NC0026441_Fact Sheet_20190430

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: April 30, 2019—Final 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 reopened permit NCO026441 for the Siler City Wastewater Treatment Plant (WWTP)
and proposed to incorporate an effluent limit for total nitrogen(TN) load and related control
requirements and compliance schedules. A public hearing was requested and held,and the results
of that process are presented in full in the April 25,2019 Hearing Officer's report. The Director
accepted most of the Hearing Officer's recommendations and prescribed additional changes to the
permit. The permit was issued
The Director signed the permit on April 30,2019,with an effective date of May 1,2019 and the
current expiration date of May 31,2019. (The Town has submitted timely application,so the permit
will be administratively continued until it is renewed.)
This Fact Sheet describes the permitted facility,wastewater nutrient sources,receiving streams,and
current nutrient requirements;the revised terms and conditions of the permit and the rationale for
the proposed changes;the schedule and process for accepting and considering public comments;the
results of a public hearing on the permit;and final action 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' fib)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.
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 Town has complied with these limits (2012-2018)with a few minor exceptions. The plant has
bypassed its final filters multiple times due to storm events and inflow and infiltration(I/I) into its
collection system,but it has still met the 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.
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
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 Divisions 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.
Fact Sheet—NPDES Permit Modification
Siler City WWTP—NCO026441
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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.
Figure 1.Water quality monitoring sites
B5950000 Rocky River-Upstream
April 20P December 2010
Median6--Total Nitrogen=.89 mgIL sg
1 s
B5920000 Loves Greek-D—.tream
APHI 2009-December 2010
Median Total Nitrogen=18-07 mgIL
B589000D Lava Creek-Upstream
April2009.December 2010 \
Nadia.Total Nitrogen=97 mgIL B59900M Rocky River-Downstream
qw April 2009-Decenher 2010 'Z
Median Total Nitrogen=7.T7 mgIL
r �*
1918000000 Rocky River--10 Miles Downstream e
April2009-December 2010
Median Total Nitrogen=3.79 mgIL
wa aD
Woody's Dam
v Legend .tune-'s a mber2009
Medi-Chlorophyll.=49-3agIL
sir cM wwrP "J� ��
♦ Nvartvun9sae o 1 z .Hues J
f �Q�
—20101mpaired Water o
�s a
Rather than add TN limits to the Towri 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
Fact Sheet—NPDES Permit Modification
Siler City WWTP—NC0026441
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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.
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 Towns 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 Towns
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 667 lb/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 Towns 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 Towns 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
Fact Sheet—NPDES Permit Modification
Siler City WWTP—NC0026441
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■ 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.
■ 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
989
1,000
791
800
a 692
667
v 643
a_
Y 600
v
0 514
450
d00
202 200
200
Actual, 2004 Actual, 2016- Est'd w/ -20%thru -30%thru Est'd w/ -20%thru -30%thm Target,4 mgd,
2008 2017 Mountaire- optimization optimization Mountaire-full optimization optimization end of2022
(2 poultry) (no poultry) initial
V. PUBLIC REVIEW, PUBLIC HEARING,AND FINAL ACTION
Public notice of the draft permit was originally published in The Chatham News on October 25,2018
and posted on the DWQ website. In response to multiple requests received,the Division agreed to
hold a public hearing.Public notice of the hearing was published in The Chatham News +Record on
December 20,2018,and posted on the DEQ website at https://deq.nc.gov/news/events/public-
hearing-siler-city-wwtp-permit-nc002644. The public hearing was held on January 24,2019,at 6:00
p.m.,at the Siler City Town Hall Courtroom in Siler City.The purpose of the hearing was to gather
comments regarding the proposed reopening and modification of the NPDES permit for the Towri s
WWTP.Oral and written comments were received at the hearing,and additional written comments
were received during the comment period.The comment period ended on January 31,2019,except
that comments from U.S.Fish&Wildlife Service staff were accepted on February 7,in light of the
federal government's partial shutdown in January.
Fact Sheet—NPDES Permit Modification
Siler City WWTP—NCO026441
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Approximately 54 people attended the public hearing including 38 members of the general public;
five Town employees or consultants;ten staff members of DWR's Central Office (Raleigh),the
Raleigh Regional Office,and DEQ's Public Information Office;and the hearing officer.Nineteen
individuals spoke at the hearing.
The public comments and the Division's responses are contained in the April 25,2019 Hearing
Officer's report.After considering all comments received,the Hearing Officer concluded that the
proposed permit action is the most effective and timely approach to limit the impacts of the
discharge on downstream waters.
The report recommended the following actions:
• The permit should include the total nitrogen limit and the January 1,2023,compliance date
as originally proposed.This leaves the Town slightly more than 31/2 years to complete its
treatment plant upgrades.
• The milestones for the optimization study should be extended by four months to allow for
the delay in permit issuance.The overall schedule should be shortened to 20 months by
reducing the time for report preparation from six months to four months.
The report also recommended that the Division:
• Meet with the Chatham County Soil and Water Conservation staff and the Town to consider
how to promote projects that would reduce nutrient contributions from farms and other sites
in the watershed.
• Continue the surface water monitoring project begun in January 2019 and use the results in
developing a watershed model for the Rocky River.
• Assist the Town in updating its Headworks Analysis for nitrogen if an update is warranted
following completion of the treatment plant upgrades.
• Continue to support the Town in its efforts to reduce 1/I flows into its collection and
treatment systems.
• Continue to support the Town in its water quality protection efforts.
• Support resolution of the low dissolved oxygen problem at the Hackney Millpond,as
appropriate.
The Hearing Officer submitted these recommendations to the Director.The Director generally
agreed with the recommendations,including the addition of the 2023 Total Nitrogen(TN)Load
limit,and instructed the staff to make the following additional changes:
• Interim TN Load limit.A TN Load limit was added to Special Condition A.(1). The limit is
effective from January 1,2020 through December 31,2022. It is equivalent to 667 lb/day TN
and is meant to ensure the Towri s nitrogen load does not exceed historic (2004-2008) levels.
This does not affect the 2023 TN Load limit originally proposed.
• Process Optimization. Conditions A.(10.) Compliance Schedule and A.(11.)Treatment
Optimization were removed from the permit.The requirements are no longer necessary,
given the addition of the interim TN Load limit.The Town may still pursue optimization in
its nitrogen removal efforts,but it no longer needs prior approval from the Division to
implement measures found to be effective.
The permit was modified accordingly.The Director signed the permit on April 30 with an effective
date of May 1,2019.The permit's expiration date remains May 31,2019.The Town has submitted its
application for renewal,and the permit will be administratively extended after expiration.
Fact Sheet—NPDES Pernlit Modification
Siler City WWTP—NC0026441
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