Chronic-Silver-Standard PPt

Overview of the Class C (Freshwater) Chronic Aquatic Life Standard
for Silver & Comments on the NCWQA Petition
Christopher Ventaloro, NCDEQ, Water Quality Standards Coordinator
NC Water Quality Committee
January 12, 2022
History of the Chronic Silver Standard
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Current chronic standard adopted by EMC in 1989
Adopted to address discharge of silver from industrial
facilities
Implemented as an “Action Level” for NPDES
•Facilities required to show reasonable potential to exceed
standard
•Facilities required to pass Whole Effluent Toxicity (WET) testing
•Failure resulted in permit limit based on action level value (0.06
ug/L)
History of the Chronic Silver Standard
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Silver standard timeline:
•1989 -Action levels established
•2016 –Most metals revised from total to dissolved including
•Acute silver (EPA NRWQC) -dissolved, hardness-dependent
•Chronic silver (02B .0208) as NC Action Level -dissolved, not hardness-dependent
•***EPA disapproved use of the action levels
•2019 -Action level language removed from 02B .0211 due to EPA
disapproval of action levels in 2016
•Chronic silver standard retained @ 0.06 ug/L (dissolved, not hardness-dependent)
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CWA requires states adopt standards to protect designated uses
(such as aquatic life)
NC adopts numeric & narrative standards to achieve this goal
Chronic silver standard is a numeric standard that is based on
the narrative standard for toxic substances as described in 15A
NCAC 02B .0208
Regulatory & Scientific Basis
Standard uses the final acute value (FAV) from EPA's
1980 Ambient Water Quality Criteria for Silver
FAV is an estimated concentration that should be protective
of 95% of aquatic species excluding the most sensitive
species
~80 toxicity data points from 10 freshwater species
Eight of the ten species evaluated are found in NC surface
waters with the most sensitive species being common
throughout NC
•Water flea (most sensitive), Fathead minnow (second most sensitive), Bluegill
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Regulatory & Scientific Basis
The standard of 0.06 ug/L was calculated per 02B .0208
as:
The lowest LC50 x safety factor, where
•Lowest LC50 = 1.2 ug/L (1980 EPA FAV @ 50 mg/L hardness)
•Safety factor = 0.05 (per 02B .0208)
EPA (2016) determined this to be consistent with NC's
standards & scientifically defensible for CWA purposes as
required per 40 CFR 131.11
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Regulatory & Scientific Basis
Silver is demonstrated via toxicity testing to be toxic to aquatic life
Aquatic life standards designed to protect for various
health effects
Chronic standards protect organisms from long-term
exposures to toxics that may result in impacts to:
•Growth
•Reproduction
•Behavior (social, hunting/foraging, survival)
Acute standards protect organisms from short-term exposures that may result in mortality
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Significance of the Chronic Silver Standard
Other states & tribes have also adopted a chronic silver
standard to protect freshwater aquatic life including:
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Other States & Tribes
State/Tribe Chronic Silver Standard
(ug/L)
Florida 0.07
Minnesota 0.12
New York 0.1
Oregon 0.1
St. Regis Mohawk Tribe (NY)0.1
Northern Cheyenne Tribe (MT)0.12
Statements in the petition do not accurately reflect some
aspects of the standard:
•Regulatory & scientific basis of the standard
•Use of Water Effects Ratios (WERs)
•Significance of chronic standard in protecting aquatic life
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Division Comments
Petition questions the regulatory basis of the standard
NC DWR comments:
40 CFR 131.11 requires states to adopt standards to protect designated uses
Accomplished via numeric & narrative standards
No existing federal NRWQC for chronic silver
15A NCAC 02B .0208 provides narrative standard for toxic substances
•Indicates that toxics cannot result in chronic toxicity to aquatic life
•Informs how to interpret the narrative standard through calculation of numeric criteria
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Division Comments
Petition questions the scientific basis of the standard
NC DWR Comments:
Basis is the 02B .0208 narrative standard for toxic substances
Details of the scientific basis discussed earlier in this presentation
(EPA FAV x safety factor)
EPA 2016 decision document for the triennial review determined
the chronic silver standard to be:
1.Consistent with the approved language in the 02B .0208 narrative
standard for calculation of toxics criteria to protect aquatic life
2.Scientifically defensible as required per 40 CFR 131.11
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Division Comments
Petition states that chronic silver standard would be better if it was
a hardness-dependent standard
NC DWR Comments:
Not untrue, however...
•Standard is based on the 1980 EPA FAV @ 50 mg/L hardness
•Developing hardness based chronic standard requires
additional tox information to establish relationship between
hardness & chronic toxicity (data may not be available)
•Stakeholders can provide data
•Stakeholders can also recommend a scientifically supported
alternative to the existing standard
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Division Comments
Petition states that Water Effects Ratios (WER)are not allowed for
chronic silver
NC DWR Comments:
15A NCAC 02B .0211 (11)(c) provides WER option (eff. date Jan. 1,
2015)
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Division Comments
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Division Comments
Petition states that Water Effects Ratios (WER)are not
allowed for chronic silver
NC DWR Comments:
•WER would account for the site-specific effects of hardness
and organics on chronic silver toxicity
•One facility has already used this approach
The petition states chronic standard unnecessary
NC DWR Comments:
Protecting aquatic life from the effects of chronic exposure is
required per 02B .0208 narrative standard for toxic substances
Significance of chronic impacts touched on earlier in this
presentation
•Protection from long-term exposures and impacts to growth,
reproductions, and behavior
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Division Comments
Petition states that standard is unecessary due to Whole Effluent Toxicity (WET) testing:
NC DWR Comments:
•WET testing was integral to the Action Level implementation
•EPA 2016 triennial review decision document disapproved
Action Levels stating that:
•"Per 40 CFR 122.44(d)(1)(i), controls must be in place for discharges with reasonable potential to cause or contribute to an excursion of standards in surface waters"
•"WET testing alone is not suitable to protect uses because a discharge can pass WET while still contributing to an excursion of a standard in-stream"
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Division Comments
Next Steps
Should EMC grant the petition:
•Proceed to rulemaking with proposed deletion in 02B .0211
•Satisfy NC APA & CWA public notice & hearing requirements
•If adopted, EPA will review change to 02B .0211 for compliance
with CWA
•Requires scientific justification for removal of standard
•Includes EPA consultation with USFWS or NOAA for ESA
compliance
*Note: The NC acute hardness-dependent standard (0.3
ug/L @ 25 mg/L hardness) remains in effect
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Questions?
Christopher Ventaloro
Water Quality Standards Coordinator
Phone: [phone]
[e-mail]
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