### MEMORANDUM

TO: Bill Swietlik , EPA

FROM: Jill Lucy , ERG

DATE: September 21, 2015

SUBJECT: Review of Toxic Weighting Factors in Support of the Final Steam Electric

Effluent Limitation s Guidelines and Standards (DCN SE0 447 9 )

To support its revision of the effluent limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Point Source Category (40 CFR Part 423)

, EPA calculate d annual pollutant loadings from steam electric power plants that discharge to receiving wa ters
, either directly or via pass through at publicly owned treatment works (POTWs). For the evaluated waste streams, EPA calculate d the loadings for baseline (existin g) conditions and the pollutant removals for regulatory o ptions. EPA use d the pollutant removal s (baseline loadings minus option loadings ) to evaluate the effectiveness of the regulatory option treatment technologies, to estimate benefits gained from removing pollutants discharged from plants, and
to evaluate the cost

- effectiveness of the regulatory o ption in reducing the pollutant loadings . In addition to expressing pollutant loadings in pounds of pollutant discharged per year, EP A used toxic weighting factors (TWFs) to account for differences in toxicity across pollutants. EPA calculate d a toxic

- weighted pound equivalent (TWPE) value for each pollutant discharged to
compare pollutant mass loadings based on normalized toxi city. To perform this comparison, EPA multiplie d the mass loadings of pollutant in pounds per year (lbs/yr) by the pollutant

specific TWF to derive a “toxic

- equivalent” loading (lb

- equivalent/yr), or TWPE.

EPA explain ed the concept, calculation, use, and limitations of TWFs in the March 2012 document, Toxic Weighting Factors Methodology (EPA

- 820

- R

- 12

- 005). The document describe d how EPA first developed the TWF equation that combines information about toxic effects to aquatic life and human health. The docu ment also explain ed how EPA determine d the aquatic life component and human health component of the TWF calculation. Finally, the document discusse d that ELG rulemakings and program planning are the appropriate uses for TWFs and discussed the limitations o f the TWFs. EPA used TWFs developed using this methodology to support its propose d revised ELGs for the steam electric power generating industry (see 78 FR 34432, June 7, 2013). EPA received comments on the proposed ELG s that EPA should review toxicity benchmarks used to calculate TWFs for copper and other metals 1 and identify any more recent data.

1 See EPA

- HQ

- OW

- 2009

- 0819

- 4655.Memorandum

September 21, 2015 Page 2

The purpose of this memorandum is to provide background on how EPA use d TWFs for the steam electric power generating indust ry ELG development and to document the review of toxicity benchmarks, including identifying new data and determining whether the new data are

more appropriate for TWF development

. ERG reviewed the benchmarks (and underlying input data) included in the calc ulation of 1 6 pollutant TWFs. EPA chose these 16 pollutants due to their high modeled pollutant loadings for the evaluated waste streams discharged by steam electric power plants

. Based on this analysis, EPA revised TWFs for seven pollutants. This memorandu m includes the following sections:

 Section 1 : Overview of TWF Methodology

– general methodology that EPA use d to develop TWFs.

 Section 2 : Review of TWF s for Selected Steam Electric Power Generating Industry Pollutants of Concern

– evaluation of toxicity benchmarks and other input data that EPA use d to calculate TWFs.

 Section 3 : Summary of Revised TWFs

.

 Section 4: References

– a list of references used in support of this memorandum

.

 Attachment A

– details on TWF calculations and equation parameters.

 Attachment B

– summary of how EPA use d the TWFs.

1. O VERVIEW OF TWF METHODOLOGY
Toxicity is the degree to which a substance can harm or damage an organism, such as aquat ic species, wildlife, or humans

. As described in EPA’s Toxic Weighting Factors Methodology

, EPA Office of Water (OW) Engineering and Analysis Division (EAD) use s TWFs to compare the relative cost

- effectiveness of treatment technology options for ELGs and to relatively rank industries by their TWPEs as part of the effluent guidelines program planning. EPA has developed TWFs for 1,064 chemicals [U.S. EPA, 2012a]. EPA calculate d the TWFs using the MS Excel TM TWF Database for all pollutan ts except for boron ; EPA used a separate analysis to update the boron TWF in 2008 [U.S. EPA, 2012b ; Abt, 2008].

EPA calculate d TWFs for pollutants in water environments using two toxicity components :

1. Aquatic Life Value (AQ) : the concentration in water at w hich the pollutant becomes harmful to aquatic life

.

2. Human Health Value (HH) : the concentration in water that corresponds to a human health effect threshold for noncarcinogen ic pollutants and a non

- threshold cancer risk

- based factor for carcinogen ic polluta nt s.Memorandum

September 21, 2015 Page 3

AQ is a pollutant concentration in the water ( μg/L ) that is protective of aquatic life. EPA select ed AQ using the following benchmark values, in order of descending preference:

 Freshwater chronic benchmark value ( e.g. , National Recommended Water Quality Criteria (NRWQC) developed by EPA).

 Freshwater acute benchmark value.

 Salt water chronic benchmark value.

 Salt water acute benchmark value.

Section 2.1 discusses the review of aquatic life b enchmark values used in calculating TWFs for the selected steam electric power generating industry pollutants of concern.

HH is a pollutant concentratio n in the water ( μg/L ) that is protective for humans that eat fish and shellfish ( i.e. , aquatic organisms). As outlined in the Toxic Weighting Factors Methodology , EPA assume d the primary exposure pathway is fish consumption and assume d the drinking water exposure pathway is negligible. This assumption is reasonable for screening

- level analyses, considering that most Americans drink treated water and generally are not exposed to unsafe levels of toxic chemicals via the drinking water exp osure route.

EPA uses different equations or input values based on the following two factors : 1) whether the pollutant is noncarcinogenic or carcinogenic and 2) whether EPA OW Health and Ecological Criteria Division (HECD) used the 1980 or 2000 NRWQC meth odology for its National Recommended Water Quality Criteria: 2002. Human Health Criteria Calculation Matrix (EPA

- 822

- R

- 02

- 012) [U.S. EPA, 2002 a ]. 2 Table 1

- 1 presents the four different equations that EPA use d to calculate HH in the TWF Database

.

Table 1

- 1

. Equations Used to Calculate the Human Health (HH) Component of Pollutant Toxic Weighting Factors (TWFs)

Methodology and Pollutant Type Equation 1980 methodology, noncarcinogen, HH = RfD × BW × 1000
FI × BCF Equation 1

2 EPA’s National Recommended Water Quality Criteria: 2002 Human Health Criteria Calculation Matrix (EPA

822

- R

- 02

- 047) provided information regarding the calculation of the human health criteria contained in the document entitled, National Recommended Water Quality Criteria: 2002 (EPA

- 822

- R

- 02

- 047)

. The National Recommended Water Quali ty Criteria: 2002 Human Health Criteria Calculation Matrix document provides cancer potency factors; reference doses ; relative source contributions ; fish intake values; and equations used to derive the human health criteria for EPA’s 2002 NRWQC

.Memorandum

September 21, 2015 Page 4

Methodology and Pollutant Type Equation organism consumption only Where: HH = Human health value (μg/L) RfD = Reference dose, as milligrams per kilogram

- day (mg/kg/ day) BW = Body weight for an adult, 70 kg [U.S. EPA, 2000] 1000 = μg/mg conversion FI = Fish consumption rate, 0.0065 kg/day [U.S. EPA, 2000] BCF = Bioconcentration factor (L/kg) a

1980 methodology, carcinogen, organism consumption only HH = ( Crisk CPF ) × BW × 1000

FI × BCF Equation 2

Where: HH = Human health value (μg/L) C risk = Cancer risk level, typically between 1 ×10

- 4 and 1 ×10

- 6 CPF = Cancer potency factor (kg

- day/mg) BW = Body weight for an adult, 70 kg [U.S. EPA, 2000] 1000 = μg/mg conversion FI = Fish consumption rate, 0.0065 kg/day [U.S. EPA, 2000] BCF = Bioconcentration factor (L/kg) a

2000 methodology, noncarcinogen, organism consumption only HH = RfD × RSC × BW × 1000
FI × BCF Equation 3

Where: HH = Human health value (μg/L) RfD = Reference dose, as milligrams per kilogram

- day (mg/kg/day) RSC = Relative source contribution (%) BW = Body weight for an adult, 70 kg [U.S. EPA, 2000] 1000 = μg/mg conversion FI = Fish consumption rate, 0.0175 kg/day [U.S. EPA, 2000] b
B CF = Bioconcentration factor (L/kg) a
2000 methodology, carcinogen, organism consumption only HH = ( Crisk CPF ) × BW × 1000

FI × BCF Equation 4

Where: HH = Human health value (μg/L) C risk = Cancer risk level, typically between 1 ×10

- 4 and 1 ×10

- 6 CPF = Cancer potency factor (kg

- day/mg) BW = Body weight for an adult, 70 kg [U.S. EPA, 2000] 1000 = μg/mg conversion FI = Fish consumption rate, 0.0175 kg/day [U.S. EPA, 2000] b BCF = Bioconcentration factor (L/kg) a

a

– Bioaccumulation factors (BAFs) may also be used in place of bioconcentration factors ( BCFs ) [U.S. EPA, 2000]

. b

– The default fish consumption rate for general adult population and sport anglers is 0.0175 kg/day [U.S. EPA, 2000]. For mercury TWF calcul ations (noncarcinogenic pollutant) , EPA OW EAD used a fish consumption rate of 0.0187 kg/day, the fish intake rate used as a basis for the 1998 NRWQC. For the 2002 NRWQC, EPA OW HECD used the fish consumption rate of 0.0175 kg/day for mercury [U.S. EPA, 20 02a].Memorandum

September 21, 2015 Page 5

Attachment A provides more details on the calculation of TWFs using AQ and HH and descriptions of the input values used to calculate HH. Section 2.2 discusses ERG’s review of human health benchmark values used in calculating HH for the selected steam electric power generating industry pollutants of concern.

2. R EVIEW OF TWF S FOR S ELECTED S TEAM E LECTRIC P OWER G ENERATING I NDUSTRY P OLLUTANTS OF C ONCERN

ER G focused the TWF review described in this memorandum on 16 pollutants found in steam electric power plant wastestreams , listed in Table 2

- 1

. ERG selected t hese pollutants for review because of the high modeled pollutant loadings from steam electric power plants

. Table 2

- 1 also indicates whether the current TWF for that pollutant is based on AQ, HH, or both values and references the current equ ations being used to calculate HH

. For the 16 reviewed pollutants, EPA set AQ equal to freshwater chronic criteria values

. When developing the TWF methodology, EPA selected the freshwater chronic criteria as the most preferred value of AQ due to their availab i l ity [U.S. EPA, 2012 a ]

.

EPA derived the HH values from separate equations to estimate effects thresholds for noncarcinogens and non

- threshold cancer risk

- based factors for carcinogens (see Table 1

- 1)

. Of the evaluated pollutants , only arsenic is considered carcinogenic for purposes of the TWF calculation . Although cadmium

, chromium VI , and nickel are potential ca rcinogens, EPA has not developed final cancer potency factors for these three pollutants. Therefore, EPA use d the equation for noncarcinogenic pollutants to calculate HH for cadmium, c hromium VI , and nickel

.

Table 2

- 1 . Proposal TWFs: Values and Calculation for 16 Pollutants

Pollutant Proposal TWF AQ Calculation HH Calculation
Aluminum 0.0647 Freshwater chronic criteria Equation 3 : 2000 methodology; noncarcinogens
Arsenic 4.041 Freshwater chronic criteria Equation 2 : 1980 methodology; carcinogens

Boron 0.0083 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens
Cadmium 23.1 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens
Chloride 0.00002435 Freshwater chronic criteria No Value
Chromium VI 0.517 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens Copper 0.635 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens

Iron 0.0056 Freshwater chronic criteria No Value
Lead 2.24 Freshwater chronic criteria No Value Manganese 0.07043 Freshwater chronic criteria HH = 100 a Mercury 117 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens
Nickel 0.1089 Freshwater chronic criteria Equation 1: 1980 methodology; noncarcinogens
Selenium 1.121 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens
Thallium 1.027 Freshwater chronic criteria Equation 1: 1980 methodology; noncarcinogens
Vanadium 0.035 Freshwater chronic criteria No Value
Zinc 0.0469 Freshwater chronic criteria Equation 3: 2000 methodology; noncarcinogens Source: U.S. EPA, 2012b ; Abt, 200 8

.Memorandum

September 21, 2015 Page 6

a EPA set HH for man ganese at 100 μg/L for human health protection from consum ption of aquatic organisms only [U.S. EPA, 20 0 2b]

.

T he remainder of this section describes ERG ’s review of the data used to calculate TWFs for the 16 pollutants listed in Table 2

- 1

. In addition to reviewing the toxicity benchmarks ( i.e.

, freshwater chronic aquatic life criteria, reference doses , and cancer potency factors ) for the 16 pollutants, ERG also reviewed data f or the BCFs used in the calculation of the HH value. Based on this review, EPA updated TWF calculations for seven pollutants (see Section 3 ).

2.1 Review Benchmark Values for AQ

As described in Section 1, EPA determine d AQ for each pollutant as a concentration in the water ( μg/L ) that is protective of aquatic life. EPA’s 2012 document

, Toxic Weighting Factors Methodology

, describes how EPA select ed AQ based on a three

- tiered hierarchy in order of decreasing data quality [U.S. EPA, 2012a] . The three data sources are :

 Tier 1: A quatic life criteria published by EPA OW HECD as NRWQC

.

 Tier 2: E ffects data based on testing of aquati c organisms.

 Tier 3: E stimated toxicity effects data derived from various nationally

- recognized

sources.

EPA use d aquatic life benchmarks from Tier 1 data sources where available. EPA used Tier 2 data sourc es if the Tier 1 data sources did not include an aquatic life benchmark for the pollutant. EPA used Tier 3 data sources if the T ier 1 and Tier 2 data sources did not include an aquatic li fe benchmark for the pollutant.

Table 2

- 2 summarizes the AQ review for the 16 pollutants, the current AQ used to calculate the TWF, and the data source of the AQ. ERG performed the following steps in reviewing the current AQ :

 For pollutants using an NRWQC ( Tier 1 ) data source

, ERG determine d if the aquatic life benchmark is t he most recent . See the EPA NRWQC w eb site, http://water.epa.gov/scitech/swgu idance/standards/criteria/current/index.cfm

.

 For pollutants using Tier 2 or Tier 3 data sources , ERG confirm ed there are no aquatic life benchmarks from the Tier 1 data source

.

 For pollutants using Tier 2 or Tier 3 data sources, ERG determine d if there are other data sources and aquatic life benchmarks that can potentially be used to update AQ.Memorandum

September 21, 2015 Page 7

Table 2

- 2

. Summary of AQ Review s for Selected Steam Electric Pollutants of Concern

Pollutant AQ U sed in TWF

Calculation (μg/L) Data Source (Hierarchy

of Data Source ) ERG Review
Aluminum 87 NRWQC web site ( Tier 1 ) No update (most recent value from 1988)

. Arsenic 150 NRWQC web site ( Tier 1 ) No update (most recent value from 1995)

. Boron 750 EPA’s Quality Criteria for Water 1986 ( Tier 2 ) No update. NRWQC web site refers to EPA’s Quality Criteria for Water 1986

. See discussion in Section 2.1.2

. Cadmi um 0.25 NRWQC web site ( Tier 1 ) No update (most recent value from 2001)

. Chloride 230,000 NRWQC web site (Tier 1) No update (most recent value from 1986)

. Chromium VI 11 NRWQC web site (Tier 1) No update (most recent value from 1995)

. Copper 9 2002 NRWQC [U.S. EPA, 2012b] ( Tier 1 ) No update. See discussion in Section 2.1.1

.

Iron 1,000 NRWQC web site (Tier 1) No update (most recent value f rom 1986)

. Lead 2.5 NRWQC web site (Tier 1) No update (most recent value from 1980)

. Manganese 388 Birge, 1979 (Tier 2 or 3) U pdate. No NRWQC ; ERG identified a 1996 reference that discuss es aquatic life criteria for
manganese. See discussion in Section 2.1.2

. Mercury 0.77 NRWQC web site (Tier 1) No update (most recent value from 1995)

. Nickel 52 NRWQC web site (Tier 1) No update (most recent value from 1995)

. Selenium 5 NRWQC web site (Tier 1) No update (most recent value from 1999)

. Thallium 40 EPA Ambient Water Quality Criteria [U.S. EPA, 1980 a ] ( Tier 2 ) U pdate. No NRWQC; ERG identified a 1996 reference that discuss es aquatic life criteria for thallium. See discussion in Section 2.1.2

. Vanadium 160 Birge, et. al, 1977 (Tier 2 ) U pdate. No NRWQC; ERG identified a 1996 reference that discuss es aquatic life criteria for vanadium

. See discussion in Section 2.1.2

. Zinc 120 NRWQC web site (Tier 1) No update (most recent value from 1995)

. Sour ce: U.S. EPA, 2012b; U.S. EPA, 2014. Acronyms: AQ (aquatic life value); NRWQC (National Recom mended Water Quality Criteria).

2.1.1 Review of Tier 1 Data Sources for the Aquatic Life Benchmark

Of the 16 pollutants included in this review, EPA has set NRWQC (Tier 1 data source) for 12 pollutants. EPA use d the NRWQC as AQ when calculating TWFs. The only pollutant with a potential updated aquatic life benchmark based on the revised NRWQC is copper.

The current AQ for copper is 9 μg/L (based on the NRWQC set in 1998). In 2007, EPA published a revised methodology for calculating freshwater chronic aquatic life criteria for copper; however, the recommendation is to develop criteri a specific to the water body characteristics ( e.g. , te mperature, pH, dissolved organic compounds, suspended particles, and presence of various cations and anions including those that comprise hardness and alkalinity)

. EPA recommends that states use a Biotic Ligand Model (or bioavailability model) to set aquat icMemorandum

September 21, 2015 Page 8

life criteria for copper. Rather than developing a single national value, the document recommends calculating the final chronic value (FCV) for a specific water body chemistry [U.S. EPA, 2007]. For a national

- scale, screening level analysis, EPA decided to continue using the 2002 NRWQC value of 9 μg/L in TWF calculations

.

2.1.2 Review of Tier 2 and Tier 3 Data Sources for Pollutants without Tier 1 Data Sources

Of the 16 pollutants included in this review, four did not have NRWQC benchmarks and instead relied on Tier 2 or Tier 3 data sources for their AQ value. To develop TWFs, EPA used Tier 2 data sources for the boron, thallium, and vanadium aquatic life benchmarks

. EPA developed the aquatic life benchmarks for boron and thallium as part of ambient wat er quality criteria analyses in 1986 and 1980, respectively. EPA used a 1979 EPA document as the data source for the manganese aquatic life benchmark

. ERG was unable to locate the 1979 reference to determine if it was a Tier 2 ( effects data based on testin g of aquatic organisms ) or Tier 3 ( estimated toxicity effects data derived from various nationally

- recognized sources ) data source

. For the current review, ERG identified a Tier 2 data source that include d aq uatic life benchmarks for these pollutants

, which could potentially be used to update the AQs for bor o n, manganese, thallium

, and/or vanadium

. Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Aquatic Biota: 1996 ( Suter & Tsao , 1996 ) is a Department of Energy do cument which includes U.S. chronic National Ambient Water Quality Criteria (NAWQC) and Secondary Chronic Value s (SCV). SCVs

, used for pollutants that do not have NAWQC

, are calculated using the “Tier II method” described in the EPA's Proposed Water Quality Guidance for the Great Lakes System

. SCVs are aquatic benchmarks established with fewer data than are required for the NAWQC. SCVs for boron, manganese, thallium

, and vanadium are based on multiple studies (included in the reference document ’s Appendix A) that

measure d impacts to aquatic organisms. Suter & Tsao, 1996 includ e d the following SCVs:

 Boron: 1.6 μg/L.

 Manganese: 120 μg/L.

 Thallium: 12 μg/L.

 Vanadium: 20 μg/L.

EPA decided to not update the AQ value for boron in the TWF calculations. The current AQ value for boron is based on a 1986 aquatic life benchmark that EPA OW HECD includes on its NRWQC web site. EPA completed a review of the boron TWF calculations in 2008, more recent than the Suter & Tsao reference [Abt, 2008]

.

Based on this revie w, EPA decided to update the AQ values for manganese, thallium, and vanadium. T he SCVs for these three pollutants are from a Tier 2 reference (Suter & Tsao, 1996) based on a more recent analysis than the current AQs. EPA decided to update the AQs for these three pollutants in the TWF calculations to match the SCVs identified

.Memorandum

September 21, 2015 Page 9

2.2 Review Benchmark Values for HH

The equations and human health benchmarks EPA use d to calculate HH depend on whether the pollutant is noncarcinogenic or carcinogenic . For noncarcinogen ic pollutants, EPA

use d a reference dose

. For carcinogenic pollutants, EPA calculate d HH using a cancer potency factor and cancer risk level

. EPA classifie d t he data sources for the reference doses and cancer potency factor into the following three tiers, as outlined in EPA’s Toxic Weighting Factors Methodology document :

Tier 1

 EPA NRWQC , published after 2000

.

 EPA Integrated Risk Information System (IRIS) Oral reference doses or Oral cancer potency f

actors [ M ost recent ly available online ]

. Tier 2

 U.S. EPA’s Health Effects Assessment Summary Tables (HEAST) [ Most recent table is from 1997 ]

.

 U.S. EPA’s Region III Risk

- Based Concentration (R BC ) Table [ Most recent version is dated November 2013; see Summary Table available at http://www.epa.gov/reg3hwmd/risk/human/rb

concentration_table/Generic_Tables/index.htm ]

.

 California Environmental Protection Agency health assessments and toxicity criteria (CalEPA)

.

Tier 3

 U.S. EPA NRWQC d ocuments
, published before 2000

.

 Agency for Toxic Substances and Disease Registry (ATSDR) profiles

.

EPA use d reference doses and cancer potency factors from Tier 1 data sources where available. EPA used Tier 2 data sources if the Tier 1 data sources d id not include a reference dose or cancer potency factor for the pollutant. EPA use d Tier 3 data sources if the T ier 1 and Tier 2 data sources did not include a reference dose or cancer potency factor for th e pollutant. In cases where a pollutant has both a reference dose and cancer potency factor ( e.g. , arsenic), EPA calculated HH using the cancer potency factor and cancer risk level , unless the reference dose

was from a higher tier data source

.

Table 2

- 3 summarizes reviews for the 16 pollutants included in this analysis , the current reference dose or cancer potency factor used to calculate HH , the data source of the reference dose or cancer potency factor , and the results of ERG’s review

. As part of the review, ERG performed the following steps:

 For pollutants using the Tier 1 data sources

, ERG determine d if the reference dose

or cancer potency factor is the most rece nt available . See the EPA NRWQC w eb site, http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm and EPA IRIS w eb site, http://www.epa.gov/IRIS/

.Memorandum

September 21, 2015 Page 10

 For pollutants using Tier 2 or Tier 3 data sources , ERG confirm ed that there is no reference dose ( or cancer potency factor) from the Tier 1 data sources

.

 For pollutants using Tier 2 or Tier 3 data sources, ERG determine d if the reference dose ( or cancer potency factor ) is the most recent available

.

 For Tier 3 data sources, ERG confirmed that there is no reference dose (or c ancer potency factor ) available from Tier 2 data sources.

 For pollutants with no re ference dose ( or cancer potency factor )

, ERG determine d if any data sources are available

.Memorandum

September 21, 2015 Page 11

Table 2

- 3

. Summary of Reference Dose ( RfD ) and Cancer Potency Factor ( CPF ) Review s for Select ed Steam Electric Generating Industry Pollutants of Concern

Pollutant RfD (or CPF) U sed in

TWF Development Data Source (Hierarchy of Data Source ) ERG Review Notes
Aluminum RfD: 1.0 mg/kg/day EPA Region III RBC Table (Tier 2) No update (most recent value in RBC table). No Tier 1 data.
Arsenic RfD: 0.0 0 03 mg/kg/day

CPF: 1. 7 5 kg

- day/mg NRWQC (Tier 1) U pdate. The CPF value in IRIS is 1.5 kg

day/mg

. See discussion in Section 2.2.1

. Boron RfD: 0.2 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS )

. Cadmium RfD: 0.0005 mg/kg/day IRIS web site (Tier 1) U pdate. Value used in current TWF calculations is for intake of water

. IRIS also includes a diet

- based RfD of 0.001 mg/kg/day. See discussion in Section 2.2.1

. Chloride No value No value No update. No data for chloride RfD.
Chromium VI RfD: 0.003 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS)

. Copper RfD: 0.04 mg/kg/day EPA Region III RBC Table (Tier 2) No update (most recent value in RBC table). No Tier 1 data.

Iron RfD: 0.3 mg/kg/day EPA Region III RBC Table (Tier 2) U pdate. Most recent EPA Region III RBC Table lists the RfD as 0.7 mg/kg/day. See discussion in Section 2.2.2

. No Tier 1 data.
Lead No value No value No data for lead RfD. Manganese RfD: 0.14 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS)

. a Mercury RfD: 0.0001 mg/kg/day NRWQC [U.S. EPA, 2002 a ] (Tier 1) No updat e (most recent RfD developed by EPA in 2001 )

. b

Nickel RfD: 0.02 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS)

. Selenium RfD: 0.005 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS)

. Thallium RfD: 0.000068

mg/kg/day NRWQC [U.S. EPA, 2002 a ] (Tier 1) No updat e (most recent RfD developed by EPA)

. Vanadium RfD: 0.001 mg/kg/day EPA_NCEA Provisional Value from Region III data table, dated 10/8/2004 c U pdate. EPA Region III RBC Table lists an RfD for vanadium and vanadium compounds as 0.005 mg/kg/day

. See discussion in Section 2.2.2

. No Tier 1 data.
Zinc RfD: 0.3 mg/kg/day IRIS web site (Tier 1) No update (most recent value in IRIS)

. Acronyms: CPF (cancer potency factor); IRIS (Integrated Risk Information System) ; NCEA (National Center for Environmental Assessment); NRWQC (National Recommended Water Quality Criteria); RBC ( Risk

- Based Concentration ); RfD (reference dose); TWF (toxic weighting factor).

a The current TWF calculation for manganese uses HH equal to 100 μg/L [U.S. EPA, 2012b]. Although there is a reference dose for manganese, there is no BCF to calculate the HH using the methodology equations. Therefore, EPA did not revise the current HH used to calculate the TWF.

b See http://www.epa.gov/mercury/exposure.htm

.
c Reference as listed in TWF Database

.

2.2.1 Review of Tier 1 Data Sources for Reference Doses and Cancer Potency Factors

EPA use d Tier 1 d ata sources for reference doses and cancer potency factors for 10 of the 16 pollutants included in ERG’s review. Based on a review of the se Tier 1 data sources, ERGMemorandum

September 21, 2015 Page 12

identified the following updates to reference doses and cancer potency factors used to calculate HH:

 For ar senic, IRIS lists the cancer potency factor as 1.5 kilogram

- day per milligram

( kg

- day/mg )

. The 2002 National Recommended Water Quality Criteria 2002: Human Health Criteria Calculation Matrix lists the cancer potency factor for arsenic as 1.75 kg

- day/mg. Th is latter value was “derived from the risk per unit concentration in drinking water from IRIS: 5 x 10

- 5 risk per μg/L in drinking water” [U.S. EPA, 2002a]

. EPA decided to upda te the HH calculation with the cancer potency factor currently recommended on the IRIS web site

.

 For cadmium, IRIS lists the reference dose for diet

- intake as 0.001 milligram per kilogram per day ( mg/kg/day ) and for water

- intake as 0.0005 mg/kg/day . Current TWF calculations use the water

- intake reference d ose

. EPA use d the ambient water quality criteria equation to calculate HH based o n consumption of organisms only. EPA decided t he use of the diet

- intake reference dose is more consistent with the methodologies used for other pollutants than t he use of the
water

- intake reference dose for the TWF calculation and updated this value

.

2.2.2 Review of Tier 2 and Tier 3 Data Sources for Reference Doses and Cancer Potency Factors

EPA did not have Tier 1 data sources for reference doses and cancer potency factors for six of the 16 pollutants included in ERG’s review. ERG confirmed that no Tier 1 data were available for those pollutants. Next, ERG determined if the reference dose (or cancer potency factor ) based on Tier 2 or Tier 3 data sources was the most recently availa ble.

U.S. EPA’s Region III Risk

- Based Concentration (RBC) Table , a Tier 2 data source, included reference doses for four of the six pollutants without a Tier 1 data source. Aluminum and copper reference doses used to calculate HH matched the U.S. EPA Region III RBC Table; therefore

, EPA did not make any changes to HH values for those two pollutants. U.S. EPA Region III’s RBC Table included updated reference do s es for iron and vanadium. EPA decided to update the following reference doses used to calcula te HH:

 For iron, use the reference dose of 0.7 mg/kg/day as listed in the latest version of the U.S. EPA Region III RBC Table (replace 0.3 mg/kg/day in TWF calculations).

 For vanadium, use the reference dose of 0.005 mg/kg/day as listed in the latest

vers ion of the U.S. EPA Region III RBC Table (replace 0.001 mg/kg/day in TWF calculations).

For two of the six pollutants ( chloride and lead ), ERG did not identify any Tier 2 or Tier 3 data sources. Therefore, EPA made no changes to the TWF calculations and t his results in an HH value of zero ( i.e. , there is no human health component in the TWF for these two pollutants).Memorandum

September 21, 2015 Page 13

2.2.3 Bioconcentration Factors (BCFs) and Bioaccumulation Factors ( BAF s)

A BCF is the ratio of the pollutant concentration in the tissue of an aqua tic organism to the pollutant concentration in the ambient water. For all 16 pollutants included in this review, EPA used BCFs (not BAFs) to calculate the HH value for TWFs, because national

- level BAFs are not available for these pollutants. BAFs are devel oped to account for pollutants entering fish tissue from both the ambient water and from food sources; this makes them more complex to develop.

ERG performed a cursory review of the BCFs used in the TWF calculations and determined that updates were needed only if the BCF (or BAF) used in the TWF calculation did not correspond to the BCF (or BAF) used in development of EPA’s NRWQC. ERG identified one update: revising the BCF for copper to be 36 rather than 360. EPA’s 1980 Ambient WQC document lists the weig hted

- average BCF for the edible portion of freshwater and estuarine fish as 36 (not 360). The overall mean BCF, including scallops, mussels, clams, and oysters, is 290 [U.S. EPA, 1980b]. The 2002 National Recommended Water Quality Criteria 2002: Human Heal th Criteria Calculation Matrix lists the BCF for copper as 36 [U.S. EPA, 2002a].Memorandum

September 21, 2015 Page 14

3. S UMMARY OF R EVISED T OXIC W EIGHTING FACTORS
Based on a review of the TWF general methodology and documentation available, EPA decided to update the TWF calculations as outlined in Table 3

- 1. Attachment B provides details on how EPA used TWFs for the steam electric ELGs.

Table 3

- 1. Revised TWFs

Pollutant TWF Calculation Update Previous TWF Revised TWF Arsenic Revised CPF

. 4.04 3.47 Cadmium Revised RfD (diet

- based)

. 23.1 22.8 Copper Revised BCF. 0.635 0.623 Iron Revised RfD

– EPA does not have a BCF to use

in the HH calculation; therefore, RfD update does not change the TWF. 0.00560 0.00560

Manganese Revised AQ benchmark

. 0.0704 0.103 Mercury Revise the fish consumption rate used to

calculate HH for mercury to 0.0175 kg/day (same as other pollutants using the 2000 Methodology). 117 110

Thallium Revised AQ benchmark ; use the 2000

methodology. NRWQC updated in 2003 [U.S. EPA, 2003]

. 1.03 2.85

Vanadium Revised AQ benchmark

.

Revised RfD

– EPA does not have a BCF to use in the HH calculation; therefore, RfD update does not affect the TWF. 0.035 0.280

Acronyms: AQ (aquatic life value); BCF (bioconcentration factor); CPF (cancer potency factor); HH (human health value); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TWF (toxic weighting factor)

.

4. REFERENCES

1. Abt. 2008. Abt Associates, Inc. “ Revised Draft

– Updating the Boron TWF. ” ( D ecember )

.

2. Birge, WJ. 1979. Aquatic Toxicity Tests on Inorganic E lements Occurring in Oil Shale ( EPA

- 600/9

- 80

- 022 ). Oil Shale Symposium

- Sampling, Analysis and Quality Assurance ( March )

.

3. Birge, et.al. 1977. WJ Birge, JA Black, and AG Westerman

. Evaluation of Aquatic Pollutants Using Fish and Amphibian Eggs as Bioassay Organisms

. In SW Nielsen, G. Migaki, and DG Scarpelli (Eds.) Symp. Animals Monitors Environ. Pollut

. 1977, Storrs, CT 12:108

- 118.

4. Suter & Tsao. 1996. G.W. Suter II and Tsao, C.L. Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Aquatic Biota: 1996 Revision. ES/ER/TM

- 96/R2. Prepared for the U.S. Department of Energy. ( June )

.Memorandum

September 21, 2015 Page 15

5. U. S

. EPA. 1980 a. Ambient Water Quality Criteria for Thallium (EPA

- 440

- 5

- 80

- 074). Washington

, DC

. ( October )

.

6. U. S

. EPA. 1980 b. Ambient Water Quality Criteria for Copper (EPA

- 440

- 5

- 80

- 036). Washington

, DC

. (October).

7. U.S. EPA. 1986. Quality Criteria for Water 1986 (EPA

- 440

- 5

- 86

- 001). Washington, DC. ( May )

.

8. U.S. EPA. 2000. M ethodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) (EPA

- 822

- B

- 00

- 004). (October).

9. U.S. EPA. 2002a. National Recommended Water Quality Criteria: 2002. Human Health Criteria Calculation Matrix (EPA

- 822

- R

- 02

- 012)

. ( November )

.

10. U.S. EPA. 2002b. National Recommended Water Quality Criteria: 2002 (EPA

- 822

- R

- 02

- 047). (November).

11. U.S. EPA. 2003. Revised National Recommended Water Quality Criteria for the Protection of Human Health. ( December )

. Available online at: http://water.epa.gov/scitech/swguidance/standards/criteria/health/15table

- fs.cfm

.

12. U.S. EPA. 2005. Guidelines for Carcinogen Risk Assessment (EPA

- 630

- P

- 03

- 001F) . Risk Assessment Forum. Washington, DC. ( March )

.

13. U.S. EPA. 2007. Aquatic Life Ambient Freshwater Quality Criteria

— Copper (EPA

- 822

- R

- 07

- 001). Washington, DC. ( February )

.

14. U.S. EPA. 2012 a

. Toxic Weighting Factors Methodology (EP A

- 820

- R

- 12

- 005)

. Washington, DC. ( March )

.

15. U.S. EPA. 2012b. TWF Database (EPA

- HQ

- OW

- 2008

- 0517

- 0713). MS Excel TM

. Washington, DC.

16. U.S. EPA. 2014. National Recommended Water Quality Criteria ( w eb site). http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm

. Accessed March 2014

.

17. U.S. EPA Region III

. 2013. Ecological Risk Assessment ( w eb site). http://www.epa.gov/reg3hwmd/risk/eco/btag/sbv/fw/screenbench.htm

. Accessed March 2014

.Attachment A

September 21, 2015 Page A

- 1

Attachment A. TWF Calculations

This a ttachment provides more detailed information on how EPA calculate d TWFs and the parameters used to determine the human health component (HH).

Equation to Calculate TWF

EPA calculate d TWFs for a given pollutant by comparing that po llutant’s AQ and HH to a scaling factor value for AQ and HH. EPA combine d aquatic life and human health effects information to help compensate for the incompleteness of data sources, to simplify waste stream evaluations, and to simplify the TWF calculation. In some cases, a pollutant TWF may be derived solely from an AQ, and less commonly, a pollutant TWF may be derived solely from a HH. In its methodology, EPA note d that the approach of combining the AQ and HH is not appropriate for more rigorous analysis, such as risk assessments [U.S. EPA, 2012a]. However, the combining of these effects is a reasonable approach for the purposes used in ELGs, specifically “informing regulatory decisions about the relative cost effectiveness of treatment technologies, and fo r identifying industries that may warrant additional analysis.” Equation A

- 1 shows the calculat ion of TWF s :

TWF = 5

. 6 AQ + 5

. 6
HH

Where: 5.6 = scaling factor (original copper freshwater chronic aquatic

- life criterion of

5.6 micrograms per Liter [μg/L]) AQ = Aquatic Life Value (μg/L) HH = Human Health Value (μg/L)

Equations to Calculate HH

As discussed in Section 1 of the memorandum, EPA use d different equations or input values based on the following two factors: 1) whether the pollutant is noncarcinogenic or carcinogenic and 2) whether EPA OW HECD used the 1980 or 2000 NRWQC methodology for its 2002 NRWQC analyses [U.S. EPA, 2002a]. Noncarcin ogenic pollutants are those pollutants that EPA does not consider to have the potential to cause cancer in humans based on EPA’s Guidelines for Carcinogen Risk Assessment (2005).

The 1980 methodology, compared to the 2000 methodology, use d a different equ ation for noncarcinogenic pollutants and a different fish consumption rate for all pollutants. EPA OW HECD present ed both methodologies in the 2002 EPA document, National Recommended Water Quality Criteria 2002: Human Health Criteria Calculation Matrix [U. S. EPA, 2002 a ] . In 2002, EPA OW HECD began using the 2000 methodology to calculate the NRWQC. At that time, EPA OW HECD chose to continue using the 1980 methodology for 17 pollutants. EPA OW Equation A

- 1Attachment A

September 21, 2015 Page A

- 2

HECD planned to update the NRWQC for the subset of pollutants at a later date. 3 For purposes of calculating TWFs, EPA OW EAD used these same equations to calculate HH.

The TWF Database include d calculations using the following methodologies (equations and inputs) for HH, based on the consumption of aquatic organisms:

 19 80 methodology to calculate the NRWQC for noncarcinogenic pollutants based on the consumption of organisms only. See Equation 1 in Table 1

- 1.

 1980 methodology to calculate NRWQC for carcinogenic pollutants based on the consumption of organisms only. See Equation 2 in Table 1

- 1.

 2000 methodology to calculate the NRWQC for noncarcinogenic pollutants based on the consumption of organisms only. See Equation 3 in Table 1

- 1.

 2000 methodology to calculate NRWQC for carcinogenic pollutants based on the

consum ption of organisms only. See Equation 4 in Table 1

- 1.

For noncarcinogenic pollutants, EPA calculate d HH using a reference dose, or other benchmark protective of human health from the consumption of aquatic organisms ( i.e. , fish and shellfish). If a bench mark for the consumption of aquatic organisms only is not available, EPA uses a reference dose or benchmark based on the consumption of water and aquatic organisms. The calculation of HH for noncarcinogenic pollutants in the 1980 NRWQC m ethodology differs from the 2000 methodology in two ways: 1) no use of the Relative Source Contribution ( RSC ) factor and 2) different fish consumption intake value.

Description of Input Values to the HH Equations

For noncarcinogenic pollutants, EPA calculate d HH using the reference dose

. A pollutant reference dose is an estimate of a daily oral exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime. Reference doses may be derived from a no observed adverse effect level ( NOAEL )

, lowest observed adverse effect level ( LOAEL ) , or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data . See U.S. EPA Risk Assessment Glossary at http://www.epa.gov/risk_assessment/glossary.htm for additional details.

The relative source contribution (RSC) factor is the percentage of pollutant exposure apportioned to the fish consumption (or fish and water consumption) pathway. Other exposure

3 In 2003, EPA HECD proposed new criteria for 14 of the 17 pollutants (plus 1,1

- dichloroethylene ). For these proposed new criteria, EPA HECD used the 2000 methodology [U.S. EPA, 2003]. EPA updated the thallium methodology (only updated pollutant that is also include d in EPA OW’s list of 16 pollutant TWFs evaluated in this memorandum). Note that EPA HECD continues to recommend using the 1980 methodology for arsenic, nickel, and chloroform.Attachment A

September 21, 2015 Page A

- 3

pathways include air (inhalation), dermal, and other dietary intake

. From EPA’s 2012 Toxic Weighting Factors Methodology :

“ The RSC approach is documented in the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health [U.S. EPA, 2000]. EPA, however, has published RSCs for only 28 chemicals. The RSCs were calculated as part of the development of NRWQC. For TWF human health calculat ions for all other chemicals, fish consumption is assumed to be the only exposure pathway, and thus an RSC of 100 percent is applied. Consequently, the drinking water exposure pathway is assumed to be zero percent for most TWFs. EPA considers this assumpti on to be reasonable for the purpose of screening

- level analysis, considering that most Americans drink treated water, or tested well water, and thus generally are not exposed to unsafe levels of toxic chemicals with TWFs through drinking water. ”

A b ioconcentration factor (BCF) is the ratio of the pollutant concentration in the tissue of an aquatic organism to the pollutant concentration in the ambient water. For TWF development, EPA relied on BCF values, rather than bioaccumulation factors (BAFs) . Th e rationale for this approach is described in EPA’s 2012 Toxic Weighting Factors Methodology :
“An aquatic bioaccumulation factor (BAF) is the ratio of a toxic chemical in an organism to its concentration in the ambient water, considering exposure from all potential pathways. An aquatic bioconcentration factor (BCF) is the ratio of a toxic chemical in an organism to its concentration in the ambient water, considering direct contact with the water as the only exposure pathway. Bioaccumulation typically accoun ts for significantly more chemical build up in tissues than bioconcentration, especially for highly toxic and highly persistent chemicals like dioxin compounds. National

- level BAFs are not available, however, because they are complex to develop. BCFs, on t he other hand, are readily available, and EPA uses them to calculate most TWFs.”

For carcinogenic pollutants, EPA calculate d HH using a cancer potency factor

, or cancer slope factor. EPA used cancer potency factor s to estimate the risk of cancer associated with exposure to a carcinogenic pollutant

. EPA’s Integrated Risk Information System (IRIS) 4 defin es

a cancer slope factor as “an upper bound

, approximating a 95% confidence limit, on the increased cancer risk from a lifetime exposure to an agent (pollutant) by ingestion. ” EPA then weight ed this estimated cancer risk against a selected cancer risk leve l . For NRWQC development, EPA uses a cancer risk level of 10

- 6 (one in 1,000,000 people), which reflects an appropriate risk level for the general population and is consistent with Agency

- wide practices. EPA note d that both the 10

- 5 (one in 100,000 people) and 10

- 6 cancer risk levels are appropriate for determining risks to the general population. EPA recommends using the cancer risk level of 10

- 4 (one in 10,000 people) when evaluating risks for highly exposed populations [U.S. EPA, 2000]. The 2000 NRWQC me thodology and the 1980 NRWQC methodology recommend a

c ancer risk level of 10

- 6 [U.S. EPA, 2002 a ] . For the HH calculations, EPA OW EAD used a cancer risk factor of 10

- 5 ( i.e. , one in 100,000 people).

4 http://www.epa.gov/iris/help_ques.htm

.Attachment B

September 21, 2015 Page B

- 1

Attachment B

. How EPA Uses TWFs

EPA received comments on the use of TWFs for the proposed Steam Electric Power Generating Point Source Category ELGs . One comment noted that TWFs assume a uniform characterization of toxicity of pollutants from all discharges and relate the toxicity to pol lutant loadings rather than to pollutant concent rations in the receiving water. This attachment summarizes the use of the TWFs in the ELG program. For a more detailed summary, see the Toxic Weighting Factors Methodology [U.S. EPA

, 2012a ]

.

EPA use d TWFs as a way to better understand how treatment technologies, individual plant discharges, and industry dis charges compare to one another [ U.S. EPA, 2012 a ]

. For development of ELGs, EPA use d available data such as survey responses, sampling episode data, and other wastewater monitoring data to characterize discharges from a specific plant. EPA calculate d plant

- specific (and for the Steam Electric ELG, wastestream

- specific) pollutant loadings as mass per year ( e.g. , lb/yr or grams/yr) based on the pollutant concentration in the discharge and the discharge flow rate . EPA calculate d pollutant loadings to establish baseline (current) discharge quantities of pollutants and calculate d regulatory opt ion pollutant loadings to determine pollutant removal s. To determine the toxicity of a specific wastestream, EPA use d TWFs to allow the addition of discharges across multiple pollutants. The result is the TWPE.

EPA used the pollutant removals to evaluate t he effectiveness of the regulatory option treatment technologies, estimate benefits gained from pollutant removals , and evaluate the cost

effectiveness of the regulatory options.

EPA use d TWFs and the estimated TWPEs as an indicator of the relative potenti al of a pollutant to cause harm and not to represent actual aquatic or human health impacts that may

occur at specific locations due to these pollutant loadings

. To assess impacts to aquati c life or human health, EPA use d the pollutant loadings discharged to the receiving water, as lbs/year, as input to the n ational

- s cale i mmediate r eceiving w ater (IRW) m odel used for the environmental
assessment

. EPA use d t he model to predict pollutant concentrations in the specific receiving
water body, sediment, and fish tissue . Using the concentration in the fish tissue, EPA calculate d

an average daily dose (ADD) for humans consuming fish. EPA did not use TWFs or TWPEs in the n ational

- s cale IRW m odel

. See the Environmental Assessment for the Effluent Limitations Guidelin es and Standards for the Steam Electric Power Generating Point Source Category ( EPA

- 821

- R

- 15

- 006 ) for further details on the environmental assessment and IRW model.