1. Water Quality-Based Effluent Limits
WQBELs
Erika Crespo
May 2017

2. Permit limits apply to discharges
Permit limits apply to discharges. Water quality criteria apply to water bodies.
In other words, criteria in the Texas Surface Water Quality Standards do not apply directly to a discharge.
Note: Stay tuned for an important exception.
The TCEQ is responsible for maintaining and enhancing water quality is the state.
The Texas Surface Water Quality Standards are the legal standards for the quality of surface water in Texas, and they are described in Title 30 of the Texas Administrative Code (TAC) Chapter 307.
TCEQ will apply these standards when issuing permits for wastewater discharges or other authorized discharges to the surface waters of the state.
The water quality criteria in the Texas Surface Water Quality Standards apply to waterbodies and do not directly apply to a wastewater discharge.
However, there is an exception that will be discusses later.

3. Questions we will explore…
What factors influence water quality-based permit limits?
What should I do if there is a new water quality-based limit in my draft permit?
How do I know whether a new water quality-based limit is correct?
Read slide

4. What factors influence water quality-based permit limits?
Numerical criteria (toxic pollutants)
Water body quality
Effluent fraction (mixing)
Bioavailable fraction
WQBELs – A Four-Piece Puzzle
Numerical criteria for toxic pollutants
The water quality in the receiving water body
Effluent fraction associated with mixing
Bioavailable fraction associated with aquatic life

5. Texas has numerical criteria for aquatic life and human health protection.
◊ Found in Texas Surface Water Quality Standards
(30 TAC Chapter 307 Section 6 – Toxic Materials)
The first puzzle piece that we will be discussing today is the purple one, which represents numerical criteria for toxic pollutants.
Texas has numerical criteria for toxic pollutants so that aquatic life and human health are protected.
These numerical criteria can be found in the Texas Surface Water Quality Standards (30 TAC Chapter 307 Section 6 – Toxic Materials)
Table 1 – aquatic life criteria…. represented in the table on the slide
Table 2 – human health criteria

6. Numerical criteria for toxic materials can change over time.
◊ Criteria revisited every three years
Pollutant
2010 Criteria
2014 Criteria
% Change
Aldrin Freshwater, acute
3.0 μg/L
No change
Hexachloroethane Human health, water & fish
27 μg/L
4.97 μg/L
-82 %
Benzo(a)anthracene Human health, fish only
0.33 μg/L
3.28 μg/L
994 %
Numerical criteria is revisited every three years.
The criteria for Aldrin did not change during the most recent revision.
The criteria for Hexachloroethane became more stringent by 82% in the most recent revision.
The criteria for Benzo(a)anthracene became more relaxed by 994% in the most recent revision.

7. Numerical criteria for aquatic life reflect an organism’s environment and exposure.
Table 1. Criteria in Water for Specific Toxic Materials
Aquatic Life Protection
Table 1 is divided up based on freshwater or saltwater environments and based on acute or chronic exposure.
When it comes to ACUTE toxicity, we are dealing with exposures of ≤ 4 days.
(Acute toxicity deals with lethality – things will die.)
When it comes to CHRONIC toxicity, we are dealing with exposures of ≥ 7 days.
(Chronic toxicity deals with growth and reproduction – life survives, but do they thrive?)
(d) – Indicates that the criteria for a particular parameter are for the dissolved portion in water.
The absence of the (d) means that the criteria are for the total recoverable concentration.
w – Indicates that a criterion may be multiplied by a water-effect ratio (WER) in order to incorporate the effects of local water chemistry on toxicity.
The WER is equal to 1 except where sufficient data is available to establish a site-specific WER.
WERs for individual water bodies are listed in Appendix E when standards are revised.
The number preceeding the w in the freshwater criterion equation is an EPA conversion factor.
A site-specific WER that affects an effluent limitation in a wastewater discharge permit, and that has not been incorporated into Appendix E of § must be
noted in a public notice during the permit application process. An opportunity for public comment must be provided, and the WER may be considered in any
public hearing on the permit application.
e – the mathematical constant that is the base of the natural logarithm ≈

8. Not all of the numerical criteria are expressed in the same way.
◊ Most criteria are for total concentrations.
◊ Some metals criteria are for dissolved concentrations:
• aluminum
• arsenic
• cadmium
• chromium (tri and hex)
• copper
• lead
• nickel
• silver (free ion)
• zinc
But wait!
Permit limits are written for total concentrations.
These metals can be identified by the (d) denotation in the table.
READ THE QUOTE: “But wait! Permit limits are written for total concentrations.”
GO TO NEXT SLIDE.

9. 𝑪𝒅 𝑪𝑻 = 1 1+(𝐾𝑝 × 𝑻𝑺𝑺 × 10−6) 𝐾𝑝=10𝑏 × 𝑻𝑺𝑺 𝑚
Metals criteria may be expressed as a dissolved concentration because local water quality affects toxicity.
◊ Conversion from dissolved criteria
to total limits uses ambient total
suspended solids (TSS) of the nearest downstream classified segment.
◊ Hint:
Dissolved fraction = bioavailable fraction.
𝑪𝒅 𝑪𝑻 = 1 1+(𝐾𝑝 × 𝑻𝑺𝑺 × 10−6) 𝐾𝑝=10𝑏 × 𝑻𝑺𝑺 𝑚
For most metals, which the exception of mercury and selenium, the water quality criteria for aquatic life protection are expressed as dissolved concentrations.
The dissolved concentration of a metal is the bioavailable fraction of the total metal concentration.
The ratio of the dissolved concentration to the total recoverable concentration is expressed in terms of the partition coefficient (Kp) and TSS concentrations.
This topic will be further discussed when we get to the bioavailability fraction portion of this presentation (the red puzzle piece).
However, we are starting to incorporate more than just numerical criteria into our discussion… we are now involving water body quality into the mix, which is represented by the blue puzzle piece.

10. Criteria for pentachlorophenol
are affected by pH.
𝐴𝑐𝑢𝑡𝑒 𝑐𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛= 𝑒 (1.005 𝒑𝑯 −4.869)
𝐶ℎ𝑟𝑜𝑛𝑖𝑐 𝑐𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛= 𝑒 (1.005 𝒑𝑯 −5.134)
◊ Pentachlorophenol is more toxic at lower pH values.
For an example on how water body quality (the blue puzzle piece) affects the numerical criteria of toxic pollutants (the purple puzzle piece), we can look at the example of pentachlorophenol.
The toxicity of pentachlorophenol is affected by pH.
Looking at the formulas used to calculate the numeric criteria for pentachlorophenol, it is more toxic in water that has a low pH (i.e. more acidic water).
Therefore, permit limits for pentachlorophenol are more stringent for facilities whose receiving waters have low pH.
The formulas listed on the slide are the freshwater acute and freshwater chronic criteria for pentachlorophenol, and they can be found in Table 1 of the TSWQS.
e – the mathematical constant that is the base of the natural logarithm ≈
For pH of 3: For pH of 6:
Acute criterion = Acute criterion = 3.19
Chronic criterion = Chronic criterion = 2.45

11. Some freshwater criteria depend on the hardness of the receiving water.
◊ These include:
• cadmium
• chromium (trivalent)
• copper
• lead
• nickel
• zinc
Another example of water body quality impacting numerical criteria can be seen in case of total hardness.
In general, most metals are more toxic in water that has low hardness values (soft water).
Therefore, water quality criteria are more stringent for receiving waters that have low hardness values.
The TCEQ uses the 15th percentile of basin or segment hardness data (ranked from lowest highest value) to calculate hardness-dependent criteria.
Copper is an example of a toxic metal that is affected by hardness.
m – Indicates that a criterion may be multiplied by a water-effect ratio (WER) or a biotic ligand model result in order to incorporate the effects of local water chemistry on toxicity.
The multiplier is equal to 1 except where sufficient data is available to establish a site-specific multiplier.
Multipliers for individual water bodies are listed in Appendix E when standards are revised.
The number preceding the “m” in the freshwater equation is an EPA conversion factor.
e – The mathematical constant that is the basis of the natural logarithm… ≈
Example: copper
𝐴𝑐𝑢𝑡𝑒 𝑐𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛= 𝑚𝑒 ( ln ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠 −1.6448)
𝐶ℎ𝑟𝑜𝑛𝑖𝑐 𝑐𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛= 𝑚𝑒 ( ln ℎ𝑎𝑟𝑑𝑛𝑒𝑠𝑠 −1.6463)

12. Acute Criterion (µg/L) Chronic Criterion (µg/L)
Metals affected by hardness
are more toxic in soft water.
◊ Freshwater criteria are
lower at smaller hardness values.
Example: copper
Segment Number
Water Body Name
Hardness
(mg/L of CaCO3)
Acute Criterion (µg/L)
Chronic Criterion (µg/L)
0505
Sabine River Above Toledo Bend Reservoir 42
6.27
4.51
1412
Colorado River Below Lake J. B. Thomas
310
41.2
24.8
Again, looking at Copper, which is an example of a metal that is affected by hardness.
Copper is more toxic in receiving waters that have low hardness values.
INVERSE RELATIONSHIP:
Lower hardness values – Higher toxicity – Lower criteria values
Higher hardness values – Lower toxicity – Higher criteria values

13. Human health criteria reflect exposure routes and vulnerability.
Table 2. Criteria in Water for Specific Toxic Materials
Human Health Protection
Water and Fish Concentration Criteria (column A) – these values prevent contamination of drinking water and fish/aquatic life to ensure that they are safe for human consumption. These criteria apply to surface waters that are designated or used for public drinking water supplies.
Fish Only Concentration Criteria (column B) – these values prevent contamination of fish and other aquatic life to ensure that they are safe for human consumption. These criteria apply to surface waters that have sustainable fisheries and that are not designated or used for public water supply or as a sole-source surface drinking water supply.
Waters that are not considered to have a sustainable fishery, but are classified as having either limited/intermediate/high aquatic life use, are considered to be an “incidental fishery”.
Consumption rates assumed for incidental fishery waters are 1.75 grams per person per day.
The numerical criteria applicable to incidental fishery waters are ten times the criteria listed in Column B.
[Fish consumption rates in incidental fisheries (1.75 grams/person/day) are assumed to be ten times lower than fish consumption rates in sustainable fisheries (17.5 grams/person/day).]

14. Local water quality may affect pollutant criteria or bioavailability.
◊ TSS – used to calculate the bioavailable fraction of metals
◊ pH – used to calculate the freshwater aquatic life criteria for pentachlorophenol
◊ Total hardness – used to calculate the freshwater aquatic life criteria for most metals
◊ Chloride – used to calculate the bioavailable fraction of silver in freshwater
So to recap – TSS concentrations affect the bioavailability of metals, pH affects the toxicity of pentachlorophenol, and total hardness concentrations will influence the freshwater aquatic life criteria.
Additionally, chloride concentrations impact the bioavailability of free ions of silver.

15. Water Body Quality
Critical values for water quality parameters for each classified segment are found in Procedures to Implement the Texas Surface Water Quality Standards (IPs), June 2010, Appendix D.
◊ Total suspended solids (TSS)
◊ pH
◊ Total hardness
◊ Total dissolved solids (TDS)
◊ Chloride
◊ Sulfate
The Procedures to Implement the Texas Surface Water Quality Standards, or what we refer to as the IPs, explain the procedures that the TCEQ uses when applying the Texas Surface Water Quality Stands to permits that are issued under the TPDES (Texas Pollution Discharge Elimination System) program.
Appendix D of the IPs lists the critical values for TSS, pH, total hardness, TDS, chloride, and sulfate.

16. Water Body Quality
Statistically-derived critical values are as follows (1) :
◊ TSS – 15th percentile
◊ pH – 15th percentile
◊ Total hardness – 15th percentile
◊ TDS – 50th percentile
◊ Chloride – 50th percentile
◊ Sulfate – 50th percentile
(1) Procedures to Implement the Texas Surface Water Quality Standards
(IPs), TCEQ, June 2010, Appendix D.
The segment values used for TSS, pH, total hardness, TDS, chloride, and sulfate are statistically-derived values.
TSS, pH, and total hardness are 15th percentile values.
TDS, chloride, and sulfate are 50th percentile values.
These values are based on ambient water quality data, and they are considered to be critical conditions.
Basin values are used when there is insufficient segment data available.

17. RECALL: Permit limits apply to discharges
RECALL: Permit limits apply to discharges. Water quality criteria apply to water bodies.
In other words, criteria in the Texas Surface Water Quality Standards do not apply directly to a discharge.
Note: Stay tuned for an important exception.
Now remember, permit limits apply to discharges while water quality criteria apply to water bodies… Therefore, the Texas Surface Water Quality Standards do not apply directly to a discharge… We will discuss an important discussion later.

18. Effluent fractions help convert numerical criteria into limits.
Numerical criteria apply at the edge of each zone:
Effluent fractions, or the amounts of the wastewater relative to the amount of receiving water, are important to converting numerical criteria into actual permit limitations.
Numerical criteria apply at the edge of each zone, and there are three zones associated with wastewater discharges.
Zone of Initial Dilution (ZID) - Acute Aquatic Life criteria apply at the edge
Aquatic Life Mixing Zone (MZ) - Chronic Aquatic Life criteria apply at the edge
Human Health Mixing Zone (HHMZ) - Human Health criteria apply at the edge
(The distances from the point of discharges depend on the type of receiving water body that the discharge is going into…. Diagram in slide is of a wide tidal river)
Effluent fraction at the edge of the mixing zone, when expressed as a percentage, is also referred to as the critical dilution, and it is used as the primary concentration for whole effluent toxicity testing.
Mixing zone size and shape may be varied in individual permits to account for differences in:
Stream flow
Bay, estuary, and reservoir morphometry
Effluent flow
Stream geometry
Ecological sensitivity at the discharge site
Zone of passage concerns
Discharge structures
Zones of Initial Discharge are specified for different receiving water types in TSWQS and are not usually specified in individual permits.
Complete mixing of effluent and receiving waters is assumed at mixing zone boundaries, unless available information shows otherwise.
Note:
The larger the percentage of effluent, with lesser dilution occurring, the more stringent the effluent limits.

19. Texas assumes critical low flow or low mixing conditions.
Expressed as:
◊ Critical effluent percentages
(lakes, bays, estuaries, wide tidal rivers) or
◊ Critical flows
(streams, rivers, narrow tidal rivers)
Our permits are written to account for critical low flow conditions or critical low mixing conditions.
The critical-condition concept is that if an effluent is controlled such that it does not cause water quality criteria to be exceeded in the receiving water at the critical flow condition, then the effluent controls will likely be protective (i.e., ensuring that water quality criteria are attained at all flows).
The critical conditions memo from the Water Quality Assessment Team contains either critical effluent percentages or critical flows, depending on the receiving water body.
Lakes, bays, estuaries, and wide tidal rivers – critical effluent percentages
Streams, rivers, and narrow tidal rivers – critical flow conditions

20. Zone of Initial Dilution Human Health Mixing Zone
Resulting effluent fractions
depend on the type of water body.
Water Body
Zone of Initial Dilution
(Acute)
Mixing Zone
(Chronic)
Human Health Mixing Zone
Stream
Least simple
𝑄 𝐸 𝑄 𝐸 +0.25(7𝑄2)
𝑄 𝐸 𝑄 𝐸 +7𝑄2
𝑄 𝐸 𝑄 𝐸 +𝐻𝑀
Lake
60 % effluent
15 %
effluent
8 %
Wide tidal
30 % effluent
4 %
Intermittent
Most simple
100 % effluent
The effluent fraction is determined by the type of water body and the type of mixing zone.
Qe = effluent flow
7Q2 = seven-day, two-year low-flow
HM = harmonic mean flow
For streams, a mass-balance between the effluent and the receiving water is used to determine the size of the mixing zones for the ZID, MZ, and HHMZ.
Lake mixing is based on a ZID of 25 feet (60% effluent), MZ of 100 feet (15%), and HHMZ of 200 feet (8%).
Wide Tidal River mixing is based on a ZID of 50 feet (30% effluent), MZ of 200 feet (8%), and HHMZ of 400 feet (4%).
Intermittent streams use the simplest model. With no dilution available in the stream, discharges are evaluated at 100% effluent (i.e. no mixing zone).
The information in the chart can be found in the IPs.

21. Effluent Fraction – Streams and Rivers
QE = Effluent flow
Aquatic life
• Domestic – final average permitted flow
• Industrial
◦ new or amendment to increase flow – permitted
average flow requested
◦ renewal - highest daily average flow reported in last
two years
In order to calculate the effluent fraction, the effluent flow must be provided.
When considering aquatic life protection, effluent flows that need to be provided are:
Domestic – either the final permitted daily average flow or annual average flow
Industrial:
NEW or AMENDMENT (to increase flow): The permitted average flow requested
RENEWAL: The highest daily average flow reported in the last two years

22. Effluent Fraction – Streams and Rivers
QE = Effluent flow
Human health
• Domestic – final average permitted flow
• Industrial
◦ new or amendment to increase flow – permitted
average flow requested
◦ renewal - average of the daily average flows reported in the last two years
When considering human health protection, effluent flows that need to be provided to calculate the effluent fraction are:
Domestic – either the final permitted daily average flow or annual average flow
Industrial:
NEW or AMENDMENTS (to increase flow): The permitted average flow requested
RENEWALS: The average of the daily average flows reported in the last two years

23. Most metals are not entirely bioavailable. Conversion is required.
For most metals, numerical criteria for aquatic life are dissolved concentrations, but…
Effluent limits are expressed as total concentrations.
The bioavailable fraction, which is a function of TSS, is used to make this translation.
The numerical criterial for the following toxic metals apply to dissolved concentrations:
Aluminum
Arsenic
Cadmium
Chromium
Copper
Lead
Nickel
Silver
Zinc
The saltwater and freshwater metal criteria listed in Table 1 of the TSWQS were derived by multiplying the current standard by the appropriate listed conversion factor to obtain a percent dissolved standard.
The bioavailable fraction is the fraction of the pollutant that is available to organisms, and TSS concentrations have an impact on this value.

24. Bioavailable Fraction
The bioavailable fraction equals:
where:
Cd = dissolved concentration
CT = total concentration
This fraction depends on TSS :
𝐶 𝑑 𝐶 𝑇
The bioavailable fraction is equal to the dissolved concentration divided by the total concentration.
It depends on TSS.
Cd – dissolved metal concentration
CT – total metal concentration
Kp – partition coefficient (L/kg)
TSS – total suspended solids (mg/L)… The TCEQ uses the 15th percentile of basin or segment pH data (ranked from lowest to highest value).
𝐶 𝑑 𝐶 𝑇 = 1 1+( 𝐾 𝑝 ×𝑇𝑆𝑆 × 10 −6 )

25. Bioavailable Fraction
𝐶 𝑑 𝐶 𝑇 = 1 1+( 𝐾 𝑝 ×𝑇𝑆𝑆 × 10 −6 )
The term KP, the partition coefficient, also depends on TSS:
where “b” and “m” are values found in Table 6 in the 2010 IP (p. 160).
𝐾 𝑝 = 10 𝑏 × 𝑇𝑆𝑆 𝑚
Because effluent limits are expressed as total concentrations, TCEQ staff has to use partition coefficients in order to determine instream compliance with the numerical standards for dissolved concentrations.
The use of partition coefficients determines how much metal is dissolved in the receiving water.
Kp – partition coefficient (L/kg)
TSS – total suspended solids (mg/L)… The TCEQ uses the 15th percentile of basin or segment pH data (ranked from lowest to highest value).
m and b – slope and intercept values taken from Table 6 in the Texas Surface Water Quality Standards.
The partion coefficient is also dependent on TSS.

26. Putting All the Pieces Together
Water Body Quality
Numerical Criteria
Effluent Fraction
Bioavailable Fraction

27. Putting All the Pieces Together
Four easy steps to calculate WQBELs for aquatic life and human health!
◊ Calculate waste load allocation – WLA
◊ Calculate long-term average – LTA
◊ Calculate effluent limits:
• daily average (DLY AVG)
• daily maximum (DLY MAX)
◊ Compare WQBELs for aquatic life and human health
There are three steps in calculating water quality based effluent limits for both aquatic life and human health:
Calculate waste load allocations
Calculate long-term average
Calculate effluent daily average and daily max effluent limits
Compare the WQBELs for aquatic life and human health
TEXTOX, a set of spreadsheets, does these calculations for us.

28. Numerical criteria apply at the edge of each zone:
RECALL THIS SLIDE…
The waste load allocations that are calculated for the protection of aquatic life and human health will apply at the edges of these zones.
Zone of Initial Dilution (ZID) - Acute Aquatic Life criteria apply at the outer edge
Aquatic Life Mixing Zone (MZ) - Chronic Aquatic Life criteria apply at the outer edge
Human Health Mixing Zone (HHMZ) - Human Health criteria apply at the outer edge

29. Calculate the effluent concentrations
Aquatic Life
Calculate the effluent concentrations
at the edge of the mixing zones (WLAs).
Waste Load Allocations (WLAs) consider bioavailability and dilution.
Let’s start by discussing aquatic life protection..…
The first step in developing effluent limits based on water quality criteria for aquatic life protection is to calculate the Waste Load Allocations.
Waste load allocations (WLAs) equal the effluent concentrations that will not cause the overall instream criteria to be exceeded.
WLAs factor in both bioavailability of the pollutants and the dilution that occurs in the receiving water body.
WLAa – based on the acute criterion – calculated for concentrations outside of the zone of initial dilution
WLAc – based on the chronic criterion – calculated for concentrations outside of the aquatic life mixing zone
Break-down of formulas:
Acute/Chronic Criterion – falls under the Numerical Criteria sub-piece (discussed during the first part of the presentation – purple puzzle piece)
Bioavailable Fraction – represents the fraction of the pollutant that is available to organisms (discussed earlier – red puzzle piece)
Effluent Fraction – accounts for the effluent mixing and diluting in the receiving water body before the edge of the mixing zones (a discussed earlier - green puzzle piece section)
Acute criterion for aquatic life – dealing with exposures of ≤ 4 days (focusing on lethality – things will die)
Chronic criterion for aquatic life – dealing with exposures of ≥ 7 days (focusing on growth and reproduction – things survive, but will they thrive?)
𝑊𝐿𝐴 𝑎 = 𝐴𝑐𝑢𝑡𝑒 𝐶𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛 𝐵𝑖𝑜𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 ×(𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛, 𝑍𝐼𝐷)
𝑊𝐿𝐴 𝑐 = 𝐶ℎ𝑟𝑜𝑛𝑖𝑐 𝐶𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛 𝐵𝑖𝑜𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 ×(𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛, 𝑀𝑍)

30. 2. Calculate the Long-Term Average (LTA) concentration.
Aquatic Life
2. Calculate the Long-Term Average
(LTA) concentration.
LTAs account for end-of-pipe effluent variability.
Coefficients depend on the type of water body:
◊ Streams, rivers: 𝐿𝑇𝐴 𝑎 =0.573 ×𝑊𝐿𝐴 𝑎
𝐿𝑇𝐴 𝑐 =0.770× 𝑊𝐿𝐴 𝑐
◊ Lakes, bays: 𝐿𝑇𝐴 𝑎 =0.3 2×𝑊𝐿𝐴 𝑎
𝐿𝑇𝐴 𝑐 =0.61 ×𝑊𝐿𝐴 𝑐
Second step, calculate the Long Term Average of the treatment system performance that is necessary to meet the respective WLA with a given probability.
Long Term Averages (LTAs) account for end-of-pipe effluent variability, and the coefficients in the equations depend on the type of receiving water body.
LTAa – associated with acute criteria – 24-hour averaging period
LTAc – associated with chronic criteria – 7-day averaging period
Streams/Rivers – both the LTA acute and LTA chronic have a 90% probability associated with them
Lakes/Bays – both the LTA acute and LTA chronic have a 99% probability associated with them
Full derivations of these equations are provided in the IPs.

31. 𝐷𝐿𝑌 𝐴𝑉𝐺=1.47×𝐿𝑇𝐴 𝐷𝐿𝑌 𝑀𝐴𝑋=3.11×𝐿𝑇𝐴
Aquatic Life
3. Calculate permit limits considering
the time a sample represents.
◊ Compare acute and chronic LTAs
◊ Use the smaller LTA to calculate
daily average and daily maximum permit
limits based on aquatic life criteria:
The final step in calculating WQBELs for aquatic life protection is to calculate the daily average and daily maximum permit limits.
After comparing the acute and chronic LTAs, the smaller LTA is used in the equation on the slide to calculate the permit limit.
Daily Average – for a 30-day monitoring period
Daily Maximum – for a 24-hour monitoring period
The IPs contains the derivations of these equations also.
𝐷𝐿𝑌 𝐴𝑉𝐺=1.47×𝐿𝑇𝐴
𝐷𝐿𝑌 𝑀𝐴𝑋=3.11×𝐿𝑇𝐴

32. Calculate the effluent concentration
Human Health
Calculate the effluent concentration
allowed at edge of the Human Health
Mixing Zone (WLA).
Waste Load Allocations (WLAs) consider bioavailability and dilution.
The first step in calculating effluent limits based on water quality criteria for human health protection is to calculate waste load allocations, which represent the effluent concentrations that will not exceed the instream criteria outside the human health mixing zone.
WLAs for human health protection also factor in both the bioavailability of the pollutants and the dilution that occurs in the receiving water body.
Break-down of formulas:
Human Health Criterion – the appropriate value, which falls under the Numerical Criteria sub-piece (discussed during the first part of the presentation – purple puzzle piece)
Bioavailable Fraction – represents the fraction of the pollutant that is available to organisms (discussed earlier – red puzzle piece)
Effluent fraction – accounts for the effluent mixing and diluting in the receiving water body prior to the edge of the Human Health Mixing Zone
(discussed earlier - green puzzle piece section)
𝑊𝐿𝐴 ℎ = 𝐻𝑢𝑚𝑎𝑛 𝐻𝑒𝑎𝑙𝑡ℎ 𝐶𝑟𝑖𝑡𝑒𝑟𝑖𝑜𝑛 𝐵𝑖𝑜𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 ×(𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛, 𝐻𝐻𝑀𝑍)

33. 2. Calculate the Long-Term Average (LTA) concentration.
Human Health
2. Calculate the Long-Term Average
(LTA) concentration.
LTAs account for end-of-pipe effluent variability.
Coefficients depend on the type of water body:
Second step, calculate the Long Term Average of the treatment system performance that is necessary to meet the respective WLA with a given probability.
Long Term Averages (LTAs) account for end-of-pipe effluent variability, and the coefficients in the equations depend on the type of receiving water body.
LTAh is considered to be an annual average, with an averaging period of 365 days.
𝐿𝑇𝐴 ℎ =0. 930×𝑊𝐿𝐴 ℎ

34. 𝐷𝐿𝑌 𝐴𝑉𝐺=1.47×𝐿𝑇𝐴 𝐷𝐿𝑌 𝑀𝐴𝑋=3.11×𝐿𝑇𝐴
Human Health
3. Calculate permit limits considering
the time a sample represents.
◊ Compare acute and chronic LTAs
◊ Use the smaller LTA to calculate
daily average and daily maximum permit
limits based on human health criteria:
The final step in calculating WQBELs for aquatic life protection is to calculate the daily average and daily maximum permit limits.
After comparing the acute and chronic LTAs, the smaller LTA is used in the equation on the slide to calculate the permit limit.
Daily Average – for a 30-day monitoring period
Daily Maximum – for a 24-hour monitoring period
These daily average and daily maximum concentrations are calculated at 99% probability using the same process that was used for aquatic life calculations.
The derivations for these equations can also be found in the IPs.
𝐷𝐿𝑌 𝐴𝑉𝐺=1.47×𝐿𝑇𝐴
𝐷𝐿𝑌 𝑀𝐴𝑋=3.11×𝐿𝑇𝐴

35. Compare Aquatic Life and Human Health Limits
FINAL STEP –
Compare Aquatic Life and Human Health Limits
Some pollutants have both aquatic life and human health criteria.
◊ Compare limits based on aquatic life with limits based on human health
◊ The lower limit goes in the permit
If a pollutant has both numerical criteria for both the protection of aquatic life and human health, the daily average and daily maximum limits for both are compared against each other. The most protective limits will be included in the permit.

36. Call your permit writer!
Help!
My draft permit includes a new or more stringent WQBEL – what can I do?
Call your permit writer!
Read slide

37. Why did I get this limit? Get down in the weeds: New limit
Outfall location
Need site-specific numerical standard
More stringent limit
Need to use site-specific water quality data
Mixing assumptions
Get down in the weeds:
New limit
Average concentration from application is
≥ 85% of calculated daily average WQBEL
More stringent limit
Calculated WQBELs are more stringent than existing limits
Mixing Assumptions
Critical flows for rivers or streams – 7Q2/harmonic mean/stream gauge data (lower flow -> less dilution -> more stringent effluent limits)
Which stream type is assumed (intermittent/perennial/intermittent with perennial pools) & which numeric criteria apply (acute/chronic/human health)
Consider moving outfall location if there are issues with the effluent fractions associated with discharges to lakes or bay – must coordinate with TCEQ
Consider developing a site-specific standard for your discharge, which requires coordination with the TCEQ to conduct a Water Effects Ratio (WER)
Consider using site-specific water quality data (e.g. Hardness affects the numeric criteria of certain metals / TSS affects the bioavailable fraction of toxic metals) – must coordinate with TCEQ to conduct study
numerical criteria,
water body quality
effluent fraction
bioavailable fraction

38. Water Quality-Based Effluent Limits
QUESTIONS
Water Quality-Based Effluent Limits
Erika Crespo
May 2017