NC0085359_wasteload allocation_20120710

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Belnick, Tom
Noross3sq oray , �►
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7/kin L
From: Belnick, Tom
Sent: Tuesday, July 10, 2012 5:37 PM
To:'[e-mail]_us'; 'Struve, James N.'
Cc: Behm, Pamela; Headrick, Hannah; Poupart, Jeff
Subject: FW: Attached Letter: DO Modeling associated with the proposed expansion of the Union
County (NC)/Twelve Mile Creek WWTP (NPDES #NC0085359) from their permitted flow of 6
MGD to 12 MGD
Attachments: FinalLetter UnionCoNC_12MiCrkExpansion_JuIy2012_HBR.pdf
Ed/Jim- looks like Jim already received this email from SCDHEC. I just want to highlight the SCDHEC comment regarding
seasons. The spec limits that NC DWQ issued to Union County on 9/1/2010 are still applicable, with the exception that
the seasonal limits for BODS and NH3-N will need to be adjusted to reflect SC seasons (Le., Summer= March -October,
Winter= November -February). Additionally, it appears that Union County will not be seeking an expansion beyond 12
MGD at this time. NC DWQ does not plan to issue a revised speculative limits letter, but will address these changes
during the SEPA review process. Let me know if you have any questions.
Tom Belnick
Supervisor, Complex NPDES Permitting Unit
NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
E-mail correspondence to and from this address is subject to the North Carolina Public Records Law and may be
disclosed to third parties unless the content is exempt by statute or other regulation.
From: Rizzuti, Heather B Lmailto:[e-mail]
Sent: Friday, July 06, 2012 11:19 AM
To: Behm, Pamela
Cc: Hedrick, Hannah; Belnick, Tom; Struve, Jim; Clements, Trevor; Graves, David; Montebello, Michael; Gorman, Chuck;
Preston, Heather; David Baize; Kirkland, Gina
Subject: Attached Letter: DO Modeling associated with the proposed expansion of the Union County (NC)/Twelve Mile
Creek WWTP (NPDES #NC0085359) from their permitted flow of 6 MGD to 12 MGD
Ms. Behm,
Please see the attached letter in pdf format. I also sent it to you by mail today. Please contact me if you have
any questions.
Best Wishes,
Heather Bartley Rizzuti, M.S.
Environmental Health Manager II
SCDHEC Bureau of Water
Water Quality Monitoring & Modeling Section
[phone]
rizzuthb r&dhec. sc. g o v
1

� z/Zo r2.
Belnick, Tom
From: Behm, Pamela
Sent: Monday, July 09, 2012 9:34 AM
To: Belnick, Tom
Cc: Headrick, Hannah
Subject: FW: Union County Twelve -Mile Creek WWTP Expansion
Importance: High
Hi Tom,
It looks like we are ready to move on the EA circulation for Union County Twelve -Mile Creek WWTP Expansion based on
the comments we received from SC last Friday. But, do we need to reissue specs first based on my comments below?
Or do these changes just need to be outlined in our_ EA comments? 1
Thanks, %''''�S
Pam
***************************************************************
Pam Behm
NC DWQ Modeling and TMDL Unit
1617 Mail Service Center
Raleigh, NC 27699
Email: [e-mail]
Phone: [phone]
Fax: [phone]
E-mailcorrespondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties.
From: Behm, Pamela
Sent: Tuesday, July 03, 2012 10:33 AM
To: Belnick, Tom
Cc: Headrick, Hannah
Subject: Union County Twelve -Mile Creek WWTP Expansion
Hey Tom,
Just about finished with the Union County Twelve -Mile Creek remodeling review with South Carolina. There are 2 parts
of the speculative limits letter that need to be revised, not sure how this happens. I don't have electronic original spec
limits letter, but it is dated Sept 1, 2010.
1. The expansion permit can only be 12 MGD, 9 MGD and 15 MGD are no longer applicable.
2. To comply with the South Carolina natural conditions law, the seasonal limits will need to be adjusted:
March —October and November— February.
Not sure if the spec limits letter needs to be adjusted, or just the actual permit. I wanted to point this out to you
because there are now parts of the spec limits that are no longer valid.
Thanks,
Pa m
***************************************************************
Pam Behm
NC DWQ Modeling and TMDL Unit
1

1617 Mail Service Center
Raleigh, NC 27699
Email: [e-mail]
Phone: [phone]
Fax: [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties.
2

Sc 01-1t (Caywin-r/vih (9v4t. Moited
DHEC
poMo £ PkOiT P cLsP;,#:
Inly6a 2012
Ms. Pameli
Acting r, Modeling & TMDL Unit
North Carolina Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 2709-1617
11)tenyatt*I0
CIFATM,a0411:.•
Ann taroff Din
)401k0; A#10. gr.:MO
RE: DO modeling associated with the Proposed Expansion of the Union County CYrweive Mile
Creek WWTP ES C0085359) from their permitted flow of 6 MGD to 12 we
nearl\ Rehm.
On behalf-OfSCDHEC, I would like tofleintryou for welcoming our t on
„
affects both of our states. As know, Twelve Mile Creek originates in North
through se Where it joins the Catawba River as a trbutary. The section ofTwelve
Mile CAT*:in SC is located in Watershed Management tink 0301i.:1010,005.00$414 Twelve
Creekis tot iillatitled On South Carolina's 2012 Draft 303(d)-list for dissolved oxygen (DO) but the creek
is listed as impaired forlow DO on North Carolina's Draft 2043044) List. 4Twelve Mile Creek itself
not specifically classifted'hi,SOUtheatOlintr's aassifteligiiifirs (R.61.69) but, as a tributary of the
Catawba River, it is classified in South Carolina as. a .17W, stream, which has a DO standard of not less
than.5.0 mg/1 daily average a low of 44 Me. The available data on,:twOve-Mile Creek indicate
that this creek isuatumily109.khkDO,
In 2010, Union County, NC, requested to expand their Twelve MileCreek WW1? (10,DES
#NC0085359) from the permitted Ile* of 6 MGD to 12 MGD. ThespeculatiVelimitslhoW that the
effluent would be highly treated, with critical monthly average permit limits of s.cfingtie E0D5, 1.0 mg/L
and 6.0 mg/L minimum DO (NCDENR letter, T. Belnick, 9/1/2010). SeaSonat monthly average
pernit limits would be 10.0 mg/L B0135, 1.9 mg/L N113..N, and 6.0 mgX Minimum DO. The WWTP is
currently discharging about 3.4 MOD- (5.26 cfs) to Twelve Mile Creek and would keep the same outfall
location if they expand. Union County also requested to expand to 15 MGD, but ,that part Oftherequeit
has been abandoned. 1112010, SCDHEC and NCDENR recommended additional data collection in ogler -
to refine the existing Qu .412g.4404el, Union County, NC, hired a consul tatit,..flaXen and Sawyer,
who then hired .a subcontractor, ?dared*, to gather necessatydata and produce a calibratetinvidel to
address the two agencies' concerns; In February 2012, Jim Strove ofHazen litawyer sent to
SCDHEC the modelingreport and associated Wedding files. SCDHEC reviewed these documents and
communicated several comments to and Union Comity in a letter dated April 23, 2012.
On May 14, 2012, SCDHEC sent an email to the Union County consultants requesting that an
SOD range -of 0.067 to 0.213.`g/e/Claybensed in Qua12E model and asking that atentlitivitYasidYPis
be p.0E0=64. This SOD range was absolute SOD range at Rick Fork Creek, a Piedmont
stream that is similar to Twelve Mile Creek. In the model, TettaTeeli had used SOD up ..to 0.400
. ,
Iday, which was much higher than any measured 04 a Piedmont stream Roth Carolina. In
response to SCDI-LEC's request, Mr. Trevor Clements of TenaTech, in coordination with Hazen and
Sawyer, sent a memorandum entitled "Response to SCDHEC Model Comments,' dated May 3
bleiuded in this memo was "Attachment A: Model SOD Rate Sensitivity and Overall Qual2E Model
Petto, 1.tif 2
u cik . '1"- .01...
• • • • • . „!. • ..... . „ . ••• . • •- -•• •- ,..-•••:, .......
• 26:

.Refinementy 31,2012)." The consultantsdid what we asked ofthem. Alierthe SOD in the.
Mcdolto nMaXinitint of 0213 gitridat TetreteaticOMpleted a refined:critical model. The Sflned model
' is,a.well,calibrated model that better reflects actual conditions ia Twelve Mile -Creek. Consequently, the
• refined MOON liOlottertla and its 12 MOD effluent run are suitable to bg'uteil.)#4s.,
compliance with South Carolina's water quality standards, specificallythe 0.1 OC
Regulation 61418,. Water aintilka-,00etni Standards, Section m,
The 0.1 Rule states that inwaterbodies,with naturally low DO, during March thronth October,.
• the quality ofthe Steam waters shall not be cumulatively lowered more thank/ for DO (as a daily
average) due to point sources or other activities. The intent is to limit degradation of the streatifs. water
Given that a small percentage of the modeled stream length exceeds the 0.1 me, allowable D0
deficit and given that the proposed :LIMO) of highly treated and highlyaerated effluent are shown to
I have a positive effect in most .DO -deficient areas of the model, the refined Qual2E model forTwelve
Mile Creek demonstrates emnpliancc with the 0.1 Rule, The refined model is a well-cahbrated
model that shows an overall improvement in Twelve MileCreek's DO COncentrations";during thecritical
months. In addition, South Carcdina water quality standards require critical permit limits be applicable to
the months of March through October and require that seasonal pemiit liinits be applicable only to the
months of November through February; therefore, this should be addressed in the proposed Union County
expansion permit.
Itypg.44ve any further questions, please contact me.
motel*,
Heather &Rizatiti,.1VLS.
Environmental Health Manager 11
Water Quality, Monitoring & Modeling Section
(803)8983903
[e-mail]
cc: Hannah Hedrick, SEPA Coordinator, NCDENR, DWQ,,harmith.hedrick@ncdentitov
Tom Belnick, NCDEINIR,'DWQ, tom.helilick@ncrienr,gov
James X. Struve, PE and Vice President; Hazen & Sam*, P.C.; [e-mail]
Trevor Clements, Director, Water Resources - RTP, TetraTech, trevor.clementSetetrateekcorn
David A. Graves, Manager, WQ Monitoring & Modeling Section, SCDREC,
[e-mail]
Michael Montebello, Manager, Domestic Wastewater Permitting Sooting; =am.
[e-mail]
Chuck Gorman; Director; Division ofWQ Monitoring, Assessment,& Pa -Median; KMIEC;
[e-mail]
Heather Preston, Director, Division of Water Quality, SCDIIEC; [e-mail]
David G. Baize, Assistant Bureau Chief, Allman or Water! SCDREC,[e-mail],g0
Gina Kirkland, Water Quality Standards Coordinator, SCDREC, Ginalarkland@dhoo440v
Page 2 On
CAROLINA DEPARTMENT OF Htf.A LTH AND ENV l RONMENTAL CO NTR
BuliStrect • columbia,SC29201 Phonz.[phone] • www.scdueplao

Vitzs+CaNNl� wPiIf1,4/7ooG1/sa,0 s/2o/
Belnick, Tom
From: Rizzuti, Heather B [[e-mail]]
Sent: Monday, May 14, 2012 12:38 PM
To: Clements, Trevor; Behm, Pamela; Struve, Jim
Cc: Turner, Larry; Graves, David; Gorman, Chuck; Hedrick, Hannah; Belnick, Tom; Montebello,
Michael; DeBessonet, Jeff
Subject: Re: Measured SOD rates in NC, in relation to Union County, NC, Proposed Expansion and
QUALE Modeling
Mr. Struve and Mr. Clements,
We have reviewed the supplemental data supplied by TetraTech in justification of the SOD rates
utilized in the Twelve Mile Creek model. We continue to have concerns about the SOD rates used in
the model and their impact on model calibration. In his email from 5/2/2012, Mr. Clements stated that
the model inputs of 0.4 g/ft2/day "may be a bit on the high side" but has implied that the values were
not inconsistent with those measured as part of the NCDWQ sampling and those measures by
HydrO2 in Rich Fork Creek. Based on the information provided, this does not seem to be the case.
The Twelve Mile Creek model uses SOD rates ranging from 0.075 to 0.400 g/ft"2/day. In 5 of the
16 reaches on the model, 0.400 g/ft2/day (equal to 4.3 g/m2/day) was used for the SOD rate. These 5
reaches are all pools, which would be expected to have higher SOD rates than the riffles.
In the NCDWQ SOD Database, there are approximately 160 distinct SOD sample -sets (expressed
in ranges) measured at various water bodies across the state. Of these approximately 160 SOD
entries, when looking at the average SOD rates corrected to 20°C, only two were higher than 4.0
g/m2/day (0.372 g/ft2/day). Of these two stations/entries, one was in a swamp in the Coastal Plain
(Raft Swamp at Hwy 71) and the other was in a coastal marina (Tangle Oaks Marina, Wilmington).
With the exception of these two values (which would not be representative of a Piedmont stream),
the SOD values used in the pool reaches of Twelve Mile Creek are higher than any other values
measured anywhere in North Carolina.
In addition, in his email on 5/2/2012, Mr. Clements mentioned SOD data measured at six stations
in Rich Fork Creek in Davidson County by HydrO2 (Phil Murphy, Del Hicks and crew) in August 2006.
Mr. Clements indicated during our conference call on May 1st that Rich Fork Creek is a Piedmont
stream in a watershed that is adjacent to Twelve Mile Creek. After the conference call, Mr. Clements
sent us the SOD data for Rich Fork Creek (see below). The absolute range of SOD at 20°C for all six
stations on Rich Fork Creek was 0.067 to 0.213 g/ft2/day. Note that the 0.400 g/ft2/day used in five of
the reaches in the Twelve Mile Creek model is 1.88 times higher than the highest SOD value at 20°C
measured at Rich Fork Creek.
We are concerned that 0.400 g/ft2/day (equal to 4.3 g/m2/day) is much higher than the range of
SOD rates measured on Piedmont streams in North Carolina. Therefore, we request a sensitivity
analysis to show the impact of high SOD rates on the calibration of the model. We suggest that the
absolute SOD range of 0.067 to 0.213 g/ft2/day measured at Rich Fork Creek be used for comparison
purposes in a calibration run during the sensitivity analysis. This sensitivity analysis would be the
only additional item that we request that you include in your formal response to our comments
concerning the Twelve Mile Creek Modeling Report.
Please let me know if you have any questions.
i

Sincerely,
Heather Bartley Rizzuti, M.S.
Environmental Health Manager II
SCDHEC Bureau of Water
Water Quality Monitoring & Modeling Section
[phone]
rizzuthb (cif dhec. sc. gov
On Tue, May 8, 2012 at 2:08 PM, Clements, Trevor <Trevor.Clements( z tetratech.com> wrote:
Larry,
I just returned from a meeting in Greensboro and received your message. Here are the individual stations data from
Rich Fork Cr:
Water Temperature
L `)
i gee gSOD
`d
Average SOD
of of 20
Ave g -ROD OD at 20
°C (g'ft21d)
Upstream of WVVfP
22.7
0.078 - 0.098
0.088
0.067 - 0.084
0.075
Highway 109
25.0
0.167 - 0.210
0.194
0.125 - 0.157
0.145
Ball Road
26.0
0.143 - 0.158
0.147
0.101 - 0.111
0.104
200 yards below
Ball Road
23.3
0.089 - 0.259
0.198
0.074 - 0.213
0.163
500 yards below
Ball Road
23.3
0.094 - 0.234
0.140
0.077 - 0.193
0.116
Kanoy Road
22.5
0.080 - 0.094
0.087
0.069 - 0.081
0.075
Evans Road
25.0
0.089 - 0.201
0.127
0.067 - 0.150
0.095
Trevor Clements I Director, Water Resources - RTP
Direct: 919.485.2058 I Main: 919.485.8278 Fax: [phone]
trevor cleme ntstetratech. com
Tetra Tech I Complex World, Clear Solutions
P.O. Box 14409 13200 Hwy 54, Suite 105 I Research Triangle Park, NC 27709 I www.ttwater.com
PLEASE NOTE: This message, including any attachments, may include privileged, confidential and/or inside information. Any distribution or use of this
communication by anyone other than the intended recipient is strictly prohibited and may be unlawful. If you are not the intended recipient, please notify
the sender by replying to this message and then delete it from your system.
2

from: Turner, Larry [mailto:turnerle©adhec.sc.gov]
Sent: Tuesday, May 08, 2012 9:20 AM
To: Clements, Trevor
Cc: Rizzuti, Heather B
Subject: Re: Measured SOD rates in NC
Trevor, you state below: "Six SOD stations measured in Rich Fork Creek in Davidson County by HydrO2 (Phil
Murphy, Del Hicks and crew) in August 2006 ranged between 0.067 and 0.213 g/ft2/day at 20 degrees C."
However, I can't find where you provide the actual values. Were they evenly distributed between 0.067 and
0.213? Were 5 in the 0.07 range and only one in the 0.2 range...or the reverse? Please provide the 6 measured
values. Thanks, LT
On Wed, May 2, 2012 at 3:07 PM, Clements, Trevor <[e-mail]> wrote:
Heather and Larry,
Thank you for taking the time yesterday to discuss your questions with us regarding the Twelve Mile Creek
modeling analysis. During our discussion, we promised to forward information on SOD rate measurements in
NC. The attached database contains data collected by NCDWQ through 2006. The rates are shown in
g/m2/day which can be converted to g/ft2/day by dividing by a conversion factor of 10.76.
The NCDWQ database shows an extensive range of values (all corrected to 20 degrees C), from 0.0169 to 6.533
g/m2/day or 0.002 to 0.607 g/ft2/day. The vast majority of rates are in the 0.1 to 0.3 g/ft2/day.
Six SOD stations measured in Rich Fork Creek in Davidson County by HydrO2 (Phil Murphy, Del Hicks and
crew) in August 2006 ranged between 0.067 and 0.213 g/ft2/day at 20 degrees C.
The values assumed for Twelve Mile Cr ranged from 0.075 g/ft2/day for riffle areas to 0.4 g/ft2/day for the
highest pool SOD rates. As discussed on the call, the 0.4 rate may be a bit on the high side and its impact the
farther we move from 20 degrees C for model application is likely overestimation of oxygen demand (thus
contributing to the steeper predicted DO sags in the lower reaches of Twelve Mile Creek relative to observed).
Although further adjustment and data collection could continue to improve model prediction fit with observed
profiles, it is our belief that such model enhancements would not result in a substantive change in the
conclusion that the effluent from the Union County WWTP enhances dissolved oxygen profiles in Twelve Mile
Creek below the outfall during summer low flow conditions, and that permitting of the facility's expansion at
the proposed limits is the best alternative.
3

We will need to prepare a formal response to your questions, but wish to wait until you provide us with your
additional thoughts based on the conference call discussion and additional SOD data provided here. Please feel
free to call me for any further questions or items to discuss. We look forward to hearing from you as soon as
possible so that the permit review process can continue accordingly.
Regards,
Trevor
Trevor Clements Director, Water Resources — RIP
Direct: 919.485.2058 ! Main: 919.485.8278 l Fax: [phone]
trevor. cleme nts(catetratech. com
Tetra Tech Complex World, Clear Solutions
P.O. Box 14409 j 3200 Hwy 54, Suite 105 i Research Triangle Park, NC 27709 www.ttwater.com
PLEASE NOTE: This message, including any attachments, may include privileged, confidential and/or inside information. Any distribution or use of this
communication by anyone other than the intended recipient is strictly prohibited and may be unlawful. If you are not the intended recipient, please notify
the sender by replying to this message and then delete it from your system.
Larry Turner, MSPH
SC DHEC
803.898.4005
turnerlendhec.sc.gov
4

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PROMOTE PROTECT PROSPER
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April 23, 2012
Ms. Patricia Behin
Acting Supervisor, Modeling & TMDL Unit
North Carolina Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
BOARD:
KII/TOO Vklia
Clantke Batt Jr,
Mn 1Wol, DDS
JoluvO, Marco, :Sri, MD
Comments on "QUAL2 Model Update for Twelve Mile Creek below the Union County
WWTP":(F0b,20P); prepared by Tetra Tech for dieljnionCOnntf (NC)
Works Dept and..Ilezen&:AawYer,-P.C:.
Dear Ms
cwb.0.401rof...$0)fir, (hereafter referred f04ktbe'pOpa#rnont);,,.-4 would like to thank
you for WeICOMing:.the.Departrnent'Sinpnt on this that affects both ,of our states. As you
kaoucTikiNukhkOteek originates iifNottk.CAtelind and..flOvitt:tbitiogbLOastet.0?iinty,'SC,.
vhere'itioills:thd::Catt*bt River as a tributary. The section ofTwelvelMtle.Creek that is in SC
isJoowstin IffnprAbpd,Mouqgetrient:Put, 0301, KLIC,:(WOQI44402. The upstream section of
TAs*Ne mile Creek in NC :is included on the NC 2010 303(d) list foreopper, turbidity, and
Ecological/biological . Integrity fiShCont;:.frein the headwaters to the NC/SC state line. In South
Carolina, Twelve Mile .Creetis impaired : only for copper at ttatian',0.410. There is also an
Approved TIVIDL for fecal colifonn; boyever,:00:Strearn oseisnOtopporte,t4 according W(40:
2019 SC 303(4) list. Twelve Kilo Creek is not included on tbe:.2914393(d) list for dissolved
oitygen:.OpYindther state Twelve Mile Creek itselfis not specifically classified
but. as a itibuinty.oftbe::tattObnItiye4 itis classified in South Carolina as a FW stream,which
bA5 ADO.:•StandA#1.*.itbia daily average :ornot:jesAthat 5.0 mg/1 With a 10*; Of:44 :OA
In 21)1(/Pnion, County, NC, requested p4e?ipandlheir T*TelyeMilAcreek.wwr:
(sipnEs..0E0003-59).frookeoifototte4.,:floti*:06;;VICpt0 12 MC11). The wwrp is
currently discharging :34.1V161) (546 Of4)14.:TelVetilifeCreekarid.*Mild::lieep the same
ontfift10:0494if they expand.In 2014:Tfoi00 County otiotequosteOto•ovau4:tu.1$4104 but
that part of the request haajboen-AtalgtOle4, In atriot#41.01140010 dated 7/2$4010;.the
Department responded to the request 01<at4y$tgckpr,cofNCP01: ppopp*pg*;:pr9pq400,
expansion. The Department iticoniitiodtd additiOnatMenitering)ofthe*roam frkprderlef.
prodUeet4alibrateditioda-Whielitould adequately support the idea tu'UtD0;04504iiigitiO in:
the creek 401*(4001e'to natural •conditions.
The Union pout* (NC.:)PubliOWO40::POtArtncnt:bitedAeonsultAnti:fiagenA041'
Sawyer, who then hired a subcontractor, TetraTech, gathernecesserydataanaprodnoeg,
calibrated model to aildresa the conterni:ofNCDENR4nd SCDWC. In Vottint*.01Z4 Jim
Pago•I:Of
Ot T11 (..RUJ.IN:\. IEPARI .4EN1'OJ itEA:117 U
06,Boli:Stift* • Coitimbh SP:2041.-Phiiii0,4051.898-343.• viittlystAtee0t-
L

Struve of Hazen & Sawyer, PC, sent the modeling report and associated modeling files tothe
ent. Mr. Struve asked the, Department to share any commons about the documents with
'am Bebni ofthe NO Division of Water Quality (ICDWQ) at Is10041, The Department has
reviewed these documents and has several comments; concerns, and questions. On April 4,
2012, Heather Rizzufi and Larry Turner shared these comments in a Conference call With Pam
Rehm and Hannah Hedrick of NCONVQ, This Memo clescribesthe D- comments that
were discussed during that conference call. The page. numbers correspond to those in the
"QUALI Model update,..” document.,
Comments -and Questions:
1.) page 14. Temperature
- It is unclear how temperature was handled. Are they correct in saying that they Attempted
to control.forvarmgompspherie temperature .(pg. 14), or did they attempt to normalize
the instream temperatures based on instream temperature variability? During the data.
collection, was the atmospheric/air temperature or the water temperature measured?
Was the model calibrated to actual temperatures or to normalized temperatures?
- What was the actual differencein the measured and normalized temperatures?
- With the different scales on Figures -11 and 12, it is difficult to tell ifthere was any
sipnficant . difference between the observed DO concentrations and the "temperature
nomaline DO concentrations. What were the actual differences?
- It appears that the "nonnaliied" 90ItPereentile temperature ia24,16C1(16.517), which la
Apparently the temperature at which all "production runs'. wereMade. Alsoit pears
tiatthekinneineOelXen used an initial condition temperature of 7446°F, which appears to
be the -lowest temperature measured during the June sampling period. HOWisibia Value
the appropriate ternperanire for the calibration run whenthe measured temperatures
varied significantly as you move downstream? In contrast, the July validation run
temperature of110.s“is near the mid -range of the observed values, not the lowest value
measured. Additional explanation is needed on how the model's initial temperatures
were determined.
2.) page 18.
- Section 3.1.2 says that the soaping model estimated stream slopes from 10-meter LIDAR
contours. Is: a typo?
3.) Page 21, Table 4,
- While we do not expect the slopes and velocities to correlate perfectly, there are instances
where reaches with equal velocities have significantly different slopes. For example,
reaches 1, 9, and 13 all:have a velocity of 0.24 feet/second in the June run, but the slopes
ate 4.12, 123, and -LSO feet/mile, respectively. How is this explained/ Also, that are
some instances where reaches with greater slopes have lower velocities tun reaches -with
lower Slopes. Please explain.
4.) Page 24Table ?
CBODu for headwater, incremental, and tributary inflow is estimatedto be 0.75
This seems to be below the detection limit for BOD5. The detection limit for 130135 for
Page 2 of 4
st)trni tAg()LINA oF,p.ARTmk:NT OF JJEALIII AND ENVIlt0.NIVIFNTAL (:()NIR()].
,
MOO DonStreet • erAintbia,SC2k101 ?hour:00M 898-343 • wwwscdlicegov

South Carolina's monitoring data is 2,0 m
ratio is used?
•, How is this low value justified? What• F-
5.) Page 25, Table &
- SOD values appear overly high when compared to Values in Table 3-25 in Rates,
Conga ntz &-rineties when giftziday are converted to eln4idaY)- Were CM) decay
rates calculated first, and then was SOD used as the primary calibration knob and simply
varied until an acceptable calibration was achieved? Are the SOD values within the
acceptable range? The Department's main concern is whether this is a valid calibration
That can be used as a tool to compare a realistic no-load run with various runs that include
wastewater.
6-,) Page 26, Figure 1.6; and Page 28, Figure 20.
- Figure 16 shows a pretty good calibration for the June model ran with the Mined model
results. It shows a visually pretty good fit with the June observed data. However, Figure
20, which compares the July model run to the July observecitlata,:does not seem to
calibrate as well. Explanation is needed as to why this verification is acceptable.
1) Page 27, Figure 17.
This figure shOws., the model's predicted components ofthe DO deficit. Is this
reasonable, or is it just an artifact of the somewhat high SOD values used?
The Department thinks that this Qual2E model for Twelve Mile creekia based etiverY
good measurements ofchannel elevation, slope, DO, and other physical Characteristics, Which
resulted in an accurate model structure. The available data on Twelve Mlle Creek indicate that
this creek is naturally low in DO, and, therefore, the Department would need to evaluate whether
the Union County/Twelve Mile coot WWTP expansion proposal will meet the 0.1 .mgef.,, DO
deficit rule (SC Regulation 61-68, Water CiassOcation'anc 1Stanf,ard4 Section D), However,
based on our review of the model calibration and the questions stated above, the Department is
unsure whether the model is calibrated well enoughatthis time to serve as an adequate tool for
determining compliance with the 0:1 Rule. The Department looks Anwerd'to Union County's
response to the comments above.
Sincerely,
Heather B. Riazuti,
Environmental Health Manager 11
Water Quality Monitoring &ModelintSection
3).898-3903
rizziithhadhecsc.gov
Hannah Hedrick, SEPA coordinator, NCDENR, DWQ, tutatia0edrickee,nodenrcgov
Page3 Of4
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a d A. Manager, V. Q,Monitoring & Modeling. SectiTWC, ( .sc 1ov'
WQ Monitoring & Modeling Section, SCDNEC, turnerle@dlec sc
Michael Montebello., Manager, Domestic Wastewater Permitting,S tion, SC:DREOt
1)ttii ? dSieizan.prt
Chuck M, Gorman, Director, Division ofWQ Morita g, A sment, &Protection, SC HEC
g dhec sc gov
J deBessonet,,Di reoioor DiVision ofWater,faciliti s P
Page 4of4
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Belnick, Tom
`From: Behm, Pamela
Sent: Tuesday, April 24, 2012 9:53 AM
To: Rizzuti, Heather B
Cc: Headrick, Hannah; Belnick, Tom; Graves, David; Turner, Larry; Montebello, Michael; Gorman,
Chuck; DeBessonet, Jeff
Subject: RE: Letter regarding Comments on the "QUAL2 Model Update for Twelve Mile Creek below
the Union County WWTP"
Thank you Heather. I appreciate the thorough review and will see that these comments are addressed.
Regards,
Pam
***************************************************************
Pam Behm
NC DWQ Modeling and TMDL Unit
1617 Mail Service Center
Raleigh, NC 27699
Email: [e-mail]
Phone: [phone]
Fax: [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties.
From: Rizzuti, Heather B [mailto:rizzuthb©dhec.sc.govl
Sent: Monday, April 23, 2012 10:17 AM
To: Behm, Pamela
Cc: Hedrick, Hannah; Heather B Rizzuti; Belnick, Tom; Graves, David; Turner, Larry; Montebello, Michael; Gorman,
Chuck; DeBessonet, Jeff
Subject: Letter regarding Comments on the "QUAL2 Model Update for Twelve Mile Creek below the Union County
WWTP"
Ms. Pamela Behm,
As we discussed during our conference call on April 12th, I have written a letter detailing SCDHEC's comments
on the report referenced above. I have attached a PDF of the letter, and a hard copy will be mailed today.
Please call or email me if you have any questions. Thank you.
Sincerely,
Heather Bartley Rizzuti, M.S.
Environmental Health Manager II
SCDHEC Bureau of Water
Water Quality Monitoring & Modeling Section
[phone]
rizzuthbn dhec. sc. gov
1

rNccroe s35i_
Presentation to DWQ for Union County
Twelve Mile Creek Modeling Study Update
- /1 2.e-hrt+4 GCvll%tt etw /HA 6 SAW,'41/rekoT,4
- n'Idpte (edit-1e + SFel-haets
Twelve Mile Creek Data Collection
and Model Refinement Summary
March 1, 2012
TETRA TECH
Background
• Scoping study (2010) indicated that maintaining
Union County discharge to Twelve Mile Creek is better
for dissolved oxygen (DO) in the receiving water
— E,M40 MO:M Het • 34 YOa — Zero Mumma
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Tetra Tech Data
Collection Overview
11111111
• Stream Reconnaissance: Feb 2011
- Accessibility/feasibility of survey In lower section
- Support field planning
• Channel Elevation Survey
- Initial survey: Mar 2011
• 113 points from 65,800 feet (12.5 miles) of channel
— Upper section refined survey: Aug 2011
• 90 points replaced 17 original points over 3.3 miles
• Water Quality Profiles
- June, July, August, September 2011
3/1/2012
:::)
Twelve Mile Creek
Location Map
E▪ d
NCDWQ Response
• Collect data to validate model predictions or
refine the model
• October 18, 2010 Tt-DWQ conference call
- survey channel elevation
- collect multiple low flow DO profiles
Stream
Reconnaissance
SIM=
• Channel accessibility/survey feasibility
challenged by log jams and limited put in
and take out points
PS—.Ortt/f eWI1- e03/d)
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11- I'✓1�J< C ' of
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County pato May - Aug
Presentation to DWQ for Union County
Twelve Mile Creek Modeling Study Update
Twelve Mile Creek
defined by series of
riffles and pools
Comparison to
Previous Estimation
Ao
sta. WI
1M
DO Profiling:
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9
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05
051
Monitoring Location
052
3/1/2012
Channel Elevation
Survey Results 11111111111
lieelvee Creek Surveyed Profile
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July
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Tetra Tech 2

- Presentation to DWQ for Union County
Twelve Mile Creek Modeling Study Update
Tetra Tech DO
Profiling Results
9.5
0.5
7.5
6.5
I 5.s
1 as
9.5
2.5
1.5
Old USGS Gage
12-Dille Discharge
2 4 -- - _6 g 10
Stream Length (m0
12
1•
Areas to Address in
Model Refinement
• Modify model reach definitions to reflect
improved understanding of pools and riffles
- Refines reach velocities and travel time
• Refine calibration to reflect upper section
DO sag and decrease magnitude of DO sag
in the lower section ; •
- Recalibrate for June 2011
- Validate for July 2011
New Model Reach
Delineation
.
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3/1/2012
Implications for
Model Refinement
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Refinement
ISM=
• Reach redefinition based on channel
elevation survey and observations
• Hydraulics recalibration to account for pool
and riffle configuration
• Water quality recalibration using DO profiles
Refined Model
Stream Hydraulics
• Velocities ranged from 0.10 to 0.44 ft/s
• Depths ranged from 0.64 to 2.60 ft
• Total time of travel through the model
domain for the June 2011 simulation was
4 days
LT1
Tetra Tech 3

Presentation to DWQ for Union County
Twelve Mile Creek Modeling Study Update
Refined Model
Kinetics
• Reaeration ranged from 0.35 to 3.95 /day
• CBOD decay ranged from 0.033 to 0.144
/day ( )
• SOD ranged from 0.075 to 0.4 /day
pdiapitzL r)
Model Validation Fit
July 2011
w.
•
0 2
111•1•Mli6 8
Model Reach Mlles
10
12 24
Model Application:
2 Primary Questions
1) Is there a sag in DO concentration below
the WWTP outfall that is increased by the
WWTP discharge?
2) Does DO concentration in the receiving
waters improve with increased wasteflow?
311 /2012
Refined Model
Calibration Fit
:m,
6 6
Model Reach Miles
1D
• D414
�-• Relined Model
P06I
6 melt
12 14
Comparison for
August 2009
10
9 •
8 +
a
Dot,
-Relined M02,6
4•1110PPock
2 4 4 4 10 12
Model Reach Mlles
14
Model Application:1.1111111
4 Scenarios
10
9
8
s
0
—...
Pools ..... 0MS0
3.4MGD — 6MGD
— 12MGD
I I l
A TAIIMr‘Wilii
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2 4 6 8 10 12 14
Model Reach Mlles
Tetra Tech 4

Presentation to DWQ for Union County
Twelve Mile Creek Modeling Study Update
Conclusions from
Refined Modeling
• The Union Co. WWTP discharge does not
cause DO to worsen downstream
• The discharge significantly increases DO
(particularly in pooled water zones)
• DWQ can use the calibrated and validated
model for wasteload allocation purposes for
the discharge in Twelve Mile Creek
•
3/1/2012
Contact
Information
Email: [e-mail]
Phone: (919) 485 - 2058 (direct)
.=_1 Tetra Tech 5

TINY Nlti11, k aZ 11144 qFcR
Uni svi aw.14171
- Belnick, Tom
s
From:
Sent:
To:
Cc:
Subject:
Attachments:
Tom /Jeff,
Struve, James N. [[e-mail]]
Wednesday, February 08, 2012 3:43 PM
Belnick, Tom; Poupart, Jeff
Krebs, Rob; Stecker, Kathy; Sadler, Mary;[e-mail];
[e-mail]; Struve, James N.; Clements, Trevor; Alpert, Scott
Union County 12-Mile Creek WWTP Expansion - Meeting Request
TM - 12 Mile Expansion Alternatives_Rev6.pdf
NC wss351
Back in June 2010, Union County Public Works (UCPW) and Hazen and Sawyer (H&S) staff met with Division of Water
Quality (DWQ) staff to discuss the expansion of the County's 12-Mile Creek WWTP from 6 to 12 mgd. An expansion
alternatives development study, as prepared by H&S (refer to attached PDF), was presented to DWQ Staff at this time.
In this study, a scoping level model, as developed by Tetra Tech, demonstrated that the receiving stream (Twelve Mile
Creek) had sufficient assimilative capacity for the flow increase and that the additional flow actually improved overall
water quality within the receiving stream.
As a result, DWQ issued speculative discharge limits for 9, 12 and 15 mgd flow conditions on September 1, 2010. There
was also an understanding among all parties at this time that additional field testin and associated modeling would be
required to validate the scopinlevel model. Over the last 12 months, this work has been completed by Tetra Tech.
trrrng is same time rame, H&S has also prepared a "draft" environmental assessment (EA) for the plant expansion.
Therefore, the purpose of this email is to request a meeting with DWQ's NPDES Permitting and Modeling/TMDL Units to
present the field calibrated QUAL2E modeling results for the expanded discharge into Twelve Mile Creek. We would like
to receive DWQ's input and concurrence of the model prior to submitting the EA to SEPA for a completeness review.
Below, I have provided several potential meeting dates and times. Please review and let me know which, if any,
dates/times are conducive to your schedule.
• Monday, Feb 13th - betwee '0 and 4:00 PM
• Wednesday, Feb 15th — . y time
• Thursday, Feb 16th between 2:00 and 4:00 PM
• Monday, Fe. 'th — between 1:00 and 4:00 PM
• Tuesda , eb 215t — between 10:30 AM and 3:00 PM
• W:. nesday, Feb 22nd — between 1:00 and 4:00 PM
We Zook forward to hearing and meeting with you.
Warmest regards,
Jim
James N Struve, PE
Vice President
Hazen & Sawyer, P.C.
4944 Parkway Plaza Blvd, Ste. 375
Charlotte NC 28217
[phone] - Office
a [phone] - Cell
jstruve' hazenandsaw, er.com
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Belnick, Tom
'From: Belnick, Tom
Sent: Tuesday, October 26, 2010 11:59 AM
To: 'Clements, Trevor'
Cc: Stecker, Kathy; Behm, Pamela; Nowell, Jackie
Subject: Union County/12 Mile Creek
Trevor- just a recap of our phone discussion on 10/18/2010 regarding extent of follow-up studies to be undertaken to
validate model predictions for Union County/12 Mile Creek:
• The study can be limited to evaluation of physical changes in the stream channel (stream elevation, cross
section, slope, multiple DO profiles)
• Tetra Tech plans a Winter Recon to measure slopes/elevation.
• Tetra Tech plans a Summer 2011 survey to validate DO conditions at modeled DO sag points. Depending on the
results, it is possible that the model will need to be recalibrated.
Tom Belnick
Supervisor, Complex NPDES Permitting Unit
NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be
disclosed to third parties.
1

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- Belnick, Tom
'From:
Sent:
To:
Subject:
Clements, Trevor [Trevor. Clements©tetratech.com]
Tuesday, October 12, 2010 10:23 AM
Belnick, Tom
RE: Monitoring/Modeling in Union County 12 mile Creek
Very good. I will call you then. Thank you.
Trevor Clements I Director, Watershed Management Services
Direct: 919.485.8278 x100 I Fax: [phone]
trevor.clem ents{tetratech. com
Tetra Tech I Complex World, Clear Solutions
F.O. Box 14409 13200 Hwy 54. Suite 105 I Research Triangle Park, NC 27709 i www.ttwater.com
PLEASE NOTE: This message, including any attachments, may include privileged, confidential and/or inside inform. lion. Any distribution or use of this
communication by anyone other than the intended recipient is strictly prohibited and may be unlawful. If you are not he intended recipient, please notify
the sender by replying to this message and then delete it from your system.
From: Belnick, Tom jmailto:tom.belnick(a ncdenr.gov]
Sent: Tuesday, October 12, 2010 8:54 AM
To: Clements, Trevor
Subject: RE: Monitoring/Modeling in Union County 12 mile Creek
Trevor- Works for me. 807-6390
Tom Belnick
Supervisor, Complex NPDES Permitting Unit
NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
apt
I WI 411
PrA rib/
Artrte IV
E-mail correspondence to and from this address may be subject to the NortlfCarolina Public Records Law and may be
disclosed to third parties.
From: Clements, Trevor f mailto:[e-mail]
Sent: Tuesday, October 12, 2010 8:40 AM
To: Belnick, Tom
Subject: RE: Monitoring/Modeling in Union County 12 mile Creek
Tom,
How about Monday afternoon at 1:30 pm?
Thanks,
Trevor
Trevor Clements 1 Director, Watershed Management Services
Direct: 919.485.8278 x100 I Fax: [phone]
trevor.clements(atetratech.com
1 .1411/4.1
Whit4f4va If,4 h' 1.1 tree"
Tetra Tech I Complex World, Clear Solutions
P.O. Box 14409 13200 Hwy 54, Suite ,05 I Research Triangle Park, NC 27709 I www.ttwater.com
PLEASE NOTE: This message, including any attachments, may include privileged, confidential and/or inside information. Any distribution or use of this
communication by anyone other than the intended recipient is strictly prohibited and may be unlawful. If you are not the intended recipient, please notify
the sender by replying to this message and then delete it from your system.
1

From: Belnick, Tom Finailto:tom.belnick(8ncdenr. ov
Sent: Friday, October 08, 2010 5:46 PM
To: Clements, Trevor
Subject: RE: Monitoring/Modeling in Union County 12 mile Creek
Trevor- won't work. I'm only in Mon/Tues next week but have several commitments, and several folks involved in this
project are at an EPA meeting Mon-Thur. The following week, I'm good most days (except for Monday 9-10 and all
Tuesday).
Tom Belnick
Supervisor, Complex NPDES Permitting Unit
NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be
disclosed to third parties.
From: Clements, Trevor jmailto:Trevor.Clements _ tetratech.coml
Sent: Thursday, October 07, 2010 2:50 PM
To: Belnick, Tom
Subject: Monitoring/Modeling in Union County 12 mile Creek
Hello Tom,
Would you have time either Monday morning before 9 am or Tuesday before 10:30 am for a quick call to discuss DWQ
expectations for the follow up monitoring studies in 12-Mile Creek referred to in the speculative limits letter for Union
County?
Please let me know if either of these time windows are possible for you and to confirm that [phone] is the
correct number to call.
Thank you,
Trevor
Trevor Clements 1 Director, Watershed Management Services
Direct: 919.485.8278 x100 I Fax: 919,485.8280
trevor.clements. tetratech.com
Tetra Tech I Complex World, Clear Solutions
P.O. Box 14409 13200 Hwy 54. Suite 105 I Research Triangle Park, NC 27709 I www.ttwater.com
PLEASE NOTE: This message, including any attachments, may include privi!eged, confidential and/or inside information. Any distribution or use of this
communication by anyone other than the intended recipient is strictly prohibited and may be unlawful. If you are not the intended recipient, please notify
the sender by replying to this message and then delete it from your sy: tem.
2

U11 I 0 HkVP-
Belnick, Tom
.?/u IQ
'From: Stecker, Kathy
Sent: Thursday, September 09, 2010 2:43 PM
To: Behm, Pamela; Belnick, Tom
Cc: Nowell, Jackie
Subject: RE: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County, NC;
discharge to Twelve Mile Creek
also had two calls with SC people — one before and one after they submitted their comments. The first call was with
permitting staff, and the second was with modeling staff.
From: Behm, Pamela
Sent: Thursday, September 09, 2010 2:41 PM
To: Belnick, Tom
Cc: Nowell, Jackie; Stecker, Kathy
Subject: RE: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County, NC; discharge to Twelve
Mile Creek
Yes they do.
From: Belnick, Tom
Sent: Thursday, September 09, 2010 11:56 AM
To: Stecker, Kathy; Behm, Pamela
Cc: Nowell, Jackie
Subject: FW: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County, NC; discharge to Twelve
Mile Creek
Question- does our comments for additional sample collection/model validation address comments submitted by SC
DHEC to Kathy?
Tom Belnick
Supervisor, Complex NPDES Permitting Unit
NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be
disclosed to third parties.
1

From: Michael Montebello [mailto:[e-mail]]
Sent: Thursday, September 09, 2010 11:43 AM
To: Belnick, Tom
Subject: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County, NC; discharge to Twelve Mile
Creek
Tom,
This went to Kathy Stecker on July 27, 2010. Please confirm receipt.
Thanks
Mike Montebello
Michael Montebello, Manager
Domestic Wastewater Permitting Section
Phone [phone]
Fax [phone]
montebm j:f': dhec.sc.nov
This electronic mail and any files transmitted with it are confidential and are intended solely for the use of individual or
entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the
electronic mail to the intended recipient, be advised that you have received this electronic mail in error and that any
use, dissemination, forwarding, printing, or copying of this electronic mail is strictly prohibited. If you have received this
electronic mail in error, please immediately notify the sender by return mail.
2

Belnick, Tom
From: Michael Montebello [[e-mail]]
Sent: Thursday, September 09, 2010 11:43 AM
To: Belnick, Tom
Subject: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County, NC;
discharge to Twelve Mile Creek
Attachments: Memo: Proposed expansion of Twelve Mile Creek WWTP (NC0085359) in Union County,
NC; discharge to Twelve Mile Creek
Tom,
This went to Kathy Stecker on July 27, 2010. Please confirm receipt.
Thanks
Mike Montebello
Michael Montebello, Manager
Domestic Wastewater Permitting Section
Phone [phone]
Fax [phone]
montebmiiii :dhec.sc.gov
This electronic mail and any files transmitted with it are confidential and are intended solely for the use of individual or
entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the
electronic mail to the intended recipient, be advised that you have received this electronic mail in error and that any
use, dissemination, forwarding, printing, or copying of this electronic mail is strictly prohibited. If you have received this
electronic mail in error, please immediately notify the sender by return mail.
1

641/0160e6/uy►1.le/c-g/t .1/tit 40o
- Belnick, Tom
From: Belnick, Tom
Sent: Wednesday, September 08, 2010 1:08 PM
To: Matthews, Matt; Poupart, Jeff
Subject: FW: re possible expasion of Union Co. WWTP - 12 Mile Creek - NC0085359
Attachments: Region 10 Natural Conditions Manual.pdf
Fyi... EPA input on proposed expansion for Union County/12 Mile. Facility has collected the
data during Summer 2009 to show low DO upstream of discharge. We can place burden on them to
summarize results in SEPA EA.
Tom Belnick
Supervisor, Complex NPDES Permitting Unit NC DENR/Division of Water Quality
1617 Mail Service Center, Raleigh, NC 27699-1617
[phone]; fax [phone]
E-mail correspondence to and from this address may be subject to the North Carolina Public
Records Law and may be disclosed to third parties.
Original Message
From: [e-mail][mailto:[e-mail]]
Sent: Wednesday, September 08, 2010 10:18 AM
To: Belnick, Tom; Vinzani, Gil
Cc: [e-mail]; [e-mail]
Subject: re possible expasion of Union Co. WWTP - 12 Mile Creek - NC0085359
sorry for the delay in getting back to you. Below is input from our
WQS and monitoring folks...will be glad to discuss whenever you want
From the WQS side of the house (Lisa);
NC has a provision in their WQS at 15A NCAC 02B .0205 entitled, Natural Characteristics
Outside Standards Limits, which says in part, "...WQS will not be considered violated when
values outside the normal range are caused by natural conditions." It goes on, "...the
discharger will not be considered a contributor to substandard conditions provided maximum
treatment in compliance with permit requirements is maintained and, therefore, meeting the
established limits is beyond the discharger's control."
To my knowledge, I have not seen NC use the natural provisions WQS reference much. If they
were to use it for CWA purposes, though, such as an NPDES permit, or for the 303(d) list,
they would need to document that the waterbody truly had natural conditions outside of the
range of the State WQS. Attached is an EPA document from R10 that suggests how states should
document such a decision. Under the Executive Summary it discusses principals to follow,
indicating that the demonstration of natural conditions should be:
1. geographically specific
2. scientifically defensible
3. well documented and supported with data and information 4. highlighted in a process that
provides the public and opportunity for review and comment when natural conditions provisions
are applied (such as an NPDES permit) 5. tracked and accessible to the public (i.e. listed
on a webpage.)
1

Let us know if we can help NC in this process.
(See attached file: Region 10 Natural Conditions Manual.pdf)
from the monitoring side of the house (Marion):
Dissolved oxygen (DO) data from DWQ's Ambient Monitoring Station C9819500 from 2004 to 2009
show, with the obvious exception of the latter half of 2007, levels above the WQS (from
STORET). According to the NC Drought Managment Advisory Council (ncdrought.org, 2009 Annual
Report), "the drought in 2007 was the worst for NC since record keeping began..." And since
"(t)hese tributaries to the Catawba River in South Carolina have very low flows during the
summer and may stop flowing during drought periods" (DWQ Catawba River Basinwide Water
Quality Plan), it is not surprising that these low levels of DO were recorded during that
year. If you have data that indicate that low DO levels are prevalent, we would like to see
that data.
2

TECHNICAL MEMORANDUM
PREPARED FOR: Union County Public Works
Union County, North Carolina
PREPARED BY: Hazen and Sawyer, P.C.
Jim Struve, PE; Scott Alpert, PhD, PE; Julie Doll, PE
DATE: August 2, 2010
SUBJECT:
Twelve Mile Creek Wastewater Treatment Plant
Expansion Alternatives Development Study
Task Order No. 28
DISTRIBUTION: Union County Public Works
Ed Goscicki, PE; Scott Huneycutt, PE; Mark Tye; John Hahn
Introduction
The Twelve Mile Creek Wastewater Treatment Plant (WWTP) is currently rated for treatment of a
maximum month flow rate of 6 million gallons per day (MGD). The plant's liquid treatment process
consists of screening and grit removal, advanced secondary treatment for BOD, nitrogen, and
phosphorus removal, secondary clarification, filtration, UV disinfection, and cascade aeration prior to
discharge into Twelve Mile Creek. Solids treatment includes gravity belt thickening and aerobic
digestion with final biosolids disposal onto permitted agricultural farmland.
Currently, the Twelve Mile Creek WWTP treats approximately 3.3 MGD with a maximum month flow of
3.72 MGD. Union County (County) has expressed concern that the remaining plant capacity will be
quickly consumed once the economy improves and the housing market rebounds. The North Carolina
Department of Environment and Natural Resources' (NCDENR's) Division of Water Quality (DWQ) has
previously indicated that the permitting of additional discharge into Twelve Mile Creek is unlikely
because of upstream and downstream dissolved oxygen (DO) concentrations below 5.0 mg/L.
To avoid a shortage of wastewater capacity in the near future, alternatives for expansion of the Twelve
Mile Creek WWTP and/or disposal of wastewater generated in southwestern Union County need to be
developed and evaluated. The objective of the Expansion Alternatives Development Study is to provide
the County with the required information to shortlist the alternative(s) that could be further refined and
developed to cost-effectively provide approximately 3 MGD of additional capacity at the Twelve Mile
Creek WWTP.
Twelve Mile Creek VvWTP Expansion Alternatives - 1 -
August 2010
IEN AND S&WYER
Environmental Engineers & Scientists

Expansion and Disposal Alternatives
The County and Hazen and Sawyer have previously met with NC DWQ and the South Carolina
Department of Health and Environmental Control (SCDHEC) to discuss a proposed expansion of the
Twelve Mile Creek WWTP. These meetings confirmed that a new permit for additional discharge to
Twelve Mile Creek (Creek) is highly unlikely based on the apparent lack of assimilative capacity for
oxygen -demanding wastes in the Creek. As such, alternative disposal and/or treatment options will
need to be developed for future wastewater treatment capacity in this service area. As part of the
current study, six alternatives have been developed and are listed below:
• Alternative 1:
• Alternative 2:
• Alternative 3:
• Alternative 4:
• Alternative 5:
• Alternative 6:
Buy Additional Capacity at Charlotte Mecklenburg Utilities' (CMU's) McAlpine
Creek Wastewater Management Facility (WWMF)
Build and Buy Capacity at Lancaster County (SC) Water and Sewer District's
(LCWSD's) Indian Land WWTP
Partner with LCWSD to Build a New WWTP
Develop a Non -Conjunctive Reuse System
Discharge Additional Plant Effluent into Twelve Mile Creek
Pump Additional Plant Effluent to the Catawba River
Each of these alternatives was evaluated based on cost, constructability, permitting, schedule, and
feasibility. These alternatives are discussed in detail in this section.
Alternative 1: Buy Additional Capacity at the McAlpine Creek WWMF (Charlotte -Mecklenburg
Utilities)
As part of Alternative 1, the County would negotiate with Charlotte -Mecklenburg Utilities to buy additional
treatment capacity at the McAlpine Creek WWMF. The County currently holds a contract with CMU that
defines a total treatment allocation of up to 3 MGD at the McAlpine Creek WWMF, under which the
current financed capacity by the County is 1 MGD. However, the County has exceeded the 1 MGD of
purchased capacity and has reached a maximum month flow of 1.3 MGD. As such, the County has
requested and received approval from CMU for an additional 1.7 MGD of flow from the proposed
Diversion Force Main and Pump Station. Thus, Alternative 1 would require an agreement with CMU for
an additional 3 MGD of treatment capacity (i.e., 1.3 MGD current flow + 1.7 MGD of recently approved
flow + 3.0 MGD of additional flow for this alternative = 6 MGD total flow). Capital improvements required
for this alt native include:
V i
• Expansion of the proposed Diversion Pump Station, or construction of a new parallel pump
statton at the Twelve Mile Creek WWTP, to convey an additional 3 MGD to the Six Mile Creek
Interceptor. Conversations with the design engineers of the Diversion Pump Station (Kimley-
,Horn).indicated that the Diversion Pump Station as designed could be expanded to 9 MGD by
replacement of the proposed pumps with those rated for higher flow rates. However, the
Twelve Mile Creek VVWTP Expansion Alternatives - 2 -
August 2010
HAM AND S4WwYER
Environmental Engineers & Scientists
qs

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QUAL2 Model Update for
Twelve Mile Creek
below the Union County WWTP
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Permit Wri-141/1
Prepared for
Union County
Public Works Department
500 N. Main St. Suite 500
Monroe, NC 28112-4730
and
Hazen & Sawyer, P.C.
4944 Parkway Plaza Blvd., Suite 375
Charlotte, NC 28217
Prepared by
TETRA TECH
3200 Chapel Hill -Nelson Hwy, Suite 105 • PO Box 14409
Research Triangle Park, NC 27709
04 avivt)d)la,o evziopett<b-�)Z . ,,J;// �►r*-
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Tt QUAL2 Model Update - Twelve Mile Creek
Table of Contents
1 Introduction 1
2 Data Collection 3
2.1 Channel Elevation Survey 3
2.1.1 Methods 3
2.1.2 Results 4
2.1.3 Discussion 5
2.2 Dissolved Oxygen Profiling 7
2.2.1 Methods 7
2.2.2 Results 8
2.2.3 Discussion 15
3 QUAL2E Model Update 17
3.1 Evaluation of Previous Model 17
3.1.1 Comparison of Model Predictions to Observed Profiles 17
3.1.2 Indentification of Needed Refinements 18
3.2 Model Recalibration 18
3.2.1 Revised Model Setup 18
3.2.2 Refined Calibration 26
3.3 Model Application 29
3.3.1 Scenario Description 29
3.3.2 Updated Model Predictions 30
3.3.3 Summary 31
4 References 33
Appendix A. Raw Elevation Survey Data A-1
Appendix B. Raw DO Profile Data B-1
Appendix C. June 2011 Model Input and Output C-1
T
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Tt QUAL2 Model Update — Twelve Mile Creek
List of Tables
Table 1. Summary of Temperature Data Collected by Union County 12
Table 2. Summary of Flow and Temperature Data Collected by Tetra Tech 13
Table 3. Hydraulic Parameters for the QUAL2E Modeling Reaches 19
Table 4. QUAL2E Velocity Coefficient and Exponent Values and Predicted June 2011
Velocity and Time of Travel 21
Table 5. QUAL2E Depth Coefficient and Exponent Values and Predicted June 2011
Depth 22
Table 6. Summary of Model Flow Input Assumptions 23
Table 7. Water Quality and Typical Summer Flow Rates Assumed for the Twelve Mile
Creek QUAL2E Model 24
Table 8. Summary of Model Kinetic Rate Assumptions 25
OTETRA TECH

Tt QUAL2 Model Update - Twelve Mile Creek
List of Figures
Figure 1. Location Map for Twelve Mile Creek Watershed and Union County WWTP 2
Figure 2. Combined Longitudinal Survey Between WWTP Discharge and Van Wyck
Rd. 5
Figure 3. Left Bank Slope and Old Model Reaches Plotted With Surveyed Channel
Elevation 6
Figure 4. Major Physical Features Identified From Channel Elevation Survey 6
Figure 5. Box Plots of DO Concentration at Union County Monitoring Sites (May -
Aug) 9
Figure 6. Box Plots of DO Concentration at Union County Monitoring Sites (May) 9
Figure 7. Box Plots of DO Concentration at Union County Monitoring Sites (June) 10
Figure 8. Box Plots of DO Concentration at Union County Monitoring Sites (July) 10
Figure 9. Box Plots of DO Concentration at Union County Monitoring Sites (August) 11
Figure 10. USGS Gage Flow at Six Mile Creek between June and September 2011 13
Figure 11. Observed DO Profiles 14
Figure 12. Temperature -normalized DO Profiles Adjusted to 24.7° C 15
Figure 13. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile
Creek 17
Figure 14. Map of Refined Model Reach Configuration 20
Figure 15. Twelve Mile Creek Riffle Dowstream of WWTP (left) and Typical Riffle
(Right) 25
Figure 16. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile
Creek (June 2011) 26
Figure 17. Components of Dissolved Oxygen Deficit in Twelve Mile Creek (June 2011) 27
Figure 18. Predicted in CBOD-Ultimate in Twelve Mile Creek (June 2011) 27
Figure 19. Predicted in Ammonia-N in Twelve Mile Creek (June 2011) 28
Figure 20. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile
Creek (July 2011) 28
Figure 21. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile
Creek (August 2009) 29
Figure 22. Simulated Dissolved Oxygen Concentrations for Modeling Scenarios 30
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Tt QUAL2 Model Update - Twelve Mile Creek
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TETRA TECH
iv

Tt QUAL2 Model Update - Twelve Mile Creek
1 Introduction
Union County is evaluating expansion of its Twelve Mile Creek wastewater treatment plant (WWTP) to
support population and economic growth in the region (see Figure 1 for location map). Frequent low
dissolved oxygen (DO) concentrations in Twelve Mile Creek during summer low flow periods have
historically been of concern to the North Carolina Division of Water Quality (DWQ). However,
preliminary scoping and modeling analysis conducted by Tetra Tech (2010) indicated that low dissolved
oxygen levels in the receiving stream were not caused by the County's discharge. Rather, the effluent
volume was found to be a resource to the stream during low flow periods, increasing stream velocity and
dissolved oxygen above levels that are predicted without the plant flow incorporated. While agreeing with
the diagnostics in principle, DWQ stated that since the scoping level model was based on limited.,field
datat the scoping level water quality model needed to be validated or refined via additional data
collection. This report summarizes the additionaldata collected and the corresponding water quality
modeling refinements made based on the new data.
Tetra Tech spoke with DWQ permitting and modeling staff on October 18, 2010 to clarify the level of
additional data collection required. Per DWQ directive, data collection focused on two areas specifically:
1) validating channel physical characteristics with regard to model reach assumptions (particularly
channel slope), and 2) obtaining multiple summer low flow DO profiles. Subsequently, on behalf of the
County, Tetra Tech conducted additional reconnaissance on Twelve Mile Creek, surveyed channel
elevation extensively for approximately 13 miles below the County WWTP, and collected extensive DO
profile information during baseflow conditions between June and September 2011. Supplemental
information on stream characteristics was noted to help with refinement of model reach configuration and
physical assumptions for model setup. Data collection methods and findings are summarized in Section 2
of the report.
The new DO monitoring data showed that the previous scoping level model did a remarkably good job of
predicting the basic profile of dissolved oxygen in Twelve Mile Creek below the WWTP outfall.
However, greater variability in DO patterns was noted in the observed data related to physical features not
previously understood due to the lower resolution of LIDAR (light detection and ranging) data compared
to actual survey. The magnitude of some of the DO sags (i.e., spatial locations of lowest DO
concentrations) was different enough from the model predictions that the modeling team determined that
model predictive capabilities could be improved upon by refining the model calibration using the updated
jafarmatica. The evaluation of the previous model and the modeling refinements aresummarizedin
Section 3 of the report.
Summaries of the field collected data are provided in the appendices, along with a copy of the model
input and output for the June recalibration run.
QTETRATECH
1

Tt QUAL2 Model Update - Twelve Mile Creek
...................
North Carolina
South Carolina
South Carolina 'NorthCarolina
Twelve Mile Creek Watershed
"Mp722o .o"a:�..:"F.«
MECKLENBURG COUNTY
UNION COUNTY
Legend
® Point Source Discharge
— Modeled Reach
ONC Boundary
County Boundary
Six Mile Creek Subwatershed
Twelve Mile WWTP Subwatershed
Twelve Mile Watershed
I 1
0 0.5 1 2 3 4
Miles
Figure 1. Location Map for Twelve Mile Creek Watershed and Union County WWTP
11, t TETRA TECH
2

Tt QUAL2 Model Update - Twelve Mile Creek
2 Data Collection
Data in Twelve Mile Creek were collected between February 15, 2011 and September 2, 2011 comprising
stream reconnaissance, channel elevation survey, and DO concentration profiling. Stream reconnaissance
was conducted in February to obtain greater understanding of the physical features of the Twelve Mile
Creek system to support field planning for both the channel elevation survey and DO profiling work.
Specific goals of the reconnaissance included:
1. Obtain channel cross -sections to support estimation of depth during summer periods when stream
width below the outfall drops to 10 to 15 ft.
2. Observe channel features to support scoping model reach delineation.
a. Identify locations of noticeable elevation changes (e.g., falls).
b. Note locations and length of pooling areas.
c. Note upstream and downstream locations of significant changes in other channel features
(e.g., width).
d. Note locations of minor tributaries not currently identified.
3. Observe condition of channel bottom material to help with estimates of sediment oxygen demand
and channel roughness.
4. Check for cell phone reception frequently (one -quarter to one-half mile) to ensure viability of
satellite survey unit.
5. Locate additional possible takeout/launch points between major road crossings.
The reconnaissance was conducted by boat on February 15 and February 16, 2011, covering 12.5 miles of
stream. Results obtained from the reconnaissance trip included a GPS tracked thalweg route with
locations of significant stream features and characteristics, and a corresponding spatially referenced photo
log. These results further provided the basis for the elevation survey and DO profiling and supported the
development of later field plans.
2.1 CHANNEL ELEVATION SURVEY
2.1.1 Methods
Tetra Tech conducted two separate survey trips to Twelve Mile Creek to refine channel slopes for the
model. For both trips, the survey team used a canoe to traverse the creek due to poor accessibility
throughout most of the reach and long deep pools too difficult to wade.
The initial survey trip, completed between March 23 and 25, 2011, collected channel elevations for the
entire stream section between the WWTP discharge and the Van Wyck Road bridge. Elevations were
measured using advanced GPS technology while channel distance was recorded using a simple handheld
GPS unit. During this trip, the survey team collected 113 points from 65,800 feet (12.5 miles) of channel,
which is consistent with the survey team's goal for collecting channel elevation at 500 foot intervals.
Further techniques regarding the survey procedure are noted below.
1. Three-dimensional point elevations were collected along the channel thalweg using a Tremble R8
GPS unit. The Trimble R8 GPS unit is capable of yielding a high level of accuracy, both
vertically and horizontally, while also providing mobility to survey from a canoe without having
{
' TETRATECH
_

Tt QUAL2 Model Update — Twelve Mile Creek
to rely on a base station or tripod -type survey equipment. This mobility was essential for
surveying a long, linear system with limited downstream visibility and deep pools.
2. The GPS unit was installed on a survey rod and raised/lowered as needed to receive satellite
connection.
3. Most survey shots were collected from the canoe using the extended rod, although points in
shallow areas (e.g., grade control riffles in the shallow upper reach) were collected from outside
of the canoe for increased rod stability.
4. Collection frequency goal: 500 ft intervals based on the handheld GPS tracking feature.
a. Note: Where satellite coverage was limited and an elevation could not be recorded, the
survey team had to move downstream beyond the 500 ft interval until coverage was
sufficient.
5. A separate handheld GPS unit was utilized to track the path of the channel thalweg, which more
accurately represents the flow path and reach distance at low base flows during summer months.
As a result of an unexpected DO sag of larger magnitude observed during the initial profiling trips, the
survey team re -surveyed the upper 3.3 stream miles below the WWTP discharge on August 4 and 5, 2011.
The main objective of the subsequent survey trip was to collect a high -resolution longitudinal profile to
validate the influence of channel slope on the significant DO sag and reaeration zones being observed in
the upper stream section below the discharge. See below for the specific survey techniques implemented
for this trip:
1. Two-dimensional channel elevations were collected along the thalweg using a rod and level.
2. A handheld GPS data collector was utilized to horizontally locate all of the survey shots in the
stream which could be used to calculate channel length using GIS.
3. Collection frequency goal: 200 ft intervals based on the handheld GPS tracking feature. All grade
control and riffle areas were surveyed regardless of interval location.
4. QA/QC: Real -world elevations were collected at the beginning and end of the rod/level survey
using a TOPCON GPS survey unit. This served two purposes: providing a means to connect the
relative rod/level survey to the previous GPS survey, and quantifying the amount of error
incurred during the rod/level survey.
2.1.2 Results
Figure 2 shows the combined longitudinal profile from the two surveys. Note that the higher -resolution
rod/level survey in the upper 3.3 miles replaced approximately 17 point elevations from the initial GPS
survey. The final combined longitudinal profile is comprised of 172 total channel elevations (90 of which
were collected during the subsequent rod/level survey) and covers 12.5 miles of total channel. Since all
grade control points were included in the survey, pool and riffle areas can be discerned from the
longitiudinal profile in Figure 2. The major pool areas responsible for the significant sag points in the DO
profile will be identified in the next section. All of the survey point elevations and locations are listed in
Appendix A.
"E}p TETRA TECH
4

Tt QUAL2 Model Update — Twelve Mile Creek
Point Elevation (h)
490
4a5
480
475
470
465
460
455
450
445
440
0
1241110
Discharge
2
6
8
Stream Length (mi)
10
March GPS Survey
August Ro0/Level Survey
Van Wyct Rd.
Bridge
12 14
Figure 2. Combined Longitudinal Survey Between WWTP Discharge and Van Wyck Rd.
2.1.3 Discussion
Model reaches in the preliminary scoping level model were delineated using lidar-based slopes from the
left channel overbank since bed elevation resolution was reduced due to surface water reflection.
Although this approach helped produce preliminary model results that predicted the basic DO profile
below the WWTP outfall reasonably well, the updated channel elevation survey and assessment of overall
physical features in the stream helped evaluate the influence of channel slope on DO concentration and
provided a more localized understanding of Twelve Mile Creek's channel geomorphology.
As shown in Figure 3, which displays the surveyed longitudinal profile with the left bank elevation and
preliminary model reach delineations, the channel survey provides a much better representation of
channel slope without all of the "noise" incurred from the lidar interpolation. Surprisingly, the regression
lines used to calculate reach slopes for the preliminary model capture some of the major pools and riffle
areas throughout the stream, but the resolution of physical features and slope breaks identified from the
survey is superior (see Figure 4) and correlates well with the spatial locations of the DO sags. The
updated channel elevation and physical feature information provides a basis for determining model reach
segments for Twelve Mile Creek below the Union County WWTP outfall (discussed further in Section 3).
, TETRA TECH
5

Tt QUAL2 Model Update - Twelve Mile Creek
� I
510 —
00
2.0
4.0
6.0
8.0
Station (mi)
10.0
...-Left Bank Slope from LiDAR
—Surveyed Channel Elevation
12.0
14.0
Figure 3. Left Bank Slope and Old Model Reaches Plotted With Surveyed Channel Elevation
450
485
480
475
470
z
465
1
W 450
1
455
450
445
440
0
Pool
12-Mlle
Discharge
Pool
U5 521
Bridge
2 4 6 8
Stream Length (mi)
Pool
10
—Eleva1k .
Slope Breaks
Van Wyck Rd.
Pool Bridge
r-1-1
12 14
Figure 4. Major Physical Features Identified From Channel Elevation Survey
1'4i.1 TETRATECH
6

Tt QUAL2 Model Update — Twelve Mile Creek
2.2 DISSOLVED OXYGEN PROFILING
Tetra Tech performed four DO profiling trips between June and September 2011 to collect water quality
data during critical summer low flow conditions below the WWTP discharge. Specific goals of the
monitoring trips were to:
a. Obtain more complete profiles than discrete station sampling conducted by the County.
b. Collect data on supplemental parameters including temperature, DO percent saturation,
conductivity, pH, oxidation reduction potential (ORP) and total dissolved solids (TDS) to help
with interpretation of the DO profiles.
c. Note locations of significant changes in DO concentration, specifically DO sag locations across
large riffle areas and deeper slow moving pooled segments. Note that higher resolution of data
was collected within these locations.
d. Check DO levels in flowing tributaries and monitor DO upstream and downstream of the
confluences.
e. Observe physical characteristics of stream during summer low flow conditions (e.g., average
width, depth, pool/riffle location, velocity of floating object, etc.) to help with model reach
definition.
£ Measure daily baseflow upstream of the WWTP discharge each day of monitoring for reference
when interpreting the profile data.
2.2.1 Methods
The monitoring team utilized the same protocol for all four of the DO profiling trips, which were each
conducted over the course of two full days. Water quality parameters, including DO concentration, DO
percent saturation, temperature, pH, conductivity, ORP, and TDS were measured using a YSI 556
multimeter. See below for more detailed monitoring methods.
1. Prior to deploying the field team to conduct sampling, flow was tracked at the USGS gage at Six
Mile Creek (Station Number 0214685800) to determine if low baseflow conditions were present
and the time since the most recent antecedent storm event. Based upon experience, a criterion of
no significant rain within the previous five days was established for greenlighting field team
deployment. Additionally, the Union County WWTP supervisor was contacted to obtain
information on ambient DO and water temperature to confirm that summer critical conditions
were present.
2. Upon field team deployment, each morning prior to DO monitoring, flow was measured upstream
of the WWTP at the old USGS gage (constructed weir) below the Providence Road (NC Hwy 16)
bridge.
a. The cross-section at the weir was measured on day one of each trip using a rod and level.
b. Velocity was measured at the average depth within the middle of the weir using a flow
meter.
c. Flow depth was measured using a permanent benchmark surveyed with the cross-section.
d. Flow rate was calculated from the wetted cross -sectional area and the recorded velocity.
3. DO and supplemental parameter readings were collected according to Standard Methods (APHA
4500-0 G) at a minimum interval of 500 ft.
TETRA TECH
7

Tt QUAL2 Model Update — Twelve Mile Creek
a. More frequent measurements (approximately <500 ft intervals) were collected when DO
readings changed more than 0.2 mg/L between readings.
b. DO readings were also collected within the tributaries of Six Mile Creek, Delaney Creek,
and several other unnamed tributaries with active flow. Readings were collected far
enough upstream in the tributary to ensure that the data reflect the tributary and not
backwater from the mainstem.
4. Stream location and relative distance between monitoring points was recorded using a handheld
GPS unit.
5. Additional physical characteristics representative of low -flow summer conditions were also noted
within model reach, including average width, depth, velocity, algal presence, significant
debris/backwater areas, etc. Locations of major riffle areas providing possible aeration that were
not obvious during previous field visits were also noted and spatially recorded with GPS.
As part of the DO profiling and assessment, Tetra Tech also utilized Union County's self -monitoring
data collected at the three Twelve Mile Creek locations: 50 feet upstream of the WWTP discharge (US),
'/ mile downstream of the WWTP discharge (DS1), and approximately 3,500 feet downstream of the
discharge at the SR 1301 bridge (DS2). The County's data establishes a longer -term DO trend at the
three locations and provides a statistical comparison for the discrete samples collected by Tetra Tech
during the DO profiling trips.
2.2.2 Results
Between May and August 2011, the County collected a total of 43 water quality samples at each of the
three monitoring locations. Figure 5 through Figure 9 show box and whisker plots for the County's data
plotted both with all the data and separated by month. Box plots represent the overall distribution of a
data set. The upper and lower ends of the box equate to the inner quartile range (IQR representing the
bulk of the data between the 25th and 75th percentiles), the middle line equals the median (50t
percentile/midpoint), and the "whiskers" represent the lowest/highest datum within 1.5*IQR of the
lower/upper quartile. Any outliers are shown outside of the whiskers.
As seen in Table 1 below, which provides a statistical summary of the County's observed temperature
data, the median temperature peaks in July at all three locations, respectively, at 24.7, 25.0, and 24.8
degrees Celcius. As expected, the County's corresponding observed July median DO concentrations are
also the lowest— 4.2, 5.4, 5.0 mg/L — respectively, at the three locations.
[.J TETRA TECH
8

Tt QUAL2 Model Update - Twelve Mile Creek
9
8
7
E 6
c
0
A 5
c
c
d
e 4
Iu
0 3
2
0
x
i
i
x
US
DS1
Monitoring Location
x
i
i
x Min/Max Outlier
DS2
Figure 5. Box Plots of DO Concentration at Union County Monitoring Sites (May- Aug)
DO Concentration (mg/L)
9
8
7
6
5
4
3
2
0
x
T
1
1
1
x
X Min/Max Outlier
US
DS1
Monitoring Location
DS2
Figure 6. Box Plots of DO Concentration at Union County Monitoring Sites (May)
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9

Tt QUAL2 Model Update — Twelve Mile Creek
9
0
US
1
I
i
1
x Min/Max Outlier
DS1 DS2
Monitoring Location
Figure 9. Box Plots of DO Concentration at Union County Monitoring Sites (August)
Nit TETRA TECH
11

Tt QUAL2 Model Update - Twelve Mile Creek
Table 1. Summary of Temperature Data Collected by Union County
Percentile
May -Aug
US
Temperature (°C)
DS1
DS2
Percentile
July
US
Temperature (°C)
DS1
DS2
Max
90th
26.8
26.6
26.7
Max
26.8
26.6
26.7
25.3
25.6
25.4
90th
25.9
26.3
26.0
75th
24.8
25.0
50th
23.6
24.0
24.9
75th
25.2
25.5
25.4
23.7
50th
24.7
25.0
24.8
25th
10th
Min
22.9
21.5
15.3
23.5
23.1
25th
23.7
24.6
23.9
22.2
16.3
21.8
16.0
10th
Min
23.5
23.3
23.8
23.5
23.5
23.4
May US DS1
DS2
August
US
DS1
DS2
Max
23.2 23.3
23.1
Max
25.7
25.8
25.7
90th
22.0 22.3
21.9
90th
25.1
25.4
25.4
75th
19.3 20.3
50th 19.0
20.1
19.8
19.7
75th
50th
24.9
23.7
25.0
24.1
25.1
23.8
25th
18.8
19.6 19.2 25th
22.3 23.5 23.2
10th
16.7 17.6 17.3 10th 22.2 23.0 22.8
Min
15.3 16.3 16.0 Min
21.8
22.7 22.7
June US DS1 DS2
Max
25.4 25.73 25
90th
24.6 25.1 24.7
75th
24.0 24.5 24.2
50th
23.6 23.9 23.6
25th
23.2 23.4 23.1
10th
22.8 23.0 22.3
Min 21.4 22.1 21.7
Streamflow measured at the USGS Gage (0214685800) at Six Mile Creek from May through early
September is shown in Figure 10.
TETRATECH
12

ti
Tt QUAL2 Model Update - Twelve Mile Creek
1000 -USGS Flow
• Observed Twelve Mile
Flow
100
1
0.1 --
6/1/11
6/21/11
7/11/11
7/31/11
Date
8/20/11
9/9/11
9/29/11
Figure 10. USGS Gage Flow at Six Mile Creek between June and September 2011
Daily temperature ranges observed by Tetra Tech during the DO profile trips are displayed in Table 2. As
shown, observed temperatures are noticeably the highest during the July trip. Also shown in both Figure
10 and Table 2 are the instantaneous flow measured each morning at the old USGS gage location
upstream of the WWTP discharge. The flow measurements were used to help interpret the DO data
relative to daily flow conditions.
Table 2. Summary of Flow and Temperature Data Collected by Tetra Tech
Date
Flow (cfs) at
Old Gage
Monitoring
Reach
Daily Temp.
Range (C)
Daily Temp.
Range (F),•
6/7/2011
6.2
Upper
22.4 - 25.4
72.4 - 77.7
6/8/2011
5.3
Lower
20.2 - 26.0
68.3 - 78.8
7/12/2011
5.1
Upper (1st half)
25.4 - 28.6
77.8 - 83.5
7/13/2011
1.7
Lower
26.2 - 28.6
79.2 - 83.4
8/18/2011
7.6
Lower
22.7 - 24.4
72.9 - 75.9
8/19/2011
5.2
Upper
22.6 - 25.1
72.6 - 77.2
8/31/2011
0.9
Lower
21.4 - 24.8
70.6 - 76.7
9/1/2011
0.9
Upper
21.5-24.4
70.7-76.0
OTETRATECH
13

Tt QUAL2 Model Update - Twelve Mile Creek
Figure 11 displays all four of the DO profiles overlayed with the surveyed channel elevation. Note that
the DO profile for July is missing in the bottom half of the upper reach due to inclement weather that
canceled part of the field work. The profiles start at the old USGS gage and procede downstream. The
location of the WWTP is shown on the figure, corresponding to a large spike in DO due to the effluent.
9.5
8.5
7.5
£ 6.5
0 5.5
d
c 4.5
N
IA
i3
3.5
2.5
1.5
0 2
Old USGS Gage
12-Mile Discharge
4 6 8
Stream Length (mi)
June DO —July DO
Aug DO —Sept DO
10
12
14
Figure 11. Observed DO Profiles
To control for the influence of varying atmospheric temperatures on DO saturation in the water, the DO
profile data was temperature -normalized to a summer critical temperature defined as the 90th percentile
temperature from Union County's 2001-2011 set of stream monitoring data between June and September
months. Observed DO concentrations were then normalized by multiplying the ratio of the observed DO
value to the calculated DO saturation value (at observed temperature) by the DO saturation value
(8.04 mg/L) at the critical summer temperature (24.7° C). Figure 12 shows the temperature -normalized
DO profiles along with the surveyed channel elevation and major pool/riffle locations.
TETRA TECH
14

Tt QUAL2 Model Update - Twelve Mile Creek
An isolated rain event prior to the August monitoring trip was another factor that caused profile
variability. Tetra Tech's field plan required at least a five day dry period prior to profile monitoring, using
the USGS gage at Six Mile Creek as an indicator of baseflow and hydrologic impacts in the greater
Twelve Mile Creek watershed. However, an isolated rainstorm that occurred in the eastern part of the
watershed on the Sunday evening prior to the Thursday, August 18th monitoring trip was not represented
by the Six Mile Creek gage. Although the hydrograph had stabilized upon initial DO monitoring, residual
interflow and influence from the stormwater "flush" was enough to lessen the impact of the pool/riffle
zones and reduce the overall range of DO concentration. This effect is evident by the "flattened" DO
profile for August that is plotted in Figure 11.
Diurnal influence of algal photosynthesis and respiration was observed at least at small levels during each
profiling trip and contributes in part to the "micro" DO sags and rises observed in the profiles. This is not
atypical for stream conditions. However, a more pronounced diurnal impact from algal growth was
exhibited during the September profile trip where macrophytic algae, not previously observed, was
widespread through the bottom third of the lower reach. Notice that in Figure 11 the DO profile for
September continues to rise in the bottom third of the lower reach, thus not representing the most
downstream DO sag previously profiled. Table B4 in Appendix B also shows large variability in pH
providing more evidence of the strong impact of the algae at the time of sampling. Several factors likely
contributed to this late summer occurrence of algal growth, including several large rain events between
the August and September profile trips that could have provided pulses of nutrient loading into the stream
system, followed by a significant antecedent dry and hot period prior to monitoring. Late August to mid -
September is also the ideal time for fall planting of agricultural row crops and it is likely that the excess
nutrient loading might be associated with the crop lands most present in this part of the watershed.
In summary, the collection of the profile data provides good information regarding general trends. The
June and July profiles were less influenced by antecedent rain events and in the case of the September
profile, more extreme algal growth. Thus, the June and July profiles provide the best guide for model
calibration refinement. The extreme heat in July made the water temperatures warmer than our defined
critical summer conditions and with a portion of the July profile missing due to a storm event onset
ending data collection early, the June profile was selected as the primary data set for model recalibration.
QTETRA TECH
16

Tt QUAL2 Model Update - Twelve Mile Creek
3 QUAL2E Model Update
3.1 EVALUATION OF PREVIOUS MODEL
Dissolved oxygen inTwelve Mile Creek was previously modeled using a scoping level QUAL2E model
to evaluate the assimilative capacity of the stream. That model used a combination of LIDAR data and
cross section measurements to characterize the hydraulics of the stream. Water quality inputs from
upstream, Six Mile Creek, the County WWTP and groundwater inflow were incorporated into the model
and used to estimate the dissolved oxygen conditions.
3.1.1 Comparison of Model Predictions to Observed Profiles
Figure 13 compares the QUAL2E scoping model output to observations collected in Twelve Mile Creek
during the summer of 2009 (median, 10th percentile, and 90th percentile). This model was thought by
Tetra Tech to approximate conditions in Twelve Mile Creek fairly well as a scoping level model. Note
that the model predicts a rapid decline in DO concentration from mile 6.8 to 10.4 because the assumed
slope of this reach is very low relative to the rest of the model (0.0001 $/ft). Road access in this section is
limited and there were no monitoring data available at the time of the scoping model setup to confirm
whether or not DO decreases to 2 mg/L in this section during the summer critical flow and temperature
periods.
10
9-
8 -
7 -
2
1
0
0
2 4 6 8
Model Reach Miles
• Data
—Scoping Model
10 12 14
Figure 13. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile Creek
1tt
TETRA TECH
17

Tt QUAL2 Model Update — Twelve Mile Creek
3.1.2 Indentification of Needed Refinements
The scoping model estimated stream slopes from 10-meter LIDAR contour data measured along the top
of bank for the entire length of the channel. That information was used to coarsely characterize stream
slopes but did not allow for detailed pools and riffles to be represented in the model. Thus oxygen
consumption in the slow moving pools and reaeration in the faster riffles were not as accurately
represented. This is confirmed by comparing the profiles in Figure 11 to the simulated scoping model
results in Figure 13. While the general shape of the scoping level model prediction plot for DO is quite
good, it can be improved upon by taking into consideration the additional field data.
The DO data used to calibrate the scoping model were relatively coarse with only five sample locations in
the 15 mile length of the model, and three of those stations were located in the upper 2 miles of the
stream. This did not allow for a rigorous calibration of the model nor sufficient information to determine
if the second sag was an artifact of the model or a real feature of the system.
The sampling efforts in 2011 aimed to resolve those two main issues. Detailed longitudinal surveys of the
thalweg stream slope allowed for a better representation of pools and riffles. Higher resolution DO
sampling allowed for a better characterization of the dissolved oxygen levels in the stream for model
calibration and validation.
3.2 MODEL RECALIBRATION
The additional data collected in 2011 were used to refine the scoping model and confirm that the
secondary DO sag was not an artifact of the model. The QUAL2E scoping model segmentation was
refined using information from the longitudinal elevation survey. The results from those simulations were
calibrated against the DO profile measured in June 2011. The DO measurements in July 2011 and August
2009 were used as validation datasets since their longitudinal resolution was less than the June 2011 data.
3.2.1 Revised Model Setup
The QUAL2E model (Brown and Barnwell, 1987) was selected for a steady-state simulation of the fate
and transport of the WWTP discharge and its impacts on the DO balance for Twelve Mile Creek. The
application of QUAL2E is well established in North Carolina and USEPA Region 4. The key parameters
that impact simulation of dissolved oxygen are 1) the average depth and velocity of each model reach, 2)
the water quantity and water quality of the receiving stream and the effluent, and 3) the rates of
reaeration, sediment oxygen demand, and deoxygenation. This section summarizes the methods used to
refine the previous QUAL2E model and calibration for these parameters.
3.2.1.1 Reach Delineation
The QUAL2E model simulates fate and transport of chemicals in uniformly spaced increments that make
up modeling reaches. Conditions within each reach are generally consistent with respect to channel slope,
width, depth, and velocity. The pool/riffle regions shown in Figure 4 were used to define the model
reaches (Table 3 and Figure 14). The six cross sections measured on March 9 and 10, 2010 were applied
to the same regions of the stream as in the previous modeling efforts. Within QUAL2E, reaches are
divided into smaller sub -units, "elements" and each element was approximately 0.1 mi in length.
O TETRA TECH
18

Tt QUAL2 Model Update - Twelve Mile Creek
Legend
Riven/Stream
Road
State Boundary
Sts M:le Creek Subwatershed
Twelve Mtle WIMP Subwatershed
0 Twelve Mile Watershed
Twelve Mite Creek: Model Reach Delineation
NM3 19b3 Sta1M(ane_North Cavfina FIPS 92CC Feet
Mart produced C1-22.2612-C. Carl.
Twelve Mile
WWrP
Discharge
HIS
North Carotins
4
kMlea
TECH
Figure 14. Map of Refined Model Reach Configuration
3.2.1.2 Reach Hydraulics
The QUAL2E model setup for Twelve Mile Creek uses a power relationship between flow and depth and
flow and velocity to characterize water movement through the reaches. Reach slopes were input to a
program, WinXSPro, which uses cross section information to develop relationships between flow and
depth and flow and velocity. The Manning's n value of 0.20 used in the scoping model was also used in
the refined model. The Manning's n value was chosen to replicate the observed velocity at the USGS
gaging station and represent the multiple log jams on Twelve Mile Creek. Depths were defined as the
cross sectional area divided by the top width and velocity by flow divided by cross sectional area.
Regressions were made between depth/velocity and flows under 30 cfs, which was the approximate upper
limit of the anticipated flows under future design scenarios (Table 4 and Table 5). The regression
equations fit in the general power equation:
Velocity or Depth = a * Flowb
Model velocities ranged from 0.10 to 0.44 ft/s and depths ranged from 0.64 to 2.60 ft. The total time of
travel through the model domain for the June 2011 simulation was four days (Table 4).
9LI TETRATECH
20

Tt QUAL2 Model Update - Twelve Mile Creek
Table 4. QUAL2E Velocity Coefficient and Exponent Values and Predicted June 2011 Velocity
and Time of Travel
QUAL2E Reach
Velocity (cfs)
June 2011
Coefficient
Exponent
Velocity
(ftis)
Time of
Travel (hrs)
1
0.12
0.28
0.24
6.98
2
0.05
0.28
0.10
7.44
3
0.17
0.21
0.28
5.81
4
0.06
0.30
0.12
12.00
5
0.13
0.30
0.27
7.73
6
0.10
0.31
0.21
4.87
7
0.11
0.25
0.20
6.43
8
0.09
0.27
0.18
8.98
9
0.13
0.24
0.24
5.62
10
0.06
0.37
0.15
3.84
11
0.10
0.39
0.27
6.07
12
0.19
0.33
0.44
1.68
13
0.09
0.39
0.24
5.40
14
0.12
0.39
0.32
2.74
15
0.11
0.38
0.29
3.02
16
0.14
0.36
0.35
7.34
Cumulative Travel Time (hrs) =
95.95
TETRA TECH
21

Tt QUAL2 Model Update - Twelve Mile Creek
Table 5. QUAL2E Depth Coefficient and Exponent Values and Predicted June 2011 Depth
QUAL2E Reach
Depth (ft)
June 2011
Coefficient
Exponent
Depth (ft)
1
0.45
0.42
1.23
2
0.99
0.39
2.53
3
0.51
0.26
0.95
4
0.84
0.47
2.60
5
0.52
0.46
1.57
6
0.63
0.47
1.95
7
0.49
0.38
1.24
8
0.52
0.39
1.40
9
0.44
0.36
1.10
10
0.42
0.53
1.62
11
0.26
0.49
0.90
12
0.17
0.52
0.64
13
0.30
0.48
1.02
14
0.24
0.49
0.84
15
0.26
0.49
0.90
16
0.22
0.49
0.77
Flows into the modeled portion of Twelve Mile Creek originate from upstream, Six Mile Creek, the
County WWTP, and groundwater flows (Table 6). Twelve Mile Creek flows above the County WWTP
were measured by Tetra Tech personnel during the field surveys. Five-day average flows from Six Mile
Creek as measured at the the USGS gage (#0214685800) were used to quantify those inputs. Flow records
from the County WWTP were used to quantify the five-day average flow into the creek. A five-day
window was selected because the travel time from the headwaters to the end of the model domain was
approximately five days under the modeled scenarios. The groundwater contributions (i.e., incremental
baseflow rates), normalized to stream length, were estimated from differences in historic low flow
measurements at two gages on Twelve Mile Creek.
74I TETRATECH
22

Tt QUAL2 Model Update — Twelve Mile Creek
Table 6. Summary of Model Flow Input Assumptions
Model Input
Twelve Mile Creek
Headwaters (cfs)
Six Mile Creek
(cfs)
WWTP
(cfs)
Groundwater
(cfs/mile)
August 2009
1.35
0.70
5.26
0.0028
June 2011
5.70
1.66
5.33
0.0028
July 2011
3.40
1.83
3.25
0.0028
3.2.1.3 Water Quality Model Input Assumptions
Along with water quantity information, the QUAL2E model uses the water quality of the receiving stream
and all point source discharges in the fate and transport simulation. Table 7 summarizes the upstream,
WWTP, and Six Mile Creek water quality inputs to the system. Upstream temperature and DO
concentration assumptions were based on four observations each by Union County during the period
between August 18 and 27, 2009 for the 2010 model. Upstream DO concentrations for the 2011
samplings were taken as a part of the longitudinal DO survey. Upstream concentrations for ammonia,
nitrate -nitrite, and organic nitrogen were assumed to reflect the long-term data collected by DWQ and
reported in their Catawba River Ambient Monitoring System Report (NCDENR, 2008) at Station Number
C9819500 in Twelve Mile Creek upstream of the discharge (represents reported mean of 60
observations). Background conditions in Six Mile Creek were estimated to be the same as Twelve Mile
Creek. Upstream and Six Mile Creek BOD5 and BOD ultimate concentrations were based upon data
available for a similar piedmont stream system (Tetra Tech, 2008).
Effluent (WWTP) temperature and DO were also taken from data collected by the County. The August
2009 ammonia, nitrate -nitrite, organic nitrogen, and BOD5 concentrations for the effluent input were
based upon information provided in the January 10, 2010 NPDES permit application, which provided
averages for 955 observations (from which representative summer values were estimated). The June and
July 2010 concentrations were quantified by averaging the previous weeks' water quality measurements.
BOD ultimate concentration for the effluent was estimated by multiplying the BOD5 concentration by
2.47 which is the F-ratio recommended by Thomann and Mueller (1987) for converting BOD5 to BOD
ultimate for this type of discharge.
Groundwater and Six Mile Creek concentrations were assigned the same concentration as upstream
Twleve Mile Creek background measurements.
['�d. TETRA TECH
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Tt QUAL2 Model Update - Twelve Mile Creek
Table 7. Water Quality and Typical Summer Flow Rates Assumed for the Twelve Mile Creek
QUAL2E Model
Model Input
Twelve Mile Creek Above
the Effluent Discharge
Six Mile Creek and
Groundwater
WWTP
Aug
2009
June
2011
July
2011
Aug
2009
June
2011
July
2011
Aug
2009
June
2011
July
2011.
Temperature (°F)
75.9
71.6
80.6
75.9
71.6
80.6
76.3
72.9
76.8
DO (mg/L)
3.3
5.48
5.35
3.3
5.48
5.35
6.5
6.6
6.8
Ammonia (mg-N/L)
0.05
0.05
0.05
0.05
0.05
0.05
0.1
0.97
1.56
NO3 plus NO2 (mg-N/L)
0.34
0.34
0.34
0.34
0.34
0.34
4.03
3.93
6.53
Organic N (mg-N/L)
0.46
0.46
0.46
0.46
0.46
0.46
1.2
1.17
1.91
BOD5(mg/L)
No instream measurement.
Use BODult = 0.75 mg/L
No instream measurement.
Use BODult = 0.75
0.80
1.93
2.00
BODult m /L
( 9 )
mg/L
1.98
4.77
4.94
3.2.1.4 Methods for Estimating Model Kinetics
Primary kinetic parameters for BOD-DO simulation in QUAL2E are the deoxygenation rate (kd) for
carbonaceous BOD, sediment oxygen demand (SOD), and reaeration rate (ka). The lower end of the range
for temperature correction factor (1.02) was used because of the high water temperatures reaching the
level where metabolic rates are slowing. Table 8 summarizes the model assumptions for these key
reaction rates.
Model rates for kd were calculated for each reach based on the Bosco equation, which incorporates slope,
velocity, and depth into the estimation of kd (USEPA, 1985).
SOD was used as a calibration parameter to adjust simulated dissolved oxygen concentrations to mimic
the longitinal DO profiles. To simulate observed DO measurements in this channel, the background SOD
rate was set to 0.075 L/d at 20 °C with greater SOD rates in the pools where organic matter would likely
settle out.
The QUAL2E model provides the user a choice of eight simulation options for estimating the reaeration
coefficient ka for each modeling reach when measured values are not available. The Langbein and Durum
(Langbein and Durnum, 1967) method was chiefly used in this modeling effort. This method deviates
from the Thackston and Krenkel (Thackston and Krenke1,1969) method employed in the scoping
modeling. With the refined representation of the stream slopes and water movement, the Thackston and
Krenkel reaeration method produced unrealisticly high reaeration rates. The Langbein method produced
reaeration rates similar to those measured in a North Carolina Piedmont stream with similar channel
characteristics with wide, relatively low -sloped channels (Tetra Tech, 2008). The riffle reach immediately
downstream of the pool into which the County WWTP discharges was a unique section of the stream (see
Figure 15) with features which would lead to increased reaeration in the stream that the Langbein method
did not characterize. Aeration in that section of stream was characterized using the Churchill method
(Churchill et al, 1962) (Table 8). Reach 5 in the upper section of the modeled portion of Twelve Mile
Creek was also found to be better represented by the Churchill method.
f� ITETRATECH
l �7 24

Tt QUAL2 Model Update - Twelve Mile Creek
Figure 15. Twelve Mile Creek Riffle Dowstream of WWTP (left) and Typical Riffle (Right)
Table 8. Summary of Model Kinetic Rate Assumptions
QUAL2E
Reach
1
Reach
Description
Riffle
Reaeration Method
Langbein and Durum
Reaeration
(day')
1.46
CBOD
Decay
(day')
0.055
SOD
(g/ft&/d)
0.075
SOD
Temperature
Correction
1.020
2
Pool
Langbein and Durum
0.35
0.034
0.400
1.020
3
Riffle
Churchill
3.69
0.091
0.075
1.020
4
Mixed
Langbein and Durum
0.46
0.033
0.100
1.020
5
Mixed
Churchill
1.54
0.051
0.075
1.020
6
Pool
Langbein and Durum
0.75
0.041
0.400
1.020
7
Riffle
Langbein and Durum
1.19
0.046
0.075
1.020
8
Pool
Langbein and Durum
0.92
0.052
0.250
1.020
9
Riffle
Langbein and Durum
1.64
0.052
0.075
1.020
10
Pool
Langbein and Durum
0.78
0.037
0.400
1.020
11
Riffle
Langbein and Durum
2.38
0.057
0.075
1.020
12
Riffle
Langbein and Durum
3.17
0.144
0.075
1.020
13
Pool
Langbein and Durum
2.69
0.050
0.400
1.020
14
Riffle
Langbein and Durum
3.94
0.083
0.075
1.020
15
Pool
Langbein and Durum
1.46
0.059
0.400
1.020
16
Riffle
Langbein and Durum
0.35
0.086
0.075
1.020
O TETRA TECH
25

Tt QUAL2 Model Update - Twelve Mile Creek
3.2.2 Refined Calibration
The refined QUAL2E model was able to replicate the dissolved oxygen levels and general patterns
observed during the stream surveys. Percent dissolved oxygen saturation was selected as the comparative
metric instead of the dissolved oxygen concentrations because the QUAL2E model assumes a steady state
and the longitudinal stream sampling occurred at different times during the day over multiple days. The
June 2011 sampling provided the best dataset for calibration because there was DO sampling along the
entire length of the stream and the antecedent conditions were relatively steady. The model fits the
observed DO profile well (Figure 16). The effect of the pools and riffles on the dissolved oxygen levels is
readily apparent in both the measured and modeled DO profiles.
100%
c
0
� Vf
" 60%
a: 0
N
yas
c
eo 3
p 40%
80%
v
as
0
E 20%
0%
0
a Data
Refined Model
Pool
5 mg/L
2 4 6 8
Model Reach Miles
10 12 14
Figure 16. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile Creek
(June 2011)
Overall, the model predicts that DO has a net gain in the modeled portion of Twelve Mile Creek.
Approximately 753 mg/L/day of oxygen are added to the system with 618 mg/L/day consumed. Sediment
oxygen demand accounted for 89 percent of the DO consumption and nitrification accounted for 9 percent
(Figure 17). Predicted CBOD and NH3-N profiles are shown in Figure 18 and Figure 19.The ammonia
rates are fixed stoichiometrically, and sensitivity runs increasing CBOD decay rates by 25 and 50 percent
had almost no effect on predicted DO concentrations.
O TETRA TECH
26

Tt QUAL2 Model Update — Twelve Mile Creek
0.6
0.5
0.4
0.3
0.2
0.1
0
2 4 6 8
Model Reach Miles
Pools
10 12 14
Figure 19. Predicted in Ammonia-N in Twelve Mile Creek (June 2011)
The July 2011 dataset was used to validate the model configuration. Stream temperatures in July were
about 9 °F higher than in the June sampling (Table 7). The predicted DO profile matches the average
observed levels relatively well, although the peaks and valleys are more exaggerated in the simulation of
the lower section of stream (Figure 20).
100%
0
0
20%
0
112
80%
v.,60%
Lt. N
c
ea
40%
0%
0
2
4
6 8
Model Reach Miles
10
Data
—Refined Model
Pools
5 mg/L
12
14
Figure 20. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile Creek
(July 2011)
TETRA TECH
28

Tt QUAL2 Model Update - Twelve Mile Creek
The second validation compared the refined model to the scoping model. The refined model replicated the
overall dissolved oxygen patterns predicted by the scoping model (Figure 21). The greater variation in
predicted DO caused by the refined definition of pool and riffle zones still fits within the observed range
of DO concentrations at the County's fixed monitoring stations. It is possible that at the historically high
water temperatures observed in July (roughly 9 degrees F higher than June, and among the highest on
record) the metabolic reaction rates begin to decrease such that observed demand is less than predicted
with the constant temperature correction factor assumed in the model. However, the higher resolution of
the June and July 2011 datasets did provide insight into the profile shape between the downstream
stations and resulted in a greater degree of overall confidence in the refined model predictions.
10
5
3
0
2
4
6 8
Model Reach Miles
• Data
Scoping Model
—Refined Model
Pools
10 12
14
Figure 21. Comparison of Simulated and Observed Dissolved Oxygen in Twelve Mile Creek
(August 2009)
3.3 MODEL APPLICATION
3.3.1 Scenario Description
The two primary questions from the previous modeling analysis (Tetra Tech, 2010) were again asked to
compare model responses under the refined calibration:
1. Is there a sag in DO concentration below the outfall that is increased by the WWTP discharge?
2. Does DO concentration in the receiving waters improve with increased wasteflow?
The following scenarios were set up and run to help answer the questions.
1) Zero Discharge: Model setup reduces WWTP discharge flow rate to 0 MGD.
2) Existing Actual Conditions: Model setup reflects existing average WWTP discharge flowrate
(3.4 MGD) and permit limits for dissolved oxygen (6 mg/L), BOD5 (5 mg/L), and ammonia
V ) TETRATECIi
�29

Tt QUAL2 Model Update - Twelve Mile Creek
(1 mg-N/L). Other nitrogen components were set based on long term monitoring levels for
organic nitrogen (1.2 mg-N/L), nitrite (0.1 mg-N/L), and nitrate (3.93 mg-N/L).
3) Existing Permitted Conditions: Model setup reflects an increase in WWTP discharge flow rate to
6 MGD with permit limits for dissolved oxygen (6 mg/L), BOD5 (5 mg/L), and ammonia
(1 mg-N/L). Other nitrogen components were set based on long-term monitoring levels for
organic nitrogen (1.2 mg-N/L), nitrite (0.1 mg-N/L), and nitrate (3.93 mg-N/L).
4) Expanded Flow: Model setup reflects an increase in WWTP discharge flow rate to 12 MGD with
permit limits for dissolved oxygen (6 mg/L), BOD5 (5 mg/L), and ammonia (1 mg-N/L). Other
nitrogen components were set based on long-term monitoring levels for organic nitrogen
(1.2 mg-N/L), nitrite (0.1 mg-N/L), and nitrate (3.93 mg-N/L).
For all scenarios, the upstream (headwater) flow was assumed to be 1.35 cfs consistent with the
assumption in the previous scenario analyses (Tetra Tech, 2010). Headwater BOD-ultimate, ammonia,
and DO concentrations were assumed to be 0.75 mg/L, 0.05 mg/L and 3.8 mg/L, respectively consistent
with previous data analysis and modeling.
3.3.2 Updated Model Predictions
Figure 22 shows the impacts of increasing the Union County discharges on simulated dissolved oxygen
concentrations.
Dissolved Oxygen (mg/L)
10
9
8
7
6
5
4
3
1
0
Pools — 0 MGD
— 3.4 MGD ---- 6 MGD
— 12 MGD
A
AEU /
1V/ rv-i,om
2
4
6
8
Model Reach Miles
10
12
14
Figure 22. Simulated Dissolved Oxygen Concentrations for Modeling Scenarios
DO sag zones are predicted to be lower than observed for model calibration largely because effluent
permitted DO is less than actual DO (i.e., 6.0 mg/L versus 6.6 mg/L for the calibration run), and upstream
(headwater) flows are lower than the calibration and validation measured flows (i.e., 1.35 cfs versus 5.7
cfs and 3.4 cfs respectively). Assuming a lower effluent DO for these model application scenarios means
that DO concentration at the mixpoint downstream is predicted to be about 0.6 mg/L lower than observed
El TETRA TECH
i "-I 30

Tt QUAL2 Model Update — Twelve Mile Creek
for the calibration run. Additionally, the lower headwater flow causes a decrease in velocity, which
increases residence time allowing for greater oxygen demand to be exerted while simultaneously
generating lower reaeration rates. Consistent with these findings, the model scenario results also indicate
that an increased WWTP discharge would raise the DO levels through the pooled section. Additionally, if
the County's discharge is removed from the stream, decreases in DO of more than 1 mg/L can be
expected in the pooled zones.
3.3.3 Summary
Per directive from DWQ in its September 1, 2010 speculative effluent limits letter (addressed to
Ed Goscicki with Union County from Tom Belnick, DWQ Complex Permitting Unit Supervisor),
additional field data were collected to validate previous scoping model results. Extensive channel survey
data provided a high degree of resolution for channel slope calculation and to determine the actual pool -
riffle structure of the receiving stream. Additionally, four multi -day dissolved oxygen profiling trips were
conducted, one each in June, July, August and September. The channel elevation and DO profile data
provided the basis for refining model reach characteristics and further enhancing QUAL2E model
calibration.
The updated modeling results further validate the primary conclusion of the previous scoping modeling
analysis, i.e., that the existing Union County WWTP discharge does not cause DO to worsen downstream
of the outfall. To the contrary, the discharge significantly increases DO concentrations (particularly in
pooled water zones) over what would be expected without the effluent flow present in the channel during
critical summer low flow periods. The additional field studies and model recalibration resulted in a more
refined and accurate model that DWQ can use for wasteload allocation purposes for maintaining the
discharge in Twelve Mile Creek.
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4 References
Brown and Barnwell. 1987. The Enhanced Stream Water Quality Models QUAL2E and QUAL2E-
UNCAS: Documentation and User Manual. EPA/600/3-87/077, May 1987.
Churchill, M.A., H.L. Elmore and R.A. Buckingham. 1962. The Prediction of Stream Reaeration Rates
ASCE Journal of Sanitary Engineering Division. Vol 88, SA4: 1-46.
Langbein, W.B. and W.H. Durum. 1967, The Aeration Capacity of Streams US Geological Survey
Circular S42.
NCDENR. 2008. Basinwide Assessment Report — Catawba River Basin. North Carolina Department of
Environment and Natural Resources DWQ Environmental Sciences Section. Tetra Tech. 2008. Results of
Phase I Field Monitoring and Model Updates for the High Point Westside Discharge to Rich Fork Creek.
Prepared for the City of High Point, NC.
Tetra Tech. 2010. Scoping Level Assessment of Assimilative Capacity in Twelve Mile Creek Below the
Union County WWTP. Prepared for Union County Public Works Department.
Thackston. E.L. and P.A. Krenkel. 1969. Reaeration Prediction in Natural Streams. ASCE Journal of
Sanitary Engineering Division. Vol 95, SA1:65.
Thomann, R.V. and J.A. Mueller. 1987. Principles of Surface Water Quality Modeling and Control. New
York: Harper and Row.
USEPA. 1985. Rates, Constants, and Kinetics Formulations in Surface Water Quality Modeling (Second
Edition). EPA/600/3-85/040, June 1985.
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