NC0023906_Response to Pending Imposition of Sewer Line_20210818

WiLSON AUG , 82021
NORTH C A R O L I N A DIVISION OF WATER RESOURCES
. _ DIRECTOR'S OFFICE
WATER RESOURCES -�-
RESPONSE TO PENDING IMPOSITION OF SEWER LINE MORATORIUM
August 16, 2021
CERTIFIED MAIL
RETURN RECEIPT REQUESTED
Mr. S. Danny Smith, Director
N.C. Department of Environmental Quality
Division of Water Resources
512 North Salisbury Street
1617 Mail Service Center
Raleigh, N.C. 27699-1617
Subject: Pending Imposition of Sewer Line Moratorium
Demonstration of Future Wastewater Treatment
Capacities
NPDES Permit NC0023906
City of Wilson-Wilson WWTP
Wilson County
Dear Mr. Smith,
The following should be considered a response to your letter dated July 1, 2021 and received by my office on
July 23, 2021 regarding the "Demonstration of Future Wastewater Treatment Capacities" per 15A NCAC
02T.0118.The City performed an expansion study dated March 2001 to 16, 18, and 20 MGD and submitted
same to DWQ following CY 2003 and high wastewater flows at that time. We believe that this report (attached
95 pages and sent electronically by e-mail) meets all the requirements per 15A NCAC 02T.0118. Due to the age
of the expansion study and because the City already has in their CIP plans to design and expand the Wilson
WWTP capacity, we have already contracted with Hazen and Sawyer to perform a PER to expand the facility to
17.3 MGD, 18.9 MGD, and to 20.7 MGD.The increased flows correspond with already long term proven low
Nitrogen levels well below 3.7 mg/I achieved by our facility for almost 20 years.

We ask that you respond back to us with acknowledgement of an already received expansion study(included
again in this packet) performed by Hazen and Sawyer for the City of Wilson in 2001, which is currently being
updated, which already meets the 02T.0118 requirements. Please contact us if you have any additional
questions or concerns at [phone]. Otherwise, we will consider this as a complete and final response to
your letter of July 1, 2021.
Sincerely,
Ay / °
Barry G. Parks
Director of Water Resources
City of Wilson
Cc: Harry Tyson, Deputy City Manager
Jimmy Pridgen, Water Reclamation Manager
Todd Young, Water Infrastructure Manager
Jim Cauley, City of Wilson Attorney

Draft - Issued For Review and Comment
Hominy Creek
Wastewater Management Facility
Wilson, North Carolina
Hominy Creek
Expansion and Upgrade Study
March 2001
Draft - Issued For Review and Comment

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30,2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen&Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 1 —Expansion Alternatives StudyScope
P
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility is planned for upgrade and expansion to treat future
flows of 20 mgd and beyond. This current expansion study specifically will evaluate requirements for
expanding the 14-mgd rated capacity to a future design average flow capacity of 16-mgd, 18-mgd, and-20
mgd. This memorandum identifies scope and goals of the expansion study, outlines the types of treatment
technologies to be considered for each unit process and defines the subject matter of forthcoming technical
memorandums anticipated for the plant expansion evaluations.
STUDY SCOPE AND GOALS
The City of Wilson is upgrading and expanding the Hominy Creek Wastewater Management Facility under
a phased construction program. The Phase I upgrade of the 12-mgd plant was completed several years ago.
The Phase II project to expand the design treatment capacity of the plant to 14-mgd is nearly complete with
all the major unit process equipment on-line and functional. Hazen and Sawyer has performed an engineering
study for the City in 1993 that investigated and recommended additional facilities and improvements to bring
the capacity to 16-mgd. Due to changes in NPDES permit requirements and other factors, the City desires
to undertake a wastewater treatment capacity study to update the recommendations in the 1993 Wastewater
Collection and Treatment System Study.
This current study,the Hominy Creek Wastewater Management Facility Expansion Study,will involve analysis
of the various major unit processes at the Hominy Creek plant and consideration of different treatment
technologies to meet the City's long term compliance goals. The nearly completed Phase II project made
major process improvements to the liquid treatment train, but deferred major sludge management
improvements at the Hominy Creek plant. For this reason, sludge management facilities are currently the
most pressing need for the plant. Additionally,the City has expressed a desire to gain additional capacity for
the Hominy Creek plant. The expansion study will evaluate requirements for expanding the 14-mgd rated
capacity to a future design rated flow capacity of 16-mgd, 18-mgd, or 20-mgd. A range of expansion flows
are being considered to allow the City to develop a long term master plan to accommodate capacity growth
at the treatment plant, and to better understand the economic implications of the next plant expansion project.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.1 DRAFT- For Review and Comment
City of Wilson
Page 2 of 3
TREATMENT TECHNOLOGIES
Recent upgrade and expansion projects have largely defined the treatment technologies to be considered for
future expansions. In particular, the current expansion project modifies the biological process for 5-stage
biological nutrient removal. Also, the tertiary filtration facilities are configured as deep bed filters for possible
future denitrification operation. However,there are several areas where alternate treatment technologies will
be evaluated in the study as follows:
Unit Process Current Process Type Alternative Technologies to be Evaluated
Disinfection Sodium Hypochlorite Ultraviolet
Effluent Discharge Single Discharge Pipe i • Parallel Discharge Piping
• Flow Equalization
• Effluent Pumping
Sludge Stabilization 1 Anaerobic Digestion/Lime • Anaerobic Digestion
Stabilization • Aerobic Digestion
• Dewatering with Lime Stabilization
• Dewatering without/Lime Stabilization
• Composting
• Thermal Drying
TECHNICAL MEMORANDUMS
Hazen and Sawyer plans to issue a series of technical memorandums defining the development of the
wastewater evaluations for the Hominy Creek plant. These evaluations and feedback from the City will form
the basis for the engineering report for the plant expansion. Planned memorandums are as follows:
Memo No. Topic
1 Expansion Study Scope
Outline scope and goals of the expansion study
2 Influent Flows and Wastewater Loads
Develop influent WW characteristics for current conditions, 16, 18, and 20 mgd)
3 Influent Pumping
Evaluate potential to expand existing pump station, flood protection issues, and new pump
station capacity
4A/4B Preliminary and Primary Treatment
Evaluate potential to expand the existing facilities. Evaluate potential effectiveness of
chemical addition to enhance primary settling and impacts to sludge management and
disposal
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.1 DRAFT- For Review and Comment
City of Wilson
Page 3 of 3
Memo No. Topic
5 Biological Treatment
Evaluate need for process improvements, and expansion requirements. Address
secondary clarifier, RAS/WAS and blower capacity issues
6 Tertiary Filtration
Evaluate expansion requirements
7 Disinfection Alternatives
Evaluate expansion requirements for sodium hypochlorite versus ultraviolet disinfection
8 Effluent Discharge Alternatives
Evaluate capacity of existing outfall line and expansion alternatives such as paralleling and
effluent pumping
9 Solids Handling and Stabilization
Evaluate alternatives for stabilization to Class A and Class B criteria, evaluate sludge
thickening and dewatering alternatives, address on-site sludge storage requirements
10 Electrical/Instrumentation Systems
Evaluate existing electrical system and requirements for improvements.
11 Site Development Alternatives
Evaluate site layout alternatives and develop master plan layout for expansions through 20
mgd.
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30,2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen&Sawyer
Mr. Ronald L.Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 2—Influent Flows and Wastewater Loads
H&S Job No. 30500
The Hominy Creek Wastewater Management Facility is planned for upgrade and expansion to treat future
flows of 20 mgd and beyond. This technical memorandum evaluates the historical influent flows and loadings
and estimates future influent annual average, peak month, and peak day loadings based on the historical
variation observed. Historical operating data from January 1997 through April 2000 were analyzed to develop
the average concentration and mass based peaking factors for the major influent constituents. These
characteristics were then used to develop estimated influent loads for plant expansion scenarios at the 16-
mgd, 18-mgd and 20-mgd maximum month flows.
Historical Plant Flow
Hominy Creek Wastewater Management Facility flow data were reviewed for the period from January 1995
through April 2000 to establish specific peaking factors for maximum month and maximum daily flows. Peak
hour, or instantaneous peak flow, requirements were estimated based on typical peaking factors for facilities
the size of the Hominy Creek facility. These values are summarized in Table 1.
Maximum daily influent flows to the Hominy Creek Wastewater Management Facility are strongly influenced
by wet weather flows as shown in Figure 1. During the period from January 1997 through April 2000,
representing over 1,200 daily observations, nearly 70%of the daily influent flows were less than 10-mgd and
almost 92% of the daily-influent flow values were less than 14-mgd. High wet weather flow events impact
facility design and operation particularly in the areas of biological treatment and solids/liquid separation by
clarification.
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.2 - DRAFT-For Review and Comment
City of Wilson
Page 2 of 10
Table 1. Hominy Creek Plant Influent Flow and Peaking Factors
Historic Current Future Study Flows
Data Design 16-mgd 18-mgd 20-mgd
Average Flow, mgd 11.1 11.9 13.3 14.8
Peak Month Flow, mgd 14.0 16.0 18.0 20.0
Peaking Factor 1.35 1.27 1.35 1.35 1.35
Peak Day Flow, mgd 28.0 33.3 37.2 41.4
Peaking Factor 2.80 2.52 2.80 2.80 2.80
Peak Hour Flow, mgd 33.2 40.0 45.0 50.0
Peaking Factort2 3.00 2.50 2.50 2.50
I Peak Hour Flow for 16-mgd,18-mgd and 20-mgd is estimated as 2.5 times the design basis(i.e.,maximum month flow)
2 Peak Hour Flow for the current design(14-mgd)was estimated at 3.00 times annual average flow
Figure 1 Hominy Creek Influent Flow Rate Histogram(01/97-04/00)
30.0%
25.0%
20.0%
e
15.0% - 17
LL
10.0% -.
5.0% h
- -.
0.0% _ r ' ' ® ® N f r ct rm C 1 - . _
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
24-hour Influent Flow Rate(mgd)
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.2 - DRAFT-For Review and Comment
City of Wilson
Page 3 of 10
As shown in Table 1, the maximum month and maximum day flow peaking factors have increased over the
values used in the 14-mgd expansion design. The data in September and October 1999 resulting from
Hurricane Floyd and related atypical wet weather events were eliminated from the data set for the purpose
of calculating the flow based peaking factors presented. The remaining peaking factor increases could be a
result of higher than normal wet weather during the period of data examined. The City's continued efforts to
reduce inflow and infiltration(I/I)in the collection system should result in lower peaking factors over time and
extend the useful capacity further into the future.
Influent flow rate peaking factors for periods other than the maximum day and maximum month were also
determined to examine the duration of high flow events. A graph of the peaking factors for moving average
periods up to 28 consecutive days are shown in Figure 2_ This graph supports the conclusion that there are
extended periods of higher than average flows entering the Hominy Creek facility in addition to discrete—short
duration—high flow events. An investigation of the top 20% of high flow events,flow greater than or equal
to 11-mgd, was conducted to determine if seasonal influences could be determined. With the exception of
Hurricane Floyd, and the related September-October 1999 events, most(--68%)of the high flow events were
clustered in January, February and March. Results of this investigation are shown in Table 2.
Figure 2. Influent Peaking Factor for Selected Periods
3.00
2.80 —
2.60 _
—
•
2 40 I\
W �
2
2.20 • • •
• •
•
w
i 2.00
•
E
g 1.60 _--. -._- - --
1.40 ---- _-- - ---
1 20 — - Peaking Factor -0.2823 Ln(MA Period)+2.8175'
R2=0.9527
1.00 -
0 2 4 6 8 10 12 14 18 18 20 22 24 26 28 30
Moving Average Period(days)
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.2 DRAFT-For Review and Comment
City of Wilson
Page 4 of 10
Table 2. Distribution of High Flow(>_11-mgd)Events
Month 1997 1998 1999 2000 Total % of Days
January 11 24 19 9 63 51%
February 8 28 10 26 72 64%
March 7 29 0 3 39 31%
April 2 13 1 1 17 14%
May 2 0 0 2 2%
June 0 0 0 0 0%
July 0 0 1 1 1%
August 0 2 0 r, 2 2%
September 0 2 `ZZ J .0 o e� /
October 0 1 23 25°o
November 1 0 9 10 11%
December 2 2 0 4 4%
Total 33 101 82 39 255
% of Days 9% 28% 23% 32%
Extended periods of high flow during the winter months represent the most critical operating conditions for
biological treatment and clarification processes at the Hominy Creek plant. Based on the seasonal high
influent flow pattern, higher process safety factors may be warranted for the treatment facility.
Wastewater Characteristics
Historical influent data for the period from January 1997 through April 2000 were examined to determine the
average influent characteristics for the primary influent constituents. Influent concentrations for each specific
constituent and the corresponding daily flow were used to determine the daily incoming mass loading for each
parameter. Mass based peaking factors were developed for each of the constituents based on the ratio of
the peak mass to the annual average mass for both the maximum month and maximum day periods for each
calendar year. Mass weighted average annual concentrations were calculated from the average annual flow
and average annual mass for each incoming parameter. The results of this historical data analysis and the
associated peaking factors are shown in Table 3.
Influent total suspended solids (TSS) data for the period from January 1997 through April 2000 were
examined. The data set contained 40 events where influent total suspended solids concentrations exceeded
900 mg/L. Most of the events were clustered in 1997 (22-events)and 1998(17-events). The last recorded
influent total suspended solids concentration greater than 900 mg/L was on January 26, 1999. An
operating examination of the detailed plant operating records does not tend to support conditions consistent
with the high influent solids concentrations and loads reported. Discussions with City personnel were held
to determine if these high solids concentration and solids loading events were data anomalies, or should be
considered in the evaluation and design of wastewater management facility improvements. These discussions
concluded the following:
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.2 - DRAFT-For Review and Comment
City of Wilson
Page 5 of 10
• Possible sampling location and sampler operational irregularities may have been the cause of some high
influent total suspended solids concentrations. Plant operating personnel have since corrected the
operational issues associated with sample collection and believe recent sample data better represent
actual influent conditions.
• Historically the plant received alum solids at the wastewater management facility and this was attributed
to some of the high daily solids loads observed in the plant influent. According to City personnel this
practice has since been discontinued.
Based on these discussions, data with influent total suspended solids concentration greater than 900 mg/L
were removed from this historical data set prior to calculating the peak day mass peaking factor. The median
(5011 percentile) influent TSS concentration was 260 mg/L. The 90th and 95th percentile influent TSS
concentrations,were respectively, 480 mg/L and 610 mg/L. The mass weighted average TSS concentration
for the period was 286 mg/L reflecting skewness from high TSS data remaining in the data set. For the
average TSS concentration of 260 mg/L will be used.
evaluations an annual a 9
9
Influent biochemical oxygen demand (BOD5), total Kjeldahl nitrogen (TKN), ammonia (NH3 N) and total
phosphorus(TP) data for the period from January 1997 through April 2000 were also examined to determine
median concentrations and mass based peaking factors. These data are also shown in Table 3. City
personnel recommended increasing the design annual average annual concentration for BOD5 from 210 mg/L
to 250 mg/L to reflect potential future increased loadings from industrial contributors and reductions in dilution
through Ill reduction in the collection system.
The Hominy Creek WWMF is under expansion from 12-mgd to 14-mgd peak month flow capacity(Contract
3A/3B). Table 4 compares the most recent historical loadings to the design capacity provided with the most
recent expansion project to develop a capacity utilization index. Recent historical data would indicate
maximum month loadings for flow,TKN and TP are capable of exceeding the maximum month design capacity
provided under the Contract 3A/3B expansion. The recent data also indicate maximum month organic(BOD5)
and total suspended solids loads are capable of exceeding greater than 90%of the installed capacity. An
examination of the annual average BOD5 loading data for January 1997 to April 2000 confirms the facility is
consistently operating near, or above, 100% capacity utilization on an average annual basis.
Plant capacity expansion will be required to accommodate future residential,commercial and industrial growth
5.
area. Projected loads for these exp
ansion optionsTable
in the City of Wilson service are shown in
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.2 DRAFT-For Review and Comment
City of Wilson
Page 6 of 10 I
Table 3. Hominy Creek Plant Historical Wastewater Characteristics
01/97-12/97 01/98-12/98 01/99-12/99 01/00-04/00 Average'
Annual Average
Flow, mgd 8.86 9.83 10.09 10.61
TSS, Ib./day 23,990 24,990 19,150 27,190
TSS, mg/L 325 305 228 307 286.0
BOD5, lb./day 17,260 17,770 16,000 18,200
BOD5, mg/L 234 217 190 206 213.0
TKN, lb./day 1,950 1,940 1,720 1,660
TKN, mg/L 26.4 23.7 20.4 18.8 23.0
NH3-N, lb./day 980 970 930 1,030
NH3-N, mg/L 13.3 11.8 11.1 11.6 12.0
TP, lb./day 380 410 320 360
TP, mg/L 5.1 5.0 3.8 4.1 4.6
Maximum Month
Flow, mgd 11.15 15.46 15.95 12.86
TSS, lb./day 31,990 31,740 24,080 40,200
TSS Peak Factor 1.33 1.27 1.26 1.48 1.29
BOD5lb./day 20,260 21,230 19,700 21,520
BOD5 Peak Factor 1.17 1.19 1.23 1.18 1.20
TKN, lb./day 2,600 2,860 1,990 1,770
TKN Peak Factor 1.33 1.47 1.16 1.07 1.32
NH3-N, lb./day 1,230 1,070 1,000 1,050
NH3N Peak Factor 1.26 1.10 1.08 1.02 1.14
TP, lb./day 560 540 450 480
TP Peak Factor 1.47 1.32 1.41 1.33 1.40
1
Maximum Day
Flow, mgd 20.00 23.40 26.98 22.47
TSS, lb./day 81,050 100,580 60,080 66,070
TSS Peak Factor 3.38 4.03 3.14 2.43 3.51
BOD5lb./day 54,290 56,380 40,000 32,760
BOD5 Peak Factor 3.15 3.17 2.50 1.80 2.94
TKN, Ib./day 8,320 5,060 6,130 2,930
TKN Peak Factor 4.27 2.61 3.56 1.77 3.48
NH3 N, lb./day 1,740 1,860 1,390 2,210
NH3-N Peak Factor 1.78 1.92 1.50 2.15 1.73
TP, Ib.day 2,590 1,770 1,220 600
TP Peak Factor 6.82 4.32 3.81 1.67 4.98
1 Average peak factor values only include 1997-1999 data.
HAZEN AND SAWYER,P.C.
Job,No.30500

Memorandum No.2 DRAFT-For Review and Comment
City of Wilson
Page 7 of 10
Table 4. Hominy Creek Plant Influent Characteristics-Capacity Utilization
Design' 01/97-12/97 01/98-12/98 01/99-12/99 01/00-04/00
Annual Average
Flow, mgd 11.1 8.86 9.83 10.09 10.61
Flow Capacity 80% 87% 91% 96%
TSS, lb./day 30,100 23,990 24,990 19,150 27,190
TSS Capacity 80% 83% 64% 90%
BOD5, lb./day 16,620 17,260 17,770 16,000 18,200
BOD5 Capacity 104% 107% 96% 110%
TKN, lb./day 2,010 1,950 1,940 1,720 1,660 1
TKN Capacity 97% 97% 86% 83%
NH3-N, lb./day 1,110 980 970 930 1,030
NH3-N Capacity 88% 87% 84% 93%
TP, lb./day 380 380 410 320 360
° 108% 84% 95%
TP Capacity 100%
Maximum Month
Flow, mgd 14.0 11.15 15.46 15.95 12.86
Flow Capacity 80% 110% 114% 92%
TSS, lb./day 41,100 31,990 31,740 24,080 40,200
TSS Capacity 78% 77% 59% 98%
BOD5lb./day 22,300 20,260 21,230 19,700 21,520
BOD5 Capacity 91% 95% 88% 97%
TKN, lb./day 2,590 2,600 2,860 1,990 1,770
TKN Capacity 100% 110% 77% 69%
NH3 N, lb./day 1,420 1,230 1,070 1,000 1,050
NH3-Capacity 87% 75% 70% 74%
TP, lb./day 540 560 540 450 480
TP Capacity 104% 100% 83% 89%
'Current design basis data were taken from the August 1997 Contract 3 design calculations.
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.2 DRAFT-For Review and Comment
City of Wilson
Page 8 of 10
Table 5. Hominy Creek Plant Influent Characteristics-Evaluation Basis
14-mgd1 16-mgd 18-mgd 20-mgd
Annual Average
Flow, mgd 11.1 11.9 13.3 14.8
TSS, lb./day 30,100 25,700 28,900 31,100
TSS, mg/L 326 260 260 260
BOD5, lb./day 16,620 24,700 27,800 30,900
BOD5, mg/L 180 250 250 250
TKN, lb./day 2,010 2,270 2,560 2,840
TKN, mg/L 22 23 23 23
NH3-N, lb./day 1,110 1,280 1,450 1,610
N 13-N, mg/L 12 13 13 13
TP, lb./day 380 420 470 520
TP, mg/L 4.1 4.2 4.2 4.2
Maximum Month
Flow, mgd 14.0 16.0 18.0 20.0
TSS, lb./day 41,100 33,400 37,600 41,800
TSS Peak Factor 1.37 1.30 1.30 1.30
BOOS lb./day 22,300 29,700 33,400 37,100
BOD5 Peak Factor 1.34 1.20 1.20 1.20
TKN, lb./day 2,590 3,060 3,460 3,830
+ TKN Peak Factor 1.29 1.35 1.35 1.35
NH3 N, lb./day 1,420 1,540 1,740 1,930
NH3-N Peak Factor 1.28 1.20 1.20 1.20
TP, lb./day 540 590 660 730
TP Peak Factor 1.42 1.40 1.40 1.40
Maximum Day
Flow, mgd 33.2 37.2 41.5
TSS, lb./day 90,000 101,200 112,400
TSS Peak Factor 3.50 3.50 3.50
BOOS lb./day 74,100 83,400 92,700
BODS Peak Factor - 3.00 3.00 3.00
TKN, lb./day 5,450 6,140 6,820
TKN Peak Factor 2.40 2.40 2.40
NH3-N, lb./day 2,300 2,610 2,900
NH3 N Peak Factor 1.80 1.80 1.80
TP, lb./day 1,130 1,270 1,400
TP Peak Factor 2.70 2.70 2.70
' Conditions are based on the Contract 3N3B Design Basis
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.2 - DRAFT-For Review and Comment
City of Wilson
Page 9 of 10
Temperature
Influent wastewater temperature data were also examined for the period from January 1997 to April 2000 to
determine the range of process operating temperatures that should be accommodated during the design
evaluations. A histogram of the historical data is shown in Figure 3. Table 4 presents monthly average
influent wastewater temperature data for each month during the evaluation period in order to show seasonal
influences.
Data for the extreme low influent temperature(9°C and 10°C)were from January 2000 and can be directly
attributed to high wet weather influent flows following a major winter snowstorm that produced record snowfall
levels. This event was clearly not typical of normal winter influent temperature as evidenced by the'gap' in
the histogram. For the purposes of this evaluation a minimum operating temperature of 12°C (53°F)will be
used to evaluate winter period nitrification process performance and assess reactor adequacy against the
winter nitrification process performance standards. With seasonal nitrification limits starting April 15t a
minimum operating temperature of 15°C(59°F)—the minimum March monthly average influent temperature
—will be used to evaluate process adequacy against summer nitrification process performance standards.
Figure 3 Influent Wastewater Temperature
12.0% --
10.0%
3
8.0%
,1
C
Q
lL
::: Q --
0.0% _.
9 10 11 12 13 14 15 18 17 18 19 20 21 22 23 24 25 26 27 28 29
Influent Temperature CC)
HAZEN AND SAWYER, P.C.
Job. No.30500

Memorandum No.2 - DRAFT-For Review and Comment
City of Wilson
Page 10 of 10
Table 6. Monthly Average Influent Wastewater Temperature(°C)
1 Month 1997 1998 1999 2000 Average Minimum
January 16 15 15 14 14.0 14
February 16 15 14 14 14.5 14
March 18 17 15 17 16.8 15
April 19 19 17 18 18.3 17
May 21 21 20 20.7 20
June 24 24 22 23.3 22
July 27 26 25 26.0 25
August 26 26 27 26.3 26
September 26 25 25 25.3 25
October 24 24 23 23.7 23
November 20 19 20 19.7 19
December 16 19 19 18.0 16
Design Effluent Limits
The Hominy Creek Wastewater Management facility operates under NPDES permit NC-0023906. The permit
was issued in draft form May 25,2000 with discharge effluent limits for both the 12-mgd and 14-mgd operating
1 conditions. The proposed limits for major constituents at the 14-mgd capacity condition are shown in Table
7. These limits will be used to evaluate capacity of the existing facility and proposed expansion facilities.
Table 7 Hominy Creek Discharge Limits— 14-mgd Capacity
Summer Limits(04/01-10/31) Winter Limits(11/01-03/31)
Monthly Average Weekly Average Monthly Average Weekly Average
BOD,,20.c, mg/L 5.0 7.5 10.0 15.0
TSS, mg/L 30.0 45.0 30.0 45.0
NH3 N, mg/L 1.0 -- 2.0 --
Total P1, mg/L 2.0 2.0
Dissolved Oxygen2, mgt. >7.0 >7.0
Fecal Coliform3, MPN/mL <200 <400 <200 <400
Total Residual Chlorine4 18 18
1 Total P is Quarterly Average w/weekly composite sampling.
2 Dissolved Oxygen is based on a daily grab.
3 Fecal Coliform is based on geometric mean.
4 Total Residual Chlorine is a daily grab and units are µg/L
HAZEN AND SAWYER,P.C.
Job.No. 30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L.Taylor, Hazen & Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 3—Influent Pumping
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility(HCWWMF) is planned for upgrade and expansion to
treat future peak month flows of 20-mgd. This technical memorandum evaluates the influent pumping
requirements to accommodate expansion to maximum month flow capacities of 16-mgd, 18-mgd and 20-mgd.
The existing influent pumping station will be retained and upgraded or supplemental pumping capacity
provided to accommodate the increased flow requirements.
Existing Influent Pumping Facilities
The existing influent pump station at the Hominy Creek Wastewater Management Facility consists of four
vertically mounted centrifugal pumps. Each of the pumps has a rated capacity of 6-mgd for a firm station
capacity of 18-mgd and a peak station capacity of 24-mgd. Three pumps are configured with variable speed
drives and the remaining pump is configured as a constant speed pump.
Influent Pumping Flow Rates
Influent pumping is controlled by influent flow to the wastewater treatment plant. Total average annual, peak
peak dayand hour flow rate for each of the design peak flow conditions is shown in Table 1.
Table 1. Total Influent Wastewater Flow
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Average Annual Flow, mgd 11.1 11.9 13.3 14.8
Peak Month Flow, mgd 14.0 16.0 18.0 20.0
Peak Day Flow, mgd 28.0 33.3 37.2 41.4
Peak Hour Flow, mgd '.2 33.2 40.0 45.0 50.0
' Peak Hour Flow for 16-mgd, 18-mgd,and 20-mgd is estimated as 2.5 times the design basis(i.e.,maximum month flow).
2 Peak Hour Flow for the current(14-mgd)design basis was estimated at 3.00 times annual average flow.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.3 DRAFT- For Review and Comment
City of Wilson
Page 2 of 4
Influent raw sewage flow to the Hominy Creek treatment facility is delivered via the 36-inch diameter Hominy
Swamp interceptor, the 30-inch diameter Contentnea Creek interceptor, and the 20-inch Toisnot Swamp
interceptor. Flow from the Toisnot interceptor is delivered to the treatment plant preliminary treatment works
from a pump station located off the plant site. Flow from the Hominy Swamp and Contentnea Creek
interceptors is combined at the treatment plant and pumped to the preliminary treatment facilities. The
combined flow from the Hominy Swamp and Contentnea Creek interceptors is estimated at 75 percent of the
total plant influent flow. The remaining 25 percent of the total plant influent flow is assigned to the Toisnot
interceptor sewer. The estimated distribution of flow between the Toisnot interceptor and the influent pump
station is shown in Table 2.
Table 2. Influent Wastewater Flow
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Hominy Swamp/Contentnea Creek
Average Annual Flow, mgd 8.3 8.9 10.0 11.1
Peak Month Flow, mgd 10.5 12.0 13.5 15.0
Peak Day Flow, mgd 21.0 25.0 27.9 31.1
Peak Hour Flow, mgd 24.9 30.0 33.8 37.5
Toisnot
Average Annual Flow, mgd 2.8 3.0 3.3 3.7
Peak Month Flow, mgd 3.5 4.0 4.5 5.0
Peak Day Flow, mgd 7.0 8.3 9.3 10.4
Peak Hour Flow, mgd 8.3 10.0 11.3 12.5
Estimated peak hour Hominy Swamp/Contentnea Creek influent flow at the 14-mgd design condition is slightly
greater than the influent pump station's available rated pumping capacity. Therefore, any expansion beyond
the currently permitted flow capacity will require an upgrade to the influent pump station's overall pumping
capacity. Influent pumping improvement options will include upgrading the pumping capacity within the
existing pump station, or constructing a new adjacent pump station and related facilities to accommodate the
increased influent flow.
Upgrade Existing Facility
One option for developing additional influent pumping capacity is to upgrade the existing pumping station with
new larger capacity and larger horsepower pumps. The two existing 100-hp Allis-Chalmers pumps connected
to the 24-inch diameter discharge line are reported by plant operating staff to be in need of replacement.
Replacement and upgrade of these pumps to 200-hp variable speed pumps with a capacity of 9.4-mgd (6,500
gpm)each will give a total installed pumping capacity of 30.8-mgd which will be sufficient to meet the peak
hour flow associated with the 16-mgd design condition. Replacement of the existing pumps, motor control
centers, variable speed drives, and related piping modifications could be accomplished for an estimated cost
of$400,000, excluding engineering and contingencies.
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.3 DRAFT-For Review and Comment
City of Wilson
Page 3 of 4
Subsequent expansion to the 18-mgd and 20-mgd design conditions could be accommodated by replacement
of the two existing Fairbanks-Morse pumps. Replacement and upgrade of these pumps to 250-hp variable
speed pumps with a capacity of 9.4-mgd(6,500 gpm)each will give a total installed pumping capacity of 37.6-
mgd which will be sufficient to meet the peak hour flow associated with the 20-mgd design condition.
Replacement of the existing pumps, motor control centers, variable speed drives, and related piping
modifications could be accomplished for an estimated cost of $450,000, excluding engineering and
contingencies.
New Pump Station Facility
A second option for developing additional influent pumping capacity would be to construct a new pumping
station,wet well, and discharge line in parallel service with the existing influent pump station. The new pump
station would house two 150-hp variable speed pumps each with a capacity of 6.75-mgd (4,700 gpm)
discharging into a new 24-inch diameter force main. The estimated total construction cost, excluding
engineering and contingencies, of the new lift station is$800,000. The estimated construction cost, excluding
engineering and contingencies, of the new discharge force main is$150,000. Approximately$100,000 of the
estimated total construction cost could be deferred for the 16-mgd design condition by only installing one of
the two pumps. The total flow capacity of 30.8-mgd would be sufficient to carry the anticipated peak hour flow
at the 16-mgd design condition.
Within the current lift station the two existing Allis-Chalmers pumps would stilt require upgrading, but could
be based on a similar size and design basis as the currently in place pumps. Replacement and upgrade of
these pumps to 100-hp variable speed pumps with a capacity of 6.0-mgd (4,200 gpm) each will give a total
installed pumping capacity of 24-mgd in the existing lift station. Replacement of the existing pumps could be
accomplished for an estimated cost of$200,000, excluding engineering and contingencies.
The total estimated construction cost, excluding engineering and contingencies,for the new lift station, influent
force main, and existing pump station upgrade is$1,150,000.
Summary and Recommendations
The total estimated construction costs, excluding engineering and contingencies, for both upgrading the
existing station and constructing a new station are shown in Table 3. Upgrading the existing lift station is the
lower cost option based on the estimated construction costs. However, upgrading the existing facility does
not provide the operational flexibility associated with a dual wet well provided with a new pumping station. At
the 16-mgd design condition the incremental cost for the dual wet well is estimated at$650,000. However,
at the 18-mgd and 20-mgd design conditions the incremental cost for the dual wet well flexibility falls to
$300,000.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.3 DRAFT-For Review and Comment
City of Wilson
Page 4 of 4
Table 3. Estimated Construction Costs
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Upgrade Existing Station
Upgrade A/C Pumps $400,000 $400,000 $400,000
Upgrade F/M Pumps $450,000 $450,000
Total $400,000 $850,000 $850,000
Construct New Station
Upgrade NC Pumps $200,000 $200,000 $200,000
New Lift Station $700,000 $800,000 $800,000
New Discharge Main $150,000 $150,000 $150,000
Total $1,050,000 $1,150,000 $1,150,000
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L.Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 4A—Enhanced Primary Treatment
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility(HCWWMF) is planned for upgrade and expansion to
treat future flows of 20 mgd and beyond. This technical memorandum evaluates enhanced primary treatment
as a full-time process alternative to reduce solids and organic loadings to the biological treatment process.
This technical memorandum will evaluate enhanced primary treatment for the current 14-mgd and future peak
monthly flows of 16-mgd, 18-mgd, and 20-mgd.
Existing Primary Clarification Facilities
Currently the Hominy Creek facility operates three circular primary clarifiers as part of its liquid treatment
process. Two clarifiers have a diameter of 95-feet and the third clarifier has a diameter of 90-feet. All the
clarifiers have a 9-foot sidewater depth. The total installed primary clarifier surface area is 20,540 ft2 and the
design surface overflow rate is 680 gpd/ft2 at the current 14-mgd design capacity. Historical operating data
indicate the primary clarifiers remove from 25% to 30% of influent wastewater BOD5 and 50% to 60% of
influent suspended solids. The PC-1 sludge collection mechanism was replaced during the summer of 2000,
the PC-2 and PC-3 mechanisms appear to be in good condition.
Enhanced Primary Treatment
Chemically enhanced primary treatment involves addition of inorganic and/or organic coagulation and
flocculating agents to raw influent wastewater to enhance BOD5 and suspended solids removal during primary
clarification. Typical inorganic coagulating and flocculating agents used for enhanced primary treatment are
aluminum sulfate (alum, ferric chloride,and/or ferric sulfate. Cationic, anionic and non-ionic polymers may
also be used to stimulate coagulation and flocculation during enhanced primary treatment.
Enhanced primary treatment at the Hominy Creek facility was investigated as an interim solution to address
high influent organic loads and limited downstream biological treatment capacity during construction of the
14-mgd expansion project. Jar and pilot testing indicated that enhanced primary treatment could be used to
reduce primary clarifier effluent BOD5 and suspended solids concentrations, resulting in reduced loadings to
the downstream biological treatment process. Pilot and field testing indicated primary clarifier BOD5 removal
effectiveness could be increased from 25%-30% to approximately 50%, total suspended solids removal
effectiveness increased from 50%-60%to approximately 80%at chemical doses of approximately 40 mg/L.
The evaluation of enhanced primary treatment will be based on annual average loadings, flows at the dose
and performance levels stated above.
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.4A DRAFT-For Review and Comment
City of Wilson
Page 2 of 4
Enhanced Primary Treatment Operating Costs
A summary of the estimated incremental enhanced primary treatment operating cost is shown in Table 1.
Table 1. Estimated Incremental Enhanced Primary Treatment Operating Costs
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Average Daily Flow, mgd 11.1 11.9 13.3 14.8
Chemical Usage'
Annual Chemical Usage, lb./year 1,340,000 1,440,000 1,620,000 1,800,000
Annual Chemical Cost, $/year $174,500 $187,600 $211,100 $234,500
Aeration Power Savings2
BOD5 Removed from Aeration, lb./day 5,750 6,180 6,950 7,720
Aeration Power Savings, KWH/year 308,300 331,500 372,900 414,300
Aeration Power Savings, $/year $18,500 $19,900 $22,400 $24,900
Estimated Sludge Production 3.4
With Chemical Additions, lb./day 20,230 21,750 24,470 27,190
Without Chemical Addition, lb./day 16,040 17,250 19,410 21,560
Sludge Production Increase, lb./day 4,190 4,500 5,060 5,630
Solids Handling and Disposal Cost
Sludge Dewatering6, $/year $32,740 $35,200 $39,600 $44,000
Sludge Disposal', $/year $76,400 $82,140 $92,410 $102,670
Incremental Operating Cost, $/year $265,140 $285,040 $320,710 $356,270
Net Present Cost9, $ $2,807,000 $3,019,000 $3,397,000 $3,774,000
' Based on 40 mg/L-Fe2(SO4)3 at$0.13/Ib.
2 Based on 0.147 KWH/lb. BODSr at$0.06/KWH
3 Settled Influent VSS/TSS=0.70; 50%VSS reduction for Primary Solids in Anaerobic Digester
4 Yobs= 0.50 lb. VSS/lb. BOD5r, 0.75 MLVSS/MLSS, 50%VSS reduction for WAS in Anaerobic Digester
5 Includes inert loading attributed to chemical solids
6 Based on sludge dewatering at 10 IbdJdT polymer dose, $4.30/lbd,,polymer cost
Based on 20%cake solids, $20/wT disposal cost
s Based on average annual flow, actual ratepayer impact might be greater
9 Based on 7% interest rate,20-year life(P/A, 7%, 20-yr)= 10.593
HAZEN AND SAWYER, P.C.
Job No.30500

Memorandum No.4A DRAFT-For Review and Comment
City of Wilson
Page 3 of 4
Enhanced Primary Treatment Capital Costs
Installation of enhanced primary treatment capability at the Hominy Creek facility will require incremental
capital investment over facilities required for conventional primary treatment followed by biological nutrient
removal activated sludge. Permanent chemical storage, feed and mixing facilities would be required to
accommodate enhanced primary treatment. Increased sludge quantities associated with enhanced primary
treatment would also require additional digester storage volume to meet digester minimum HRT requirements.
Assuming new anaerobic digestion facilities are provided for the sludge stabilization process these
incremental costs would range from approximately$200,000 to$300,000 over-and-above the cost required
to accommodate the conventional primary treatment alternative.
Reduced BOD5 loadings to the aeration basins provides and opportunity to defer costs associated with
construction of new aeration tankage under expanded flow conditions. Increased aeration tankage
requirements were estimated for each of the maximum month design scenarios and compared to aeration
tankage scenarios associated with the conventional treatment options. Estimated incremental capital costs
for new equipment, and anticipated savings in new aeration tankage are shown in Table 2.
Table 2. Estimated Incremental Enhanced Primary Treatment Capital Costs
Maximum Monthly Flow Design Condition (mgd)
14.0' 16.0 18.0 20.0
Chemical Storage and Feed Facility $450,000 $450,000 $450,000 $450,000
Increased Digester Storage Volume $200,000 $230,000 $260,000 $290,000
Aeration Trains Required
Conventional Treatment2 6 10 12 13
Enhanced Primary Treatment 5 8 9 10
Incremental Change NA3 -2 -3 -3
Aeration Tankage Savings'', $0 $2,500,000 $3,750,000 $3,750,000
' 14-mgd condition based on Contract 3A13B design basis
2 Based on requirements for 1 mg NH3-N/L Summer and 2 mg NH3-N/L Winter Limits
3 No savings realized since capital expenditure is already been made
4 Based on $1,250,000 per aeration train
Impact on Liquid Train Treatment Operations
Utilization of enhanced primary treatment will lower organic loadings to the downstream biological treatment
process. The reduced organic loading will impact the activated sludge process. These impacts may be
summarized as follows:
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.4A DRAFT-For Review and Comment
City of Wilson
Page 4 of 4
• Increased organic (BOD5) removal in the primary treatment process will lower the F/M ratio in the
biological phosphorus removal tank that could result in reduced biological phosphorus removal
effectiveness.
• Increased organic(BOD5) removal in the primary treatment process also will result in reduced BOD5:TP
ratios in the biological treatment process. Recommended BOD5:TP ratios of at least 20:1 are
recommended to achieve effluent TP concentrations of 1.0 mg/L.
• Increased organic(BOD5) removal in the primary treatment process will lower the F/M ratio in the 1s'stage
anoxic tank resulting in a reduced denitrification rate. A reduced specific denitrification rate could result
in incomplete denitrification in the 1st stage anoxic tank and pass through of nitrates to the 2nd stage anoxic
tank requiring increased methanol feed rates to accomplish nitrogen removal.
• Increased organic(BOD5)removal in the primary treatment process will also lower the BOD5:TKN ratio
in the biological treatment process. The reduced BOD5:TKN ratio will result in a lower percentage of
influent nitrogen removal by cell synthesis and an increased removal rate requirement for nitrification.
Recommendation
The estimated incremental costs for implementing enhanced primary treatment as a full-time process option
are shown in Table 2. Under each design condition evaluated the enhanced primary treatment incremental
net present cost over conventional treatment was positive indicating that enhanced primary treatment would
. be more expensive than conventional treatment. Implementation of enhanced primary treatment as a full-time
process option is not recommended based on the results of this analysis.
Table 2. Estimated Incremental Enhanced Primary Treatment Costs
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Present Worth Operating Cost $2,807,000 $3,019,000 $3,397,000 $3,774,000
Chemical Storage and Feed Facility $450,000 $450,000 $450,000 $450,000
Increased Digester Storage Volume $200,000 $230,000 $260,000 $290,000
Subtotal of Costs $3,457,000 $3,699,000 $4,107,000 $4,514,000
Aeration Tankage Savings, NA $2,500,000 $3,750,000 $3,750,000
Net Present Cost $3,457,000 $1,199,000 $357,000 $764,000
HAZEN AND SAWYER,P.C.
Job No.30500

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L. Taylor, Hazen&Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 4—Primary and Preliminary Treatment Facilities
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility (HCWWMF) is planned for upgrade and expansion to
treat future peak month flows of 20-mgd. This technical memorandum evaluates the primary and preliminary
treatment process improvements required to accommodate expansion to maximum month flow capacities of
16-mgd, 18-mgd and 20-mgd. The existing primary and preliminary treatment technologies currently applied
at the plant will be utilized to meet treatment needs through the expansion flows.
Treatment Process Hydraulic Loading Rates
Primary and preliminary treatment facility sizing is typically controlled by hydraulic loading rates to the various
unit process facilities. Average annual, peak month, peak day and peak hour flow rates for each of the design
flow conditions is shown in Table 1.
Table 1. Influent Wastewater Loading
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Average Annual Flow, mgd 11.1 11.9 13.3 14.8
Peak Month Flow, mgd 14.0 16.0 18.0 20.0
Peak Day Flow, mgd - 28.0 33.3 37.2 41.4
Peak Hour Flow, mgd 33.2 40.0 45.0 50.0
'Peak Hour Flow for 16-mgd, 18-mgd,and 20-mgd is estimated as 2.5 times the design basis(i.e.,maximum month flow).
2 Peak Hour Flow for the current(14-mgd)design basis was estimated at 3.00 times annual average flow.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No. 4 DRAFT-For Review and Comment
City of Wilson
Page 2 of 3
Primary Clarification
Primary clarification is recommended to reduce influent total suspended solids and organic loading rates to
the biological treatment process. Primary clarification requirements will be assessed based on the following
recommended design criteria:
Surface Overflow Rate at Design Flow 1,000 gpd/ft2
Surface Overflow Rate at Peak Hour Flow 3,000 gpd/ft2
Primary clarification capacity is currently provided with three circular clarifiers. Two of the clarifiers have a
diameter of 95-ft and the remaining clarifier has a diameter of 90-ft. The total installed clarifier surface area
is currently 20,540 ft2. Based on the recommended design criteria the current primary clarification capacity
is 20.5-mgd design flow or 61.6-mgd peak hour flow with all units in service. The total installed clarifier surface
area with one of the large diameter clarifiers out-of-service is 13,450 ft2. Based on the recommended design
criteria the current primary clarification capacity is 13.4-mgd design flow or 40.4-mgd peak hour flow with one
of the larger diameter primary clarifiers out of service. Estimated surface overflow rates for each of the design
conditions is shown in Table 2.
Table 2. Primary Clarifier Surface Overflow Rate
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Number of Primary Clarifiers 3 3 3 3
All Clarifiers in Service
SOR Average Annual Flow, gpd/ft2 540 580 650 720
SOR Peak Month Flow, gpd/ft2 680 780 880 970
SOR Peak Day Flow, gpd/ft2 1,360 1,620 1,810 2,020
SOR Peak Hour Flow, gpd/ft2 1,620 1,950 2,190 2,430
One Clarifier Out-of-Service
SOR Average Annual Flow, gpd/ft2 830 880 990 1,100
SOR Peak Month Flow, gpd/ft2 1,040 1,190 1,340 1,490
SOR Peak Day Flow,gpd/ft2 2,080 2,480 2,770 3,080
SOR Peak Hour Flow,gpd/ft2 2,470 2,970 3,350 3,720
The existing clarification capacity should be adequate to accommodate the 16-mgd, 18-mgd, and 20-mgd
expansion levels when all units are in service. Installed primary clarification capacity, however, is marginal
for the 20-mgd design condition and would be seriously compromised with the largest unit out of service.
Therefore, it is recommended that one additional 95-ft diameter clarifier be constructed for the 20-mgd design
condition expansion. The estimated cost of the primary clarifier and associated primary sludge pumping
ti capacity is$1,200,000.
HAZEN AND SAWYER,P.C.
Job.No.30500
Ii

Memorandum No. 4 DRAFT-For Review and Comment
City of Wilson
Page 3 of 3
Preliminary Treatment
Preliminary treatment facilities consist of two mechanically cleaned bar screens,with a manual bypass screen
installed in a parallel channel for back-up. Preliminary screening facilities are followed by grit removal. The
two 3.5-ft width climber-type bar screens discharge screenings into a screen conveyor/press,which deposits
the screenings into a dumpster for disposal in a landfill. Each bar screen has a maximum flow capacity of
18.5-mgd.
Grit removal is provided prior to the pre-aeration tanks and primary clarifiers to removal heavy inorganic
particles that would otherwise settle in process tankage and/or cause excessive abrasion and wear on pumps
and other process equipment. Grit removal is accomplished by two 18-ft diameter stirred vortex type grit
collectors,with three grit pumps for transporting the settled grit to grit cyclones and classifiers. The two grit
cyclones and classifiers deposit the dewatered grit into dumpsters for landfill disposal. Each stirred vortex
grit collector has a peak hydraulic flow capacity of 30-mgd. Each grit cyclone and grit collector has a design
flow capacity of 200 gpm.
The two current climber screens have a combined capacity of 37-mgd, almost the peak daily flow associated
with the 18-mgd design condition. It is recommended that additional screening facilities be installed to
accommodate expansion to either the 18-mgd or 20-mgd flows. Additional mechanical screening capability
could be retrofitted into the existing channel currently equipped with the manually cleaned bar screen. The
installed hydraulic capacity with the additional mechanical screen is estimated at 55.5-mgd. A replacement
by-pass channel with manual screen would also be provided as a part of the 18-mgd or 20-mgd flow upgrades
for reliability purposes.
The two current stirred vortex grit units would have a total combined flow capacity of 60-mgd in the absence
of other downstream flow restrictions. However,the 4-ft width Parshall flume located downstream of the grit
removal system has an unsubmerged flow measurement capacity of 43.9-mgd and is thus capacity limiting
for the grit removal system. The downstream flow limitation through the existing Parshall flume will
accommodate expansion through the 16-mgd design flow condition. Expansion to the 18-mgd and 20-mgd
design condition will require an additional stirred vortex grit removal system, including grit pumping, and flow
measurement capability to accommodate the peak flow conditions with one grit removal unit out of service.
The estimated cost of the additional mechanical climber screen, bypass channel, 18-ft stirred vortex grit
removal system, grit pumps, Parshall flume, and associated piping is$850,000.
Summary and Recommendations
No additional primary clarification and preliminary treatment facilities are recommended for the 16-mgd design
condition. Additional preliminary treatment facilities are recommended for expansion to the 18-mgd or 20-mgd
design condition at an estimated cost of$850,000. Additional primary clarification facilities are recommended
for expansion to the 20-mgd design condition at an estimated cost of$1,200,000.
HAZEN AND SAWYER,P.G.
Job.No.30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen&Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 5—Biological Treatment Processes
H&S Job. No. 30500
•
The Hominy Creek Wastewater Management Facility (HCWWMF) is planned for upgrade and expansion to
treat future peak month flows of 20-mgd. This technical memorandum evaluates the liquid treatment process
options required to accommodate expansion to maximum month flow capacities of 14-mgd, 16-mgd, 18-mgd
and 20-mgd. The existing liquid treatment process configuration, 5-stage biological nutrient removal, will be
utilized to meet liquid treatment needs through the expansion flows.
Current Biological Treatment Process Description
The current 14-mgd biological treatment process at the Hominy Creek facility consists of a 5-stage activated
sludge system designed and operated for enhanced biological phosphorus removal and total nitrogen removal
(nitrification and denitrification). Fine bubble aeration is used for oxygen transfer capability in the main
aeration tank and jet mixing with aeration capability is provided in the 1s` and 2"8 anoxic tanks. Solids
separation is accomplished in conventional secondary clarifiers. An overview of the primary biological
treatment unit process tankage and equipment is summarized in Table 1.
Table 1. Biological Treatment Unit Process Summary
Unit Process Description
Biological Phosphorus Removal(BPR)Tankage
Number 1
Number of Cells 5
BPR Tankage Volume
Cell No 1 Volume, m-gallons 0.32
Cell No 2 Volume, m-gallons 0.32
Cell No 3 Volume, m-gallons 0.32
Cell No 4 Volume, m-gallons 0.30
Cell No 5 Volume, m-gallons 0.32
Total Tankage Volume, m-gallons 1.58
HRT at 14-mgd, hrs 2.70
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 2 of 14
Table 1. Biological Treatment Unit Process Summary (Continued)
Unit Process Description
Biological Phosphorus Removal (BPR)Tankage
BPR Tank Mixing
Cell No 1 Mixers 2
Cell No 2 Mixers 2
Cell No 3 Mixers 2
Cell No 4 Mixers 2
Cell No 5 Mixers 4
Total Mixers
12
BPR Recirculation Pumping
From Cell No.4 to Cell No. 1 2
Capacity, gpm each 250
Aeration Tankage
Number of Trains 6
Design MLSS, mg/L 2,500
MLVSS/MLSS Ratio 0.75
Design Nitrification Safety Factor 1.0
Aeration Tankage Volume
1st Anoxic Zone Tank Volume, m-gallons 0.153
Aerobic Zone Tank Volume, m-gallons 0.480
2nd Anoxic Zone Tank Volume, m-gallons 0.153
Re-aeration Zone Volume, m-gallons 0.057
Total Aeration Tankage Volume, m-gallons 5.058
HRT at 14-mgd, hrs 8.7
Aeration System
Type—Aeration Basin Fine Bubble
Number of Diffusers per Train 918
Type— 15S and 2nd Anoxic Basins Jet Mixing/Aeration
Number of Nozzles per Basin 8
Aeration Blowers
Number 3
Blower Capacity, scfm each 6,200
Firm Capacity, scfm 12,400
Total Capacity, scfm 18,600
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 3 of 14
Table 1. Biological Treatment Unit Process Summary(Continued)
Unit Process Description
Secondary Clarification and RAS Pumping
Number of Clarifiers 5
Total Installed Surface Area, ft2 38,800
SOR at 14-mgd, gpd/ft2 360
Design RRAs(i.e., QRAs/QINF) 1.0
Design CRAS, mg/L 5,000
Applied SLR at 14-mgd, lb/day-ft2 15.0
Clarifier No. 1
Diameter,ft 130
Sidewater Depth,ft 14
Number of RAS Pumps 2
RAS Pump Capacity, gpm each 3,000
Firm RAS Pump Capacity, gpm 3,000
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAS=5,000 mg/L, lb/day-ft2 13.6
Total SLR @ CRAs=5,000 mg/L, lb/day-ft2 27.2
Clarifier No. 2&3
Diameter,ft 95
Sidewater Depth, ft 9.83
Number of RAS Pumps 4
RAS Pump Capacity, gpm each 1,900
Firm RAS Pump Capacity, gpm 3,800
Total RAS Pump Capacity, gpm 7,600
Firm SLR @ CRs=5,000 mg/L, lb/day-ft2 16.1
Total SLR @ CRs=5,000 mg/L, lb/day-ft2 32.2
Clarifier No. 4&5
Diameter, ft 85
Sidewater Depth, ft- 12.25
Number of RAS Pumps 3
RAS Pump Capacity, gpm each 1,750
Firm RAS Pump Capacity, gpm 3,500
Total RAS Pump Capacity, gpm 5,250
Firm SLR @ CRAS=5,000 mg/L, lb/day-ft2 18.5
Total SLR @ CRs=5,000 mg/L, lb/day-ft2 27.8
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.5 DRAFT- For Review and Comment
City of Wilson
Page 4 of 14
Liquid Treatment Process Loading Rates
The raw influent is treated by primary clarification for organic(BOD5)and solids removal(TSS) upstream of
the biological treatment process. For the purpose of this study it was assumed that 25 percent of the influent
BOD5, 50 percent of the influent total suspended solids, and 10 percent of the influent total Kjeldahl nitrogen
were removed by primary clarification upstream of the biological treatment process. The influent loadings,
post-primary clarification, are shown in Table 2.
Table 2. Biological Treatment Process Loadings
Maximum Month Design Flow
14-mgd' 16-mgd 18-mgd 20-mgd
Annual Average
Flow, mgd 11.1 11.9 13.3 14.8
TSS, lb./day 15,050 12,850 14,450 15,550
BOD5, lb./day 12,470 18,530 20,850 23,180
TKN, lb./day 1,810 1,150 1,310 1,450
TP, lb./day 380 420 420 420
Peak Month
Flow, mgd 14.0 16.0 18.0 20.0
TSS, lb./day 20,550 16,700 18,800 20,900
BOD5, lb./day 16,780 22,280 25,050 27,830
TKN, lb./day 2,330 2,750 3,110 3,450
TP, lb./day 540 590 660 730
1 Conditions are based on the Contract 3A/3B Design Basis
Design Effluent Limits
The Hominy Creek Wastewater Management Facility operates under NPDES permit NC-0023906. The permit
is currently undergoing regulatory review and was issued in draft form May 25, 2000 with discharge effluent
limits for both the 12-mgd and 14-mgd operating conditions. The proposed limits for major constituents at the
14-mgd capacity condition are shown in Table 3. The most significant change in effluent limits are a reduction
in the allowable ammonia concentration from 4 mg/L to 2 mg/L in the winter period (11/01-03/31) and from
2 mglL to 1 mg/L during the summer period (04/01-10/31). These proposed limits for will be used to evaluate
capacity of the existing facility and proposed expansion facilities.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 5 of 14
Table 3 Hominy Creek Proposed Discharge Limits
Summer Limits(04/01-10/31) Winter Limits(11/01-03/31)
Monthly Average Weekly Average Monthly Average Weekly Average
6ODe,20' , mg/L 5.0 7.5 10.0 15.0
TSS, mg/L 30.0 45.0 30.0 45.0
NH3-N, mg/L 1.0 — 2.0 --
Total P1, mg/L 2.0 2.0
Dissolved Oxygen2, mg/L >7.0 >7.0
Fecal Coliform3, MPN/mL <200 <400 <200 <400
Total Residual Chlorine° 18 18
1 Total P is Quarterly Average w/weekly composite sampling.
2 Dissolved Oxygen is based on a daily grab.
3 Fecal Coliform is based on geometric mean.
' Total Residual Chlorine is a daily grab and units are µg/L
Process Evaluation Loading—14-mgd
Proposed reductions to the allowable summer and winter ammonia discharge concentrations that are
proposed in the permit renewal will have an adverse impact on the adequacy of aeration tankage provided
at the facility. The current tankage under construction (Contract 3A&3B)was designed to meet much less
stringent ammonia limits with a nitrification safety factor of 1.0 during winter operating conditions. Reductions
in the allowable effluent ammonia concentration effectively reduce the nitrification safety factor to less than
1.0 under the same operating conditions. Several options are available to address the lower proposed
ammonia limits, as follows:
Option A—Increase System Inventory
Under this option the activated sludge system is operated with a higher overall solids inventory resulting in
an increased sludge age. implementation of Option A would require the design MLSS concentration to be
raised approximately 28 percent to 3,200 mg/L in order to re-establish a nitrification safety factor of 1.0 for the
system. Under the increased MLSS concentration the return activated sludge underflow concentration would
need to be maintained at greater than 6,200 mg/L in order to remain within the facility's firm RAS pumping
capacity. There is no additional capital cost associated with Option A.
More Aeration Tankage
Option B Operate g
P p
Under this option the activated sludge system is operated with the 2nd anoxic tank volume functioning in an
aerobic treatment mode using the recently installed jet aeration/mixing system. Utilization of the 2nd anoxic
tank volume in this service will result in the loss of this volume for denitrification service. Loss of the 21d anoxic
tank from denitrification service will result in effluent nitrate concentrations from the aeration tankage in the
range of 6-10 mg/L based on typical influent loadings and nitrified recycle flows to the 1St anoxic tank.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 6 of 14
Implementation of Option B maintains the current design MLSS concentration of 2,500 mg/L. The increased
active aeration volume also resulted in an increase to the nitrification safety factor to approximately 1.1. Under
this option the return activated sludge underfiow concentration would need to be maintained at greater than
5,000 mg/L in order to remain within the facility's firm RAS pumping capacity. There is no additional capital
cost associated with Option B.
Option C—Construct More Aeration Tankage
Under this option one additional train of aeration tankage is installed in the activated sludge treatment system.
The additional aeration tankage allows operation at an increased solids inventory while maintaining a lower
MLSS concentration than possible under Option A. The lower MLSS concentration will result in decreased
solids loading rates to the clarifiers. The Option C design uses a MLSS concentration of 2,700 mg/L to yield
a nitrification safety factor of approximately 1.0. Under this option the return activated sludge underflow
concentration would need to be maintained at greater than 5,300 mg/L in order to remain within the facility's
overall firm RAS pumping capacity. The additional capital cost of one aeration basin train is estimated at
$1,500,000 without contingencies. A process summary for the biological treatment tankage proposed under
Option C is presented in Table 4. No additional clarification capacity is anticipated.
Table 4. Biological Treatment Unit Process Summary—Option C
Unit Process Description
Aeration Tankage
Number of Trains 7
Design MLSS, mgfL 2,700
MLVSS/MLSS Ratio 0.75
Nitrification Safety Factor 1.0
Aeration Tankaae Volume
1s`Anoxic Zone Tank Volume, m-gallons 0.153
Aerobic Zone Tank Volume, m-gallons 0.480
2"4 Anoxic Zone Tank Volume, m-gallons 0.153
Re-aeration Zone Volume, m-gallons 0.057
Total Aeration Tankage Volume, m-gallons 5.901
HRT at 14-mgd, hrs 10.1
Aeration Blowers
Number 3
Blower Capacity, scfm each 6,200
Firm Capacity, scfm 12,400
Total Capacity, scfm 18,600
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 7 of 14
Process Evaluation Loading—16-mqd
Based on the plant's compliance history and the proposed lower ammonia limits, it is recommended that
aeration tank sizing for the expanded flow condition be based on a minimum nitrification safety factor of 1.25.
Expansion to the 16-mgd maximum month design condition will require construction of four additional aeration
trains(10-total at 1.6-mgd per train)operating at a design MLSS concentration of 2,500 mg/L to yield a 1.25
nitrification safety factor. Total nitrogen removal capability is provided in a 4-stage Bardenpho process
configuration. The increased design flow will increase the clarifier surface overflow rates to 412 gpd/ft2 which
is slightly greater than the recommended 400 gpd/ft2 surface overflow rate typically used for design. For this
expansion increment it is recommended that no additional secondary clarification facilities be provided. •
Accommodation of this expansion option will also require demolition of several other existing facilities located
on the plant site. The additional aeration basin tankage will also encroach on the existing NPW Storage
Building and Blower Building located south of the existing aeration tanks. Both of these structures and their
associated functionality will need to be relocated and reestablished prior to constructing the new aeration
tankage. Estimated costs for demolition and construction for expanding biological treatment facilities to 16-
mgd, excluding contingencies are shown in Table 5.
Table 5. Estimated Capital Cost—16mgd
Unit Process Capital Cost
Aeration Tankage $6,000,000
Demolition $200,000
Blower Building $600,000
Blower Building Electrical $400,000
NPW Storage Building $200,000
TOTAL $7,400,000
A process summary for expansion to 16-mgd is shown in Table 6.
Table 6. Biological Treatment Unit Process Summary—16mgd
Unit Process Description
Aeration Tankage
Number of Trains 10
Design MLSS, mg/L 2,500
Nitrification Safety Factor 1.25
Total Aeration Tankage Volume, m-gallons 8.430
HRT at 16-mgd, hrs 12.64
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 8 of 14
Table 6. Biological Treatment Unit Process Summary—16mgd (Continued)
Unit Process Description
Aeration Blowers
Number 3
Blower Capacity, scfm each 6,200
Firm Capacity, scfm 12,400
Total Capacity, scfm 18,600
Secondary Clarification and RAS Pumping
Number of Clarifiers 5
Total Installed Surface Area, ft2 38,800
SOR at 16-mgd, gpd/ft2 412
Design RRAs(i.e., QR,,s/QINF) 1.0
Design CR,s, mg/L 5,000
Applied SLR at 16-mgd, lb/day-ft2 17.2
Clarifier No. 1
Diameter, ft 130
Firm RAS Pump Capacity, gpm 3,000
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAs=5,000 mg/L, lb/day-ft2 13.6
Total SLR @ CRAs= 5,000 mg/L, Ib/day-ft2 27.2
Clarifier No. 2 & 3
Diameter, ft 95
Firm RAS Pump Capacity, gpm 3,800
Total RAS Pump Capacity, gpm 7,600
Firm SLR @ CRAs= 5,000 mg/L, lb/day-ft2 16.1
Total SLR @ C,,s= 5,000 mg/L, lb/day-ft2 32.2
Clarifier No.4 &5
Diameter, ft S5
Firm RAS Pump Capacity, gpm 4,500
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAs= 5,000 mg/L, lb/day-ft2 14.3
Total SLR @ C,As=5,000 mg/L, lb/day-ft2 19.0
Process Evaluation Loading—18-mqd
Expansion to the 18-mgd maximum month design condition will require construction of six additional aeration
trains(12-total at 1.5-mgd per train)operating at a design MLSS concentration of 2,500 mg/L. Twelve aeration
trains would yield a slightly improved nitrification safety factor of 1.35 under design conditions. Total nitrogen
removal capability is provided in a 5-stage Bardenpho process configuration. The increased design flow will
require additional clarification surface area in order to keep hydraulic loadings rates below 400 gpd/ft2 and
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 9 of 14
solids loading rates within the firm RAS pumping capacity. For this expansion increment it is proposed that
the existing FC-2 and FC-3 95-ft diameter clarifiers be replaced with two new 130-ft diameter clarifiers along
with upgraded RAS pumping capacity to accommodate the larger diameter clarifiers. Following these
modifications, and the loss of FC-5 due to space conflicts with the additional aeration basin tankage,the total
operable clarification surface area will be increased to 45,500 ft2. Increased organic loadings to the process
under the 18-mgd design condition will also require the addition of another blower to meet the peak day
aeration demand. Further description of the aeration requirements is included below in the section on
"Process Oxygen Transfer Capacity".
Accommodation of this expansion option will also require demolition of several other existing facilities located
on the plant site. The additional aeration basin tankage will also encroach on the existing NPW Storage
Building, Blower Building, Emergency Generator,and Fuel Storage Area located south of the existing aeration
tanks. These structures and their associated functionality will need to be relocated and reestablished prior
to constructing the new aeration tankage. Estimated costs for demolition and construction for expanding
biological treatment facilities to 18-mgd,excluding contingencies are shown in Table 7.
Table 7. Estimated Capital Cost—18mgd
Unit Process Capital Cost
Aeration Tankage $9,000,000
Demolition $200,000
FC-2A Clarifier Construction $1,200,000
FC-3A Clarifier Construction $1,200,000
RAS Pump Station $500,000
Blower Building $600,000
Aeration Blower $100,000
Blower Building Electrical $400,000
NPW Storage Building $200,000
Relocate Generator and Fuel Storage $100,000
TOTAL $13,500,000
A process summary for biological treatment facilities expansion to 18-mgd is shown in Table 8.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 10 of 14
Table 8. Biological Treatment Unit Process Summary—18mgd
Unit Process Description
Aeration Tankage
Number of Trains 12
Design MLSS, mg/L 2,500
Nitrification Safety Factor 1.25
Total Aeration Tankage Volume, m-gallons 10,12
HRT at 18-mgd, hrs 13.49
Aeration Blowers
Number 4
Blower Capacity, scfm each 6,200
Firm Capacity, scfm 18,600
Total Capacity, scfm 24,800
Secondary Clarification and RAS Pumping
Number of Clarifiers 4
Total Installed Surface Area, ft2 45,500
SOR at 18-mgd, gpd/ft2 396
Design RRAs (i.e., QRAS/QINF) 1.0
Design CRAB, mg/L 5,000
Applied SLR at 18-mgd, lb/day-ft2 16.5
Clarifier No. 1
Diameter,ft 130
Firm RAS Pump Capacity, gpm 3,000
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CR,s=5,000 mg/L, lb/day-ft2 13.6
Total SLR @ CRAs=5,000 mg/L, lb/day-ft2 27.2
Clarifier No. 2A&3A
Diameter, ft 130
Firm RAS Pump Capacity, gpm 7,200
Total RAS Pump Capacity, gpm 10,800
Firm SLR @ CRAs=5,000 mg/L, lb/day-ft2 16.3
Total SLR @ CRAs=5,000 mg/L, lb/day-ft2 24.4
Clarifier No.4
Diameter, ft 85
Firm RAS Pump Capacity, gpm 4,500
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAS=5,000 mg/L, lb/day-ft2 47.6
Total SLR @ CRAS= 5,000 mg/L, lb/day-ft2 63.5
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 11 of 14
Process Evaluation Loading—20-mgd
Expansion to the 20-mgd maximum month design condition will require construction of seven additional
aeration trains(13-total at 1.54-mgd per train)operating at a design MLSS concentration of 2,500 mg/L.This
would yield a 1.30 nitrification safety factor. Total nitrogen removal capability is provided in a 5-stage
Bardenpho process configuration. The increased design flow will require additional clarification surface area
in order to keep hydraulic loadings rates below 400 gpd/ft2 and solids loading rates within the firm RAS
pumping capacity. For this expansion increment it is proposed that the existing FC-2 and FC-3 95-ft diameter
clarifiers and FC-4 85-ft diameter clarifier be replaced with three new 130-ft diameter clarifiers along with
upgraded RAS pumping capacity to accommodate the larger diameter clarifiers. Following these
modifications, and the loss of FC-5 due to space conflicts with the additional aeration basin tankage, the total
operable clarification surface area will be increased to 53,000 ft2. Increased organic loadings to the process
under the 20-mgd design condition will also require the addition of another blower to meet the peak day
aera
tion demand. Further description of the aeration requirements is included below in the section on
"Process Oxygen Transfer Capacity".
Accommodation of this P
expansion option will also require demolition of several other existing facilities located
P
on the plant site. The additional aeration basin tankage will also encroach on the existing NPW Storage
Building, Blower Building, Emergency Generator, and Fuel Storage Area located south of the existing aeration
tanks. These structures and their associated functionality will need to be relocated and reestablished prior
to constructing the new aeration tankage. Estimated costs for demolition and construction for expanding
biological treatment facilities to 20-mgd, excluding contingencies are shown in Table 9.
Table 9. Estimated Capital Cost—20mgd
Unit Process Capital Cost
Aeration Tankage $10,500,000
Demolition $300,000
FC-2A Clarifier Construction $1,200,000
FC-3A Clarifier Construction $1,200,000
FC-4A Clarifier Construction $1,200,000
RAS Pump Station (FC-2A&FC-3A) $500,000
RAS Pump Station (FC-4A) $400,000
Blower Building $600,000
Aeration Blower _ $100,000
Blower Building Electrical $400,000
NPW Storage Building $200,000
Relocate Generator and Fuel Storage $100,000
TOTAL $16,700,000
A process summary for biological treatment facilities expansion to 20-mgd is shown in Table 10.
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 12 of 14
Table 10. Biological Treatment Unit Process Summary—20mgd
Unit Process Description
Aeration Tankage
Number of Trains 13
Design MLSS, mg/L 2,500
Nitrification Safety Factor 1.25
Total Aeration Tankage Volume, m-gallons 10.96
HRT at 20-mgd, hrs 13.15
Aeration Blowers
Number 4
Blower Capacity, scfm each 6,200
Firm Capacity, scfm 18,600
Total Capacity, scfm 24,800
Secondary Clarification and RAS Pumping
Number of Clarifiers 4
Total Installed Surface Area, ft2 53,000
SOR at 20-mgd, gpd/ft2 380
Design RRAS(i.e., QRAg/QINF) 1.0
Design CRAB, mg/L 5,000
Applied SLR at 20-mgd, lb/day-ft2 15.7
Clarifier No. 1
Diameter, ft 130
Firm RAS Pump Capacity, gpm 3,000
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAs=5,000 mglL, lb/day-ft2 13.6
Total SLR @ CRA3=5,000 mg/L, lb/day-ft2 27.2
Clarifier No. 2A&3A
Diameter, ft 130
Firm RAS Pump Capacity, gpm 7,200
Total RAS Pump Capacity, gpm 10,800
Firm SLR @ CRAS=5,000 mg/L, lb/day-ft2 16.3
Total SLR @ CRAs=5,000 mg/L, lb/day-ft2 24.4
Clarifier No.4A
Diameter, ft 130
Firm RAS Pump Capacity, gpm 4,500
Total RAS Pump Capacity, gpm 6,000
Firm SLR @ CRAS=5,000 mg/L, lb/day-ft2 20.3
Total SLR @ C'RAS=5,000 mg/L, lb/day-ft2 27.1
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 13 of 14
Process Oxygen Transfer Capability
Oxygen transfer capability in the biological treatment process is provided by a combination of fine bubble
diffusers in the aeration basins and jet aeration nozzles in the anoxic treatment zones. Compressing
atmospheric air provides aeration basin oxygen transfer capacity. Total aeration air demand is a function of
both the organic and nitrification oxygen requirements and the oxygen transfer efficiency of the fine bubble
diffusers and jet aeration systems. Aeration blower volumetric capacity for each of the expansion conditions
is shown in Table 11.
Table 11. Aeration Blower Capacity Requirements
Design Condition 5-Stage BNR 3-Stage BNR
(Peak Month) Peak Month Peak Day Peak Month Peak Day
14-mgd 5,930 18,750 6,590 16,320
16-mgd 6,630 18,460 7,610 17,620
18-mgd 7,460 20,780 8,570 19,840
20-mgd 8,290 23,090 9,520 22,040
The existing blower firm capacity is 12,400 scfm with two of the three 6,200 scfm blowers operating. Peak
aeration volumetric capacity is 18,600 scfm with all blowers operating. The existing blower capacity is
sufficient to meet the 14-mgd and 16-mgd design conditions operating in either a 3-stage or 5-stage BNR
process configuration. Additional blower capacity will be required to accommodate the 18-mgd and 20-mgd
design conditions. One additional 6,200 scfm blower would provide a firm capacity of 18,600 scfm and a peak
aeration capacity of 24,800 scfm. The cost of an additional blower, excluding contingencies, is$100,000.
Summary and Recommendations
Estimated capital cost, excluding contingencies, for the selected expansion options are shown in Table 12.
Costs for the 14-mgd option assume Option C is selected to accommodate full BNR capability under winter
peak month loading condition. Options A and B do not require construction of additional tankage or installation
of additional equipment.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.5 DRAFT-For Review and Comment
City of Wilson
Page 14 of 14
Table 12. Capital Cost Summary
Maximum Month Design Flow
14-mgd 16-mgd 18-mgd 20-mgd
Aeration Tankage $1,500,000 $6,000,000 $9,000,000 $10,500,000
Demolition $200,000 $200,000 $300,000
FC-2A Construction $1,200,000 $1,200,000
FC-3A Construction $1,200,000 $1,200,000
FC-4A Construction $1,200,000
RAS Pump Station (FC-2A&FC-3A) $500,000 $500,000
RAS Pump Station(FC-4A) $400,000
Blower Building $600,000 $600,000 $600,000
Blower Building Electrical $400,000 $400,000 $400,000
New Aeration Blower $100,000 $100,000
NPW Storage Building $200,000 $200,000 $200,000
Relocate Generator and Fuel Storage $100,000 $100,000
Total $1,500,000 $7,400,000 $13,500,000 $16,700,000
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30,2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 6—Effluent Filtration Systems
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility(HCWWMF)is planned for upgrade and expansion to
treat future flows of 20 mgd and beyond. This technical memorandum evaluates effluent filtration alternatives
to accommodate future expansion.This technical memorandum will evaluate requirements for expansion to
a future design peak month flow capacity of 16-mgd, 18-mgd, and 20-mgd. The range of expansion flows
considered are provided to allow the City to develop a long term master plan to accommodate capacity growth
at the treatment plant, and to better understand the economic implications of the next plant capacity expansion
project. This memorandum specifically will examine the issues related to effluent filtration.
Existing Effluent Filtration Facilities
Effluent filtration facilities were provided as a part of the 14-mgd Hominy Creek Wastewater Management
Facility Upgrade and Expansion (Contract 3A and 38). The existing major effluent filtration equipment
installed during the upgrade project is as follows:
Coarse Media Effluent Filters Five(5) Filter Bays
9.5-ft x 53-ft(503.5-ft2 each)
Backwash Pumping Two(2) Pumps
3,250 gpm @ 27-ft TDH (each)
Backwash Storage One Bay
15.5-ft x 49-ft(46,900 gallons)
Backwash Reclaim Pumping Two(2) Pumps
1,400 gpm @ 58-ft TDH (each)
Backwash Reclaim Storage Two(2) Bays
15-ft x 53-ft(60,400 gallons each)
Expansion Conventional Effluent Filtration
The current effluent filtration facility was sized using a filter hydraulic loading rate of 4.0 gallons per minute
per square foot(gpm/ft2)at the 14-mgd maximum month flow design condition. Expansion of the conventional
effluent filtration capacity will be based on maintaining the hydraulic loading rate at less than 4.0 gpm/ft2 with
all filters in service under peak month loading conditions. The proposed expansion effluent filtration
requirements are shown in Table 1
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.6 DRAFT-For Review and Comment
City of Wilson
Page 2 of 4
Table 1. Conventional Effluent Filtration Requirements
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Average Annual Flow, mgd 11.0 11.9 13.3 14.8
Number of Filter Beds 5 6 7 7
Filter Area(All-in-Service), ft2 2,518 3,021 3,525 3,525
Filter Area(One-Out-of-Service), ft2 2,014 2,518 3,021 3,021
Filter Hydraulic Loading (All in Service)
Average Annual Flow, gpmlft2 3.04 2.72 2.63 2.92
Maximum Month Flow, gpm/ft2 3.86 3.68 3.55 3.94
Filter Hydraulic Loading (One-out-of Service)
Average Annual Flow, gpm/ft2 3.80 3.27 3.06 3.41
Maximum Month Flow, gpm/ft2 4.83 4.41 4.14 4.60
One additional filter bay, added to the existing effluent filtration facility,will be necessary for expansion to 16-
mgd and two additional filter bays will be required to expand the facility to 18-mgd or 20-mgd. The existing
filter backwash reclaim pumping system will continue to be adequate and will provide the necessary capacity
to empty one filter backwash reclaim storage tank in approximately 45-minutes following a filter backwash
event. The existing filter backwash pump will be adequate to handle expansion to the 7-filter bay condition
associated with the 20-mgd maximum month design condition. The estimated incremental capital cost,
excluding engineering and contingencies, associated with adding a single filter bay for the 16-mgd expansion
is$450,000. The estimated capital cost, excluding engineering and contingencies, is$900,000 for adding two
filter bays for the 18-mgd and 20-mgd expansions.
Expansion Denitrification Effluent Filtration
Additional denitrification capacity can be provided by expanding the current filters using a filter hydraulic
loading rate of 2.0 gpm/ft2 which would effectively double the hydraulic residence time in the filter bed. The
increased residence time, combined with an external carbon substrate(i.e., methanol),would allow the filter
to serve the dual purpose of filtration and biological denitrification. Operation in a denitrification mode would
also allow for increased total nitrogen removal effectiveness when operating the upstream biological treatment
process in a 3-stage(anaerobic-anoxic-aerobic) process configuration.
Expansion of the effluent filtration capacity at the plant for each of the design condition maximum month flow
rates using denitrification filtration will be evaluated using a 2.0 gpm/ft2 maximum hydraulic loading rate with
all units in operating service. The proposed expansion effluent filtration requirements are shown in Table 2.
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.6 DRAFT-For Review and Comment
City of Wilson
Page 3 of 4
Table 2. Denitrification Effluent Filtration Requirements
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Average Annual Flow, mgd 11.0 11.9 13.3 14.8
Number of Filter Beds 10 12 13 14
Filter Area (All-in-Service),ft2 5,035 6,042 6,546 7,049
Filter Area (One-Out-of-Service), ft2 4,532 5,539 6,042 6,546
Filter Hydraulic Loading (All in Service)
Average Annual Flow, gpm/ft2 1.52 1.36 1.41 1.46
Maximum Month Flow, gpm/ft2 1.93 1.84 1.91 1.97
Filter Hydraulic Loading (One-out-of Service)
Average Annual Flow, gpm/ft2 1.69 1.49 1.53 1.57
Maximum Month Flow, gpm/ft2 2.15 2.01 2.07 2.12
Each additional filter bay, above the currently installed will cost approximately $450,000. The process and
economic evaluation of 3-stage BNR(anaerobic-anoxic-aerobic)followed by denitrification filters versus 5-
stage BNR(anaerobic-anoxic-aerobic-anoxic-aerobic)followed by conventional filtration is presented in the
evaluation of liquid treatment options in Technical Memoranda No. 5.
Summary and Recommendations
Expansion of the facility beyond the current 14-mgd maximum month rated capacity will require an expansion
to the effluent filtration facilities to maintain reasonable filter hydraulic loading rates for either the conventional
or denitrification filtration options. Approximately one additional filter cell is recommended for each 2.9-mgd
capacity for conventional filtration and 1.45-mgd capacity for denitrification filtration. The recommended
facilities and estimated costs for both the conventional and denitrification filtration options are shown in Table
3. An evaluation of costs and benefits of conventional filtration versus denitrification filtration is presented in
the evaluation of liquid treatment options in Technical Memoranda No. 5.
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.6 DRAFT- For Review and Comment
City of Wilson
Page 4 of 4
Table 3. Summary of Facilities and Estimated Costs
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Conventional Filtration
Number of Filter Beds 5 6 7 7
Filtration Cost $450,000 $900,000 $900,000
Denitrification Filtration
Number of Filter Beds 10 12 13 14
Filtration Cost $2,250,000 $3,150,000 $3,600,000 $4,050,000
Incremental Denitrification Facilities
Number of Filter Beds 5 6 6 7
Filtration Cost $2,250,000 $2,700,000 $2,700,000 $3,150,000
HAZEN AND SAWYER,P.C.
Job No.30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 7—Effluent Disinfection Systems
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility is planned for upgrade and expansion to treat future
flows of 20 mgd and beyond. This technical memorandum evaluates alternatives for effluent disinfection for
expansion to a maximum monthly flow capacity of 16-mgd, 18-mgd, and 20-mgd. This memorandum
specifically examines the issues related to effluent disinfection by ultraviolet irradiation; or chlorination and
dechlorination using liquid sodium hypochlorite and liquid sodium bisulfite.
Existing Disinfection Facilities
Effluent disinfection facilities were upgraded as a part of the 14-mgd Hominy Creek Wastewater Management
Facility Upgrade and Expansion (Contract 3A and 3B) to include equipment for liquid sodium hypochlorite
storage and dosing and liquid sodium bisulfite storage and dosing. The major disinfection equipment installed
is as follows:
Sodium Hypochiorite Storage Two (2)tanks at 7,000 gallons each
Sodium Hypochiorite Feed Pumps Four(4) pumps at 25-gph capacity each
Sodium Bisulfite Storage One(1) tank at 7,000 gallons
Sodium Bisulfite Feed Pumps Two(2) pumps at 25-gph capacity each
Chlorine Contact Tankage Post-Aeration Basin
383,700-gallons(total volume)
302,400-gallons(chlorination)
71,300-gallons(dechlorination)
Sodium Hypochiorite-Sodium Bisulfite Disinfection
This technical memorandum section will evaluate the existing facilities for performance at the selected
expansion conditions and recommend improvements to accommodate the increased flow conditions.
Chemical Feed Requirements
The chemical usage and feed rate requirements for average and peak use are shown in Table 1. Average
chlorine usage rates are based on an average chlorine dose of 4.0 mg C12/L at maximum month flow design
conditions. Peak chlorine usage rates are based on a maximum chlorine dose of 8.0 mg Cl2JL at process peak
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.7 DRAFT-For Review and Comment
City of Wilson
Page 2 of 5
(2X design flow)conditions. Sodium bisulfite usage rate is based on a dose of thee pounds sodium bisulfite
per pound of chlorine residual. A chlorine residual of 1.0 mg Cl2/L was used for the design condition and 2.5
mg CIA_for the peak condition to determine sodium bisulfite usage.
Table 1. Chemical Usage Requirements
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Process Peak Flow, mgd 28.0 32.0 36.0 40.0
Average Cl2 Usage, lb/day 470 530 600 670
Peak Cl2 Usage, lb/day 1,870 2,140 2,400 2,670
Average NaHSO3 Usage, lb/day 350 400 450 500
Peak NaHSO3 Usage, lb/day 1,750 2,000 2,250 2,500
Existing Chemical Feed Equipment Adequacy
The existing sodium hypochlorite feed system consists of four chemical feed pumps with an installed feed
capacity of 100-gph. When feeding a 10%sodium hypochlorite solution the installed pumping capacity will
deliver 1,990 pounds of chlorine per day. The existing chemical feed pumping capacity is adequate to meet
a peak 8.0 mg Cl2/L dose under the 14-mgd process peak condition when feeding a 10%sodium hypochlorite
solution. The existing sodium hypochlorite pumps could provide a peak daily dose of 2,490 pounds per day
if the feed concentration were increased to 12.5% sodium hypochlorite solution. Increasing the feed
concentration to 12.5% would enable the current system to meet peak demands up to the 18-mgd design
condition. At the 20-mgd condition the sodium hypochlorite pumps will need to be replaced with four pumps
with a capacity of approximately 35-gph. The estimated cost, excluding contingencies,to replace the existing
pumps with larger pumps of the same type is$80,000.
The existing sodium bisulfite feed system consists of two chemical feed pumps with a pumping capacity of
25-gph each for a total installed chemical feed capacity of 50-gph. The existing chemical feed pumping
capacity is adequate to meet the peak dose under peak daily flow at the 20-mgd maximum month flow design
condition when feeding a 25% sodium bisulfite solution. No improvements or expansions to the sodium
bisulfite feed system are recommended to accommodate any of the proposed expansion design conditions.
Chlorine Contact Tanks
The existing chlorination and dechlorination contact time is provided in the 54"diameter filter effluent line and
post aeration basin. Average chlorination and dechlorination contact time, calculated based on volume
allocated to each use and flow, is shown in Table 2. Generally, a chlorine contact time of at least 30-minutes
is desired under design flow conditions and 15-minutes under peak flow conditions in a plug flow type reactor.
The existing post aeration tankage volume meets the residence time evaluation criteria for the 14-mgd design
condition. However, the post aeration basin length-to-width aspect ratio, combined with the post-aeration
HAZEN AND SAWYER, P.C.
Job No.30500

Memorandum No.7 DRAFT-For Review and Comment
City of Wilson
Page 3 of 5
mixing,would point toward an expected performance behavior closer to that of a complete mixed reactor than
a plug flow reactor. Therefore, the hydraulic residence time may not be fully adequate to provide consistent
disinfection performance at any of the expanded flow conditions. It is recommended that separate single-pass
chlorination and dechlorination tankage be constructed for expansion beyond the current 14-mgd design
condition to address limitations of the existing combined post aeration, chlorination and dechlorination
tankage.
Table 2. Existing Tankage Chlorination & Dechlorination Contact Time
Maximum Monthly Flow Design Condition(mgd)
14.0 16.0 18.0 20.0
Design Daily Flow, mgd 11.1 11.9 13.3 14.8
Peak Hour Flow, mgd 32.3 40.0 45.0 50.0
Chlorination Time
HRTDDF, min 44.3 41.4 37 33.3
HRTPHF, min 15.2 12.3 11.0 9.8
Dechlorination Time
HRTDDF, min 9.2 8.6 7.7 6.9
HRTPHF, min 3.2 2.6 2.3 2.1
A 4-channel single-pass chlorine contact tank would be provided to accommodate a capacity expansion to
the 16-mgd maximum month design condition.The tank would have a channel depth of 12-feet, channel width
of 10-feet and a channel length of 120-feet. The total installed tank volume would be approximately 430,900
gallons. A 5-channel single-pass chlorine contact tank of similar geometry would be provided to
accommodate a capacity expansion to the 18-mgd and 20-mgd maximum month design conditions. These
tankage configurations would provide hydraulic residence times in excess of the 30-minute at design flow and
15-minute at peak hour flow.
Capital Cost
The capital costs associated with this alternative are in providing new chlorination and dechlorination contact
tankage.The estimated capital cost for a new 4-channel contact tank is$600,000 to accommodate up to the
16-mgd maximum month flow design condition.The estimated capital cost for a new 5-channel contact tank
is$700,000 to accommodate expansion to the 18-mgd and 20-mgd maximum month flow design conditions.
The estimated incremental cost to expand the 4-channel tank to a 5-channel tank is$100,000.
Operating Cost
Annual operating costs for liquid sodium hypochlorite chlorination and liquid sodium bisulfite dechlorination
are primarily driven my chemical costs. For this analysis, 12.5% liquid sodium hypochlorite unit cost is
estimated at$0.50 per gallon and 38% liquid sodium bisulfite unit cost is estimated at $1.00 per gallon.
Estimated annual chemical usage and estimated annual chemical costs are shown in Table 3.
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.7 DRAFT-For Review and Comment
City of Wilson
Page 4 of 5
Table 3. Estimated Annual Chemical Usage and Costs
Maximum Monthly Flow Design Condition(mgd)
14.0 16.0 18.0 20.0
Average Daily Flow, mgd 11.1 11.9 13.3 14.8
12.5% NaOCl Usage,gal. 128,700 138,400 155,600 173,000
38.0% NaHSO3 Usage, gal 24,400 26,300 29,600 32,800
NaOCI Cost, $/year $64,300 $69,200 $77,800 $86,500
NaHSO3 Cost, $/year $24,400 $26,300 $29,600 $32,800
Total Chemical Cost,$/year $88,700 $95,500 $107,400 $119,300
Ultraviolet Disinfection Facilities
This technical memorandum section will develop recommendations for installation of ultraviolet disinfection
facilities at the selected expansion conditions to replace the existing sodium hypochlorite and sodium bisulfite
chlorination and dechlorination facilities.
Equipment and Facility Requirements
Wastewater is disinfected by ultraviolet (UV) light concentrated at the optimal germicidal wavelength. UV
lamps are typically arranged in modules and placed in open channels or closed reactor vessels so that
wastewater is exposed to the UV light generated by the lamps. The number of lamps provided in a UV
disinfection system for a given plant flow depends on the UV dosage required(per regulations),the physical
characteristics of the water(absorbency and transmittance),and the power and type of lamps. Based on the
configuration of the Hominy Creek facility and the lack of available hydraulic head, without supplemental
pumping, a low pressure channel based UV system is recommended.
A minimum of three channels sized to provide disinfection for 5-mgd each would be required to provide UV
treatment for the 14-mgd design condition. A minimum of four channels each sized to provide disinfection for
5-mgd would be required to provide UV treatment for flows up to the 20-mgd maximum month design flow
condition. Each treatment channel would be designed to handle a bank of UV lamps arranged in the
manufacturer's design configuration to emit a sufficient dose of UV light to disinfect filtered effluent to the
desired level. Fixed weirs would be installed in each channel to minimize water level fluctuation as required
by the given UV system design.
Capital and Operatina Costs
Capital costs, including engineering and contingencies, are estimated at $800,000 for the three channel
configuration recommended for the 14-mgd maximum month flow condition and $1,100,000 for the 16-mgd,
18-mgd and 20-mgd maximum month flow conditions. The UV equipment is estimated at approximately
HAZEN AND SAWYER,P.C.
Job No.30500

Memorandum No.7 DRAFT-For Review and Comment
City of Wilson
Page 5 of 5
$180,000 per channel with the balance of the costs in tankage and other mechanical equipment. Operating
costs are estimated based on a flow placed dosing system with consideration for lamp replacement. A
summary of UV system capital and operating costs is shown in Table 4.
Table 4 Capital and Operating Cost Summary
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
Total Installed Capital Cost, $ $800,000 $1,100,000 $1,100,000 $1,100,000
Annual O&M Cost, $/yr $ 33,400 $38,200 $43,000 $47,700
Summary and Recommendations
Capital and operating costs for the existing sodium hypochlorite/sodium bisulfite system and the UV system
are summarized in Table 5,
Table 5 Disinfection Capital and Operating Cost Summary
Maximum Monthly Flow Design Condition (mgd)
14.0 16.0 18.0 20.0
NaOC1/NaHSO3
Total Installed Capital Cost, $ NA $600,000 $700,000 $780,000
Annualized Capital Cost, $/yr. NA $56,700 $66,100 $73,600
Annual O&M Cost, $/yr. $88,700 $95.500 $107.400 $119,300
Total Annual Cost, $/yr. $88,700 $152,200 $173,500 $192,900
Ultraviolet
Total Installed Capital Cost, $ $825,000 $1,100,000 $1,100,000 $1,100,000
Annualized Capital Cost, $/yr. $77,900 $103,800 $103,800 $103,800
Annual O&M Cost, $/yr. $33.400 $38.200 $43,000 $47.70.0
Total Annual Cost, $/yr: $111,300 $142,000 $146,800 $151,500
Note: Annualized Cost based on 7% interest rate, 20-year debt service. (A/P, 7%, 20yr)=0.0944.
It is recommended that the City transition from sodium hypochlorite and sodium bisulfite disinfection to
ultraviolet disinfection for flow conditions beyond the current 14-mgd permitted flow, or at such time as the
existing post-aeration/chlorine contact tank proves inadequate to meet permitted disinfection requirements.
HAZEN AND SAWYER, P.C.
Job No.30500
L

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30,2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen&Sawyer
Mr. Ronald L.Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 8—Effluent Discharge Systems
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility is planned for expansion to treat future flows of up to
20 mgd. Specifically, this technical memorandum will evaluate requirements for expansion to design
maximum monthly flows of 16-mgd, 18-mgd, and 20-mgd. The range of expansion flows considered are
provided to allow the City to develop a long term master plan to accommodate capacity growth at the
treatment plant, and to better understand the economic implications of the next plant capacity expansion
project. This memorandum specifically will examine the following issues related to effluent flow measurement
capacity and effluent discharge outfall capacity for the current and expanded flow conditions.
Effluent Flow Measurement
Effluent flow measurement is currently provided by a 3-foot width Parshall flume located adjacent to the post
aeration basin. The existing flume is installed at with a crest elevation at approximately 82.75.The estimated
water surface elevation at the outfall discharge is 83.0±at the 25-year flood condition and 85.5±at the 100-
year flood condition. Therefore, under extreme flood conditions backwater influences through the outfall line
will result in flume operation in a submerged condition resulting in limited flow measurement capacity.
The unsubmerged flow measurement capacity of the existing flume is approximately 32.6 mgd. Effluent flow
measurement capacity will therefore need to be upgraded in order to accommodate unsubmerged operation
at any of the higher peak monthly flow operating conditions. The minimum flume width for each expansion
condition is shown in Table 1.
Table 1. Effluent Parshall Flume Capacity Needs
Peak Month Peak Hour Flow Flume Width Minimum Maximum
(mgd) (mgd) (ft) (mgd) (mgd)
14.0 28.5 3.0 0.84 32.6
16.0 40.0 4.0 0.84 43.9
18.0 45.0 5.0 1.03 55.3
20.0 50.0 5.0 1.03 55.3
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.8 DRAFT- For Review and Comment
City of Wilson
Page 2 of 6
Based on the free discharge minimum and maximum flow capacity it is recommended that the City expand
the existing Parshall flume to a 5.0-foot width flume. The estimated cost for decommissioning the existing
flume and constructing a new Parshall flume including re-routing effluent piping is$300,000.
Effluent Discharge Duffel!Capacity
The existing outfall consists of a 48-inch diameter gravity outfall pipe which runs approximately 7,700 linear
feet from the current plant site to the permitted discharge point on Contentnea Creek. The existing gravity
outfall has a hydraulic capacity as shown in Table 2.
Table 2. Effluent Outfall Capacity
Operating Condition Capacity
No Backwater without submerging Parshall Flume 26 mgd
No Backwater without submerging Chlorine Contact Tank(CCT) 31 mgd
100-yr Flood in Contentnea Creek without submerging CCT 19 mgd
Based on examination of the historical operating data(1997-1999)and the associated instantaneous and daily
peaking factors the existing discharge outfall is operating near its capacity without submerging the chlorine
contact tank with no backwater effect from Contentnea Creek. The existing effluent outfall therefore must be
expanded to accommodate increased flow rates. The following options were considered in detail to
accommodate limited capacity in the existing outfall:
• Flow Equalization
• Parallel Gravity Discharge Outfall
• Parallel Pumped Discharge Outfall
An additional option, not considered for this analysis, would be to discharge peak flows from the treatment
facility directly to Hominy Swamp adjacent to the plant site. Since this would involve an intermittent discharge
and a new discharge location significant permitting issues would be involved which were beyond the scope
of this work. If this option were pursued, additional study and discussion with the regulatory agency would
be required.
Flow Equalization
Flow equalization was examined as an alternative to providing expanded effluent outfall capacity. Flow
equalization could be installed following preliminary and primary influent treatment in order to gain a dual
benefit in hydraulic control upstream of the biological treatment process in addition to relief on the outfall
discharge line. Alternatively, flow equalization capacity could be installed following secondary and tertiary
treatment in order to benefit only the outfall diffuser. In either case, the required equalization volume would
be the same.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.8 DRAFT-For Review and Comment
City of Wilson
Page 3 of 6
Equalization volume estimates were made based on peaking factors developed from the 1997-1999 effluent
flow data for selected consecutive day operating periods. These peaking factors are shown on Figure 1.
These peaking factors were applied to the selected design condition annual average flow to develop average
flows for each of the moving average periods. These flows, when they exceeded 26 mgd,were then utilized
to calculate a required equalization storage volume. The required equalization storage volumes are shown
in Figure 2.
Figure 1. Effluent Peaking Factors
3.00
2.80
2.60 • •
•
•
o
2.40
� • I
o i
•
•
rn •
•
E
E
g 1.60
1.40 -- - ---------
1.20 Peaking Factor=-0.2823•Ln(MA Period)+2.8175
R2=0.9527
1.00 - _ -
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Moving Average Period(days)
Utilization of equalization to avoid increasing hydraulic capacity of the existing outfall discharge system will
require development of significant storage volumes. The required volumes and associated storage times
preclude development of influent equalization capacity due to considerations associated with extended
storage of untreated wastewater for maximum month flow capacities beyond the current 14-mgd level.Treated
wastewater storage could be utilized for flow equalization since the extended liquid storage issues related to
raw wastewater would not apply. The estimated storage volumes and surface area requirements are shown
in Table 3.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.8 DRAFT- For Review and Comment
City of Wilson
Page 4 of 6
Figure 2. Required Equalization Storage Volume
150.00
140.00 --- - ---.- .. _ - _-------___-. _.------ ---___.------ -
130.00 —
120.00
110.00
E 100.00
0
m
3 90.00
Q
80.00
m
co
2 70.00
.q
60.00
m 50.00
Q
40.00
W
30.00
20.00 - r,
10.00 - - - - -
0.00
10 12 14 16 18 20 22 24
Maximum Month Flow(mgd)
Table 3. Effluent Flow Equalization Volume Requirements
Max Mon. Volume Required Area Required at Selected Depth (ft2)
Flow(mgd) (mg) (acre-ft) 8-ft SWD 10-ft SWD 12-ft SWD
16 11.2 34.2 186,300 149,100 124,200
18 29.9 91.8 499,900 399,900 333,300
20 66.3 203.5 1,110,000 886,600 738,800
The estimated cost to provide a lined surface impoundment for each peak month flow condition,excluding land
acquisition costs, is shown in Table 4. It was assumed that the existing fine solids storage basins could
provide sufficient equalization capacity to handle the current 14-mgd peak month flow condition. However,
the current practice of utilizing the fine solids basins for sludge storage limits the volume available for flow
equalization.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.8 DRAFT-For Review and Comment
City of Wilson
Page 5 of 6
Table 4. Estimated Effluent Equalization Costs
Max Mon. Volume Required Estimated Capital Cost($)
Flow(mgd) (mg) (acre-ft) 8-ft SWD 10-ft SWD 12-ft SWD
16 11.2 34.2 $1,900,000 $1,840,000 $1,800,000
18 29.9 91.8 $2,670,000 $2,490,000 $2,370,000
20 66.3 203.5 $4,190,000 $3,800,000 $3,530,000
Parallel Gravity Discharge Outfall
A parallel gravity discharge outfall could be constructed to increase the peak flow discharge capacity at the
treatment facility. Since this project would represent a significant capital investment with a long expected
service life flow the capacity for the'build-out' plant capacity should be provided. The peak instantaneous flow
rate associated with the 20-mgd maximum month design condition is estimated at 50-mgd. A parallel 7,700
linear foot, 48-inch diameter outfall would provide sufficient capacity (-55-mgd) to handle the peak
instantaneous flow associated with the 20-mgd maximum month build-out condition. The estimated capital
cost for a new gravity outfall line is$2,400,000.
Parallel Pumped Discharge Outfall
A parallel pumped discharge line and associated pump station could be constructed to increase peak flow
discharge capacity at the treatment facility. Again, since this project would represent a significant capital
investment with a long expected service life the flow capacity for the 'build-out' plant capacity should be
provided. The estimated costs for a 16,000-gpm capacity lift station(4-pumps @ 4,850 gpm each with a 40-ft
TDH) with submersible pumps is estimated at $3,100,000. A parallel 7,700 linear foot, 36-inch diameter
pressure line would provide sufficient discharge capacity to handle the peak instantaneous flow at the 20-mgd
maximum month condition. The estimated cost for a new pressure discharge line is $1,500,000. The
estimated total capital cost for phased development of a pumped discharge alternative is shown in Table 5.
The estimated total capital expenditure for this option is$4,600,000.
Table 5. Estimated Capital Cost for Pumped Discharge Capacity
Max. Month Capacity (gpm) Estimated Capital Cost($)
(mgd) Minimum Installed Pipeline Pump Station Total
14.0 NA NA $- $- $-
16.0 9,700 9,700 $1,500,000 $2,600,000 $4,100,000
18.0 13,200 14,500 $- $250,000 $250,000
20.0 16,700 19,400 $- $250,000 $250,000
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.8 DRAFT- For Review and Comment
City of Wilson
Page 6 of 6
Summary and Recommendations
Estimated capital costs for addressing the outfall flow measurement and discharge capacity limitations are
shown in Table 6.
Table 6. Summary of Estimated Costs
Estimated Total Installed Capital Cost
(@ Selected Maximum Month Flow)
16-mgd 18-mgd 20-mgd
Parshall Flume Replacement $300,000 $300,000 $300,000
Equalization w/Current Outfall1 $1,840,000 $2,490,000 $3,800,000
New Parallel Gravity Outfall $2,400,000 $2,400,000 $2,400,000
New Pressure Outfall and Pump Station $4,100,000 $4,350,000 $4,600,000
Equalization cost exclude land related costs
It is recommended that the existing 3-ft width Parshall flume be replaced with a new 5.0-ft width Parshall
flume. The crest elevation of the new flume should be located at the highest elevation possible without
impacting upstream unit process equipment or tankage. This will minimize the backwater influences caused
by high water conditions in Contentnea Creek under flooded conditions. Additionally, it is recommended that
the existing gravity outfall to Contentnea Creek be paralleled with a 48-inch diameter line to increase the total
installed outfall capacity. The estimated cost, excluding engineering and contingencies,for the Parshall flume
and new outfall line is$2,700,000.
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT-For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 9—Solids Handling and Stabilization
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility (HCWWMF) is planned for upgrade and expansion to
treat future peak month flows of 20-mgd. This technical memorandum evaluates the solids handling and
stabilization unit process options required to accommodate expansion to maximum month flow capacities of
14-mgd, 16-mgd, 18-mgd and 20-mgd. Waste activated sludge thickening and sludge digestion requirements
will be evaluated for each of the design capacities since these unit processes occur regardless of the
downstream disposal option selected. Following solids stabilization the following ultimate disposal options
will be examined:
• Disposal Option A—Class B liquid sludge land application
• Disposal Option B—Class B dewatered sludge land application
• Disposal Option C—Class A post-dewatering lime stabilization
• Disposal Option D—Class A post dewatering solids composting
• Disposal Option E—Class A thermal drying
Current Solids Management Practices
Residuals generated during the treatment process at Hominy Creek are currently managed using a liquid lime
stabilization process followed by land application. Two of the four digester tanks at the facility have been
converted to liquid lime storage and mixing service. The remaining two digester tanks remain in service as
anaerobic sludge digesters and are utilized for partial stabilization of primary sludge. Unthickened waste
activated sludge storage is also provided in a surface storage lagoon to accommodate periods of limited land
application disposal. The current sludge management practices are described in the "Hominy Creek
Wastewater Management Facility Sludge Management Plan"prepared by Hazen&Sawyer in February 1998
as a part of the expansion of the facility to its current 14-mgd capacity.
Estimated Solids Production Rates
Primary and waste activated sludge solids production rates were estimated for each design condition at the
maximum month and annual average operating conditions. These estimated sludge production rates are
shown in Table 1.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 2 of 18
Table 1. Estimated Solids Production Rates
Design Flow
14-mgd1 16-mgd 18-mgd 20-mgd
Peak Month Conditions
Primary Sludge Production, lb/day 21,200 16,700 18,800 20,900
Primary Sludge @ 4%, gpd 63,500 50,100 56,400 62,600
Secondary Sludge Production, lb/day 11,600 13,800 15,200 17,000
Secondary Sludge @ 0.5%, gpd 278,200 330,900 364,500 407,700
TWAS @ 5.0%, gpd 27,820 33,090 36,450 40,770
Annual Average Conditions
Primary Sludge Production, lb/day 15,600 12,900 14,000 16,000
Primary Sludge @ 4%, gpd 46,800 38,700 42,000 48,000
Secondary Sludge Production, lb/day 7,400 9,300 11,500 12,000
Secondary Sludge©0.5%, gpd 177,500 223,000 275,800 287,800
TWAS @ 5.0%, gpd 17,750 22,300 27,580 28,780
1. Sludge production estimates for the 14-mgd condition are based on the February 1998"Sludge Management Plan"prepared in
conjunction with the Contract 3A/3B Hominy Creek Expansion Project.
Waste Activated Sludge(WAS) Thickening
The existing waste activated sludge thickening facilities consist of one 1-1/2 meter gravity belt thickener and
a liquid polymer make-up and dosing system. The maximum loading rate capacity of the existing thickener
is estimated at 450 gpm at a feed solids concentration of 0.5 percent(750 pounds per hour per meter width)
by plant operating personnel. However, plant personnel report that hydraulic limitations in the current
thickening process effectively limit the hydraulic loading rate to approximately 350 gpm. Plant operating
personnel have also indicated that the existing 1-1/2 meter thickener is unreliable and requires continual
maintenance in order to remain functional and recommend replacement with a larger unit in a new thickening
facility.
Reliable WAS thickening operation is critical to the operational performance of the treatment facility since the
WAS removal rate determines the mean cell residence time (MCRT) of the biological treatment system.
Downstream sludge stabilization processes are also dependent on reliable performance of the WAS
thickening operation. Additional waste activated sludge thickening capacity is recommended to provide
capacity, redundancy, reliability and operational flexibility in the biological sludge wasting operation.
Recommended facilities and estimated operating times are shown in Table 2.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 8 of 18
A new sludge dewatering facility is proposed for housing the belt filter presses, belt filter press feed pumps,
spray wash pumps, filtrate pumps, polymer system and dewatered sludge cake materials handling equipment.
Initially the sludge dewatering facility would house three 2.0-meter belt filter presses for the 14-mgd and 16-
mgd design conditions. The estimated cost for constructing the new sludge dewatering facility, excluding
contingencies, is $2,500,000 for the 14-mgd, 16-mgd and 18-mgd design conditions. Expansion to
accommodate the 20-mgd design condition would require installation of one additional 2.0-meter belt filter
press at an estimated incremental cost, excluding contingencies, of$200,000. The estimated total cost,
excluding contingencies, to expand to the 20-mgd design condition is$2,700,000.
Disposal Option A—Class B liquid sludge land application
Class B liquid sludge land application will require sludge stabilization prior to ultimate sludge disposal.
Therefore capital costs associated with the construction of sludge thickening and digestion facilities would be
incurred in order to make this disposal option feasible. The estimated total capital cost, excluding
contingencies, for the sludge thickening and digestion facilities is$8,100,000.
Stabilized sludge would be removed from the plant site in tanker trucks with a capacity of 6,500 gallons each.
Sludge hauling is currently conducted under contract with an external service provider and is typically
conducted on a 5-day per week schedule, but could be extended to a 6-day or 7-day per week operating
schedule if required due to high sludge disposal demands. In order to make up for wet weather periods when
sludge cannot be land applied, it is estimated that the capability must be provided to haul and dispose of
sludge at a rate 1.5 times the sludge production rate. Hauling requirements based on daily sludge production
are shown in Table 7.
Table 7. Liquid Sludge Generation
Design Flow
14-mgd' 16-mgd 18-mgd 20-mgd
Peak Month Conditions _
Anaerobically Digested Sludge, gpd 91,320 83,190 92,850 103,370
Tanker Trailers/day(5-day/week) 20 18 20 23
Tanker Trailers/day(7-day/week) 14 13 15 16
Peak Trailers/day (7-day/week) 21 21 23 24
Annual Average Conditions
Anaerobically Digested Sludge, gpd 64,550 61,000 69,580 76,780
Tanker Trailers/day(5-day/week) 14 13 15 17
Tanker Trailers/day(7-day/week) 10 10 11 12
Peak Trailers/day (7-day week) 15 15 17 18
1. Estimates for the 14-mgd condition were based on the February 1998"Sludge Management Plan"prepared in conjunction with
the Contract 3A/3B Hominy Creek Expansion Project.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 9 of 18
The City of Wilson currently owns or leases a total of 1,451 acres of land for applying sludge of which 1,130
acres are planted in corn, soybeans, and wheat and can only be used for land application during the fall,
winter and spring seasons. Seasonal restrictions, due to high water table, impacts 562 acres and disqualifies,
on average, about 33%of the total(-187 acres)per year from use. Seasonal restrictions lower the available
land disposal acreage to approximately 1,264 acres. The City also has fescue and coastal bermuda hay land
that can be used for land application during the summer months when the other cropland is unavailable.
Sludge application rates vary based on the type of land, but the estimated land application capacity of the
City's available acreage is about 6,810 tons per year. Fall, spring and winter land application capacity is
estimated at 4,050 dry tons per year. Summer land application capacity is estimated at 2,760 tons per year.
At the 20-mgd design condition the average anaerobically digested sludge generation rate is 10.7 dry tons
per day, or about 3,905 dry tons per year. This sludge disposal rate represents a resource utilization rate of
about 60 percent of the total available capacity. It would appear that the City has adequate capacity to handle
the annual average land application demands. However, if this option is selected the City should pursue
additional land application permitted capacity concentrating on developing sites without seasonal application
limitations.
Supplemental sludge storage volume will be required to accommodate seasonal and wet weather limitations
on liquid sludge disposal. Seasonal limitations are most likely to impact operations during the'winter season'
from December through February (-90-days). The Hominy Creek facility should have capacity available to
store sludge that cannot be land applied during this season. Conservatively, total sludge storage
requirements were estimated assuming no land application during the winter period at peak month wasting
rates. Estimated storage requirements are shown in Table 8.
Table 8. Sludge Storage Volume Requirements
Design Flow
14-mgd1 16-mgd 18-mgd 20-mgd
Annual Average Conditions
Anaerobically Digested Sludge, gpd 91,320 83,190 92,850 103,370
Sludge Generated, gallons 8,218,800 7,487,100 8,356,500 9,303,300
Old Digester Storage, gallons 2,346,000 2,346,000 2,346,000 2,346,000
FSB No. 1 Storage, gallons 4,766,000 4,766,000 4,766,000 4,766,000
Total Available Storage, gallons 7,112,000 7,112,000 7,112,000 7,112,000
Additional Storage Required, gallons NA 375,100 1,244,500 2,191,300
1. Estimates for the 14-mgd condition were based on the February 1998"Sludge Management Plan"prepared in conjunction with
the Contract 3A/3B Hominy Creek Expansion Project.
2. Assumes none of the existing digester volume is utilized for secondary digestion capacity. If existing digestion volume is utilized
then this available storage volume is lower.
HAZEN AND SAWYER, P.C.
Job. No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 10 of 18
It is proposed that the existing anaerobic sludge digester tankage be converted to sludge storage volume to
supplement storage volume in Fine Solids Basin No. 1 (FSB-1). The existing digester volume,approximately
2,346,000 gallons, in combination with the FSB-1 volume would almost provide sufficient storage to handle
the 16-mgd design condition at average sludge production rates.Additional sludge storage volume would be
required to accommodate expansion beyond 16-mgd, if liquid land application is the selected disposal option.
For the purpose of this study it was assumed that additional volume in the existing fine solids basins(FSB-2
or FSB-3) could be converted to sludge storage for an estimated capital cost, excluding engineering and
contingencies, of$500,000. Annual operating cost, based on Hominy Creek's current liquid sludge disposal
contract cost, is estimated in Table 9.
Table 9. Class B Liquid Sludge Disposal Operating Costs
Design Flow
14-mgd' 16-mgd 18-mgd 20-mgd
Anaerobically Digested Sludge, gpd 64,600 61,000 69,600 76,800
Anaerobically Digested Sludge, gpy 23,560,000 22,265,000 25,397,000 28,028,000
Disposal Cost2, $/gallon $0.0204 $0.0204 $0.0204 $0.0204
Disposal Cost, $/year $480,600 $454,200 $518,100 $571,700
1. Estimates for the 14-mgd condition were based on the February 1998"Sludge Management Plan"prepared in conjunction with
the Contract 3A/3B Hominy Creek Expansion Project.
2. Disposal Cost is based on current liquid land application cost for sites within a 0-20 mile radius of the Hominy Creek facility
excluding the cost of lime treatment. Lime treatment cost is approximately$0.01/gallon.
Disposal Option B—Class B dewatered sludge land application
Class B dewatered sludge land application would require sludge stabilization and sludge dewatering prior to
ultimate sludge disposal. Capital costs associated with the construction of sludge thickening, anaerobic
digestion, and sludge dewatering facilities would be incurred in order to make this disposal option feasible.
The estimated capital cost, excluding engineering and contingencies, for the sludge thickening, anaerobic
digestion and sludge dewatering facilities is $10,600,000 for the 14-mgd, 16-mgd and 18-mgd design
conditions and $10,800,000 for the 20-mgd design condition. On-site covered storage (8,000 ft2) for
dewatered cake is also recommended at an additional cost, excluding engineering and contingencies,
estimated at$400,000.
Operation of the sludge dewatering unit process will also involve additional expenses related to operational
chemicals and maintenance. Plant staff have indicated that additional operations personnel would not be
required to accommodate the sludge thickening and dewatering operations. Conditioning chemical costs are
estimated at a polymer usage rate of 12.0 dry pounds of polymer per dry ton of sludge produced at a unit cost
of$4.00 per dry pound of polymer. Maintenance costs are estimated based on average annual equipment
runtime and a unit maintenance cost of$4.00 per hour runtime. Estimated final disposal costs are estimated
at$16.00 per cubic yard of solids at a wet cake density of 1,700 pounds per cubic yard and 20 percent cake
solids content. A summary of the estimated annual operating and maintenance cost for Class B dewatered
sludge land application is shown in Table 10.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.9 DRAFT- For Review and Comment
City of Wilson
Page 16 of 18
the biological process is solely dependent on dryer functionality. Alternative#2 partially addresses this issue
by providing sludge thickening capability for the waste activated sludge; however, digestion capacity to
assimilate the biological process sludge may be limited during peak sludge production periods. The annual
cost of Alternative#2, based on a 7.0%cost of capital and a 20-year design horizon, is approximately$2.36
million dollars. Alternative#3,which provides for a full Class B back-up to the sludge dryer in the anaerobic
digestion process, has an annual cost, based on a 7.0% cost of capital and a 20-year design horizon, of
approximately$2.43 million dollars. A summary of estimated thermal drying costs for the various alternatives
is shown in Table 15.
Table 15. Thermal Drying Costs Summary
Design Flow
14-mgd1 16-mgd 18-mgd 20-mgd
Annual Sludge Production, dry ton/year
Alternative#1 3,343 3,345 3,887 4,234
Alternative#2 3,343 3,345 3,887 4,234
Alternative#3 3,140 3,090 3,572 3,906
Estimated Capital Cost
Alternative#1 $14,800,000 $14,800,000 $14,800,000 $15,000,000
Alternative#2 $16,300,000 $16,300,000 $16,300,000 $16,500,000
Alternative#3 $17,500,000 $17,500,000 $17,500,000 $17,700,000
Annualized Capital Cost, $/year
Alternative#1 $1,397,100 $1,397,100 $1,397,100 $1,416,000
Alternative#2 $1,538,700 $1,538,700 $1,538,700 $1,557,600
Alternative#3 $1,652,000 $1,652,000 $1,652,000 $1,670,900
Annualized O&M Costs, $/year
Alternative#1 $583,130 $583,380 $657,490 $704,900
Alternative#2 $644,350 $660,320 $752,630 $804,170
Alternative#3 $615,570 $624,150 $707,910 $757,510
Total Annualized Costs, $/year
Alternative#1 $1,980,230 $1,980,480 $2,054,590 $2,120,900
Alternative#2 $2,183,050 $2,199,020 $2,291,330 $2,361,770
Alternative#3 $2,267,570 $2,276,150 $2,359,910 $2,428,410
Total Unit Costs,$/dry ton
Alternative#1 $592 $592 $529 $501
Alternative#2 $653 $657 $589 $558
Alternative#3 $722 $737 $661 $622
MAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 17 of 18
Summary of Operating and Capital Cost 1
A summary of the estimated capital and operating costs for the selected solids handling and disposal
alternatives investigated are shown in Table 16
Table 16. Solids Handling and Disposal Cost Comparison
Design Flow 1
14-mgd1 16-mgd 18-mgd 20-mgd
Annual Sludge Production, tond,,,/year 3,140 3,090 3,570 3,905
Option A—Liquid Land Application
Annualized Capital Cost2, $/year $764,600 $811,800 $811,800 $811,800
Annual O&M Costa, $fyear $480,600 $454,200 $518,100 $571,700
Total Annual Cost, $/year $1,245,200 $1,266,000 $1,329,900 $1,383,500
Unit Disposal Cost, $Idry ton $397 $410 $373 $354
Option B—Dewatered Land Application
Annualized Capital Cost2, $/year $1,038,400 $1,038,400 $1,038,400 $1,057,300
Annual O&M Cost, $/year $470,000 $462,500 $534,400 $584,700
Total Annual Cost, $/year $1,508,400 $1,500,900 $1,572,800 $1,642,000
Unit Disposal Cost, $Idry ton $480 $486 $441 $420
Option C—Dewatered Lime Stabilized
Annualized Capital Cost2, $/year $1,104,500 $1,104,500 $1,104,500 $1,123,400
Annual O&M Cost, $fyear $489,400 $482,100 $556,600 $608,900
Total Annual Cost, $/year $1,593,900 $1,586,600 $1,661,100 $1,732,300
Unit Disposal Cost, $Idry ton $508 $513 $465 $444
Option D—Dewatered Composting
Annualized Capital Cost2, $/year $1,217,800 $1,217,800 $1,217,800 $1,236,600
Annual O&M Cost, $/year $668,300 $661,700 $725,400 $777,000
Total Annual Cost, $/year $1,886,100 $1,879,500 $1,943,200 $2,013,600
Unit Disposal Cost, $/dry ton $601 $608 $544 $516
Option E—Thermal Drying
Annualized Capital Cost2, $/year $1,652,000 $1,652,000 $1,652,000 $1,670,900
Annual O&M Cost, $/year $615,570 $624,150 $707,910 $757,510
Total Annual Cost, $/year $2,267,570 $2,276,150 $2,359,910 $2,428,410
Unit Disposal Cost, $/dry ton $722 $737 $661 $622
1. Estimates for the 14-mgd condition were based on the February 1998"Sludge Management Plan"prepared in conjunction with
the Contract 3A/3B Hominy Creek Expansion Project.
2. Annualized capital cost is based on 20-year life at 7%rate of return, (A/P,7%,20year)=0.0944.
3. Thermal Drying Costs are based on Alternative#3(full digestion and full drying for both Class A and Class B capability).
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.9 DRAFT-For Review and Comment
City of Wilson
Page 18 of 18
Liquid sludge disposal(Option A)following waste activated sludge thickening and anaerobic digestion has the
lowest cost per ton of solids disposed on a fully allocated cost basis among the Class B solids treatment
options investigated. However, from a functional and operational perspective, management of liquid sludge
storage during land application limited periods,and subsequent disposal periods, has proven problematic at
the plants current loading rate. Temporary sludge dewatering equipment has been required on the site to aid
in the management of lagoon stored biosolids at significant cost to the City. (Note: costs associated with
temporary sludge dewatering equipment have not been factored into the process economics for Option A.)
With the increased solids loadings associated with increased loads, it is anticipated that these problems will
become more significant in the future should liquid sludge disposal be selected as the primary solids
management option. Based primarily on limitations currently experienced with the liquid sludge management
program, we recommend that sludge dewatering capability (Option B) be provided as a part of the solids
management program.
Dewatered cake lime stabilization (Option C) following thickening, digestion and dewatering has the lowest
cost per ton of solids disposed on a fully allocated cost basis among the Class A solids treatment options
investigated for each design scenario. In each of the design scenarios composting and thermal drying capital
and operating costs both exceeded the capital and operating cost associated with lime stabilization. It is
recommended that provision be made during the design of sludge dewatering and handling facilities to
accommodate a Class B residuals program that consideration be given to providing for eventual addition of
lime stabilization facilities at the Hominy Creek site.
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. Bryan R. Lisk, Hazen &Sawyer
Mr. Gerald J. Ratasky, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 10—Electrical System Evaluation
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility (HCWMF) is planned for expansion to treat future flows
of up to 20 mgd. This technical memorandum evaluates the electrical requirements for expansion to design
maximum monthly flows of 14-mgd, 16-mgd, 18-mgd, and 20-mgd. The range of expansion flows considered
are provided to allow the City to develop a long term master plan to accommodate capacity growth at the
treatment plant.
Existing Electrical Power Distribution System
The existing electrical service to the Hominy Creek Wastewater Management Facility is furnished and
maintained by the City of Wilson's Electrical Utility Department (Department). The electrical service
conductors enter the plant site overhead at the northeast end of the plant near the Pre-treatment Facility. The
overhead conductors are generally routed around the perimeter of the plant site. Step-down transformers are
located at the various structures about the plant to reduce the service voltage to the utilization voltage required
by the equipment, typically 480 VAC. The electrical service voltage is 12.47kV, three-phase, 60 Hertz.
Near the Blower Building, one set of"down" conductors is routed from a power pole, underground, to an
existing line-up of metal-clad, air-break, circuit breaker type switchgear. This main switchgear is rated 1200A,
12.47kV, three-phase. The switchgear includes a 1200A main circuit breaker and two 1200A feeder circuit
breakers. One of the feeder breakers supplies an existing 2000kVA, 12.47kV-2.4kV, three-phase liquid-filled
transformer which powers the Blower Building. The other feeder breaker protects conductors which are
routed underground to an existing power pole. These conductors used to be connected to existing overhead
conductors to supply the entire plant but are currently disconnected at the power pole.
Near the Blower Building, the Department has furnished and installed a 1600kW,480VAC, three-phase, prime
rated, diesel-fueled standby generator to supply standby power to the plant upon loss of normal utility power.
The generator is connected to a 2000kVA, 480VAC-12.47kV liquid-filled step-up transformer.This transformer
is connected to a circuit breaker that protects the conductors that are then connected to the overhead service
conductors. A motor operated gang switch located on a power pole near this equipment is used to isolate the
generator from the overhead lines when required. Under normal operating conditions, the plant loads are
served by the utility power supply via the step-down transformers and respective motor control centers,
panelboards, and other distribution equipment. Upon loss of normal power, the generator serves the plant
loads via the same overhead conductors routed about the plant site.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 2 of 13
The electrical system also has the capability of paralleling the generator with the electric utility system to"peak
shave". Under"peak shave" operation,the utility supplies 50kW of load and the standby generator serves
the balance of the operating plant load. From discussions with the Department, the current average demand
load is approximately 1000kW.
14 MGD Upgrade
The 14 MGD Upgrade will consist of adding one (1) new Aeration Basin (Aeration Basin 7) and a new
Anaerobic Digestion Facility. Aeration Basin 7 will be installed beside the existing Aeration Basin 6.The new
Anaerobic Digestion Facility will be located east of the existing Digesters 1-4. The additional loads to be
served by the plant's electrical system for the 14MGD upgrade are shown in Table 1 below.
Table 1. 14-MGD Upgrade Load List
Quantity Description HP Total Hp Total kW
Aeration Basin No.7
2 NRCY Pumps 15hp 30hp 22kW
2 Jet Mixing Pumps 10hp 20hp 15kW
2 Influent Channel Mixers 5hp 10hp 7.5kW
Subtotal 60 hp 44.5kW
Anaerobic Digestion Facility
3 Digester Recirc. Pumps 20hp 60hp 45kW
2 Digester Transfer Pumps 20hp 40hp 30kW
3 Digester Gas Compressors 20hp 60hp 45kW
3 Hot Water Pumps 7.5hp 22.5hp 17kW
3 Sludge Grinders 5hp 15hp 11kW
2 Digester Sump Pumps 3hp 6hp 4.5kW
3 BFP Feed Pumps 15hp 45hp 34kW
3 Felt Filter Presses 10hp 30hp 22kW
3 BFP Polymer Feed Pumps lhp 3hp 2.5kW
2 Conveyors 5hp 10hp 7.5kW
3 GBT Feed Pumps 15hp 45hp 34kW
2 GBTs 10hp 20hp 15kW
2 GBT Polymer Feed Pumps 1hp 2hp 1.5kW
2 TWAS Collection Pumps 15hp 30hp 22kW
Subtotal 388.5 hp 291kW
Total 448.5hp 335.5kW
A
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.10 DRAFT- For Review and Comment
City of Wilson
Page 3 of 13
Aeration Basin 7
As indicated in Table 1, a total of 60hp/44.5 kW of electrical load is associated with Aeration Basin 7. The
channel mixers, NRCY pumps and the jet mixing pumps required for Aeration Basin 7 will be supplied from
the existing motor control center, MCC-10,that is located inside the existing power center(Power Center 2)
currently supplying the existing Aeration Basins 4-6. MCC-10 is an 800A,480V,three-phase, three-wire motor
control center. One (1)new MCC section must be added to MCC-10 to accommodate the six(6)new starters
required for the new loads. There is physical space within the power center to accommodate this new section.
The estimated electrical cost, excluding engineering and contingencies, for the new Aeration Basin 7 is
$70,000.0.
Anaerobic Digestion Facility
The new Anaerobic Digestion Facility will be located east of the existing digesters. The major process
equipment to be installed at the new facility includes three(3)digester recirculation pumps, three(3)digester
transfer pumps, three (3) digester gas compressors, three (3) belt filter presses, and two (2) gravity belt
thickeners with provisions for a third. The new Anaerobic Digestion Facility will be a "stand-alone"facility that
will require a new electrical service and power distribution equipment. As indicated in Table 1, the total
connected load associated with this facility under the 14 MGD Upgrade is approximately 389hp/291kW. All
loads associated with the Anaerobic Digestion Facility will be supplied from a new motor control center(MCC-
12) that will be located in an electrical room that is part of the Digester Control Building. MCC-12 will be
designed to accommodate the third gravity belt thickener and other possible future loads at this facility. MCC-
12 will be an 800A,480V, three-phase, three-wire motor control center supplied by a new 750 KVA, 12.47kV-
480VAC, three-phase liquid-filled, pad-mount transformer. This new transformer will be supplied from the
plant's overhead electrical power system. The overhead system will have to be extended to the east by the
Department to serve the new transformer. The estimated electrical cost, excluding engineering and
contingencies, for the new Anaerobic Digestion Facility is$470,000.
16 MGD Upgrade
In addition to the modifications described above for the 14 MGD Upgrade, the 16 MGD Upgrade will consist
of the addition of three (3) new aeration basins (Aeration Basins 8-10), a new ultraviolet (UV) disinfection
facility, one (1)tertiary filter, and the replacement of two (2) existing influent pumps. An alternative design
option to replacing the two existing influent pumps is to install a new influent pumping station located near the
existing influent pumping station. Both of these design influent pumping options will be addressed in this
memorandum.The additional loads, not including small tertiary filter loads,for the 16MGD Upgrade are shown
in Table 2.
Aeration Basins
In addition to the aeration basins described in the 14MGD Upgrade, three (3) additional aeration basins
(Aeration Basins 8-10) will be installed during the 16 MGD Upgrade project. The channel mixers, NRCY
pumps and the jet mixing pumps required for Aeration Basins 8-10 will be supplied from a new motor control
center(MCC-14) located in a pre-fabricated power center(Power Center 7) similar to Power Center 2 that
currently supplies the existing Aeration Basins 4-6. Power Center 7 will house MCC-14, a dry-type
transformer and lighting panelboard, and other electrical distribution equipment required to supply the new
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 4 of 13
aeration basin loads. The new power center will also include space for additional sections of motor control
center to be used for the future Aeration Basins 11-13. MCC-14 will be an 800A,480V, three-phase,three-
wire, motor control center supplied by a new 750KVA, 12.47kV-480VAC liquid-filled, pad-mount transformer.
This new transformer will be supplied from the plants overhead electrical power system. The estimated
electrical cost,excluding engineering and contingencies, for the Aeration Basins 8-10 and related equipment
is$300,000.
Table 2. 16-MGD Upgrade Load List
Quantity Description HP Total Hp Total kW
Aeration Basins#8-10
6 NRCY Pumps 15hp 90hp 67kW
6 Jet Mixing Pumps 10hp 60hp 45kW
4 Influent Channel Mixers 5hp 20hp 15kW
Subtotal 170hp 127kW
UV Facility
4 UV Lamp Banks 20kW 80kW
Subtotal 80kW
Influent Pump Station
2 Influent Pumps (Replace old 200hp 400hp 300kW
100hp constant speed pumps)
"Option A"only
1 Influent Pumps (New pump in 150hp 150hp 112kW
new pumping station)"Option B"
only. Not included in totals below
Subtotal' 400hp 300kW
Total' 570hp 507kW
' Value represents loading for Influent Pumping Station"Option A"only.
Existing Blower Building
The addition of the new Aeration Basins 8-10 will require the existing Blower Building to be demolished. The
existing building houses three(3) 350hp, 2.4kV, motor-driven constant speed blowers which will be relocated
to the new Blower Building. The blower motors are powered from a medium voltage motor control center
located in an electrical room within the building. The motor control center is supplied by the existing main
switchgear and 2000kVA transformer described at the beginning of this memorandum. The switchgear,
transformer, and medium voltage motor control center will all be required to be demolished to allow space for
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.10 DRAFT- For Review and Comment
City of Wilson
Page 5 of 13
the construction of Aeration Basins 8-10. This equipment is also nearly 30 years old and is nearing the end
of its useful life. To keep the existing blowers in operation during the construction of the new Blower Building,
and given the age of the existing switchgear,transformer, and motor control center, it is recommended that
the new Blower Building be furnished with all new electrical distribution equipment before the existing blowers
are relocated. There are two electrical design options to consider for the new Blower Building:
Option A- Under this option, the existing blowers would be relocated with their respective 2.4kV motors. A
new 1200A, 5kV class motor control center,supplied by a 2000kVA, 12.47kV-2.4kV liquid-filled, pad-mount
transformer, would be furnished and installed with three (3) 5kV class reduced-voltage, auto-transformer
(RVAT)motor starters and space for two(2)future RVATs for future blowers. A 12.47kV-480VAC transformer
and respective power panelboard would also be required to supply the miscellaneous 480V loads associated
with the new Blower Building. Each transformer would be supplied from the plants overhead power
distribution system. The estimated electrical cost, excluding engineering and contingencies, for the new
Blower Building and related equipment for Option A is$300,000.
Option B-Under this option, the existing blowers would be relocated, but their motors would be replaced with
new 350hp,480VAC,three-phase motors. A new 2500A, 480VAC motor control center(MCC-13)would be
furnished and installed with three(3), NEMA size 6, RVAT starters and space for two(2)future RVAT starters
for future blowers. The new MCC would also house motor starters and feeder breakers necessary to supply
other loads associated with this facility. By utilizing new 480VAC motors, medium voltage equipment is not
necessary which has its benefits not only in initial cost but also maintenance activities. The estimated electrical
cost, excluding engineering and contingencies but including new blower motors,for the new Blower Building
and related equipment for Option B is$370,000.
Tertiary Filters
One (1) tertiary filter will be added to the existing tertiary filters under the 16 MGD Upgrade. The existing
tertiary filters are located on the westside of the plant. The tertiary filter electrical room is located on the south
side of the filters and contains a 1200A,480V motor control center(MCC-11) and power and lighting panels.
MCC-11 is supplied from a 750kVA, 12.47kV-2.4kV liquid-filled, pad-mount transformer, located near the south
end of the tertiary filter structure. The electrical scope for the additional tertiary filter includes the installation
of motor operated valves, level instrumentation, and tank area lighting all of which would be supplied from the
existing power panel and lighting panel located in the tertiary filter electrical room. The estimated electrical
cost, excluding engineering and contingencies,for the tertiary filter portion of the 16 MGD design is$15,000.
UV Facility
A new Ultraviolet Disinfection Facility will be installed near the west side of the Tertiary Filters. A new 400A,
480/277V power panelboard will supply each of the four(4) UV lamp ballast enclosures. Each of these ballast
enclosures will add approximately 25kW of electrical load to the plant. The new power panel will be supplied,
via a 480-480/277V isolation transformer, from a new feeder breaker installed in the existing motor control
center MCC-11. MCC-11 is located inside the Tertiary Filter Electrical Room and has the required physical
space and arnpacity to power the new UV Disinfection Facility. The isolation transformer and the UV
panelboard will be located outside near the UV Disinfection Facility. The estimated electrical cost, excluding
engineering and contingencies, for the UV facility is$50,000.
ti
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 6 of 13
Influent Pumping Station
Two options for developing additional pumping capacity as part of the 16MGD Upgrade project are presented
below:
Option A-Option A is to upgrade the existing influent pumping facility. The existing influent pumping station
includes two(2), 125hp Fairbanks-Morse variable speed pumps and two(2), 100hp Allis-Chalmers constant
speed pumps. All four(4) influent pumps are currently supplied by an existing 600A, 480VAC, three-phase
motor control center(MCC-6) located inside the influent pumping station. The 16 MGD Upgrade requires the
two existing 100 HP Allis-Chalmers constant speed pumps to be upgraded to 200hp variable speed pumps.
This upgrade, along with the existing panelboards and hoist, will increase the connected load to MCC-6 to
approximately 600hp. This increase in load will exceed the main bus rating of 600A thus requiring MCC-6 be
replaced.
A new 1600A, 480VAC motor control center (MCC-15)will be required to serve the load at the upgraded
influent pumping station. This MCC will have the necessary capacity to accommodate the influent pump
revisions for both the 16MGD and 18MGD upgrades and other future loads. A new pre-fabricated power
center(Power Center 8), similar to the power center supplying the existing Aeration Basins 4-6,would house
the new MCC-15. MCC-15 would include two(2)new variable frequency drives(VFDs)for the Allis-Chalmers
pumps, a dry-type transformer and lighting panelboard, and any other electrical and control equipment
required for the influent pumping station 16MGD upgrade. The new Power Center 8 will also include space
for two (2) new VFDs for the 18MGD upgrade. A new 1000KVA, 12.47kV-480VAC liquid-filled, pad-mount
transformer would be required to supply the new MCC-15. The new power center would provide a more
suitable environment for the VFDs and MCC-15 than the existing influent pumping station. This approach also
simplifies maintenance of plant operations during the construction period. The estimated electrical cost,
excluding engineering and contingencies, for the Influent Pumping Station 16 MGD upgrade is$270,000.
In addition to the electrical work described above, it is recommended that the existing VFDs for the existing
125hp Fairbanks-Morse pumps be replaced. Based on conversations with staff and field observations, the
existing 125hp VFDs have not been performing adequately and are obsolete. Also, renewal parts are
becoming more difficult to obtain. New VFDs for the existing Fairbanks-Morse pumps may be installed inside
Power Center 8 under the 16 MGD Upgrade. This design suggestion is applicable to the 16 MGD upgrade
only since the 18 MGD upgrade involves the replacement of these pumps with new 250hp variable speed
pumps. The additional electrical cost, excluding engineering and contingencies,to replace the existing VFDs
for the Fairbanks-Morse pumps is $130,000.
Option B - Another alternative for developing additional influent pumping capacity is to construct a new
pumping station to be located near the existing pumping station. The new influent pumping station would
include one (1) new 150hp variable speed pump with space for a second 150hp variable speed pump. In
addition to the new pumps, the two(2) existing 100 HP Allis-Chalmers constant speed pumps located in the
existing pumping station would be upgraded to 100hp variable speed pumps. A new pre-fabricated power
center(Power Center 8), similar to the power center described above, would house the new 1600A, 480V,
MCC-15. MCC-15 would include one(1) new VFD for the 150hp influent pump, and two (2) new VFDs for
the 100hp Allis-Chalmers pumps, and other electrical distribution equipment required for the influent pumping
station 16MGD upgrade. The new Power Center 8 would include space for the VFD for the second 150hp
influent pump.A new 1000KVA, 12.47kV-480VAC liquid-filled, pad-mount transformer would be installed to
supply the new MCC-15. Under this option, all loads associated with both the new and existing influent
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 7 of 13
pumping stations would be supplied from the new MCC-15. The estimated electrical cost, excluding
engineering and contingencies, under this option for the Influent Pumping Station 16 MGD Upgrade is
$280,000.
18 MGD Upgrade
In addition to the modifications described in the 14 MGD and 16 MGD designs, the 18 MGD Upgrade will
consist of the addition of two(2) aeration basins(Aeration Basins 11-12), one (1)tertiary filter, and one(1)
blower. It will also include the replacement of two (2) existing influent pumps or the addition of a second
influent pump in the new influent pumping station. The additional loads for the 18MGD upgrade are shown
in Table 3.
Table 3. 18-MGD Upgrade Load List
Quantity Description HP Total Hp Total kW
Aeration Basins#11 and#12
4 NRCY Pumps 15hp 60hp 45kW
4 Jet Mixing Pumps 10hp 40hp 30kW
3 Influent Channel Mixers 5hp 15hp 12kW
Subtotal 115hp 87kW
Blower Building
1 Aeration Blower 350hp 350hp 260kW
Subtotal 350hp 260kW
Influent Pump Station
2 Influent Pumps (Replace 125hp 250hp 500hp 370kW
variable speed pumps)
"Option"A"only
1 Influent Pumps (Second new 150hp 150hp 112kW
pump in new pump station)
"Option B" only not included in
totals below
Subtotal' 500hp 370kW
Total' 975hp 717kW
' Value represents loading for Influent Pumping Station"Option A"only.
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 8 of 13
Aeration Basins
In addition to the aeration basins described in the 14 MGD and the 16 MGD designs, two (2) additional
aeration basins(Aeration Basins 11-12)will be installed under the 18 MGD design. The electrical equipment
required for the channel mixers, NRCY pumps, and the jet mixing pumps, installed with the new Aeration
Basins 11-12 would be located in MCC-14 as described for the 16 MGD upgrade. The estimated electrical
cost, excluding engineering and contingencies, for Aeration Basin 18 MGD design is$140,000.
Tertiary Filters
In addition to the tertiary filter discussed for the 16 MGD design, an additional tertiary filter will be added for
the 18 MGD design. The electrical scope for the additional tertiary filter includes the installation of new motor
operated valves, level instrumentation, and lighting all of which would be supplied from the existing power
panelboard and lighting panelboard located in the tertiary filter electrical room. The estimated electrical cost,
excluding engineering and contingencies, for the tertiary filter portion of the 18MGD design is$15,000.
Blower Buildina
In addition to the blower building work previously discussed for the 16 MGD design, a new 350hp blower
would be added to accommodate the 18 MGD and 20 MGD design conditions. The new blower MCC installed
under the 16 MGD upgrade would be expanded to accommodate this new load. The estimated electrical cost,
excluding engineering and contingencies,for the blower building for Option A(2.4kV motors as described in
the 16 MGD design)for the 18 MGD design is$45,000. The estimated electrical cost, excluding engineering
and contingencies, for the blower building for Option B(480VAC motors as described in the 16 MGD design)
for the18 MGD design is$38,000.
Influent Pumping Station
Two options for developing additional pumping capacity as part of the 18MGD Upgrade project are presented
below:
Option A-In addition to the modifications described in Option A for the Influent Pumping Station 16 MGD
design, the 18 MGD design will involve replacing the two(2)existing 125hp Fairbanks-Morse variable speed
pumps with two (2), 250hp variable speed pumps. The two (2) new VFDs would be furnished and installed
in Power Center 8 previously described in the 16MGD Upgrade. The estimated electrical cost, excluding
engineering and contingencies, for the Influent Pumping Station 18 MGD upgrade for Option A is$230,000.
Option B - In addition to the modifications described in Option B of the Influent Pumping Station 16 MGD
design, a second 150hp variable speed pump would be installed in the new Influent Pumping Station. The
VFD for this second influent pump would also be located in Power Center 8. The total estimated electrical
cost, excluding engineering and contingencies, for the Influent Pumping Station 18 MGD upgrade for Option
B is$70,000.
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.10 DRAFT- For Review and Comment
City of Wilson
Page 9 of 13
20 MGD Upgrade
In addition to the items previously described in this memorandum, the 20 MGD design will consist of the
addition of one(1)new aeration basin(Aeration Basin 13), and one(1) new belt filter press. The press would
be located in the Anaerobic Digestion Facility described above. The additional loads for the 20MGD upgrade
are shown in Table 4.
Table 4. 20-MGD Upgrade Load List
Quantity DescriptionHP Total
Hp
Total kW
Aeration Basins#13
2 NRCY Pumps 15hp 30hp 22kW
2 Jet Mixing Pumps 10hp 20hp 15kW
1 Influent Channel Mixers 5hp 5hp 4kW
Subtotal 55hp 41kW
Anaerobic Digestion Facility
1 BFP Feed Pump 15hp 15hp 12kW
1 Belt Filter Press 10hp 10hp 8kW
1 BFP Polymer Feed Pump 1 hp 1 hp .8kW
Subtotal 26hp 20.8kW
Total 81 hp 61.8kW
Aeration Basin 13
In this expansion,one(1) new aeration basin (Aeration Basin 13)will be constructed.The electrical equipment
for the channel mixers, NRCY Pumps,jet mixing pumps, and other miscellaneous loads required for the new
basin will be installed in MCC-14 located in Power Center 7 furnished under the 16 MGD upgrade. The
estimated electrical cost, excluding engineering and contingencies, for Aeration Basin 20 MGD design is
$65,000.
Anaerobic Digestion Facility
In addition to the belt filter presses located in the Anaerobic Digestion Facility as described in the 14 MGD
design, one additional belt filter press will be installed during the 20 MGD design. The motor control center
(MCC-12)installed during the 14 MGD upgrade would be expanded to include the motor starters and variable
frequency drives required for the new equipment. The estimated electrical cost, excluding engineering and
contingencies, for the new Anaerobic Digestion Facility 20 MGD design is$25,000.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 10 of 13
Standby Power Considerations
A description of the standby power system for the HCWMF was presented at the beginning of this
memorandum. As indicated in the system description,the current average demand load that has been served
by the existing generator is approximately 1000kW. Table 5 below identifies the additional load to be served
by the standby power system for the 14-MGD through 20-MGD upgrade scenarios.
Table 5. Standby Power Load List
Design Additional Diversity Factor Additional Load' (kW)
Connected Load (kW)
14 MGD 335 0.7 235
16 MGD2 507 0.7 355
18 MGD2 717 0.7 502
20 MGD 62 0.7 43
Total 1621 1135
'The Additional Load=Additional Connected Load x Diversity Factor
2 Value represents loading for Influent Pumping Station"Option A"Only
The existing 1600kW prime rated generator is sufficient to operate the total plant load under normal operating
conditions through the 14MGD expansion. However, the additional load from the 16-MGD, 18-MGD,and 20-
MGD designs may require the addition of a second generator or upgrading the existing generator.
Summary and Recommendations
The required modifications to the electrical system at the HCWMF to accommodate the 14-MGD through 20-
MGD expansions have been presented in this memorandum. The following summarizes the work to be
completed on a per project basis.
14MGD
• Modify MCC-10 to serve Aeration Basin 7 loads.
• Install MCC-12 and respective service transformer to serve the new Anaerobic Digestion Facility loads.
16MGD
• Demolish the existing electrical equipment in the existing Blower Building.
• Install Power Center 7, which contains MCC-14, and respective service transformer to serve Aeration
Basin 8-10 loads.
• Furnish and install new 2400V or 480VAC motor control center and respective service transformer(s)for
the new Bower Building.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 11 of 13
• Install a new feeder breaker in MCC-11 to serve a new isolation transformer and panelboard for the new
UV Disinfection Facility.
• Install electrical equipment required for a new Tertiary Filter.
• Influent Pumping Station"Option A"_Install Power Center 8, which houses the new MCC-15 with VFDs,
and respective service transformer to serve two(2)existing 125hp variable speed influent pumps with and
the two (2)new 200hp variable speed influent pumps in the existing influent pumping station. The new
Power Center 8 will also contain power and lighting panelboards to serve any other loads associated with
the existing Influent Pumping Station.
Influent Pumping Station"Option B"-Install Power Center 8,which contains the new MCC-15 with VFD's,
and respective service transformer to serve two (2) new 100hp variable speed pumps, two (2) existing
125hp variable speed pumps located in the existing Influent Pumping Station and a new 150hp variable
speed pump located in a new Influent Pumping Station. The new Power Center 8 will also contain power
and lighting panels to serve any other loads associated with the Influent Pumping Stations.
18 MGD
• Install electrical equipment required for Aeration Basins 11-12 in MCC-14.
• Install electrical equipment required for a new Tertiary Filter.
• Install electrical equipment required for a new 350hp blower in the new blower building.
• Influent Pumping Station "Option A" - Install the VFDs in Power Center 8 required for the two (2) new
250hp variable speed influent pumps. The new 250hp influent pumps will replace the existing 125hp
influent pumps in the existing pumping station.
Influent Pumping Station "Option B" - Install the VFD in Power Center 8 required for the second new
150hp variable speed influent pump. The new 150 influent pump will be located in the new Influent
Pumping Station.
20 MGD
• Install electrical equipment required for Aeration Basin 13 in MCC-14.
• Install electrical equipment in MCC-12 required for one additional GBT in the Anaerobic Digestion Facility.
Estimated Costs
The estimated electrical costs, excluding engineering, contingencies, and any costs associated with standby
power modifications, for the 14-MGD, 16-MGD, 18-MGD, and-20 MGD upgrades are summarized in Table
6 below.
HAZEN AND SAWYER, P.C.
Job.No.30500

Memorandum No.10 DRAFT- For Review and Comment
City of Wilson
Page 12 of 13
Table 6. Estimated Electrical Costs.
Maximum Month Design Flow
14-mgd 16-mgd3 18-mgd 20-mgd
Influent pumping station-Option A $400,000 $230,000
Influent pumping station-Option B1 ($410,000)*** ($70,000)
Aeration Basins $70,000 $300,000 $140,000 $65,000
Anaerobic Digestion Facility $470,000 $25,000
Blower Building-Option A $300,000 $45,000
Blower Building-Option B2 ($370,000) ($38,000)
UV Facility $50,000
Tertiary Filters $15,000 $15,000
Total $540,000 $1,065,000 $430,000 $90,000
Cumulative Total $540,000 $1,605,000 $2,035,000 $2,125,000
1 Cost for Option B (new pump station option). Not included in total cost.
2 Cost for Option B (480VAC motors and motor control equipment). Not included in total cost
3 16-mgd influent pumping station costs include replacement of the existing 125hp VFDs.
It is recommended that the electrical system modifications be implemented in the various expansion projects
as outlined herein.
In the case of the Influent Pumping Station, it is recommended that the new MCC, VFDs, and all other
electrical distribution equipment be installed in a new"pre-fabricated" power center(Power Center 8). The
new power center will provide a more suitable environment for the VFDs, MCC, and any other required
electrical equipment than the interior of the existing Influent Pumping Station. Also,the"pre-fabricated"power
centers have a lower cost per square-foot than a comparable new structure built on site. A new power center
is recommended for both"Option A", and"Option B" Influent Pumping Station designs.
In the case of the new Aeration Basins, a new"pre-fabricated" power center(Power Center 7), similar to the
existing Power Center 2, is recommended for the same reasons described above. Power Center 7 will contain
a new motor control center(MCC-14)and any other electrical equipment required to serve Aeration Basins
8-13. It is recommended to expand existing MCC-10 in Power Center 2 to serve loads for Aeration Basin 7.
The existing Blower Building will be demolished to make room for the new Aeration Basins 8-13. The existing
main switchgear, transformer, and medium voltage motor control center must be demolished. This electrical
equipment is approximately 30 years old and is near the end of its useful service. New electrical equipment
should be installed in the new Blower Building. Of the two (2)options discussed for the new Blower Building
under the 16 MGD design, "Option B" (new 480VAC motors) is recommended. The 480V motor control
equipment will have a lower initial cost than the medium voltage equipment and the additional 12.47kV-
480VAC transformer required under "Option A" would not be necessary. Based on conversations with
Electrical Utility Department personnel, 480V motor control equipment is preferred.
HAZEN AND SAWYER,P.C.
Job. No.30500

Memorandum No.10 DRAFT-For Review and Comment
City of Wilson
Page 13 of 13
The existing 1600kW prime rated generator is sufficient to operate the existing plant under normal operating
conditions through the 14MGD upgrade; however, the additional loads from the 16MGD, 18 MGD, and 20
MGD designs may require the addition of additional stand-by power generation capacity. The design
alternatives and their respective costs are not included in this memorandum.
HAZEN AND SAWYER,P.C.
Job.No.30500

DRAFT- For Review and Comment
MEMORANDUM
Date: March 30, 2001
TO: Mr. Barry Parks, City of Wilson
Mr. Russell Brice, City of Wilson
FROM: Mr. C. Michael Bullard, Hazen &Sawyer
Mr. Ronald L. Taylor, Hazen &Sawyer
SUBJECT: Hominy Creek Wastewater Management Facility
Expansion Alternatives Study
Memorandum No. 11 —Site Plan and Layout
H&S Job. No. 30500
The Hominy Creek Wastewater Management Facility (HCWWMF) is planned for upgrade and expansion to
treat future peak month flows of 20-mgd. This technical memorandum presents proposed site plan layouts
for an upgrade to capacity at the 14-mgd flow rate and development of additional capacity at 16-mgd, 18-mgd
and 20-mgd.
Proposed 14-mad Upgrade Option
The proposed 14-mgd upgrade option includes the following major unit process equipment:
• Aeration Basins Aeration Basin Trains(1)
• Waste Activated Sludge Thickening Gravity Belt Thickeners (2)
• Sludge Dewatering Belt Filter Presses(3)
• Anaerobic Digestion Digester Tanks(3)
The estimated construction cost for the 14-mgd upgrade project is$13,200,000, excluding engineering and
contingencies (approximately $17,030,000 with contingencies and engineering). The proposed site layout
for the 14-mgd upgrade project is shown on the attached drawing.
Proposed 16-mad Upgrade and Expansion Option
The proposed 16-mgd upgrade option includes the following major unit process equipment:
• Influent Pumping Pumps(2)
• Aeration Basins Aeration Basin Trains(4)
• Effluent Filters Filter Bays (1)
• UV Disinfection Channels (4)
• Effluent Outfall and Flow Measurement Trains(1)
• Waste Activated Sludge Thickening Gravity Belt Thickeners(2)
• Sludge Dewatering Belt Filter Presses (3)
• Anaerobic Digestion Digester Tanks(3)
HAZEN AND SAWYER,P.C.
Job.No.30500

Memorandum No.3 DRAFT-For Review and Comment
City of Wilson
Page 2 of 2
The estimated construction cost for the 16-mgd upgrade project is$24,150,000, excluding engineering and
contingencies (approximately $31,150,000 with contingencies and engineering). The proposed site layout
for the 16-mgd upgrade project is shown on the attached drawing.
Proposed 18-mqd Upgrade and Expansion Option
The proposed 18-mgd upgrade option includes the following major unit process equipment:
• Influent Pumping Pumps(4)
• Preliminary Treatment Trains Grit Trains(1)
• Aeration Basins Aeration Basin Trains (6)
• Secondary Clarifiers Secondary Clarifiers (2)
• Effluent Filters Filter Bays(2)
• UV Disinfection Channels(4)
• Effluent Outfall and Flow Measurement Trains (1)
• Waste Activated Sludge Thickening Gravity Belt Thickeners(2)
• Sludge Dewatering Belt Filter Presses(3)
• Anaerobic Digestion Digester Tanks(3)
The estimated construction cost for the 18-mgd upgrade project is$32,280,000, excluding engineering and
contingencies(approximately$41,640,000 with contingencies and engineering).. The proposed site layout
for the 18-mgd upgrade project is shown on the attached drawing.
Proposed 20-mqd Upgrade and Expansion Option
The proposed 20-mgd upgrade option includes the following major unit process equipment:
• Influent Pumping Pumps (4)
• Preliminary Treatment Trains Grit Trains (1)
• Primary Clarifiers Primary Clarifiers (1)
• Aeration Basins Aeration Basin Trains(7)
• Secondary Clarifiers Secondary Clarifiers(3)
• Effluent Filters Bays(2)
• UV Disinfection Channels(4)
• Effluent Outfall and Flow Measurement Trains(1)
• Waste Activated Sludge Thickening Gravity Belt Thickeners(2)
• Sludge Dewatering Belt Filter Presses(3)
• Anaerobic Digestion Digester Tanks(3)
The estimated construction cost for the 20-mgd upgrade project is$36,930,000, excluding engineering and
contingencies(approximately$47,640,000 with contingencies and engineering).. The proposed site layout
for the 20-mgd upgrade project is shown on the attached drawing.
HAZEN AND SAWYER, P.C.
Job. No.30500
I J

.. Centrate Tank—�� ��-Blowers
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_ti;
re-
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City of Wilson
Hominy Creek Wastewater Management Facility
R u JU• .a ' Proposed Facilities
14 MGD Capacity Upgrade
) 30500-001-SP-02.cdr

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ec,
r Abandoned ' No.4 )No:5 \ a►.
Fine Solids ;� ` Maintenance Shop 1'
r Basin No.1 td
\ RAS Pump
Station No.3 1 Legend
ti ti
ti '\, `\, im 14 MGD Upgrade
"1 16 MGD Upgrade
\ .. _ . \.1
Abandoned Abandoned i \
Fine Solids Basin No.3 Fine Solids Basin No.2 '2:'%
Soil/Demolition
Disposal Area
�., f tvi/� City of Wilson
y Hominy Creek Wastewater Management Facility
u } U - ) (. . Proposed Facilities
so__.
yNORTH�PQ 16 MGD Capacity Upgrade
` ) 30500-001-SP-03.cdr

Centrate Tank-fit ��Blowers Preliminary
(----\-rj
Pretreatment Facility q Treatment
f, u t� I s ilii
Facilities
?71
Influent Pump Station 1 1 ra Pre- )
Aeration I i
�- Basins` Pretreatment
Facility I I
Final I r
Clarifier Biological Phosphorous PrEr
ary
No. 1 Removal Tank Clfie
(Anaerobic Tank) 1 i Solids Drgef,ter
RAS Meter Storage
• Vault Diges!!r Tank I
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4 ❑ - Digester
RAS Pump I / ' 'Thickening Digester
Dewatering
Sludge Drying Beds Station No. 1 - Alum Storage Tanks ►:..p ;� Sgox r t (- Building
WAS Meter/Flow PrimaryClarifier Digester • Solids
Ultraviolet Filter Bays FC1.4 No.2 Storage
Disinfection I Control Vault I (`- Filter Pump Station �6 p�Collection Box No.2 No•7 g
Tank
No.7 I -• ^ No.2 Digester
i
i Final t Primary- .
Clarifier 1 Clarifier, \
Effluent No.2A No 2
Flow r ► ; v� Primary 1 1\
,Ter
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.., [fterr Final Clarifier RAS Pump Aeration Tanks Nos.1-6 Pump ��
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c
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rination r Primary
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11111
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❑❑U �° Collection/ Building
13
z.�.6 • p ❑ Distribution a J
J Structure
Methanol Storage ,---. • • J \ J J
and Feed Facilities i
i �--� o Aeratip `
Final t Primary
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,'
Si 1� r Aeration Tank No 8
Q �\ No.3A .No.3 Emergency
r 4 El `,. — 'i Aeration.Tank No 9 Generator
p vi-., and Fuel
_
C) k C Aeration Tank No. 10 Storage
• 1e 1
4 Chlorine Contact 3
e Aeration Tank No. 11 /
Tank/Post-Aeration
--. +-Blower Building
I. I—I fl ' ❑ Q Aeration Tank No. 12
/ 1 - p t:`.
°•Final,- ' 0
1-•,Clarifierr,. 4 r s .
ti
' abandoned / .'' No.4,•` \ }
ine Solids Maintenance Shop ;:
asin No. 1 -v-v
RAS Pump
Station No.3 Legend
�. ti U 14 MGD Upgrade
r-- 1 16 MGD Upgrade
r--1 18 MGD Upgrade
Abandoned Abandoned ` T \
Fine Solids Basin No.3 Fine Solids Basin No.2
Soil/Demolition
r Disposal Area
t_ 0) City of Wilson
Hominy Creek Wastewater Management Facility
} \ u J u J
Proposed Facilities
\ MGD Capacity Upgrade
�oRrtt�� 18
' _t ' 30500-001-SP-04.cdr

Centrate Tank—► oN-Blowers I Preliminary
Vi- 1 II Pretreatment Facility Treatment
r L •a p7 La Facilities
0
\
\ Influent Pump Station 1— •
Aeraan._
�- £iasins', Pretreatment
r `.t Facility
`
Final ¢ \ 1
Clarifier ` `_.
Biological Phosphorous PrimarII y 0 ^,�
No.1 ' tom\ Removal Tank q Clarifier
(� Drg*ester
(Anaerobic Tank) 7,4 No, ti,71.Y'' Solids I
RAS Meter , .v"':•4 Storage I
• Vault ;digester Tank _
a No. 1
Na1 '`- �,,
T Ill � • ihueStNr I
(htrkrnirii
RAS Pump / 0 Dewaienng C i� t,tSludge Drying Beds Station No. 1 Alum Storage TanksUltraviolet Filter Bays WAS Meter/Flow ,� p Primary Clarifier 11-(---ILI
•Solids T 8wldir �Ultravolet Control Vault i�-Filter Pump Station p Collection Box No.2 Storage
Tank
��--�� tl LY N0.2 Dcj.,ttr s
No.7 e \ r
No.B j Final `� aPnma
r I Clarifier Y z larifre '� ``.
Effluent No.2Al0.'2. -
• i ri Prima (�
Metering ► Tertiary _ / 0 ❑ Sludge \ '
Filters Final Clarifier RAS Pump Aeration Tanks Nos-1-6 Pump o�
Chlorination/ ._ Collection Box Station No.2 ® Station
`n Filter Bypass No.2
Dechlorination ► I Primary
Storage Facility �� Y ❑ Effluent Lab g in 4 Centrifuge Building
C7� Collection! Building
NPW Pumping D 0 Distribution a
o J ® Structure
Methanol Storage J \ J L. J
and Feed Facilities i
Chlorine Building o► a ,,r^� f Final `Y Aeration Tank Nn. r' •,-'Pnmari
❑ 1 1 :..: \ I Clarifier Y Clarifier '''
NO.3A / Aeration Tank NO 8 'No. :-:
` Emergency
i -b Generator
r c 1 ID _ ., Aeration Tank No,9
4-0 C J and Fuel
OC eat Aeration Tank No 10 Storage
► Sludge
4 - Chlorine Contact Storage
Tank/Post-Aeration Basin 1 Aeration Tank No. 11 /
)
' ..- --4 •4---Blower Building
r (� (—] Aeration Tank No. 12
0 4 �i o Aeration Tank No. 13 • • ,
! Final ! v
% Clarifier 1 Primary
' Abandoned ' % No. 1 Clarifier '
Fine Solids s No.4 t„ ,
' Basin No. 1 `� _ Maintenance Shop `I
� ,� ,� Legend,
1111.1111 V- 14 MGD Upgrade
I 116 MGD Upgrade
. ip .
-- rl 18 MGD Upgrade
120 MGD Upgrade
Abandoned Abandoned r T \
Fine Solids Basin No.3 Fine Solids Basin No.2
Soil/Demolition?
£ Disposal Area, ,
L + t w' City of Wilson
so Hominy Creek Wastewater Management Facility
Proposed Facilities
yflioenit 20 MGD Capacity Upgrade
' 30500-001-SP-O5.cdr