NC0024333_Report_19961219

NPDES DOCUMENT :SCANNING COVER SHEET
NC0024333
Monroe WWTP
NPDES Permit:
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Correspondence
Owner Name Change
Report
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
December 19, 1996
This document is printed on reuse paper - ignore any
content on the reirerse side

CITY OF MONROE
P.O. BOX 69 • MONROE, NORTH CAROLINA 28111-0069
FAX [phone]
December 19, 1996
Mr. David Goodrich, P. E., Supervisor
NCDEHNR-DEM
NPDES Group
Post Office Box 27687
Raleigh, North Carolina 27611-7687
RE: Preliminary Engineering Report for Proposed Expansion of Monroe Wastewater Treatment Plant
from 9 MGD to 11 MGD
NPDES Permit No. NC0024333
Dear Mr. Goodrich:
Pursuant to the requirements of 15A NCAC 02H .0223 (1), please find enclosed for your review three
copies of a preliminary engineering report prepared on behalf of the City of Monroe by Hazen & Sawyer,
P. C. for a proposed expansion of the City's Wastewater Treatment Plant from 9.0 MGD to 11.0 MGD.
We are also providing one copy of this same report with a copy of this letter directly to the Regional
Supervisor, Mr. D. Rex Gleason, P. E., in your Mooresville office.
If you have any questions on this report, please call Mr. Jim Cramer of Hazen & Sawyer at (919) 833-
7152 or call me at [phone].
ctfull
Tom L. erick, ' . E.
Director of Water Resources
c: Mr. Jerry Cox
Mr. Jim Cramer, P. E.
Mr. D. Rex Gleason, P. E.
Mr. Kim Hinson
tom12961davg1217.doc

8
SECTION 1
INTRODUCTION
The City of Monroe is served by a single wastewater treatment plant with a design
capacity of 9.0 mgd. An expansion of the Monroe Wastewater Treatment Plant
(WWTP) from 7.0 mgd to 9.0 mgd was completed in January 1995. A study
prepared by Hazen & Sawyer for the City of Monroe in 1992, prior to the most recent
expansion, addressed planning and preliminary engineering for a two-phase expansion
of the plant from 7.0 mgd to 9.0 mgd and then to 11.0 mgd. The current NPDES
Permit (NC002433) for the Monroe Wastewater Treatment Plant reflects the planning
performed at that time and provides effluent limits for 9.0 and 11.0 mgd. Based on
current wastewater flows and flow projections for future growth, the City authorized
this study to evaluate facilities required for the planned second phase expansion to
11.0 mgd and to comply with State requirements for submittal of a Preliminary
Engineering Report when average annual flow at the plant increases to 80% of
permitted capacity. Recommended facilities the proposed expansion are addressed
in this report. The report includes an evaluation of process, hydraulic, site, and
operational considerations and costs for the proposed expansion.
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HAZEN AND SAWYER
Environmental Engineers & Scientists

0
i
SECTION 2
EXISTING FACILITIES
The Monroe Wastewater Treatment Plant is located at 775 Treeway Drive, off Walkup
Avenue, in the eastern portion of the City of Monroe. The original plant was
constructed in 1965 with a design capacity of 3.5 mgd. The plant was expanded to
7.0 mgd in 1976 and to 9.0 mgd in 1995. In addition, major improvements were
constructed in 1984, 1989, and 1993 to provide further treatment enhancements and
reliability to meet the increasingly stringent permit requirements which became
effective at those times. Solids handling improvements consisting of new sludge
pumps, rehabilitation of the Centrifuge Building, and a new 3.0 MG sludge .storage
tank are currently under design and will be bid and constructed in 1997.
2.1 Existing Facilities
The Monroe Wastewater Treatment Plant is located along Richardson Creek, just
downstream of the confluence of Richardson Creek and Joe's Branch, at the eastern
end of the Monroe City Limits. Richardson Creek is a significant tributary of the
Rocky River, which then flows into the Pee Dee River at the boundary between
Anson, Stanly, Montgomery, and Richmond Counties approximately 4.5 miles
downstream of the Lake Tillery dam. Approximately 4 miles upstream of the
discharge point on Richardson Creek is the Lake Lee dam, operated by the City of
Monroe as a water supply impoundment. A second water supply impoundment, Lake
Monroe, is on the Richardson Creek basin further upstream of Lake Lee.
The City of Monroe operates a sewer collection system which conveys the
wastewater to two Influent Pump Stations on the plant site. The two influent pump
stations operate in parallel to pump flows for the collection system to the plant
headworks. The wastewater from the sewer collection system is conveyed through
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

f"°•
major trunk interceptors along Richardson Creek, Bearskin Creek, and Stewart's Creek
to parallel 54-inch and 30-inch pipelines along Richardson Creek, which then convey
the wastewater to the Influent Pump Stations.
The existing treatment plant provides tertiary treatment for a permitted capacity of
9.0 mgd. Pumped flow from the Influent Pump Stations is conveyed through three
parallel force mains (16-inch, 20-inch and 24-inch diameter) to preliminary screening
facilities. The screens consist of two fine -mesh rotary screens. In addition, a force
main from the Union County East Side sewer collection system pumps flow directly
to the Screening Building. Screenings and grit removed by the screens are dewatered
and disposed of at the Union County Landfill. The screened flow can be diverted to
a 4.15-million gallon flow equalization basin or flow directly to an aeration basin
splitter box. A flow equalization basin pump station pumps flow from the flow
equalization basin to the splitter box during lower flow periods. From the splitter box,
flow is distributed to five aeration basins with fine bubble EPDM membrane diffuses.
The aeration basin effluent is distributed to four secondary clarifiers. Each pair of
clarifiers includes a return activated sludge (RAS) pumping station with three self
priming pumps. Each RAS Pump Station has a single wet well for collecting both
settled solids and scum from the clarifiers. The RAS and scum are returned to the
aeration basin splitter box. The return activated sludge force mains also include
valves for periodically wasting activated sludge to the aerobic digesters. The valves
are manually operated as required to maintain the appropriate mixed liquor suspended
solids concentration. Secondary clarifier effluent flows are combined in a common
filter influent flume and distributed to six dual media tertiary filters. Filtered effluent
is chlorinated and then flows through two chlorine contact tanks. The chlorine
contact tank effluent is dechlorinated with sulfur dioxide, metered in a flow
monitoring basin by a rectangular weir, and discharged through a cascade aeration
flume before discharge to Richardson Creek.
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

Existing solids handling facilities at the plant are being upgraded as part of a $1.3
million construction project scheduled for completion in 1997. The project includes
new sludge pumps, rehabilitation of the Centrifuge Building, and construction of a 3.0
MG sludge storage tank. The upgraded solids handling facilities will consist of the
following:
1. Waste activated sludge is pumped from the RAS Pump Station to
Digesters 3 and 4 which are operated as aerobic digesters and
thickeners. Solid concentrations as high as 6 to 8 percent solids are
achieved in Digesters 3 and 4.
2. 0ne of the existing thickened sludge pumps is being replaced as part of
the $1.3 million construction project with a progressing cavity pump for
pumping solids at 6 to 8 percent concentration to the centrifuges or to
other digester/storage tanks.
3. Thickened sludge will be pumped to the centrifuges for additional
thickening as required. Operation of the centrifuges needs to be
modified to provide a wetter cake to allow pumping of thickened sludge
to Digester/Storage Tanks No. 1 and No. 2 and the new 3.0 MG sludge
storage tank using progressing cavity pumps in the existing Centrifuge
Building. The $1.3 million construction project also includes
improvements to electrical enclosures and new walls and roof for the
existing Centrifuge and Polymer Building, respectively, as an Alternate
Bid, i.e., construction of the Centrifuge and Polymer Building
improvements will depend on receiving bids within the City's budget.
4. Digestion and storage are provided in existing Digesters No. 1 and No.
2 and in the new 3.0 MG digester/storage tank. Flexibility is being
provided as part of the $1.3 million construction project for transfer of
REPO RTSIMO NRO EPERISECT1O N.2
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HAZEN AND SAWYER
Environmental Encino= & Scientists

sludge among tanks, for adding lime to the sludge, and for loading
trucks for land application from any one of the three digester/storage
tanks. Lime will be added to liquid sludge to comply with Class B sludge
disposal requirements at times when stabilization criteria is not
otherwise satisfied by aerobic digestion.
Design data for the existing facilities is summarized in Table 2-1. A process flow
schematic for the existing plant is shown in Figure 2-1.
2.1.1 Liquid Treatment Facilities
Influent Pump Stations
Raw wastewater enters the two parallel influent pump stations from the parallel 54-
inch and 30-inch interceptors, which are immediately upstream of the pump stations.
Pump Station No. 1 includes four influent pumps, two variable speed and two
constant speed, each with a capacity of 4.5 mgd. Pump Station No. 2 includes two
variable speed influent pumps, with space for two additional pumps. Each pump has
a capacity of 6.5 mgd. The present firm capacity of the combined stations is 24.5
mgd, including five pumps operating together with one of the larger 6.5 MGD pumps
out of service. Influent flow is measured through four magnetic flow meters, one on
each of the three parallel discharge force mains from the influent pump stations and
the fourth on the County East Side force main carrying flow from an off -site Union
County pump station.
Preliminary Treatment Facilities
Raw wastewater from the three force mains from the Influent Pump Stations and the
County force main is combined before the flow is directed to the Screening Building.
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 2-1
DESIGN DATA
EXISTING FACILITIES
9 MGD DESIGN CAPACITY
Influent Pump Stations*
Pump Station No. 1
Number of pumps
Type
Capacity of each pump, mgd
Type of drive
Pump Station No. 2
Number of pumps
Type of pumps
Design capacity of each pump, mgd
Type of drive
Total firm capacity, mgd
Influent Flow Measurement
Method of flow measurement
Number
Size, inches
Rotary Screens
Number
Screen openings, inches
Capacity of each screen, mgd
Firm capacity, mgd
Flow Equalization Basin
Number of basins
Dimensions at water surface
Length, ft.
Width, ft.
4
Centrifugal, non -clog
4.5
Constant speed (2),
variable speed (2)
2
Centrifugal, non -clog
6.5
Variable speed
24.5
Magnetic flow meter
4
1 @ 8 (Union County)
1 @ 14
1 @ 16
1 @ 18
2
0.06
9
9
1
404
190
* The influent pump stations pump the wastewater from the City of Monroe only.
Flow from Union County enters the plant directly upstream of the Screening
Building.
REPO RT S1M O N RO EPERISECTIO N.2
2-5 HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 2-1 (CONTINUED)
Flow Equalization Basin (continued)
Average depth, ft.
Side slope, horizontal to vertical
Volume, mil. gal
Aeration Basins
Number
Dimensions
Length, ft.
Width, ft.
Sidewater depth, ft.
Volume, each basin, mil. gal.
Total volume, mil. gal.
Detention time at design flow, hours
Aeration System
Type
Type of diffusers
Number of diffusers per basin
Total number of diffusers
Blowers
Number
Capacity of each blower, scfm
Secondary Clarifiers
Number
Diameter, ft.
Sidewater depth, ft.
Total volume, mil. gal.
Total surface area, ft.2
Overflow rate at design flow, gpd/ft.2
9
3:1
4.15
5
120
4@ 60
1 @ 90
16
4 @ 0.86
1 @ 1.29
4.74
12.6
Fine bubble diffused air
Membrane
4 @ 1,060
1 @ 1,610
5,850
3
7,885
4
85
12
2.04
22,700
395
REPO RTSWO N RO EPERISECTI O N.2
2-6
HAZEN AND SAWYER
Environmental Engineers & Scientists

1,0" TABLE 2-1 (CONTINUED)
Return/Waste Activated Sludge Pumping Stations No. 1 and No. 2
Number of pumps, each station 3
Type Horizontal, centrifugal, non -clog,
self priming
Capacity of each pump, gpm (mgd) 1,630 (2.35)
Total firm capacity, mgd 11.75
Type of drive Constant speed motor, adjustable
sheaves
Tertiary Filters
Number 6
Type Dual media, w/ air scour
Dimensions of each filter
Length, ft. 24
Width, ft. 20
Depth of media
Anthracite, in. 24
Sand, in. 12
Gravel, in. 18
Total surface area, ft.2 2,880
Filtration rate at design flow, gpm/ft.2 2.17
Backwash Supply Pumps
Number 2
Capacity of each pump, mgd 14.1
Backwash Waste Pumps (to Flow Equalization Basin)
Number 2
Capacity of each pump, mgd 13.8
Chlorine Feed Facilities
Total ton container inventory capacity
(including containers on manifolds) 10
Number of ton containers on manifolds 4
Normal withdrawal of chlorine Gas
Number of chlorinators 2
Capacity, each, lb./day 500
Sulfur Dioxide Feed Facilities
Total 150-lb cylinder inventory capacity
(including cylinders on manifolds) 12
Number of 150-lb cylinders on manifolds 8
Number of scales 1
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 2-1 (CONTINUED)
Sulfur Dioxide Feed Facilities (continued)
Number of cylinders on scale
Normal withdrawal of sulfur dioxide
Number of sulfonators
Capacity, each, lb./day
Chlorine Contact Tanks
Number
Total volume, gal.
Detention time at design flow, min.
Post Aeration
Type
Aerobic Digesters/Thickeners/Storage Tanks
Number
Dimensions of each digester
Diameter, ft.
Volume of each digester, mil. gal.
Total volume, mil. gal
Aeration and mixing system
Type
Digester/Storage Tank No. 1
Aerators
Mixers
Digester/Storage Tank No. 2
Aerators
Mixers
Digesters/Thickeners Nos. 3 and 4
Aerators
Digester/Storage Tank No. 5
Aerators
2
Gas
2
100
2
222,470
36
Cascade
5
2 @ 65
1@80
1@115
1 @ 140
2@ 0.25
1@ 0.49
1@ 1.15
1@ 3.00
5.14
Mechanical, floating
1@ 40 HP, 2 @ 7.5 HP
2@ 7.5 HP
3@ 40 HP
1@ 40 HP
1 each @ 30 HP
3@ 60 HP
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & S«arnissts

TABLE 2-1 (CONTINUED)
Centrifuge Dewatering Facilities
Number of centrifuges
Capacity of each unit, gpm (2% solids)
2
90
Sand Drying Beds (Backup)
Number 15
Dimensions of each bed
Length, ft. 120
Width, ft. 20
Total surface area, ft.2 36,000
Suspended solids loading, lb/ft.2-year 15
Solids loading capacity, lb/day 1,480
Vacuum Drying Beds (Not in Service)
Number 2
Dimensions
Length, ft. 40
Width, ft. 20
Total surface area, ft. 2 1,600
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

PLOT DATE 12 03 9. AM PLOT SCALE = 1:1 CAD FILE = H: DRAYANGS 3515-3 0&M 3515-007 b al. XREF FL. -1 NONE
INFLUENT
PUMPING
STATIONS
COUNTY FLOW
METER
CITY FLOW
METERS
CENTRATE
ROTARY
SCREENS
SUPERNATANT
AEROBIC
DIGESTERS/
THICKENERS
NO 3&4
uME�
AEROBIC
DIGESTER/
STORAGE
TANK NO
FLOW
EQUALIZATION
BASIN
FILTER BACKWASH RETURN
AERATION BASINS
SPUTTER BOX
WAS
AERATION
BASINS
SECONDARY
CLARIFIERS
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CENTRIFUGES
AEROBIC
DIGESTER/
STORAGE
TANK NO 1
STATIONS
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DIGESTER/
r __.. STORAGE
L TANK NO 5
f-L-• LIME
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TRUCK LOADING PUMP
LAND APPLICATION
HAZENAND SAYERR
Environmental Engineers & Scientists
RALEIGH. NORTH CAROLINA
J
TERTIARY
FILTERS
FILTER
BACKWASH
LJ'
LEGEND
© PUMPS
WASTEWATER FLOW
— — SOLIDS FLOW
CHLORINE
CONTACT
TANKS
FLOW
MEASUREMENT
CASCADE
AERATION
EFFLUENT TO
RICHARDSON CREEK
CL2
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NPW
MONROE WASTEWATER TREATMENT PLANT
MONROE, NORTH CAROLINA
EXISTING PLANT
PROCESS FLOW SCHEMATIC

roEN
Incoming wastewater flows through two rotary screens, which remove solids which
will not pass through the 0.06-inch screen openings. Rotation of the cylindrical
screens directs the captured screenings to screw conveyors which then carry the
solids to the screenings dumpster. Screenings are presently disposed of at the Union
County Landfill.
Flow Equalization Basin
Screened effluent is conveyed by gravity from hoppers under the Screening Building
to the aeration basin splitter box. Piping is also provided to convey excess flow to
a separate splitter box with weir level control to convey the excess flow to flow
equalization basin. The equalization basin may be filled and emptied under several
control strategies, including equalizing diurnal flows, equalizing weekend vs. weekday
flows, equalizing wet weather flows, or equalizing dry weather flows to equalize
diurnal organic demands on the aeration basins. A flow equalization return pump
station on the west end of the equalization basin returns flows to the aeration basin
splitter box during low flow periods. In addition to equalization, the basin receives
filter backwash wastewater from the filter backwash waste pumps at the tertiary
filters.
Aeration Basins
Screened wastewater, including return flows from the flow equalization basin, is
distributed to five aeration basins through the aeration basin splitter box. Aeration
Basin No. 1 through 4 each have a volume of 0.86 million gallons, and Aeration Basin
No. 5 has a volume of 1.29 million gallons. The total aeration basin volume is 4.74
million gallons, which provides a detention time of 12.6 hours at the plant design
capacity of 9.0 mgd. Aeration basin effluent flows into effluent boxes and is then
conveyed into a secondary clarifier splitter box.
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HAZEN AND SAWYER
Environmentsl Engineers & Scientists

Airflow to the aeration basins is conveyed in a process air pipeline form the Blower
Building. Two drop legs in each basin convey the airflow to fine bubble diffusers
mounted on the floor of the basins. Aeration Basin No. 1 through 4 have each 1,060
diffusers and Aeration Basin No. 5 has 1,610 diffusers.
Secondary Clarifiers
A total of four secondary clarifiers are provided for settling of the activated sludge.
The four clarifiers are operated in two parallel trains with two clarifiers in each train.
Each clarifier is center feed, peripheral overflow -type, with suction -type solids
collection and removal.
Return Activated Sludge Pumping Stations
f'"'N, Two return activated sludge (RAS) pumping station are provided, one for each pair
of secondary clarifiers. Both pump stations pump return settled solids and scum from
the secondary clarifiers to the aeration basin splitter box. Each station includes three
pumps, and may operated continuously or intermittently based on timers. The
combined RAS pump stations have a firm capacity of 11.75 mgd, or approximately
131 percent of plant design flow. The RAS pump stations are also used for wasting
activated sludge to the aerobic digesters through manually -operated valves on the
RAS and WAS piping.
Tertiary Filters
Six dual media tertiary filters with air scour are provided for final effluent polishing
following the secondary clarifiers. Each filter has a total media depth of 36 inches,
and is 24 feet long by 20 feet long by 20 feet wide. At the plant design flow of 9
mgd, the filters have a hydraulic loading rate of 2.17 gpm/ft2. Filter backwash is
pumped from the influent end of the chlorine contact tanks by two filter backwash
REPORTSIMONRO EPERIS£CTION.2
2-11 HAZEN AND SAWYER
Environmental Engineers & Scientists

rmaN
supply pumps. Two separate vertical turbine filter backwash waste pumps are used
to convey filter backwash wastewater to the flow equalization basin for return at a
controlled rate to the aeration basin splitter box.
Chlorination Facilities
Chlorination facilities consist of a Chlorine Feed Building with two wall -mounted
chlorinators, each with a capacity of 500 pounds per day. Adjacent to the building
is a covered storage area with space for ten chlorine ton containers, four of which
can be connected to a chlorine manifold. A vacuum regulator is provided at the end
of the manifold to control vacuum feed to the chlorinators. No scales are provided
for the ton containers. The duty chlorinator is flow -paced and conveys chlorine gas
at a controlled rate to an injector, where the chlorine is mixed with water and then
conveyed as chlorine solution to the chlorine contact tanks.
Filtered effluent enters the chlorine contact tanks through a 30-inch pipeline to an
influent chamber that also serves as a wet well for the filter backwash supply pumps
and as the chlorine feed point. Chlorinated wastewater flows through the two parallel
contact tanks which have a total volume of approximately 0.22 million gallons. The
detention time is approximately 36 minutes at the plant design flow of 9.0 mgd.
Dechlorination Facilities
Dechlorination facilities consist of a Sulfur Dioxide Feed Building with two rooms.
One room contains the sulfur dioxide cylinders and two wall -mounted vacuum
regulators. The other room contains two wall -mounted sulfonators, each with a
capacity of 100 pounds per day, and two sulfur dioxide injectors. Space is provided
for eight 150-pound sulfur dioxide containers to be connected to a pair of manifolds,
four connected to each vacuum regulator, and additional storage for empty or full
containers. The regulators are connected by an automatic switchover device.
REPO RTSIM O N RO EPERIS ECTIO N.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

Sulfur dioxide solution is mixed with the plant effluent flow at the chlorine contact
tank effluent box. The plant effluent flow is discharged to the effluent box from two
rectangular weirs at the effluent end of the two contact tanks.
Plant Effluent Discharge
The plant effluent flow rate is measured by a rectangular weir and an effluent flow -
proportional composite sample is taken in the effluent pipeline immediately upstream
of the cascade aeration flume. The cascade aeration flume assures that the dissolved
oxygen content in the discharge to Richardson Creek meets or exceeds NPDES
permit requirements.
2.1.2 Solids Handling Facilities
Solids treatment and disposal facilities consist of aerobic digestion for stabilization of
waste activated sludge, centrifuges for solids thickening or dewatering, and storage
of liquid sludge associated with contract land application of liquid sludge on privately -
owned farms.
Sand drying beds are available for backup dewatering and dewatered cake storage.
Aerobic Digesters/Thickeners/Storage Tanks
Five aerobic digesters/thickeners/storage tanks are provided for stabilization,
thickening and storage of waste activated sludge. The aerobic digesters provide
volume reduction by destruction of volatile solids and by decanting to achieve a solids
concentration of approximately 6 to 8 percent. Decant water is conveyed by gravity
to Influent Pump Station No. 1 for return to the liquid treatment process.
REPORTSIMONROEPERISECTION.2
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HAZEN AND SAWYER
Environmental Engineers & Scientists

Aerobic Digester/Storage Tank No. 1 has a diameter of 80 feet with a volume of 0.49
million gallons. Digester/Storage Tank No. 2 has a diameter of 115 feet with a
volume of 1.15 million gallons. Digesters/Thickeners No. 3 and 4 each have a
diameter of 65 feet with a volume of 0.25 million gallons. The new digester/storage
tank (No. 5) has a diameter of 140 feet with a volume of 3.0 MG. The total volume
of all digesters in approximately 5.14 million gallons.
Except for Digester/Storage Tank No. 5, the aerobic digesters/thickeners/storage
tanks are mixed and aerated using surface mechanical aerators, supplemented in
Digester/Storage Tanks No. 1 and No. 2 by surface mixers. Digester/Storage Tank
No. 1 includes a 40-HP aerator, - two 7.5-HP mixers and two 7.5-HP aerators.
Digester/Storage Tank No. 2 includes one 40-HP mixer and three 40-HP aerators.
Digester/Storage Tanks No. 3 and 4 each include one 30-HP aerator. Two 200-HP
blowers and a diffused air aeration system are currently proposed in new
Digester/Storage Tank No. 5.
Piping interconnections allow several treatment schemes. Normally, waste activated
sludge is first conveyed to either Digester/Thickeners No. 3 or No. 4, where most of
the thickening takes place. Solids are then conveyed to the centrifuges and thickened
sludge stored in Digesters/Storage Tanks No. 1, 2, and 5.
Centrifuges
Two centrifuges are provided for dewatering or thickening of digested solids. The
centrifuges each have a capacity of 90 gpm and, with cationic polymer conditioning,
produce a dewatered cake with a solids concentration of approximately 15 percent.
The dewatered cake is currently trucked to a solids lagoon; however, after completion
of the current $1.3 million sludge handling improvements project, thickened sludge
will be pumped from the centrifuges to Digester/Storage Tanks No. 1, No. 2 or No. 5.
Centrate is returned by gravity to Influent Pump Station No. 1. Each centrifuge is fed
REPO RTSIMO N RO EPERISECTI O N.2
2-14 HAZEN AND SAWYER
Environmental Engineers Sr Scientists

by a new centrifuge feed pump, which is being replaced as part of the $1.3 million
solids handling improvements project. Polymer storage, mixing and aging is provided
for either liquid or dry polymer.
Solids Lagoon
An existing lagoon is currently used to store solids before being removed for land
application. The solids lagoon has a capacity of approximately 4.5 million gallons.
Biosolids are pumped from the lagoon to a tanker truck for land application at a solids
concentration of approximately 8 percent. Dilution is achieved either by rainfall
during storage, or by blending unthickened digested biosolids from Digester No. 1 to
provide a thickened slurry suitable for pumping.
Sand Drying Beds
Fifteen sand drying beds are provided, two for backup dried cake storage and thirteen
for backup dewatering. The sand drying beds are each 120 feet long by 20 feet
wide, for a total area of 4800 ft2 for storage and 31,200 ft2 for dewatering. The sand
drying beds have a design loading rage of 15 lb/ft2 per year, for a total of 234 dry
tons per year. Biosolids removed from the drying beds are also removed from the
plant site for beneficial use by land application. Two vacuum drying beds are no
longer in use.
2.2 Influent and Effluent Wastewater Characteristics and Design Data
Wastewater characteristics of significance in the design and operation of wastewater
treatment facilities include flow; conventional parameters , including BOD, ammonia
nitrogen, and total suspended solids; toxic parameters, such as heavy metals,
cyanide, and total toxic organics; and large solids and floating material.
REPORTSIMONROEPERISECTION.2
2-15 HAZEN AND SAWYER
Environmental Engineers Si Scientists

Influent and effluent data for the Monroe Wastewater Treatment Plant from January
1993 through September 1996 is summarized in Tables 2-2 and 2-3. Based on the
data presented in Table 2-2, influent wastewater concentrations for BOD5, TSS and
ammonia nitrogen (NH3 N) have increased each year. This is due to increased
wastewater loadings from the industries discharge to the Monroe WWTP. The most
recent 12-month period was evaluated to determine annual average and maximum
month influent wastewater characteristics. Influent data for the 12-month period
from October 1995 through September 1996 is presented in Table 2-4.
From a review of the influent data for October 1995 through September 1996, design
average daily influent BOD5 and TSS concentrations are projected to be 380 influent
and 430 mg/L, respectively. Design average daily TKN and NI-13-N concentrations are
estimated at 31.5 and 21 mg/L, respectively. Maximum month influent BOD5 and
TSS concentrations are 450 and 480 mg/L, respectively. Maximum month TKN and
NH3-N concentrations are 36 and 24 mg/L, respectively.
Maximum month influent BOD concentrations at the Monroe WWTP have increased
from 217 mg/L in 1992 to 450 mg/L in 1996, representing more than double the BOD
loading at the plant over the past 4 years based on increases in concentration alone.
A maximum month to annual average flow ratio of 1.17 was assigned based on data
over the 12-month period. A 2.5 ratio was assigned for peak day flow, except for
the influent pump stations which were assigned a peak day flow ratio of 3.0. From
a review of the three years of data, peak influent flows in excess of 2.5 were all
associated with heavy rainfall events.
REPORTSIMONROEPERISECT1ON.2
2-16
HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 2-2
MONROE WASTEWATER TREATMENT PLANT INFLUENT CHARACTERISTICS
Month
Flow BOD5 BOD5 TSS TSS NH3-N NH3-N
(MGD) (mgll) (lb/day) (mg/I) (Ib/day) (mg/I) (lb/day)
Jan-93 8.90 182.8 13571.6 218.1 16192.3 11.9 883.5
Feb-93 7.60 232.1 14703.7 262.1 16604.2 14.5 918.6
Mar-93 9.16 199.1 15201.8 214.9 16408.2 10.7 817.0
Apr-93 7.25 225.1 13608.8 196.1 11855.6 15.2 918.9
May-93 5.33 257.8 11451.2 269.1 11953.1 19.8 879.5
Jun-93 4.60 238.7 9165.4 242.8 9322.9 23.1 887.0
Jul-93 4.79 161.3 6442.4 167.7 6698.0 24.9 994.5
Aug-93 5.12 148.0 6324.7 168.0 7179.3 23.0 982.9
Sep-93 5.19 143.0 6183.7 155.0 6702.6 22.0 951.3
Oct-93 5.39 220.0 9884.1 212.0 9524.6 22.0 988.4
Nov-93 5.93 265.0 13105.9 274.0 13551.0 25.5 1261.1
Dec-93 6.84 346.0 19746.4 334.0 19061.6 20.0 1141.4
Jan-94 7.63 262.0 16672.2 332.0 21126.6 15.5 986.3
Feb-94 8.23 327.0 22444.7 315.0 21621.0 16.0 1098.2
Mar-94 7.53 276.0 17332.9 230.0 14444.0 16.6 1042.5
Apr-94 5.66 261.0 12320.3 246.0 11612.3 22.4 1057.4
May-94 5.51 211.0 9696.2 186.0 8547.3 18.0 827.2
Jun-94 6.25 166.0 8652.8 145.0 7558.1 21.0 1094.6
Jul-94 5.99 187.7 9376.9 275.0 13738.1 23.2 1159.0
Aug-94 6.55 274.3 14984.2 350.7 19157.7 22.8 1245.5
Sep-94 6.88 231.0 13254.6 279.0 16008.8 23.8 1365.6
Oct-94 6.65 344.0 19078.6 610.0 33831.2 21.7 1203.5
Nov-94 5.97 341.0 16978.3 702.0 34952.4 25.0 1244.7
Dec-94 6.87 315.0 18048.2 453.0 25955.0 17.6 1008.4
Jan-95 7.70 247.0 15861.8 217.0 13935.3 16.0 1026.2
Feb-95 9.16 286.3 21881.3 259.5 19833.0 16.3 1245.0
Mar-95 7.88 265.0 17415.6 381.0 25039.0 18.4 1209.2
Apr 95 5.61 332.0 15533.4 441.0 20633.2 28.6 1338.1
May-95 5.94 308.0 15258.2 443.0 21946.0 25.7 1273.2
Jun-95 6.95 298.0 17273.0 388.0 22489.6 21.6 1252.0
Jul-95 5.93 364.0 18002.1 350.0 17309.7 31.0 1533.1
Aug-95 7.26 230.0 13928.6 407.8 24696.1 24.9 1509.7
Sep-95 6.72 329.3 18443.7 415.5 23275.2 23.7 1324.8
Oct-95 8.06 276.2 18566.3 296.8 19951.0 20.0 1343.1
Nov-95 7.78 310.0 20114.4 388.0 25175.5 16.8 1090.1
Dec-95 6.34 366.0 19352.5 492.0 26014.8 21.6 1142.1
Jan-96 9.10 334.0 25348.6 439.0 33317.5 12.7 963.9
Feb-96 8.26 392.0 27004.3 420.0 28933.1 21.8 1501.8
1993 Average 6.34 218.2 11615.8 226.2 12087.8 19.4 968.7
1993 Max Month 9.16 346.0 19746.4 334.0 19061.6 25.5 1261.1
Ratio 1.4 1.6 1.7 1.5 1.6 1.3 1.3
1994 Average 6.64 266.3 14903.3 343.6 19046.0 20.3 1111.1
1994 Max Month 8.23 344.0 22444.7 702.0 34952.4 25.0 1365.6
Ratio 1.2 1.3 1.5 2.0 1.8 1.2 1.2
1995 Average 7.11 301.0 17635.9 373.3 21691.5 22.0 1273.9
1995 Max Month 9.16 366.0 21881.3 492.0 26014.8 31.0 1533.1
Ratio 1.3 1.2 1.2 1.3 1.2 1.4 1.2

TABLE 2-3
INFLUENT AND EFFLUENT CHARACTERISTICS FOR CONVENTIONAL POLLUTANTS
Influent Effluent Removal Effluent Influent Effluent Removal • Effluent Influent Effluent Removal Effluent
BOO BOD Rate BOD Limit TSS TSS Rate TSS Limit NH3-N NH3-N Rate NH3-N Limit
Month (mgA) (mgA) BOD (mgA) (mgA) (lb/day) TSS (mgA) (mgA) (mgA) NH3-N (mgA)
Jan-93 182.8 7.7 95.81% 21.0 218.1 25.6 88.26% 30.0 11.9 5.32 55.29% 6.0
Feb-93 232.1 12.3 94.71% 21.0 262.1 28.2 89.26% 30.0 14.5 8.29 42.83% 6.0
Mar-93 199.1 13.9 93.04% 21.0 214.9 21.7 89.90% 30.0 10.7 3.23 69.81% 6.0
Apr-93 225.1 9.0 96.02% 21.0 196.1 15.9 91.89% 30.0 15.2 2.06 86.45% 6.0
May-93 257.8 2.9 98.88% 21.0 269.1 15.8 94.13% 30.0 19.8 5.51 72.17% 6.0
Jun-93 238.7 4.0 98.32% 21.0 242.8 9.0 96.29% 30.0 23.1 7.36 68.14% 6.0
Jul-93 161.3 6.2 96.14% 21.0 167.7 10.0 94.04% 30.0 24.9 6.60 73.49% 6.0
Aug-93 148.0 7.1 95.20% 21.0 168.0 16.0 90.48% 30.0 23.0 1.50 93.48% 6.0
Sep-93 143.0 5.8 95.94% 21.0 155.0 18.2 88.26% 30.0 22.0 2.60 88.18% 6.0
0c1-93 220.0 8.3 96.23% 21.0 212.0 26.0 87.74% 30.0 22.0 1.90 91.36% 6.0
Nov-93 265.0 9.6 96.40% 21.0 274.0 20.0 92.70% 30.0 25.5 1.10 95.69% 6.0
Dec-93 346.0 13.1 96.21% 21.0 334.0 28.5 91.47% 30.0 20.0 1.26 93.70% 6.0
Jan-94 262.0 10.2 96.11% 21.0 332.0 17.0 94.88% 30.0 15.5 1.10 92.90% 6.0
Feb-94 327.0 19.0 94.19% 21.0 315.0 27.0 91.43% 30.0 16.0 1.00 93.75% 6.0
Mar-94 276.0 8.5 96.92% 21.0 230.0 11.7 94.91% 30.0 16.6 3.40 79.52% 6.0
Apr-94 261.0 5.0 98.09% 21.0 246.0 4.5 98.17% 30.0 22.4 0.39 98.26% 6.0
May-94 211.0 4.1 98.06% 10.0 186.0 3.4 98.17% 30.0 18.0 0.00 100.00% 3.0
Jun-94 166.0 3.9 97.65% 10.0 145.0 3.8 97.38% 30.0 21.0 0.00 100.00% 3.0
Jul-94 187.7 5.2 97.25% 10.0 275.0 8.4 96.96% 30.0 23.2 0.00 100.00% 3.0
Aug-94 274.3 3.3 98.80% 10.0 350.7 4.0 98.86% 30.0 22.8 0.13 99.43% 3.0
Sep-94 231.0 2.8 98.79% 10.0 279.0 4.1 98.53% 30.0 23.8 0.00 100.00% 3.0
0ct-94 344.0 2.7 99.22% 10.0 610.0 3.7 99.39% 30.0 21.7 0.00 100.00% 3.0
Nov-94 341.0 2.1 99.38% 20.0 702.0 3.6 99.49% 30.0 25.0 0.00 100.00% 6.0
Dec-94 315.0 3.1 99.01% 20.0 453.0 4.9 98.93% 30.0 17.6 0.33 98.13% 6.0
Jan-95 247.0 3.4 98.64% 10.0 217.0 3.0 98.62% 30.0 16.0 0.09 99.44% 4.0
Feb-95 286.3 7.4 97.42% 10.0 259.5 35.6 86.28% 30.0 16.3 0.05 99.69% 4.0
Mar-95 265.0 5.1 98.08% 10.0 381.0 6.0 98.43% 30.0 18.4 0.18 99.02% 4.0
Apr-95 332.0 5.0 98.49% 5.0 441.0 4.0 99.09% 30.0 28.6 0.36 98.74% 2.0
May-95 308.0 3.4 98.90% 5.0 443.0 4.0 99.10% 30.0 25.7 0.06 99.75% 2.0
Jun-95 298.0 4.7 98.42% 5.0 388.0 3.0 99.23% 30.0 21.6 0.13 99.40% 2.0
Ju1.95 364.0 4.5 98.76% 5.0 350.0 6.0 98.29% 30.0 31.0 0.05 99.84% 2.0
Aug-95 230.0 5.2 97.75% 5.0 407.8 10.6 97.40% 30.0 24.9 0.06 99.76% 2.0
Sep-95 329.3 4.5 98.64% 5.0 415.5 4.4 98.94% 30.0 23.7 0.08 99.67% 2.0
0ct-95 276.2 3.5 98.75% 5.0 296.8 8.3 97.21% 30.0 20.0 0.13 99.36% 2.0
Nov-95 310.0 2.0 99.34% 10.0 388.0 5.5 98.60% 30.0 16.8 0.04 99.76% 4.0
Dec-95 366.0 2.1 99.42% 10.0 492.0 7.0 98.58% 30.0 21.6 0.10 99.54% 4.0
Jan-96 334.0 4.8 98.57% 10.0 439.0 9.0 97.95% 30.0 12.7 0.10 99.21% 4.0
Feb-98 392.0 7.0 98.22% 10.0 420.0 10.0 97.62% 30.0 21.8 0.08 99.63% 4.0
Mar-96 448.0 4.4 99.03% 10.0 462.0 7.0 98.48% 30.0 19.5 0.05 99.74% 4.0
Apr-96 416.0 2.9 99.30% 7.3 526.0 4.0 99.24% 30.0 20.5 0.29 98.59% 1.0
May-96 412.0 5.0 98.79% 7.3 320.0 5.0 98.44% 30.0 25.6 0.05 99.80% 1.0
Jun-96 469.0 4.6 99.01% 7.3 377.0 4.0 98.94% 30.0 29,6 0.08 99.73% 1.0
JuI-98 395.0 4.5 98.86% 7.3 588.0 3.0 99.49% 30.0 26.1 0.07 99.73% 1.0
Aug-96 382.0 2.2 99.43% 7.3 886.0 2.3 99.74% 30.0 22.9 0.04 99.83% 1.0
Sep-96 332.0 3.4 98.97% 7.3 336.0 5.0 98.51 % 30.0 17.0 0.06 99.65% 1.0

TABLE 2-4
MONROE WUVfP
INFLUENT WASTEWATER CHARACTERISTICS
MONTH FLOW BOD5 TSS NH3-N
mgd mg/L lb/day mg/L lb/day mg/L lb/day
OCT 95 8.06 276 18,566 297 19,951 20.0 1,344
NOV 95 7.78 310 20,114 388 25,175 16.8 1,090
DEC 95 6.34 366 19,352 492 26,015 21.6 1,142
JAN 96 9.01 334 25,098 439 32,988 12.7 954
FEB 96 8.26 392 27,004 420 28,933 21.8 1,502
MAR 96 8.85 448 33,066 462 34,100 19.5 1,439
APR 96 8.08 416 28,033 526 35,446 20.5 1,381
MAY 96 7.24 412 24,877 320 19,322 25.6 1,546
JUN 96 7.15 469 27,967 377 22,481 29.6 1,765
JUL 96 6.77 395 22,302 588 33,200 26.1 1,474
AUG 96 6.62 382 21,091 496 27,385 22.9 1,264
SEP 96 6.94 332 19,216 336 19,448 17.0 984
1995-96
AVG 7.59 378 23,891 428 27,037 21.2 1,324
MAX 9.01 469 33,066 588 35,446 29.6 1,765
MIN 6.34 276 18,566 297 19,322 12.7 954

2.3 Existing Treatment Plant Performance
Performance data showing conventional parameter influent and effluent
characteristics for the period from January 1993 to September 1996 is summarized
in Table 2-3 above. Effluent characteristics for heavy metals, cyanide, and effluent
toxicity for January 1995 through October 1996 are summarized in Table 2-5.
The Monroe Wastewater Treatment Plant operated under an SOC during the first part
of this review period, from January 1993 through April 1994. Performance data
between May 1994 and December 1994 is for a plant upgraded to meet higher
effluent quality standards at a capacity of 7.0 mgd. Data since January 1995 is for
the expanded plant capacity of 9.0 mgd.
The effluent data from May 1994 reveals consistently good performance of the
treatment plant. There have been no violations of the ammonia nitrogen limit since
the plant upgrade was completed in 1994. Since May 1994, there has been only one
BOD excursion, a 5.17 mg/L monthly average concentration in August 1995 (the limit
was then 5 mg/L). However, when combined with the ammonia nitrogen effluent
concentration, the combined oxygen demand of the effluent was less than the total
allowed (the plant NPDES permit has since been revised to summer limits of 7.3 mg/L
for BOD and 1.0 mg/L for ammonia nitrogen). The only other excursions during this
period was for total suspended solids in February 1995, when a washout of the
secondary clarifiers occurred during an intense storm event; one failed chronic
toxicity test in December 1995, which was resampled the following week and
passed; and two months of heavy rainfall when the monthly average flow exceeded
9.0 mgd. The plant has consistently met all permit limits for pH, fecal coliforms,
dissolved oxygen, heavy metals and cyanide. Since dechlorination facilities were
placed on line in January 1995, the plant effluent has met the stringent residual
chlorine effluent limit, allowing the first 30 days for start-up and "debugging" the new
equipment.
REPORTSIMO NROEPERISECTION.2
2-20
HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 2-5
EFFLUENT CHARACTERISTICS*
Cadmium Lead Nickel Cyanide Chronic
Month (ug/I) (ug/I) (ug/I) (ug/I) Toxicity
Jan-95 < 1 24 15 4
Feb-95 2 10 < 10 3
Mar-95 1 6 < 10 5 Pass
Apr-95 <1 7 <10 5
May-95 < 1 15 15 5
Jun-95 < 1 10 13 7 Pass
JuI-95 2 32 < 13 5
Aug-95 1.75 < 25 < 13 4
Sep-95 2 < 25 60 4 Pass
Oct-95 2 < 25 < 10 < 2
Nov-95 < 2 < 25 25 < 2
Dec-95 < 2 8 100 3 Fail,Pass
Jan-96 < 2 11 130 4
Feb-96 < 2 < 25 27 2
Mar-96 < 2 < 25 8 < 2
Apr-96 2 2 15 3 Pass
May-96 3 5 3 6
Jun-96 < 1 < 2 110 5
Jul-96 < 1 < 5 8 3 Pass
Aug-96 < 1 < 5 12 4
Sep-96 < 1 < 5 6 3
Oct-96 < 1 < 5 < 5 3.2 Pass
*Daily maximum value in each month

2.4 Future Effluent Limits
As referenced above, the plant effluent limits were amended in March 1996 based
on an accepted formula for total ultimate oxygen demand from carbonaceous BOD
(BOD5) and nitrogenous BOD (ammonia nitrogen). The BOD5 limit is now 7.3 mg/L
during the summer months and 14.6 mg/L during the winter months. The
ammonia nitrogen limit is 1.0 mg/L in the summer and 2.0 mg/L in the winter.
Other present limits include a monthly average of 30 mg/L for total suspended
solids, a pH between 6.0 and 9.0, a minimum dissolved oxygen of 6.0 mg/L,
residual chlorine of 17 ug/L, a fecal coliform monthly geometric mean of 200
colonies per 100 mg/L, and metal and cyanide limits as follows: 2 ug/L cadmium,
25 ug/L for lead, 88 ug/L for nickel, 5 ug/L for cyanide.
The existing permit includes the same effluent limits for 11.0 mgd as are presently
in effect at 9.0 mgd. The existing permit expires November 1, 1999. The N.C.
Division of Water Quality is presently sampling and analyzing the Yadkin -Pee Dee
River Basin under the basinwide management program and does not expect to
have tentative conclusions from this study before 1997. While it cannot be
determined at this time if any effluent limits will be changed when the permit is
issued, one possible area of concern is total nitrogen and phosphorus. Since this
decision is unknown at this time, this report recommends a plan for the plant
expansion to 11 mgd based on the limits in the present permit.
REPO RTSIMO N RO EPERISECT1O N.2
2-22 HAZEN AND SAWYER
Environmental Engineers & Saantists

SECTION 3
EVALUATION OF ALTERNATIVES FOR TREATMENT PLANT EXPANSION
3.1 Future Wastewater Flows
Wastewater flow projections for the Monroe WWTP are shown in Table 3-1. The
projections are based on growth projections provided by the City of Monroe Water
Resources Department for the City of Monroe and for Union County's East Side
collection system. These projections indicate that the Monroe Wastewater Treatment
Plant annual average flow will exceed 80 percent of the current 9.0 mgd permitted
capacity in 1996, 90 percent of the current capacity in 2000, and 100 percent of the
current capacity by 2005.
The projections in Table 3-1 assume that Union County will expand the capacity of
its East Side collection system to accommodate its growth and will continue to
discharge all flows from this service area to the Monroe Wastewater Treatment Plant.
Based on this assumption, plant flows (maximum month) are expected to reach 11.0
mgd by the year 2007 and 14 mgd by the year 2020.
However, Union County has not made a commitment at this time to expand its
collection system and increase its flow to the Monroe Wastewater Treatment Plant.
Union County has initiated discussion with the City of Monroe but no agreement has
been completed. If the County does not expand the capacity of its collection system
to the Monroe Plant, it is projected that County discharge to the Monroe Plant would
never exceed an annual average flow of 1.5 mgd (based on an existing contract for
a maximum month flow of 1.95 mgd and a maximum month to average annual ratio
of 1.3).
REPO RTSIMO N RO EPERISECTIO N.3
3-1 HAZE AND SAWYER
Environmental Engineers & Scientists

TABLE 3-1
MONROE WASTEWATER TREATMENT PLANT FLOW PROJECTIONS
ANNUAL AVERAGE FLOWS
YEAR CITY OF MONROE
COLLECTION
SYSTEM (MGD)
Actual Data:
1993
1994
1995
Projected Data:
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
4.97
5.27
5.69
5.98
6.28
6.40
6.53
6.66
6.79
6.93
7.07
7.21
7.35
7.50
7.65
7.80
7.96
8.12
8.28
8.45
8.61
8.79
8.96
9.14
9.32
9.51
9.70
9.90
UNION COUNTY
EAST SIDE
COLLECTION
SYSTEM (MGD)
TOTAL
ANNUAL
AVERAGE
FLOW (MGD)
1.37 6.34
1.37 6.64
1.42 7.11
1.45
1.48
1.50
1.53
1.57
1.60
1.63
1.66
1.69
1.73
1.76
1.80
1.83
1.87
1.91
1.95
1.99
2.03
2.07
2.11
2.15
2.19
2.24
2.28
2.33
7.42
7.75
7.91
8.06
8.23
8.39
8.56
8.73
8.90
9.08
9.26
9.45
9.64
9.83
10.03
10.23
10.43
10.64
10.85
11.07
11.29
11.52
11.75
11.98
12.22
Assumptions:
1. Assumes City growth in flow at 5% for 1996 and 1997; 2% per year from 1998-2020
2. Assumes County growth at 2% per year; also assumes County will expand
capacity of collection system to continue to use Monroe WWTP for all treatment.
3. It is noted that Union County has recently completed a sewer master plan study
which has a more aggressive growth scenario than shown above. Projected County
flow in 2015 is 2.83 MGD average annual flow and 5.84 MGD peak flow. City and
County have not negotiated a contract for this more aggressive growth scenario at this
time.
4. Maximum month to annual average flow ratio is approximately 1.17.
TOTAL
MAXIMUM
MONTH
FLOW (MGD)
9.16
8.23
9.16
8.65
9.03
9.22
9.40
9.59
9.78
9.98
10.18
10.38
10.59
10.80
11.02
11.24
11.46
11.69
11.93
12.16
12.40
12.65
12.91
13.16
13.43
13.70
13.97
14.25

raik
This planning study assumes a plant expansion by the City of Monroe to 11.0 mgd,
which would be adequate until 2009 based on the City's current flow projections and
no increase in the County's contract.
3.2 1992 Planning Study
In 1992, Hazen & Sawyer prepared a planning study for the City of Monroe which
provided for a two-phase expansion of the Monroe Wastewater Treatment Plant to
9.0 mgd and 11.0 mgd, of which the first phase of construction is completed. Many
of the facilities constructed in this first phase, and all piping and electrical
modifications, were intended to accommodate the future second phase expansion.
Recommendations from the 1992 study for the second phase expansion included the
following: (1) the addition of a sixth aeration basin with piping to connect to the
existing aeration basin influent splitter box and secondary clarifier influent splitter box,
(2) addition of a fourth centrifugal blower with piping connections, space and
electrical connections provided to accommodate the fourth blower, (3) the addition
of a pump in the new influent raw wastewater pump station (No. 2), (4) the addition
of a third rotary screen, and (5) modifications to the chlorination facilities to increase
chlorine feed capacity.
Since the 1992 study, increases in BOD loading to the wastewater treatment plant
from area industries, increases in wet weather flows, additional wear on equipment,
and changing regulations require a revision of the second phase expansion facilities
originally recommended. The following areas have been addressed in updating the
City's previous plan for expansion to 11.0 mgd:
(1) Recent records have shown that the peak day flows to the wastewater treatment
plant during intense but infrequent rainfall events can exceed the 2.5 ratio to plant
design average annual flow assumed in the 1992 study.
REPORTSIMONROEPERISECT1ON.3
3-3
HAZENv AND SAWYER
Environmental Engineers & Scientists

(2) Recent records have shown that the maximum month to average month flow ratio
of 1.3 assumed in 1992 has decreased and current design criteria should be based
on a ratio of 1.17.
(3) Influent concentrations for BOD5, NH3-N, and TSS have increased significantly
since 1992, resulting in revised design criteria for these parameters for the proposed
plant expansion.
(4) Improvements are needed to insure reliability of equipment.
The following sections of this report discuss the evaluations of the required expansion
facilities for 11 mgd with consideration of the above issues.
3.3 Evaluation of Alternatives and Recommendations
influent Pumping Stations
In order to pump wastewater from the City of Monroe collection system to the
treatment plant processes or to the flow equalization basin, sufficient capacity will be
required to meet a firm pumping capacity of 3.0 times the maximum month flow.
Assuming a maximum month flow of 1.95 mgd continues to be reserved for the
County East Side collection system under the existing contract, the maximum month
influent pumping rate from the City collection system is 9.05 mgd. With a peak flow
rate of 3.0 times 9.05 mgd, the influent pump stations must have a firm capacity of
approximately 27 mgd. Since the present firm capacity is 24.5 mgd, one additional
pump with a capacity of 6.5 mgd should be added for the plant expansion. The
.existing parallel 16-inch, 20-inch, and 24-inch force mains have been evaluated and
have been determined to have adequate capacity for conveying the increased firm
pumping capacity.
REPO RTSIMO N RO EPERISECTIO N.3
3-4
HAZEN AND SAWYER
Environmental Engineers & Scientists

Preliminary Screening
The two existing rotary screens each have a capacity of 9.0 mgd. As part of the
plant expansion, a third screen of the same capacity as the existing screens should
be added. The new screen will be a fine screen and will be located in a separate
structure near the Blower Building. This will provide a screening capacity of
27.0 mgd, or a firm capacity of 18.0 mgd. A diversion box already exists to allow
the operators to divert peak flow around the existing screens. It will remain in service
after the plant expansion to allow the plant to handle the highest peak flows
expected.
Flow Equalization Basin
The existing flow equalization basin is a clay -lined unaerated lagoon on the east side
of the treatment plant, with a storage capacity of 4.15 million gallons. Operating
experience indicates that additional equalization volume is required to accommodate
current peak wet weather flows. In addition, increased BOD loadings have reduced
the safety factor for nitrification from 2.0 to 1.0 at 9.0 mgd permitted capacity.
Diurnal and wet weather flow equalization is required at a safety factor for
nitrification of 1.0 to consistently meet NPDES permit requirements.
An evaluation of wet weather flow data for the 21-month period from January 1995
through September 1996 was conducted to determine flow equalization basin
capacity for proposed plant expansion. Hourly peak flows for the ten wettest days
over this period were evaluated. A maximum peak flow of 15 mgd after flow
equalization was assumed based on operating experience for the existing secondary
clarifiers. Based on this evaluation, a total flow equalization basin capacity of
5.0 million gallons is recommended for the proposed plant expansion to 11 mgd.
REPORTSIMO NROEPERISECTION.3
3-5
HAZEN AND SAWYER
Environmental Engineers & Scientists

The increased flow equalization basin capacity will provide other advantages besides
equalization of peak flows. It may also be used to equalize blower electrical loads,
or improve "peak shaving", by lowering the oxygen demand on the plant during peak
electrical demand periods.
Aeration Basins
Two new aeration basins will be required to provide nitrification at 11.0 mgd. The
additional basins will be located south of Secondary Clarifiers No. 1 and No. 2. The
two new aeration basins will each be the same size as the existing Aeration Basin
No. 5. The two basins, in combination with the existing basins, will provide a total
aeration basin capacity of 7.33 million gallons and a detention time of 16.0 hours at
the plant design flow of 11.0 mgd. The existing and new aeration basins will provide
complete nitrification at maximum month design loadings at a temperature of 14°C,
a pH of 6.8, and a DO of 2.0 mg/L, with a safety factor of approximately 1.0. The
need for two aeration basins for 11 mgd instead of one, as proposed in the 1992
study, is due to the increased loadings to the Monroe Plant from industrial sources.
The activated sludge influent BODS concentration has more than doubled since the
time of the 1992 study.
The existing aeration basin splitter box will be modified to distribute flow evenly to
all basins based on equal detention time. The effluent box at the end of Aeration
Basins No. 1 through 4 will be modified, as necessary, to receive the effluent from
the new aeration basins and convey the flow to the secondary clarifier splitter box.
New piping will be constructed from the aeration basin influent splitter box and the
aeration basin effluent box to the new aeration basins.
REPORTSIMO N RO EPERISECTI ON.3
3-6
HAZEN AND SAWYER
Environmental Engineers & Scientists

Aeration Blowers
The Blower Building presently includes three centrifugal blowers, each with a capacity
of 7,885 scfm, for a firm capacity of 15,770 scfm. The present building also has
space for a fourth blower. The airflow requirements for an 11.0 mgd plant based
upon design loading conditions discussed above is approximately 32,000 scfm. Two
new 7,885-scfm blowers will ultimately be required to meet this need. For the
purpose of this study, the price for one new blower is included as part of the
expansion, assuming that the fifth blower is deferred until the time it is actually
needed.
Only a minor amount of air piping within and immediately outside of the Blower
Building will be required to add the fourth blower. The suction and discharge piping
are already sized for this additional blower and the manifolds designed to
accommodate the additional connection. A new blower building or a blower building
extension would be required for a fifth blower.
Secondary Clarifiers
The four existing secondary clarifiers have adequate capacity for the proposed plant
expansion to 11 mgd. The four clarifiers will have surface overflow rate of
480 gpd/ft.2 at the expanded flow capacity of 11 mgd.
RAS Pump Stations
The existing RAS pumps provide a firm pumping capacity of 11.75 mgd. A firm
pumping capacity of 100 percent of plant design flow, or 11 mgd, is recommended
for nitrification activated sludge facilities.
REPO RTSIMO N RO EPERISECTiO N.3
3-7
HAZEN AND SAWYER
Environmental Engineers & Scientists

Tertiary Filters
The six existing tertiary filters are performing satisfactorily and have adequate
capacity for the expanded plant flow of 11 mgd. The existing filters will have a
hydraulic loading rate of 2.65 gpm/ft.2 at the design flow of 11 mgd.
Chlorination/Dechlorination Facilities
The existing chlorine contact tanks will have a detention time of 29.1 minutes at the
expanded plant flow of 11 mgd: A contact time of 30 minutes is required at
permitted flow by State regulations. Methods of increasing contact time by
approximately 1 minute will be investigated. It is assumed for the cost estimate that
construction of an additional contact tank will not be required.
It is recommended that the capacity of the chlorine and sulfur dioxide feed facilities
be increased for the expanded plant flow. It is recommended that the existing
500 lb/day chlorinators be replaced with 2,000 Ib/day. chlorinators. Each of the new
chlorinators would have capacity for a chlorine feed dosage of 8.7 mg/L at the peak
design flow of 27.5 mgd. One chlorinator would be a duty chlorinator, with the other
on standby. It is recommended that an additional manifold and automatic switchover
unit be provided to allow automatic switchover from one manifold to the other, with
four containers on each manifold. Addition of ton container scales is also
recommended to monitor available chlorine remaining in the duty ton containers.
It is recommended that the existing 100 lb/day sulfonators be modified to provide a
sulfur dioxide feed rate of 200 lb/day for each sulfonator. Each of the modified
sulfonators would provide a sulfur dioxide feed rate of 0.9 mg/L at the peak design
flow of 27.5 mgd. The construction cost estimate assumes addition of scrubbing
facilities to contain and neutralize chlorine and sulfur dioxide Teaks.
REPORTSIMONRO EPERISECTION.3
3-8 HAZEN AND SAWYER
Environmental Engineers & Scientists

Aerobic Digesters/Thickeners/Solids Storage Tanks
Solids handling facility requirements for the expanded plant capacity of 11 nrigd were
evaluated based on solids production projections for annual average and maximum
month conditions. Solids production estimates are based on the influent wastewater
characteristics presented above and are as follows:
Annual Average
Maximum Month
Projected WAS
Production. lb/day
21,870
31,710
It is assumed that Aerobic Digesters No. 3 and 4 will continue to be used as
thickeners for the expanded plant. Existing tanks provide 120 days storage at
8 percent solids for the design annual average sludge production.
Centrifuges
The existing centrifuges are currently used to thicken the digested solids from
Digesters No. 1 and 2 to provide a solids concentration of 6 to 8 percent to
Digester/Storage Tanks Nos. 3, 4, and 5. Because of the limited useful life remaining
for the centrifuges, it is recommended that one of the existing centrifuges be replaced
with a new centrifuge for the proposed plant expansion to 11 mgd. The new
centrifuge would have slightly higher capacity than the existing centrifuges and the
thickened solids from the centrifuges would be blended with solids which bypass the
centrifuges to achieve a blended solids concentration of 6 to 8 percent.
REPO RTSSM O N RO EPERISECTIO N.3
3-9
HAzEN AND SAWYER
Environmental Engineers & Scientists

SECTION 4
RECOMMENDED FACILITIES
4.1 Recommended Facilities and Estimated Cost
Recommended facilities for the proposed expansion of the Monroe WWTP to 11 mgd
are based on the evaluations discussed in Section 3 and include the following:
• One (1) additional pump in Influent Pump Station No. 2 to increase total
firm pumping capacity to 31 mgd.
• One (1) additional fine screen to increase capacity of the screening
•
facilities.
Expansion and upgrade of the existing flow equalization basin to a
volume of 5.0 million gallons and flow equalization pump station
modifications.
Two (2) new aeration basins to provide adequate capacity for BOD
removal and nitrification for the expanded plant flow and increased
wastewater loadings from industrial sources.
• One (1) new blower in the existing blower building to provide aeration
for the expanded plant flow and increased wastewater loadings.
Modifications to the Aeration Basin Splitter Box and piping to the
Secondary Clarifier Splitter Box to accommodate the two additional
aeration basins.
REPORTSIMONROEPERISECTION.4
4-1
HAZEN AND SAWYER
Environmental Engineers & Scientists

Two (2) new chlorinators and sulfonator modifications to provide
increased chlorine and sulfur dioxide feed capacities for the expanded
plant.
• One (1) new centrifuge to replace one of the existing centrifuges which
are reaching the end of their useful life.
Design data for the existing and recommended facilities for the expanded plant are
presented in Table 4-1. A plant layout showing the recommended facilities is shown
on Figure 4-1. The estimated cost for the recommended facilities is summarized in
Table 4-2.
The schedule for design and construction of the recommended facilities is based upon
the time of need demonstrated by the flow projections in Table 3-1. The final design
schedule also attempts to accommodate as much as possible the schedule for
renewing the Monroe Plant NPDES Permit in 1999. The tentative design and
construction schedule is as follows:
Update Preliminary Engineering Report
Final Design
Prepare NPDES Permit Renewal Application
Bidding
Begin Construction
Complete Construction
July -December 1998
January -October 1999
November 1999-January 2000
February -April 2000
May 2000
September 2001
The above schedule is subject to change based on actual wastewater flow increases
and other factors.
REPORTSIMONRO EPERISECT1ON.4
4-2
HAZEN AND SAWYER
Environmental Enginoers & Scientists

TABLE 4-1
Design Data
Recommended Facilities
11 MGD Design Capacity
Design Basis
Average Daily Flow, mgd 9.44
Maximum Month Flow, mgd 11.0
Peak Flow, mgd 27.5
Influent Characteristics
Annual Average Conditions:
BOD5, mg/L 380
Total Suspended Solids, mg/L 430
Total Kjeldahl Nitrogen, mg/L 31.5
Ammonia Nitrogen, mg/L 21.0
Maximum Month Conditions:
BOD5, mg/L 450
Total Suspended Solids, mg/L 480
Total Kjeldahl Nitrogen, mg/L 36.0
Ammonia Nitrogen, mg/L 24.0
Design Basis for NPDES Effluent Limits
Monthly Average, Summer (Winter)
BOD5, mg/L 7.3(14.6)
Ammonia Nitrogen, mg/L 1.0(2.0)
Total Suspended Solids, mg/L 30
Dissolved Oxygen, mg/L 6
Fecal Coliforms, No.I100 mL 200
Total Residual Chlorine, ug/L 17
Influent Pump Stations (City of Monroe wastewater only)
Pump Station No. 1
Number of pumps 4
Type Centrifugal, non -clog
Capacity of each pump, mgd 4.5
Type of drive Constant speed (2),
variable speed (2)
Pump Station No. 2
Number of pumps 3
Type of pumps Centrifugal, non -clog
Design capacity of each pump, mgd 6.5
Type of drive Variable speed
Total firm capacity, mgd 31.0
REPORTSIMONROEPERISECTION.4
4-3
HAZEN AND SAWYER
Environmental Engineers & Scientists

%amlb TABLE 4-1 (Continued)
Influent Flow Measurement
Method of flow measurement Magnetic flow meter
Number 4
Size, inches 1 @ 8 (Union County)
1 @ 14
1 @ 16
1 @ 18
Fine Screens
Number 3
Screen openings, inches 2 @ 0.06, 1 @ 0.25
Capacity of each screen, mgd 9
Firm capacity, mgd 18
Flow Equalization Basin
Number
Volume, mil. gal.
Aeration Basins
Number
Dimensions
Length, ft.
Width, ft.
Sidewater depth, ft.
Volume, each basin, mil. gal.
Total volume, mil. gal.
Detention time at design flow, hours
1
5.0
7
120
4 @ 60
3 @ 90
16
4 @ 0.86
3 @ 1.29
7.33
16.0
Aeration System
Type Fine bubble diffused air
Type of diffusers Membrane
Number of diffusers per basin 4 @ 1,286
3 @ 1,929
Total number of diffusers 10,931
Blowers
Number 4
Capacity of each blower, scfm 7,885
REPORTSIMONROEPERISECTION.4
4-4
HAZEN AND SAWYER
Environmental Engineers & Scientists

TABLE 4-1 (Continued)
Secondary Clarifiers
Number 4
Diameter, ft. 85
Sidewater depth, ft. 12
Total volume, mil. gal. 2.04
Total surface area, ft.2 22,700
Overflow rate at design flow, gpd/ft.2 480
Return/Waste Activated Sludge Pumping Stations No. 1 and No. 2
Number of pumps, each station 3
Type Horizontal, centrifugal, non -clog,
self priming
Capacity of each pump, gpm (mgd) 1,630 (2.35)
Total firm capacity, mgd 11.75
Type of drive VFD
Tertiary Filters
Number 6
Type Dual media, w/ air scour
Dimensions of each filter
Length, ft. 24
Width, ft. 20
Depth of media
Anthracite, in. 24
Sand, in. 12
Gravel, in. 18
Total surface area, ft.2 2,880
Filtration rate at design flow, gpm/ft.2 2.65
Backwash Supply Pumps
Number 2
Capacity of each pump, mgd 14.1
Backwash Waste Pumps (to Flow Equalization Basin)
Number 2
Capacity of each pump, mgd 13.8
REPORTSIMO NROEPERISECTION.4
4-5
HAZEN AND SAWYER
Environmental Engineers as Scientists

TABLE 4-1 (Continued)
Chlorine Feed Facilities
Total ton container inventory capacity
(including containers on manifolds)
Number of ton containers on manifolds
Normal withdrawal of chlorine
Number of chlorinators
Capacity, each, lb./day
Sulfur Dioxide Feed Facilities
Total 150-lb cylinder inventory capacity
(including cylinders on manifolds)
Number of 150-lb cylinders on manifolds
Number of scales
Number of cylinders on scale
Normal withdrawal of sulfur dioxide
Number of sulfonators
Capacity, each, lb./day
Chlorine Contact Tanks
Number
Total volume, gal.
Detention time at 11 mgd, min.
Post Aeration
Type
Aerobic Digesters/Thickeners/Storage Tanks
Number
Dimensions of each digester
Diameter, ft.
Volume of each digester, mil. gal.
Total volume, mil. gal
Aeration and mixing system
Type
10
8
Gas
2
2,000
12
8
1
2
Gas
2
200
2
222,470
29.1
Cascade
5
2 @ 65
1 @80
1 @ 115
1@140
2 @ 0.25
1 @ 0.49
1@ 1.15
1@ 3.00
5.14
Mechanical, floating
REPORTSIMONROEPERISECTtON.4
4-6
HAZEN AND SAWYER
Environmental Engineers & Scientists

A
Q
TABLE 4-1 (Continued)
Aerobic Digesters/Thickeners/Storage Tanks (Continued)
Digester/Storage Tank No. 1
Aerators
Mixers
Digester/Storage Tank No. 2
Aerators
Mixers
Digesters/Thickeners Nos. 3 and 4
Aerators
Digester/Storage Tank No. 5
Aerators
Centrifuge Dewatering Facilities
Number of centrifuges
Capacity of each unit, gpm (2% solids)
Sand Drying Beds (Backup)
Number
Dimensions of each bed
Length, ft.
Width, ft.
Total surface area, ft.2
Suspended solids loading, lb/ft.2-year
Solids loading capacity, lb/day
Vacuum Drying Beds (Not in Service)
Number
Dimensions
Length, ft.
Width, ft.
Total surface area, ft. 2
1@ 40 HP, 2 @ 7.5 HP
2@ 7.5 HP
3@ 40 HP
1@40HP
1 @ 30 HP
(2) - 200 Hp Blowers
Diffused Air
2
1 @ 90
1 @ 105
15
120
20
3 6, 000
15
1,480
2
40
20
1,600
REPORTSIMONROEPERISECTION.4
4-7
HAZEN AND SAWYER
Environmental Engineers & Scientists

CHLO
BUILDIN
EXPAND
CHLORINATOR/
SULFONATOR
CAPACITIES
INFLUENT
PUMPING
STATION
TERTIARY
FILTERS
U `
EW
ERTIARY
FI LTE
INSTALL ONE ADDITIONAL
INFLUENT PUMP
R�oHP�9so-
c'RE>GK
rya NEW SOLIDS
HANDLING PUMP
RAS PUNIP STATION
AERATION
BASIN NO. 5
SECONDARY
CLARIFIER NO. 2
AEROBIC
SLUDGE
DIGESTER,
NO. 4
AEROBIC
SLUDGE
DIGESTER
NO.3
AERATION
AERATION
AERATION
AERATION
BASIN 1
BASIN 2
BASIN 3
BASIN 4
RAS
L4ETER
ire,yAULTS
CLARIFIER
SPUTTER BOX NO. 2
SECONDARY
CLARIFIER NO. 1
CONSTRUCT
TWO ADDITIONAL
AERATION BASINS
s-1
LEGEND
ri SOLIDS HANDLING IMPROVEMENT PROJECT
I I SCHEDULED FOR BID IN EARLY 1997
®FACILITIES REQUIRED FOR EXPANSION
TO 11 MGD CAPACITY
MODIFY SPLITTER BOX —
FOR NEW AERATION BASINS
AERATION
BASIN
SPUTTER
BOX
ACUUV
DRYING
BEDS
AEROBIC DIGESTER
NO. 2
ADD FLOW
EQUALIZATION
DRAIN PUMP
SCREENING
BUILDING
INSTALL NEW
FINE SCREEN
SLUDGE
DRYING
BEDS
1
REPLACE CENTRIFUGE
AEROBIC
DIGESTER
NO. 1
—CENTRIFUGE BUILDING
REHABILITATION
BLOWER
BUILDING
CNEW 3.0 MG
STORAGE
TAN K
EXPAND EQUALIZATION BASIN
AND PROVIDE SYNTHETIC LINER
ADD BLOWER
MONROE WASTEWATER TREATMENT PLANT
MONROE, NORTH CAROLINA
FACILITIES FOR EXPANSION
TO 11 MGD CAPACITY

TABLE 4-2
MONROE WWTP
Estimated Construction Costs
For Expansion to 11 MGD Capacity
Item Estimated Cost
Influent Pump $200,000
Fine Screen 250,000
Flow Equalization Tank and Pump Station 400,000
Aeration Basins 2,550,000
Aeration Basin Splitter Box Modifications 100,000
Additional Blower 200,000
Aeration Basin Effluent Piping/Modifications 100,000
Chlorination/Dechlorination Facilities Expansion 25,000
Replace One Centrifuge 300,000
Subtotal $4,125,000
Engineering and Contingencies @ 20% 825,000
Total Capital Cost $4,950,000
REPORTSIMONROEPEMSECTION.4 _
4-8
HAVEN AND SAWYER
Environmental Enainecrs & Scientists