NCS000574_Email RE Response to Comments on Benchmarks_20160321

From:
Georaoulias, Bethany
To:
Bennett, Bradley
Cc:
Randall, Mike; Pickle, Ken; Riddle, Rick L
Subject:
Comments from Cape Fear Hearing and Letters
Date:
Monday, March 21, 2016 2:39:51 PM
Attachments:
image002.pnng
Bradley,
You asked me to help with responses to benchmark related comments. Below is a summary of the
related comments and proposed responses:
From Hearing, speaker #1 Martha Giralami
5. 1 think all metal benchmarks are very high and depend on dilution to cure pollution. Benchmarks
should be reduced by one tenth of FAV. In Cape Fear, these coal ash metals will biomagnify by
factors of 10,000 to 100,000 in the bodies of fish and other animals that live in the downstream
ecosystem. Biomagnification and persistence in the environment argue for much lower
benchmarks.
From Duke Energy's comment letter:
Part II Page 10 of 14
Under Table 4 some of the benchmark values are very low. For Copper the benchmark value is listed
as 0.01 mg/I. The Silver value is listed at 0.0003 mg/I. Plus for Silver the practical quantification level
listed in the Fact Sheet is 0.001 mg/I, which as noted in the Fact Sheet is higher than the benchmark
level. Could these two values be re-evaluated? The potential exists that these parameters could be
measured in stormwater run-off from the influence of background soil containing metals, instead of
industrial activities.
Consider a response based on our website FAQ on this topic, expanded to address the questions
raised during this comment period. See below:
Benchmarks are numerical action levels for stormwater monitoring. Benchmarks are
not effluent limits. Benchmarks are determined with help from Division of Water
Resources' Classification and Standards Unit and are determined using data from
multiple sources including regulations such as EPA's National Recommended Water
Quality Criteria, the National Primary Drinking Water Regulation in 40 CFR 141.11,
and NC Surface Water Quality Standards (found in 15A NCAC 02B regulations).
When regulations do not contain information for a particular pollutant of concern,
benchmarks are calculated per 15A NCAC 2B .0200 using peer -reviewed toxicity
data.
In general, benchmarks are calculated to mimic acute water quality standards. The
DEQ follows established Federal procedures for calculation of an acute standard
when developing stormwater benchmarks (acute standard/benchmark is set at of

the calculated FAV or Final Acute Value) and typically applies those values in NPDES
stormwater permits without any dilution allowance. Benchmarks based on acute
standard calculations reflect a conservative protection level for aquatic life against
negative impacts from short-term, undiluted exposure to higher levels of chemicals.
NC DEMLR believes this approach to be the most appropriate for protecting against
potential impacts of stormwater discharge exposures and consistent with DEQ's
NPDES permitting program. Adjusting these calculated values because they are
perceived as "too low" or "too high" compromises the scientific basis. If these values
are lower than the current PQL, Section III, Section D. 4 (Test Procedures) guides the
permittee on action "To meet the intent of the monitoring required by this permit, all test
procedures must produce minimum detection and reporting levels and all data generated must be
reported down to the minimum detection or lower reporting level of the procedure. If no approved
methods are determined capable of achieving minimum detection and reporting levels below permit
discharge requirements, then the most sensitive (method with the lowest possible detection and
reporting level) approved method must be used." In this way, the permit does not constrain
the permittee from using approved methods that may achieve a lower PQL in the
future.
DEQ acknowledges that background soil containing metals may influence discharge
values enough to exceed established benchmark values for metals like copper, zinc,
and possibly others. The Tier Responses in the permit allow DEQ flexibility to relieve
monthly monitoring if the permittee demonstrates circumstances are appropriate
(discharge levels reflect natural background or background influences beyond the
permittee's control, for example) and/or all reasonable stormwater pollution
prevention measures have been attempted but cannot bring levels down. For several
years, DEQ has considered requests from general permit holders in Tier II or III to
relieve monthly copper and/or zinc monitoring frequency when the permittee
demonstrates levels are not attributable to industrial activity or are beyond reasonable
(e.g., road runoff influenced by these metals in tires and break pads or metal roofs on
buildings) because these metals are so ubiquitous. In these instances, DEQ must
also consider whether there are water quality problems in the receiving waters
resulting from these metals before making a decision on whether to grant the
permittee's request for reduced monitoring or to require additional efforts to reduce
concentrations.
When human health standards warrant a different reference value, such as in the
case of mercury's accumulation in the food chain as methyl mercury for example, an
alternative value is considered. In the case of mercury, however, a 12 ng/I
benchmark value (set at the WQ standard instead of/2 FAV because of its
bioaccumulative potential) is more likely to be exceeded when regional air deposition

is driving elevated levels and would prompt monthly monitoring with little gain for the
permittee's pollution prevention efforts. Therefore, sampled levels will have to be
considered in conjunction with fish tissue monitoring for mercury, arsenic, and
selenium required by the plant's wastewater permit <<verify this will be required for
Cape Fear and Asheville plants — it is proposed for Riverbend's WW permit>> , a
measure of bioaccumulation of these metals.
Bethany Georgoulias
Environmental Engineer
Stormwater Permitting Program, Division of Energy, Mineral, and Land Resources
N.C. Department of Environmental Quality
919 807 6372 office
Bethany. Gorgoulias o ncdenr.gov
1612 Mail Service Center, Raleigh, NC 27699-1612 (mailing)
512 N. Salisbury Street, Raleigh, NC 27604 (location)
Website: ham://portal.ncdenr.org/web/lr/stortnwater
Email correspondence to and from this address is subject to the
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