NCG240000_Draft Permit Fact Sheet to Notice_20220513

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: March 18, 2022
Entire permit organization has changed to improve the usability of the permit.
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 and
SIC 2879). SIC 2875 is fertilizers, mixing only, but the definition includes composting operations. Similarly, SIC
2879 is pesticides and agricultural chemicals, not classified elsewhere, but the definition includes soil
conditioners of which compost can be considered one. 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). Coverage is also
applicable to stormwater point source discharges from like industrial activities deemed by the Division of
Energy, Mineral, and Land Resources (DEMLR) to be similar to these operations in the process, or the
discharges, or the exposure of raw materials, intermediate products, by-products, products, or waste
products.
Except upon DEMLR 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:
DEMLR has determined that limited DEMLR 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 areal extent. although the small Type 1 facilities are captured by the NPDES rules, DEMLR
intends to continue to regulate the small yard waste facilities on a substantiated complaint basis,
rather than a state-wide blanket approach via the General Permit. In January 202Z it was confirmed
by DWM that these facilities do not require a permit, but must complete a notification process that
also includes annual notification.
• Backyard composting and on -farm composting as described in 13B .1402(g). Rationale: These facilities
are not captured by NPDES regulations and are not subject to permitting required under those
regulations.
• Composting operations classified in 13B .1402(f) as Type 4 Facilities and large Type 3 Facilities.
Rationale: DEMLR's judgment is that this subsector processes feedstocks of greater potential for
water quality impacts, and consequently should be permitted under the increased scrutiny attendant
with individual permits, rather than under the General Permit. The Division has allowed some large
Type 3 and Type 4 facilities when circumstances were appropriate (ex. Only having a stormwater
discharge, and no wastewater).
• Composting operations for residuals management as described in regulations administered by DWR
and found at 15A NCAC 2T .1100. Rationale: DEMLR's judgment is that this subsector processes
feedstocks of greater potential for water quality impacts, particularly with respect to the potential for
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NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
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, SA 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.
Mulching only operations are not regulated by NCG240000. Where mulching operations are co -
located at composting facilities and function to provide feedstocks to composting operations, they
are included with rest of the composting operations, and are subject to regulation by NCG240000.
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 SIC 2875, compost mixing and 2879, manufacturing soil conditioners, part of Major Group 28, and is
subject to NPDES stormwater permitting. SIC 2875 is fertilizers, mixing only, but the definition includes
composting operations. Similarly, SIC 2879 is pesticides and agricultural chemicals, not classified elsewhere,
but the definition includes soil conditioners of which compost can be considered one. 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 the following: 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.
In accordance with NC General Statute 143-214.7A, "stormwater is water that does not contact anything
considered a feedstock, intermediate product, or final product of composting operations". Water that
contacts any of these items would be considered process wastewater. It should be noted that later in this
same statute, a Type 1 solid waste compost facility shall not be required to obtain a National Pollutant
Discharge Elimination System (NPDES) permit for discharge of process wastewater based solely on the
discharge of stormwater that has come into contact with feedstock, intermediate product, or final product
at the facility. For purposes of that G.S., "Type 1 solid waste compost facilities" are facilities that may receive
yard and garden waste, silvicultural waste, untreated and unpainted wood waste and any combination
thereof.
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 resulting from the
manufacturing process activities and from contact with on -site materials can be highly variable in pollutant
strength.
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During initial permit development in 2011, DWQ (now DEMLR) reviewed two published studies of untreated
compost discharges, as well as pollutant monitoring results collected under three DWQ (now DEMLR)
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 Appendices A and B for a tabulation of compost site monitoring data. Appendix A
includes 1998-2009 data and Appendix B includes 2014-2021 data. Absent larger and more differentiated
data set, DWQ concluded that the following categories of pollutants may potentially appear in both
stormwater and wastewater discharges associated with composting activities.
1. BOD COD: These measures of oxygen demand were highly variable. The highest were reported at levels
several times greater than general characterizations of raw sewage. As stated earlier in this factsheet, in
accordance with NC General Statute 143-214.7A, "stormwater is water that does not contact anything
considered a feedstock, intermediate product, or final product of composting operations". Water that
contacts any of these items would be considered process wastewater. It should be noted that later in
this same statute, a Type 1 solid waste compost facility shall not be required to obtain a National
Pollutant Discharge Elimination System (NPDES) permit for discharge of process wastewater based
solely on the discharge of stormwater that has come into contact with feedstock, intermediate product,
or final product at the facility. For purposes of that G.S., "Type 1 solid waste compost facilities" are
facilities that may receive yard and garden waste, silvicultural waste, untreated and unpainted wood
waste and any combination. Examination of monitoring data appear to indicate that the majority (all?) of
the compost facilities covered under NCG24 are Type 1 and not monitoring for process wastewater.
BOD5 has been required to be monitored in process wastewater, but not stormwater. With no facilities
monitoring process wastewater, there are no data to indicate whether BOD5 is occurring at
concentrations of concern. For this next permit cycle BOD5 will be added to the stormwater monitoring
discharge, so that there will be BOD5 stormwater discharge data to examine.
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 and Enterococcus: 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. 2013 Benchmarks Rational document recommends Enterococcus monitoring.
4. Nitrojzen/TKN/NO3-NO2/NH3: 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. More recent data indicate only a
few TN exceedances.
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. More recent data
also indicate several TP exceedances above the benchmark.
6. Metals - Cu, Pb, Zn: DWQ found limited data even within the limited data set 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. DEMLR reviewed 2014-2021 stormwater discharge data
from about ten composting facilities permitted under NCG24. Please see Appendix B at the end of this
factsheet. At all the facilities examined, Pb was either below the benchmark value or not detected and
Zn was only detected above the benchmark value twice. Data support removing Pb and Zn monitoring
from the permit. Another reason to remove Zn monitoring is because background Zn levels sometimes
cause problems at facilities. Cu monitoring will remain in the permit because there were several
instances of stormwater discharges with Cu levels above the benchmark.
7. Non Polar Oil & grease: Limited data, but Non -Polar Oil and Grease was incorporated as a standard
monitoring parameter for all SDOs, not just those with vehicle or equipment maintenance areas. With
this change, we have removed the separate monitoring requirements for outfalls only associated with
vehicle/equipment maintenance areas.
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NCG240000 Fact Sheet - Composting General Permit
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8. pH.. The limited data included some pH values outside North Carolina Water Quality Standards range, but
most values were within water quality standards.
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 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 site specific, and the degree of the impact of the moderating
factors has not been quantifiable.
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 DEMLR, 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, SA 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) are not
eligible for coverage under this General Permit. SA waters was added to this list because it is a more highly
sensitive classification that was previously omitted. DEMLR 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.
CONSTRUCTING AND OPERATION OF A TREATMENT FACILITY
An "Authorization to Construct" (ATC) permit for new or expanding wastewater treatment facilities was once
required by 15A NCAC 02H .0100 for the construction and operation of water pollution control facilities necessary
to comply with NPDES permit conditions. That authorization was incorporated into the NCG240000 General Permit
to streamline the permitting process. In 2011, Session Law 2011-394, Section 9 eliminated the ATC requirement for
industrial wastewater treatment facilities.
Also now absent from the revised General Permit is the authorization to construct and operate a Closed -Loop
Recycle System (CLRS) that meets the requirements of the 15A NCAC 02T .1000 Rules. (Requirements for these
recycle systems are driven by a State program and were not impacted by SL 2011-394s changes to the State
Statute.) Facilities that construct and operate CLRS facilities must apply and obtain the necessary permits or
approvals through the Non -Discharge Permitting Program in the Division of Water Resources (DWR). This change
was prompted by the Stormwater Permitting Program's move out of DWR into DEMLR and helps ensure
appropriate Division oversight of these systems. Systems not designed as closed -loop and have the potential to
discharge to surface waters are still covered by NCG240000.
The Session Law did not remove authority for the Division to require that permittees notify the DEMLR Regional
Office in advance of operation of newly installed or expanded wastewater treatment facilities. This directive
remains a condition of this proposed permit (Part K - Permit Administration, K-3 - Planned Changes). The rationale
is that this notification alerts NC DEQ of potentially significant changes to wastewater discharges and allows the
opportunity for an inspection to verify compliance with the NPDES permit.
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NCG240000 Fact Sheet - Composting General Permit February 23, 2022
3. PROPOSED DISCHARGE CONTROLS AND LIMITATIONS
a. Stormwater Pollution Prevention Plan
As in the previous version of this General Permit, stormwater pollution must be controlled by the development
and implementation of a Stormwater Pollution Prevention Plan (SWPPP). DEMLR continues to believe that
effective control of the pollutant content in industrial stormwater discharges can only be achieved when site
management implements a written, site -specific management plan serving that objective. The revised draft permit
contains several minor improvements in the SWPPP largely related to improved clarity of language in the permit
text. See the draft permit for the proposed new version of the SWPPP requirements. All facilities covered under
this General Permit must develop and implement an SWPPP.
b. Qualitative (Visual) monitoring of stormwater discharges
As in previous versions of this General Permit, the permittee must perform quarterly qualitative (visual) monitoring
at all stormwater discharge outfalls. The proposed revised permit requires visual monitoring to coincide with
analytical monitoring.
c. Stormwater discharges from vehicle maintenance areas (VMA)
In the previous version of this General Permit and like most other industrial general permits, permittees were
required to separately monitor stormwater discharges originating from site areas where vehicle maintenance
activities are conducted. With this renewal, Non -Polar Oil and Grease was incorporated as a standard monitoring
parameter for all SDOs, not just those with vehicle or equipment maintenance areas. With this change, we have
removed the separate monitoring requirements for outfalls only associated with vehicle/equipment maintenance.
DEMLR's view continues to be that monitoring discharges from qualifying vehicle maintenance areas contributes
to the prevention of stormwater pollution from those activities.
d. Stormwater discharge analytical monitoring
As in the previous version of this General Permit, all permittees must perform quarterly analytical monitoring of
the stormwater discharges, must respond to any exceedances of the numerical benchmark values for the
monitored parameters, must keep records of the monitoring results and the permittee's response actions, and
must report the monitoring results to DEMLR. As before, the permittee has the option of applying and obtaining
Representative Outfall Status (ROS) for one or more outfalls to reduce the obligation to monitor all stormwater
discharge outfalls (SDOs) on site. ROS designation is handled outside of the permit and is not available for
wastewater outfalls.
The renewal permit maintains the analytical monitoring requirements for all stormwater discharge outfalls
associated with industrial activity. As mentioned in the previous section, the following change has been made to
the analytical monitoring requirements: Non -Polar Oil and Grease was incorporated as a standard monitoring
parameter for all SDOs, not just those with vehicle or equipment maintenance areas. With this change, we have
removed the separate monitoring requirements for outfalls only associated with vehicle/equipment maintenance.
e. Numerical benchmarks and tiered response structure
As in the previous version of this General Permit, the permittee must respond to benchmark exceedances with
increased monitoring, increased management actions, increased record keeping, and/or the installation of
stormwater BMPs in a tiered program. The exceedance of a numerical benchmark is not considered a violation of
the permit conditions, although failure to respond as per the Tiered response structure would be. In that context,
the benchmark value is not a numerical 'permit limit', but rather a management action level value. It provides
guidelines to enable site management's continuing and responsive implementation of a facility's Stormwater
Pollution Prevention Plan (SWPPP). Four (4) benchmark exceedances require the permittee to notify the DEMLR
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NCG240000 Fact Sheet - Composting General Permit
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Regional Office and may prompt additional requirements under provisions of Tier Three. See Appendix C for
identification of the basis for the numerical benchmark values applicable in this General Permit.
f. Wastewater discharge analytical monitoring and limitations
The draft permit specifies monitoring and reporting requirements for process wastewater discharges. DEMLR 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, DEMLR 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 final product and did not address feedstocks and other in -process materials. DEMLR considers that
those other materials give rise to process wastewater discharges per the federal definition cited above.
DEMLR has sought to identify under what circumstances a discharge from the final product at a compost facility
may be permitted as a wastewater discharge, or a stormwater discharge. In 2010, DEMLR 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 DEMLR 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, DEMLR 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, DEMLR 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, Enterococus, BOD5, and pH. 2013 Benchmark Rational document recommends Enterococcus monitoring
for discharge to saltwaters. The General Permit requires quarterly sampling. DEMLR 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.
DEMLR 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 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
This General Permit specifies monitoring and reporting requirements for both qualitative (visual) and quantitative
(analytical) assessment of the stormwater discharges, and operational inspections of the entire facility. Sample
parameters and sample frequency are based upon pollutants potentially generated from composting operations as
reported in the literature and in on -site monitoring reports from current DEMLR permittees.
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NCG240000 Fact Sheet - Composting General Permit February 23, 2022
The draft permit proposes specific monitoring requirements for the following parameters for stormwater
discharges: TSS, COD, BODS, fecal coliform, Enterococcus, total nitrogen, total phosphorus, total copper, pH, Non
Polar Oil and Grease, and total rainfall.
As stated earlier in the factsheet, examination of monitoring data appear to indicate that the majority (all?) of the
compost facilities covered under NCG24 are Type 1 and not monitoring for process wastewater. BODS has been
required to be monitored in process wastewater, but not stormwater. With no facilities monitoring process
wastewater, there are no data to indicate whether BODS is occurring at concentrations of concern. For this next
permit cycle BODS will be added to the stormwater monitoring discharge, so that there will be BODS stormwater
discharge data to examine.
In addition, DEMLR reviewed 2014-2021 stormwater discharge data from about ten composting facilities permitted
under NCG24. Please see Appendix B at the end of this factsheet. At all the facilities examined, Pb was either
below the benchmark value or not detected and Zn was only detected above the benchmark value twice. Data
support removing Pb and Zn monitoring from the permit. Another reason to remove Zn monitoring is because
background Zn levels sometimes cause problems at facilities. Cu monitoring will remain in the permit because
there were several instances of stormwater discharges with Cu levels above the benchmark.
2013 Benchmark Rational document recommended Enterococcus monitoring, so it has been added to this permit
for facilities discharging to saltwater. Since compost facilities are not allowed to discharge to SA waters, this
monitoring will only pertain to facilities discharging to SB or SC waters.
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: DEMLR 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 DEMLR that not all labs will receive samples
on weekends.)
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 DEMLR's other stormwater discharge permits.
The draft General Permit includes quarterly monitoring for stormwater discharges. Quarterly sampling is now
required in most of the other General Permits and is also more common in the individual stormwater permits
issued by DEMLR's Stormwater Permitting Unit. Rationale: DEMLR 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 might one month contain windrows; and later in the season might contain bagged
and shrink-wrapped product, • and later might contain just bare ground. DEMLR judges that these changes in
function and configuration can have a significant impact on the pollutant discharges from subdrainage areas at the
facility. Quarterly sampling is appropriate on composting sites given the potential for a very fluid site configuration
over relatively short time periods. It is also a way for the site manager to be alerted to how changes in site
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NCG240000 Fact Sheet - Composting General Permit
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activities and configuration maybe related to the pollutants discharged from his site. Additionally, compost
industry representatives have indicated that DEMLR'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
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 discharge" (in the case of extended
drought), or like explanation. DEMLR'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.
In addition, outfalls not sampled during the first measurable storm event in the monitoring period shall be sampled
during the next measurable storm event in the monitoring period until a sample has been collected. If during the
entire monitoring period, there is no discharge from an outfall during any measurable storm event then the
permittee shall report "No discharge" in the DMR.
For stormwater only discharges, the draft permit provides that the permittee may petition DEMLR 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.
The permit section exempting basins or ponds designed to contain the 25-year, 24-hour storm without discharging
that can regain capacity to hold such an event within five (5) days' time through means other than discharge to
surface waters from analytical monitoring has been removed. If designed and operated properly, these ponds
would likely only discharge during very heavy rainfall events that could be considered adverse weather events in
which case monitoring would not be required. If there was heavy rainfall during a nonadverse weather event, it
may be valuable to get the stormwater discharge monitoring data in those cases.
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 on site monitoring reports from current DEMLR 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: BODS, TSS, fecal coliform, Enterococcus, Nonpolar Oil and Grease, pH, and total flow.
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.
S. 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
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thereafter on an annual basis. Secondary containment, as specified in Section B-9 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 Section B-9 of this permit shall be accomplished
prior to the beginning of discharges from the operation of the industrial activity.
6. SPECIAL CONDITIONS WHICH WILL HAVE A SIGNIFICANT IMPACT ON THE DISCHARGE
There are no proposed special conditions in the draft general permit.
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 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
Page 9 of 21

NCG240000 Fact Sheet — Composting General Permit February 23, 2022
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 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).
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NCG240000 Fact Sheet - Composting General Permit February 23, 2022
8. 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.
THE ADMINISTRATIVE RECORD
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 Energy, Mineral and Land Resources
1612 Mail Service Center
Raleigh, North Carolina 27699-1612
The above documents are available for review and copying at:
Archdale Building, 6`" Floor
Stormwater Permitting Branch
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. DEMLR 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: Paul Clark at [phone]. Email:
paul.clark@ ncdenr.gov
11. SCHEDULE OF PERMIT ISSUANCE
Draft Permit Public Notice -Statewide notice published 2022;
Draft available on DWQ website 2022;
Comment Period Ends 2022.
Permit Scheduled to Issue -June 30, 2022 (Effective July 1, 2022).
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.
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:
Page 11 of 21

NCG240000 Fact Sheet - Composting General Permit February 23, 2022
Stormwater Permitting Unit
Division of Energy, Mineral and Land Resources
1612 Mail Service Center
Raleigh, North Carolina 27699-1612
Attn: Paul Clark
[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 12 of 21

NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
APPENDIX A
DWQ Report to the Compost Stakeholder Advisory Group
Revised 4/19/2010
DWQ Report to the Compost Operation Stakeholder Advisory Group,
DWQ 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
01, 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, (mg/L)
0.61,
0.42,
0.46
<0.10
0.34, 0.14
0.012,
12-50
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
m /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 Engineering, 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.
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NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
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
10,000,000
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 14 of 21

NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
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 15 of 21

NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
Clean Washington Center study data'
Published January 2000
Yard debris'2 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 16 of 21

NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
Oregon study by CH2M Hill 1
Published May 2004
Compost
Leachate2
Compost
Runoff3
Compost
Stormwater°
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
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NCG240000 Fact Sheet - Composting General Permit February 23, 2022
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.
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NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
In most cases a single test value is the basis for establishing a wastewater permit
limit violation.
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 BOD5.
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
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NCG240000 Fact Sheet - Composting General Permit February 23, 2022
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
period. The SPU does 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 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 CoRper benchmark is 0.007 mg/L, and is based on 1/2 FAV reported in EPA's
National Recommended Water Quality Criteria, 2006.
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NCG240000 Fact Sheet - Composting General Permit
February 23, 2022
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.
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 21 of 21