NC0028916_Speculative Limits_20040409

April 9, 2004
Mr. Gray Walls, P.E.
Town Engineer/ Public Services Director
Town of Troy
444 North Main Street
Troy, North Carolina 27371-2799
Subject: Speculative Limits
Regional System on Little River
Ref. NPDES Permit NC0028916
Towns of Troy,Star,rBiscoe
Montgomery County
Dear Mr. Walls:
Michael F. Easley, Govemor
State of North Carolina
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Alan W. Klimek, P.E., Director
Division of Water Quality
1i N F
APR3Q .
Prf
This letter is in response to a request for speculative effluent limits for the potential
expansion and relocation of the Troy wastewater treatment plant. It is the Division of Water
Quality's understanding that there is a potential for a regional -type system to be built and to
discharge at the proposed location along Highway 24/27. The Division encourages the Towns of
Troy, Biscoe, and Star to work diligently towards a regional system. The speculative limits
provided below are for a discharge to the Little River at a flow of 2 MGD (with the understanding
that the existing discharge on Denson's Creek would be removed). You may also wish to refer to
Table 1 attached to this letter. In addition, an addendum is attached to this letter which presents
the various discharge scenarios requested by the Towns of Troy, Star, and Biscoe.
These speculative limits are based on our understanding of the proposal and of present
environmental conditions. The Division of Water Quality (DWQ) cannot guarantee that it will
issue the Town an NPDES permit to expand its discharge of treated wastewater into waters of the
State. Nor can we guarantee that the effluent limitations and other requirements included in any
permit will be exactly as presented here. Final decisions on these matters will be made only after
the Division evaluates a formal permit application for the discharge and notices the proposal for
public comment.
Environmental Assessments of New Projects and Expansions
Any entity proposing to construct new or expanded wastewater treatment facilities using
public funds or public (state) lands must first prepare an environmental assessment (EA) when
wastewater expansions equal or exceed 0.5 MGD. Please contact the Division's State
Environmental Policy Act (SEPA) coordinator, currently Alex Marks, at (9191733 - 5083, ext. 555
for further information on EA requirements. DWQ will not accept a permit application for a
project requiring an environmental assessment until the Division has approved the EA and sent a
Finding of No Significant Impact (FONSI) to the state Clearinghouse for review and comment.
Engineering Alternatives Analysis (EAA)
In accordance with the North Carolina General Statutes, the most practicable wastewater
treatment and disposal alternative with the least adverse impact on the environment is required to
be implemented with any expansion. Therefore, as a component of all NPDES permit applications
for new or expanding flow, a detailed engineering alternatives analysis (EAA) must be prepared.
The EAA must justify requested flows and provide an analysis of potential wastewater treatment
alternatives. Alternatives to a surface water discharge, such as a spray/drip irrigation,
wastewater reuse, or inflow/infiltration reduction, are considered to be environmentally
preferable. A copy of the EAA requirements is attached to this letter. Permit applications for new
or expanding flow will be returned as incomplete if all EAA requirements are not adequately
addressed. You may also wish to refer to the NPDES Unit website for more information regarding
requests for expansion, http://h2o.enr.state.nc.us/NPDES/.
North.Carolina Division of Water Quality
1617 Mail Service Center
Raleigh. North Carolina 27699-1617
[phone]
FAX [phone]
On the Internet at http://h2o.enr.state.nc.us/

Mr. Walls
Page 2
Speculative Effluent Limits
Based on the available information, tentative limits for the proposed discharge of 2 MGD flow to
the Little River are outlined below. Also refer to Table 1 for an outline of the speculative limits.
Stream Flow. Streamflow yields were taken from a nearby site in the area. The drainage area at
this site (Highway 24/27 crossing on Little River) is approximately 148 square miles. This yields
a 7Q10s flow of 1.48 cubic feet per second (cfs) and a 7Q 10w flow of 11.2 cfs. The average flow for
this site is 148 cfs. Little River is a Class C stream in this portion of the watershed (Stream Index
No. 13-25-(19)).
Flow Limits. The flow would be limited to 2 MGD at your request. This limit would be applied as
a monthly average. Y.
BOD5 and NH3-N. The proposed limits for a 2 MGD discharge into the Little. River would be 5 mg/1
(BOD5) and 1.2 mg/1 (NH3-N) during the summer months, 30 mg/1 (BOD5) and 7.5 mg/1 (NH3-N)
during the winter months. These limits are based on an EPA -approved water quality model.
The 7Q10s flow is fairly low for this size drainage area (but is typical for this hydrologic area), so
the summer limits are fairly stringent. Because the 7Q 10w flow is relatively higher, the winter
limits are less stringent.
Dissolved Oxygen. A minimum daily average dissolved oxygen level of 6 mg/l must be maintained
in the effluent.
TSS. The limits for total suspended solids are standard for secondary treatment of municipal
wastewater and would remain the same as in the existing permit (30 mg/1 monthly average).
Fecal Coliform, pH. The limits for fecal coliform bacteria and pH are derived to protect water
quality in the receiving stream and will likely remain the same as in the previous permit.
Chlorine. A total residual chlorine limit of 25 ug/1 (daily maximum) would be implemented in this
permit.
Chronic Toxicity Testing: The chronic toxicity limit for the 2.0 MGD flow would be Pass/Fail at
68%. This is based on the 7Q10s streamflow of 1.48 cfs.
Toxicant Parameters: Estimation of toxicant parameters will not be given with this speculative
letter, but will be submitted as appropriate with the draft NPDES permit.
As stated previously, these speculative limits are appropriate for a discharge of 2 MGD on
Little River at Highway 24/27; these limits are appropriate only if the Town's discharge on
Denson s Creek is eliminated. As discussed with Ms. Susan Wilson of the NPDES Unit, there is
some possibility of lowering the NH3-N limit and slightly raising the BOD5 limit if Troy wishes to
pursue that option. If you would like to discuss this possibility in further detail or if you have any
additional questions about these limits, feel free to contact Ms. Wilson at [phone],
extension 510.
cc:
Sincerely,
David A. Goodrich(/ Supervisor
NPDES Unit
Water Quality Section
Fayetteville Regional Office/ WQS
Central Files
NPDES Unit Files
Cooper Burton, P.E. WIC Dickson & Co., Inc.
616 Colonnade Drive
Charlotte, NC 28205

Mr. Walls
Page 3
Table 1. Speculative Limits for a Flow of 2.0 MGD
(Discharge point at Hwy. 24/27 on the Little River)
Parameter
Monthly Average
WeeklyAverage
Daily Maximum
Flow
2.0 MGD
BOD5 (summer)
5.0 mg/1
7.5 mg/1
BOD5 (winter)
30 mg/1
45 mg/1
NH3-N (summer) _
1.2 mg/1
3.6 mg/1
NH3-N (winter)
7.5 mg/1
22.5 mg/1
TSS
30 mg/1
45 mg/1
Fecal coliform
200 #/100 m1
400 #/100 ml
Total residual chlorine
25 ug/1
Dissolved Oxygen
6.0 mg/1
(minimum)
Chronic Toxicity
Quarterly P/F at 68%

Addendum
Troy, Biscoe, Star Issues & Potential Regional System Scenarios
Scenarios
Site Description
Proposed
Flow (MGD)
BOD5 mg/1
(sum/win)
NH3-N mg/1
(sum/win)
D.O.
mg/1
Instream waste
concentration
(IWC %)
1
Regional system at
Troy's existing site,
Denson's Creek
(Troy/ Biscoe/ Star)
2.0
8.5 / 30
1.1 / 3.0
6.0
90
2
Regional system for
Biscoe/ Star
At Hwy. 24/27-
(w/Troy as is)
1.0 (Biscoe/
Star)
5.0 / 30
1.0 / 13
6.0
51
3
Regional system
2 MGD plant at
Hwy. 24/27
(no Troy discharge
upstream)
2.0
5.0 / 30
1.2 / 7.5
6.0
68
Scenario 1 -
This scenario assumes all permitted flow at the existing Troy discharge site on Denson's Creek.
Scenario 2 -
This scenario assumes a Biscoe/Star regional system at a flow of 1.0 MGD to Little River at Hwy. 24/27. This
scenario also assumes Troy continues its discharge of 1.2 MGD to Denson's Creek.
Scenario 3 -
This scenario assumes a regional system of 2.0 MGD with discharge to Little River at Hwy. 24/27. This
scenario also assumes that Troy will relocate its discharge to this point.
Stream flows:
Denson's Creek, Class C
(Town of Troy's existing outfall site on Denson's Creek, above confluence with Spencer Branch)
DA = 32 mi2
7Q10s = 0.35 cfs
7Q 1 Ow = 2.42 cfs
Qavg = 32
Little River (at Hwy. 24/27), Class C
DA = 148 mi2
7Q 10s = 1.48 cfs
7Q 10w = 11.2 cfs
Q avg = 148 cfs
On Denson's Creek - although the stream flows are lower, the slopes are much higher than Little River, which
affects the water quality model (likely why the limits are just as low on Little River as on Denson's Creek).

DICKS
community infrastructure consultants
January 8, 2004
Mr. Dave Goodrich, NPDES Unit Supervisor
North Carolina Department of Environment and Natural Resources
Division of Water Quality
NPDES Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
Re: Speculative Limits
To Serve the Towns of Biscoe, Star and Troy
WKD #30043.00.CL
Dear Mr. Goodrich:
The Towns of Biscoe, Star and Troy are exploring some regional wastewater treatment
alternatives and would like to request speculative discharge limits for two potential
locations. One option would be to combine the flows from Star and Biscoe and treat and
discharge one (1) MGD to the Little River near the Smitherman Dam. The other option
would be to combine the flows from all three towns (2 MGD) and discharge near the
confluence of Spencer Branch and Densons Creek as shown on the map. Enclosed is a
copy of a USGS map showing the two potential discharge sites and their flows. I have also
included an email from the U. S. Geological Survey showing the low -flow characteristics of
the streams in question for your reference.
Please contact me if you have any questions.
Sincerely,
W. K. Dickson & Co., Inc.
er J. Burton, PE
cc: °lvtr__ -autl R�, awls - DWQ
Enclosures
616 Colonnade Drive
Charlotte, NC 28205
Tel. [phone]
Fax [phone]
www.wkdickson.com
L/Projects/bi sco/30043/Good rich 10804
North Carolina • South Carolina • Georgia • Florida

Nool
•
Cooper Burton
From: John C Weaver [[e-mail]]
Sent: Tuesday, December 23, 2003 12:40 PM
To: Cooper Burton
Cc: [e-mail]
Subject: Low -flow characteristics for streams near Troy, Montgomery County...
Mr. Burton,
In response to your inquiry about the low -flow characteristics for some locations near
Troy in Montgomery County, the following information is provided.
It appears the 7Q10 discharge yield (expressed as flow per square mile of drainage area)
for streams in this area is about 0.01 cfs per sqmi. This is based on records of
discharge that have been collected at a couple of locations near Troy.
Rough estimates of the drainage areas for your sites of interest are as
follows:
Site 1 - Cedar Creek just dnstrm of confluence with White Oak Creek - approx 6.5 sqmi Site
2 - Little River at NC 24/27 - 148 sqmi Site 3 - Cedar Creek at mouth - 11.4 sqmi Site 4 -
Densons Creek at confluence with Spencer Branch - approx 32 to 33 sqmi.
Thus the estimated 7Q10 discharges for each of these locations would be the product of the
above yield (0.01 cfs per sqmi) and the respective drainage areas (sqmi).
In July 1999, the low -flow characteristics for a site on Densons Creek upstream of Spencer
Branch were the focus of a letter sent to the NC Division of Water Quality. Included in
the letter is some discussion about the effects of underlying geology (Carolina Slate Belt
region), soils characteristics, and high degree of topographic relief observed in that
area. Areas underlain by the Carolina Slate Belt geologic belt are characterized by some
of the lowest water -yielding rocks in the State. Thus, combined with the "thin" soils
known to occur in the area with relatively high land -surface slopes, the low -flow
characteristics for streams in this region are regarded as having little to no potential
for sustained base flows.
Hope this information is helpful.
Thank you.
Curtis Weaver
***********************************************************************
J. Curtis Weaver, Hydrologist, PE
U.S. Geological Survey
3916 Sunset Ridge Road
Raleigh, NC 27607
Telephone: [phone] // Fax: [phone]
E-mail address -- [e-mail]
Internet address -- http://nc.water.usgs.gov/
***********************************************************************
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