Louisiana Administrative Code
Title 33 - ENVIRONMENTAL QUALITY
Part IX - Water Quality
Subpart 1 - Water Pollution Control
Chapter 11 - Surface Water Quality Standards
Section IX-1115 - Application of Standards

Universal Citation: LA Admin Code IX-1115

Current through Register Vol. 50, No. 9, September 20, 2024

A. Background

1. The water quality standards set forth in this Chapter are the foundation for a range of programs that establish water quality goals for water body segments thereby ensuring suitable aquatic ecosystems. Water quality standards are derived for individual water segments on the basis of the designated use or uses of the segment and the natural qualities of the waters.

2. An established water quality criterion represents the general or numeric concentration limit or characteristic of a constituent in a water body segment that is allowed by the state. For some toxic substances, however, criteria provide both acute and chronic limits for the protection of aquatic life in fresh and marine waters, and separate limits for the protection of human health. Criteria apply at all times, except where natural conditions cause them to be exceeded or where specific exemptions in the standards apply. Water uses, pollution sources, natural conditions, and the water quality criteria are all considered in the departments determination of appropriate permit limits for each wastewater discharge to a water body.

3. The difference between an ambient concentration and a water quality criterion should not be construed as the amount of a constituent that can be discharged. The antidegradation statement requires that all waters which exceed the water quality standards be maintained at their existing high quality, which can be lowered only after demonstrating that allowing lower water quality is necessary to accommodate important economic and or social development in the area in which the waters are located. In addition, before a lowering of high water quality can be allowed, an analysis of alternatives shall be performed to demonstrate that the lowering of high water quality is necessary. More stringent requirements apply to those waters designated as outstanding natural resource waters, as described in LAC 33:IX.1109.A.3.

B. Flow Conditions. Except where indicated elsewhere in this Chapter, the water quality standards specified herein shall apply during all flow conditions greater than the critical flows defined in LAC 33:IX.1115.C. (See LAC 33:IX.1107 and intermittent streams exception category, LAC 33:IX.1109.C.1.)

C. Mixing, Mixing Zone, and Flow Application

1. Mixing zones are those portions of water bodies where effluent waters are dispersed into receiving waters. These are areas where effluents and receiving waters mix and not areas where effluents are treated. Mixing zones are not considered a part of the wastewater treatment process. Mixing must be accomplished as quickly as possible to ensure that the waste is mixed in the smallest practicable area. Outfall structures should be designed to minimize mixing zone size. Mixing zones and fractions of flow apply only to aquatic life criteria. Human health criteria are to be met below the point of discharge after complete mixing.

2. Mixing zones are exempted from general and numeric criteria as specified in LAC 33:IX.1113, except as required in Paragraph C.5 of this Section. The waters outside of mixing zones must meet all the standards for that particular body of water. For toxic substances, this requires meeting chronic aquatic life criteria beginning at the edge of the mixing zone.

3. For aquatic life criteria, small zones of initial dilution will be allowed at each discharge site within a mixing zone. Numeric mixing zones and other receiving water criteria, including both aquatic life acute and chronic water quality criteria, will not apply in these zones of initial dilution. Zones of initial dilution are, however, restricted to the immediate point of discharge and are substantially smaller than the designated mixing zone. They shall not exceed 10 percent of the size of the mixing zone unless conditions specified in Paragraph C.13 of this Section are met. Numeric acute aquatic life criteria apply beginning at the edge of the zone of initial dilution.

4. A mixing zone shall not be allowed to adversely impact a nursery area for aquatic life species, habitat for waterfowl or indigenous wildlife associated with the aquatic environment except as provided in Paragraphs C.2 and 3 of this Section, or any area approved by the state for oyster propagation. Mixing and mixing zones shall not include an existing drinking water supply intake if they would significantly impair the drinking water intake.

5. Mixing zones must be free of the following:
a. floating debris, oil, scum, and other material in concentrations that constitute a nuisance or negatively impact the aesthetics;

b. substances in concentrations which produce undesirable or nuisance aquatic life; and

c. materials in concentrations that will cause acute toxicity to aquatic life. Acute toxicity refers to aquatic life lethality or other deleterious effects caused by the passage through a mixing zone of migrating fish moving up or downstream, or by the passage through a mixing zone of less mobile forms such as zooplankton that drift through the mixing zone. Numeric acute criteria or other acute quantitative limits for toxic substances will be applied in the mixing zone to protect aquatic life from acute toxicity.

6. Applicable limits of mixing zones shall include, but may not be limited to, the linear distances from point source discharges, surface area involvement, and volume of receiving water, and shall take into account other nearby mixing zones. A mixing zone shall not overlap another mixing zone in such a manner, or be so large, as to impair any designated water use in the receiving water body when the water body is considered as a whole.

7. For the application of aquatic life criteria, state water bodies are separated into seven categories as described in Table 2a, and for the application of human health criteria, state water bodies are separated into six categories as described in Table 2b. Mixing zones apply to the implementation of chronic aquatic life criteria, and zones of initial dilution apply to the implementation of acute aquatic life criteria.
a. Chronic aquatic life criteria apply outside the mixing zone, beginning at the edge. The 7Q10 is specified in Table 2a with the intention of limiting 7-day average concentration exceedances to no more than once every 10 years.

b. In perennial, flowing streams (Table 2b, Categories 1 and 2), harmonic mean flow is specified for human health protection against carcinogens, and the 7Q10 is specified for human health protection against non-carcinogens.

c. These specified flows will not be appropriate under some circumstances, and alternative formulations will be required to determine appropriate effluent limitations for equivalent protection of human health and aquatic life uses of the stream. These exceptions may include, but are not limited to, seasonally variable effluent discharge rates, hold and release treatment systems, and effluent dominated sites. The department may approve an alternative which is protective of designated uses, to be determined on a case-by-case basis.

8. For chloride, sulfate, and total dissolved solids, criteria are to be met below the point of discharge after complete mixing. Because criteria are developed over a long-term period, harmonic mean flow will be applied for mixing.

9. Dilution at the edge of the mixing zone and at the edge of the zone of initial dilution for water body categories 5, 6, and 7 (Table 2a) will be determined on a case-by-case basis.

10. Mixing zones shall not preclude the occurrence of continuous water routes of the volume, area, and quality necessary to allow passage of free-swimming and drifting fish and aquatic life with no significant effects on their populations.

11. In those cases, such as wetlands, where unique site-specific conditions or other considerations preclude the application of specific mixing zone requirements, the department may specify definable, geometric limits for mixing zones.

12. In those cases where unique site-specific conditions preclude the application of the flow requirements for Category 2 water bodies as stated in Tables 2a and 2b, the department may on a case-by-case basis approve an alternative flow when determining 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) permitted effluent concentrations. Any flow specifications shall be protective of designated uses.

13. In cases for which a diffuser has been approved or required for use with a wastewater discharge, the department may increase the dilution allowed for the application of acute aquatic life criteria at the edge of the zone of initial dilution. The dilution allowed will be determined by the department after consideration of receiving water body characteristics and diffuser capabilities. No increase in dilution will be allowed at the edge of the mixing zone for the application of chronic aquatic life criteria. Physical constraints of a particular water body may preclude the approval and use of a diffuser. The following conditions must be met with the use of a diffuser:
a. the diffused discharge velocity must be sufficient to provide adequate mixing such that acutely toxic conditions are minimized;

b. the diffused discharge must not adversely impact nursery areas for aquatic life species or indigenous wildlife associated with the aquatic environment except as provided in Paragraphs C.2 and 3 of this Section, propagation areas, zones of passage for aquatic life (see Paragraph C.10 of this Section), wildlife uses, recreational uses, or drinking water supply intakes;

c. the diffused discharge must not cause erosion or scour of the water body banks or bottom;

d. the diffused discharge must be submerged and located in areas with sufficient depth available so that surface water uses of the receiving water are not impaired and the design mixing capabilities of the diffuser are achieved;

e. diffused discharges must not be located in areas where the diffuser may be damaged or impaired by scouring, deposition, or periodic dredging; and

f. diffused discharges must not be located in areas where eddies or whirlpools can cause buildup of effluent concentrations by obstructing or trapping the discharge jet flow.

Table 2a. Water Body Categorization for the Determination of Appropriate Dilution and Mixing Zone Application for Aquatic Life

C A T G

Description

Aquatic Life

Flow

Fraction of Flow or Radial Distance (feet)

ZIDa

MZb

1

Streams with 7Q10 flow greater than 100 cfsc

7Q10

10 cfs or 1/30 of the flow, whichever is greater

100 cfs or 1/3 of the flow, whichever is greater

2

Streams with 7Q10 flow less than or equal to 100 cfs

7Q10

1/10

1

3

Tidal channels with flows greater than 100 cfs

1/3 of the average or typical flow averaged over one tidal cycle irrespective of flow direction

10 cfs or 1/30 of the flow, whichever is greater

100 cfs or 1/3 of the flow, whichever is greater

4

Tidal channels with flows less than or equal to 100 cfs

1/3 of the average or typical flow averaged over one tidal cycle irrespective of flow direction

1/10

1

5

Freshwater lakes and ponds

Not Applicable

25 feet

100 feet

6

Coastal bays and lakes

Not Applicable

50 feet

200 feet

7

Gulf of Mexico

Not Applicable

100 feet

400 feet

aZID = zone of initial dilution

bMZ = mixing zone

ccfs = cubic feet per second

Table 2b. Water Body Categorization for the Determination of Flow for Human Health

C A T G

Description

Human Health

Flow

Noncarcinogens

Carcinogens

1

Streams with 7Q10 flow greater than 100 cfs

7Q10

Harmonic Mean

2

Streams with 7Q10 flow less than or equal to 100 cfs

7Q10

Harmonic Mean

3

Tidal channel

The average or typical flow averaged over one tidal cycle irrespective of flow direction

4

Freshwater lakes and ponds

Not Applicable

Not Applicable

5

Coastal bays and lakes

Not Applicable

Not Applicable

6

Gulf of Mexico

Not Applicable

Not Applicable

AUTHORITY NOTE: Promulgated in accordance with R.S. 30:2074(B)(1).

Disclaimer: These regulations may not be the most recent version. Louisiana may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.