NCG02 Comments from US EPA

EPA Region 4 Comments on North Carolina's General NPDES Permit for Mineral Mining Discharges of
Wastewater and Stormwater(NCG020000)
1. Continuous discharges are required to have both maximum daily limits (MDL) and average monthly limits
(AML) in accordance with 40 CFR§ 122.45(d)(1).1
The additional limitations applicable to phosphate mines and industrial sand mines in Table 10 of the draft
permit show that the water quality-based effluent limits (WQBELs) expressed as an AML for total flouride and
chromium III are "TBD."
Unless impracticable,2 EPA recommends that the permit contain AML and MDL for all mining wastewater
discharges that are continuous, pursuant to the NPDES implementing regulations (similar to the parameters
listed in Table 8). In circumstances where the mining-related discharge is less than continuous, butthe discharge
occurs frequently enough such that the discharge may cause or contribute to chronic water quality impacts(i.e.,
a continuously intermittent duration), EPA recommends these discharges also have an AML and MDL.
EPA also notes that Table 10 contains a freshwater chromium III MDL that is likely equal to the arsenic saltwater
limit within Table 9. EPA requests that NCDEQ revise Table 10 with the appropriate effluent limit.
2. Water quality-based conditions are not subject to storm water discharges or outfalls with pond design
exemptions in accordance with the applicable industry specific mineral mining category within 40 CFR Part
436.
The draft permit provides monitoring exemptions for certain ponds designed for the 10-year, 24-hour storm
event and the 25-year, 24-hour storm events. Draft permit condition B-14 states that "only basins or ponds
designed to contain the 25-year, 24-hour storm event without discharging,and that can regain capacity to hold
such an event within five (5) days'time through means other than discharge to surface waters, may be exempt
from analytical monitoring requirements." Draft permit condition H-2(g)for wastewater discharges states that
"except for clay pits, grab sampling is not required for discharges from a basin/pond designed to contain or
treat mine dewatering wastewater which only discharges in response to rainfall in excess of the 10-yr, 24-hr
storm."
EPA recognizes that these treatment basins are designed to retain or treat the water from certain precipitation
events in order to keep them from discharging pollutants to a Waters of the United States,which may effectively
eliminate the outfalls as a point source during storm events below their design capacity. EPA also acknowledges
that certain mineral mines have effluent limit guidelines (ELG) precipitation exemptions for treatment basins
that are designed, constructed, and maintained to contain or treat the volume of water resulting from a 10-
year, 24-hr precipitation event.3The ELG exemptions are only available to the technology-based effluent limits
(TBEL) applicable to specific mineral mining subcategories, and do not apply to any WQBELs or water quality-
based monitoring that NCDEQ determined were appropriate to protect water quality standards (WQS).
1 40 CFR§ 122.45(d)(1):For continuous discharges all permit effluent limitations, standards, and prohibitions, including those necessary to
achieve water quality standards,shall unless impracticable be stated as:(1)Maximum daily and average monthly discharge limitations for all
dischargers other than publicly owned treatment works;and(2)Average weekly and average monthly discharge limitations for POTWs.
2 EPA notes that there are only a limited number of technical considerations that would make it "impracticable" or infeasible to develop
appropriate effluent limit expressions.
3 40 CFR§436.42(b)provides an example precipitation exemption that applies to TBELs for the industrial sand mining industry.

Given that the ELG-based monitoring exemption only applies to TBEL-limited parameters, EPA suggests that all
discharges with water quality-based conditions in the final permit, regardless of the pond holding capacity,
should not be subject to precipitation exemptions. Additionally, EPA recommends that the TBEL-related storm
exemptions should only be applied to those specific mineral mining subcategories allowed by the regulations
(See 40 CFR Part 436) unless a written determination is made in the fact sheet that applies precipitation
exemptions from certain mineral mining categories based on best professional judgement(BPJ).
EPA also notes that the exemption language in Section H-2(g) contradicts the requirements stated in Section 13-
14 which only exempts ponds designed to contain the 25-year, 24-hour storm without discharging to surface
waters. EPA suggests that this contradiction be revised in the final permit.
3. The final permit should contain the appropriate stormwater and wastewater turbidity limits to comply with
North Carolina's WQS and 40 CFR§ 122.44(d)(1)(iii).4
The North Carolina WQS state that the turbidity numeric criteria applicable to the receiving water body shall
not be increased if a turbidity exceedance occurs due to natural background conditions.5 For stormwater
discharges, Section F-5 of the draft permit states the permittees are allowed to sample during the next
measurable storm event after the discharge has been determined to be exceeding the applicable turbidity
criteria.
EPA acknowledges that in-stream turbidity levels increase during certain precipitation events; however,
compliance with effluent limitations should be based on the in-stream conditions at the time of effluent
sampling. Permit conditions that allow effluent sampling during a future precipitation event after a discharge
exceedance has occurred do not adequately ensure that WQS are not being exceeded because the future storm
event isn't representative of the initial storm event. EPA recommends that the turbidity limit be expressed as
an effluent limit as required by 40 CFR § 122.44(d)(1)(iii)to ensure compliance is achieved prior to mixing with
the receiving stream unless numeric effluent limitations are infeasible to calculate (see footnote 2). If NCDEQ
makes a written determination within the fact sheet that numeric effluent limits for turbidity are infeasible and
continues to use instream monitoring to support effluent conditions, EPA recommends that all effluent and in-
stream sampling be conducted contemporaneously. EPA notes that 40 CFR § 136 allows turbidity meters as an
acceptable measurement method that would allow for concurrent measurement of the discharge and stream.
Additionally, the turbidity monitoring requirements in Section F-5 of the draft permit allows the permittee to
collect and analyze a grab sample upstream and downstream of the discharge point to help determine
compliance with the permit's turbidity limits. The permit's use of "upstream" and "downstream" are vague
terms that can be widely interpreted by the permittee and likely do not adequately consider the full range of
conditions that ensure compliance with WQS. EPA recommends that if NCDEQ wants to use in-stream sampling
to help comply with effluent limitations, then the final permit should require more explicit and defensible
4 40 CFR 122.44(d)(1)(iii):When the permitting authority determines, using the procedures in paragraph (d)(1)(ii)of this section, that a
discharge causes,has the reasonable potential to cause,or contributes to an in-stream excursion above the allowable ambient concentration
of a State numeric criteria within a State water quality standard for an individual pollutant, the permit must contain effluent limits for
that pollutant.
s 15 NCAC 02B.0211(21) - The turbidity in the receiving water shall not exceed 50 Nephelometric Turbidity Units (NTU) in streams not
designated as trout waters and 10 NTU in streams,lakes,or reservoirs designated as trout waters;for lakes and reservoirs not designated as
trout waters, the turbidity shall not exceed 25 NTU; if turbidity exceeds these levels due to natural background conditions, the existing
turbidity level shall not be increased. Compliance with this turbidity standard can be met when land management activities employ Best
Management Practices (BMPs) [as defined by Rule .0202 of this Section] recommended by the Designated Nonpoint Source Agency [as
defined by Rule .0202 of this Section]. BMPs shall be in full compliance with all specifications governing the proper design, installation,
operation,and maintenance of such BMPs;

sampling locations that account for each facility's discharge and stream flow rate, or apply an appropriate
mixing zone.
EPA also notes that Sections F-5 (stormwater) and H-5 (wastewater) of the draft permit contain different
turbidity monitoring provisions. It is EPA's understanding that the turbidity monitoring requirements in Sections
F-5 and H-5 should be the same in the final permit.
4. NCDEQ should increase the monitoring frequency for wastewater discharges to a frequency sufficient to yield
data that is representative of the activity pursuant to 40 CFR§ 122.48(b)'and 40 CFR§ 122.41(j)(1).'
EPA notes that the monitoring frequency for both wastewater and stormwater discharges has been increased
to quarterly in this draft permit.
Given the highly variable nature of mining effluents in terms of discharge frequency, discharge duration, and
pollutant concentrations, EPA believes that quarterly monitoring is not sufficient to adequately account for the
monitored activity (mining wastewater discharges) in accordance with 40 CFR § 122.48(b) and 40 CFR §
122.41(j)(1). Increased monitoring frequencies allows for a more accurate characterization of the effluent and
protects water quality. EPA suggests increasing the monitoring frequency to 2/month or monthly for all
wastewater discharges. EPA's recommendation is especially applicable in circumstances where the outfall
discharges to high quality waters, water bodies with mining related impairments or total maximum daily loads
(TMDLs), or receiving waters with Endangered Species Act (ESA)-listed species or critical habitat.
EPA also notes that the NPDES regulations in North Carolina state that monthly sampling is the minimum
monitoring frequency required for turbidity, settleable matter, total suspended solids (TSS), and pH, and
quarterly is the minimum for toxics and toxicity for wastewater discharges at mining facilities with SIC codes
1400-1499 (15 NCAC 02B.0508(d)). It is EPA's understanding that all mining facilities covered by the general
permit are within the SIC codes listed in North Carolina's implementing regulations. Unless NCDEQ makes a
written determination that a monthly monitoring frequency is not applicable to the mineral mining industry as
required by North Carolina's regulations,' EPA suggests that the final permit contain the minimum monthly
monitoring for the pollutants listed within the NPDES implementing regulations in North Carolina.
5. Certain mineral mining industries should include effluent limits, benchmarks, or an additional explanation
that there is no reasonable potential to cause or contribute to an in-stream exceedance above a narrative or
numeric criteria within North Carolina's WQS consistent with 40 CFR§ 122.44(d)(1).
Chromium Limits for Stormwater Discharges
The draft permit contains chromium effluent limits for wastewater discharges from brick pits and industrial
sand mines (Tables 9 and 10), and chromium benchmarks for stormwater discharges from brick pits (Table 3).
It is unclear why reasonable potential for chromium was determined for both stormwater and wastewater
discharges from brick pits but only for wastewater discharges from industrial sand mines.
6 40 CFR§ 122.48(b): Required monitoring including type, intervals, and frequency sufficient to yield data which are representative of the
monitored activity including,when appropriate,continuous monitoring;
7 40 CFR§122.41(j)(1):Samples and measurements taken for the purpose of monitoring shall be representative of the monitored activity.
s 15 NCAC 02B.0508(b)(1):If any of the tests and measurements,sampling points,or frequency of sampling requirements,as required in this
Rule for a particular SIC group,are not applicable to the discharge of a particular water pollution control facility,or if it can be demonstrated
that the objectives of this Section can be achieved by other acceptable means,then such requirements may be waived or modified to the
extent that the Director determines to be appropriate.

EPA recommends that stormwater discharges from industrial sand mines also contain chromium benchmarks.
Alternatively, NCDEQ could provide an explanation in the fact sheet about how chromium does not have the
reasonable potential to cause or contribute to a violation of North Carolina's WQS in the stormwater discharge,
if that was the finding from the reasonable potential analysis (RPA) required by 40 CFR § 122.44(d)(1).
TSS Benchmarks for Stormwater Discharges
The stormwater effluent benchmarks in the draft permit for TSS are listed as 50 mg/L for all discharges to higher
quality waters and 100 mg/L for all other waters.The draft permit contains more stringent TSS limits for several
categories of higher quality waters at wastewater outfalls.
EPA suggests changing the TSS stormwater benchmarks to match the MDL for wastewater discharges to all
higher quality waters (HQW/ORW = 30 mg/L; Trout and PNA= 15 mg/L).9 This recommendation would ensure
that aquatic life is protected in certain high-quality waters during precipitation events that may cause acute
harm. Alternatively, NCDEQ could explain in the fact sheet why the less stringent TSS stormwater benchmarks
do not have the reasonable potential to cause or contribute to a violation of WQS in North Carolina.
pH Benchmarks for Stormwater Discharges
Table 8 establishes pH limits of 6.0—9.0 standard units (s.u.) for mine wastewater discharging to freshwater
and 6.8—8.5 s.u. for mine wastewater discharging to saltwater. The pH limitations provided in Tables 3 and 9
for wastewater discharges from brick pits to all receiving stream types is 6.0—9.0 s.u.Tables 8 and 9 appear to
be contradictory.
EPA recommends clarifying the pH requirements for brick pits discharging to salt water. If separate saltwater
limitations are not required for brick pits, further explanation should be provided in the fact sheet about
whether there is reasonable potential to cause or contribute to an exceedance of North Carolina's WQS for pH.
6. Additional limitations are required for discharges from phosphate mines and industrial sand mines pursuant
to40CFR§436.
The draft permit does not appropriately limit TSS in the wastewater effluent from phosphate mines in
accordance with the industry specific TBELs. Also, the draft permit may not appropriately limit TSS and total
fluoride in the wastewater effluent from industrial sand mines that use hydrofluoric acid (HF) floatation
treatment techniques pursuant to the mineral mining ELGs.
EPA suggests that the final permit have appropriate phosphate mining effluent limits for TSS to comply with 40
CFR § 436 subpart R10 or the applicable water quality criteria, whichever is more stringent. Similarly, EPA
recommends that the final permit contain the appropriate industrial sand mining effluent limits for TSS and
total flouride to comply with 40 CFR § 436 subpart D11 or the applicable water quality criteria, whichever is
more stringent.
9 The TSS limits for high quality waters for new and expanded discharges are based on 15A NCAC 026.0224(c)(2)(13).
i0 40 CFR§436.182 and 40 CFR§436.185 state that TSS shall be limited (MDL=60 mg/L;AML=30 mg/L)for the existing and new source
performance categories.
"40 CFR§436.42 states that TSS shall be limited(MDL=45 mg/L;AML=25 mg/L)for mine dewatering and facilities not using HF flotation.
Facilities using HF floatation must have TSS limits(MDL=0.046 Ib/1,000 lb of total product;AML=0.023 Ib/1,000 lb of total product)and
total flouride limits(MDL=0.006 Ib/1,000 lb of total product;AML=0.003 Ib/1,000 lb of total product).

7. NCDEQ should include an explanation in the fact sheet about how new and expanded discharges to high
quality waters from mineral mines conform with 15 NCAC 0213.0224 pursuant to 40 CFR§ 124.8(b)(4).12
Nutrients
North Carolina regulations require effluent limitations for phosphorus or nitrogen, or both,when nutrient over
enrichment is projected to be a concern (15 NCAC 02B.0224(c)(2)(F)). The draft permit does not include any
nutrient monitoring or limits for phosphate mining activities.
Phosphate mines can discharge nutrient related parameters. Nutrient effluent conditions are often found in
other NPDES permits within Region 4 states with phosphate mining facilities. EPA suggests including monitoring
or limits for nutrients from phosphate mining discharges to high quality waters with enrichment concerns, or
an explanation that the discharge will not cause or contribute to a numeric or narrative excursion above any
North Carolina WQS. Alternatively, NCDEQ can consider making a determination that there are no new or
expanded discharges from phosphate mines that will flow into any high-quality waters for which nutrient
enrichment is an issue.
Toxic Substances
North Carolina regulations require, in cases where complex wastes (those containing or potentially containing
toxicants) may be present in a discharge, an additional safety factor be applied to the discharge of toxic
substances. 15 NCAC 02B.0224(c)(2)(G) states that "the limit for a specific chemical constituent shall be
allocated at one-half of the normal standard design conditions."
In order to document protection of North Carolina's WQS, EPA recommends that the fact sheet explain how
the outfalls at each mining facility covered under the general permit would not be considered to discharge toxic
substances. Alternatively, the limits for those parameters that could be considered a toxic substance could be
limited using one-half the normal standard design conditions.
8. NCDEQ should consider revisions to the Notice of Intent (NOI) to support effluent limitations or monitoring
conditions in the final permit in accordance with 40 CFR§ 122.28(b)(2)(ii)."
The NOI accompanying the draft permit requests that applicants provide outfall location, description of
wastewater, and the maximum effluent flow rate; however,the NOI does not contain requests for information
about other effluent characteristics regarding outfall discharge frequency or duration.
EPA recommends that NCDEQ add to the NOI topics related to discharge frequency and discharge duration
(continuous vs non-continuous) to comply with the application requirements within the NPDES implementing
regulations in 40 CFR§ 122.21(g)14 and 40 CFR§ 122.21(k)."NCDEQ should also consider requiring information
12 40 CFR§124.8(b):The fact sheet shall include,when applicable:(4)A brief summary of the basis for the draft permit conditions including
references to applicable statutory or regulatory provisions and appropriate supporting references to the administrative record required by§
124.9(for EPA-issued permits);
13 40 CFR§ 122.28(b)(2)(ii):The contents of the notice of intent shall be specified in the general permit and shall require the submission of
information necessary for adequate program implementation,including at a minimum,the legal name and address of the owner or operator,
the facility name and address, type of facility or discharges, the receiving stream(s), and other required data elements as identified in
appendix A to part 127.General permits for stormwater discharges associated with industrial activity from inactive mining, inactive oil and
gas operations,or inactive landfills occurring on Federal lands where an operator cannot be identified may contain alternative notice of intent
requirements.
14 40 CFR§122.21(g)(2),(3),and(4)requires existing mines to submit average flows at discharge points and intermittent effluent flow data
(frequency,duration,and magnitude).
1s 40 CFR § 122.21(k)(3) and (5) requires new mining operations to submit estimated effluent information regarding frequency, duration,
maximum,and average flow rates.

about ESA-listed species or critical habitat that is publicly available to applicants online that is later verified by
NCDEQ.16 EPA believes that these additions will help the permittee to understand the permit requirements that
are applicable to the covered facility, support conditions in the draft permit, and protect water quality.
Additionally,this additional information is important for NCDEQto consider during the general permit coverage
process to adequately implement the program (and potentially require an individual permit if necessary).
9. NCDEQ should consider revising the permit language regarding the Secondary Containment Plan.
The draft permit requires that the applicant visually observe any accumulated stormwater prior to release for
color, foam, outfall staining, visible sheens, and dry weather flow, as these could be indications of
contamination.A record must be kept of every release from a secondary containment system (see draft permit
Sections B-9(c) and B-9(d)).
As currently stated, language in the draft permit could be interpreted as allowing the release of visibly
contaminated stormwater,so long as a record of the release is noted. EPA suggests adding in language to clarify
that accumulated stormwater should be released only if it is found to be uncontaminated.
16 ESA-listed species information is available at:ecos.fws.gov/ipac/