NCS000389_Benchmarks Rationale_20131101

NCDENR
North Carolina Department of Environment and Natural Resources
Division of Energy, Mineral, and Land Resources
Land Quality Section
Tracy E. Davis, PE, CPM Pat McCrory, Governor
Director John E. Skvarla, III, Secretary
November 1, 2013
To: Stormwater Permitting Program
Through: Bradley Bennett, Stormwater Permitting Program Supervisor
From: Bethany A. Georgoulias, Stormwater Permitting Program
Subject: Stormwater Benchmark Concentrations and Rationale, 2013 Revisions
The Stormwater Permitting Program has revised its guidance on stormwater benchmark
concentrations. Guidance on these benchmarks was first developed by the Division of Water Quality in 1994
and last revised in August 2007. Stormwater benchmarks are used to make decisions about monitoring in
permit development, as well as provide a tool for permittees to evaluate pollution prevention plan
effectiveness and respond to possible problems. This guidance is based on a number of sources, including
more recent National Recommended Water Quality Criteria (NRWQC).
An outline of the rationale and methodology for the current benchmarks is attached, as well as the
current Stormwater Benchmark Table. Our Program will revise this table no more frequently than triennially
(if necessary), unless major changes or corrections to criteria warrant revision. Ideally, updates will be
coordinated with the Division of Water Resource's Triennial Review of N.C. Water Quality Standards.
Several metals have been updated to reflect the most recent NRWQC, and other benchmarks have
been corrected or revised with more recent toxicity data available from EPA's ECOTOX database and/or other
sources. Guidance on nutrients has been revised, and the use of "Non -polar Oil & Grease"/ Total Petroleum
Hydrocarbons (TPH) by Method 1664 (SGT-HEM) was added, along with discussions on polychlorinated
biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs).
Attachments: Stormwater Benchmark Rationale and Guidance Document
NC DEMLR Stormwater Benchmarks and Sources Table (October 2013)
cc: Jeff Manning, Supervisor, DWR Planning Section
Connie Brower, DWR Planning Section
Cindy A. Moore, DWR Aquatic Toxicology Unit
Tom Belnick, DWR NPDES Complex Permitting Unit Supervisor
John Hennessy, DWR NPDES Compliance and Expedited Unit Supervisor
DEMLR RE, Asheville Regional Office
DEMLR RE, Fayetteville Regional Office
DEMLR RE, Mooresville Regional Office
DEMLR RE, Raleigh Regional Office
DEMLR RE, Washington Regional Office
DEMLR RE, Wilmington Regional Office
DEMLR RE, Winston-Salem Regional Office
1612 Mail Service Center, Raleigh, North Carolina 27699-1612 • Telephone [phone] / FAX: [phone]
512 North Salisbury Street, Raleigh, North Carolina 27604 • Internet: http://portal.ncdenr.org/web/Ir/land-quality
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NC DEMLR Stormwater Permitting Program:
Stormwater Benchmark Rationale and Guidance Document
Introduction
Stormwater benchmarks are numerical action levels for stormwater monitoring. Benchmarks are
not effluent limits. North Carolina's NPDES stormwater permits incorporate benchmarks to provide
facilities a tool for assessing the significance of pollutants in stormwater discharges, and the effectiveness of
best management practices (BMPs). For the permittee, benchmark concentrations provide a guideline for
implementing the facility's Stormwater Pollution Prevention Plan (SPPP).
Exceedences of the numerical benchmark values are not a violation of the permit. However,
benchmark exceedances typically require the permittee to increase monitoring, increase management
actions, increase record keeping, and/or install stormwater BMPs in a tiered program. The tiered approach
outlines actions the permittee must take in response to analytical results above benchmark concentrations.
Not responding to benchmark exceedances as per the permit is a violation of permit conditions.
For permit development, monitoring is generally recommended for any parameter identified as a
pollutant of concern (either from past measured levels in the discharge or because of the potential for
stormwater exposure at the site). Benchmarks should not be applied without best professional judgment
(BPJ). In some cases, monitoring without a benchmark or a different benchmark might be more appropriate
than what is listed in the table here.
The groundwork for these benchmarks and much of the supporting information has been carried
over from the Division of Water Quality's original stormwater benchmark guidance (C. Sullins, 1994).
However, there have been significant updates to several values and policies over the years. Benchmarks are
determined with help from Division of Water Resources' Planning Section. Values are based on a variety of
sources, including EPA's National Recommended Water Quality Criteria (NRWQC), the National Primary
Drinking Water Regulation in 40 CFR 141.11, and NC Surface Water Quality Standards (15A NCAC 02B
regulations). When federal or NC water quality regulations do not contain information for a pollutant,
benchmarks are calculated per 15A NCAC 213.0200 with peer -reviewed aquatic toxicity data or with an
alternate approach. Permit writers should consult with DWR's Planning Section when a benchmark
based on limited data is noted.
I. Toxicants and Metals
Toxicants
Because of the sporadic nature of rainfall, acute (short-term) effects are considered when
establishing stormwater benchmarks for toxicants. Toxicant benchmarks are equal to one half the Final
Acute Value (1/2 FAV) for constituents like arsenic, chromium, cyanide, lead, nickel, and silver. N.C. DENR
also uses the 1/2 FAV to set daily maximum wastewater limits for toxicants. The FAV is estimated by a
statistical analysis of acute toxicity data and protects 95 percent of the species in the most sensitive genera
that has been tested. A safety factor of two is applied for water quality protection purposes.
The Stormwater Benchmark and Sources Table shows total recoverable metal and cyanide values.
The benchmarks are based on NRWQC dissolved criteria and translated into total for permitting purposes
(as required by federal regulations for the NPDES program). Where metal values are hardness -dependent,
the benchmark is now based on an assumed hardness of 25 mg/l. The value has dropped from the previous
default of 50 mg/1 because DWR's review of ambient hardness data concluded a lower value is more
representative of streams of North Carolina. Several of the metals benchmarks are converted from
dissolved values into total recoverable with EPA's partition factor and a calculation that assumes a total
suspended solids (TSS) concentration of 10 mg/l. Even though the TSS stormwater benchmark is typically
much higher, 10 mg/1 assumes a "best case" stormwater discharge with low solids, resulting in a

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conservative benchmark value for the total recoverable metal. For special cases, the permit writer may
consider modifying the variables to calculate a site -specific benchmark.
The Division of Water Resources has proposed new dissolved metals water quality standards
based on the current NRWQC, but the new standards are not yet adopted. The NPDES wastewater program
intends to translate dissolved values into total recoverable metals as described above. Because these
values reflect the most recent recommended water quality criteria, and because benchmarks are not
effluent limits, the Stormwater Permitting Program will transition to revised metals benchmark values in
permits with effective dates beginning in January 2014.
Ubiquitous Metals
Copper (Cu) is a ubiquitous (prevalent) substance that does not readily bioaccumulate and has a
high affinity for organic compounds. Zinc (Zn) is also very prevalent, but has the potential to bioaccumulate
[EPA-310-R-95-010]. Historically, these metals have been associated with adverse effects in very few
streams in North Carolina, and the sources of contamination in those streams have primarily been non -
point. Iron (Fe) and manganese (Mn) are also ubiquitous substances that have not been associated with
many point source discharges from urban areas. To a certain extent, these metals are naturally present in
N.C. soils, depending on regional geography. Benchmarks for copper and zinc have been established but
should be applied only when the facility's industrial processes, activities, or exposed materials could
introduce significant amounts of these metals into the stormwater discharges.
The benchmark for iron was removed. We believe that in most cases, a benchmark for iron is not
suitable or useful for stormwater discharge monitoring. North Carolina has proposed removing the current
water quality standard for iron because of its natural occurrence in soils.
A benchmark for manganese has not been set. We believe that samples analyzed for manganese
may reflect presence of this compound in the in situ soils, as opposed to its presence in the permitted
facility's industrial stormwater. An appropriate manganese benchmark could not be established.
Because copper and zinc are so pandemic, in natural soils and in some urban environments,
monitoring for them is recommended only when industrial activities or materials have the potential to
contribute significant amounts to discharges. In those cases, one or both of these metals may be
appropriate indicators of BMP effectiveness (e.g., lapses in good housekeeping) or stormwater
contamination, and should be included in the permit. Water quality problems related to these metals in the
receiving waters also warrant attention. When monitoring for any ubiquitous metal is required, the default
approach is to include the benchmark in the permit, but alternative approaches may be considered.
We recognize that acute values for zinc and especially copper are low, and that their toxicity is
highly variable (depending on the amount dissolved, which is affected by many factors). Whether because
of hardness or other assumptions, there may be instances when benchmarks for these parameters are
considered impractical. In such cases, the permit writer may consider site -specific BMPs in lieu of
benchmarks for one or more of these parameters. This approach is consistent with 40 CFR §122.44(k)(3),
which grants N.C. DENR the authority to use BMPs to control or abate the discharge of pollutants when
numeric effluent limitations are infeasible. The permit writer may also consider other options (e.g., Action
Level Implementation Policy for Copper and Zinc in NPDES [wastewater] Permits, October 2000).
Mercury
Because it is extremely toxic and bioaccumulative in its methyl mercury form, mercury (Hg) is a
different case. We do not use the 1/2 FAV as the stormwater benchmark for mercury. The benchmark (12
ng/L) is instead taken from the N.C. Water Quality Standard in 15A NCAC 213.0211. While historically we
would have expected values to be below detectable level, Method 1631 now makes a mercury detection
limit as low as 0.5 ng/L possible. However, the method is expensive, and collection procedures are labor
intensive. Because mercury from distant sources is introduced into stormwater and streams by air

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deposition, it is not reasonable to expect no detects of mercury in every case. Therefore, mercury should
only be monitored when there is reason to suspect the activity or materials on site, including local source
deposition, could contaminate runoff. Industrial activities should not contribute any mercury to
stormwater discharges.
II. Volatile Organics
Under normal circumstances, organics would not be expected in stormwater discharges. The
presence of these compounds may indicate poor management practices. Stormwater can have significant
flow velocity and aeration, providing opportunity for organics to volatilize. The presence of organics at
concentrations above the detection limit is cause for concern. However, interference commonly associated
with stormwater samples may cause false positives in volatile organic testing.
Monitoring on an individual basis should be required when industry specific sources of volatile and
semi -volatile organics are identified. For some organic compounds, more stringent 1/2 FAVs for stormwater
discharges to Trout (Tr) waters have been established based on acute tests with salmonid species. These
include phenol and toluene. For benchmarks not already recorded in the attached stormwater benchmarks
table, the permit writer should refer to the most recent EPA NRWQC for criterion maximum concentrations
(CMC) or consult DWR's Planning Section for further guidance.
III. Oxygen Consuming Wastes
Biochemical Oxygen Demand
There is little documentation available that associates problematic concentrations of dissolved
oxygen with stormwater runoff. Therefore, the benchmark for Biochemical Oxygen Demand (BOD - 5 day, or
BODs) is based on the Secondary Treatment Regulation specified in the Code of Federal Regulations, Title 40,
Part 133 (40 CFR §133). That regulation defines the minimum level of effluent quality attainable by
secondary wastewater treatment as 30 mg/1 for the 30-day average of BODs. We do not anticipate that
unpolluted stormwater discharges will exceed BODs concentrations in excess of this standard.
Chemical Oxygen Demand
The benchmark for Chemical Oxygen Demand (COD) was set using best professional judgment.
Generally, COD is found at levels four times the BODs levels in domestic wastewaters. We do not anticipate
that unpolluted stormwater discharges will exceed BODs concentrations in excess of this standard, and so the
benchmark for COD is based on four times the BODs benchmark (120 mg/1).
Nitrate + Nitrite Nitrogen
Nitrate and nitrite nitrogen (NO3 + NO2 as N) is a component of Total Nitrogen (TN) and is not
generally monitored. Monitoring may be required when industry -specific sources of these pollutants are
identified. The National Primary Drinking Water Regulation (40 CFR §141.11) specifies a maximum
contaminant level of 10 mg/1 nitrate (as N). This value is the same as the N.C. water quality standard for
water supply (WS) waters in the T15A NCAC 213.0200 rules.
The EPA Multi -Sector permit establishes 0.68 mg/1 as the NO3 + NO2 benchmark, based on a median
concentration from the National Urban Runoff Program (NURP) study in 1983. We feel a value reflecting
nitrate levels in urban runoff is not appropriate for industrial sites where nitrates are a potential pollutant
source. Therefore, unless a 1/2 FAV for this parameter becomes available, the benchmark remains 10 mg/l.

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Total Kjeldahl Nitrogen (TKN)
The benchmark for TKN ("Total Kjeldahl Nitrogen," or organic nitrogen) is based on an approximate
equivalency to secondary treatment of wastewater. The majority of TKN found in stormwater is unlikely to
be directly bio-available. Organic nitrogen, in the form of decaying leaves and twigs for example, will exert
less demand on in -stream dissolved oxygen (DO) than TKN from domestic wastewater. Furthermore, low DO
in receiving streams is rarely attributed to rainfall events. The lack of documented water quality problems,
coupled with the sporadic nature of rainfall events, is the basis of a TKN benchmark of 20 mg/l.
Ammonia
Large amounts of ammonia are not expected in industrial stormwater discharges, and persistent
elevated levels may indicate a wastewater issue. Ammonia is normally reported in mg/l of nitrogen (or "as
N") and should be specified this way in the permit. Current benchmark values are based on guidance in the
EPA Ammonia Criteria 1999 Update Document [EPA-822-R-99-014]. Because ammonia's toxicity is highly
dependent upon temperature and pH, refer to the Stormwater Benchmarks and Sources Table for
assumptions. Keep in mind that a very small change in pH can dramatically increase or decrease the
ammonia concentration which is toxic; therefore, it is important to consider pH when assessing
monitoring data. Please consult the Criteria Document and/or DWR's Planning Section staff if there is reason
to adjust the ammonia benchmark for a different pH. A more stringent ammonia benchmark based on acute
tests with salmonid species is specified for Trout waters.
IV. Nutrients (Nitrogen and Phosphorus)
Monitoring for nutrients may be required if (1) nitrogen and/or phosphorus are associated with the
industrial activity or materials stored on site, or (2) if the discharge is to nutrient sensitive waters (NSW) and,
either past data show the site to be a significant contributor of nutrients, or no data are available to
characterize the contribution. The permit writer should apply best professional judgment in situations where
years of data or numerous samples have demonstrated nitrogen or phosphorus levels are consistently below
benchmarks.
Total Nitrogen (TN)
The benchmark for total nitrogen is the sum of the TKN and (nitrate + nitrite) benchmarks: 30 mg/l.
Total Phosphorus (TP)
The benchmark for total phosphorus (2.0 mg/1) is based on BPJ and consistent with wastewater
permit limits imposed on NSW dischargers.
V. Inorganics
Conductivity
This parameter (measured in uS/cm) is a good indicator of inorganic pollutants (salts, minerals, etc.)
However, there is no benchmark for conductivity because natural background levels vary widely and reflect
the constituents specific to the water in that location. In the NPDES Wastewater Program, conductivity is
usually monitored up- and downstream; significant increases will evidence inorganic pollutants in the
discharge. If inorganic contamination is expected in the stormwater discharge, the permit writer may
consider monitoring conductivity.

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Chloride
The stormwater benchmark for chloride is based on EPA's NRWQC (860 mg/1).
Sulfate
The stormwater benchmark for sulfate is based on the 1/2 FAV (500 mg/1), derived from EPA's
ECOTOX Database. A separate value for water supply watersheds was considered but is no longer applied. A
WS benchmark was considered (250 mg/1) because there is a significant cost to remove this compound when
water treatment plants treat drinking water for distribution. While a lower value is advantageous for water
treatment plants downstream, stormwater benchmarks are based on acute effects to aquatic life when
possible. Therefore, unless a special case warrants a more stringent concentration, we believe that 500 mg/1
is a more appropriate benchmark concentration for sulfate.
VI. Radioactive Substances
Uranium
There are several options for assigning a uranium benchmark if necessary. The permit writer should
work with the Radiation Protection Section to determine this level. As of March 2007, there is only one
facility in North Carolina that manufactures uranium: General Electric in Wilmington. The decision not to
include uranium in that facility's NPDES stormwater individual permit is documented in the memorandum
from Beverly Hall, Chief Radiation Protection Section to Kelly Johnson on February 28, 2007.
Facilities that manufacture uranium are regulated under a license issued by the United States Nuclear
Regulatory Commission (USNRC). The USNRC retains exclusive federal jurisdiction for radioactive materials
within the site boundary unless such materials are not directly covered by the USNRC license. Because the
radioactive materials that could potentially appear in stormwater runoff are covered by the USNRC license,
the site is subject to the requirements of Table 2, Column 2 in Appendix B to 10 CFR §20 under the current
facility license.
VII. Bacteria
Historical perspective: The fecal coliform standards in N.C.'s Water Quality Standards until May 2007
were based on guidance found in Virginia's standard. Virginia removed this standard from its guidance, and
this change affected N.C. policy. The N.C. Water Quality Standards referencing fecal coliform for saltwaters
were amended on May 1, 2007. This change requires enterococcus rather than fecal coliform as the indicator
bacteria for saline waters. There was no change to the freshwater bacteria or shellfish fecal coliform
standards in May 2007.
Statistical significance of sampling: Data for either indicator must represent a statistically significant
geometric mean. Currently most permits require sampling twice per year, but this number of samples does
not yield a statistically significant mean. A single high analytical test may represent an anomaly on -site,
rather than a problem with the facility's stormwater. The number of samples required for statistically
significant results would introduce a burden to permittees. When determining the appropriate analytical
sampling, permit writers should consider how the data collected will be used. Will the data serve as
appropriate corrective guidance for BMP implementation onsite? Will the data help make decisions about
future analytical requirements? If there was a single high test in the previous permitcycle, did that test
represent statistically significant data?

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Risk assessment: Permit writers should consider whether people may be at risk. Is it likely that
people are either eating shellfish from the receiving water or are swimming in the receiving water? The
Division of Marine Fisheries (DMF) Shellfish Sanitation Program aggressively samples many saltwaters (SA
and SB) for fecal and enterococcus to protect for shellfish consumption and recreation. The DMF samples
only some SC waters for recreational use protection. In addition, the DMF has different Use Classifications
than the DWR, and those Use Classifications change regularly (often seasonal). Permit writers should
remember that the DMF data are typically available for summer months. Therefore, there is greater risk for
human contamination from facilities that drain to either SC or freshwaters not being detected by the DMF
sampling. Permit writers should use best professional judgment to decide if the facility will contaminate the
receiving water, and balance this possibility against the potential burden of requiring statistically significant
testing. Also consider what BMPs may be put in place if the facility detects high bacteria levels.
Requiring sampling: If the permit writer determines that the facility should conduct statistically
significant testing for bacteria, consider the following potential requirements:
Fecal Coliform
Guidance for fecal coliform:
➢ Require for freshwaters (B and C)
➢ Benchmark Guidance Value (freshwater): Fecal - 1000 col/100 ml. This value is based on BPJ
and was consistent with the maximum (one -sample) threshold specified in Virginia's older
Water Quality Standards. The N.C. Water Quality Standard (for all Class C waters, based on
human health) says that fecal coliforms shall not exceed a geometric mean of 200/100ml (MF
count) based upon at least five consecutive samples examined during any 30-day period, nor
exceed 400/100ml in more than 20 percent of the samples examined during such period. We do
not consider these values practical for a stormwater benchmark. In addition, the N.C. Standard,
213.0211, specifies that violations of that standard "are expected during rainfall events." The
most recent N.C. Water Quality Standard maintains the fecal coliform indicator for freshwaters.
If sampling is necessary, monthly sampling is recommended in order to yield statistically
significant results. Consider comparing the Benchmark Guidance Value to a geometric mean of
at least 10 samples.
➢ N.C.'s fecal coliform Water Quality Standard for SA (shellfishing) waters is 14 col/100 ml. This
value is based on a geometric mean as described above. If sampling for bacteria because of SA
waters, enterococcus sampling is recommended; however, a permit writer may consider this
fecal value (and appropriate sampling) as well.
Enterococcus
Guidance for enterococcus:
➢ Require for saltwaters (SA, SB, SC) Human Health
➢ Benchmark Guidance Value (saltwater): 500 enterococcus/100 ml. This value was set using
EPA's 1986 Ambient Water Quality Criteria for Bacteria. However, the data supporting this value
was collected through non-traditional means. Many people who had been exposed to waters
with varying enterococcus levels were interviewed several days after exposure. Though this
method was an attempt to determine an appropriate value, North Carolina considers this value
to be BPJ. However, this value does represent a single -sample maximum for saltwaters, and so if
enterococcus sampling is necessary, comparison to the benchmark may be based on a single
sample, rather than by multiple samples to ensure statistical significance. (Note, Rules 15A
NCAC 02B .0220 and .0222 were amended on May 1, 2007 to reflect the new standard of 35
enterococci/100 ml, based on a minimum of five samples within any consecutive 30 days.)

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VIII. Chlorinated and Fluorinated Compounds
Polychlorinated Biphenyls (PCBs)
There are several concerns with polychlorinated biphenyls (PCBs) in the environment. Arochlors are
both a human health concern (0.064 ng/1) and an aquatic life concern (1 ng/L). However, practical
quantitation limits (PQLs) are much higher than even aquatic life standards. PQLs are usually at or near 1
µg/L (much higher than the standard). PQLs also change daily within and between labs. These factors make
it difficult to establish a numeric benchmark. Therefore, any detection over the PQL is an exceedence of the
benchmark. The most sensitive appropriate method should be used. Consult the DWR Planning Section for
updates on advances in PCB detection methods and PQLs.
Polyaromatic Hydrocarbons (PAHs)
Polyaromatic hydrocarbons (PAHs) are a group of over 100 different chemicals. Many PAHs in the
environment are from incomplete burning of carbon -containing materials like oil, wood, garbage or coal.
PAHs are found in coal tar, crude oil, creosote, roofing tar, blacktop, and mothballs. PAHs are also found at
low concentrations in some special-purpose skin creams and antidandruff shampoos that contain coal tars,
and a few are used in medicines, dyes, plastics, and pesticides.
Benzo(a)pyrene (CAS # 50-32-8) and Benzo(b)fluoranthene (CAS # 205-99-2) are carcinogens and
are included in the N.C. water quality standard for total PAHs (.0311 ug/L all waters). However, the DWR has
had issues with using human health data for stormwater in the past, and therefore the benchmarks for PAHs
listed in the table are based on aquatic life acute standards (1/2 FAVs).
VIII. Other Parameters
Oil and Grease (O&G) vs. "Non -polar O&G" (or TPH)
The traditional Oil & Grease (0&G) benchmark of 30 mg/1 is based on BPJ and reflects typical
wastewater limits. Monitoring may be required when industry specific sources of these pollutants are
identified and are not limited to petroleum -based hydrocarbons (e.g., animal fats and greases are potential
pollutants).
Historically, 0&G was the parameter used for many facilities where handling, storage or use of
petroleum products is of concern. By definition, 0&G is composed of fatty matter from animal and vegetable
sources and hydrocarbons of petroleum origin. Laboratory analysis of "Non -Polar 0&G" with EPA Method
1664 (SGT-HEM) requires the sample to be mixed with a silica gel, or similar substance, to remove polar
materials from the sample (typically, fatty materials that are not petroleum based). It is basically a cheaper
alternative method to estimating "Total Petroleum Hydrocarbons" (TPH) with a more expensive GC analysis
usually used for "TPH." Petroleum hydrocarbons cover a broad family of several hundred chemical
compounds that originally come from crude oil such as gasoline, diesel, kerosene, etc. Instead of measuring
each compound separately, TPH is a practical monitoring parameter for targeting petroleum contamination.
"TPH" or "Non -polar 0&G" with Method 1664 (SGT-HEM) is not meant to replace 0&G as a monitoring
parameter. It is available to permit writers as a more -specific parameter at facilities expected to discharge
only petroleum -based hydrocarbons. As an example, non -polar O&G could be well -suited to monitor a site
that stores bulk fuel oil to fire its boiler, but it would not be as useful as 0&G at a biodiesel production plant
that handles both petroleum and non -petroleum based oils.
There are some limitations to the non -polar O&G parameter as measured by EPA Method 1664
(SGT-HEM) that the permit writer should understand. Method 1664 is not applicable to measurement of
materials that volatilize at temperatures below 85 degrees C. Petroleum fuels from gasoline through No. 2
Fuel Oil may be partially lost in the solvent removal step, and because some crude oils and heavy fuel oils

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contain significant amounts of materials that are not soluble in n-hexane, recoveries may be low. Motor oils,
however, are consistently detected using Method 1664.
A 15 mg/L benchmark is consistent with other states' stormwater benchmarks or maximum daily
concentration limits for TPH in a grab sample [New Jersey Hot -Mix Asphalt General Permit, Texas Petroleum
Bulk Stations and Terminals General Permit, and Washington Port of Seattle Permit]. We would expect only
stormwater discharges with significant oil contamination (ex. concentrated parking lot runoff) to exceed this
concentration.
Because "TPH" is normally associated with more expensive GC analysis methods at laboratories, we
now refer to this parameter in permits specifically as "Method 1664 SGT-HEM (Non -polar O&G)"
instead of TPH to reduce confusion. Currently the Division of Water Resources does not certify labs for "TPH"
with EPA Method 1664 (SGT-HEM) because the only TPH listed in the Certification Rules is based on GC
analysis (gas -range and diesel -range hydrocarbons analysis). Performing Method 1664 with the extra silica
gel treatment step is simply considered an option for "O&G" analysis. The technicality is not an impediment
because N.C. rules do not require certification for stormwater sample analysis.
pH
The benchmarks for pH are based on water quality standards for freshwater classes, which specify a
pH range of 6.0 - 9.0 standard units. Because pH is often critical to interpreting monitoring data, and because
it is a surrogate indicator for problems when other parameters are not monitored directly, the permit writer
should always consider including pH whenever analytical monitoring is in the permit. However, in some
cases, pH monitoring may not offer extensive benefit. The permit writer should use BPJ when deciding to
exclude pH monitoring. Note that NPDES wastewater discharges to saltwaters are typically limited to 6.8 -
8.5 standard units (N.C. Water Quality Standard, T15A NCAC 02B .0220). The permit writer may consider this
more restrictive range of benchmarks for saline receiving waters.
Total Suspended Solids (TSS)
The benchmark for TSS (100 mg/1) reflects a median concentration from the NURP study. While the
Stormwater Permitting Program does not use the NURP study value for nitrates, TSS at industrial sites is
expected to come from similar sources (parking lots, etc.). In addition, an equivalent secondary wastewater
treatment level is established by the wastewater discharge limit of 90 mg/1 for lagoon systems.
The lower 50 mg/1 TSS stormwater benchmark for Outstanding Resource Waters (ORW), High
Quality Waters (HQW), trout (Tr) waters, and primary nursery area (PNA) waters is one half of the standard
benchmark. That value was set to flag problems that might be especially detrimental to sensitive waters
(which are subject to effluent limitations of 20 mg/1 TSS for HQW and 10 mg/1 TSS for Tr waters in the N.C.
Water Quality Standards) and is based on BPJ.
Turbidity
The benchmark for turbidity varies according to whether receiving waters are lake, trout, or saline
waters. The Water Quality Standards specified in the 213.0200 rules serve as benchmarks: 50 NTU, 25 NTU
(lakes/reservoirs and saltwaters), and 10 NTU (Tr). However, these levels are in -stream standards. The
narrative part of the standard also acknowledges that natural background conditions may be higher.
Turbidity is highly variable in stormwater events and can be influenced by run-off up -land of an
industrial site. Therefore, this parameter is not commonly included in a stormwater permit unless
there are specific concerns. The permit writer should exercise BPJ when considering if and how to include
turbidity monitoring. One option is to measure turbidity up- and downstream of the discharge instead, to
account for background levels and evaluate contribution by the point source in between.
The NPDES general permit for Mining Activities currently includes turbidity monitoring without a
benchmark and the language that "The discharge shall not cause the turbidity of the receiving water to
exceed Water Quality Standards...." (See NCG020000, effective January 1, 2010).

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IX. Freshwater vs. Water Supply and Saltwater
Most of the benchmarks in the attached table are based on fresh water criteria. The permit writer
should consider whether any benchmarks should be adjusted specifically for Water Supply (WS) or saline
receiving waters. However, staff should keep in mind that human health -based criteria reflect standards for
treated drinking water and may not be appropriate for stormwater discharges. For example, the current
antimony (Sb) criterion based on human consumption of fish and water is 0.0056 mg/l. This value is suitable
for purified drinking water but is too stringent for a stormwater benchmark.
Some specific parameters are discussed in this guidance. Many parameters are beyond the scope of
this guidance; others may need revision because more recent toxicity data are available, or testing methods
have changed. If there is a question about a pollutant of concern, a permit writer should consider how
difficult and/or expensive the constituent is to remove in water treatment, potential human health impacts,
and whether or not a level based on acute effects to aquatic life is still the most appropriate benchmark in
making the decision about what value to use.

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References:
Action Level Policy: 'Implementation of Action Levels for Copper and Zinc in NPDES Permits. " North
Carolina Division of Water Quality. October 25, 2000. Available on-line at:
httR//www.esb.enr.state.nc.us/ATUwww/Default.html (accessed 5 October 2006).
EPA Office of Compliance Sector Notebook Project: Profile of the Nonferrous Metals Industry.
September 1995. EPA-310-R-95-010.
National Recommended Water Quality Criteria (2009). U.S. EPA. Available on-line at:
httR//water.epa.govlscitechIswguidance/standards/criteria/current/index.cfm (accessed 22 October
2013).
N.C. Division of Environmental Management/Water Quality Section Memorandum dated April 12,
1994, from C. Sullins to Regional Water Quality Supervisors with attached draft `Determining Monitoring
Requirements for Stormwater Permitting' document (March 31, 1994).

NC DEMLR Stormwater Benchmark Rationale and Guidance Document
November 1, 2013
Page 12 of 16
NC DEMLR Stormwater Permitting Program
Stormwater Benchmarks and Sources
Last Revised October 25, 2013
Most values listed in this table represent freshwater values. Permit writers should investigate whether criteria for
saltwater and human health (water supply waters) are applicable and would serve as a more appropriate basis for a
permit benchmark. Also note that some facilities may have different benchmarks to address unique circumstances.
Parameter
Benchmark Conc.
Units
ource
Acetone
17
mg/I
: FAV (N. Remington, 9/2008).
crylamide
28
mg/I
2 FAV (N. Remington, 10/2009).
Acrylonitrile
3.8
mg/1
Y2 Lowest Observed Effect Level (LOEL); EPA's 1986 Water Quality
Criteria for acrylonitrile
Aluminum, total recoverable
JW5
mg/I
FAV (Final Acute Value); EPA's National Recommended Water
�uality Criteria (Acute) for aluminum. Not hardness dependent.
Aluminum Sulfate
1.1
mg/I
Y2 FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Ammonium Sulfate
19
mg/I
Y2 FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Ammonia, total as Nitrogen
7.2
mg/I
Y2 FAV @pH 8; EPA's 1999 Update of Ambient Water Quality Criteria
or ammonia
Ammonia, total as Nitrogen
5.6
mg/I
Y2 FAV @ pH 8; EPA's 1999 Update of Ambient Water Quality Criteria
(Trout)
or ammonia. More stringent to protect trout species.
Anthracene
0.005
mg/I
/: FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Antimony, total recoverable
0.09
mg/I
Y2 FAV; EPA's National Recommended Water Quality Criteria (Acute)
or antimony (III).
Arsenic, total recoverable
0.34
mg/I
Y2 FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved arsenic (not hardness dependent), converted to total
it In EPA partition translator = 1.0 (revised 2013). Note human
health standard is 10 ug/I, but normally would not use that for a
tormwater benchmark.
Bacteria, enterococcus
500
Entero-
- Enterococcus includes: Enterococcus faecalis, Enterococcus
coccus/100
faecium, Enterococcus avium, and Enterococcus gallinarium
ml
- Require for saltwaters if necessary. See Rationale Document.
- This value is based on EPA's 1986 Ambient Water Quality Criteria
for Bacteria. (July 2007, K. Johnson and C. Brower)
Based on single sample maximum value.
Bacteria, fecal coliform
1000
col/100 ml
Require for freshwaters if necessary. See Rationale Document.
(June 2007, K. Johnson and C. Brower)
- Based on geometric mean of 10'samples/year. See Rationale
Document.
Benzene
6.7
mg/I
/z FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Benzo(a)pyrene (PAH),
2.5
ug/I
Y2 FAV (N. Remington, 9/2010)
CAS # 50-32-8
0.0025
mg/l
Beryllium
0.065
mg/I
Y2 FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved beryllium (not hardness dependent), converted to total
with EPA partition translator = 1.0 (revised 2013)
BODS (Biological Oxygen Demand,
30
mg/I
BPJ, Based on Secondary Treatment Regulation (40 CFR 133.03).
5-day)
Cadmium
0.003
mg/I
Y2 FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved cadmium, calculated with assumed 25 mg/l hardness,
and then converted to total with EPA partition translator based on
assumed 10 mg/I TSS (revised 2013)

NC DEMLR Stormwater Benchmark Rationale and Guidance Document
November 1, 2013
Page 13 of 16
Parameter
Benchmark Conc.
Units
Source
Cadmium (Trout)
0.002
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved cadmium, calculated with assumed 25 mg/I hardness,
and then converted to total with EPA partition translator based on
assumed 10 mg/I TSS. More stringent to protect trout species
(revised 2013).
Chloride
860
mg/I
EPA's National Recommended Water Quality Criteria, 2006 (Note:
There was previously a water supply chloride value. K. Johnson
removed it on 12 June 2007 after discussion with C. Brower and J.
Dent.)
Chlorine, Total Residual (TRC)
28
ug/I
% FAV (NC's calculation, not EPA's); See 'Total Residual Chlorine: An
0.028
mg/I
Overview of North Carolina's Standard Development' (value from
Carns et al., 1978).
Chromium (total)
N/A
mg/I
REMOVED. Assume all chromium III in most cases; chromium VI only
if suspected source (revised 2013).
Chromium III, total recoverable
0.905
mg/L
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved chromium III, calculated with assumed 25 mg/I
hardness, and then converted to total with EPA partition translator
based on assumed 10 mg/I TSS (revised 2013).
Chromium VI, total recoverable
0.016
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved chromium VI (not hardness dependent), converted to
otal with EPA partition translator = 1.0 (revised 2013).
Cobalt
N/A
mg/I
No longer use % FAV from 2005 that was based on limited data.
There is human health information. Consult DWR Planning Section.
COD (Chemical Oxygen Demand)
120
mg/I
BPJ, Generally found at levels 4 x (BODS) in domestic wastewaters.
Copper, total recoverable
0.010
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved copper, calculated with assumed 25 mg/I hardness, and
hen converted to total with EPA partition translator based on
assumed 10 mg/I TSS (revised 2013).
Creosote
0.3
mg/I
% EPA's FAV, EPA's ECOTOX Database (Feb 2005, J. Wynn).
Cresol
4.0
mg/I
% FAV, based on p-Cresol (4-methyl phenol) form. Derived from
EPA's ECOTOX Database (July 2003, J. Wynn).
Cyanide
0.02
mg/I
% FAV, EPA's 1984 Ambient Water Quality Criteria for Cyanide
(expressed as free CN)
2,4-Dimethylphenol
1
mg/I
% LOEL, EPA's 1980 Ambient Water Quality Criteria for 2,4-
Dimethylphenol
1,4-Dioxane
0.73
mg/I
In -stream standards for general human health exposures, Class C
waters. May not be best benchmark for all permits; consult DWR
Planning Section.
Dioxin
Any Detection
-
Connie Brower, May 2007. Dioxins are bioaccumulants. Any
detection is recognition of a problem.
Enterococcus
-
-
See "Bacteria"
Ethanol
3,900
mg/L
% FAV (Verschueren, Karel. Handbook of Environmental Data on
Organic Chemicals. 3rd Ed. 1996.) (March 2007, J. Dent)
Ethylene Glycol
8,000
mg/I
% FAV derived from EPA's ECOTOX Database (N. Remington, 9/2010).
Correction to previous benchmark.
Fecal Coliform (See "Bacteria")
-
Fluoranthene (PAH),
0.6
ug/I
%: FAV (N. Remington, DWQ, 9/2010)
CAS #206-44-0
0.0006
mg/I
Fluorene (PAH),
0.3
mg/I
% FAV (N. Remington, DWQ 9/2010)
CAS # 86-73-7

NC DEMLR Stormwater Benchmark Rationale and Guidance Document
November 1, 2013
Page 14 of 16
Parameter
Benchmark Conc.
Units
Source
Fluoride
6
mg/I
% FAV derived from EPA's ECOTOX Database (Aug. 2006)
Formaldehyde
0.5
mg/I
% FAV derived from EPA's ECOTOX Database (Sept 2005, J. Wynn).
Hexamine
25,000
mg/I
% FAV derived from PAN Pesticides Database (Dec 2005, J. Wynn).
Based on limited data; consult DWR Planning Section.
Iron
N/A
mg/I
REMOVED. Ubiquitous in NC soils and current NC Water Quality
standard proposed to be removed (revised 2013).
Isopropyl Alcohol
4,300
mg/L
% FAV (ECOTOX 3/07) (March 2007, J. Dent)
Lead, total recoverable
0.075
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved lead, calculated with assumed 25 mg/I hardness, and
hen converted to total with EPA partition translator based on
assumed 10 mg/I TSS (revised 2013).
Magnesium
32
mg/I
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Manganese
N/A
mg/I
No benchmark. See Rationale Document.
MBAS (Methylene Blue Active
0.5
mg/I
NC Water Quality Standard 15A NCAC 02B .0121 for Water Supply
Substances)
Systems (WS-1) (aesthetic standard to prevent foaming)
Mercury
0.000012
mg/I
NC Water Quality Standard 15A NCAC 02B, bioaccumulative
(12 ng/L)
neurotoxin. Not always appropriate for stormwater benchmark if
et deposition influences.
Methanol
7,700
mg/L
% FAV (ECOTOX 3/07) (March 2007, J. Dent)
Methylene Chloride
110
mg/I
% FAV (N. Remington, 2/2009). Extremely common lab
contaminant; cross-check blanks on lab sheet data if there are hits.
Methyl Ethyl Ketone (MEK)
1,600
mg/L
% FAV ( ECOTOX 1/07) (March 2007, J. Dent)
Methyl Methacrylate
96
mg/I
% FAV (N. Remington, 2/2009).
Molybdenum
510
mg/I
/: FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn)
Naphthalene
1
mg/I
% Lowest Observed Effect Level (LOEL); EPA's 1980 Water Quality
Criteria for naphthalene
Nickel, total recoverable
0.335
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved nickel, calculated with assumed 25 mg/I hardness, and
hen converted to total with EPA partition translator based on
assumed 10 mg/I TSS (revised 2013).
Nitrate + Nitrite (NO3+NO2)
10
mg/I
National Primary Drinking Water Regulation in 40 CFR 141.11 and
15A NCAC 213 for nitrate (Expressed in mg/I of N).
Nitrogen, Total Kjeldahl (TKN)
20
mg/L
BPJ, based on approximate equivalency to secondary treatment of
,wastewater (expressed in mg/I of N).
Nitrogen, Total
30
mg/I
TKN + Nitrate + Nitrite Benchmarks (Expressed in mg/I of N).
Non -polar Oil and Grease, Method
15
mg/I
Targets petroleum -based hydrocarbons with silica gel treatment step
1664 SGT-HEM (Estimate of Total
and hexane extraction. Value based on review of other states'
Petroleum Hydrocarbons, or TPH)
maximum daily benchmark concentrations. Equal to one half x [O&G
benchmark]. See Rational Document.
Oil and Grease
30
mg/I
BPJ, Based on wastewater permit limits. Consider "Non -polar 0&G"
instead if targeting petroleum hydrocarbons (e.g., vehicle maint.)
Polychlorinated Biphenyls (PCBs)
"There shall be no
ug/L
The aquatic life standard is 0.001 ug/L. The detection limits for
discharge of
Arochlors 1016, 1221, 1232, 1242, 1248, 1254, 1260, and 1262 are 1
polychlorinated
ug/L. Because we cannot quantify PCBs below the detection limit,
biphenyl
any detection is considered an exceedance of the benchmark. (C.
compounds."
Brower on 8/2010.)
Pentachlorophenol
0.019
mg/I
% FAV @ pH 7.8, CIVIC from EPA's 1995 Update to Ambient Water
Quality Criteria for Pentachlorophenol

NC DEMLR Stormwater Benchmark Rationale and Guidance Document
November 1, 2013
Page 15 of 16
Parameter
Benchmark Conc.
Units
Source
pH (min, max)
6-9
S.U.
Water Quality Standard (Note Swamp waters can be as low as 4.3,
but still expect stormwater discharges to fall in neutral range, unless
acid rain influence.) Measured in standard units.
Phenol (Trout)
4.5
mg/I
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Note — 0.3 mg/L may exhibit an organoleptic effect. (Note: There
as previously a non -trout phenol value. K. Johnson removed it on 8
June 2007 after discussion with C. Brower and J. Dent. It had been
set from only one data point.)
Phosphorous, Total
2
mg/l
BPJ, based on wastewater permit limits for NSW waters.
Selenium
0.056
mg/I
/ FAV based on Selenite and 1986 Study on Se impacts in NC. [July
1986; Report No. 86-02: NC Water Quality Standard Documentation:
The Freshwater Chemistry and Toxicity of Selenium With Emphasis
on its Effects in North Carolina. (Only in print)]
Silver, total recoverable
0.0003
mg/I
% FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved silver, calculated with assumed 25 mg/I hardness, and
hen converted to total with EPA partition translator based on
assumed 10 mg/I TSS (revised 2013, typo corrected 1111812013).
Sodium
865
mg/l
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Based on limited data; consult DWR Planning Section.
Sodium Sulfate
125
mg/I
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Based on limited data; consult DWR Planning Section.
Styrene
1.5
mg/I
N. Remington, 2/2009
Sulfate
500
mg/l
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Based on limited data; consult DWR Planning Section. (Note: There
as previously a water supply value; removed in June 2007 after
discussion with C. Brower and J. Dent.)
-butyl Alcohol
3,200
mg/L
% FAV (ECOTOX 3/07) (J. Dent March 2007)
hiram
0.2
ug/l
% FAV (N. Remington, 7/2009)
0.002
mg/l
Toluene (Non -Trout)
0.055
mg/l
From NC 2B Std. (11 ug/1), based on April 1986 DWQ Internal Report:
N.0 Dept. N.R.C.D., Division of Environmental Management. No-
e ect chronic levels or aquatic toxicit : Organic compounds found
near Ashland Chemical Site in Ralei h NC.
Toluene (Trout)
0.0018
mg/I
From NC 2B Trout Std. (0.36 ug/1), based on April 1986 DWQ Internal
Report: N.0 Dept. N.R.C.D., Division of Environmental Management.
No -effect chronic levels for aquatic toxicity: Organic compounds
found near Ashland Chemical Site in Raleigh, NC.
Total Petroleum Hydrocarbons
15
mg/l
Based on review of other states' maximum daily benchmark
(TPH) (see also "Non -polar O&G")
concentrations. See Rationale Document.
Turbidity
50
ntu
NC Aquatic Life Standard
Turbidity — Lakes and Saltwaters
25
ntu
NC Aquatic Life Standard, Lakes/Reservoirs, saltwaters
urbidity — Trout
10
ntu
NC Aquatic Life Standard, Trout (Tr) waters
SS (Total Suspended Solids)
100
mg/I
National Urban Runoff Program (NURP) study from 1983.
SS — ORW, HQW (incl. Tr, PNA)
50
mg/l
Based on one-half the standard benchmark of 100 mg/l.
Uranium
Facility -Specific
mg/l
See the Rational Document
Vinyl Acetate
9.0
mg/l
N. Remington, DWQ, 2/2009. Based on limited data; consult DWR
Planning Section.
Xylenes, total
6.7
mg/I
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
m-Xylene
8
mg/l
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
o-Xylene
4.03
mg/l
% FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).

NC DEMLR Stormwater Benchmark Rationale and Guidance Document
November 1, 2013
Page 16 of 16
Parameter
Benchmark Conc.
Units
Source
p-Xylene
4.2
mg/I
/: FAV derived from EPA's ECOTOX Database (Feb 2005, J. Wynn).
Zinc, total recoverable
0.126
mg/I
Y2 FAV; EPA's National Recommended Water Quality Criteria (Acute)
or dissolved zinc, calculated with assumed 25 mg/I hardness, and
hen converted to total with EPA partition translator based on
ssumed 10 mg/I TSS (revised 2013).