NCG240000_Final Revised Factsheet_20111208

DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WATER QUALITY
FACT SHEET
GENERAL PERMIT NCG240000
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM
PERMIT TO DISCHARGE STORMWATER AND WASTEWATER
Permit No. NCG240000 Date: February 10, 2011
(Revised September 29, 2011; December 8, 2011)
1. TYPES OF DISCHARGES COVERED
a. Industrial Activities Covered by this General Permit
Coverage under the NCG240000 General Permit is applicable to owners or operators of
both stormwater and process wastewater discharges associated with activities
classified as compost manufacturing, SIC 2875. Coverage is limited to those facilities
classified as large Type 1, Type 2, and small Type 3 composting operations as described
in regulations administered by the North Carolina Division of Waste Management
(DWM) and found at 15A NCAC 13B .1402(f).
In addition, the Division of Water Quality (DWQ) may require coverage under the
General Permit for stormwater and process wastewater discharges from like industrial
activities deemed by DWQ to be similar to composting operations in the process, or the
discharges, or the exposure of raw materials, intermediate products, by-products,
products, or waste products.
Except upon DWQ determination of similarity as provided immediately above, the
following activities and associated discharges are excluded from coverage under the
General Permit:
• Composting operations classified in 15A NCAC 13B .1402(g) as small Type 1
Facilities. Rationale: DWQ has determined that limited DWQ resources might
achieve better state-wide protection of water quality by first focusing on the other
portions of the industry with more problematic feedstocks or larger physical
extent. Although the small Type I facilities are captured by the NPDES rules, DWQ
intends to regulate the small yard waste facilities on a substantiated complaint
basis, rather than a state-wide blanket approach via the General Permit for at
least the first five year permit cycle.
• Backyard composting and on -farm composting as described in 13B .1402(g).
Rationale: These facilities are not captured by the NPDES regulations, and are not
subject to the permitting required under those regulations.
• Composting operations classified in 13B .1402(f) as Type 4 Facilities and large
Type 3 Facilities. Rationale: DWQ s judgment is that this subsector processes
feedstocks ofgreater potential for water quality impacts, and consequently should
be permitted under the increased scrutiny attendant with individual permits,
rather than under the General Permit,
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NCG240000 Fact Sheet - Composting General Permit February 10, 2011
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Composting operations for residuals management as described in regulations
administered by DWQ and found at 15A NCAC 2T .1100. Rationale: DWQ's
judgment is that this subsector processes feedstocks ofgreater potential for water
quality impacts, particularly with respect to the potential for the concentration of
heavy metals, and consequently should be permitted under the increased scrutiny
attendant with individual permits, rather than under the General Permit.
Composting operations with discharges to especially protected receiving waters
classified as ORW, HQW, trout waters, PNA waters, areas with special water
quality management strategies established in North Carolina rules at 15A NCAC
2B .0200, and zero -flow streams as described in 15A NCAC 2B .0206. Rationale:
North Carolina rules include prohibitions on waste discharges to some of these
receiving water classifications. In general, all of these classifications deserve the
extra administrative attention and regulatory protection available through the
individual permitting process, rather than though the General Permit.
Stand-alone mulching -only operations are not regulated by NCG240000.
Where mulching operations are co -located at composting facilities and
function to provide feedstocks to the composting operations, they are
included with the rest of the composting operations, and are subject to
regulation by NCG240000. (Added 911412011 per public comment.)
Generally, composting operations that are not eligible for coverage under the General
Permit may apply for separate coverage under an individual stormwater discharge
permit and an individual wastewater discharge permit.
b. Types of Operations Covered
Basis for coverage: The federal NPDES program rules at 40CFR122.26(b)(14) specifically
define the industrial activities that are subject to regulation for storm water discharges
associated with industrial activity. These rules at 40CFR122.26(b)(14)(ii) and (xi)
capture all of SIC Major Group 28. Composting is a listed industrial activity in SIC2875,
part of Major Group 28, and is subject to NPDES stormwater permitting. The General
Permit covers all on -site activities and features associated with the compost
manufacturing activity. Covered industrial activities and site features may include, but
are not limited to: scales, receiving, staging, grinding, screening, rejects piles, storage,
composting, turning, aeration, moisture addition, curing, blending, packaging, labeling,
warehousing, loading, and other related on -site manufacturing activities. Also covered
are stormwater runoff flows from on -site vehicle and equipment maintenance areas.
c. Characteristics of Discharged Stormwater and Wastewater
The composting process might be described as accelerated biological decomposition of
organic materials. Basic process control parameters include temperature, moisture
content, particle size, aeration rate, bulk porosity, feedstock selection, salts content, and
carbon to nitrogen ratio. Feedstocks vary greatly across the industry, and can include
leaves, wood chips, grass clippings, pre -consumer food wastes, post -consumer food
wastes, manures, sludges, septage, and specialized industrial wastes. The flows
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NCG240000 Fact Sheet - Composting General Permit February 10, 2011
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resulting from the manufacturing process activities and from contact with on -site
materials can be highly variable in pollutant strength.
DWQ reviewed two published studies of untreated compost discharges, as well as
pollutant monitoring results collected under three DWQ stormwater permits previously
issued to composting operations. The very limited data set available, along with the
inherent high variability of feedstocks, do not allow for a single definitive
characterization of the pollutant concentrations in discharge flows. However, several
categories of pollutants consistently appeared at high levels in the literature, in
permittee monitoring, or in independent DWQ testing at compost manufacturing sites.
See Appendix A for a tabulation of compost site monitoring data. Absent a larger and
more differentiated data set, DWQ concludes that the following categories of pollutants
may potentially appear in both stormwater and wastewater discharges associated with
composting activities.
BODJCOD: These measures of oxygen demand were highly variable. The highest
were reported at levels several times greater than general characterizations of raw
sewage.
2. TSS: The highest levels of TSS were similarly reported at levels well above raw
sewage, and well above the stormwater permitting benchmark for North Carolina.
3. Fecal coliform/E. coli: While reported bacteriological contamination was not as
high as raw sewage, it was still reported as several orders of magnitude greater than
North Carolina water quality standards.
4. Nitrogen JTKNIN03-NO2JNH3: Again, highly variable results. In one published
study, ammonia, an especially problematic form of nitrogen in the aquatic
environment due to its toxicity, was reported at levels many times greater than
general characterizations of raw sewage.
5. Phosphorus: Again, reported at levels several times greater than general
characterizations of raw sewage, and well beyond the North Carolina stormwater
discharge benchmark value.
6. Metals - Cu. Pb. Zn. Al. Fe. K: DWQ found limited data even within the limited data
set we reviewed. For Cu, Pb, and Zn there were some reports of discharge levels
above the stormwater discharge benchmark values for North Carolina. Industry
representatives reported to DWQ that woody feedstocks can sequester metals, and
are a probable source in discharged flows.
7. Oil & grease: Limited data.
8. pH.. The limited data included some pH values below North Carolina Water Quality
Standards, but most values were within water quality standards.
9. Conductivity JTDS/salts content: Limited data. At one North Carolina site high
conductivity was implicated in observed impacts to the receiving water.
Despite the potential for high absolute concentrations of pollutants in compost site
discharges, two aspects of the discharges may serve to moderate the impact on
receiving waters. First, discharges are typically associated with rain events. This
means that the delivery of pollutants is not typically continuous, and that receiving
waters may have the benefit of increased flows and increased pollutant dilution at the
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NCG240000 Fact Sheet - Composting General Permit February 10, 2011
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time of discharge. Second, industry representatives report that for many composting
sites, and under good conditions, small rain events may be substantially absorbed by
the composting materials, reducing the discharge volume. These moderating factors
are of course very site specific, and the degree of the impact of the moderating factors
has not been quantifiable.
A consistent element in other DWQ stormwater discharge permits has been the
additional focus at industrial sites on vehicle and equipment maintenance activities.
Where these activities are present to a significant degree, DWQ imposes stormwater
monitoring for total petroleum hydrocarbons (TPH), total suspended solids (TSS), and
pH. DWQ believes that the monitoring and control of stormwater discharges from
those activities continues to benefit and improve water quality in North Carolina.
d. Geographic Area Covered by this General Permit
Discharges covered by this general permit are located at any place within the political
boundary of the State of North Carolina. However, discharges located on the Cherokee
Indian Tribal Reservation are subject to permitting by the U.S. Environmental
Protection Agency, rather than NC DWQ, and are not eligible for coverage under this
General Permit.
e. Receiving Waters
As suggested by the potential pollutant strengths noted above, composting operations
directly or indirectly discharging to especially protected receiving waters (receiving
waters classified as ORW, HQW, trout waters, PNA waters, areas with special water
quality management strategies established in North Carolina rules at 15A NCAC 2B
.0200, and zero -flow streams as described in 15A NCAC 213.0206) are not eligible for
coverage under this General Permit. DWQ believes that while exceptions to this
prohibition may be warranted on a case -by -case basis, individual permits should be
strongly preferred for such facilities.
2. AUTHORIZATION TO CONSTRUCT AND OPERATE A TREATMENT FACILITY
North Carolina rules in 15A NCAC2H.0138 provide for DWQ to issue an Authorization to
Construct (ATC) upon satisfactory review of final plans and specifications for the construction
and operation of water pollution control facilities necessary to comply with the terms and
conditions of an NPDES permit. For this General Permit, DWQ will implement the ATC
review when treatment facilities for process wastewater are included in the applicant's
application for coverage under NCG240000. The ATC review will be performed
concurrently with the review of the NOI application to allow the discharge of process
wastewater. Final plans and specifications will be a requirement of a complete application.
Note: Session Law 2011-394 was enacted on July 1, 2011. It amended G.S. 143-215.1,
and directed that no Authorization to Construct permit may be required for industrial
wastewater treatment discharges already covered under an existing discharge permit.
DWQ has amended draft NCG240000 to comply with this requirement of law by
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NCG240000 Fact Sheet - Composting General Permit February 10, 2011
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excluding existing facilities from the ATC requirement previously in the draft version of
the permit since they will be covered by the permit before it is reasonable to expect
development of plans for treatment facilities. However, for new facilities seeking
coverage under NCG240000, we note that the law is applied conditionally to those
facilities already covered by a discharge permit, and new composting facilities will not
meet this condition. (Added 911412011 in response to the revisions to G.S. 143-215.1)
Further Note (added 12LB120111: In further development in response to the
requirements of SL 2011-394 Section 9, DWQ has determined to eliminate the ATC
review and requirement from our procedures and permit, irrespective of whether the
composting facility qualifies as an existing facility or a new facility.
3. PROPOSED DISCHARGE CONTROLS AND LIMITATIONS
Stormwater Discharges
Benchmark concentrations: Rationale: DWQ s permitting program strategy addresses the
potential to pollute. Permittees must be able to demonstrate that on -site industrial materials
are not reaching receiving waters or becoming water pollutants, and must be able to show
that pollutant loads from on -site industrial runoff are not increased above levels of concern.
DWQ s methodology for achieving this is through scheduled self -monitoring by each
permittee. The General Permit requires quarterly monitoring, and incorporates benchmark
concentrations for Stormwater discharges in order to provide compost facilities with a tool
with which to assess the effectiveness of best management practices (BMPs). The
benchmark concentrations are not effluent limits, but provide guidelines to enable site
management's continuing and responsive implementation of a facility's Stormwater
Pollution Prevention Plan (SPPP or Plan). Numerical exceedences of benchmark values
require the permittee to increase monitoring, increase management actions, increase
record keeping, and/or install stormwater BMPs in a tiered program. Four (4) benchmark
exceedences trigger notification to the DWQ Regional Office and may prompt additional
requirements (Tier 3). DWQ has been phasing in the benchmark and tiered permit
structure for industrial stormwater permits since 2007. See Appendix B for identification
of the bases for the numerical benchmark values applicable in this General Permit.
Stormwater Pollution Prevention Plan: Rationale: DWQ's perspective is that the
permittee's effective control of the pollutants potentially present in industrial site runoff
cannot occur without a deliberate management plan that serves that specific objective. The
General Permit requires the permittee to develop and implement a written plan to manage
and control the discharge of pollutants in the stormwater flows leaving the site. The
particular requirements are detailed in the permit text, but in summary the required
elements of the plan are as follows.
Site Plan: a description of the physical facility and the pollutant sources that have
the potential to contribute to contamination of stormwater discharges. At a
minimum the site plan includes:
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(a) A general location map showing the facility's location in relation to
transportation routes and surface waters, and whether each receiving water
is impaired or is located in a watershed for which a TMDL has been
established, and what the parameter(s) of concern are.
(b) A narrative description of the on -site industrial activities and a description of
the potential pollutants that could be expected to be present in the
stormwater discharge from each outfall.
(c) A site map drawn at a scale sufficient to clearly depict the physical features
and location of industrial activities.
(d) A list of significant spills or leaks of pollutants, as well as any wastewater
treatment unit bypasses, that have occurred during the previous three (3)
years and any corrective actions taken to mitigate the impacts. (Bypasses
added 912912011).
(e) And, annual certification that the stormwater outfalls have been evaluated
for the presence of non-stormwater discharges.
Stormwater Management Plan: a description of the materials management practices
employed which control or minimize the exposure of significant materials to
stormwater. At a minimum, the stormwater management plan includes:
(a) A feasibility study that reviews the economic and technical feasibility of
changing the methods of operation or physical configuration of the site in
order to reduce or eliminate the generation of highly contaminated
stormwater and wastewater discharges.
(b) A list of the required secondary containment structures provided for bulk
storage of liquid materials; storage of Section 313 water priority chemicals;
and storage of hazardous substances, in order to prevent leaks and spills
from contaminating stormwater runoff.
(c) A BMP summary section identifying all BMPs and the rationale for their
implementation on site.
(d) A rain gauge and record of daily rainfall amounts.
3. Spill Prevention and Response Plan: an assessment of potential pollutant sources
based on a materials inventory of the facility. It shall detail the permittee's spill
prevention and spill response preparations and actions.
4. Preventative Maintenance and Good Housekeeping Program: including schedules of
inspections, preventative maintenance, and housekeeping measures along with
records evidencing implementation.
5. Annual Employee Training: for the prevention of stormwater and wastewater
pollution.
6. Identification: of the on -site person responsible for implementation of the SPPP.
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NCG240000 Fact Sheet - Composting General Permit February 10, 2011
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7. Requirement to amend the Plan: whenever there is a change affecting the potential
for the discharge of pollutants to surface waters.
8. Requirement for regular facility inspections.
9. Requirement to implement the Plan.
Process Wastewater Discharges
Rationale: DWQ relies primarily on the definition of process wastewater found in the NPDES
federal regulations at 40CFR122.2, 'Process wastewater means any water which, during
manufacturing or processing, comes into direct contact with or results from the production or
use of any raw materials, intermediate product, finished product, byproduct, or waste
product." In addition, DWQ received an informal opinion in 2010, from the state's Attorney
General's Office concluding that discharges from final product at a compost manufacturing
facility meet the federal NPDES definitions of both wastewater discharges and stormwater
discharges. The Attorney General's Office opinion was confined to finished product, and
did not address feedstocks and other in -process materials. DWQ considers that those other
materials give rise to process wastewater discharges per the federal definition cited above.
DWQ has determined to identify under what circumstances a discharge from the final product
at a compost facility may be permitted as a wastewater discharge, or instead a stormwater
discharge. In 2010, DWQ enlisted the assistance of DWM to develop a new criterion for
presumptively identifying the polluting potential for the final product produced by a
composting operation, and to presumptively distinguish wastewater flows from
stormwater flows. The term 'finished compost' has been adopted by DWM and DWQ, and is
used in the General Permit to identify final products that have reached a higher degree of
degradation and completion of the composting process. In the permitting process, DWQ
will presumptively consider that stormwater discharges arise from contact with 'finished
compost.' Not all final products produced at a compost facility go to the same end user
market. Some final products can be delivered to the customer in less time, at less cost, and
at a lesser degree of degradation. That means that more organic and nutrient pollution
potential remains in the compost final product, compared to more mature 'finished
compost.' In the permitting process, DWQ will presumptively consider that flows
originating from contact with these less effectively composted final products give rise to
process wastewater discharges.
Process wastewater discharges are subject to effluent limitations for the conventional
pollutants of TSS, fecal coliform, BODS, and pH. The General Permit requires quarterly
sampling. DWQ considered that unlike many wastewater flows from other industrial
activities, flows from composting operations are likely to be intermittent and to be
associated with sporadic rainfall events.
DWQ intends that if our presumptive determination that a flow should be permitted as a
stormwater does not lead to the permittee's effective control of pollutant discharges from
any particular site, we may on a case -by -case basis revisit that presumptive determination
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to assess whether such a flow might be more effectively controlled if re-classified as a
process wastewater discharge, in accordance with the more inclusive scope of the
40CFR122.2 definition of process wastewater.
4. MONITORING AND REPORTING REQUIREMENTS
Stormwater Discharges
The draft General Permit specifies monitoring and reporting requirements for both
quantitative and qualitative assessment of the stormwater discharge, and operational
inspections of the entire facility. Specific pollutant parameters for which sampling must be
performed and the frequency of the sampling are based upon the pollutants potentially
generated from composting operations as reported in the literature and in site monitoring
reports from current DWQ permittees. See section 1 c. above for a summary of pollutants
potentially present at a composting operation.
The draft permit proposes specific monitoring requirements for the following parameters
for stormwater discharges: TSS, COD, fecal coliform, total nitrogen, total phosphorus, total
copper, total lead, total zinc, pH, total petroleum hydrocarbons (vehicle maintenance areas
only), and total rainfall.
The draft permit incorporates a modified definition of a representative storm event,
different from the definition used in most other stormwater General Permits. NCG240000
requires only a 48-hour period of no or little precipitation (less than 0.1 inch) instead of the
standard 72-hour period that must precede a representative storm event required in most
other stormwater permits. Rationale: DWQ considered the different nature of most
composting operations when compared to most other industrial manufacturing facilities, in
that typically the source of exposure is expansive, and that successive rains may not readily
deplete the pollutant sources: we judge that the source and concentration of the potential
pollutants should differ little if collected from a rain event following a two-day, rather than a
three-day dry period. Further, we judge that the quarterly sampling requirement may be
more readily complied with by the permittee if the three-day dry period constraint were
reduced to just two days. This revised definition may also provide more opportunities to
collect samples earlier in the work week, making hold time constraints on fecal coliform
samples less of a concern for lab pick-up and analysis schedules. (Compost industry
representatives have advised DWQ that not all labs will receive samples on weekends.)
The draft General Permit includes quarterly monitoring for stormwater discharges. Most
other stormwater General Permits include semi-annual sampling. Quarterly sampling is
more common in the individual stormwater permits issued by DWQ's Stormwater
Permitting Unit. Rationale: DWQ considered the different nature of most composting
operations, when compared to other industrial manufacturing facilities, in that typically the
compost manufacturing activity is largely, or wholly, exposed to precipitation. Further,
typically to a large degree the footprint of compost manufacturing activities is not
constrained by fixed walls that limit the configuration of site activities. A portion of the site
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might one month contain windrows; and later in the season might contain bagged and
shrink-wrapped product, and later might contain just bare ground. DWQ judges that these
changes in function and configuration can have a significant impact on the pollutant
discharges from subdrain age areas at the facility. We judge that quarterly sampling is
appropriate on composting sites given the potential for a very fluid site configuration over
relatively short time periods. Quarterly sampling is a way for the site manager to be alerted
to how changes in site activities and configuration may be related to the pollutants
discharged from his site. Additionally, compost industry representatives have indicated
that DWQ's permitting process might be informed and improved by more data on which to
assess the industry's pollutant discharges and consequent impact on North Carolina
receiving waters. DWQ concurs, and our intent is that after the first five-year permit cycle,
DWQ will review the collected quarterly data and will revisit the quarterly sampling
requirement, and assess its usefulness for site management and control of pollutant
discharges.
The General Permit specifies qualitative (visual) monitoring of each stormwater outfall for
the purpose of evaluating the effectiveness of the Stormwater Pollution Prevention Plan
and assessing new sources of stormwater pollution. Qualitative monitoring parameters
include color, odor, clarity, floating and suspended solids, foam, oil sheen, erosion or
deposition, and other obvious indicators of stormwater pollution. Qualitative monitoring is
a consistent feature of DWQ's other stormwater discharge permits.
The General Permit requires reporting the monitoring results on Discharge Monitoring
Forms (DMR). The permit text also provides that the permittee may be excused from
stormwater monitoring during extended periods of adverse weather, AND upon submittal
of a DMR with the notation, "No Flow This Period" (in the case of extended drought), or like
explanation. DWQ's practice in the past under other stormwater General Permits has been
to advise permittees that failure to monitor due to extended drought throughout the entire
monitoring period; or due to discharges only available from dangerous thunderstorms,
hurricanes, or tropical storms; or due to discharges only available from night-time storms
have all been excused. On the other hand, we do not consider that rainfall occurring only
on weekends is a sufficient impediment to excuse failure to monitor during the monitoring
period.
For stormwater only discharges, the draft permit provides that the permittee may petition
DWQ for reduction in the sampling requirements when four consecutive quarters show
analytical results below benchmark values. This provision for a 'step-down' in the
sampling frequency for any parameter will be provisional: Any subsequent result that
exceeds the benchmark value will re -instate the quarterly frequency.
Wastewater Discharges
The draft General Permit specifies monitoring and reporting requirements for quantitative
assessment of the wastewater discharge. Specific pollutant parameters for which sampling
must be performed and the frequency of the sampling are based upon the pollutants
potentially generated from composting operations as reported in the literature and in site
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monitoring reports from current DWQ permittees. See section 1 c. above for a summary of
pollutants potentially present at a composting operation.
The draft permit proposes specific monitoring requirements for the following conventional
parameters for wastewater discharges: BOD, TSS, fecal coliform, pH, and total flow. The
process wastewater permit limits are taken from federal rule for the minimum level of
effluent quality attainable by secondary treatment as established in 40CFR133.102.
(Added 911412011 in response to a verbal question during the permit public notice
period.)
Unlike stormwater discharges, a monitoring value for these wastewater discharge
parameters higher than the permit limit constitutes a violation of the terms and conditions
of the permit.
5. COMPLIANCE SCHEDULE
The draft permit text establishes the following schedule:
Existing facilities already operating, but applying for coverage under this General
Permit for the first time: The Stormwater Pollution Prevention Plan shall be
developed and implemented within 12 months of the effective date of the initial
Certificate of Coverage issued pursuant to this General Permit and updated
thereafter on an annual basis. Secondary containment, as specified in Part I1,
Section A, Paragraph 2(b) of this permit, shall be accomplished within 12 months of
the effective date of the initial Certificate of Coverage.
New facilities applying for permit coverage for the first time and existing facilities
previously permitted and applying for renewal under this General Permit: All
requirements, conditions, limitations, and controls contained in this permit become
effective immediately upon issuance of the Certificate of Coverage. The Stormwater
Pollution Prevention Plan shall be developed and implemented prior to the
beginning of discharges from the operation of the industrial activity and be updated
thereafter on an annual basis. Secondary containment, as specified in Part I1,
Section A, Paragraph 2(b) of this permit shall be accomplished prior to the
beginning of discharges from the operation of the industrial activity.
Additionally, several commenters in the public comment period noted that
existing facilities would be in violation of the permit upon issuance of the COC,
and that a specific compliance schedule contained in the permit would serve to
provide time for existing facilities to come into compliance. DWQ concurs with
the comments and has amended NCG240000 with a compliance schedule.
(Added 911412011 in response to public comment.)
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Outside of the draft hermit text.
For the first five-year permit cycle only, DWQ proposes to implement the permitting
program for all existing facilities by establishing a programmatic requirement that all
existing facilities must apply for the appropriate DWQ water quality permit not later than
July 1, 2012. Existing composting facilities otherwise eligible for the General Permit would
receive coverage under the General Permit. Composting facilities operating under a DWM
composting permit as of January 1, 2011 will be considered existing facilities. This
programmatic schedule requirement does not appear in the General Permit text.
Similarly for new facilities, DWQ will use the same programmatic implementation date of
January 1, 2011 as the differentiation between new and existing facilities. Proposed
facilities not operating under a DWM composting permit on that date must apply for the
appropriate DWQ water quality permit before discharges from the site may be authorized.
6. SPECIAL CONDITIONS WHICH WILL HAVE A SIGNIFICANT IMPACT ON THE
DISCHARGE
There are no proposed special conditions in the draft general permit.
7. BASIS FOR CONTROLS AND LIMITATIONS
Stormwater Discharges
The conditions of this general permit has been designed using best professional judgment
to achieve water quality protection through compliance with the technology -based
standards of the Clean Water Act (Best Available Technology [BAT] and Best Conventional
Pollutant Control Technology [BCT]). Where the Director determines that a water quality
violation is occurring and water quality -based controls or effluent limitations are required
to protect the receiving waters, coverage under the general permit may be terminated and
an individual permit may be required. Based on a consideration of the appropriate factors
for BAT and BCT requirements, and a consideration of the factors discussed below in this
fact sheet for controlling pollutants in stormwater discharges associated with the activities
as described in Item 1 (Types of Discharge Covered), this permit contains a set of
requirements for developing and implementing stormwater pollution prevention plans,
and specific requirements for monitoring and reporting on stormwater discharges.
The permit conditions reflect the Environmental Protection Agency's (EPA) and North
Carolina's pollution prevention approach to stormwater permitting. The quality of the
stormwater discharge associated with an industrial activity will depend on the availability
of pollutant sources. This permit reflects the Division's position that implementation of
Best Management Practices (BMPs) and traditional stormwater management practices
which control the source of pollutants meets the definition of BAT and BCT. For
stormwater discharges the permit conditions are not numeric effluent limitations, but
rather are designed to be flexible requirements for developing and implementing site
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specific plans to minimize and control pollutants in the stormwater discharges associated
with the industrial activity.
Title 40 Code of Federal Regulations (CFR) Part 122.44(k)(2) authorizes the use of BMPs in
lieu of numeric effluent limitations in NPDES permits when the agency finds numeric
effluent limitations to be infeasible. The agency may also impose BMP requirements which
are "reasonably necessary" to carry out the purposes of the Act under the authority of 40
CFR 122.44(k)(3). The conditions of the renewal permit are based on the authority of both
of these regulatory provisions. The pollution prevention requirements (BMP
requirements) in this permit operate as limitations on effluent discharges that reflect the
application of BAT/BCT. The basis is that the BMPs identified require the use of source
control technologies which, in the context of these general permits, are the best available of
the technologies economically achievable (or the equivalent BCT finding).
All facilities covered by this General Permit must prepare, retain, implement, and (at a
minimum of annually) update a stormwater pollution prevention plan. The term "pollution
prevention" distinguishes this source reduction approach from traditional pollution control
measures that typically rely on end -of -pipe treatment to remove pollutants in the
discharges. The plan requirements are based primarily on traditional stormwater
management, pollution prevention and BMP concepts, providing a flexible basis for
developing site -specific measures to minimize and control the amounts of pollutants that
would otherwise contaminate the stormwater runoff.
The pollution prevention approach adopted in the stormwater pollution prevention plans
in this permit focuses on two major objectives: 1) to identify sources of pollution
potentially affecting the quality of stormwater discharges associated with industrial
activity from the facility; and 2) to describe and ensure that practices are implemented to
minimize and control pollutants in stormwater discharges associated with industrial
activity from the facility and to ensure compliance with the terms and conditions of the
permit.
The Division believes that it is not appropriate, at this time, to require a single set of
effluent limitations or a single design or operational standard for all facilities which
discharge stormwater associated with industrial activity. This permit instead establishes a
framework for the development and implementation of site -specific stormwater pollution
prevention plans. This framework provides the necessary flexibility to address the variable
risk for pollutants in stormwater discharges associated with the industrial activities that
are addressed by this permit, while ensuring procedures to prevent stormwater pollution
at a given facility are appropriate given the processes employed, engineering aspects,
functions, costs of controls, location, and age of facility (as discussed in 40 CFR 125.3). This
approach allows flexibility to establish controls which can appropriately address different
sources of pollutants at different facilities.
In 1979, EPA completed a technical survey of industry best management practices (BMPs)
which was based on a review of practices used by industry to control the non -routine
discharge of pollutants from non -continuous sources including runoff, drainage from raw
Page 12 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
material storage areas, spills, leaks, and sludge or waste disposal. This review included
analysis and assessment of published articles and reports, technical bulletins, and
discussions with industry representatives through telephone contacts, written
questionnaires and site visits. The technical survey identified two classes of pollution
control measures.
The first class of controls are those management practices which are generally considered
to be essential to the development of an effective and efficient BMP program, low in cost,
and applicable to broad categories of industries and substances. These controls include the
following: developing a Spill Control Committee and implementing spill reporting, material
inventorying and compatibility reviews, employee training, visual inspections, preventative
maintenance programs, good housekeeping, and addressing security issues. These
practices are broadly applicable to all industries and can be implemented by each facility
independent of the category of industry, ancillary sources, specific chemicals used at
different sites, and/or plant site locations. The survey concluded that these controls should
be minimum requirements for any effective BMP program.
The second class of controls includes management practices which provide for a second
line of defense against the release of pollutants. These controls include prevention
measures, containment measures, mitigation and cleanup measures and treatment
methods. The types of chemicals, industrial operations and various ancillary sources
specify the controls applicable to an individual facility.
The EPA and NPDES States have, on a case -by -case basis, imposed BMP requirements in
NPDES permits. The EPA has also continued to review and evaluate case studies involving
the use of BMPs and the use of pollution prevention measures associated with spill
prevention and containment measures for oil. The development of the NPDES permit
application requirements for stormwater discharges associated with industrial activity
resulted from the evaluation and identification of the potential contaminants and the
resultant water quality impacts of stormwater discharges from industrial sites. Public
comments received during the rule making provided additional insight regarding
stormwater risk assessment, as well as appropriate pollution prevention and control
measures and strategies. During that time EPA again reviewed stormwater control
practices and measures. These experiences have shown the Division that pollution
prevention measures such as BMPs can be appropriately used and that permits containing
BMP requirements can effectively reduce pollutant discharges in a cost-effective manner.
BMP requirements are being appropriately imposed in general permits in lieu of numeric
effluent limitations pursuant to 40 CFR 122.44(k)(2).
B. REQUESTED VARIANCES OR ALTERNATIVES TO REQUIRED STANDARDS
There are no requested variances or alternatives to required standards. Facilities
requesting variances to required standards will not be covered under this General Permit
but will instead be required to seek coverage under an individual permit.
Page 13 of 24

NCG240000 Fact Sheet - Composting General Permit
9. THE ADMINISTRATIVE RECORD
February 10, 2011
(Revised 9/29/2011; 12/8/2011)
The administrative record, including the draft permit, fact sheet, public notice, comments
received, and additional information is available by writing to:
Stormwater Permitting Unit
Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
The above documents are available for review and copying at:
Archdale Building, 9th Floor
Surface Water Protection Section
Stormwater Permitting Unit
512 N. Salisbury Street
Raleigh, North Carolina
between the hours of 8:00 AM and 5:00 PM Monday through Friday. Copies will be
provided at DWQ's currently established estimate of the cost of reproduction.
10. DWQ CONTACT
Additional information about the draft permit may be obtained at the above address
between the hours of 8:00 AM and 5:00 PM Monday through Friday by contacting: Ken
Pickle at [phone]. Email: [e-mail]
11. SCHEDULE OF PERMIT ISSUANCE
Draft Permit Public Notice - Statewide notice published February 8, 2011;
Draft available on DWQ website February 8, 2011;
Comment Period Ends March 18, 2011.
Permit Scheduled to Issue - April 1, 2011 (Effective May 1, 2011).
12. PROCEDURE FOR THE FORMULATION OF FINAL DETERMINATIONS
a. Comment Period
The Division of Water Quality proposes to issue an NPDES General Permit for the above
described stormwater and process wastewater discharges subject to the outlined
controls, limitations, benchmarks, management practices, and special conditions. These
determinations are open to comment from the public.
Page 14 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
Interested persons are invited to submit written comments on the General Permit or on
the Division of Water Quality's proposed determinations to the following address:
Stormwater Permitting Unit
Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Attn: Ken Pickle
[e-mail]
All comments received within thirty days following the date of public notice are
considered in the formulation of final determinations.
b. Public Meeting
The Director of the Division of Water Quality may hold a public meeting if there is a
significant degree of public interest in a proposed permit or group of permits. Public
notice of such a meeting will be circulated in newspapers in the geographical area of the
discharge and to those on the Division of Water Quality mailing list at least thirty days
prior to the meeting.
c. Appeal Hearing
An applicant whose permit is denied, or is granted subject to conditions he deems
unacceptable, shall have the right to a hearing before the Commission upon making
written demand to the Office of Administrative Hearing within 30 days following
issuance or denial of the permit.
d. Issuance of a Permit When No Hearing is Held
If no public meeting or appeal hearing is held, after review of the comments received,
and if the Division of Water Quality determinations are substantially unchanged, the
permit will be issued and become effective on the first day of the month following the
issuance date. This will be the final action of the Division of Water Quality.
If a public meeting or appeal hearing is not held, but there have been substantial
changes, public notice of the Division of Water Quality revised determinations will be
made. Following a 30-day comment period, the permit will be issued and will become
effective on the first day of the month following the issuance date. This will be the final
action of the Division of Water Quality unless a public meeting or appeal hearing is
granted.
Page 15 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
APPENDIX A
DWQ Report to the Compost Stakeholder Advisory Group
Revised 4/19/2010
DWO Report to the Compost Operation Stakeholder Advisory Group,
DWO Report #3: Data characterizing runoff from composting facilities
February 15, 2010
In response to: In our first stakeholder meeting in December 2009, stakeholders requested that DWQ provide
any available data relevant to our current posture on water quality permitting in the composting industry. DWQ
accepted that homework assignment, and provides the following data summaries for discussion in the February
17, 2010 meeting.
Mecklenburg Co. Compost Central (Type 1 feedstock)
DWQ stormwater permit #NCS000382
DMR Data 2002, 2003, 2007, 2008, 2009
2002
2003
20071
20081
2008
2009
Raw
(outfalls
(outfalls
(outfall
(outfall
(outfalls
(outfalls
sewage
O1 02)
01 02)
01
02
01 02
01 02
range*
Biological Oxygen
14.3,
22.3,
28
3.6
19,
130,
110-400
Demand, BOD
50.8
31.4
32
90
m /L
Chemical Oxygen
486, 244
842, 247
270
98
700,
480,
250-1000
Demand, COD
310
290
m /L
Fecal coliform,
44,000,
170,000
1600
300,000,
93,000
1,000,000-
#/100 ml
43,000
74,000
5,900
10,000,000
Ammonia,
0.61,
0.42,
0.46
<0.10
0.34, 0.14
0.012,
12-50
m /L
0.10
0.77
0.12
TKN (mg/L)
15,
19,
5.9
2.0
8.2,
7.0,
5.3
5.8
6.6
3.3
Nitrate + Nitrite
0.14,
0.24,
0.15
0.16
0.48,
<0.05,
m /L
0.59
0.25
7.0
<0.05
Phosphorus
3.61,
10.4,
2.5
0.11
3.6,
4.2,
4-15
(mg/L)
1.76
1.95
1.7
2.8
-
6.38
6.5
6.75 (02)
PH (SU)
(02)
14
<5.0
6.6,
<6.0
Oil &Grease
6.3
(mg/L)
49
2.6
290,
89,
100-350
Total Suspended
110
23
Solids, TSS
(mg/L)
* Wastewater Enoineerina, Third Edition, Metcalf and Eddy, 1991, p.109-110.
1 Drought conditions in late 2007 prevented the collection of a sample from outfall #02. Compost Central
successfully collected a sample in early 2008, for the year 2007, from outfall #02.
Page 16 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
Brooks Farm Composting Facility (Type 3 feedstock)
DWQ stormwater permit #NCS000371
Permit Application and DMR Data
19981,
2000
20012
20033,
Raw sewage
1999
(two
2004
range*
events
Biological Oxygen
160,
250
<11,
482,
110-400
Demand, BOD m /L
130
<14
122
Chemical Oxygen
1220,
1360
3130,
4040,
250-1000
Demand, COD
1600
372
1960
m /L
Fecal coliform,
>600,000
>1600
164,000,
82,000,
1,000,000 -
(#/100 ml)
13x10e6
6500
206,000
10,000,0
00
Ammonia, (mg/L)
-
91.3
69,
11.3,
12-50
104
15
96.5
TKN (mg/L)
156,
119
157,
175,
87.1
29.2
158
Nitrate + Nitrite
124,
14.9
32.8,
17.3,
m /L
91.5
21.4
15.8
Phosphorus (mg/L)
1.19,
0.96
1.5,
3.5,
4-15
1.75
0.7
1.1
7.6,
7.9
7.7,
7.6,
pH (SU)
7.6
7.1
7.62
<5.0
Oil &Grease (mg/L)
-
57
28,
518,
100-350
Total Suspended
-
114
204
Solids, TSS (mg/L)
* Wastewater Engineering, Third Edition, Metcalf and Eddy, 1991, p.109-110.
1 This 1998 data was submitted with the initial permit application. Samples were received at the laboratory at 13
degrees C, instead of required 6 degrees C; consultant directed the lab to complete the analyses, and the
applicant submitted the data.
2 Drought conditions in the next year, 2002, prevented collection of discharge samples.
3 A second sampling event in 2003 is not reported in this data set because the consultant reported that he
sampled from a ditch on site, rather than from a discharging flow.
Page 17 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
Wallace Farm Composting Facility (Type 3 feedstock)
DWQ stormwater permit #NCS000525
DMR Data
Dec
June
Raw sewage
2008
2009
range
Biological Oxygen
5
7.1
110-400
Demand, BOD m /L
Chemical Oxygen
153
101
250-1000
Demand, COD m /L
Fecal coliform,
2200
6000
1,000,000 -
#/100 ml
10,000,000
Ammonia, m /L
12-50
TKN m /L
4.9
Nitrate + Nitrite
0.98
m /L
Phosphorus m /L
1.1
0.59
4-15
7.8
6.7
pH (SU)
Oil &Grease (mg/L)
400
510
100-350
Total Suspended
Solids, TSS (mg/L)
* Wastewater Engineering, Third Edition, Metcalf and Eddy, 1991, p.109-110.
Sun Gro Composting Facility (Type 2 feedstock)
No DWQ permits
DWQ Sampling Data
August 19, 2009
Upstream
on Knobs
Creek
Outlet
ditch 1
Outlet
ditch 2
Downstream
on Knobs
Creek
Water
Quality
Standards
for Knobs
Creek*
Dissolved Oxygen
m /L
1.7
0.73
0.28
1.02
4.0
H
6
5.2
7
5.8
6-9
Fecal coliform
#/100m1)
540
6000
(TNC)
6000
(TNC
1400
400
BOD m /L
3
1500
42
3.1
COD m /L
59
5600
1500
95
Ammonia m /L
0.51
2.9
18
0.47
TKN m /L
1.9
38
91
2.4
Conductivity
241
3197
1396
184
Phosphorus (mg/L)
0.33
30
47
0.6
TSS (mg/L)
23
44
75
17
*North Carolina Administrative Code Title 15A 213 .0211 Fresh Surface Water Quality Standards for Class C
Waters. Knobs Creek is a Class C Sw water. As such, the Class C water quality standards apply. The additional
classification of Sw denotes a swamp water classification, and some relaxation of water quality standards for pH
and for DO may apply, if based on natural conditions.
Page 18 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
Clean Washington Center study data'
Published January 2000
'Yard debris'Z contact
runoff3 range
Raw sewage range*
BOD m /L
390 - 32,000
110-400
COD m /L
250-1000
Fecal coliform,
#/100 ml
110 - 4,900,000
1,000,000 -
10,000,000
Ammonia, m /L
23 - 1600
12-50
TKN m /L
85 - 2600
Nitrate + Nitrite
m /L
Phosphorus m /L
10- 170
4-15
pH (SU)
Oil &Grease (mg/L)
TSS (mg/L)
2000 - 20,000
100-350
Copper (mg/L)
0.07 - 0.8
Potassium (mg/L)
170 - 4500
Zinc (mg/L)
0.1 - 1.5
* Wastewater Engineering, Third Edition, Metcalf and Eddy, 1991, p.109-110.
1 Compost Facility Requirements Guideline, British Columbia Ministry of Water, Land and Air Protection,
March 2004, p. 6-2. This guideline was produced to assist composters in complying with the British
Columbia Organic Matter Recycling Regulation, 2002. British Columbia cites the earlier work by the Clean
Washington Center, and reproduces their data in this Guideline.
The source documents are, Evaluation of Compost Facility Run off for Beneficial Reuse - Phase 1, and
same title - Phase 2, Clean Washington Center, January 2000.
2 The data here is reported as originating from 'yard debris composting ' sites; however it appears that the
British Columbia Ministry of Water, Land and Air Protection defines yard debris sites more broadly than
we do in North Carolina. The sites are described as: a large yard debris and food waste composter, a
yard debris site, a site composting manures and brush, and a zoo manure composting site.
3 In this Guideline British Columbia treats non -contact runoff as stormwater, and all other contact waters as
'leachate'.
Page 19 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
Oregon study by CH2M Hill 1
Published May 2004
Compost
Leachate2
Compost
Runoff3
Compost
Stormwater4
Raw sewage
range*
BOD m /L
>41
20 - 3200
4 - 940
110-400
COD m /L
56
250-1000
Fecal coliform,
# 100 ml
<0.02 -
50,000
200 -
24,000,000
12 - 400,000
E. Coli
1,000,000 -
10,000,000
Ammonia m L
0.44 - 34.3
0.43 - 1600
12-50
TKN m L
14 - 3000
Nitrate +Nitrite m L
0.96 - 120
0 - 8
Phosphorus m /L
0.07 - 9
4 - 170
0.57 - 250
4-15
PH (SU)
7.8
6.7 - 9.5
5.3 - 8.2
Oil &Grease (mg/L)
ND-23
TSS (mg/L)
1100 -
20,000
18 - 5000
100-350
Aluminum (mg/L)
0.33
Copper (mg/L)
0.033 - 0.82
ND - 0.45
Iron (mg/L)
0.57
Lead (mg/L)
0.01
0.02 -0.53
Potassium (mg/L)
2.7
170 - 4600
Zinc (mg/L)
0.11
0.1-1.5
ND-2.4
* Wastewater Engineering, Third Edition, Metcalf and Eddy, 1991, p.109-110.
1 Commercial Composting Water Quality Permit Development, prepared for Oregon DEQ Land Quality and
Water Quality Divisions, by CH2M Hill, May 12, 2004.
2 Data reported in this column is combined from Tables 2-2, 2-3, and 2-4 on pages 7-9. Several types of
facilities are represented in the data, including facilities receiving yard waste, food waste, and manure.
3 Data reported in this column is combined from Tables 2-5 and 2-6 on pages 11-12 from several types of
facilities receiving yard waste, food waste, and manure. Note that in the Oregon study, `runoff' is a non-
specific catch all description of the ultimate disposal of the fluids, not a description of the source of the
fluids. Runoff is specifically defined in the study as potentially containing stormwater, process
stormwater, leachate, and washwater.
4 Data reported in this column is from Table 2-7 on page 13. This is data from multiple years of sampling
at a green feedstock' site (yard debris, wood waste, vegetative food waste) in Oregon. We note that the
table is labeled "Stormwater Data", but it is not clear from the study whether this data is from what North
Carolina would call, `non -contact' stormwater only, or whether it includes both of the Oregon categories of
Stormwater (non -contact) and Process Stormwater (contact). North Carolina currently considers contact
flows (Oregon's Process Stormwater) as wastewater.
END
Page 20 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
APPENDIX B
Discussion of Benchmark Values
a) An explanation of the benchmarks concept in stormwater permitting
(This information was originally compiled for the Monitoring Committee of the
Compost Operation Stakeholders Advisory Group, and was presented to the
Committee on June 6, 2010.)
Many permittees are familiar with wastewater permit limits, but not all permittees
have experience with stormwater permit benchmarks. The use of permit limits and
permit benchmarks is widespread throughout DWQ's permitting programs. It may
be useful to generally compare and contrast these two types of numerical triggers in
DWQ permits.
• A test value greater than a wastewater permit limit is a violation of the terms and
conditions of the wastewater permit. DWQ may issue a Notice of Violation, and the
permittee is subject to enforcement action for that violation. The permittee must
subsequently act to prevent a recurrence of the violation.
A test value greater than a stormwater permit benchmark is not a permit violation.
The 'exceedence' of the benchmark is intended to prompt the permittee: to
acknowledge the high result, to investigate the cause or source, to evaluate whether
economically feasible and environmentally effective response actions are available,
and if so to implement those response actions in order to bring subsequent test
results below the benchmark.
DWQ assumes a different perspective for these two numerical triggers. A
wastewater permit limit may be viewed as a numerical performance requirement
on the permittee.
A stormwater permit benchmark is intended to be an aid to effective site
management in order to reduce the pollutant content in stormwater runoff.
DWQ would rarely grant relief based on a permittee's assertion that he cannot
reasonably achieve a wastewater permit limit. Compliance with the wastewater
permit limit is required.
DWQ has in the recent past, and will in the future, grant relief from meeting
stormwater permit benchmarks when it is apparent that site circumstances so
dictate. The language authorizing this provision is in our standard template for
stormwater permits.
In most cases a single test value is the basis for establishing a wastewater permit
limit violation.
Page 21 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
DWQ's stormwater permit benchmarks are set up in a tiered system that only
involves DWQ intervention (management assistance) on the occasion of the fourth
test value exceedence. Even at that point, there is no permit violation based on the
exceedence of the stormwater benchmark.
b) Pending revisions to existing stormwater permit benchmarks
Stormwater benchmark values are derived from several sources, including North
Carolina's water quality standards. Those standards and the methodology for
calculating them undergo a periodic review within DWQ and by EPA Region IV. The
Triennial Review is currently in progress, and is not expected to be complete by the
time this General Permit will be published in final form.
DWQ expects that three benchmark values in this General Permit will be affected
upon completion of the Triennial Review.
o We anticipate that the copper benchmark will be revised upward from the
current benchmark value of 0.007 mg/L to 0.0105 mg/L.
o We anticipate that the lead benchmark will be revised upward from the
current benchmark value of 0.03 mg/L to 0.126 mg/L.
o We anticipate that the zinc benchmark will be revised upward from the
current benchmark value of 0.067 mg/L to 0.075 mg/L.
DWQ intends to implement the revised metals benchmarks within this General
Permit when the Triennial Review process is completed and the revised
benchmarks are finalized.
c) Technical basis for current stormwater permit benchmarks
The Total Suspended Solids (TSS) benchmark is 100 mg/L. The benchmark reflects a
median concentration from the 1983 National Urban Runoff Program (NURP) study. In
addition, the value is consistent with an equivalent secondary wastewater treatment level
for the wastewater discharge limit of 90 mg/L for lagoon systems.
The Chemical Oxygen Demand (COD) benchmark is 120 mg/L. A ratio of 4:1 has been
adopted as within the characteristic range for COD:BOD in domestic wastewaters. The
benchmark for BODs is based on the Secondary Treatment Regulation specified in the Code
of Federal Regulations, Title 40, Part 133 (40 CFR §133). This regulation defines the
minimum level of effluent quality attainable by secondary wastewater treatment as 30
mg/L for the 30-day average of BODs.
The Fecal Coliform benchmark is 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) provides 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
Page 22 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
period. The SPU does not consider these values practical for a stormwater benchmark. In
addition, the N.C. Standard, 2B .0211, specifies that violations of that standard "are
expected during rainfall events."
The Total Nitrogen benchmark is 30 mg/L. The benchmark for total nitrogen is the sum of
the (nitrate + nitrite) and TKN benchmarks. The National Primary Drinking Water
Regulation (40 CFR §141.11) specifies a maximum contaminant level of 10 mg/L nitrate.
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 benchmark for TKN (organic nitrogen) is based on an approximate equivalency to
secondary treatment of wastewater. This is reasonable, given that 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, justifies the use of a TKN
benchmark of 20 mg/L.
The Total Phosphorus benchmark is 2.0 mg/L, and is based on BPJ and is consistent with
wastewater permit limits imposed on NSW dischargers.
Total Copper, Total Lead, and Total Zinc benchmarks:
Because of the sporadic nature of rainfall, acute (short-term) effects are considered when
establishing stormwater benchmarks for toxicants. Toxicant benchmarks are set at one
half the Final Acute Value (1/2 FAV) for constituents like arsenic, chromium, cyanide, lead,
nickel, and silver. NCDENR uses the 1/2 FAV to set daily maximum wastewater limits for
toxicants in conjunction with weekly average limits. 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. EPA's recommended Criteria Maximum Concentrations [CMC = 1/2 FAV] are
based on dissolved criteria, but N.C. translates the values into total. Where metal values
are hardness -dependent, the value is based on a hardness of 50 mg/L.
The SPU recognizes that acute values for these metals are low, and that their toxicity is
highly variable (depending on the amount dissolved, which is affected by many factors).
One of the primary factors influencing toxicity for Cu and Zn is hardness. North Carolina
currently uses 50 mg/L hardness when calculating toxicity values for these metals. This
value is under review, however, and DWQ anticipates that the benchmark values for Cu, Pb,
and Zn may change in the future.
The Total Copper benchmark is 0.007 mg/L, and is based on 1/2 FAV reported in EPA's
National Recommended Water Quality Criteria, 2006.
The Total Lead benchmark is 0.03 mg/L, and is based on 1/2 FAV reported in EPA's 1980
Ambient Water Quality Criteria for Lead.
Page 23 of 24

NCG240000 Fact Sheet - Composting General Permit February 10, 2011
(Revised 9/29/2011; 12/8/2011)
The Total Zinc benchmark is 0.067 mg/L, and is based on 1/2 FAV and is converted to total
zinc from dissolved zinc as reported in EPA's National Recommended Water Quality
Criteria, 2006.
The pH benchmark is in the range of 6.0 - 9.0 standard units. The benchmark for pH is
based on water quality standards for freshwater classes, which specify a pH range of 6.0 -
9.0 standard units.
The Total Petroleum Hydrocarbons (TPH) benchmark is 15 mg/L. The TPH benchmark is
based on review of other states' maximum daily benchmark concentrations, and is equal to
one-half of the similar Oil & Grease benchmark. TPH is more specific for petroleum
hydrocarbons in that some of the fatty animal compounds are excluded from the analysis in
the lab preparation steps. We would expect only stormwater discharges with significant
oil contamination (ex. concentrated parking lot runoff) to exceed a 15 mg/L concentration.
END
Page 24 of 24