Waters of the State that
				  are not also Waters of the United States, such policy is not subject to U.S.
				  EPA review and approval.
A.
Natural Conditions
: Natural conditions are defined as
				background water quality conditions due only to non-anthropogenic sources. The
				criteria herein apply specifically with regard to substances attributed to
				sources (permitted discharges, nonpoint sources, or in-stream activities) as
				opposed to natural phenomena. Some waterbodies may have characteristics that
				are naturally outside the limits established herein. Therefore, naturally
				occurring conditions that preclude attainment of these criteria should not be
				interpreted as violations of the criteria.
B.
Applicable Flow
:
				All criteria contained herein shall apply to all stages of stream flow greater
				than or equal to the 7-day, 10-year minimum flow (7Q10) in unregulated, natural
				streams, and the legally guaranteed minimum flow in regulated streams, unless
				otherwise provided in these regulations. This requirement shall not be
				interpreted to permit any unusual waste discharges during periods of lower
				flow.
Notwithstanding the above, a stream flow equal to the 7-day,
				  2-year minimum flow (7Q2) in unregulated, natural streams shall be utilized in
				  establishing permit limitations for stormwater permits. In cases in which
				  either (1) the data are indefinite or inconclusive, or (2) the 7-day, 2-year
				  minimum flow and/or the 7-day, 10-year minimum flow are inappropriate because
				  of the hydrology of the area, other appropriate State and federal agencies will
				  be consulted in order to establishing the appropriate and applicable stream
				  flow.
C.
Mixing
				Zones
: It is recognized that limited areas of mixing are sometimes
				unavoidable; however, mixing zones shall not be used as a substitute for waste
				treatment. Mixing zones constitute an area whereby physical mixing of a
				wastewater effluent with a receiving waterbody occurs. Application of mixing
				zones shall be made on a case-by-case basis and shall only occur in cases
				involving large surface waterbodies in which a long distance or large area is
				required for the wastewater to completely mix with the receiving waterbody.
The location of a mixing zone shall not significantly alter
				  the designated uses of the receiving water outside its established boundary.
				  Adequate zones of passage for the migration and free movement of fish and other
				  aquatic biota shall be maintained. Toxicity and human health concerns within
				  the mixing zone shall be addressed as specified in the U.S. EPA
Technical Support Document for Water Quality-Based Toxics
				  Control
(U.S. EPA-505/2-90-001, March 1991) and amendments thereof.
				  Under no circumstances shall mixing zones overlap or cover tributaries, nursery
				  locations, locations of threatened or endangered species, or other ecologically
				  sensitive areas.
D.
				Schedules of Compliance:
When appropriate, the State, UIC, or NPDES permit issued by
				  the Permit Board pursuant to Rule
				  1.1.3.H may contain a schedule of
				  compliance leading to compliance with the Federal Water Pollution Control Act
				  and the Mississippi Air and Water Pollution Control Law. Additional information
				  and requirements regarding schedules of compliance can be found within 11 Miss.
				  Admin. Code Pt. 6, R.
				  1.1.4.A(9).
E. Water Quality Standards Variances:
As defined in
				  40
				  CFR 131.3(o), a water
				  quality standards variance is a time-limited designated use and criterion for a
				  specific pollutant(s) or water quality parameter(s) that reflect the highest
				  attainable condition during the term of the variance. A water quality standards
				  variance must meet certain provisions according to
				  40 CFR
				  131.14 and must meet
certain
				  public participation requirements within
				  40 CFR
				  131.20(b). A WQS variance is
				  a water quality standard subject to U.S. EPA review and approval or
				  disapproval. MDEQ will apply the same provisions of
				  40 C.F.R. §
											131.14 in considering a WQS variance for
				  State waters that do not meet the definition of Waters of the United States and
				  will use the same public participation requirements within § 131.20(b) for
				  such waters. A WQS variance to Surface Waters of the State which do not meet
				  the definition of "Waters of the United States" will not be subject to U.S. EPA
				  review and approval or disapproval.
(1) Applicability:
(a) A WQS variance may be adopted for a
				permittee(s) or waterbody/waterbody segment(s), but only applies to the
				permittee(s) or waterbody/waterbody segment(s) specified in the WQS
				variance.
(b) Where the State
				adopts a WQS variance, the State must retain, in its standards, the underlying
				designated use and criterion addressed by the WQS variance, unless the State
				adopts and U.S. EPA approves a revision to the underlying designated use and
				criterion consistent with
				40 CFR 131.10
				and 131.11. All other
				applicable standards not specifically addressed by the WQS variance remain
				applicable. U.S. EPA approval is not required for State waters that are not
				waters of the United States.
(c) A
				WQS variance, once adopted by the State and approved by U.S. EPA, shall be the
				applicable standard for purposes of the Clean Water Act under
				40 CFR
				131.21(d) through (e), for
				the following limited purposes. An approved WQS variance applies for the
				purposes of developing NPDES permit limits and requirements under 301(b)(1)(C),
				where appropriate, consistent with paragraph (1)(a) of this section. States and
				other certifying entities may also use an approved WQS variance when issuing
				certifications under section 401 of the Clean Water Act. U.S. EPA approval is
				not required for Surface Waters of the State that are not Waters of the United
				States.
(d) The State may not adopt
				WQS variances if the designated use and criterion addressed by the WQS variance
				can be achieved by implementing technology-based effluent limits required under
				sections 301(b) and 306 of the Clean Water Act.