NC0003719_Correspondence_20230830

This document is intended for guidance only and may be impacted by changes in legislation, rules, policies, and procedures adopted after
the date of publication. Although this publication makes every effort to teach users how to meet applicable compliance obligations, use of
this document does not constitute the rendering of legal advice.
Background
In its Technical Fact Sheet, the United States Environmental Protection Agency (EPA) describes 1,4-dioxane as "a
synthetic industrial chemical that is completely miscible in water." Its primary historical use was as a stabilizer of
chlorinated solvents. The EPA fact sheet states 1,4-dioxane is a by-product present in many goods, including paint
strippers, dyes, greases, anti -freeze, and aircraft deicing fluids, consumer goods, and personal care products.
EPA risk assessments indicate that the drinking water conc hation representing a 1 x 10-6 cancer risk level for 1,4-
dioxane is 0.35 µg/L (EPA IRIS 2013). EPA has classified 1,4-dioxane as a likely human carcinogen but has not
established a federal water quality criterion un Clean Water Act or maximum contaminant level (MCL) under the
Safe Drinking Water Act.
Elevated concentrations of 1,4-dioxane were rep ed in e Cape Fear fiver Basin based on the sampling effort
conducted as part of the EPA's Third Unregulated Contaminant Monitoring Rule (UCMR3). As a result, in 2014, DWR
initiated ambient sampling for 1,4-dioxane in the Cape Fear Rive&pasiW and NPDES staff worked with Upper Piedmont
Permittees on assessing and reducing 1,4-dioxane in their wastewaters. Ambient sampling has continued in the Cape
Fear to the present, and sampling results can be found on the DWR website .
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Follow-up screenings were conducted by DWR to better characterize the presence of 1,4- dioxane in various types of
wastewaters. As art of the screening, DWR sent letters to 28 Publicly Owned Treatment Works (POTWs) that have
pretreatment pr and that discharge into the Cape Fear River Basin. The POTWs were asked to sample for 1,4-
dioxane for th nsecutive months starting in July 2019DWR also requested sampling of 18 selected industrial
facilities in the Cape Fear River Basin. The industrial facilities were asked to sample their effluent for 1,4-dioxane for
three consecutive months starting in October 2019. Based on the data received, DWR has asked several of those POTWs
and industries to continue monitoring for 1,4-dioxane in their effluent. The sampling results from the screening are
presented in this map locate4,W our website.
In this document, these numerical standards are referred to as in -stream target values (or ITVs). The Division of Water
Resources (DWR) has established 1,4-dioxane ITVs of 0.35 µg/L in surface waters classified as water supplies, and 80
µg/L in all other surface waters.
In North Carolina, specific standards for toxic substances to protect all surface water uses are listed in 15A NCAC 02B
rules. The narrative standard for toxic substances and numerical standards applicable to all waters shall be interpreted as
described under 15A NCAC 02B .0208. As part of the 2020-2022 Triennial Review, DWR is proposing to adopt these
ITVs as specific surface water quality standards in the 15A NCAC 02B rules. More information on the 2020-2022
Triennial Review can be found here.
The NPDES strategy is to identify, investigate, reduce, or eliminate the discharge of 1,4-dioxane from NPDES
dischargers with the goal of bringing permittees into compliance with in -stream target values of 0.35 µg/L in
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surface waters classified as water supplies, or at the boundary of a water supply water for sources above a
drinking water classification, and 80 µg/L in all other surface waters.
DWR is working with municipalities (POTW's) and their pretreatment program coordinators to determine potential
sources and treatment or product substitutions their industrial dischargers (or other significant users SIU) can make to
reduce or eliminate 1,4-dioxane in their effluent. This step is currently underway and involves reviewing individual
significant dischargers to ensure that they have an active program for monitoring 1,4-dioxane. Dischargers should also
employ best management practices to reduce 1,4-dioxane discharges entering their facilities.
Reductions of 1,4-dioxane will primarily be achieved by POTWs requiring SIU dischargers to install best available
treatment to remove 1,4-dioxane or to substitute products used in their industrial processes. DWR will work closely with
these POTWs and their implementation of approved Pretreatment Programs sure compliance is achieved as soon as
possible.
While we plan to take a proactive approach through the pretreatment program and its SIU regulations to achieve 1,4-
dioxane reductions, we will also use administrative compliance actions, as necessary. A complete evaluation of the
POTWs capability of improving treatment or meeting final of mitations%1,4-dliox
with each permit renewal
every five years.
All Permittees shall be required to continue to improve trea or eliminein their wastewaters until
the in -stream target values are achieved. Additionally, we have utilized our compliance and enforcement program where
necessary, by issuing Notices of Violations and working within the S ecial Order by Consent process with facilities to
meet initial reduction goals.
DWR is utilizing a tiered approach by first Vaddin%*ties with ig concentrations of 1,4-dioxane in their
discharge. DWR has started the process to protect downstream drinking water supplies by ensuring facilities with
significant discharges will not cause concentrations of 1-4-dioxane in or above drinking water supply waters to rise above
EPA's Drinking Water Heath Advisory level of 35 µg/L1 In the next ste DWR will work with Permittees to establish
permit compliance schedules to achieve in -stream target values or levels eq alent to the Best Available Technology
analysis as soon as practicable. This stepwise approach may utilize NPDES permit, special orders by consent, or both.
Finally, permittees must comply with antidegradation rule under 15A NCAC 02B .0201.
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NPDES Permitting Action Level Tiers- 1,4 Dioxane
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The following tiers have been developed to apply to any discharges that may affect water supplies. The tiers shall be
used as action levels by DWR to determine the appropriate permitting requirements and monitoring frequencies of 1,4-
dioxane for permittees with the goal to meet the in -stream target values as soon as practicable. Discharges shall be
categorized based on data collected, the stream classification of the discharge, the calculated allowable discharge limit
for 1,4-dioxane, and the potential impact to water supplies. In addition, continued monitoring has been requested of
POTWs and industries with 1,4-dioxane levels above their calculated allowable discharge limit using reasonable potential
protocols or when insufficient effluent data is available to make this determination. The current strategy does not apply
to Water Treatment Plants since they are unlikely sources of 1,4-dioxane.
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Applicability -These tiers will apply to:
• Major facilities (for POTW's- 1 MGD or more)
• Minor facilities with Pretreatment programs
• Facilities associated with industry categories known or suspected to discharge 1,4-dioxane, or for facilities which
have reported 1,4 dioxane concentrations from NPDES permit application data, or other supplemental
information from verified sources using certified laboratory data.
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oEffluent concentration of 1,4-dioxane >_ 35 µg/L
oDischarges directly to WS classified waters
oEffluent maximum predicted value > allowable concentration at discharge (RP to exceed
applicable ITV at discharge is demonstrated)
oMonitor weekly (and limits with a compliance schedule) grab sampling
oEffluent concentration of 1,4-dioxane >_ 35 µg/L
oDischarges to non-WS with downstream WS classified waters
oEffluent maximum predicted value > allowable concentration at downstream WS (RP to exceed
applicable ITV at downstream WS boundary is demonstrated)
oMonitor weekly (and limits with a compliance schedule) grab sampling
oEffluent concentration of 1,4-dioxane (>_ 10 µg/L+<35 µg/L)
oDischarges directly to WS classified waters
oEffluent maximum predicted value > allowable concentration at discharge (RP to exceed
applicable ITV at discharge is demonstrated)
oMonitor monthly (and limits and compliance schedule) grab sampling
oEffluent concentration of 1,4-dioxane (>_ 10 µg/L + < 35 µg/L)
oDischarges to non-WS with downstream WS waters
oEffluent maximum predicted value > allowable concentration at downstream WS (RP to exceed
applicable ITV at downstream WS boundary is demonstrated)
oMonitor monthly (and limits with o compliance schedule) grab sampling, but can be reduced if
all samples in future < PQL of 1 µg/L
oEffluent concentration of 1,4-dioxane (>_ 1 µg/L+ < 10 µg/L)
oDischarges directly to a WS waters or above WS waters
oEffluent > allowable concentration at discharge (RP to exceed applicable ITV at discharge or at
downstream WS boundary is demonstrated)
oMonitor quarterly (and limits with a compliance schedule, if needed) grab, but can be reduced if
future samples < PQL of 1 µg/L
Tier 6
•Discharges to a non-WS waters with no downstream WS classified waters
•ITV will be 80 µg/L
•Monitoring (and limits and compliance schedule, if needed) will be determined using a
reasonable potential analysis
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Discussion on NPDES Sampling Frequencies and Permitting Actions
Effluent data are evaluated via the Reasonable Potential Analysis (RPA) to determine if a Reasonable Potential (RP)
exists to exceed the calculated ITV. If the respective NPDES permit is up for renewal and there is limited data (typically
<12 samples), then effluent monitoring for 1,4-dioxane will be added to the permit with a frequency as noted above.
When sufficient data is available (typically 12 samples or more) and the permit is up for renewal or expansion, a
reasonable potential analysis will be performed on 1,4-dioxane effluent.
If the Permittee demonstrates reasonable potential to exceed the state's in -stream target values either at the point of
discharge or at the WS boundary downstream, then a limit will be added to the permit and, if needed, a requirement
included to perform an analysis of the best available technology for reducing or eliminating 1,4-dioxane in its effluent.
DWR recognizes there may be technological limitations in meeting 1,4 dioxane effluent limits below 10 µg/L. If that is
the case, the facility will be asked to incorporate best available technology and continue to optimize treatment and
reductions until the state's in -stream target values of 0.35 µg/L for water sup 1 waters (including protecting downstream
WS classifications) and 80 µg/L for non -water supply waters are achieved.
Compliance schedules, if needed would be for the existing permitted flows only. Compliance schedules may be
developed to achieve the in -stream target values, or to achieve levels equivalent to the Best Available Technology
analysis, as soon as practicable. First phase interim NPDES limit target will be no more than 35 ug/1 (if practicable)
provided the calculated effluent 1,4 dioxane limits are lower than this value. Permittees will be required to continue to
improve treatment or eliminate 1,4-dioxane from their wastewater until the in -stream target values are met, or they
achieve levels equivalent to the Best Available Technology analysis.
Currently, the practical quantitation limit (PQL) for 1,4-dioxane is 1 µg/L. Permittees reporting less than the PQL will
be considered in compliance with limits less than 1 µ /L.
Please Note: There may be situations that do not fall into the above tiers in which DWR may ask for continued monitoring when
warranted
appropriat
Approvedl
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