Michigan Administrative Code › Department - Environmental Quality › Water Resources Division › Water Resources Protection › Part 4 - WATER QUALITY STANDARDS › Section R. 323.1082 - Mixing zones

Current through Vol. 24-12, July 15, 2024
Rule 82.
(1) A
				  mixing zone is that portion of a water body allocated by the department where a
				  point source or venting groundwater discharge is mixed with the surface waters
				  of the state. Exposure in mixing zones shall not result in deleterious effects
				  to populations of aquatic life or wildlife. As a minimum restriction, the final
				  acute value (FAV) for aquatic life shall not be exceeded when determining a
				  wasteload allocation (WLA) for acute aquatic life protection, unless it is
				  determined by the department that a higher level is acceptable or it can be
				  demonstrated to the department that an acute mixing zone is acceptable
				  consistent with subrule (7) of this rule. The mixing zone shall not prevent the
				  passage of fish or fish food organisms in a manner that would result in adverse
				  impacts on the immediate or future populations of the fish or fish food
				  organisms. The area of mixing zones shall be minimized. To this end, devices
				  for rapid mixing, dilution, and dispersion are encouraged where practicable.A
				  watercourse or portions of a watercourse that, without 1 or more point source
				  discharges, would have no flow except during periods of surface runoff may be
				  considered as a mixing zone for a point source discharge. A mixing zone
				  established in this manner shall not apply to pollutants of initial focus
				  specified in 40 C.F.R. §132 (1995) unless a site-specific determination
				  under R 323.1057(2) has been conducted that shows that the existing and
				  expected aquatic life in the watercourse will be adequately protected in the
				  absence of chronic aquatic life water quality values.
(2) Unless otherwise stated in this rule, not
				  more than 25% of the receiving water design flow for lotic systems, as stated
				  in R 323.1090(2), shall be used when determining a whole effluent toxicity
				  limit or a wasteload allocation for a toxic substance, in the absence of, or
				  consistent with, a total maximum daily load, unless it can be demonstrated to
				  the department that the use of a larger volume is acceptable consistent with
				  subrule (7) of this rule.
(3) For
				  ammonia and substances not included in subrule (2) of this rule, the design
				  flow for lotic systems, as stated in R 323.1090(2)(a) or (3), shall be used
				  when determining WLAs if the provisions in subrule (1) of this rule are met,
				  unless the department determines that a more restrictive volume is
				  necessary.
(4) For all substances,
				  physical mixing zone boundaries may be established and shall be determined by
				  the department on a case-by-case basis.
(5) Mixing zones in the Great Lakes and
				  inland lakes for the purpose of determining WLAs and WET limits shall assume no
				  greater dilution than 1 part effluent to 10 parts receiving water, unless it
				  can be demonstrated to the department that use of a larger volume is acceptable
				  consistent with subrule (7) of this rule. Except for ammonia, a larger mixing
				  zone shall not be granted if it exceeds the area where discharge-induced mixing
				  occurs. Mixing zones established under this subrule for thermal discharges to
				  meet the Great Lakes and inland lake requirements of R 323.1069, R 323.1070, R
				  323.1072, R 323.1073, and R 323.1075 shall be determined by the department on a
				  case-by-case basis.
(6) In
				  addition to subrules (1), (2), (4), and (5) of this rule, the following
				  provisions are applicable to bioaccumulative chemicals of concern (BCCs) when
				  establishing WLAs:
(a) There shall be no
				  mixing zones available for new discharges of BCCs to the surface waters of the
				  state.
(b) Mixing zones for BCCs
				  may be allowed for existing discharges to the surface waters of the state
				  through November 14, 2010, pursuant to the provisions of this rule. After this
				  date, except as provided in subdivisions (c) and (d) of this subrule, permits
				  shall not authorize mixing zones for existing discharges of BCCs to the surface
				  waters of the state, and WLAs for such discharges shall be set equal to the
				  most stringent water quality value for that BCC.
(c) The department may grant mixing zones for
				  any existing discharge of BCCs to the surface waters of the state where it can
				  be demonstrated, on a case-by-case basis, that failure to grant a mixing zone
				  would preclude water conservation measures that would lead to overall load
				  reductions in BCCs.
(d) Upon the
				  request of an existing discharger of a BCC to the surface waters of the state,
				  the department may grant mixing zones beyond November 14, 2010, based upon
				  technical and economic considerations, subject to all of the following
				  provisions:
(i) The department must determine
				  that all of the following provisions are satisfied:
(A) The discharger is in compliance with, and
				  will continue to implement, all applicable technology-based treatment and
				  pretreatment requirements of the clean water act of 1972, as amended, 33 U.S.C.
				  §§301, 302, 304, 306, 307, 401, and 402, and is in compliance with
				  its existing NPDES WQBELs, including those based on a mixing zone.
(B) The discharger has reduced, and will
				  continue to reduce, to the maximum extent possible, the loading of the BCC for
				  which a mixing zone is requested, by the use of cost-effective controls or
				  pollution-prevention alternatives that have been adequately demonstrated and
				  are reasonably available to the discharger.
(C) The discharger has evaluated alternative
				  means of reducing the BCC elsewhere in the watershed.
(ii) In making the determination in paragraph
				  (i) of this subdivision, the department shall consider all of the following
				  factors:
(A) The availability and feasibility,
				  including cost effectiveness, of additional controls or pollution prevention
				  measures for reducing and ultimately eliminating BCCs for the discharger,
				  including additional controls or pollution prevention measures used by similar
				  dischargers for reducing and ultimately eliminating BCCs.
(B) Whether the discharger or affected
				  communities will suffer unreasonable economic effects if the mixing zone is
				  eliminated.
(C) The extent to which
				  the discharger will implement an ambient monitoring plan to ensure compliance
				  with water quality values at the edge of any authorized mixing zone.
(D) Other information the department deems
				  appropriate.
(iii) Any
				  exceptions to the mixing zone elimination provision for existing discharges of
				  BCCs granted pursuant to this subdivision shall comply with all of the
				  following provisions:
(A) Not result in any
				  less stringent limitations than the limitations that existed on July 29,
				  1997.
(B) Be limited to 1 permit
				  term unless the department makes a new determination in accordance with this
				  subrule for each successive permit application in which a mixing zone for the
				  BCC is sought.
(C) Not likely
				  jeopardize the continued existence of any endangered or threatened species
				  listed or proposed under section 4 of the endangered species act or result in
				  the destruction or adverse modification of the species' critical
				  habitat.
(iv) For each
				  draft NPDES permit that allows a mixing zone for a BCC after November 14, 2010,
				  the NPDES fact sheet shall specify relevant information used to establish the
				  mixing zone, including the mixing provisions used in calculating the permit
				  limits and the identity of each BCC for which a mixing zone is
				  proposed.