Calculating Water Quality-based Effluent Limits

Calculating Water Quality-based Effluent Limits

Water Quality-Based Effluent Limits WQBELs Dex D. Dean, P.E. October 13, 2016 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. Questions we will explore

1. What factors influence water quality-based permit limits? 2. What should I do if there is a new limit in my draft permit? 3. How do I know whether a new limit is correct? What factors influence water

quality-based permit limits? 1. Numerical criteria (toxic pollutants) 2. Water body quality 3. Effluent fraction (mixing) Texas has numerical criteria for aquatic life and human health protection. Found in 30 TAC Chapter 307 Texas Surface Water Quality Standards Table 1 aquatic life

Table 2 human health Numerical criteria can change over time. Criteria revisited every three years Pollutant Aldrin Freshwater, acute Hexachloroethane Human health, water & fish

Benzo(a)anthra cene Human health, fish 2010 Criteria 2014 Criteria % Change 3.0 g/Lg/L 3.0 g/Lg/L No

change 4.97 g/Lg/ L -82 % 0.33 g/Lg/ 3.28 g/Lg/ L L 994 % 27 g/Lg/L Criteria for aquatic life reflect an

organisms environment and exposure. Table 1 in the Standards Freshwater acute chronic Saltwater acute chronic Note: Acute toxicity exposures of 4 days. Chronic toxicity exposures of

7 days. Not all of the numerical criteria are expressed in the same way. Most criteria are for total concentrations. Some metals criteria are for dissolved But wait! concentrations: Permit limits aluminum are written for arsenic total cadmium concentrations chromium (tri and hex)

. copper lead nickel silver (free ion) zinc 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. Criteria for pentachlorophenol are affected by pH. Pentachlorophenol is more toxic at lower pH values. = (1.005 ( ) 4.869) (1.005 ( ) 5.134) h = Some freshwater criteria depend on

the hardness of the receiving water. These include: cadmium chromium (trivalent) copper lead nickel zinc Example: copper =0.960 (0.9422 ( ln ( h ) ) 1.6448) (0.8545 (ln ( h ) ) 1.6463)

h =0.960 Metals affected by hardness are more toxic in soft water. Freshwater criteria are lower at smaller hardness values. Example: copper Segmen t Number 0505 1412 Water Body Name Sabine River Above

Toledo Bend Reservoir Colorado River Below Lake J. B. Thomas Hardness (mg/L of CaCO3) Chroni Acute c Criterio Criterio n n (g/L)

(g/L) 42 6.27 4.51 310 41.2 24.8 Human health criteria reflect exposure routes and vulnerability.

Table 2 (2014) Water and Fish Fish Only Water column based criteria Note: Human health criteria based on Childhood exposure (non-carcinogens) Lifetime exposure (carcinogens). 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 Water quality data for each classified segment is provided in RG-194(1). Statistically-derived values include: TSS 15th percentile

pH 15th percentile Total hardness 15th percentile Chloride 50th percentile (1) RG-194: Procedures to Implement the Texas Surface Water Quality Standards (IPs), TCEQ, June 2010. 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.

Effluent fractions help convert numerical criteria into limits. Numerical criteria apply at the edge of each zone: Name of Zone Zone of Initial Dilution Aquatic Life Mixing Zone Human Health Mixing Zone Acronym ZID MZ

HHMZ Applicable Criteria Acute Aquatic Life Chronic Aquatic Life Human Health 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) Resulting effluent fractions depend on the type of water body. Zone of Initial Dilution (Acute) Mixing Zone (Chronic) Human

Health Mixing Zone Lake 60 % effluent 15 % effluent 8% effluent Wide tidal

30 % effluent 8% effluent 4% effluent 100 % effluent 100 % effluent 100 %

effluent Water Body Stream Least simple Intermitt ent Most simple 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 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 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. Bioavailable Fraction

The bioavailable fraction equals: Cd CT where: Cd = dissolved concentration CT = total concentration This fraction depends on TSS : 1 = 1+( 10 6 ) Bioavailable

Fraction The term KP, the partition coefficient, also depends on TSS: =10 where b and m are values found in Table 6 in the 2010 IP (p. 160). Putting All the Pieces Together Numerical Criteria Effluent Fraction Water Body Quality

Bioavailable Fraction Putting All the Pieces Together Three 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) 1. Calculate the concentration allowed at mixing zone edge (WLA). WLAs consider bioavailability

and dilution are calculated for both acute and chronic aquatic life protection: 2. Calculate an average concentration (LTA) that will meet the WLA. LTAs account for end-of-pipe effluent variability. Calculate LTAs for both acute (24-hour) and chronic (7-day) aquatic life protection. Coefficients depend on the type of water body: Streams, rivers:

3. Calculate permit limits considering the time a sample represents. Compare acute and chronic LTAs Use the smaller LTA to calculate daily average (30-day) and daily maximum (24-hour) permit limits based on aquatic life criteria: =1.47 =3.11 For human health, the LTA is based on an annual average concentration.

Calculate WLA for human health protection: Calculate LTA for human health protection: h=0. 930 h Convert the human health LTA to permit limits (as with aquatic life). Calculate daily average (30-day) and daily maximum (24 hour) permit limits based on human health criteria: =1.47

=3.11 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 Help! My draft permit includes a new or more stringent WQBEL what can I do? Call your permit writer! Why did I get this limit? Big Picture: New limit Average concentration from application is 85% of calculated daily average WQBEL

More stringent limit Calculated WQBELs are more stringent than existing limits Its time to get down in the weeds: numerical criteria, water body quality, effluent fraction, Double-check mixing assumptions. For a river or stream: Critical flows Stream type which criteria apply? intermittent acute (no

dilution) perennial chronic, acute, HH intermittent with perennial pools chronic (no dilution), acute (no dilution), Consider moving your outfall. Effluent fraction lake or bay: Critical mixing conditions Relocate outfall narrow arm smaller mixing zones = larger effluent fractions = lower permit limits

wider area larger mixing zones = smaller effluent fractions = higher permit limits Consider developing a sitespecific standard. Numerical Criteria: Site-specific standards change all of your limits adopted in Appendix E of the Standards Temporary variance allows time for permittee to develop comprehensive information to support site-specific standard. Permittee must request a variance Permit must show that existing standard may not be appropriate

Permittee must provide public notice of Consider developing a sitespecific standard. Numerical Criteria: Site-specific standard (cont.) Temporary variance (cont.) Must be approved by EPA Three-year permit term Permit language requires a study Variance may be extended Coordinate with TCEQ staff For metals: is the TCEQs water effect ratio reasonable? (except mercury or selenium)

Numerical criteria: Site-specific water-effect ratio (WER) Use whole effluent toxicity testing to account for difference in toxicity in receiving water. This is w or m factor in Table 1 of Standards Saltwater: ~2; freshwater: ~3.58.5 Streamlined procedure for copper (freshwater) For metals: is the TCEQs hardness data representative? Numerical criteria, water body quality Site-specific hardness: affects criteria for

cadmium, trivalent chromium, copper, lead, nickel, and zinc 30 samples from receiving water upstream of discharge and outside of MZ 1 week between successive samples Coordinate study design with TCEQ staff For metals: does local TSS give a different bioavailable fraction? Water body quality, bioavailable fraction Site-specific TSS: affects bioavailable fraction

30 samples from receiving water upstream of discharge and outside of MZ 1 week between successive samples Coordinate study design with TCEQ staff For metals: does local TSS give a different bioavailable fraction? Bioavailable fraction Site-specific ratio of dissolved to total metal concentration 30 samples from receiving water upstream

of discharge and outside of MZ 1 week between successive samples Mix samples with effluent to equal critical dilution If no water upstream, critical dilution is 100% effluent For metals: does local TSS give a different bioavailable fraction? Bioavailable fraction Site-specific ratio of dissolved to total metal concentration (cont.) Measure total and dissolved metal

concentrations Measure TSS of receiving water and effluent each time a sample is collected and mixed with effluent (unless critical dilution is 100%) Coordinate study design with TCEQ staff QUESTIONS Water Quality-Based Effluent Limits Dex D. Dean, P.E. October 13, 2016

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