NC0070157_Fact Sheet_20240806

NCDEQ / DWR / NPDES
EXPEDITED FACT SHEET - NPDES PERMIT RENEWAL
NPDES Permit NCO070157
Catherine Shadwell / Compliance & Expedited Permitting Unit / kate.shadwellgdeq.nc.gov / July 2024
FACILITY INFORMATION
Applicant/Facility Name
Dare County, Patrick Irwin (Utilities Director)
Dare County North Reverse Osmosis WTP
Applicant Address
600 Mustian Street, Kill Devil Hills, NC 27948
Facility Physical Address
600 Mustian Street, Kill Devil Hills, NC 27948
Max, Monthly Avg Flow (MGD)
2.04 MGD
New Flow limit (max monthly avg
+ 15%)
2.35 MGD
Type of Waste
Reverse osmosis reject water
Facility Class
PC-1
County
Dare
I
Permit Status
Renewal
Regional Office
WaRO
STREAM CHARACTERISTICS
Receiving Stream
The Atlantic Ocean
Stream
Classification
SB
Stream Segment
99-(7)
Outfall Lat.
360 00' 56.9" N
7Q10 - Summer (cfs)
NA
Outfall Long.
750 39' 10.1" W
7Q 10 - Winter (cfs)
NA
Drainage basin
Contiguous to Pasquotank
30Q2 (cfs)
NA
Subbasin
03-01-56
Average Flow (cfs)
NA
HUC
030102051704
IWC (%)
NA
303(d) List
Not listed
FACILITY SUMMARY
Dare County North Reverse Osmosis WTP is a Membrane & Ion exchange water treatment plant. It
includes a reverse osmosis (RO) reject concentrate and secondary containment stormwater/process
monitoring wastewater from an existing potable water treatment plant. It is then discharged in the Atlantic
Ocean.
Chemical usage consists of:
• Sodium hydroxide
• Arsenic Chlorine
• Chlorine
• Fluoride
RENEWAL SUMMARY
This renewal contains the following changes:
• Added limits for Total Copper in Section A. (1) Effluent table as the RPA shows a reasonable
potential to exceed water quality standards.
• Added Section A. (2.) Compliance Schedule for new Copper limits and monitoring, as well as
corresponding footnote #2.
• Added flow monitoring per new water treatment plant guidance. Flow limit was calculated by using
the max monthly average flow from the past 3 years of data and adding a 15% reserve capacity.
Fact Sheet for Permit Renewal
July 2024 - NPDES Permit NCO070157 - Page 1

COMPLIANCE HISTORY
Looking through the past 5 years (since 2019), there have been no enforcements or violations on record for
this facility.
WHOLE EFFLUENT TOXICITY (WET) TESTING
In accordance with current strategies designating this facility as a Membrane and Ion Exchange water
treatment plant, WET testing is required in this permit as saltwater Chronic [TGP3E] Pass/Fail Quarterly
monitoring with Mysidopsis bahia at an effluent concentration of 5.5%. This facility has passes 12 out of
the past 12 toxicity tests.
REASONABLE POTENTIAL ANALYSIS
A reasonable potential analysis (RPA) was performed for a discharger going to a saltwater stream. Per the
new guidance for Water Treatment plants. A flow (Qw) of 2.35 MGD was used. This flow is based on the
maximum, monthly average flow between June 2021 and May 2024, with a 15% reserve capacity added
and rounded to 3 significant figures.
Based on this analysis, the following permitting actions are proposed for this permit:
• Copper — reasonable potential to exceed water quality standards; applying monthly monitoring
with limits
COMMENTS ON DRAFT PERMIT
Fact Sheet for Permit Renewal
July 2024 - NPDES Permit NC0070157 - Page 2

Parameter
UoM
Value Cell Type
Location
Subbasin
50050 - Flow, in conduit or thru treatment plant
mgd
1.46406667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.59451613 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.52574194 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.3676 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.01354839 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.83743333 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.75793548 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.69651613 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.7475 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.862 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.1226 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.22890323 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.97056667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.62158065 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.5283871 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.42256667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.01451613 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.86323333 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.83251613 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.70958065 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.75742857 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.79241935 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.1206 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.43554839 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.4703 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.88232258 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
2.04035484 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.69386667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.21096774 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.91046667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.83135484 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.86748387 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.79686207 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
0.98512903 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.09456667 CAMONAVG
Effluent
03-01-56
50050 - Flow, in conduit or thru treatment plant
mgd
1.56264516 CAMONAVG
Effluent
03-01-56
Max Monthly 2.04035484
Avg
new flow limit 2.346408066
(maxmonthly x
15%)

Table 1
Facility Name
WWTP/WTP Class
NPDES Permit
Outfall
Flow, Qw (MGD)
Receiving Stream
Stream Class
7Q10s (cfs)
7Q10w (cfs)
30Q2 (cfs)
QA (cfs)
1 Q10s (cfs)
Data Source(s)
Saltwater RPA 95% Probablity/95% Confidence
MAXIMUM DATA POINTS = 58
JREQUIRED DATA ENTRY
roject Information Table 2. Parameters of Concern
❑ CHECK IF HQW OR ORW WQS
Dare County North Reverse Osmosis WTP
PC-1
NCO070157
2.346
Atlantic Ocean
SB
Tidal, IWC = 100%
Tidal, IWC = 100%
Tidal, IWC = 100%
Tidal, IWC = 100%
Tidal, IWC = 100%
Saltwater streams are tidal resulting in all IWC % = 100%.
If an approved model is conducted then a chronic dilution
factor is determined and can be applied to a discharge to
calculate its IWC % . If a stream is classified as a SA or
ORW then its is also classified as a HQW. The appropriate
IWC % must be defined to properly calculate WQS-based
Par01
Par02
Par03
Par04
Par05
Par06
Par07
Par08
Par09
Par10
Par11
Par12
Par13
Par14
Par15
Par16
Par17
Par18
Par19
Par20
Par21
Par22
Name WQs Type Chronic Modifier Acute PQL Units
Arsenic
Aquatic Life
C
36
SW
69
ug/L
Arsenic
Human Health
C
10
HH
ug/L
Cadmium
Aquatic Life
NC
7.9
SW
33.2
ug/L
Total Phenolic Compounds
Aquatic Life
NC
300
A
10
ug/L
Chromium VI
Aquatic Life
NC
50.4
SW
1107.8
ug/L
Chromium, Total
Aquatic Life
NC
N/A
SW
N/A
ug/L
Copper
Aquatic Life
NC
3.7
SW
5.8
ug/L
Cyanide
Aquatic Life
NC
1
SW
1
10
ug/L
Lead
Aquatic Life
NC
8.5
SW
220.8
ug/L
Mercury
Aquatic Life
NC
25
SW
0.5
ng/L
Molybdenum
Human Health
NC
2.0
HH
mg/L
Nickel
Aquatic Life
NC
8.3
SW
74.7
ug/L
Selenium
Aquatic Life
NC
71
SW
ug/L
Silver
Aquatic Life
NC
0.1
SW
2.2
ug/L
Zinc
Aquatic Life
NC
85.6
SW
95.1
ug/L
NOTE: The aquatic life chronic and acute WQS for several metals are calculated based on EPA conversi
see "Diss. SW stds. As TM" for more details and summary of calculated WQS..
70157_RPA,input
7/25/2024

REASONABLE POTENTIAL ANALYSIS - DATA
Date
Data
BDL=1/2DL
1 12/2/2019
<
1
0.5
2 12/17/2019
<
10
5
3 1 /7/2020
<
20
10
4 1 /21 /2020
<
10
5
5 2/4/2020
<
1
0.5
6 2/18/2020
<
20
10
7 3/3/2020
<
10
5
8 3/17/2020
<
10
5
9 4/7/2020
<
1
0.5
10 4/21 /2020
<
1.85
0.925
11 5/5/2020
<
1
0.5
12 5/19/2020
<
1
0.5
13 6/2/2020
<
1
0.5
14 6/16/2020
<
2
1
15 7/7/2020
<
1
0.5
16 7/21 /2020
<
1
0.5
17 8/5/2020
21
21
18 8/18/2020
<
1
0.5
19 9/1/2020
<
1
0.5
20 9/15/2020
<
1.85
0.925
21 10/6/2020
1
1
22 10/20/2020
<
10
5
23 11 /2/2020
<
20
10
24 11/16/2020
<
10
5
25 12/1/2020
<
10
5
26 12/15/2020
<
10
5
27 1 /5/2021
1
1
28 1 /25/2021
<
1
0.5
29 2/8/2021
1
1
30 2/22/2021
2
2
31 3/2/2021
<
1.85
0.925
32 3/16/2021
<
1
0.5
33 4/6/2021
<
20
10
34 4/19/2021
<
1
0.5
35 5/4/2021
2
2
36 5/18/2021
<
1
0.5
37 6/1/2021
<
1
0.5
38 6/15/2021
<
1
0.5
39 7/6/2021
<
25
12.5
40 7/20/2021
<
1
0.5
41 8/3/2021
7
7
42 8/17/2021
2
2
43 9/1/2021
3
3
44 9/21/2021
7
7
45 10/5/2021
9
9
46 10/19/2021
<
1
0.5
47 11 /2/2021
<
2.5
1.25
48 11/16/2021
7
7
49 12/7/2021
4
4
50 12/20/2021
12
12
51 1/11/2022
<
1
0.5
52 1 /25/2022
1.7
1.7
53 2/8/2022
4
4
54 2/22/2022
3
3
55 3/1/2022
3
3
56 3/15/2022
2
2
57 4/5/2022
2
2
58 4/20/2022
1.8
1.8
Values" then "COPY"
. Maximum data
points = 58
Res u Its
Std Dev.
4.0891
Mean
3.5091
C.V.
1.1653
n
58
Mult Factor =
1.0000
Max. Value
21.00 ug/L
Max. Pred Cw
21.00 ug/L
70157_RPA,data
Date}

Dare County North Reverse Osmosis WTP
Outfall
NCO070157
Saltwater RPA 95% Probablity/95% Confidence
MAXIMUM DATA POINTS = 58
Qw (MGD) =
2.35
WWTP/WTP Class: PC-1
1Q10S (cfs) =
Tidal, IWC = 100%
IWC% @ 1Q10S = 100
7QIOS(cfs)=
Tidal, IWC=100%
IWC% @7Q10S= 100
7Q10W (cfs) =
Tidal, IWC = 100%
IWC% @ 7Q10W = 100
30Q2 (cfs) =
Tidal, IWC = 100%
IWC% @ 30Q2 = 100
Avg. Stream Flow, QA (cfs) =
Tidal, IWC = 100%
IWC% @ QA = 100
Receiving Stream:
Atlantic Ocean
Stream Class: SB
Qw = 2.346 MGD
PARAMETER
NC STANDARDS OR EPA CRITERIA
N
REASONABLE POTENTIAL RESULTS
TYPE
aO
z
RECOMMENDED ACTION
Applied
Chronic Acute
D
n # Det. Max Prcd Cw Allowable Cw
Standard
Acute: 5.78
RP shown - apply Monthly Monitoring with
Copper
NC
3.73493976 SW(7Q10s) 5.78313253
ug/L
58 21
21.00
Limit
_ _ _ _ _ _ _ _
Chronic: 3.73
RP shown - apply Monthly Monitoring with
21 value(s) > Allowable Cw
Limit
Acute:
0 0
N/A
Chronic: ----------
--------------------------
Acute:
0 0
N/A
Chronic: ----------
--------------------------
Acute:
0 0
N/A
Chronic: ---
--------------------------
Acute:
0 0
N/A
Chronic: ----
--------------------------
Acute:
0 0
N/A
Chronic: ----------
--------------------------
Acute:
0 0
N/A
Chronic: ----------
--------------------------
Acute:
0 0
N/A
Chronic:----------
--------------------------
70157_RPA,rpa
Page 3 of 3 7/25/2024