Nebraska Administrative Code › Topic - ENVIRONMENT AND ENERGY › Title 117 - NEBRASKA DEPARTMENT OF ENVIRONMENTAL QUALITY › Chapter 2 - APPLICATION OF STANDARDS › Section 117-2-010

Current through June 17, 2024
These standards, except water quality criteria associated with
	 aesthetics (Chapter 4, 005) and recreation (Chapter 4, 002) will not apply
	 within mixing zones unless specified below.
Mixing zones for the initial assimilation of effluents or wastewaters
	 may be necessary where discharges that have received the applicable level of
	 treatment or control still do not adequately protect the water quality of a
	 receiving stream. Mixing zones are to be limited to as small an area and volume
	 of a receiving stream as is practical to prevent interference with or
	 impairment of any beneficial uses. The requirements of mixing zones for heat
	 are to be defined on a site-specific basis, in a manner consistent with Section
	 316 of the Clean Water Act.
010.01 The
  Department determines the applicability of a mixing zone, and if applicable,
  the allowable size, location, water quality, and outfall design. The following
  requirements will be used in defining all mixing zones. These requirements are
  not intended to define each individual mixing zone, but represent maximum
  limits which will satisfy most biological, chemical, physical, and radiological
  considerations. A smaller mixing zone may be required or no zone at all
  allowed, as necessary, in order to meet these requirements.
010.02 The appropriateness, if any, of
  establishing a mixing zone for a pollutant which may be bioaccumulative,
  persistent, carcinogenic, mutagenic, or teratogenic will be carefully evaluated
  by the Department. In such cases, effects such as potential ground water
  contamination, known or predicted safe exposure levels for human health,
  bioaccumulation in aquatic life, fish attraction, sediment deposition, and
  protection of downstream beneficial uses will be considered.
010.03 Mixing zones established for dissolved
  oxygen are to take into account the delayed effects caused by oxidation of
  organic matter and ammonia inside and outside the mixing zone. One-day minimum
  dissolved oxygen criteria apply at the boundary of and beyond acute mixing
  zones, but not within acute mixing zones. All applicable dissolved oxygen
  criteria, including the one-day minimum criteria, are to be met at and beyond
  the mixing zone boundaries.
010.04
  Mixing zones established for discharges impacting agricultural water supply
  criteria are to be based on the restrictions established for chronic mixing
  zones ( 010.06).
010.05 All mixing
  zone specifications are to be based on critical conditions of minimum dilution.
  Flow variable calculations that use real-time flows for a point source
  discharge and receiving stream may be allowed to determine critical conditions
  of minimum dilution. If flow variable critical conditions are not defined,
  critical conditions are to be determined as follows. The average dry weather or
  seasonal flow for a point source discharge will be used with the 7-day 10-year
  low flow of the receiving stream for application of all criteria with the
  exception of thirty-day average ammonia criteria and acute criteria for aquatic
  life. The 30-day 5-year low flow of the receiving stream will be used for
  application of thirty-day average ammonia criteria. The 1-day 10-year low flow
  of the receiving stream will be used for application of acute
  criteria.
010.06 Chronic Mixing
  Zones.
Chronic toxicity to aquatic life will not be allowed at any time
	 outside of a chronic mixing zone.
010.06A The length of a chronic mixing zone
  is not to exceed the following distances based on designated aquatic life use
  classes.
010.06A1 Chronic mixing zones in
  Coldwater Class A, Coldwater Class B, and Warmwater Class B streams are to be
  designed to not exceed 2,500 feet in length.
010.06A2 Chronic mixing zones in Warmwater
  Class A streams are to be designed to not exceed 5,000 feet in
  length.