NC0026441_Fact Sheet_20181017

DRAFT
DEQ/DWR
FACT SHEET FOR NPDES PERMIT MODIFICATION
NPDES No. NCO026441
FACILITY INFORMATION
Permittee:
Siler City
Permittee Address:
P.O. Box 769, Siler City, NC 27344-0769
Facility Name:
Siler City WWTP
Facility Address:
370 Waste Treatment Pond Road
Facility County:
Chatham
Permitted Flow:
4.0 MGD
Facility Status:
Existing
Waste Type:
Municipal (domestic and industrial)
WWTP Grade:
WW-IV
Facility Type:
Municipal, with Full Pretreatment/ LTMP
SIC Code(s):
4952
WATERBODY INFORMATION
ADDITIONAL INFORMATION
Waterbody Name:
Loves Creek
River Basin:
Cape Fear
Classification:
C
Regional Office:
Raleigh
Subbasin:
03-06-02
USGS Topo Quad:
E21NW
HUC8/12:
03030003/0503
Permit Action:
Reopening/ Modification
Drainage Area (miz):
7.9
Permit Writer:
Mike Templeton
Assessment Unit:
17-43-10c
Date:
October 17, 2018 — Draft Permit
7Q10 S/W (cfs):
0.25 / 0.4
•
Average Flow (cfs):
8.7
Listed:
Biological integrity (benthos)
Chl-a (Rocky River, downstream)
IWC (%):
96.1%
I. PERMIT ACTION
The Division is reopening and proposes to modify permit NCO026441 for the Siler City Wastewater
Treatment Plant (WWTP) to incorporate effluent limits for total nitrogen (TN) and associated control
requirements and compliance schedules.
This Fact Sheet describes the permitted facility, wastewater nutrient sources, receiving streams, and
current nutrient requirements; the proposed terms and conditions of the permit and the rationale for
the proposed changes; and the schedule and process for accepting and considering public comments
prior to the Division's final decision on the permit.
II. BACKGROUND INFORMATION
A. Facility and Permit Overview
Siler City owns and operates the Siler City WWTP, a 4.0 MGD activated sludge treatment plant.
Treatment units include bar screens, grit removal, influent pump station, flow equalization basin
(2.0 MG), dual oxidation ditches (2.015 MG each) with surface jet aeration, dual flocculating clarifiers
(90' 0) with chemical addition, four effluent filters, chlorine contact chamber, and dechlorination.
Solids are aerobically digested and removed as liquid sludge after thickening.
The Siler City WWTP has long treated a combination of high -strength wastewaters from two poultry
processing facilities (Pilgrim's Pride and Townsend Poultry) and its own municipal wastes. The
plant was designed to treat these mixed wastes and comply with the discharge limits for BOD5,
ammonia nitrogen (NH3-N), and total phosphorus (TP) presented in Table 1.

DRAFT
Table 1. Existing Effluent Limitations (Partial List)
PARAMETER
EFFLUENT LIMITATIONS
Monthly Average
Weekly Average
BOD5
(April 1- Oct 31)
5.0 mg/L
7.5 mg/L
(Nov 1— March 31)
10.0 mg/L
15.0 mg/L
NH3 as N
(April 1- Oct 31)
1.0 mg/L
3.0 mg/L
(Nov 1— March 31)
2.0 mg/L
6.0 mg/L
Total Phosphorus
(April 1— Sept30)*
0.5 mg/L (quarterly average)
(Oct 1— March 31)*
2.0 mg/L (quarterly average)
Total Nitrogen
Monitor Only
* Timeframes were modified to accommodate quarterly limits.
The permit has not included TN limits; thus, the plant was not designed with denitrification for
nitrogen removal.
B. Receiving Waters
The plant discharges treated wastewaters to Loves Creek, which flows 0.4 mile to the Rocky River
and then to the Cape Fear River. The IWC at Loves Creek is 96.1% (7Q10S = 0.25 cfs/0.16 MGD).
Although the plant has generally complied with its BOD5, NH3-N, and TP limits, a 2011 evaluation
by the Division found that:
• high nitrogen levels in its discharge (31.5 mg/L average, 2004-2008) were resulting in high
nitrogen concentrations downstream in Loves Creek and further downstream in the Rocky
River, and
• the high levels of nitrogen likely contributed to the excess aquatic plant and algal growth
observed in the Rocky River downstream of the WWTP and chlorophyll -a violations at
Woody's Dam.
The locations and median TN concentrations at the monitoring sites are shown in Figure 1.
Figure 1. Water quality monitoring sites
B5950000 Rocky River - Upstream
Pg April 2099!Decem bar 2010 q
Median Total Nitrogen =.89 mgIL s
n
,cA B5920000 Loves Creek - Downstream
Apr!12009 - December 2010
Median Total Nitrogen = 18.07 mgIL
.1190000 Loves Creek - Upstream
April 2009-December 2010 \
Median Total Nitrogen =.97 mgIL U980000 Rocky River -Downstream
ryt April 20G9- December 2010
a, Median Total Nitrogen = T77 mgIL
r
B6000000 Rocky River - -10 Miles Downstream
April 2009 - December 2010
Median Total Nitrogen = 3.79 mgIL
�oeLegend
l� Woolly's Dam
\�/", June-8eptember2009
Medan Chlorophylla =49.3 uglL
51er CRy WW7P /"" �/
Q IdonRonng SRe D � 1 2 dMies J
- 7D701rrpaired Water � `j1
n � ceo,me_
�1 S
m
Woody's Dam Lake (Reaves Lake) was found to be impaired due to the chlorophyll -a violations and
was added to the state's 303(d) list of impaired waters, where it remains. (The lake was drained in
the summer of 2017, and the dam is scheduled for demolition.) Other impoundments in the Middle
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Siler City WWTP—NCO026441
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Cape Fear watershed, such as the Cape Fear River behind Buckhorn Dam, have also shown signs of
nutrient impacts from a variety of upstream sources and have been added to the 303(d) list.
The Division has not yet conducted nutrient studies in the watershed necessary to develop a
comprehensive nutrient management strategy. The Division's Scientific Advisory Council is
beginning work on water quality criteria for nutrients. However, that process is just beginning, and
results could still be several years away.
Thus, while there is a clear need to control Siler City's nitrogen discharge in order to protect
designated uses in Loves Creek and downstream waters, it has not yet been determined what
numeric nutrient limits are necessary and sufficient to protect water quality.
C. Projected Nitrogen Increases; Permit Action
The Division's report (April 2011) recommended that total nitrogen limits representing best
available technology be added to the permit at its 2011 renewal. However, the need for the limits
changed. Pilgrim's Pride had already closed its facility (May 2008), Townsend Poultry closed in
October 2011, and neither plant was expected to reopen in the foreseeable future. Without these
industrial inputs, effluent TN concentrations from the WWTP declined significantly.
Rather than add TN limits to the Town's permit, the Division added a reopener condition that
provided for the addition of nutrient limits if needed in the future. Special Condition A.(3), Nutrient
Reopener, requires the Town to notify the Division if it intends to accept new industrial wastes with
nutrients greater than typical domestic wastes (40 mg/L TN, 5 mg/L TP). It then authorizes the
Division to reopen the permit to add supplemental nutrient limits as necessary.
In May 2016, Siler City announced that Mountaire Farms Inc. would operate a new poultry
processing facility at the former Townsend Poultry site. Per Condition A.(3.) of its permit, the Town
notified the Division on December 9, 2016, that it intended to accept wastewater from the industry
beginning in early 2019. Per its permit, the Town conducted a treatability analysis to evaluate the
impact of Mountaire Farms' initial (Phase 1) production levels on the Towri s discharge. It later
conducted a second analysis to examine the impacts at full production (Phase 2).
Mountaire Farms will employ dissolved air floatation to reduce solids, organic wastes, and fats, oils
and grease prior to discharging to the Towri s treatment plant. However, the pretreatment system is
not designed to remove total nitrogen.
The Town estimates that, with the addition of the pretreated poultry wastes, its plant's nitrogen
discharge will likely return to previous (2004-2008) levels or greater and impact the receiving waters
as before unless significant controls are implemented. The Towri s effluent TN concentrations are
predicted to be 30 mg/ L in Phase 1 and 38 mg/ L at Phase 2.
The Division notified the Town by letter on June 8, 2017, that it planned to reopen the permit to
address the nutrient issues. These proposed modifications are the result of that action.
III. RATIONALE FOR PROPOSED MODIFICATIONS
The reintroduction of poultry processing wastewaters presents several issues. The expected increase
in the Towri s nitrogen discharge raises significant concerns about downstream water quality. The
lack of a definitive treatment standard means that a chosen TN limit could either result in
insufficient nutrient removal if too lenient or unnecessary expense to the Town if too stringent, or
both.
A tiered strategy emerged from discussions between the Division and the Town. It provides a
balanced approach for addressing these issues:
1. The Town will evaluate operational and low-cost measures in order to optimize the existing
plant's removal of nitrogen in the near term.
2. If it finds the plant can consistently meet its TN limit by these simpler means, the Town will
implement these measures rather than upgrade the plant.
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DRAFT
3. If the results are less successful, the Town will:
• upgrade the plant as soon as reasonably possible to meet its annual TN Load limit and
• complete the optimization study and implement the selected measures while the plant
upgrade is underway. A 30% reduction of TN would prevent the Towri s effluent loads
from surpassing historic levels and so will serve as a working target.
The result of this strategy will be that, by the start of 2023, the nitrogen loads from the Towri s
expanded plant will not exceed its current municipal -only discharge loads (that is, with no poultry
processing wastewaters). Loads will most likely increase in the interim, while plant improvements
are underway, but the optimization of plant performance will serve to offset that increase to some
degree.
The Towri s TN loads for past, present, and estimated future discharges are summarized below and
illustrated in Figure 2.
• From January 2005 through December 2007, when the Pilgrim's Pride and Townsend Poultry
facilities were both operational, the Siler City WWTP discharged an average of 32 mg/L TN
at 2.5 MGD, or 667lb/ day TN.
• From February 2016 through August 2017, after both poultry plants had closed, the Town
discharged an average of 14 mg/L TN at 1.77 MGD, or 202 lb/day TN.
• The Town estimates that the first phase of production (0.7 MGD from Mountaire Farms) will
result in an average discharge of 30 mg/L at 2.57 MGD, or 643 lb/day TN, assuming no
improvements or optimization.
• Mountaire Farms now expects that it will increase production much sooner (Phase 2,1.25
MGD), and the Town estimates that this will increase its discharge to 38 mg/L at 3.12 MGD,
or 989 lb/ day TN.
• If optimization is effective, it can help offset the increased input from Mountaire Farms
Figure 1 shows the results of 20% and 30% reductions.
• Upgrading its existing 4.0 MGD plant to achieve 6.0 mg/L TN will result in an average
design load of 200 lb/day TN at full flow.
It appears that, in order to prevent the Towri s discharge from exceeding historic nitrogen loads,
either the Town will have to achieve greater than 30% reduction through optimization or Mountaire
Farms will have to limit its production until the start of 2023, when the Towri s plant upgrades come
online.
IV. PROPOSED MODIFICATIONS
Based on these considerations, the Division proposes to modify the Towri s permit as follows:
■ In Special Condition A. (1.), add an annual TN Load limit to become effective no later than
January 1, 2023.
TN Load = 6.0 mg/L x 4.0 MGD x 8.34 x 365 days/year = 73, 0581b/yr
■ Add a new Special Condition A.(10.) to establish a compliance schedule for conducting a
nitrogen optimization study and interim plant improvements necessary to meet the TN limit in
Condition A. (1.); the schedule is based on the timeline proposed by the Town.
■ Add a new Special Condition A.(11.) to set forth requirements for a nitrogen removal
optimization study and for reporting the results. Upon Division acceptance, the Town will fully
implement the selected measures until the interim plant upgrades are completed.
■ Add a new Special Condition A.(12.) to specify how annual mass loads are to be calculated.
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■ Add Total Monthly Flow reporting requirements to Condition A.(1.) along with footnotes
referencing the new special conditions.
The proposed permit modification does not affect other limits or requirements of the permit.
Figure 2. Comparison of Nitrogen Discharge Loads
TN Loads - Siler City WWTP
(lb/day)
1,200
1,000
800
667
v 643
n
a
60C
is
0
z
H
00
202
200
0
Actual, 2004 Actual, 2016- Est'd w/
2008 2017 Mountaire
(2 poultry) (no poultry) initial
989
514
M450
791
692
200
J
-20%thru-30%thru Est'dw/-20%thru-30%thru Target, 4mgd,
optimization optimization Mountaire - full optimization optimization end of2022
Proposed Schedule for Permit Issuance:
Draft Permit to Public Notice: October 19, 2018
Close of Comment Period: November 19, 2018
Permit Scheduled to Issue: January 1, 2019
If you have any questions on any of the above information or the attached permits, please contact
Mike Templeton at [phone] or [e-mail].
Fact Sheet —NPDES Permit Modification
Siler City WWTP—NC0026441
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