NC0063096_Permit Issuance_20050225

NPDES DOCUHENT MCANNINO COVER SHEET
NC0063096
Holly Springs WWTP
NPDES Permit:
Document Type:
Permit Issuance `
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Correspondence
Owner Name Change
Technical Correction
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
February 25, 2005
Thus document is printed on reuuse paper - ignore any
content on the re'rerine side

Michael F. Easley
Governor
William G. Ross, Jr., Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P.E., Director
Division of Water Quality
February 25, 2005
Mr. Richard G. Sears
Town of Holly Springs
P. O. Box 8
Holly Springs, North Carolina 27540
Subject: Issuance of NPDES Permit
Permit No. NC0063096
Utley Creek WWTP
Wake County
Dear Mayor Sears:
Division personnel have reviewed and approved your application for renewal of the
subject permit. Accordingly, we are forwarding the attached NPDES discharge permit.
This permit is issued pursuant to the requirements of North Carolina General Statute
143-215.1 and the Memorandum of Agreement between North Carolina and the U.S.
Environmental Protection Agency dated May 9, 1994 (or as subsequently amended).
The final permit includQs the following modification from the draft permit:
• Section A. (3.) was modified to read "Beginning upon expansion beyond 1.75
MGD and lasting until expiration or until discharge from the facility is removed
from Utley Creek, the Permittee is authorized to..."
• The limit for Total Phosphorous was changed to the corresponding mass limit
of 2,664 lbs/yr.
The town must obtain an Authorization to Operate from the Constructions Grant and
Loan Section before the facility is operated at the higher capacity of 1.75 MGD.
If any parts, measurement frequencies or sampling requirements contained in this
permit are unacceptable to you, you have the right to an adjudicatory hearing upon
written request within thirty (30) days following receipt of this letter. This request must
be in the form of a written petition, conforming to Chapter 150B of the North Carolina
General Statutes, and filed with the Office of Administrative Hearings (6714 Mail Service
Center, Raleigh, North Carolina 27699-6714). Unless such demand is made, this
decision shall be final and binding.
Please note that this permit is not transferable except after notice to the Division. The
Division may require modification or revocation and reissuance of the permit. This
permit does not affect the legal requirements to obtain other permits which may be
required by the Division of Water Quality or permits required by the Division of Land
Resources, the Coastal Area Management Act or any other Federal or Local governmental
permit that may be required.
North Carolina Division of Water Quality 1 617 Mail Service Center Raleigh, NC 27699-1617
Internet: h2o.enr.state.nc.us 512 N. Salisbury St.
Raleigh, NC 27604
NOne
s r Carolina
aturaIlji
Phone [phone] Customer Service
FAX [phone]
An Equal opportunity/Affirmative Action Employer — 50% Recycled/10°% Post Consumer Paper

Permit No. NC0063096
Utley Creek WWTP
Page 2
If you have any questions concerning this permit, please contact Teresa Rodriguez at
telephone number [phone], extension 553.
Sincerely,
ORIGINAL SIGNED BY
Mark McIntire
Alan W. Klimek, P.E.
Cc: NPDES Files
Central Files
Constructions Grants and Loan Section
US EPA Region 4
Raleigh Regional Office
Aquatic Toxicology Unit

Permit NC0063096
STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WATER QUALITY
PERMIT
TO DISCHARGE WASTEWATER UNDER THE
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM
In compliance with the provision of North Carolina General Statute 143-215.1, other lawful
standards and regulations promulgated and adopted by the North Carolina Environmental
Management Commission, and the Federal Water Pollution Control Act, as amended, the
Town of Holly Springs
is hereby authorized to discharge wastewater from a facility located at the
Utley Creek WWTP
Irving Parkway
Holly Springs
Wake County
to receiving waters designated as Utley Creek in the Cape Fear River Basin in accordance with
effluent limitations, monitoring requirements, and other conditions set forth in Parts I, II, III,
and IV hereof.
The permit shall become effective April 1, 2005.
This permit and the authorization to discharge shall expire at midnight on July 31, 2006.
Signed this day February 25, 2005.
ORIGINAL SIGNED BY
Mark McIntire
Alan W. Klimek, P.E., Director
Division of Water Quality
By Authority of the Environmental Management Commission

M
Permit NC0063096
r•
SUPPLEMENT TO PERMIT COVER SHEET
The exclusive authority to operate this facility arises under this NPDES permit. The conditions,
requirements, terms and provisions of this NPDES permit governs surface water discharges from
this facility. All previous NPDES Permits issued to this facility bearing this permit number,
whether for operation or discharge, are hereby revoked.
The Town of Holly Springs is hereby authorized to:
1. Continue to operate an existing 1.5 MGD wastewater treatment facility located in Holly
Springs off the Irving Parkway in Wake County. This facility discharges through outfall
001 and includes the following wastewater treatment components:
• Mechanical bar screen
• Grit chamber
• Anaerobic phosphorus removal basin
• Pump station
• Anoxic tank
• Aeration tank
• Package plant with two aeration tanks, two clarifiers and two sludge stabilization tanks
• Final clarifier
• Tertiary filter
• Sludge stabilization/ storage
• UV disinfection system
• Cascade aerator
2. After receiving an Authorization to Operate from the Division of Water Quality, operate the
above facility at a capacity of 1.75 MGD.
3. After receiving an X i6ntd(o {hthuct from the Division of Water Quality, construct
and operate wastewater treahURVIatititAs with an ultimate capacity of 2.4 MGD.
4. Discharge from said treatment works into Utley Creek, a class C stream in the Cape Fear
River Basin, at the location specified on the attached map.
Modified 10/2004

Town of Holly Springs - Utley CreekWWTP
State Grid/Ouad: Apex Latitude: 35° 38' 41" N
E 23 NE Longitude: 78° 51' 04" W
Receiving Stream: Utley Creek Drainage Basin: Cape Fear
Stream Class: C Sub -Basin: 03-06-07
North
NPDES Permit No. NC0063O96
Wake County

Permit NC0063096
A. (1) EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS (1.5 MGD)
Beginning on the effective date of this permit and lasting until expansion above 1.5 MGD (or expiration), the
Permittee is authorized to discharge treated wastewater from outfall 001. Such discharges shall be limited and
monitored by the Permittee as specified below:
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Continuous
Recording
Influent or
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BOD, 5 day, 20°C
(April 1 - October 31)2
5.0 mg/L
7.5 mg/L
Daily
Composite
Influent and
Effluent
BOD, 5 day, 20°C
(November 1 - March 31)2
10.0 mg/L
15.0 mg/L
Daily
Composite
Influent and
Effluent
Total Suspended Solids2
30.0 mg/L
45.0 mg/L
Daily
Composite
Influent and
Effluent
NH3 as N
(April 1 - October 31)
2.0 mg/L
6.0 mg/L
Daily
Composite
Effluent
NH3 as N
(November 1 - March 31)
4.0 mg/L
12.0 mg/L
Daily
Composite
Effluent
Dissolved Oxygen3
Daily
Grab
Effluent
pH4
Daily
Grab
Effluent
Fecal Coliform
(geometric mean)
200/100 ml
400/100 ml
Daily
Grab
Effluent
Temperature 0C
Daily
Grab
Effluent
Total Residual Chlorines
19 pg/L
Daily
Grab
Effluent
Conductivity
Daily
Grab
Effluent
Total Nitrogen
(TKN + NO3-N + NO2-N)6
Weekly
Composite
Effluent
Total Phosphorus
Weekly
Composite
Effluent
Total Copper
Monthly
Composite
Effluent
Chronic Toxicity?
Quarterly
Composite
Effluent
Notes:
1. See A. (4) for instream monitoring requirements.
2. The monthly average effluent BOD5 and Total Suspended Solids concentrations shall not exceed 15% of the
respective influent value (85% removal).
3. The daily average dissolved oxygen effluent concentrations shall not be less than 6.0 mg/L.
4. The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units.
5. Total Residual Chlorine shall be monitored only if chlorine is added to the treatment process.
6. For a given wastewater sample, TN = TKN + NO3-N + NO2-N, where TN is total nitrogen, TKN is total Kjeldahl
Nitrogen, and NO3-N and NO2-N are nitrate and nitrite nitrogen, respectively.
7. Chronic Toxicity (Ceriodaphnia) P/F at 90% with testing in February, May, August and November (see A. (6)).
There shall be no discharge of floating solids or visible foam in other than trace amounts.
Modified 10/2004

Permit NC0063096
A. (2) EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS (1.75 MGD)
Beginning upon issuance of the Authorization to Operate and lasting until expiration or expansion above 1.75
MGD, the Permittee is authorized to discharge treated wastewater from Outfall 001. Such discharges shall be
limited and monitored by the Permittee as specified below;
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Continuous
Recording
Influent or
Effluent
BOD, 5 day, 20°C
(April 1 - October 31)2
5.0 mg/L
7.5 mg/L
Daily
Composite
Influent and
Effluent
BOD, 5 day, 20°C
(November 1 - March 31)2
10.0 mg/L
15.0 mg/L
Daily
Composite
Influent and
Effluent
Total Suspended Solids2
30.0 mg/L
45.0 mg/L
Daily
Composite
Influent and
Effluent
NH3 as N
(April 1 - October 31)
2.0 mg/L
6.0 mg/L
Daily
Composite
Effluent
NH3 as N
(November 1 - March 31)
4.0 mg/L
12.0 mg/L
Daily
Composite
Effluent
Dissolved Oxygen3
Daily
Grab .
Effluent
pH4
Daily
Grab
Effluent
Fecal Coliform
(geometric mean)
200/100 ml
400/100 ml
Daily
Grab.....
Effluent
Temperature 0C
Daily
Grab , ..
Effluent
Total Residual Chlorines
17 mg/L
Daily
Grab ..
Effluent
Conductivity
Daily
Grab
Effluent
Total Nitrogen
(TKN + NO3-N + NO2-N)6
43,800 lbs/yr
Weekly
Composite
Effluent
Total Phosphorus'
2,664 lbs/yr
Weekly
Composite
Effluent
Total Copper
Monthly
Composite
Effluent
Chronic Toxicity$
Quarterly
Composite
Effluent
Notes:
1. See A. (4) for instream monitoring requirements.
2. The monthly average effluent BOD5 and Total Suspended Residue concentrations shall not exceed 15% of the
respective influent value (85% removal).
3. The daily average dissolved oxygen effluent concentrations shall not be less than 6.0 mg/L.
4. The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units.
5. Total Residual Chlorine shall be monitored only if chlorine is added to the treatment process.
6. For a given wastewater sample, TN = TKN + NO3-N + NO2-N, where TN is total nitrogen, TKN is total Kjeldahl
Nitrogen, and NO3-N and NO2-N are nitrate and nitrite nitrogen, respectively. TN load is the mass quantity of
total nitrogen discharged in a given time period. See condition A. (5) of this permit.
7. See condition A. (5) of this permit.
8. Chronic Toxicity (Ceriodaphnia) P/F at 90% with testing in February, May, August and November (see A. (6)).
There shall be no discharge of floating solids or visible foam in other than trace amounts.
Modified 10/2004

4 •
Permit NC0063096
A. (3) EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS (2.4 MGD)
Beginning upon expansion beyond 1.75 MGD and lasting until expiration or until discharge from the facility is
removed from Utley Creek, the Permittee is authorized to discharge treated wastewater from Outfall 001. Such
discharges shall be limited and monitored by the Permittee as specified below:
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Continuous
RecordingInfluent
or
Effluent
2.4 MGD
Flow
BOD, 5 day, 20°C
(April 1 - October 31)2
5.0 mg/L
7.5 mg/L
Daily
Composite
Influent and
Effluent
BOD, 5 day, 20°C
(November 1 - March 31)2
10.0 mg/L
15.0 mg/L
Daily
Composite
Influent and
Effluent
Total Suspended Solids2
30.0 mg/L
45.0 mg/L
Daily
Composite
Influent and
Effluent
NH3 as N
(April 1 - October 31)
1.0 mg/L
3.0 mg/L
Daily
Composite
Effluent
NH3 as N
(November 1 - March 31)
2.0 mg/L
6.0 mg/L
Daily
Composite
Effluent
Dissolved Oxygen3
Daily
Grab
Effluent
pH4
Daily
Grab
Effluent
Fecal Coliform
(geometric mean)
200/ 100 ml
400/ 100 ml
Daily
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Grab
Effluent
Temperature oC
Daily
Grab
Effluent
Total Residual Chlorines
17 pg/L
Daily
Grab
Effluent
Con ty
Daily
Grab
Effluent
Total Nitrogen
(TKN + NO3-N + NO2-N)6
43,800 lbs/yr
Weekly
Composite
Effluent
Total Phosphorus?
2,664 lbs/yr
Weekly
Composite
Effluent
Total Copper
Monthly
Composite
Effluent
Chronic Toxicity$
Quarterly
Composite
Effluent
Notes:
1. See A. (4) for instream monitoring requirements.
2. The monthly average effluent BOD5 and Total Suspended Residue concentrations shall not exceed 15% of the
respective influent value (85% removal).
3. The daily average dissolved oxygen effluent concentrations shall not be less than 6.0 mg/L.
4. The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units.
5. Total Residual Chlorine shall be monitored only if chlorine is added to the treatment process.
6. For a given wastewater sample, TN = TKN + NO3-N + NO2-N, where TN is total nitrogen, TKN is total Kjeldahl
Nitrogen, and NO3-N and NO2-N are nitrate and nitrite nitrogen, respectively. TN load is the mass quantity of
total nitrogen discharged in a given time period. See condition A. (5) of this permit.
7. See condition A. (5) of this permit.
8. Chronic Toxicity (Ceriodaphnia) P/F at 90% with testing in February, May, August and November (see A. (6)).
There shall be no discharge of floating solids or visible foam in other than trace amounts.
Modified 10/2004

Permit NC0063096
A. (4) INSTREAM MONITORING REQUIREMENTS
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Dissolved Oxygen
June -September
3/week
Grab
U, D
October -May
1 /week
Temperature 0C
June -September
3/week
Grab
U, D .
October -May
1 /week
Fecal Coliform
(geometric mean)
June -September
3/week
Grab
U, D
October -May
1 /week
Total Phosphorus2
June -September
1 /week
Grab
U, D
October -May
Monthly
Total Nitrogen
(NO2+ NO3 + TKN)2
June -September
1 /week
Grab
U, D
October -May
Monthly
Chlorophyll -a
June -September
1 /week 3
Grab
D
Notes:
1. U: Upstream in the pool formed immediately upstream of the instream flow weir. D: Downstream on the
existing dam structure in a location so as to avoid contact between the ground and the sample bottle.
2. Effluent and instream monitoring shall be conducted on the same day.
3. Chlorophyl -a monitoring is not required during the months of October through May.
As a participant in the Cape Fear River Basin Association, the instream monitoring requirements as stated above
are waived. Should your membership in the agreement be terminated, you shall notify the Division immediately
and the instream monitoring requirements specified in your permit shall be reinstated.
Modified 10/2004

•
Permit NC0063096
A. (5) CALCULATION OF TOTAL NITROGEN AND TOTAL PHOSPHORUS LOADS
a. The Permittee shall calculate monthly and annual TN and TP Loads as follows:
i. Monthly TN (or TP) Load (lb/mo) = TN (or TP) x TMF x 8.34
where:
TN or TP = the average Total Nitrogen (or Total Phosphorus)
concentration (mg/L) of the composite samples collected
during the month
TMF = the Total Monthly Flow of wastewater discharged during the
month (MG/mo)
8.34 = conversion factor, from (mg/L x MG) to pounds
ii. Annual TN (or TP) Load (lb/yr) = Sum of the 12 Monthly TN (or TP) Loads for the
calendar year
b. The Permittee shall report monthly Total Nitrogen and Total Phosphorus results (mg/L and lb/mo) in
the discharge monitoring report for that month and shall report each year's annual results (lb/yr) in the
December report for that year.
A. (6.) CHRONIC TOXICITY PERMIT LIMIT (Quarterly)
The effluent discharge shall at no time exhibit observable inhibition of reproduction or significant
mortality to Ceriodaphnia dubia at an effluent concentration of 90 %.
The permit holder shall perform at a minimum, quarterly monitoring using test procedures outlined in
the "North Carolina Ceriodaphnia Chronic Effluent Bioassay Procedure," Revised February 1998, or
subsequent versions or "North Carolina Phase II Chronic Whole Effluent Toxicity Test Procedure"
(Revised -February 1998) or subsequent versions. The tests will be performed during the months of
February, May, August and November. Effluent sampling for this testing shall be performed at the
NPDES permitted final effluent discharge below all treatment processes.
If the test procedure performed as the first test of any single quarter results in a failure or ChV below
the permit limit, then multiple -concentration testing shall be performed at a minimum, in each of the
two following months as described in "North Carolina Phase II Chronic Whole Effluent Toxicity Test
Procedure" (Revised -February 1998) or subsequent versions.
The chronic value for multiple concentration tests will be determined using the geometric mean of the
highest concentration having no detectable impairment of reproduction or survival and the lowest
concentration that does have a detectable impairment of reproduction or survival. The definition of
"detectable impairment," collection methods, exposure regimes, and further statistical methods are
specified in the "North Carolina Phase II Chronic Whole Effluent Toxicity Test Procedure" (Revised -
February 1998) or subsequent versions.
Modified 10/2004

Permit NC0063096
All toxicity testing results required as part of this permit condition will be entered on the Effluent
Discharge Monitoring Form (MR-1) for the months in which tests were performed, using the parameter
code TGP3B for the pass/fail results and THP3B for the Chronic Value. Additionally, DWQ Form AT-3
(original) is to be sent to the following address:
Attention: North Carolina Division of Water Quality
Environmental Sciences Branch
1621 Mail Service Center
Raleigh, North Carolina 27699-1621
Completed Aquatic Toxicity Test Forms shall be filed with the Environmental Sciences Branch no later
than 30 days after the end of the reporting period for which the report is made.
Test data shall be complete, accurate, include all supporting chemical/physical measurements and all
concentration/response data, and be certified by laboratory supervisor and ORC or approved designate
signature. Total residual chlorine of the effluent toxicity sample must be measured and reported if
chlorine is employed for disinfection of the waste stream.
Should there be no discharge of flow from the facility during a month in which toxicity monitoring is
required, the permittee will complete the information located at the top of the aquatic toxicity (AT) test
form indicating the facility name, permit number, pipe number, county, and the month/year of the
report with the notation of "No Flow" in the comment area of the form. The report shall be submitted to
the Environmental Sciences Branch at the address cited above.
Should the permittee fail to monitor during a month in which toxicity monitoring is required, monitoring
will be required during the following month.
Should any test data from this monitoring requirement or tests performed by the North Carolina
Division of Water Quality indicate potential impacts to the receiving stream, this permit may be re-
opened and modified to include alternate monitoring requirements or limits.
NOTE: Failure to achieve test conditions as specified in the cited document, such as minimum control
organism survival, minimum control organism reproduction, and appropriate environmental controls,
shall constitute an invalid test and will require immediate follow-up testing to be completed no later
than the last day of the month following the month of the initial monitoring.
Modified 10/2004

Olt
Permit NC0063096
A. (7) EFFLUENT POLLUTANT SCAN
The permittee shall perform an annual pollutant scan of its treated effluent for the following parameters:
Ammonia (as N) Trans-1,2-dichloroethylene Bis (2-chloroethyl) ether
Chlorine (total residual, TRC) 1,1-dichloroethylene Bis (2-chloroisopropyl) ether
Dissolved oxygen 1,2-dichloropropane Bis (2-ethylhexyl) phthalate
Nitrate/Nitrite 1,3-dichloropropylene 4-bromophenyl phenyl ether
Total Kjeldahl nitrogen Ethylbenzene Butyl benzyl phthalate
Oil and grease Methyl bromide 2-chloronaphthalene
Total Phosphorus Methyl chloride 4-chlorophenyl phenyl ether
Total dissolved solids Methylene chloride Chrysene
Hardness 1,1,2,2-tetrachloroethane Di-n-butyl phthalate
Antimony Tetrachloroethylene Di-n-octyl phthalate
Arsenic Toluene Dibenzo(a,h)anthracene
Beryllium 1, 1, 1-trichloroethane 1,2-dichlorobenzene
Cadmium 1,1,2-trichloroethane 1,3-dichlorobenzene
Chromium Trichloroethylene 1,4-dichlorobenzene
Copper Vinyl chloride 3,3-dichlorobenzidine
Lead ACID -EXTRACTABLE COMPOUNDS: Diethyl phthalate
Mercury P-chloro-m-creso Dimethyl phthalate
Nickel 2-chlorophenol 2,4-dinitrotoluene
Selenium 2,4-dichlorophenol 2,6-dinitrotoluene
Silver 2,4-dimethylphenol 1,2-diphenylhydrazine
Thallium 4,6-dinitro-o-cresol Fluoranthene
Zinc 2,4-dinitrophenol Fluorene
Cyanide 2-nitrophenol Hexachlorobenzene
Total phenolic compounds 4-nitrophenol Hexachlorobutadiene
VOLATILE ORGANIC COMPOUNDS Pentachlorophenol Hexachlorocyclo-pentadiene
Acrolein Phenol Hexachloroethane
Acrylonitrile 2,4,6-trichlorophenol Indeno(1,2,3-cd)pyrene
Benzene BASE NEUTRAL COMPOUNDS Isophorone
Bromoform Acenaphthene Naphthalene
Carbon tetrachloride Acenaphthylene Nitrobenzene
Chlorobenzene Anthracene N-nitrosodi-n-propylamine
Chlorodibromomethane Benzidine N-nitrosodimethylamine
Chloroethane Benzo(a)anthracene N-nitrosodiphenylamine
2-chloroethylvinyl ether Benzo(a)pyrene Phenanthrene
Chloroform 3,4 benzofluoranthene Pyrene
Dichlorobromomethane Benzo(ghi)perylene 1,2,4-trichlorobenzene
1,1-dichloroethane Benzo(k)fluoranthene
1,2-dichloroethane Bis (2-chloroethoxy) methane
1. The total set of samples analyzed during the current term of the permit must be representative of seasonal
variations.
2. Samples shall be collected and analyzed in accordance with analytical methods approved under 40 CFR Part
136.
3. Unless indicated otherwise, metals must be analyzed and reported as total recoverable.
4. Test results shall be reported to the Division in DWQ Form- DMR-PPA1 or in a form approved by the Director,
within 90 days of sampling. Two copies of the report shall be submitted along with the DMRs to the following
address: Division of Water Quality, Water Quality Section, Central Files, 1617 Mail Service Center, Raleigh,
North Carolina 27699-1617.
Modified 10/2004

,jc% sr�T.6s
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
YW REGION 4
o ATLANTA FEDERAL CENTER
F 61 FORSYTH STREET
yrq< FRcfl ATLANTA, GEORGIA 30303-8960
JAN 1 1 2005
Ms. Teresa Rodriguez
North Carolina Department of Environment and
Natural Resources
Division of Water Quality
NPDES Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
SUBJ: Draft NPDES Permit
City of Holly Springs WWTP - NPDES No. NC0063096
Dear Ms. Rodriguez:
In accordance with the EPA/NCDENR MOA, we have completed review of the draft
permit referenced above and have no comments. We request that we be afforded an additional
review opportunity only if significant changes are made to the draft permit prior to issuance, or if
significant comments objecting to the draft permit are received. Otherwise, please send us one
copy of the final permit when issued.
If you have any questions, please call me at [phone].
Sincerely,
JAN 1 3 2005
DENR - WATER QUALITY
POINT SOURCE BRANCH
Marshall Hyatt, Environmental Scientist
Permits, Grants, and Technical Assistance Branch
Water Management Division
Internet Address (URL) • http://www.epa.gov
Recycled/Recyclable • Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 30% Postconsumer)

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l'14 PRONG
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION 4
ATLANTA FEDERAL CENTER
61 FORSYTH STREET
ATLANTA, GEORGIA 30303-8960
'NOV 1 7 2004
Alan W. Klimek, Director
Division of Water Quality
North Carolina Department of Environment and
Natural Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
SUBJ: Review of Draft NPDES Permit
Town of Holly Springs WWTP - No. NC0063096
Dear Mr. Klimek:
The EPA, Region 4, is in receipt of the draft permit for the above referenced facility. The
Form 2A application transmitted to the Region for review with the draft permit did not include the
minimum of three priority pollutant scans, as required by 40 Code of Federal Regulations (C.F.R.)
Sections 122.21(j)(4)(ii) and (vi). As such, it does not serve as a complete permit application.
Because the information provided is inadequate to determine whether the draft permit meets the
guidelines and requirements of the Clean Water Act, I request that a complete permit application
for this facility be submitted that meets the requirements of 40 C.F.R. §§ 122.21(j)(4)(ii) and (vi).
Pursuant to federal regulatory requirements and language of Section MIA. of the North
Carolina/EPA National Pollutant Discharge Elimination System (NPDES) Memorandum of
Agreement (MOA), this letter constitutes an interim objection to the issuance of this permit.
In accordance with the MOA and federal regulations, the full period of time for review of
this draft permit will recommence when the requested information is received by this Office. I look
forward to receipt of the information. If you have any questions, please call me or have your staff
contact Mr. Marshall Hyatt at 404/562-9304.
Sincerely,
James D. Giattina, Director
Water Management Division
cc: Richard G. Sears, Town of Holly Springs
Internet Address (URL) • http://www.epa.gov
Recycled/Recyclable • Printed with Vegetable 011 Based Inks on Recycled Paper (Minimum 30% Postconsumer)

•
Holly Springs Permit Reissue
Subject: Holly Springs Permit Reissue
From: "Ed Powell" <[e-mail]>
Date: Fri, 19 Nov 2004 14:45:13 -0500
To: <[e-mail]>
CC:<[e-mail]>, <[e-mail]>
Teresa,
As we discussed earlier today, the Middle Cape Fear River group met
yesterday with
DWQ to review the West Wake Nutrient Strategy and discuss the speculative
limits for
Discharge from West Wake Regional and Holly Springs. As you know DWQ has
agreed
That Holly Springs expansion will be designed to Cape Fear limits but will
be allowed
To discharge into Utley Creek until the Regional Effluent force main to the
Cape Fear is
Operational.
It was generally agreed yesterday that while the Strategy recommended limits
of 6mg/1
Nitrogen and 2mg/1 phosphorus, speculative limits would be either as
recommended or
Made slightly more stringent to 6 nitrogen and 1 phosphorus. In either
event, The phosphorus
Limit is much less severe than that proposed in the Holly Springs permit
reissue.
Since no upgrade is planned until the Holly Springs WWTP is expanded to the
needed
Capacity of approximately 6MGD, we again respectfully request that the
reissued limits
Be at the level planned in this expansion/upgrade or phosphorus at 2mg/1 or
at the very
Least lmg/1. This limit is attainable at Utley under its present design.
Your strong consideration and support of this request will be greatly
appreciated!!!
Many thanks,
ed
Ed Powell
Davis -Martin -Powell and Associates
6415 Old Plank Rd
High Point, NC 27265
[phone] / Fax [phone]
Email: epowell®dmp-inc.com
1 of 1 - 11/22/2004 8:18 AM

THE TOWN OF
Iio11y
Springs
P.O.Box 8
128 S. Main Street
Holly Springs, N.C. 27540
[phone]
Fax: [phone]
Mayor's Office Fax:
[phone]
NOV 1 9 2004
DENR - ViAfER QUALITY Re:
POINT SOURCE BRANCH
mber 17, 2004
Ms. Teresa Rodrigutz
NPDES Permit Unit
Department of Environment and Natural Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Dear Ms. Rodrigutz:
Town of Holly Springs, NC
NPDES Permit No. NC0063096
Utley Creek WWTP
Wake County
As the holder of Permit No. NC 0063096, we would offer the following comments to
this Draft Permit currently being advertised. In accordance with Mr. Kimek's
correspondence of September 7, 2004, we feel strongly that Section A-3
(EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS) be revised to
include the following language as expressed in Mr. Kimek's letter.
Beginning upon expansion beyond 1.75 MGD and lasting until discharge
from the facility is removed from Utley Creek and transported to the
completed western Wake Regional WWTP force main discharging to the
Cape Fear River, the Permittee is authorized to discharge treated
wastewater into Utley Creek.
Also, we note that effluent limits for both phosphorus and nitrogen are included at
the 1.75mgd level. Please be reminded that no plant improvements are proposed
for this 250,000 gpd increase. The Town will make every possible effort to meet
these proposed permit limits of nitrogen and phosphorus including refinement of
operational activities, and closely monitoring user discharges which may be
detrimental to plant operations. The Town is proceeding with haste with the design
and ultimately construction of expanded and upgraded treatment facilities. The
requested reissue to 1.75 MGD must be treated within the existing Utley Creek
Wastewater Treatment Plant. For this reason, it is respectfully requested the
nitrogen and phosphorus limits at the 1.75 MGD reissue level remain as with the 1.5
MGD level of monitor only.
Past performance of the Utley Creek WWTP have successfully met the proposed
nitrogen limits and, with addition of a coagulant to final clarifier, such as alum, will
meet the phosphorus limit.

Ms. Teresa Rodrigutz
NPDES Permit Unit
Department of Environment and Natural Resources
Page 2
November 17, 2004
We greatly appreciate your cooperation in the re -issuance of this permit! We hope
that these comments can be incorporated in the final document.
Sincerely,
TOWN OF HOLLY SPRINGS, N.C.
Mayor Dick Sears
C: Alan W. Klimek, Director of DWQ
Colleen H. Sullins, Deputy Director of DWQ
Leo Green, P.E.
Ed Powell, P.E.
Stephanie L. Sudano, P.E., Director of Engineering

v.
•
Holly Springs
Loads
Flow TN (mg/L) TP (mg/L) TN (Ib/d) TP (Ib/d)
2.4 6 0.5 120.1 10.0 Permit 2003 , 1998
Equivalent concentration:
1.5 9.6
1.75 8.2
4.88 3.0
0.8
0.7
0.2
120.1
120.1
120.1
10.0
10.0
10.0
4.88 2.20 0.20 89.5 8.1
Equivalent concentration:
1.5 7.2
0.7
1.75 6.1 0.6
2.4
4.5
0.4
89.5
89.5
89.5
8.1
8.1
8.1
1999

Before the undersigned, a Notary Public of Chatham
PUTEIC NOTICE
County North Carolina, duly commissioned and authorized to
yTATI personally appeared Ivy
administer oaths, affirmations, etc., p Y Pp
MANAGEMENT
NA
COMMISSIONINPDEs Marsch, who, being duly sworn or affirmed, according to law,
1617 MAIL SERVICE UNIT doth depose and say that she is Billing Manager Legal
CENTER Advertising of The News and Observer a corporation
RA EIG NC7 OF 17.
NPDESINDENT t WASTEWATER organized and doing business under the Laws of the State of
PERMIT North Carolina, and publishing a newspaper known as The
On the basis ofthoroughstaff News and Observer, in the City of Raleigh Wake
General Statuttet1443•21 Pu -
stondarlic low s a0 nd
egur bons, County and State aforesaid, the said newspaper in which such
standards and regulations, notice, paper, document, or legal advertisement was published
awful
the North Carolina Environ-
mission pronposes to Issuagement Com-
National Pollutant Discharge was, at the time of each and every such publication, a
(NPDE) wa system asewater dis- newspaper meeting all of the requirements and qualifications
Eiiminocharge Spermitttot e per-
, son(s) listed below effective of Section 1-597 of the General Statutes of North Carolina
'45days Iramthe publish date and was a qualified newspaper within the meaning of Section
of this notice.
Written
ne proposed permit it will'be 1-597 of the General Statutes of North Carolina, and that as
the
accepted untiteil th0 dais such she makes this affidavit; that she is familiar with the
othaatndat nog considered In books, files and business of said corporation and by reference
the final determinationlto the files of said publication the attached advertisement for
re-
gardingior
the propo
decide
Director o the NC Devi-
slon of Water QualltY may NC DIVISION OF WATER QUALITY was inserted in the
decido to hold o Public
should for the proposed permit
aforesaid newspaper on dates as follows: 10/15/04
signld the division ofrepublic
significant degree of public
Interest.
Copies of the draft Permit and Account Number: 73350831
other supporting information
1 on file used to determine con-
ditions present in the draft
I permit are available upon re-
quest and payment of the
costs of reproduction. Mall
comments and/or requests
for information to the NC DI-
yisi0n,of Water Qual)tY at the
above address or call Ms.
Carolyn Bryant at (919)
733-5081 extension 520.
Please include the NPDES
permit number (attached) in
any communimav nlso visit
er-
ested persons
the Division of WaterQ St,
at 512 N. Raleigh, NC 276041148 be-
tween the hours of and 5:00 P.m. to review Infor-
Y mation on file: l copied from the books and files of the aforesaid Corporation and publication.
The Town of Holly Springs,
NPDES NC0063096, has art-.
plied for a modification of Its
Permit discharging to Utley
Creek In the Cape teaa River
permit
Basin to increasee
to flow to 1.75 MGD.BOD,
ammonia,residual chlo-
rine,total nitrogen and
phosphorus are water quoin,/
rmayyme�t futurdis-
charge
ations to the receiving
stream. _
N8,0: October 15;2004.
AFFIDAVIT OF PUBLICATION
NORTH CAROLINA.
Wake County. ) Ss.
B ling Manager -Legal Advertising
Sworn or affirmed to, and subscribed before me, this
18 day of OCTOBER , 2004 AD
In Testimony Whereof, I have hereunto set my hand
and affixed my official seal, the day and year aforesaid.
tary Public
My commission expires 14th day of March, 2009.

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3

DENR / DWQ / NPDES Unit
NPDES Permit No. NC0063096
Permit Modification
Facility Information
Applicant/Facility Name
Town of Holly Springs / Utley Creek WWTP
Applicant Address
850 West Ballentine St.
Facility Address
Irving Parkway
Flow (MGD)
1.5 (actual), 1.75 (proposed)
Type of Waste
Domestic
Facility Class
IV
County
Wake
Facility Status
Permit Mod
Regional Office
Raleigh
Stream Characteristics
Receiving Stream
Utley Creek
Stream
Classification
C
Drainage Area (sq. mi.)
0.73
Drainage basin
Cape Fear
Summer 7Q10 (cfs)
0.11
Subbasin
03-06-07
Winter 7Q10 (cfs)
0.25
Use Support
Not rated
30Q2 (cfs)
0.32
303(d) Listed
1 NA
Average Flow (cfs)
0.82
State Grid
Apex
IWC (%)
96 %
OSGS Topo Quad
E 23 NE
Summary The Town of Holly Springs is requesting a permit modification to increase the permitted
flow to 1.75 MGD with no expansion of the treatment system. The town needs to obtain an
Authorization to Operate in order to operate the existing treatment system at a capacity of 1.75 MGD.
This is an interim flow increase until they obtain the permits and complete the expansion to 2.4 MGD.
Facility Description The wastewater treatment facility consists of: mechanical bar screen, grit
chamber, anaerobic phosphorus removal basin, pump station, anoxic tank, aeration tank, package
plant with two aeration tanks, two clarifiers and two sludge stabilization tanks, final clarifier, tertiary
filter, UV disinfection system and cascade aerator. In order to operate the plant at a higher flow of
1.75 MGD operational improvements will be implemented.
PROPOSED LIMITS
The proposed limits for 1.75 MGD are as follows:
Parameter
Monthly
Average
Weekly
Average
Daily
Maximum
BOD, 5 day, 20°C (April 1 — October 31)
5.0 mg/I
7.5 mg/I
BOD, 5 day, 20°C (November 1 - March 31)
10.0 mg/I
15.0 mg/I
Total Suspended Residue
30 mg/I
45 mg/I
NH3 as N (April 1 — October 31)
1.0 mg/I
3.0 mg/I
NH3 as N (November 1 — March 31)
2.0 mg/I
6.0 mg/I
Fecal Coliform (geometric mean)
200/100 ml
400/100 ml
Total Residual Chlorine
17 pg/I
Total Nitrogen (NO2+ NO3 + TKN)
43,800 Ibs/yr
Total Phosphorus
0.5 mg/l
Permit NC0063096
Page 1

Nutrients - Total Phosphorus, Total Nitrogen - Due to the accumulation of nutrients, excessive algal
growth, and eutrophication problems in Utley Creek limits for nutrients are recommended.
NH3 as N - Summer and winter ammonia limits are implemented to protect for ammonia toxicity.
NPDES UNIT CONTACT
If you have questions regarding any of the above information or on the attached permit, please
contact Teresa Rodriguez at [phone] ext. 553.
NAME: --ri....,
Regional Office Comments
DATE: WO y
NAME: DATE:
NPDES SUPERVISOR: DATE:
Permit NC0063096
Page 2

AllWastConc-NH3 TRC.XLS
Allowable Waste Concentration
facility {Holly Springs
NPDES Number I NC0063096
SUMMER
Ammonia as NH3
7Q10(cfs) 0.11 F
Design Flow (MGD) 1.75
Design Flow (cfs) 2.7125
Stream Std (mg/I) 1.0
0.221 ups Bckgrnd LvI (mg.
ups Bckgrnd LvI (mg/
IWC (%)
Allow Conc. (mg/I)
WINTER t
Ammonia as NH3
7Q10(cfs) 0.25
f Design Flow (MGD) 1.75
1 Design Flow (cfs) 2.7125
Stream Std (mg/I) 1.8
0.22
96.103 IWC (%) , 91.561
1.03[ i Allow Conc. (mg/I) 1 1.95
Resdual Chlorine
7Q10(cfs) 0.11
Design Flow (MGD) 1.75
Design Flow (cfs) 2.7125
Stream Std (ug/I) 17.0
ups Bckgrnd LvI (ug/I 0.01
IWC (%) 96.103
Allow Conc. (ug/I)
17.69
Page 1

Holly Springs NC0063096
1996 algal bloom and fish kill
1997 algal bloom
1/1997 DWQ issued permit expansion from 0.5 to 1.5 MGD. No nutrient limits were
included
7/1998 DWQ issued speculative limits for 2.5 MGD, TN 6mg/1, TP 0.5 mg/1 (125 lbs/d,
10.4 lbs/d)
2/1999 DWQ issued speculative limits for 4.88 MGD, TN 2.2 mg/1, TP 0.2 mg/1 (89
lbs/d, 8 lbs/d)
1/2000 Expansion to 1.5 completed
6/2000 ISU did water quality study at Utley Creek, nutrient impacts
9/2000 HS submitted EA for expansion to 4.88 MGD
1/2001 Secretary Holman returned EA for 4.88 MGD
3/2001 HS submitted amended EA to 2.4 MGD
1/2003 DWQ issued permit for 2.4 expansion. TN 6 mg/1, TP 0.5 mg/1(120 lbs/d, 10 lbs/d)
6/2003 ESB did algal growth potential study
6/2004 Tetra Tech completed a modeling analysis for Utley Creek
8/2004 HS submitted permit modification to increase flow to 1.75 MGD (re -rate the
plant)
Future projects:
Get permit for 1.75 mgd without any expansion at the treatment plant (re -rate plant)
Expand plant to 2.44 mgd
Reclaimed water project
Reserve capacity in the Harnett County Interceptor
Reserve capacity in the West Wake Regional System

[Fwd: fie: Holly Springs Discharge]
Subject: [Fwd: Re: Holly Springs Discharge]
From: Alan Klimek <[e-mail]>
Date: Tue, 07 Sep 2004 15:00:00 -0400
To: Coleen Sullins <[e-mail]>, Dave Goodrich
<[e-mail]>
fyi
Original Message
Subject:Re: Holly Springs Discharge
Date:Tue, 7 Sep 2004 14:17:29 -0400
From: "Leo Green" <[e-mail]>
Reply -To: "Leo Green" <elgRgreeneng.com>
Organization:Green Engineering
To: "Alan Klimek" <alan.klimekRncmail.net>
References:<004c01 c48c6f$ccc81660$6700010a(aftg.greeneng.com>
<4134E2C5.4060108 @ancmail.net>
<011701 c49473$4ed52d40$3e2fa318@lgreen27>
<413DE008.1040505nuncmail.net>
Alan,
Thanks for the information. This certainly makes sense to me. I will relay this on to
the Holly Springs people tonight.
Leo
Original Message
From: Alan Klimek
To: E. Leo Green
Sent: Tuesday, September 07, 2004 12:21 PM
Subject: Re: Holly Springs Discharge
Leo,
This is how we'd suggest proceeding. In the late 90s we gave spec limits for a 2.4
mgd plant into Utley Creek with nitrogen limits of 6 mg/1 and phosphorus limits of
0.5 mg/l. This was a technology (BAT) type analysis as opposed to what is needed
to protect this system. If the town is agreeing to put all of its discharge into the
Western Wake outfall when it is completed, we could issue a permit for 2.4 mgd w/
the 6 and 0.5 limits discharging into Utley Creek. If the outfall is not completed
before the 2.4 mgd flow is reached, we'd need to enter into an SOC (would
1 of 4 12/17/2004 9:19 AM

[Fwd: Re: Holly Springs Discharge]
.71
obviously want to start at least 6 months before we came to that point so we could
work out the language) to let you discharge greater than 2.4 mgd into Utley Creek
until the outfall is ready. On a parallel path, we would begin the process of issuing a
4 mgd or 4.88 mgd or 6 mgd (whatever comes out of the process) permit discharging
into the Western Wake outfall. If the Town never exceeded 2.4 mgd before the
outfall was complete, there of course would be no need for an SOC. As we've stated
before, we should have a good handle on the initial nutrient limits for a Cape Fear
River discharge in a month or two. Give me a call if you have questions or still want
to meet.
Alan
E. Leo Green wrote:
Alan,
Ed Powell and I met with Holly Springs' staff this past Wednesday (9/1/04) and
presented the information that you had sent to me regarding the ultimate Cape
Fear discharge, interim Utley Creek discharge, SOC, etc. The Manager, Assistant
Mgr. Town Attorney, Town Engineer and others endorse this concept but are
somewhat unclear as to how the SOC will work. They are ready to instruct us to
begin the 201 Amendment process and final design to accommodate the 2025
flow projection (6.0 MGD) some portion of which will be discharged into Utley
Creek until such time as the West Wake outfall is constructed to the Cape Fear,
projected to be 2011(?). They expect me to discuss this proposition with the Town
Council tomorrow (Tuesday, Sept. 6) in a study session at 6:00 PM.
Please enlighten me on how this will work. Will DWQ issue Holly Springs a
NPDES Permit for the 6.0 MGD with projected Cape Fear limits for a temporary
discharge to Utley Creek upon satisfactory completion of the 201 update and final
plan approval or will the Permit be issued with a discharge to the Cape Fear via
the West Wake system with an SOC allowing a temporary discharge to Utley
Creek? I feel like we can convince the Town Board to accept your proposition if I
can provide them with a little more detail.
I could stop by your office around 5:00 PM tomorrow (Tuesday, 9/6) if necessary
to discuss this process if necessary or you might just give me a call or E-mail.
Please advise. 252-237-5365.
Thanks,
Leo Green
Original Message
From: Alan Klimek
To: Leo Green
2 of 4 12/17/2004 9:19 AM

[Fwd: R4: Holly Springs Discharge]
Sent: Tuesday, August 31, 2004 4:42 PM
Subject: Re: Holly Springs Discharge
Leo,
There was a meeting today w/ some of the Western Wake folks and Coleen and
Dave Goodrich met w/ them and further discussed some of these issues. We
believe that by early October we should have a pretty good handle on the
interim nutrient limits that we'll want for a discharge to the Cape Fear River.
More accurate numbers will be many years into the future after considerable
study. If the town is willing to move all of their discharge to the Cape Fear, we
would work w/ them such that they would only need to meet those limits for any
expansion built now - although this may require entering into an SOC
depending on the amount of the discharge likely to be going to Utley Creek
before the discharge would be moved. Hope this helps a bit.
Alan
Leo Green wrote:
Alan,
We thank you and your staff for meeting with us this past Tuesday and
discussing the Holly Springs issues. We recognize that it will require some
time for your staff to evaluate the modeling analysis together with the town's
request; however, we do have a meeting scheduled for next Wednesday
afternoon in Holly Springs to discuss our progress in this matter. Would it be
possible for you to provide us some idea as to when DWQ may be able to
respond to our request in order that we can provide that information to them at
that time? Please advise.
Thanks,
Leo Green
E. Leo Green, Jr., P. E.
Green Engineering PLLC
P. O. Box 609
Wilson, North Carolina 27893
Phone :[phone]
Fax:[phone]
elg [e-mail]
3 of 4 12/17/2004 9:19 AM

dmp
DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
ENGINEERING • LAND PLANNING • SURVEYING
6415 Old Plank Road, High Point, NC 27265
[phone] • Fax [phone] • www.dmp-inc.com
Mr. Dave Goodrich
NPDES Permit Unit
NC Dept. of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
Dear Dave:
August 27, 2004
Re: Town of Holly Springs, NC
Holly Springs WWTP
NPDES Permit No. NC0063096
DMP Project E-3226
30
In support of the Town of Holly Springs NPDES Permit Modification Application previously submitted,
we are providing the additional supporting data.
• A summary of recent DMR and test results related to effluent discharge concentrations of
Nitrogen and Phosphorus.
• Calculations of the existing plant's ability to meet the established limits of 6.1 milligram per
liter of total nitrogen and 0.5 milligrams per liter of total Phosphorus when operating at a flow
of 1.75 MGD.
In addition to the above, and as a part of planning for the design of expanded and upgraded Utley
Creek WWTP, the following have been undertaken by the Design Consultants and the Town Staff.
• EIMCO Water Technologies will provide field personnel to direct treatment plant staff in the
proper operation of their denit/R Carrousel process to maximize removal efficiencies and
reduction of total nitrogen and total phosphorus.
• The Town operating staff has embarked on an aggressive monitoring program to identify and
reduce system discharges exceeding the adopted industrial waste ordinance limitations. Two
minor industries have been identified as being non -compliant with respect to BODS, total
suspended solids, nitrogen, and phosphorus. The Water Quality Staff is negotiating methods
of waste reduction with these system users. Such reductions should aid in the plant's ability
to meet the established limits.

•
Mr. Dave Goodrich
NPDES Permit Unit
NC Dept. of Environment and Natural Resources August 27, 2004 Page 2
Hopefully this additional information will assist you in processing this Permit Modification request.
Should you find that additional information would be beneficial, please let us know.
With best personal regards, I remain,
CP/dd
C: Stephanie Sudano, PE
Thomas Tillage
Leo Green, PE
File
P:IPROJECT1E32261 Doc1NPDESPermit-Goodrich.doc
Very truly yours,
DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
111/
Charles E. Powell, PE

dmp
DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
ENGINEERING • LAND PLANNING • SURVEYING
6415 Old Plank Road, High Paint, NC 27265 _.
[phone] • Fax [phone] • www.dmp-inicoi l {� , ,f !`
160
AUG 2 4 2004
August 23, 2004 RAGINED iNG
Re: Town of Holly Springs, N.C.
Holly Springs WWTP
NPDES Permit No. NC0063096
DMP Project E-3226
Mr. Dave Goodrich
NPDES Permits Unit
N.C. Department of Environment and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
Dear Dave:
L
L
AUG 302
:Y
J
As we have discussed on many occasions over the past year, the Town of Holly Springs has been
diligently searching for their most viable solution to meet their future wastewater treatment needs. As
you know further, the Utley Creek downstream from the existing wastewater treatment plant has been
detailed modeled by Tetra Tech, Inc., in an effort to determine the advisability of increasing the
capacity of the wastewater treatment plant based upon mass loads rather than concentration loads.
The Town of Holly Springs has looked at future wastewater treatment capacity solutions including a
contribution to the proposed Harnett County Treatment Facility serving the Town of Fuquay Varina,
as well as a continued involvement in the West Wake Regional Facility. After long consideration and
many negotiations with the parties involved, the Town of Holly Springs has committed to continue
their involvement in the West Wake Regional System and have reserved capacity in the effluent
discharge forcemain to the Cape Fear River from the proposed Regional Treatment Facility.
Holly Springs has continued to approach the design of the expansion upgrade of the existing Utley
Creek Treatment Plant to provide current needs. This process has slowed slightly while the
determination of the ultimate available capacity in Utley Creek site has been determined.
As we had discussed previously and as indicated in the March 26, 2004 letter from Mr. Klimek, PE,
the Town was advised to submit a permit modification request to the Division for interim flow of 1.75
million gallons per day. In this respect, we are submitting two (2) copies of a completed NPDES
Permit Application reflecting the requested increase in the capacity of this existing NPDES Permit
from 1.5 MGD to 1.75 MGD to provide additional capacity for Holly Springs during the interim period
while this treatment plant is being designed and constructed at it's expanded and upgraded
capacity. In support of this NPDES Permit Application modification we will provide calculations that
will basically present how this existing facility will be able to meet limits of 6.1 milligram per liter of
total nitrogen and 0.5 milligram per liter of total phosphorus at this elevated hydraulic capacity.

• .�
Mr. Dave Goodrich
NPDES Permits Unit
N.C. Department of Environment and Natural Resources August 23, 2004 Page 2
We sincerely hope that the information provided is adequate to allow you to provide this interim
increase in the permitted capacity of the existing Utley Creek Wastewater Treatment Plant. The Town
of Holly Springs is most anxious to want to resolve their wastewater treatment needs and problems
once and for all and are continuing to exert all possible efforts in this direction.
Your assistance in this requested interim permit modification will greatly enhance the ability to
accomplish this goal.
Should you have questions, or find that additional information is needed in support of this request
please let us know.
With best personal regards, I remain,
Very truly yours,
DAVIS-MARTIN-POW & ASSOCIATES, INC.
Charles E. Powell, PE
CP/dd
C: Carl Dean
Stephanie Sudano
Thomas Tillage
Leo Green, PE
File
P:1 PROJECT1 E32261 Doc)NollySprings-Goodrich.doc

tin R;1'���o
0 0
2." i"G FLOW ,e,,,�
O'0' bWV' SPLITTER ,�4,43
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oT
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AEROBIC
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0.824 MGD
CLARIFIER
1
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TERTIARY FILTERS
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ti
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DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
d
lilil ENGINEERING - LAND PLANNING - SURVEYING
6415 OLD PLANK ROAD
THE TOWN OF
Holly
Springs
FIGURE 3
WATER BALANCE
HIGH POINT, NORTH CAROLINA 27265
NORTH CAROLINA

•
•
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IC ern
TOWN OF HOLLY
SPRINGS
UTLEY CREEK,It111�WT
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DAVIS-MARTIN-POWELL & ASSOCIATES, INC.
dm
ENGINEERING - LAND PLANNING - SURVEYING
P6415 OLD PLANK ROAD
HIGH POINT, NORTH CAROLINA 27265
FIGURE 2
ONE MILE RADIUS TOPO MAP

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6415 OLD PLANK ROAD

Utley Creek Modeling Analysis Summary
8/24/2004
Summary of i'lodeling Analysis for
Holly Springs Utley Creek
Discharge
August 24, 2004
Trevor Clements and Jon Butcher
TETRATECH, INC.
Analyzed Variations of 3 Scenarios
Expansion at current location
compared with existing permit
conditions
• Discharge at current outfall with
Thomas Mill Pond removed
• Discharge below Thomas Mill Pond
Presence of Water Primrose
affects modeling approach.
TETRA TECH, INC.
Issues involve water quality below the
I!WTP outfall for expanded wastetlows
t'wo types of modeling analyses
104
Eutrophication
— BATHTUB modeling of Thomas Mill
Pond
— Loading Analysis to Harris Lake cove
Dissolved Oxygen
— Requested by DWQ for alternative
below Thomas Mill Pond
— Streeter -Phelps analysis
Eutrophication Analysis requires
watershed approach to account for
nonpoint and point sources
Legend
• Ib II/ Sponge WWTP
- Stream
SWwlaNvd Boonda Aee
Web Bpelee
Oreentree Thomas Me.1
Reuear Pond
A / cn wafrr
C
2t.-i')

Utley Creek Modeling Analysis Summary
8/24/2004
Flow and NPS nutrient loading estimated using
Generalized Watershed Loading Function model
Prealpltation Evapotranspiration
f
Erosion
(USLE)
Land Surface —SCS Curve
Number Simulation Runoff
Unsaturated zone Groundwalm
IShallowl
Shallow saturated zone
1r
Septic System Loads
Particulate
Nutrients
Dissolved Nuuienls
Deep Seepage
Loss
BATHTUB Model — Physical
Features from Green Eng. Surve
Legend
• Ebreeen Mtewrtmentr
r hones MilPo,d Eautng WMer Level
ureenea Ma Pont Wgn WeterLevel
♦
•
5(4AP
C a/3/ Lf L
- / ." COO
BATHTUB water quality
calibrated to D\\VQ data
(ft] TETRATECH, INC.
2

Utley Creek Modeling Analysis Summary
8/24/2004
Scan
-ado
Modeling
Pond
Level
Results -Thomas
M
MiIt Pond
Thomas Mill Pond
WWTP Discharge
Flow
Iwo
TN
Pho
TN
1"a'U
TP
1
•
Pond
TN
ewala
Pond
TP
letarla
Chl
a
twti)
Fraction
> 40
gait_
2000
High
0.65
64.6
11.9
28.1
5.18
MI
1.16
23.3
34.1%
A
Low
1.5
78.8
8.0
6.3
0.50
4.2
0.40
19.3
27.9%
8
Low
2.4
120.1
6.0
9.9
0.50
4.4
0.41
19.4
28.0%
C
High
2.4
120.1
6.0
9.9
0.50
4.2
0.38
22.3
32.7%
0
Low
4.2
120.1
3.4
9.9
0.29
2.9
027
18.2
28.0%
E
Low
5.6
120.1
2.6
9.9
0.21
2.3
0.22
17.3
24.3%
F
Below
Pond
4.2
120.1
3.4
9.9
0.29
2.0
0.33
17.4
24.4%
Total Annual Loading
Creek Arm of Shearon
to White
Harris
Total Nitrogen
(Ibyr)
Oak
Lake,
Total Phosphor
(Ih(yr)
3,616
Description
Utley Creek Point Source
Discharge (Scenario 8 - baseline)
43,836
Utley Creek Total Delivered Load
50,372
7,118
Balance of Watershed NPS Load
39,022
8,063
Total Baseline Load
89,394
15,181
Increase at 4.2 MGO (Scenario D)
2,253 (2.5
%)
281 (1.9
%)
Increase at 5.6 MGD (Scenario E)
3,252 (3.6
%)
392 (2.6
%)
S
Modeling Results - Load to Harris Lake
60,000
50,000
40,000
30.000
20,000
10,000
0
2000
C D1 D2
Scenario
1
• Total N
■ Total P
it
TETRATECH, INC.
3

Utley Creek Modeling Analysis Summary
8/24/2004
DO Modeling Results
Even with very conservative
assumptions:
— 50 percent lower velocities than best
prediction
— 50 percent lower reaeration rates
— Increased effluent BOD-ult:BOD5 ratio
not predicted to fall below 5 mg/
instream.
Conclusions
Under higher wasteflows more
nutrients are delivered to the
Shearon Harris Lake cove, though
not significant
• Relocating the discharge below
Thomas Mill Pond is not
recommended
Conclusions
Conditions in Thomas Mill Pond
after WWTP upgrade and expansioi
expected to be better than 2000 an
2003 conditions observed by DWQ
Increasing wasteflows beyond 2.4
MGD results in slight decreases in
nutrient and chlorophyll -a
concentrations, though not
significant
Th
TETRA TECH, INC.
4

Utley Creek Modeling Analysis July 2004
1 Introduction
The Town of Holly Springs wastewater treatment plant (WWTP) discharges to Utley Creek, a
tributary to Shearon Harris Lake in the Cape Fear River Basin (Figure 1). Rapid growth of the
Town is generating corresponding increases in the need for wastewater treatment and discharge.
According to the US 2000 Census, the population of Holly Springs increased by nearly 500
percent during the preceding decade, from under 1,000 residents to over 9,000. In June 2001, the
Town was granted an expansion in effluent flow to allow 1.5 MGD to be discharged into Utley
Creek. In January 2003, a permit to upgrade to 2.4 MGD was issued along with effluent limits
for total nitrogen (TN) and total phosphorus (TP). Construction on this plant is scheduled to
begin in September 2004.
Figure 1. Map of Utley Creek Below the Holly Springs WWTP Discharge
For the past several years, Holly Springs has co -sponsored a study to explore regional treatment
and disposal of wastewater in western Wake County. The current time frame for a regional
facility(ies) to be up and running is around 2010 to 2012. By that time, the Town of Holly
Springs expects its wastewater treatment demand to exceed 4 MGD. Additionally, the current
preferred regional alternative does not provide for the Town's discharge to be removed from
Utley Creek. Thus, the Town is also exploring the potential for tying into the Harnett County
system. However, the Town does not expect that its full amount of flow will be accommodated
by that option.
Given these circumstances, the Town has requested that the Division of Water Quality (DWQ)
consider permitting further flow expansion into Utley Creek while holding mass amounts
allocated for TN and TP to existing permitted levels. However, because of recent field surveys
(I)
TETRA TECH, INC.
1

Utley Creek Modeling Analysis July 2004
conducted by DWQ demonstrating excessive eutrophication in the downstream receiving waters,
particularly Thomas Mill Pond, an impoundment of Utley Creek, DWQ has expressed strong
concern over additional discharge to Utley Creek. After meeting with DWQ, the Town of Holly
Springs contracted with Tetra Tech Inc. as a third -party scientific consultant to further analyze
discharge alternatives to Utley Creek.
Prior to investing in more detailed modeling analyses, Tetra Tech recommended that a scoping
level analysis be performed to determine the potential for an acceptable alternative. This report
summarizes the findings of this scoping level modeling analysis.
1.1 DISCHARGE SCENARIOS TO ANALYZE
Based on discussion between DWQ and the Town's engineering consultants on May 4, 2004,
Tetra Tech was asked to conduct modeling analyses for three alternatives:
1. Discharge at the current outfall location under the existing permitted flow of 2.4 MGD
and at the proposed flow of 4.2 MGD.
2. Discharge at the current outfall with Thomas Mill Pond restored to a flowing stream and
wetland area.
3. Relocation of the discharge point below the Thomas Mill Pond dam.
The modeling analyses focus primarily on the impact of the discharges on downstream
eutrophication in Thomas Mill Pond and the Shearon Harris Lake cove. However, under
Alternative 3, the impact on downstream dissolved oxygen in Utley Creek has also been
analyzed.
1.2 OVERVIEW OF TECHNICAL APPROACH
The eutrophication and Biochemical Oxygen Demand/Dissolved Oxygen (BOD/DO) modeling
require two separate approaches. Eutrophication modeling was conducted using linked
watershed, stream transport, and impoundment algal response models at a seasonal average time
scale. The BOD/DO modeling was performed using a Streeter -Phelps model for critical low flow
conditions.
The original intent was to model eutrophication impacts in both Thomas Mill Pond and the White
Oak Creek arm of Shearon Harris Lake using the USACE BATHTUB model. However,
reconnaissance conducted on June 2, 2004, revealed that the upper portion of the Shearon Harris
Lake arm was infested with dense mats of non-native aquatic weeds — primarily water primrose
(Ludwigia hexapatala; Figure 2). The BATHTUB model is more appropriate for evaluating
water column algal response as indicated by chlorophyll a; it is not set up to simulate response of
rooted aquatic macrophytes. Therefore, the potential impact of different wastewater discharge
scenarios on Harris Lake was evaluated in terms of relative changes in nutrient loading.
Details regarding model setup and application are summarized in the sections that follow.
11)
TETRA TECH. INC.
2

Utley Creek Modeling Analysis
July 2004
Figure 2. Water Primrose Infestation in Shearon Harris Lake Cove
TE
TETRA TECH, INC.
3

Utley Creek Modeling Analysis July 2004
(This page left intentionally blank.)
Ej
TETRA TECH, INC.
4

Utley Creek Modeling Analysis July 2004
2 Eutrophication Analysis
Holly Springs' discharge enters Utley Creek and flows through Thomas Mill Pond to Shearon
Harris Lake. Nutrients in the discharge, as well as from nonpoint sources, can promote excess
algal growth (eutrophication). Investigations by NCDWQ in 2000 noted excessive concentrations
of chlorophyll a, an indicator of algal density, in Thomas Mill Pond, although this waterbody is
not of sufficient size to require compliance with North Carolina's 40 µg/L water quality criterion
for chlorophyll a. Further downstream, nutrients from Holly Springs might contribute to excess
algal growth in Shearon Harris Lake.
To investigate potential effects of the Holly Springs discharge on eutrophication, a suite of linked
modeling tools was required. These include an analysis of watershed nonpoint source loading to
determine the background levels of nutrients in the system, an analysis of stream transport to
account for the changes in load that occur within the stream system, and an analysis of
nutrient/algal response.
2.1 MONITORING DATA
A fish kill and two algal blooms were observed in Utley Creek during the summers of 1996 and
1997. Following initial investigations in these years, the NCDWQ Intensive Survey Unit (ISU)
conducted physical and chemical sampling of Utley Creek during six site visits from May 5 to
August 31, 2000 (Williams, 2000). NCDWQ conducted additional sampling and Algal Growth
Potential Testing (AGPT) on July 28, 2003.
Eight sites were sampled by DWQ in 2000 (Figure 3). The summer 2000 chlorophyll a total
nitrogen and total phosphorus measurements are summarized in Table 1. The ISU concluded that
the nutrient load predominantly originates from the WWTP. The study found that under summer
low -flow conditions, Holly Springs WWTP effluent accounted for 91 percent of total stream flow
in Utley Creek. Based on the six grab samples that summer, the WWTP discharged averages of
65 lbs/day of total nitrogen, 26 lbs/day of total phosphorus, and 0.8 lbs/day of ammonia. The ISU
estimated that once Utley Creek reaches Harris Lake, total nitrogen in the creek is reduced by 57
percent, and total phosphorus is reduced by 67 percent. The study suggests that Thomas Mill
Pond helps reduce the nutrient load to Harris Lake, but that the impoundment encourages algal
growth.
ci
TETRATECN,INC.
5

Utley Creek Modeling Analysis
July 2004
Green Tree
FigsErvoir
acre
�0
0
Thomas Mill Po
+/- 4.5 acres
Holly Springs
WWTP
301
Figure 3. NC DWQ Sampling Sites in Utley Creek Drainage
Table 1. Summary of NCDWQ Intensive Survey Unit Sampling May through
August 31, 2000 (Williams, 2000)
Upstream
WWTP
UTC 01
WWTP
UTC 03
Down-
stream
WWTP
UTC 04
Mill Pond
UTC 05
Downstream
Mill Pond
UTC 06
Down-
stream
Green-
tree Darn
UTC 07
Harris
Lake
UTC 09
Harris
Lake
UTC 10
Chlorophyll a (pg/L)
Range
<1 to 14
<1 to 5
<1 to 120
<1 to 320
<1 to 27
<1 to 24
2 to 31
Median
4.0
4.0
22.0
26.5
20.5
13.0
14.0
Mean
5.6
3.1
37.8
75.3
17.6
13.3
14.0
Total Nitrogen (Ibs/day)
Range
0.5 to 2.7
7.4 to
174.5
26.9 to
128.1
NA
12.9 to 99
13.7 to
55.2
NA
NA
Median
1.1
56.8
57.5
NA
53.5
40.0
NA
NA
Mean
1.2
64.6
71.4
NA
55.7
37.5
NA
NA
Total Phosphorus (Ibs/day)
Range
0.0 to 0.4
2.9 to
77.1
4.5 to 29.2
NA
0.5 to 42
0.6 to 21
NA
NA
Median
0.1
12.8
10.7
NA
7.2
5.4
NA
NA
Mean
0.1
26.2
22.3
NA
13.9
8.8
NA
NA
'NA - Not calculated.
ib
TETRA TECH, INC.
6

Utley Creek Modeling Analysis July 2004
NCDWQ also performed water quality sampling and Algal Growth Potential Testing (AGPT) on
July 28, 2003. Chemical and physical parameters were measured upstream of the WWTP, at
Thomas Mill Pond, and upstream of the Utley Creek confluence with Harris Lake. AGPT was
measured at the Thomas Mill Pond and Harris Lake sampling locations.
Table 2 presents the July 28, 2003 chlorophyll a, total nitrogen, total phosphorus, and AGPT
measurements. A Mean Standing Crop (MSC) greater than 10 mg/L indicates that the water body
is subject to frequent nuisance algal blooms, whereas an MSC of less than 5 mg/L indicates that
the water body is unlikely to produce excessive algal growth. Based on the nutrient
concentrations and AGPT results, the study concluded that nutrient concentrations are more than
sufficient to promote nuisance algal growth in Thomas Mill Pond. The AGPT MSC mean control
plus nitrogen and phosphorus results indicate that nitrogen is the limiting nutrient in the pond, but
that both nitrogen and phosphorus need to be controlled to curtail algal growth. According to the
study, nutrient concentrations in Harris Lake are unlikely to produce nuisance algal blooms.
Table 2. Physical, Nutrient, and Algal Growth Potential Test Results from NCDWQ
Sampling of Utley Creek on July 28, 2003 (NCDWQ, 2003)
Parameter
Upstream of
Holly Springs
WWTP
Utley Creek and
Thomas Mill Pond
Utley Creek
0.25 mi Upstream
from Mouth at
Harris Lake
Chlorophyll a (pg/L)
<1
94
10
Total Nitrogen (mg/L)
0.19
1.58
0.62
Total Phosphorus (mg/L)
0.02
0.49
0.03
AGPT MSC Mean Control (mg/L)
NS1
12.2
0.6
AGPT MSC Mean Control + N (mg/L)
NS
33.2
0.4
AGPT MSC Mean Control + P (mg/L)
NS
10.4
3.5
Limiting Nutrient
NS
Nitrogen
Phosphorus
'NS - not sampled
2.2 WATERSHED LOADING
To evaluate total nutrient load delivery in Utley Creek it is necessary to account for nonpoint
loads as well as the point source loads from the wastewater treatment plant (WWTP). The
nonpoint loads are, however, expected to be small relative to the WWTP discharge, particularly
as most of the watershed area is currently in forest cover. Accordingly, a quick scoping analysis
of the nonpoint load component is appropriate.
The scoping level analysis is implemented using a modification of the(watershed loading model l
developed for the adjacent Jordan Lake watershed (Tetra Tech, 2003). The strategy adopted for
the Jordan Lake modeling was to simulate unit (per acre) loads on a seasonal basis, aggregate
these to the subwatershed scale by multiplying times the land use distribution, and account for
losses during transit using a modification of the USGS SPARROW methodology.
In the Jordan Lake watershed model, unit pollutant loads are simulated for each land use type
using the Generalized Watershed Loading Functions model Haith et al., 1992). The
GWLF model provides an appropriate, well -accepted tool for generating seasonal loads at the
E I RA TECH. INC.
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Utley Creek Modeling Analysis July 2004
small watershed scale. The model simulates hydrology at a daily time step using the Soil
Conservation Service (SCS) Curve Number method, estimates erosion using the Universal Soil
Loss Equation (USLE), and simulates nutrient transport as a function of buildup/washoff,
movement with eroded sediment and groundwater flux.
2.2.1 Land Use in Utley Creek
The 15 basic land uses available in the GWLF implementation for Jordan Lake are summarized in
Table 3, along with the corresponding typical impervious fraction. The residential land uses are
additionally subset into sewered and unsewered portions. For areas on sewer service, nutrient
loading via wastewater is accounted for in wastewater discharge monitoring. Residences with
onsite wastewater disposal also generate significant nutrient loads, but these must be accounted
for in the watershed nonpoint source model.
Table 3. Land Use Categories and Nominal Impervious Percentages
Land Use Name
GWLF Code
Percent Impervious
Residential — Very Low Density
(2+ acres per d.u.)
RVL
8
Residential — Low Density (1.5-2 acres per d.u.)
RLL
14
Residential — Medium Low Density
(1-1.5 acres per d.u.)
RML
18
Residential — Medium High Density
(0.5-1 acres per d.u.)
RMH
23
Residential — High Density
(0.25-0.5 acres per d.u.)
RHH
29
Residential — MultifamilyNery High Density
(< 0.25 acres per d.u.)
RVH
50
Office/Light Industrial
OFF
70
Commercial/Heavy Industrial
CIT
85
Urban Greenspace
UGR
0
Pasture
PAS
0
Row Crop
ROW
0
Forest
FOR
0
Wetlands
WET
0
Barren
BAR
0
Water
WAT
NA
The first step in characterizing land uses for Utley Creek was the delineation of subwatersheds.
The Utley Creek subwatersheds were delineated with 1999 2-foot contours from the Wake
County GIS website (Wake County, 2004). Since the USGS 1:24,000 hydrography data did not
provide adequate precision, the Utley Creek mainstem and select tributaries also were delineated
Th
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Utley Creek Modeling Analysis
July 2004
from the contours. As shown in Figure 4, the subwatersheds were delineated with the following
outlets: 1) WWTP outfall, 2) Thomas Mill Pond Outlet, 3) Greentree reservoir outlet, and
4) Confluence of Utley Creek and Harris Lake.
Legend
•
Holly Springs WWTP
Streams
Subwatershed Boundaries
Water Bodies
Greentree Thomas Mill
Reservoir Pond
N
SCALE 1,
0 025 0A
Figure 4. Utley Creek Subwatershed Delineation
The Holly Springs area has experienced rapid growth in recent years, so it is important to
evaluate land use distributions based on the most recent data. Acres of GWLF land use classes in
the four Utley Creek subwatersheds were estimated with current (2004) Wake County tax parcel
spatial coverages, with interpretation aided by 1999 aerial photographs (Wake County, 2004).
Parcels were classified as residential if they had a non -zero building value and had typical
residential characteristics, including location within a residential subdivision or the presence of a
house on the lot. The residential parcels were further divided into the GWLF residential classes
according to the acres per development unit in Table 3.
Several land use types identified in the parcel coverage do not represent a single land use class for
modeling purposes. For instance, parcels classed as farms for tax purposes contain a mixture of
crops, forest, and residences. Parcels that contained more than one GWLF land use were
classified according to the proportions in Table 4. These assumptions were based on watershed -
wide trends in the 1999 aerial photographs. The areas containing the greentree reservoir and
other wetlands were assumed to be one-half wetland and one-half forest. Parcels designated as
cropland were estimated to be one -quarter low density residential, one-half cropland, and one -
quarter forest. To account for ongoing construction, parcels within residential subdivisions and
with zero building value ("transitional" in Table 4) were classified as one-third medium density
residential, one-third forest, and one-third barren. Ten percent of forested parcels were classified
as barren land to account for dirt roads and clearings evident in the 1999 aerial photographs.
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Utley Creek Modeling Analysis
July 2004
Table 4. Proportions Used to Divide Mixed -use Parcels into GWLF Land Use Classes
GWLF Land Use Class
Parcel Type
Farms
Forested
Transitional
Wetland
Residential - Low Density
0.25
Residential - Medium Low Density
0.33
Row Crop
0.50
Forest
0.25
0.92
0.33
0.50
Wetlands
0.50
Barren
0.08
0.33
GWLF commercial and heavy industrial land uses were identified by owner descriptions and the
existence of large buildings. Roads, pools, and tennis courts were classified as 100 percent very
high density residential, and a few urban parcels were classified as 100 percent urban green
space. For subwatcrsheds 2 and 3, about 40 acres in each subwatershed were adjusted case -by -
case to approximate land use shown in the aerial photos. No parcels were classified as office,
light industrial, or pasture.
Sewage disposal method was based on location and lot size. Tetra Tech assumed that all
residential parcels in Watersheds 3 and 4 were served by septic systems and that the low and very
low -density parcels in Watershed 2 were served by septic systems, while higher density
residential parcels in Watershed 2 and all residential parcels in Watershed 1 were served by
sanitary sewer.
The estimated acreage of GWLF land use classes by subwatershed is presented in Table 5.
Table 5. Utley Land Use Distribution in Acres by Subwatershed
GWLF Land use Class
Subwatershed
Utley Creek
Watershed
Total
1
2
3
4
Residential - Very Low Density
17.1
84.1
20.6
0.0
121.9
Residential - Low Density
24.8
3.5
12.0
0.0
40.3
Residential - Medium Low Density
6.5
0.0
11.4
0.0
17.9
Residential - Medium High Density
36.1
3.5
12.2
0.7
52.6
Residential - High Density
0.0
1.5
1.5
1.7
4.8
Residential - Very Low Density
145.8
2.8
17.6
0.0
166.2
Office/Light Industrial
0.0
0.0
0.0
0.0
0.0
Commercial/Heavy Industrial
6.8
29.3
44.1
0.0
80.2
Urban Greenspace
3.5
0.0
0.0
0.0
3.5
Pasture
0.0
0.0
0.0
0.0
0.0
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Utley Creek Modeling Analysis
July 2004
GWLF Land use Class
Subwatershed
Utley Creek
Watershed
Total
1
2
3
4
Row Crop
0.0
0.0
22.6
0.0
22.6
Forest
112.8
692.8
667.1
156.4
1,629.1
Wetlands
9.9
2.6
12.0
38.6
63.0
Barren
8.9
58.6
53.3
10.2
131.0
Water
0.0
5.0
2.0
0.0
7.0
Total
372.3
883.7
876.5
207.6
2,339.9
2.2.2 Soil Properties
Unit loading rates from the GWLF modeling depend on land use parameters, meteorology, and
soil characteristics. The land use parameters (percent cover, rates of nutrient buildup, etc.) and
meteorology are taken to be the same as used in the adjacent part of the Jordan Lake watershed
model (hydrologic Response Unit or HRU 12 in Tetra Tech, 2003). Soil parameters for the Utley
Creek watershed, however, differ from those used in HRU 12, as Utley Creek lies just outside the
Triassic Basin. This in turn requires recalculation of the curve numbers, which control surface
runoff, and the Universal Soil Loss Equation, K and LS factors, which control estimation of
erosion.
The Jordan watershed model GWLF parameters are based on the NRCS State Soils (STATSGO)
coverage, which summarizes soil properties at an aggregated level. The Utley Creek drainage is
almost entirely within soil NC052, the properties of which are summarized in Table 6.
Table 6. Summary of Surface Layer Properties for Soil Group NC052
Component Soil
Percentage
Slope (low)
Slope (high)
Hydrologic
Group
K factor
MAYODAN
26
6
10
B
0.24
HERNDON
12
2
6
B
0.43
MAYODAN
12
2
6
B
0.24
PINKSTON
9
10
25
B
0.20
CREEDMOOR
9
6
10
C
0.28
WHITE STORE
6
2
6
D
0.28
WEHADKEE
2
0
2
D
0.32
CREEDMOOR
4
2
6
C
0.28
GOLDSTON
5
10
25
C
0.15
HERNDON
2
6
10
B
0.43
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11

Utley Creek Modeling Analysis
July 2004
Component Soil
Percentage
Slope (low)
Slope (high)
Hydrologic
Group
K factor
WHITE STORE
5
2
10
D
0.37
CHEWACLA
4
0
2
C
0.28
MAYODAN
1
15
25
B
0.24
WAHEE
1
0
2
D
0.28
WHITE STORE
1
6
10
D
0.28
CARTECAY
1
0
2
C
0.32
The component soils for the Utley Creek drainage were weighted by percentage within NC052
and used to recalculate runoff curve numbers (antecedent soil moisture condition II) and
erodibility (K) and slope-(LS) factors for the USLE (assumptions for C and P factors are as
documented in Tetra Tech, 2003). Results are shown in Table 7. Note that the USLE is not used
for land uses denoted as Urban, where a buildup/washoff formulation is used instead by GWLF
and was not changed from the Jordan Watershed Model.
Table 7. SCS Curve Numbers and USLE Factors Estimated for Utley Creek
Land Use
SCS Curve Number II
K•LS•C•P
Residential - Very Low Density
69.2
0.0022
Residential - Low Density
71.1
Urban
Residential - Medium Low
Density
72.3
Urban
Residential - Medium High
Density
73.9
Urban
Residential - High Density
75.8
Urban
Residential - Very High Density
82.3
Urban
Office/Light Industrial
88.6
Urban
Commercial/Heavy Industrial
93.3
Urban
Urban Greenspace
73.6
0.0044
Pasture
73.6
0.0037
Row Crop
81.3
0.0268
Forest
63.4
0.0010
Wetlands
71.1
0.0010
Barren
88.4
0.1673
Water
98.0
0
Note: Pollutant loading from Urban land uses does not employ the USLE approach.
2.2.3 Nonpoint Loading Rates for Utley Creek Watershed
To estimate unit loads at the field scale for the Utley Creek watershed, the GWLF model was re-
run for individual land uses, using 10 years of meteorological data (April 1990-March 2000).
The first,year of output was discarded to allow for model spin up, and the remainder of the output
TETRA TECH. INC.
12

Utley Creek Modeling Analysis July 2004
averaged by season. The resulting annual average loading rates for selected land uses, including
both surface and groundwater pathways, are shown in Figure 5 (for phosphorus) and Figure 6 (for
nitrogen).
10
8-
• 6—
eo
a 4—
1-
2--
♦
0
♦
N.
icyo c•a hepG �aG ��e �mG �c°6 G09 cacP
ec,b). o• coo ,.. ec, q_o „0,p,
N le
Figure 5. Average Annual Total Phosphorus Loading Rates by Land Use (Edge of Field)
45
40 —
35 —
30 —
• 25 -
'° 20 —
H 15 -
10
5
0
♦
♦
♦
•
•
+-- 1 1---- E } ---}-
•
N. � G G a G e6 °Q
°r O. c."/ N' Se' ° C
G ��� q_e5 01 Jam; 440 �G' Q- ,pa
O• N•
Figure 6. Average Annual Total Nitrogen Loading Rates by Land Use (Edge of Field)
TETRATECH, tNC.
13

Utley Creek Modeling Analysis
July 2004
The GWLF model also provides estimates of flow in Utley Creek, as shown in Figure 7. Average
annual flow above the wastewater discharge, based on the 1991-2000 meteorology and current
land use, is estimated as 1.0 cfs, with summer average flows of about 0.68 cfs. The average
annual nonpoint flow at the mouth of Utley Creek in I-Iarris Lake is estimated as 5.0 cfs,
exclusive of the wastewater discharge.
Above WWTP
--a--Thomas Mill Pond
Jan -Feb- Apr -May- Jul -Aug- Oct -Nov -
Mar Jun Sep Dec
Figure 7. Estimated Average Flow by Season in Utley Creek, Excluding Waste Discharge
Edge -of -field estimates of seasonal and annual nonpoint nutrient loading rates produced by the
model are summarized in Table 8.
Table 8. Estimated Nonpoint Source Loading Rates (Edge of Field)
Total Nitrogen Loading (lbs)
Subwatershed
Jan -Feb -Mar
Apr -May -Jun
Jul -Aug -Sep
Oct -Nov Dec
Annual
1
2,166
702
1,274
882
5,024
2
4,048
941
2,443
1,184
8,616
3
4,535
1,141
2,758
1,419
9,852
4
666
130
393
172
1,362
Total Phosphorus Loading (Ibs)
1
430
118
269
162
979
2
834
118
587
222
1,763
3
920
146
644
258
1,968
4
146
20
98
36
299
f�l
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14

Utley Creek Modeling Analysis July 2004
2.3 NUTRIENT TRANSPORT
The GWLF nonpoint loading estimates developed in Section 2.2 represent edge of field loads.
These loads are reduced by uptake and transport through the stream system. Three types of
nutrient reduction during transport are assessed, consistent with the Jordan watershed model:
(1) mainstem delivery rates, representing the fraction delivered from the pour pointofaasubbasin
or point source to a downstream point, (2)local-scale trapping within the subwatersheds, and
(3) trapping in impoundments.
2.3.1 Mainstem Delivery
Delivery through the Utley Creek mainstem is represented using a methodology similar to the
transport component of the USGS SPARROW approach (Smith et al., 1997). SPARROW refers
to patially referencediegressions of contaminant transport An watershed attributes, and was
developed based on nationwide USGS National Stream Quality Accounting Network (NASQAN)
monitoring of 414 stations. The model empirically estimates the origin and fate of contaminants
in streams and quantifies uncertainties in these estimates based on model coefficient error and
unexp ained variability in the observed data.
The SPARROW tool actually contains two portions, one to generate loads and one to account for
mass transport through stream reaches. Our approach is to use GWLF to generate the loads at the
14-digit HUC scale and then apply the portion of SPARROW that estimates instream transport
losses.
In SPARROW, nutrient mass reduction during transport is calculated using first order decay
equations that are a function of time -of -travel:
C, = Co• e-s'
where:
Co = pollutant mass present at the upstream end of a reach
= pollutant mass present at the downstream end of a reach following travel time t
8 = decay rate (1/day)
t = time of travel (days)
Time of travel within each stream segment was estimated from stream length and velocity, while
the velocity (at average seasonal flow) was estimated using NCDWQ Level B methodology. This
includes a relationship for stream velocity in North Carolina, based on 125 velocity studies
(NCDEM, 1984), as
0.75
U = 0.124 Qact 0.35 S00.29'
Qavg
where U is the velocity (ft/s), Qac, is the actual flow of interest (cfs), Qavg is the average annual
flow of the segment (cfs) and So is the stream bed slope (ftlmi). This equation was applied using
the seasonal and annual average flows generated by GWLF, yielding stream velocities (at
seasonal average flow) ranging from 0.26 to 0.55 m/s downstream of the WWTP (under current
discharge conditions).
The SPARROW loss rate for phosphorus used the modified method developed by Research
Triangle Institute for the Jordan Lake watershed model, in which the coefficient is estimated as
11)
TETRA TECH, INC.
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Utley Creek Modeling Analysis July 2004
p = —LN(Q) + 0.607 .
For nitrogen, it is now clear that the national SPARROW estimates tend to underestimate losses
in small streams. McMahon et al. (2003) developed a SPARROW application for nitrogen
delivery in the Cape Fear, Neuse, and Tar -Pamlico basins in North Carolina, and found that loss
rates in small streams (less than 37 cfs) are best represented by a value of 0.99 day-'.
Due to the short travel times, losses in transit through the mainstem (including impoundments)
are expected to be small. Estimated throughput for individual segments (1,223 to 2,027 m in
length) ranges from 5 to 98 ercent for_phosphorus and 85 to 95 percent for nitrogen.
2.3.2 Local -Scale Trapping within Subwatersheds
Nutrient trapping also occurs within the small intermittent and perennial channels that carry flow
from field edge to the Utley Creek mainstem. These are also estimated using a SPARROW -type
methodology, as was done in the Jordan Lake watershed application. The difference is that
explicit channel characteristics are not available. Travel distance is estimated assuming an
average 2:1 aspect ratio for the shape of a drainage area, in which case the average travel distance
to the outlet is (A/2)°'S, where A is the area of the subwatershed in m2. Velocity for calculation of
travel time is then estimated from the Level B equation at annual average conditions.
2.3.3 Trapping within Impoundments
Greater rates of trapping can be expected within impoundments, where the water slows, allowing
settling and uptake by plants. For Thomas Mill Pond, the trapping rate may be estimated from
the BATHTUB modeling (Section 2.4) as the ratio of influent to mixed concentration. For the
greentree impoundment, no net trapping is assumed based on visual assessment of its small size,
seasonal operation, and poor condition.
2.4 BATHTUB MODEL OF NUTRIENT RESPONSE IN THOMAS MILL
POND
Tetra Tech selected the U.S. Army Corps of Engineers' BATHTUB model (Walker, 1987) to
represent nutrient and eutrophication dynamics in Thomas Mill Pond. This model is designed to
facilitate application of empirical eutrophication models to reservoirs and was modified for use in
a spreadsheet application. The program performs water and nutrient balance calculations in a
steady-state, spatially -segmented hydraulic network that accounts for advective transport,
diffusion, and nutrient sedimentation. Eutrophication-related water quality conditions are
expressed in terms of total phosphorus, total nitrogen, chlorophyll a, transparency, organic
nitrogen, non-orthophosphorus, and hypolimnetic oxygen depletion rate. These conditions are
predicted using semi -empirical relationships developed and tested on a wide range of reservoirs.
Mass balances are computed in BATHTUB at steady state over an appropriate averaging period.
Steady-state approximation means that only seasonal or annual average loads and conditions are
simulated, although the loads and conditions may change from year to year. In other words, the
model does not represent day-to-day changes in flow, loads, or nutrient concentrations. Although
this approach represents a compromise, it has proven effective in practice: short-term variations
in lake conditions reflect variations in flow, including wind and weather effects, which require
complex and labor-intensive models; such effects tend to average out, however, over longer time
frames. Thus, annual or seasonal average conditions can be successfully predicted using data that
are insufficient for simulating day-to-day variability.
1:11
TETRATECH.tNC.
16

Utley Creek Modeling Analysis July 2004
BATHTUB provides a variety of options for simulating nutrient sedimentation, including several
first- and second -order representations proposed in the literature, as well as methods developed
explicitly for BATHTUB. Also available are five candidate sub -models for chlorophyll a, which
depend variously on nitrogen, phosphorus, light and flushing rate limitations, and three candidate
models relating Secchi depth (transparency) to chlorophyll a, turbidity, and nutrient
concentrations. BATHTUB thus provides a highly flexible tool for developing a semi -empirical,
annual -average analysis of nutrient concentrations and eutrophication. The model also includes
extensive diagnostics and capabilities for error analysis.
2.4.1 Development of Model Input
Residence time is a key factor in determining model response, and depends on inflow and lake
volume. The normal pool volume of Thomas Mill Pond has changed in recent years due to
failure of the dam at the emergency spillway, followed by a partial repair that reduced the water
level to the elevation of the concrete pad that supports the temporary culverts installed for vehicle
access (Figure 8). The former mean water level is evident from the relict shoreline surrounding
the pond.
Figure 8. Dam Failure and Repair at Thomas Mill Pond (photo 6/2/04)
The volume of Thomas Mill Pond was estimated for the existing mean, water elevation (267.5
feet) and the former pool water elevation (269.75 ft). The area of the pond was delineated with
the 268 feet and the 270 feet elevation contours for the respective water levels.
(It] TETRA TECH, INC. 17

Utley Creek Modeling Analysis July 2004
Green Engineering surveyed pond elevation along seven cross sections of the Thomas Mill Pond
in May 2004. Tetra Tech interpolated the elevation measurements to GIS raster data using the
Kriging and Inverse Distance Weighted methods. The Inverse Distance Weighted method
weights elevation around a survey point based on the distance from the survey point. The
Kriging method incorporates distance from the survey point and the statistical relationship
between the survey points (ESRI, 2001). The resulting volumes from the two methods differed
by one acre-foot or less. After interpolation, the ArcGIS 8.3 cut and fill operation was used to
measure the pond volume between water level elevations and the interpolated bottom elevation.
For each water level, the average of two calculated volumes was used.
The pond volume at the existing water elevation was estimated a 0 acre -fee and the pond
volume at the former high water elevation was estimated as 39 acre-feet. Table 9 lists the
elevation of each water level and the characteristics used as BATHTUB input. Figure 9 displays
the locations of the elevation measurements and the delineation of the existing and former water
levels.
Table 9. Estimates of Thomas Mill Pond Dimensions
Water Level
Elevation
Surface Area
(acres)
Estimated Volume
(acre-feet)
Mean Depth (feet)
Existing
267.50
5.7
19.9
1.1
Former
(High)
269.75
7.3
38.6
1.6
Thomas Mill Pond, Existing Water Level
.A Thomas Mill Pond, High Water Level
Figure 9. Thomas Mill Pond Cross Sections and Pond Surface Area for Existing and High
Water Levels
Average hydraulic residence time (volume divided by inflow rate) in Thomas Mill Pond, at the
current dam configuration, is about 7 days with a wastewater discharge of 1.5 MGD. The natural
residence time without the wastewater discharge would be about 28 days. Because residence
time in Thomas Mill Pond is much less than one year, the BATHTUB analysis was applied in a
TETRA I LCH. INC.
18

Utley Creek Modeling Analysis July 2004
seasonal mode. Extemal forcing is provided by the watershed model seasonal output for April
through September, which should approximate in -lake conditions from about May through -
September.
Thomas Mill Pond is represented in the BATHTUB model as a single segment; Due to its
shallow nature, the mill pond was assumed not to stratify, and is thus represented afull mixe
No observations on water clarity are available; however, the non -algal component of turbidity is a
required input to the algal model. This was estimated using the regional regression equation
developed as part of the BATHTUB package with an assumed Secchi depth of 0.75 m at an algal
concentration of 30 µg/L, yielding an estimate of non -algal turbidity of 0.583 m'.
2.4.2 Calibration
The BATHTUB model predicts growing season average concentrations of nutrients and
chlorophyll a, and can be applied either with or without calibration. Ideally, the model is
calibrated to multi -year series of growing season average data, but these are not available for
Thomas Mill Pon However, six summer observations are available from a DWQ Special Study
undertaken i 000 illiams, 2000), including both nutrient and chlorophyll a concentrations.
These data were used to establish a qualitative confirmation of the model's accuracy.
Nonpoint source nutrient loads for the calibration were taken from the GWLF model seasonal
output (Section 2.2) after accounting for losses in transit (Section 2.3). The water quality
observations obtained in 2000 were prior to the upgrade of Holly Springs' treatment train
(addition of biological nutrient removal), and also prior to the recent failure of the dam spillway,
as evidenced by the clear relict shoreline observed around the pond. Nutrient loads from the
WWTP were represented as the average of data reported by DWQ, amounting to 64.6 lb/day total
nitrogen and. .1 lb/day total phosphorus — substantially higher than the loads that were present
after the treatment system upgrade in early 2001. The total nitrogen loads reported by DWQ are
similar to those reported in Holly Springs self monitoring. However, samples on paired dates
suggest that DWQ's determination of total phosphorus was about twice that reported by Holly
Springs. The DWQ estimates were used for calibration, as they appear to be more consistent with
observations in the mill pond. Effluent flow was set at the average of reported values for May -
August, 2000 of 0.65 MGD.
For the BATHTUB application, net sedimentation loss of both phosphorus and nitrogen was
represented by model option 2 — a second -order representation of settling that depends on influent
nutrient partitioning and has been found to work well for other Piedmont lakes. BATHTUB
calibration is achieved by adjusting factors on the sedimentation rate calculations. Walker (1987)
suggests that these coefficients vary by a factor of 2 for phosphorus (from 0.5 to 2) and a factor of
three for nitrogen in the BATHTUB development set. A reasonable fit was obtained by setting
both the nitrogen and phosphorus sedimentation calibration factors to 0.5. This reduced rate of
net sedimentation loss is plausible for Thomas Mill Pond as the system is evidently saturated with
nutrients and substantial nutrient regeneration from the sediments likely occurs, resulting in a
smaller net loss. Chlorophyll a was simulated with BATHTUB model option 1, which reflects
joint limitation by nitrogen, phosphorus, flushing, and light availability. The calibration factor
for the chlorophyll model was left at the default value of 1. Lake volume, depth, and surface area
were estimated based on the former shoreline, prior to the recent failure of the spillway.
The BATHTUB model represents typical growing season conditions. Predictions for chlorophyll
a by the model are actually predictions of the geometric mean, which, for small samples, is best
approximated by the median. As shown in Table 10, the model provides a reasonable
approximation to the observed mean of nutrient concentrations and median chlorophyll a
concentration (corrected for pheophytin). Model predictions are compared to observations in
E.)
TETRA TECH, MC.
19

Utley Creek Modeling Analysis July 2004
Figure 10 through Figure 12. It should be noted that the statistics for chlorophyll a contained in
the DWQ report (Williams, 2000) are misleading, as they omit the late August observation in
which chlorophyll a concentration was reported as "<1." This observation is included in the
results presented here, represented at one-half of the detection limit of 1 µg/L.
Table 10. BATHTUB Model for Thomas Mill Pond, 2000 Calibration Check
Total Nitrogen (mg/L)
8
Observed
Simulated
Average
Median
Total Nitrogen (mg/L)
5.4
5.5
5.1
Total Phosphorus (mg/L)
1.2
1.1
1.2
Chlorophyll a (pg/L)
37.8
22.0
23.3
7
6-
5-
4 ♦ •
3
2 --
•
0
5/1/2000 6/20/2000 8/9/2000 9/28/2000
• Observed
Model
Figure 10. Total Nitrogen Calibration, Thomas Mill Pond
3
a,2.5
E
v7 2
0
a 1.5
O
s 1 •
o 0.5 -
0
•
•
♦
•
5/1/2000 6/20/2000 8/9/2000 9/28/2000
Figure 11. Total Phosphorus Calibration, Thomas Mill Pond
TETRATECH, INC.
• Observed
Model
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Utley Creek Modeling Analysis July 2004
Chlorophyll a (pg/L)
1000
100 - •
•
10-1 •
♦
0.1 - -
5/1/2000 6/20/2000 8/9/2000 9/28/2000
Figure 12. Chlorophyll a Calibration, Thomas Mill Pond
[• Observed
— Model
The BATHTUB model also predicts the fre uency distribution of dh oo-phyll a concentrations.
This depends on the log -space coefficient of variation of model predictions, which defaults
to 0.12 in BATHTUB. The log -space CV for chlorophy 1 a observations in Thomas Mill Pond in
2000 is 0.68. The variability in actual observations is a function of both model uncertainty and
loading uncertainty; however, it is reasonable to assume that the model CV for Thomas Mill Pond
is greater than that for the BATHTUB development data set due to the short residence time,
which leads to highly variable conditions. Accordingly, the model CV for Thomas Mill Pond
was set to an intermediate value of 0.42. With these assumptions, the model for 2000 conditions
predicts tht 4 `Percent of the growing season chlorophyll a observatipns_should.be greatez_than
the criterion of 40 µg/L, which is consistent with the 2000 observations, in which one third of the
observations were greater than 40 µg/L.
For the calibration period, the model predicts that 42 percent of the phosphorus load and 74
percent of the nitrogen load passes through Thomas Mill Pond (retention of 58 percent for
phosphorus and 26 percent for nitrogen). These retention rates are in the typical range for small
ponds, and are generally consistent with the 2000 DWQ observations.
Based on the 2000 observations, the BATHTUB model appears to provide a good fit to the
typical growing -season water quality observations in Thomas Mill Pond. Accordingly, the same
model formulation was applied to the current and future discharge scenarios, which incorporate
the current reduced pond surface elevation.
2.4.3 Scenario Evaluation for Thomas Mill Pond
The model was set up and run for five different Holly Springs discharge scenarios, in addition to
the 2000 calibration conditions. The first scenario (A) represents current conditionswitha flow
limit of 1.5 MGD. There are not nutrient limits assigned at this flow, therefore the scenario is
represented with concentrations corresponding to the averages reported in Discharge Monitoring
Reports for 2002-2003, which_are 6.295�L total nitrogen and 0.5Q4.maLL total phosphorus.
These concentrations are only slightly above the limits anticipated at 2.4 MGD discharge.
Scenarios B through E examine WWTP flows of 2..44, 4 2 and 5.6 MGD at the current location,
with a mass cap on total nutrient loads equivalent to 6 mg/L total nitrogen and 0.5 mg/L total
phosphorus (monthly average) at 2.4 MGD flow. These scenarios are examined at permitted
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Utley Creek Modeling Analysis July 2004
limits, in contrast to Scenario A and the 2000 calibration, which use actual nutrient
concentrations. In fact, to achieve the mass limits the WWTP will, on average, need to discharge
loads at a rate that is somewhat below the permitted level. The Scenarios B through F results thus
represent upper bound estimates on potential impacts.
Scenarios B and C both examine the 2.4 MGD discharge; however, Scenario B includes Thomas
Mill Pond at its current, reduced pool elevation, while Scenario C examines the impact of
restoring the dam to the original pool elevation, as deduced from the remnant shoreline. EScenario F takes a different approach, with the discharge routed below Thomas Mill Pond. This
decreases nutrient loading to the pond, but also increases residence time.
Results are shown in Table 11. All the scenarios represent a large decrease in phosphorus loading
relative to 2000 conditions. As a result, predicted chlorophyll a concentrations in the pond will
also decline. Scenario C shows that restoring the dam and raising the pool in the mill pond would
result in greater retention time and a corresponding greater response. Scenarios D and E show
that increased wastewater flows (with a mass cap) will result in declining nutrient concentrations
and corresponding reductions in summer average chlorophyll a concentrations.
Scenario F (routing the discharge below the pond) provides only a small improvement relative to
Scenario B, as the reduced nutrient load is offset by the increased residence time.
i
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Utley Creek Modeling Analysis July 2004
Table 11.
Predicted Water Quality in Thomas Mill Pond in Response to Different Holly Springs Discharge Scenarios
Pond Level
r% WTP Discharge J W
Thomas Mill Pond
Scenario
Flow
(MGD)
TN
(Ib/d)
TN
(mglL)
TP
(Ib/d)
TP
(mglL)
Pond N
(mg/L)
Pond P
(mglL)
Chlorophyll -a
(pg1L)
Fraction >
40 pg1L
2000
high
0.65
64.60
11.91
28.10
5.18
5.0
1.16
23.3
34.1%
A
low
1.5
78.8
7.99
6.3
0.50
4.2
0.40
19.3
27.9%
B
low
2.4
120.1
6
9.9
0.50
4.4
0.41
19.4
28.0%
C
high
2.4
120.1
6
9.9
0.50
4.2
0.38
22.3
32.7%
D
low
4.2
120.1
3.4
9.9
0.29
2.9
0.27
18.2
26.0%
E
low
5.6
120.1
2.6
9.9
0.21
2.3
0.22
17.3
24.3%
F
below pond
1,„`.2
120.1
3.4
9.9
0.29 ,
2.0
0.33
17.4
24.4%
fri)
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Utley Creek Modeling Analysis July 2004
2.5 IMPACTS ON SHEARON HARRIS LAKE
A portion of the load discharged by Holly Springs reaches Shearon Harris Lake, and may
contribute to eutrophication there. Tetra Tech originally proposed creating a BATHTUB model
of the arm of Shearon Harris Lake that receives the Utley Creek discharge. However, site
inspection revealed that this portion of the lake is dominated by macrophyte growth (water
primrose), for which the BATHTUB model is not applicable. Therefore, the analysis focuses on
relative changes in mass loads.
2.5.1 Utley Creek Nutrient Loads to Shearon Harris Lake
Delivery of both point and nonpoint loads through Utley Creek was estimated using the
spreadsheet model. Trapping of nutrients during the growing season in Thomas Mill Pond was
assigned consistent with the BATHTUB modeling results for the corresponding scenario, with
minimal trapping during the winter. No net trapping was assigned to the greentree impoundment,
based on its small size and poor condition on visual inspection.
In addition to the scenarios evaluated for Thomas Mill Pond, one additional scenario was
evaluated for the delivery analysis. The new scenario (D2) examines the effects of removing the
Thomas Mill Pond dam (no nutrient trapping is assigned to this segment, although it may be
possible to achieve some removal via a constructed wetland here). Scenario B (the proposed
permit limits for the 2.4 MGD discharge) is taken as a reference point for comparison to other
scenarios. Loading results are summarized in Table 12. For comparison, the model predicts that
delivered loads to the lake without any point source discharge would average 16,018 lb/yr TN and
3,276 lb/yr TP due to nonpoint sources alone.
Table 12. Estimated Annual Point and Nonpoint Nutrient Load Delivery from Utley Creek
to Shearon Harris Lake for Holly Springs Discharge Scenarios
Scenario
Thomas
Mill Pond
Condition
Wastewater Discharge
Total Load Delivered
to Lake
Change from B
Flow (MGD)
TN (Ib/d)
TP (lipid)
TN (lb/yr)
TP (Ib/yr)
TN
TP
2000
high
0.65
64.60
11.91
30136
6998
-40%
-2%
A
low
1.5
78.80
7.99
36309
4711
-28%
-34%
B
low
2.4
120.10
9.90
50372
7118
0%
0%
C
high
2.4
120.10
9.90
49364
6971
-2%
-2%
D1
low
4.2
120.10
9.90
52625
7400
4%
4%
D2
no pond
4.2
120.10
9.90
53361
7533
6%
6%
E
low
5.6
120.10
9.90
53624
7510
6%
6%
F
below pond
4.2
120.10
9.90
56517
7403
12%
4%
Results are also summarized graphically in Figure 13. An increase in nutrient load delivery from
Utley Creek of about33O ercent is expected for the 2.4 MGD discharge (at permitted flow) versus
current conditions with actual concentrations at 1.5 MGD flow (Scenario A). This increase
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Utley Creek Modeling Analysis July 2004
occurs because the plant is already close to meeting the concentration limits that will be imposed
at 2.4 MGD. Moving to higher flows with a mass cap (Scenarios B through D) results in, at most,
a 6 percent increase in nutrient delivery (due to increased flow velocities and reduced trapping).
Discharge below the mill pond is estimated to result in an increase in nitrogen delivery to Shearon -
Harris Lake (Scenario F versus DI), but little change in phosphorus delivery.
60,000
50,000
40,000
30,000
20,000
10,000 -
0-
Al
1
2000 A B C D1 D2 E F
Scenario
® Total N
■ Total P
Figure 13. Annual Nutrient Load Delivered to Shearon Harris Lake via Utley Creek Under
Different Holly Springs Discharge Scenarios
2.5.2 Significance of Potential Changes in Nutrient Loads to Shearon
Harris Lake
The significance of the potential permit modification for Holly Springs to the -White Oak Cre
arm of Shearon Harris Lake was evaluated by comparison to the total nutrient load to this arm of'
the lake, defined as the area north of the New Hill Road bridge and causeway (SR 1127). To
make this comparison it is first necessary to estimate land use in the portions of this drainage area
outside of Utley Creek, an area of 11,791 acres. An initial estimate can be made from the 1992
MRLC land use data. However, the upper portion of the White Oak Creek drainage lies in a
rapidly developing area along US 1 and NC 55 south of Apex. Therefore, it is important to
correct the MRLC land use for recent development. In addition, the MRLC tabulation is known
to underestimate the amount of rural residential land use. Corrections to the land use were
accomplished through use of the Wake Co. tax parcel data, which data indicate a substantial
increase in residential lots in the watershed since 1992.
The current tax parcel data shows 684 acres in residential parcels within the White Oak Creek
drainage; however, a portion of this is in large lot parcels. These were capped at a nominal size -
of 3 acres, with the balance assumed to remain in the original MRLC land use classes. The
remainder of the residential parcels were distributed by size and assigned proportionally to the
MRLC forest and agricultural uses. This yields an approximate tabulation of the current GWLF
land use classifications shown in Table 13.
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Utley Creek Modeling Analysis
July 2004
Table 13. Land Use Distribution in Acres for Watershed of White Oak Creek Arm of
Shearon Harris Lake Excluding Utley Creek
GWLF Land Use Class
Acres
Residential — Very Low Density
324.0
Residential — Low Density
56.3
Residential — Medium Low Density
48.5
Residential — Medium High Density
68.2
Residential — High Density
94.2
Residential — Very Low Density
78.6
Office/Light Industrial
40.3
Commercial/Heavy Industrial
40.3
Urban Greenspace
3.1
Pasture
170.6
Row Crop
466.9
Forest
9423.9
Wetlands
478.6
Barren
219.8
Water
278.2
Total
11,791.4
Annual nutrient loads were estimated by applying the per -acre loading rates for each land use
class as determined in the Utley Creek model, together with an approximate transport pass
through rate of 64 percent for total nitrogen and 72 percent for total phosphonis, consistent with
the delivery rate through Utley Creek to the lake from a point near the WWTP (exclusive of pond
trapping).
Scenario B (with Holly Springs the proposed 2.4 MGD permit limits) provides a baseline for
comparison. At the maximum discharge considered of 5.6 MGD (Scenario E), the increase in
loading relative to Scenario B (see Table 12) is 3,252 lb/yr TN and 392 lb/yr TP. As shown in
Table 14, the maximum change in nutrient loading relative to the current proposed permit from
the scenarios under consideration is less than 4 percent.
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Utley Creek Modeling Analysis
July 2004
Table 14. Analysis of Total Annual Nutrient Loading to White Oak Creek Arm of Shearon
Harris Lake
•
- • Total=Nttr Zlblyr - , -
Total=Phosphorus lb/ r)
Utley Creek PS Discharge
(Scenario B)
43,836
3,616
Utley Creek Total Delivered Load
50,372
7,118
Balance of Watershed NPS Load
39,022
8,063
Total Baseline Load
89,394
15,181
Maximum Increase (Scenario E)
3,252
392
Percentage Increase
3.6 %
2.6 %
Investigations by NCDWQ in 2000 did not reveal problem concentrations of planktonic algae in
the White Oak Creek arm of Harris Lake (concentrations ranging from less than 1 to 31 µg/L).
Presumably, planktonic algal growth is suppressed by nutrient uptake and shading from the dense
macrophyte beds in the shallow portions of this arm of Harris Lake. A study in Lake Marion, SC
(Remillard and Welch, 1993) suggests that macrophyte coverage is most strongly correlated to
nitrogen concentrations and not sensitive to water column phosphorus concentrations —
presumably because rooted macrophytes can obtain sufficient phosphorus from lake sediments.
Nitrogen load is thus likely to be of greatest concern for promotion of nuisance macrophyte
growth in Hams Lake. Under Scenario B (the 2.4 MGD permit), the Holly Springs WWTP is
estimated to contribute about 18 percent of the nitrogen entering the White Oak Creek arm of
Harris Lake. This could increase to 21 percent of the nitrogen load under Scenario E (5.5 MGD
discharge). Because the increases in loading associated with augmented discharge are small, and
the contribution of the WWTP to the total nitrogen load is less than one quarter of the total
nitrogen load, &i , re capacity expansions for the Utl�agreek discharge are unlikely to result in a
ligniftRgnt worsening of macrophyte conditions in Harris Lake. Further increasing the delivere
load by moving the discharge below T omas ill Pond would, however, appear to be
undesirable.
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Utley Creek Modeling Analysis July 2004
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Utley Creek Modeling Analysis July 2004
3 BOD/DO Analysis
41.01 M6t
BOD/DO modeling analyses were performe s for Alternative 3 onl .e., relocation of discharge
to below Thomas Mill Pond) per instruction from r ►► • . e following sections describe model
setup and application for this alternative.
3.1 REACH DELINEATION
Reach delineation was performed based on slope considerations and field reconnaissance. Green
Engineering surveyed several cross sections of Thomas Mill Pond in May 2004. That survey
determined that the lake elevation at the time was 267.5 ft above mean sea level. Discharge from
the pond is currently occurring in two locations: leakage through the older drain pipe, and
through corrugated steel pipes breeching the spillway at the northwest corner of the pond. These
pipes are situated above a concrete slab and bedrock that drops off several feet over a very short
distance. The topographic map shows the 260 ft elevation contour beginning shortly below the
pond outfall. It was assumed that the relocated pipe would discharge around the 260 ft contour
line. Thus, reach delineation was needed for the segment of Utley Creek from the 260 ft contour
to the 220 ft contour where the creek joins with an arm of Shearon Hams Lake — a total distance
of 1.67 miles.
Previous modeling by DWQ divided this segment into two reaches, one from the 270 foot contour
to the 250 contour, and the other from the 250 to the 220 contour based on slope change.
However, this delineation ignored the greentree reservoir that occurs about eight tenths of a mile
downstream of Thomas Mill Pond. Reconnaissance showed that even though the reservoir is not
impounded during the summer low flow months, the weir structure backs up the channel for
about one tenth of a mile resulting in considerably lower stream velocity through this section
(Figure 14).
Figure 14. Greentree Reservoir on Lower Utley Creek (6/2/04; flashboards removed)
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Utley Creek Modeling Analysis July 2004
The overall segment to be modeled was therefore broken into four reaches with the following
length and slope characteristics (schematic displayed in Figure 15):
Reach 1:
Description: From the 260 contour to the 250 contour
Length: 0.11 mile
Slope: 10ft/0.1 lmi = 91 fpm
Reach 2:
Description: From the 250 contour to the inlet to the greentree reservoir
Length: 0.7 mile
Slope: 0.56 mi @ 17.9 fpm + 0.14 mi @ 20.8 fpm = 18.5 fpm
Reach 3:
Description: Length of stream backed up behind the greentree reservoir weir
Length: 0.1 mile (note, at a 20 fpm grade, the 2 ft dam height behind the weir would
back up water for 0.1 mi)
Slope: 20 fpm
Reach 4:
Description: From the greentree reservoir outfall to the 220 ft contour
Length: 0.76 miles
Slope: 0.34 mi @ 20.8 fpm + 0.42 mi @ 23.8 fpm = 22.5 fpm
Legend
Streams
Water Bodies
QUtley Creek Watershed
Greentree
Reservoir
R4
SCALE
ilea
0 o.i 0.2 0.4
N
A
Thomas Mill
Pond
R1
Figure 15. Model Reach Schematic
3.2 HYDRAULICS
Model channel hydraulics are determined by average width, depth, slope and flow. Key
assumptions for hydraulics are noted below.
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Utley Creek Modeling Analysis July 2004
3.2.1 Flow Assumptions
Flow in the model segment comes from three sources: upstream boundary flow, WWTP
discharge, and incremental base flow.
Upstream Boundary Flow:
USGS provided flow estimates at the existing WWTP outfall (station no. 02.1021.7945)
reflecting a drainage area of 0.73 square miles:
S7Q10 = 0.11 cfs
W7Q 10 = 0.25 cfs
Qavg = 0.82 cfs
The drainage area (measured in ArcView) at the Thomas Mill Pond outfall is
1.96 square miles. Using the estimates from the upstream station, flows at this location
can be extrapolated as follows:
S7Q 10/DA = 0.11/0.73 = 0.1507 cfs/mi2
S7Q10 at Thomas Mill Pond outfall = 0.1507 cfs/mil * 1.96 mi2 = 0.30 cfs
W7Q 10/DA = 0.25/0.73 = 0.3425 cfs/mi2
W7Q 10 at Thomas Mill Pond outfall = 0.3425 cfs/mi2 * 1.96 mi2 = 0.67 cfs
Qavg/DA = 0.82/0.73 = 1.1233 cfs/mi2
Qavg at Thomas Mill Pond outfall = 1.1233 cfs/mi2 * 1.96 mi2 = 2.20 cfs
Incremental Baseflow:
The drainage area at the mouth of Utley Creek was determined to be 3.65 square miles.
Flow at the mouth can be estimated as:
S7Q10 = 0.1507 cfs/mi2 * 3.65 mi2 = 0.55 cfs
The total distance from the Mill Pond to the mouth is 1.67 miles. The incremental
baseflow rate can be calculated as the change in flow divided by segment length.
Therefore:
Incremental S7Q10 baseflow = (0.55 - 0.30 cfs)/1.67 mi = 0.15 cfs/mi
Incremental W7Q10 baseflow = (1.25 - 0.67 cfs)/1.67 mi = 0.35 cfs/mi
Incremental Qavg baseflow = (4.1 - 2.2 cfs)/1.67 mi = 1.14 cfs/mi
Effluent Flow:
WWTP flow = 4.2 MGD = 6.5 cfs
3.2.2 Velocity Estimates
Velocity for Reaches 1, 2, and 4 was determined using the DWQ regression equation modified
from Tsivoglou (see Section B.3.a.1 from the DWQ Wasteload Allocation Standard Operating
Procedures Manual, 1990):
Velocity (U) = [0.124 Qact°'75 Slope°29]/Qavg°35
Ell
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Utley Creek Modeling Analysis July 2004
Because of the weir structure impounding water at the greentree reservoir, however, a different
method was used for Reach 3 adapted from Finnemore and Fransini (2002) as outlined in the
QUAL2K manual.
Reach 1:
Qact = S7Q10 + wasteflow + 0.5 baseflow increase
= 0.3 cfs + 6.5 cfs + (0.5*0.15cfs/mi*0.11mi)
= 6.81 cfs
Qavg = Qavg inflow + 0.5 baseflow increase
= 2.2 + (0.5*1.14*0.11)
2.26 cfs
Slope = 91 fpm
U = [0.124 (6.81)o35 (91)0.291/(2.26)0.35
= 1.455 fps
Reach 2:
Qact = 0.3165 + 6.5 + (0.5*0.15*0.7)
= 6.87 cfs
Qavg = 2.325 + (0.5* 1.14*0.7)
= 2.724 cfs
Slope = 18.5 fpm
U = [0.124 (6.87) 0.75 (18.5)0.21/(2.724)0.35
=0.86fps
As a rough check on the likely accuracy of these values for the first two reaches, the method of
approximating velocity as flow divided by cross -sectional area was applied. Stream width and
depth varied, but were estimated as roughly averaging 15 ft wide and 0.5 ft deep.
Qact/Ac = 6.85/7.5 = 0.913 fps
Of course actual velocity will be influenced by slope. In Reach 1, there was a steep slope such
that the velocity increased. In Reach 2, with a 5 percent grade, the DWQ equation and the
approximation method are nearly equivalent. Thus, the estimates appear reasonable.
Reach 3:
From Finnemore and and Franzini (2002),
Q; = 1.83B,Hh3n in units of m3/sec
where Q; is the outflow of the segment above the weir, B; is the width of the weir
flow, and Hh is the height of the flow over the weir.
Assume that the inflow to the segment equals outflow under a low flow steady-state condition.
Inflow to Reach 3 is equal to 6.92 cfs (0.196 m3/sec) accounting for S7Q 10, wasteflow, and
incremental baseflow.
If we assume B; is 2 m, then we can solve for Hh:
ill
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Utley Creek Modeling Analysis July 2004
Hh = [0.196/(1.83 *2)f 2'3
= 0.14 m
Total height (H,) = the height of the water behind the weir (H,y) + Hh
= 0.61 m (assuming a 2 ft depth behind the weir) + 0.14 m
= 0.75 m
Calculate velocity (U) as Q,/A, where A, is the cross -sectional area of the reach.
A, = reach width (w) * H;
=10m*0.75m=7.5m2
U = (0.196 m3/sec)/7.5 m2
= 0.026 m/sec = 0.09 fps
The reach width is uncertain as based on pictures from the reconnaissance. For sensitivity, check
if width is 7 m rather than 10 m.
A,=7m*0.75m=5.18m2
U = (0.196 m3/sec)/5.18 m2
= 0.038 m/sec = 0.12 fps
Based on the above analysis, velocity in Reach 3 is assumed to be 0.1 fps.
Reach 4:
Qact = 0.4365 + 6.5 + (0.5*0.15*0.76)
= 6.99 cfs
Qavg = 3.24 + (0.5* 1.14*0.76)
= 3.67 cfs
Slope = 22.5 fpm
U = [0.124 (6.99) 0.75 (22.5)0.29]/(3.67)0 35
= 0.83 fps
3.3 BOUNDARY CONDITIONS
The physical and chemical characteristics assumed in the headwater flow and incremental
baseflow are as follows:
Temperature = 26° C (obtained from DWQ SOP Manual and previous modeling)
BODE, = 2 mg/L CBOD„ + 1 mg/L NBOD„ (from DWQ SOP Manual)
= 3 mg/L
DO Deficit = DO saturation — DO concentration
= 8.1 mg/L — 6.9 mg/L (from previous DWQ analyses)
= 1.2 mg/L
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Utley Creek Modeling Analysis July 2004
3.4 EFFLUENT CONDITIONS
The physical and chemical characteristics assumed for the wastewater discharge were based on
previous permit decisions:
Effluent BODu:
BODu = CBODu + NBODu
CBODu = 5 mg/L (assumed maximum limit) * 2 (assumed BODu/BOD5 ratio)
= 10 mg/L
NBODu = 1 mg/L NH3-N * 4.57 (stochiometric ratio)
= 4.6 mg/L
BODu = 14.6 mg/L
Effluent DO Deficit:
Minimum allowed concentration in current permit = 6.0 mg/L
DO Deficit = DO saturation — DO concentration
=8.1 mglL-6.omg/L(assume26°C)
= 2.1 mg/L
3.5 REACTION RATE ASSUMPTIONS
3.5.1 BOD Decay
Since the simplified Streeter -Phelps model lumps CBODu and NBODu, a conservative decay rate
will be used that represents both reactions adequately. The DWQ SOP Manual indicates that a
variation of the Bosko equation is used for CBOD decay, and the default NBOD decay is 0.3/day
with slope < 20 fpm and 0.5/day with slope > 20 fpm. The Bosko equation is a function of
volume and depth, as well as a coefficient of bed activity. Previous model applications by DWQ
generated values in Utley Creek between 0.43 and 1/day ® 20° C. The EPA rates manual (EPA,
1985) nomograph on page 147 shows decay rates around 1/day @ 20° C for streams < 1 ft in
depth. However, EPA acknowledges that these are based on older studies before improvements
in waste treatment were made that will definitely affect instream kinetics. The Holly Springs
discharge will reflect tertiary treated effluent which often displays decay rates of
< 0.1 /day. Thus, the actual rate will likely be between 0.1 and 1.0/day at 20° C, which translates
to 0.132 to 1.32 @ 26° C. Initial runs will reflect the most conservative end of this range
(1.32/day) to see if significant impacts would occur under this worst case scenario.
3.5.2 Reaeration
The DWQ modified versions of the Tsivoglou equations (DWQ SOP Manual) were used as
starting points for Reaches 1, 2, and 4. The O'Conner-Dobbins equation for deeper, slower
streams was applied to Reach 3 where the greentree reservoir weir creates a small impoundment.
(11)
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Utley Creek Modeling Analysis July 2004
Reach 1:
Ka = 1.8*slope*velocity
= 1.8*91 * 1.455
= 238/day (rejected)
This rate is considered too high. Using the EPA rates manual (1985) nomograph on
p 117, at a velocity of 1.455 and depth averaging < 0.5 ft, reaeration can be estimated at
approximately 70/day @ 20° C (79.8/day @ 26° C using a temperature correction factor of 1.022
(Critical Temperature - 20° C)).
Ka = 79.8/day (accepted)
Reach 2:
Ka = 1.8*18.5*0.86
= 28.6/day @ 20° C (32.6/day @ 26° C)
Reach 3:
Ka = (12.9*U°.5)/depthl.5
= (12.9*0.1os)/1 is
= 4.1/day @ 20° C (4.7/day @ 26° C)
Reach 4:
Ka = 1.8*22.5*0.83
= 33.6/day @ 20° C (38.3 @ 26° C)
3.6 BOD/DO MODEL RESULTS
The Streeter -Phelps model was initially run using the input summarized above. Model
predictions are summarized below in Table 15.
Parameter (units)
R1
R2
R3
R4
DO Deficit/Conc. — at start of reach (mg/L)
2.1/6.0
1.5/6.6
0.7/7.4
1.4/6.7
DO Deficit/Conc. — exiting reach (mg/L)
1.5/6.6
0.7/7.4
1.4/6.7
0.5/7.6
Minimum DO in reach (mg/L)
6.0
6.6
6.7
6.7
BOD„ — at start of reach (mg/L)
14.1
13.8
12.9
11.8
BODU — exiting reach (mg/L)
14.0
12.9
11.9
10.9
Table 15. Streeter -Phelps Predictions for Initial Model Settings
The results show that lowest DO concentrations under the base run modeling assumptions are at
the outfall mixpoint due to the lower DO concentration assumed in the discharge, and a decrease
in Reach 3 from 7.4 to 6.7 mg/L as the stream flows through the impounded area behind the
greentree reservoir weir.
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Utley Creek Modeling Analysis
July 2004
An informal sensitivity analysis was performed to see how the model predictions would respond.
The first change was reducing reacration rates by 50 percent. Results are displayed in Table 16.
Parameter (units)
R1
R2
R3
R4
DO Deficit/Conc. - at start of reach (mg/L)
2.1/6.0
1.7/6.4
1.4/6.7
2.1/6.0
DO Deficit/Conc. - exiting reach (mg/L)
1.7/6.4
1.4/6.7
2.1/6.0
1.2/6.9
Minimum DO in reach (mg/L)
6.0
6.4
6.0
6.0
BOD„ - at start of reach (mg/L)
14.1
13.8
12.9
11.8
BOD„ - exiting reach (mg/L)
14.0
12.9
11.9
10.9
Table 16. Streeter -Phelps Predictions with 50 Percent Decrease in Reaeration
DO concentrations are slightly lower, with the minimum in Reach 3 dropping to 6.0 mg/L, the
same as at the mixpoint of the discharge. The next sensitivity run decreased both reaeration and
velocity rates by 50 percent (Table 17).
Parameter (units)
RI
R2
R3
R4
DO Deficit/Conc. - at start of reach (mg/L)
2.1/6.0
1.5/6.6
1.1/7.0
2.4/5.7
DO Deficit/Conc. - exiting reach (mg/L)
1.5/6.6
1.1/7.0
2.4/5.7
0.8/7.3
Minimum DO in reach (mg/L)
6.0
6.6
5.7
5.7
BODu - at start of reach (mg/L)
14.1
13.7
12.0
10.1
BODu - exiting reach (mg/L)
13.9
12.0
10.2
8.7
Table 17. Streeter -Phelps Predictions with 50 Percent Decrease in Reaeration and
Velocity
Under these more conservative assumptions, the DO sag occurs in the Reach 3 impounded area
with the minimum dropping to 5.7 mg/L. The last sensitivity run reduced reacration and velocity
rates by 50 percent, and increased the CBOD/BOD5 ratio for the effluent to a factor of 3. The
results are displayed in Table 18.
TETRA TECH. INC.
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Utley Creek Modeling Analysis
July 2004
a
' :: = Paramete�ra(urtifs);
r
DO Deficit/Conc. — at start of reach (mg/L)
2.1/6.0
1.5/6.6
1.4/6.7
3.1/5.0
DO Deficit/Conc. — exiting reach (mg/L)
1.5/6.6
1.4/6.7
3.1/5.0
1.1/7.0
Minimum DO in reach (mg/L)
6.0
6.6
5.0
5.0
BODu — at start of reach (mg/L)
18.9
18.4
16.1
13.5
BODu — exiting reach (mg/L)
18.6
16.1
13.7
11.7
Table 18. Streeter -Phelps Predictions with 50 Percent Decrease in Reaeration and
Velocity and Increasing the Effluent BOD„/BOD5 Ratio to 3
Under this most stringent of scenarios, the DO minimum drops to the NC water quality standard
threshold of 5.0 mg/L. Thus, even with BOD decay rates at twice the expected level, reaeration
rates at half expected levels, velocity at half expected levels, and the effluent CBOD/BOD5 ratio
higher than expected, relocation and discharge of 4.2 MGD below the Thomas Mill Pond is not
expected to violate water quality standards under critical low flow conditions with limits of
5 mg/L BOD5, 1 mg/L NH3N, and 6 mg/L minimum DO.
TETRA TECH. INC.
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Utley Creek Modeling Analysis July 2004
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Utley Creek Modeling Analysis July 2004
4 Discussion and Conclusions
The eutrophication modeling analyses demonstrate that conditions in Thomas Mill Pond after
upgrade and expansion of the Holly Springs WWTP are expected to be better than conditions
observed by the Division of Water Quality in their 2000 and 2003 field studies. Under the
currently permitted 2.4 MGD wasteflow, 6.0 mg/L TN limit and 0.5 mg/L TP limit,
concentrations entering the pond are predicted to be significantly less than under previous
conditions (predicted TP concentrations are 35 percent of the 2000 conditions). Summer.
chlorophyll a concentrations are expected to average around 19 µg/L, with peaks exceeding
40 µg/L about 28 percent of the time during the growing season. This is not unexpected for a
small pond of this size in the Piedmont region.
Increasing wasteflows in Utley Creek beyond 2.4 MGD while holding permitted mass loads for
TP and TN constant results in slight decreases in nutrient and chlorophyll a concentrations in
Thomas Mill Pond, though notsignificarThis is to be expected as decreased wastewater TP
and TN concentrations will decrease instream concentrations, and increased wastewater flows
will decrease residence time in the pond.
The tradeoff under higher wasteflows is that more nutrients are delivered down to the Harris Lake
cove, although the increases are not significant. Under the worst case scenario, increases in
nutrient loads were less than four percent of the total nutrient load to the cove assuming current
NPS loads. Under future NPS loads, the relative impact would be even smaller.
The lake response to the nutrient loads is not subject to modeling because of the dominating
presence of Water Primrose in the cove. The occurrence of this nuisance weed is not expected to
change with or without the wastewater discharge in Utley Creek. The NPS loading is sufficient
to support its continued presence. Management guides generally indicate that it is not possible to
eradicate Water Primrose when it is well -established. It is limited by the depth of water,
generally not growing in water depths greater than four feet. A representative of Progress
Energy's Environmental Services Division indicated that the Water Primrose was not impairing
their use of the lake and that they had no management plan in place, nor did he think that they
would develop one in the future (personal communication with Tom Thompson, June 2004).
Given the above information, relocating the discharge below Thomas Mill Pond does not appear
to be a practical or helpful situation. Decreasing flow through the pond increases the residence
time and provides no significant benefit. Although no significant impact on dissolved oxygen is
predicted in the downstream waters if the discharge is relocated, more nutrients would be
delivered to the Harris Lake cove due to the shorter distance and travel time.
hi
TETRATECN,INC.
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