NC0089702_Fact Sheet Mod_20200710

NCDEQ / DWR / NPDES
FACT SHEET - for PERMIT MODIFICATION
NPDES Permit NCO089702
Facility Information
Applicant/Facility Name
Terwilliger Pappas Multi -Family Partners — Solis Brightleaf
Apartments - Permanent Subterranean Dewatering
Applicant Address
510 Glenwood Avenue, Suite 317, Raleigh 27603
Facility Address
1001 West Main Street, Durham 27701
Permitted Flow (MGD)
0.00005
Type of Waste
Treated excavation groundwater and permanent facility dewatering
Facility Class
Physical/Chemical
County
Durham
Date:
10Jul2020
Permit Writer:
Joe R. Corporon, P.G.
Facility / Permit Status
Built / MOD
Regional Office
RRO
Stream Characteristics
Receiving Stream
UT to Ellerbe Creek
Stream
Classification
WS-V; NSW
Stream Segment
27-5-(03)
Drainage basin
Neuse River Basin
Summer 7Q10 (cfs)
0.0
Subbasin
03-04-01
Winter 7Q10 (cfs)
0.0
Use Supporting
Yes
30Q2 (cfs)
0.0
303(d) Listed
NSW
Average Flow (cfs)
0.0
State Grid
D23NW
IWC %
( )
100
[discharge to storm -sewer]
USGS Topo Quad
Southwest Durham, NC
Project Summga
Terwilliger Pappas Multi -Family Partners — Solis Brightleaf Apartments applied [via their
consultant Mid Atlantic Engineering and Environmental Solutions] to develop several contiguous
real estate parcels into a 1.45-acre apartment complex with subterranean parking. The permanently
installed treatment -system effluent discharges to a City of Durham storm sewer under zero -flow
receiving -stream conditions (7Q10/30Q2 = 0.0 cfs). Mid -Atlantic Engineering presented an
Engineering Alternatives Analysis (EAA) concluding that a discharge to surface waters is the most
viable discharge alternative based on feasibility and cost. The Division of Water Resources (DWR)
concurred.
Progress. The DWR understands that construction and installation of a system for permeant
dewatering are now complete, and that follow-up analytical data have been collected in accord
provisions in the permit (effective October 1, 2019). DWR issues this modification (MOD) per the
Permittee's request received April 7, 2020 as allowed by the active permit. New analyses support this
request to revise parameters of concern, permit limits, and monitoring frequencies [see section A. (1.)].
Because the active permit provides for this MOD, additional Public Notice is not required.
Reasonable Potential Analyses (RPAs) / Modification Review. The Division review included
Reasonable Potential Analyses (RPAs) to new data submitted.
Page 1 of 7

Permit Modifications
1. Discontinued monitoring for Tetrachloroethylene (PCE) based on database RP
2. Discontinued monitoring for Trichloroethylene (TCE) based on RP
3. Discontinued monitoring for Total Kjeldahl Nitrogen (TKN) based on RP
4. Discontinued monitoring for the metals Arsenic, Cadmium, Chloride, Copper, and
Chromium VI and Zinc based on RP
5. Discontinued monitoring for Total Chromium based on RP
6. Discontinued monitoring for Fluoride based on RP
7. Discontinued monitoring for VOCs (EPA-624) and Semi-VOCs (EPA-625 based on no
parameters detected.
8. Discontinued monitoring for Biochemical Oxygen Demand (BOD,5-day) based on RP
9. Considering Total Mercury- We have reduced monitoring for Total Mercury from
Monthly to Quarterly. Because the new Hg database shows reasonable potential to
exceed its surface water -quality Standard [max predicted 19 ng/L], Hg continues as limited
in the permit/Standard (12 ng/L). However, all Hg analyses were reported below the
Standard, and facility does not otherwise generate Mercury.
10. Reduced monitoring for Total Hardness from Monthly to Quarterly consistent with similar
facilities statewide.
11. Updated facility description (see Supplement to Permit Cover Sheet)
12. Updated eDMR text consistent with current policy (see section A. (3).
13. Updated WET testing text; reduced monitoring from Monthly to Quarterly, consistent
with similar facilities.
In contrast to the above, analytical databases provided for Lead and Selenium suggest reasonable
potential for each to exceed its respective surface water -quality Standard. Therefore, the following
are required for renewal:
• Total Selenium — continue monitor Monthly with limit,
• Total Lead — continue monitor Monthly with limit.
DWR attached permit change -pages reflecting the above with instructions to insert new pages
into the active permit and discard the old pages. This permit modification becomes active upon
issuance signature.
Fact Sheet prepared by
Joe R. Corporq+ , P.G., NkDES
ittin2 1OJu12020
Page 2 of 7

NPDES Implementation of Instream Dissolved Metals Standards - Freshwater Standards
The NC 2007-2015 Water Quality Standard (WQS) Triennial Review was approved by the NC
Environmental Management Commission (EMC) on November 13, 2014. The US EPA
subsequently approved the WQS revisions on April 6, 2016, with some exceptions. Therefore,
metal limits in draft permits out to public notice after April 6, 2016 must be calculated to protect
the new standards - as approved.
Table 1. NC Dissolved Metals Water Quality Standards/Aquatic Life Protection
Parameter
Acute FW, µg/1
(Dissolved)
Chronic FW, µg/1
(Dissolved)
Acute SW, µg/1
(Dissolved)
Chronic SW, µg/1
(Dissolved)
Arsenic
340
150
69
36
Beryllium
65
6.5
---
---
Cadmium
Calculation
Calculation
40
8.8
Chromium III
Calculation
Calculation
---
---
Chromium VI
16
11
1100
50
Copper
Calculation
Calculation
4.8
3.1
Lead
Calculation
Calculation
210
8.1
Nickel
Calculation
Calculation
74
8.2
Silver
Calculation
0.06
1.9
0.1
Zinc
Calculation
Calculation
90
81
Table 1 Notes:
FW= Freshwater, SW= Saltwater
Calculatiq = Hardness dependent standard
Only the aquatic life standards listed above are expressed in dissolved form. Aquatic life
standards for Mercury and selenium are still expressed as Total Recoverable Metals due to
bioaccumulative concerns (as are all human health standards for all metals). It is still
necessary to evaluate total recoverable aquatic life and human health standards listed in
15A NCAC 213.0200 (e.g., arsenic at 10 µg/1 for human health protection; cyanide at 5
µg/L and fluoride at 1.8 mg/L for aquatic life protection).
Table 2. Dissolved Freshwater Standards for Hardness -Dependent Metals
The Water Effects Ratio (WER) is equal to one unless determined otherwise under 15A NCAC 02B .0211
Subparagraph (11)(d)
Metal
NC Dissolved Standard, /1
Cadmium, Acute
WER* 11.136672-[ln hardness] (0.04183 8)1 e"10.9151 [In hardness]-3.14851
Cadmium, Acute Trout waters
WER* 11.136672-[ln hardness](0.041838)1 eA10.9151 [In hardness]-3.62361
Cadmium, Chronic
WER* 11.101672-[ln hardness](0.041838)1 eA10.7998[ln hardness]-4.44511
Chromium III, Acute
WER*0.316 e-10.8190[ln hardness]+3.72561
Chromium III, Chronic
WER*0.860 e^{0.8190[ln hardness]+0.68481
Copper, Acute
WER*0.960 e^{0.9422[ln hardness]-1.7001
Copper, Chronic
WER*0.960 e^{0.8545[ln hardness]-1.7021
Lead, Acute
WER* I1.46203-[ln hardness](0.145712)1 • e ll.273[ln hardness]-1.4601
Lead, Chronic
WER*11.46203-[ln hardness](0.145712)1 • e ll.273[ln hardness]-4.7051
Nickel, Acute
WER*0.998 • e-10.8460[ln hardness]+2.2551
Page 3 of 7

Nickel, Chronic
WER*0.997 • e^{0.8460[ln hardness]+0.05841
Silver, Acute
WER*0.85 • e^{1.72[ln hardness]-6.591
Silver, Chronic
Not applicable
Zinc, Acute
WER*0.978 e-10.8473[ln hardness]+0.8841
Zinc, Chronic
WER*0.986 e-10.8473[ln hardness]+0.8841
General Information on the Reasonable Potential Analysis (RPA)
The RPA process itself did not change as the result of the new metals standards. However, application of
the dissolved and hardness -dependent standards requires additional consideration in order to establish the
numeric standard for each metal of concern of each individual discharge.
The hardness -based standards require some knowledge of the effluent and instream (upstream) hardness and
so must be calculated case -by -case for each discharge.
Metals limits must be expressed as `total recoverable' metals in accordance with 40 CFR 122.45(c). The
discharge -specific standards must be converted to the equivalent total values for use in the RPA
calculations. We will generally rely on default translator values developed for each metal (more on that
below), but it is also possible to consider case -specific translators developed in accordance with established
methodology.
RPA Permitting Guidance/WOBELs for Hardness -Dependent Metals - Freshwater
The RPA is designed to predict the maximum likely effluent concentrations for each metal of concern, based on recent
effluent data, and calculate the allowable effluent concentrations, based on applicable standards and the critical low -
flow values for the receiving stream.
If the maximum predicted value is greater than the maximum allowed value (chronic or acute), the
discharge has reasonable potential to exceed the standard, which warrants a permit limit in most cases. If
monitoring for a particular pollutant indicates that the pollutant is not present (i.e. consistently below
detection level), then the Division may remove the monitoring requirement in the reissued permit.
To perform a RPA on the Freshwater hardness -dependent metals the Permit Writer
compiles the following information:
• Critical low flow of the receiving stream, 7Q10 (the spreadsheet automatically
calculates the 1 Q 10 using the formula 1 Q 10 = 0.843 (s7Q 10, cfs) 0.993
• Effluent hardness and upstream hardness, site -specific data is preferred
• Permitted flow
• Receiving stream classification
In order to establish the numeric standard for each hardness -dependent metal of concern
and for each individual discharge, the Permit Writer must first determine what effluent and
instream (upstream) hardness values to use in the equations.
The permit writer reviews DMR's, Effluent Pollutant Scans, and Toxicity Test results for
any hardness data and contacts the Permittee to see if any additional data is available for
instream hardness values, upstream of the discharge.
If no hardness data is available, the permit writer may choose to do an initial evaluation
using a default hardness of 25 mg/L (CaCO3 or (Ca + Mg)). Minimum and maximum
Page 4 of 7

4
limits on the hardness value used for water quality calculations are 25 mg/L and 400 mg/L,
respectively.
If the use of a default hardness value results in a hardness -dependent metal showing
reasonable potential, the permit writer contacts the Permittee and requests 5 site -specific
effluent and upstream hardness samples over a period of one week. The RPA is rerun using
the new data.
The overall hardness value used in the water quality calculations is calculated as follows:
Combined Hardness (chronic)
_ (Permitted Flow, cfs *Avg. Effluent Hardness, mg/L) + (s7Q10, cfs *Avg. Upstream Hardness, mg/L)
(Permitted Flow, cfs + s7Q10, cfs)
The Combined Hardness for acute is the same but the calculation uses the 1Q10 flow.
The permit writer converts the numeric standard for each metal of concern to a total
recoverable metal, using the EPA Default Partition Coefficients (DPCs) or site -specific
translators, if any have been developed using federally approved methodology.
EPA default partition coefficients or the "Fraction Dissolved" converts the value for
dissolved metal at laboratory conditions to total recoverable metal at in -stream ambient
conditions. This factor is calculated using the linear partition coefficients found in The
Metals Translator: Guidance for Calculating a Total Recoverable Permit Limit from a
Dissolved Criterion (EPA 823-B-96-007, June 1996) and the equation:
Cdiss - 1
Ctotal 1 + t [K,.] [SS(l+a)] [10-6] i
Where:
ss = in -stream suspended solids concentration [mg/1], minimum of 10 mg/L used, and
Kpo and a = constants that express the equilibrium relationship between dissolved and
adsorbed forms of metals. A list of constants used for each hardness -dependent metal can
also be found in the RPA program under a sheet labeled DPCs.
The numeric standard for each metal of concern is divided by the default partition
coefficient (or site -specific translator) to obtain a Total Recoverable Metal at ambient
conditions.
In some cases, where an EPA default partition coefficient translator does not exist (ie.
silver), the dissolved numeric standard for each metal of concern is divided by the EPA
conversion factor to obtain a Total Recoverable Metal at ambient conditions. This method
presumes that the metal is dissolved to the same extent as it was during EPA's criteria
development for metals. For more information on conversion factors see the June, 1996
EPA Translator Guidance Document.
Page 5 of 7

6. The RPA spreadsheet uses a mass balance equation to determine the total allowable
concentration (permit limits) for each pollutant using the following equation:
Ca = (s7010 + Owl (Cwas) — (s7010) (Cb
Qw
Where: Ca = allowable effluent concentration (µg/L or mg/L)
Cwqs = NC Water Quality Standard or federal criteria (µg/L or mg/L)
Cb = background concentration: assume zero for all toxicants except NH3* (µg/L or mg/L)
Qw = permitted effluent flow (cfs, match s7Q 10)
s7Q10 = summer low flow used to protect aquatic life from chronic toxicity and human health through
the consumption of water, fish, and shellfish from noncarcinogens (cfs)
* Discussions are on -going with EPA on how best to address background concentrations
Flows other than s7Q10 may be incorporated as applicable:
IQ 10 = used in the equation to protect aquatic life from acute toxicity
QA = used in the equation to protect human health through the consumption of water, fish, and
shellfish from carcinogens
30Q2 = used in the equation to protect aesthetic quality
The permit writer enters the most recent 2-3 years of effluent data for each pollutant of
concern. Data entered must have been taken within four and one-half years prior to the date
of the permit application (40 CFR 122.21). The RPA spreadsheet estimates the 95th
percentile upper concentration of each pollutant. The Predicted Max concentrations are
compared to the Total allowable concentrations to determine if a permit limit is necessary.
If the predicted max exceeds the acute or chronic Total allowable concentrations, the
discharge is considered to show reasonable potential to violate the water quality standard,
and a permit limit (Total allowable concentration) is included in the permit in accordance
with the U.S. EPA Technical Support Document for Water Quality -Based Toxics Control
published in 1991.
8. When appropriate, permit writers develop facility specific compliance schedules in
accordance with the EPA Headquarters Memo dated May 10, 2007 from James Hanlon to
Alexis Strauss on 40 CFR 122.47 Compliance Schedule Requirements.
The Total Chromium NC WQS was removed and replaced with trivalent chromium and
hexavalent chromium Water Quality Standards. As a cost savings measure, total chromium
data results may be used as a conservative surrogate in cases where there are no analytical
results based on chromium III or VI. In these cases, the projected maximum concentration
(95th %) for total chromium will be compared against water quality standards for
chromium III and chromium VI.
10. Effluent hardness sampling and instream hardness sampling, upstream of the discharge, are
inserted into all permits with facilities monitoring for hardness -dependent metals to ensure
the accuracy of the permit limits and to build a more robust hardness dataset.
Page 6 of 7

11. Hardness and flow values used in the Reasonable Potential Analysis for this permit
included:
Parameter
Value
Comments (Data Source)
Average Effluent Hardness
(mg/-)
[Total as, CaCO3 or Ca+M ]
Average Upstream Hardness
(mg/-)
Total as, CaCO3 or Ca+M
7Q 10 summer cfs
1Q10 cfs
Permitted Flow MGD
Page 7 of 7

Table 1. Project Information
❑ CHECK IF HQW OR ORW WQS
Facility Name Terwilliger Pappas — Solis Brightleaf Apartments Par01
WWTP/WTP Class
NPDES Permit
Outfall
Flow, Qw (MGD)
Receiving Stream
HUC Number
Stream Class
PCNC
NCO089702
001
0.007
UT to Ellerbe Creek
03020201
WS-V; NSW
❑� Apply WS Hardness WQC
7Q10s (cfs)
7Q10w (cfs)
30Q2 (cfs)
QA (cfs)
1Q10s (cfs)
0.00
0.00
0.00
0.00
0.00
Effluent Hardness
— — — — — — — — — — — —
Upstream Hardness
Combined Hardness Chronic
Combined Hardness Acute
— — — — — — — — — — — — — — — — — — —
99 m /L
99 m /L
BIMS Database
Data Source(s)
❑ CHECK TO APPLY MODEL
Par02
Par03
Par04
Par05
Par0611111
Par07
Par08
Par09
Par10
Par11
Par12
Par13
Par14
Par15
Par16
Par17
Par18
Par19
Par20
Par21
Par22
Par23
Par24
Freshwater RPA - 95% Probability/95% Confidence Using Metal Translators
MAXIMUM DATA POINTS = 58
REQUIRED DATA ENTRY NEED ADDITIONAL DATA INPUTS
Parameters of Concern
wQs Type Chronic Moaifier Acute PQL Units
Table 2
Name
Arsenic
Aquactic Life
C
150
FW
340
ug/L
Arsenic
Human Health Water Supply
C
10
HH/WS
N/A
ug/L
Beryllium
Aquatic Life
NC
6.5
FW
65
ug/L
Cadmium
Aquatic Life
NC
1.6678
FW
10.7582
ug/L
Chlorides
Aquatic Life
NC
230
FW
Chlorinated Phenolic Compounds
Water Supply
NC
1
A
ug/L
Total Phenolic Compounds
Aquatic Life
NC
300
A
ug/L
Chromium III
Aquatic Life
NC
363.4201
FW
2793.8313
ug/L
Chromium VI
Aquatic Life
NC
11
FW
16
pg/L
Chromium, Total
Aquatic Life
NC
N/A
FW
N/A
pg/L
Copper
Aquatic Life
NC
25.5442
FW
38.2981
ug/L
Cyanide
Aquatic Life
NC
5
FW
22
10
ug/L
Fluoride
Aquatic Life
NC
1,800
FW
ug/L
Lead
Aquatic Life
NC
13.5358
FW
347.3518
ug/L
Mercury
Aquatic Life
NCI
12
FW
1
0.5
ng/L
TKN
Human Health
NC
HH
mg/L
Nickel
Aquatic Life
NC
119.2776
FW
1073.9039
pg/L
Nickel
Water Supply
NC
25.0000
WS
N/A
pg/L
Selenium
Aquatic Life
NC
5
FW
56
ug/L
Silver
Aquatic Life
NCI
0.06
FW
3.1616
ug/L
Zinc
Aquatic Life
NC
406.7415
FW
403.4414
ug/L
PCE
TCE
89702 MOD RPA 15jun202O, input
7/10/2020

?DATA?
?DATA?
89702 MOD RPA 15jun2020, input
7/10/2020

Terwilliger Pappas — Solis Brightleaf Apartments
NCO089702 Freshwater RPA - 95% Probability/95% Confidence Using Metal Translators
MAXIMUM DATA POINTS = 58
Qw (MGD) =
0.0065
WWTP/WTP Class: PCNC
1Q10S (cfs) =
0.00
IWC% @ 1Q10S = 100
7Q10S (cfs) =
0.00
IWC% @ 7Q10S = 100
7Q10W (cfs) =
0.00
IWC% @ 7Q10W = 100
30Q2 (cfs) =
0.00
IWC% @ 30Q2 = 100
Avg. Stream Flow, QA (cfs) =
0.00
IW%C @ QA = 100
Receiving Stream:
UT to Ellerbe Creek HUC 03020201 Stream Class: WS-V; NSW
Outfall 001
Qw = 0.0065 MGD
COMBINED HARDNESS (mg/L)
Acute = 99 mg/L
Chronic = 99 mg/L
YOU HAVE DESIGNATED THIS RECEIVING
STREAM AS WATER SUPPLY
Effluent Hard: 1 value > 100 mg/L
PARAMETER
NC STANDARDS OR EPA CRITERIA
J
F
REASONABLE POTENTIAL RESULTS
RECOMMENDED ACTION
TYPE
a
�
Chronic Appli
Acute
n # Det. Max Pred Cw Allowable Cw
d
StandAcute
(FW): 340.0
No RP, Predicted Max < 50 % of Allowable Cw - No
Arsenic
C
150 FW 340
ua/L
Monitoring required
15 0
5.6
Chronic (FW): 150.0
No RP, Predicted Max < 50 % of Allowable Cw - No
Max MDL = 10
Monitoring required
Arsenic
C
10 II1I/WS
ua L
NO DETECTS
Chronic (HH): 10.0
No RP, Predicted Max < 50 % of Allowable Cw - No
Max MDL = 10
Monitoring required
Acute: 10.758
not detected
Cadmium
NC
1.7 FW 10.8
ug/L
15 0
0.62
Chronic: 1.668
not detected
NO DETECTS
Max MDL = 1
Acute: NO WQS
Chlorides
NC
230 FW
mg/L
41 41
107
Chronic: 230
No RP, Predicted Max < 50 % of Allowable Cw - No
No value > Allowable Cw
Monitoring required
Acute: 16.0
No RP, Predicted Max < 50 % of Allowable Cw - No
ChromiumVI
NC
11 FW 16
µg'L
15 6
6.5
Monitoring required
Chronic: 11.0
No RP, Predicted Max >_ 50 % of Allowable Cw
No value > Allowable Cw
apply Quarterly Monitoring
Acute: 38.3
No RP, Predicted Max < 50 % of Allowable Cw - No
Copper
NC
25.5 FW 38.3
ug/L
15 2
4.8
Monitoring required
Chronic: 25.5
No RP, Predicted Max < 50 % of Allowable Cw - No
No value > Allowable Cw
Monitoring required
Acute: NO WQS
Fluoride
NC
1800 FW
ug/L
15 6
211
No RP, Predicted Max < 50 % of Allowable Cw - No
Chronic: 1,800
No value > Allowable Cw
Monitoring required
Acute: 347.4
No RP, Predicted Max < 50 % of Allowable Cw - No
Lead
NC
13.5 FW 347.4
ug/L
15 1
27
Monitoring required
— — —
Chronic: 13.54
---------------------------
RP = yes; monthly monitoring w/permit limit
1 values > Allowable Cw
Acute: NO WQS
Mercury
NC
12.0 FW
0.5
ng/L
14 14
19
Chronic: 12.0
_
RP yes; reduce monitoring from monthly to
No value > Allowable Cw
Quarterly ng w/permit limit
Acute: NO WQS
TKN
NC
HH
ma/L
15 5
1.3
Chronic:----------
---------------------------
No value > Allowable Cw
89702 MOD RPA 10Ju12020, rpa
Page 1 of 2 7/10/2020

Terwilliger Pappas — Solis Brightleaf Apartments
NCO089702 Freshwater RPA - 95% Probability/95% Confidence Using Metal Translators
Outfall 001
Qw = 0.0065 MGD
Acute (FW): 1,073.9
No RP, Predicted Max < 50% of Allowable Cw - No
Nickel
NC
119.3 FW 1073.9
µg/L
Monitoring required
14 9
25
Chronic (FW): 119.3
No RP, Predicted Max < 50% of Allowable Cw - No
No_value > Allowable Cw
Monitoring required
Nickel
NC
25.0 WS
µg/L
Chronic (WS): 25.0
No RP, Predicted Max >_ 50% of Allowable Cw
No value > Allowable Cw
apply Quarterly Monitoring
Acute: 56.0
No RP, Predicted Max >_ 50% of Allowable Cw -
Selenium
NC
5.0 FW 56.0
ug/L
15 2
7.0
apply Quarterly Monitoring
_
Chronic: 5.0
No value > Allowable Cw
RP = yes; monthly monitoring w/permit limit
Acute: 403.4
No RP, Predicted Max >_ 50% of Allowable Cw -
Zinc
NC
406.7 FW 403.4
ug/L
15 6
13
apply Quarterly Monitoring
_
Chronic: 406.7
No RP, Predicted Max >_ 50% of Allowable Cw -
No value > Allowable Cw
apply Quarterly Monitoring
PCE
34 0
1.0
Acute: NO WQS
not detected - discontinue monitoring
NO DETECTS
__ _ ___________
Chronic:
Max MDL = 2
not detected - discontinue monitoring
TCE
41 0
1.0
Acute: NO WQS
not detected - discontinue monitoring
NO DETECTS
__ --------------
Chronic:
Max MDL = 2
not detected - discontinue monitoring
89702 MOD RPA 10Jul2020, rpa
Page 2 of 2 7/10/2020