NC0026051_Permit Modification_20080627

NCDENR
North Carolina Department of Environment and'Natural Resources
Division of Water Quality
Michael F. Easley, Governor William G. Ross, Jr., Secretary
Coleen H. Sullins, Director
Joseph Pearce, P.E.
County of Durham
120 E. Parrish Street, Law Bldg.
Durham, NC 27701
Subject:
Dear Mr. Pearce:
June 27, 2008
NPDES Permit Modffication
Triangle Wastewater Treatment Plant
NPDES Permit NCO026051
Durham County
The Division of Water Quality has received and reviewed your permit modification request dated
June 17, 2008, for Triangle WWTP. In response to your request, the subject NPDES permit has
been modified to reflect the following:
• Additional language has been added to the Supplement to Permit Cover Sheet to reflect
the facility's proposed contract composting operation and changes to the Biosolids
Management Plan.
Accordingly, we are forwarding herewith the attached modified NPDES permit. Please insert
the attached permit page into your permit and discard the old one.
This permit modification is issued pursuant to the requirements of North Carolina General
Statute 143-215.1 and the Memorandum of Agreement between North Carolina and the U.S.
EPA dated October 15, 2007 (or as subsequently amended).
If you have any questions regarding any of the above, then please feel free to contact Vanessa
Manuel at 919n33-5083, extension 532.
Attachment
Cc: DWQ/SWP—RRO
DWQ/SWP — Central Files
NPDES Files
1617 Mail Service Center, Raleigh, North Carolina 27699.1617
512 N. Salisbury St., Raleigh, North Carolina 27604
Phone: [phone]/FAX: [phone]/lntemet: www.ncwaterqualitv.ore
An Equal Opportunity/Affirmative Action Employer— 500% Recycledr101/6 Post Consumer Paper
Sincer ,
Co n H. Sullins
One NhCarohna
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Permit NC0026051
SUPPLEMENT TO PERMIT COVER SHEET
All previous NPDFS Permits Issued to this facility, whether for operation or discharge are hereby revoked.
As of this permit issuance, any previously issued permit bearing this number is no longer effective.
Therefore, the exclusive authority to operate and discharge from this facility arises under the permit
conditions, requirement% terms, and provisions included herein.
Durham County is hereby authorized to:
1. Continue to operate an existing 12.0 MGD wastewater treatment facility located south of
Durham at the Durham County Triangle WWTP off NC Highway 55 in Durham County.
The facility includes the following treatment components:
• Mechanical fine screens
• Mechanical grit removal
• Parshall flume
• Influent pump station
■ Three 5-stage BNR trains
• Four secondary clarifiers
• Five tertiary sand filters
• Ultraviolet disinfection
• Post aeration
■ Sludge lagoons
■ Waste and return activated sludge pumping system
• Methanol, potassium hydroxide, and sodium hypochlorite storage and feed systems
• Liquid waste activated sludge storage (projected service date is the end of 2010)
• Dewatering facility (projected service date is the end of 2010)
• Truck loading for contract composting operation (projected service date is the end
of 2010)
2. Discharge from said treatment works (via Outfall 001) into Northeast Creek, a Class WS-IV
NSW water in the Cape Fear River Basin, at the location specified on the attached map.
Minor Permit Modification: June 27, 2008

RECEIVED
JUN 2 0 2008
DwQ STAFF SERVICES
COUNTY OF DURHAM
ENGINEERING DEPARTMENT
June 17, 2008
Mr. Gil Vinzani, P.E.
Supervisor, Eastern NPDES Program
NCDENR - DWQ
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: Triangle Wastewater Treatment Plant
Durham County, North Carolina
NPDES Permit No. NCO026051
Dear Mr. Vinzani:
Please consider this request for a MINOR modification of the above -referenced NPDES permit
for the Triangle Wastewater Treatment Plant in Durham County. In accordance with your
telephone conversations with Dave Heiser of McKim & Creed earlier this year, enclosed
herewith is a site plan for the proposed Phase III Biosolids Facility, a revised completion
schedule, and a Biosolids Management Plan Update — Basis of Design for review. No increases
in flow or pollutant loads, changes to permit effluent limits, or modifications to the permitted
facility treatment processes are included in this request — simply a modification to the method of
biosolids management as listed in the NPDES Permit.
The Phase III Biosolids Facility will provide for liquid waste activated sludge storage, a
dewatering facility and truck loading for a contract composting operation. The attached Basis of
Design documents the design elements for Phase III. Based on the current project schedule,
Phase III would be placed on-line at the end of 2010.
120 E. Parrish Street, Law Bldg., 1st Floor, Durham, N.C. 27701 [phone] Fax [phone]
Equal Employment/Affi mative Action Employer

Mr. Gil Vinzani, P.E.
June 17, 2008
Page 2
We trust you will find this information acceptable, and will be able to modify the current NPDES
Permit accordingly. If you have any questions, or require any additional information, please
contact either me or Dave Heiser, PE, at McKim & Creed (919-233-8091).
Sincerely,
mirli
ivision Manager
Durham County Engineering Department
Encl: Site Plan for the Proposed Phase III
Biosolids Facility - Basis of Design
Revised Completion Schedule
Biosolids Management Plan Update
cc: Mack Wiggins, NCDENR Raleigh Regional Office
Dave Heiser, PE, McKim & Creed, PA
Bryan Blake, PE, McKim & Creed, PA
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DURHAM COUNTY
TRIANGLE WASTEWATER TREATMENT PLANT
BIOSOLIDS PROCESS TRAIN IMPROVEMENTS
REVISED PROJECT SCHEDULE
June 2008
• Submit NPDES Permit Modification Request....
• Receive Approved NPDES Permit Modification
• Submit to State for A-T-C.......................................
• Receive A-T-C from State.........
• Advertise Project............
.June 15, 2008
.......................................August 30, 2008
.......................................September 15, 2008
.......................................March 15, 2009
.......................................March 23, 2009
• Receive Bids............................................................................................................April 30, 2009
• Award Construction Contracts............................................................................May 31, 2009
• Execute Construction Contracts..........................................................................July 31, 2009
• Notice to Proceed for Construction.....................................................................August 7, 2009
• Construction Completion.....................................................................................November 7, 2010

DURHAM COUNTY TRIANGLE WASTEWATER TREATMENT PLANT
BIOSOLIDS MANAGEMENT PLAN UPDATE
PHASE III - BIOSOLIDS FACILITY BASIS OF DESIGN
Municipal Contact:
Mr. Joseph Pearce, PE
Durham County
120 East Parrish St.
Durham, NC 27701
[phone]
DURHAM COUNTY, NORTH CAROLINA
June 13, 2008
JUN 2 0 2008 i
V'
".n
Prepared By:
Mr. David M. Heiser, PE
McKim & Creed, P.A.
1730 Varsity Drive
Raleigh, NC 27606
[phone]
V MCIQM&CREED

TRIANGLE WASTEWATER TREATMENT PLANT
DURHAM COUNTY
BIOSOLIDS MANAGEMENT PLAN UPDATE
CONTRACT COMPOSTING ALTERNATIVE
PHASE III — BIOSOLIDS FACILITY
BASIS OF DESIGN
JUNE 13, 2008
Introduction
Durham County has decided to proceed with contract composting as an interim step for
Phase III in their biosolids management program. This interim step shall provide for liquid
storage of waste activated sludge (WAS), on -site dewatering, and a truck loading facility for
dewatered sludge which will allow for contract hauling to a permitted composting facility. The
decision to proceed with contract composting was not to preclude the County from ultimately
providing for heat drying or other stabilization option in the future.
Design Influent Wastewater Characteristics and Design Biosolids Production Quantities
The design influent wastewater characteristics and design biosolids production quantities are as
contained in McKim & Creed's Phase III Biosolids Management Systems Engineering
Alternative Analysis Amendment No. 2 dated July 10, 2007 and as summarized below in Tables
1 and 2. The biosolids production quantities shown in Table 2 are calculated using both the
biological solids yield factor of 0.70 pounds per pound of BOD5 loading in the plant influent
calculated from the current WAS production at the plant, and the design solids yield factor of
0.95 pounds per pound of BODs loading.

TABLET
DURHAM COUNTY TRIANGLE WWTP
DESIGN INFLUENT WASTEWATER CHARACTERISTICS
INFLUENT PARAMETER
DESIGN CONDITION
Average Daily Flow (MGD)
12
Peak Hourly Flow (MGD)
36
Organic Loading (BOD5)
(mg/1)
200
(lbs/d)
20,020
Total Suspended Solids
(mg/1)
180
(lbs/d)
18,020
Total Nitrogen
(mg/1)
40
(lbs/d)
4,010
NH3-N
(mg/1)
25
(lbs/d)
2,500
Total Phosphorus
(mg/1)
4
(lbs/d)
400

TABLE 2
DESIGN BIOSOLIDS PRODUCTION QUANTITIES
DESIGN YEAR
CONDITIONS
DESCRIPTION
WITH CURRENT
WITH DESIGN SOLIDS
SOLIDS YIELD FACTOR
YIELD FACTOR
AVERAGE DAILY INFLUENT FLOW
12.0 MGD
12.0 MGD
ORGANIC LOADING (BODs)
20,020 Ibs/d
20,020 Ibs/d
BIOSOLIDS YIELD
Ibs/ 16 BODs
Biological Solids al
8.51bs/Ib TP
8.5l s/lb P
S.5 lbs/Ib TP
8.5
Chemical Solids (phosphorus) (1)
BIOSOLIDS PRODUCTION
Biological Solids
2,560 dry tons/yr
3,470 dry tons/yr
Chemical Solids (phosphorus) (1) (3)
155 dry tons/vr
155 dry tons/vr
Total Biosohds Production
2,715 dry tons/yr
3,625 dry tons/yr
WASTE ACTIVATED SLUDGE (WAS) PRODUCTION
@ 0.5% TS (@ 12 MGD)
356,500 gals/d
476,400 gals/d
@ 0.75% TS (@ 12 MGD)
237,600 gals/d
317,600 gals/d
EQUIVALENT DEWATERED BIOSOLIDS CAKE
PRODUCTION FROM CENTRIFUGE DEWATERING
Weight @ 22% TS
12, 330 wet tons/yr
16, 480 wet tons/yr
Volume @ 22% TS
15,415 / r
20,600 / r
(1) Based on an average influent phosphorus concentration of 4 mgl1.
(2) Includes biosolids yield from carbonaceous oxidation, as well as biological yield associated with biological nutrient removal
(both nitrogen and phosphorus).
(3) Assumes phosphorus concentration can be effectively reduced to 1.0 mg/1 biologically. The biosolids generated as a result of
biological phosphorus removal are accounted for in the Biological Solids category. The chemical solids listed assume sodium
aluminate will be utilized to reduce residual TP concentration from 1.0 mg/1 to <0.28 mg/1

Operation Overview
The contracting composting operation will allow the County to manage biosolids in a more
routine, consistent, and efficient manner than the current process of utilizing the existing sludge
lagoon, as well as allow for a future expansion to a heat drying process.
Waste activated sludge (WAS) will be wasted from the existing RAS/WAS pumping station to a
WAS liquid storage tank. The tank is proposed as a 1.0 MG two cell (0.5 MG each cell) common
wall cast -in -place concrete storage tank. The tank will be provided with an aeration and mixing
system in each cell.
The unthickened WAS (approximately 0.75% TS) will be pumped via variable speed
progressive cavity dry -pit pumps (centrifuge sludge feed pumps) to the dewatering building
housing the high solids centrifuges. The centrifuge sludge feed pumps are anticipated to be
housed below grade to allow for a flooded pump suction and to allow complete emptying of the
liquid storage tanks.
The Dewatering Building will be a one-story facility with a basement area located near the
liquid WAS storage tanks and will house the following components:
➢ Centrifuge area
➢ Polymer feed and storage area
➢ Office/control room
➢ Test sample/preparation room
➢ Electrical room
➢ Single restroom/shower
➢ Sludge feed pump area
It is anticipated that the high solids centrifuges will produce a 22% solids sludge. The
dewatered sludge will be conveyed to the truck loading station. The truck loading station shall
provide space for dual truck loading and shall be located adjacent to the Dewatering Building.
The new structures, liquid WAS storage, Dewatering Building and truck loading station, shall
be located within the "footprint" of the existing southern aeration basin. The new structures
shall be arranged to facilitate the future addition of a dryer building and additional liquid WAS
storage, minimizing impact on the contract composting operations.
The existing southern clarifier shall be modified to accept backwash water from the existing
filters and centrate from the dewatering facilities for flow equalization and pumping back to the
BNR process influent distribution box.
4

Design Criteria
Waste Activated Sludge Pumping and Storage
WAS is pumped from the existing RAS/WAS Pump Station that serves four flocculating, high -
rate center -feed clarifiers and currently discharged to the existing sludge lagoon. The discharge
of the WAS pumping station will be diverted to the new liquid WAS storage tanks via an
extension of the existing force main. WAS at approximately 0.5% TS concentration (initial year)
and 0.75% TS concentration (starting in 2012) will be pumped (via the existing submersible
WAS pumps located adjacent to the new clarifiers) to one of two new 500,000 gallon sludge
holding tanks (1.0 million gallons total storage capacity). WAS flow will be metered via the
existing in -line magnetic flow meter located at the WAS pump station. The WAS flow is
continuously monitored and totalized via the Plant SCADA system. Scum from the final
clarifiers will also be pumped to these storage tanks.
Using the current solids yield factor for biological solids, the 1.0 MG total storage volume
provides 4.2 days storage of liquid storage capacity at WAS design year (12 MGD) production
(237,600 gpd ® 0.75% TS) or 8.4 days storage at 6.0 MGD. Using the design solids yield factor, 3
days storage of liquid sludge at 12 MGD plant flow will be provided, or 6 days storage at 6
MGD.
Each of the two tanks will be equipped with independent submersible aerators and mixers that
will be used to keep the tank contents fully mixed, as well as to provide for aeration to keep the
dissolved oxygen at an acceptable level. Two mixers and two submersible aerators will be
installed in each tank.
Each tank will be provided with level indication so the operators will know the liquid levels in
each tank to assist them with selecting which tank to utilize for wasting. Separate float switches
will be installed in each tank to cut off the mixers and aerators in that tank should its water level
fall to a specified elevation below which the mixers and aerators will not be effective.
The aeration and mixing system for the sludge holding tanks will be sized for aeration and
mixing as a "nursing' tank for the centrifuges, and not to provide for aerobic digestion.
Floating decanters with submerged weirs will be used (one per tank) to withdraw supernatant
from the tanks at the maximum water level down to approximately ten feet of water depth.
This will provide an operating range of approximately twelve feet. Supernatant from these
decanters will be routed to the equalization basin.
The liquid WAS storage tank will be a cast -in -place concrete structure with common wall
construction for the two cells. The western end of the structure, walls, and footing will be
provided with water stops and dowel inserts to accommodate the future 1.0 MG storage
expansion if needed. The tanks will have open tops and no odor control system will be
provided. See Table 3 for a summary of the design criteria for the sludge holding tanks.

TABLE3
WASTE ACTIVATED SLUDGE LIQUID STORAGE SYSTEM
DESIGN CRITERIA
WASTE ACTIVATED SLUDGE HOLDING TANKS
Total Volume
1.0 MG
✓t of Independent Cells
2
Volume per Cell MG
0.50
Dimensions (each cell)
Width
33'
Length
95'
Wall Height
24'
Max Liquid Depth
22'
Materials of Construction
Cast in place concrete
Provide for expansion by addition of two future cells
Mixing System
Type
Submersible Mixers
Number of Mixers
Two Per Tank
Low Level Cut Off
1 Float Switch/Cell
Aeration System
Type
Submersible Aerators
Number of Aerators
Two Per Tank
Oxygen Transfer Rate Required
75 lbs O:/tu (Total)
Low Level Cut Off
1 Float Switch/Cell
Aeration Control
Timers and/or Dissolved Oxygen Levels
Aeration Monitoring
Type
Floating Style Dissolved Oxygen Sensors
DO Concentration Range
0.1 mg/1 to 2.0 mg/I
Decanters
Type
Floating; submerged weir
Number of Units/Cell
1 unit/cell
Maximum Decant Rate
500 gpm (minimum 4 hour cycle)
Control
Motorized plug valve
Minimum Vertical Travel Required
12' (10 to 22 foot SWD)
Flow Detection
Positive flow indicator (1/cell)
Level Indication
Type
Pressure Transducer
Number of Units
1 unit/cell

Centrifuge Dewatering
Liquid waste activated sludge will be pumped from each of the two sludge holding tanks to a
new high solids centrifuge dewatering operation. Two progressive cavity dry -pit pumps (one
per centrifuge) will be used to feed the two centrifuges. Each pump will be equipped with a
variable frequency drive to allow the operator to optimize the dewatering operation. The feed
pumps will be installed in the lower level of the Dewatering Building and will be manifolded
such that the pumps can draw suction from either of the two WAS liquid sludge holding tanks
via separately valved inlets. In addition, the discharge from the two pumps will be manifolded
to allow them to feed either of the two centrifuges.
The suction and discharge piping for the sludge feed pumps will be arranged to allow for the
addition of a third (future) sludge feed pump.
The suction header for the feed pumps shall be furnished with two in -line grinders (one per
tank suction line). The grinder units will allow for grinding of material in the waste activated
sludge that may have reformed larger solids in the holding tanks.
The waste activated sludge will be pre -conditioned with emulsion polymer injected to the feed
sludge via a flange -mounted polymer injection ring to assist in achieving a design dewatered
cake solids concentration between 20% and 22% TS. Sludge cake produced in the dewatering
process will be conveyed to the truck loading station. Centrate will be conveyed to the new
equalization basin via a new gravity sewer, and blended and equalized with other process
wastestreams before being pumped back to the BNR process influent distribution box.
The centrifuges will be installed inside the proposed new Dewatering Building located adjacent
to the sludge holding tanks. The new building will also house the new mix/feed emulsion
polymer feed systems, electrical equipment, control panels and accessory equipment.
As noted previously, for the initial year of operation two feed pumps, two polymer systems and
two centrifuge units will be installed in the new facilities.
Due to the wash down, flushing and energy requirements for startup and shutdown, it is
recommended that the County plan to operate the dewatering system continuously, 24 hours
per day for the required total number of hours each week (rather than starting and stopping the
system for limited periods during the week).
The design hydraulic loading capacity for each centrifuge is 156 GPM at a feed sludge
concentration of 0.75% TS. During the initial year (6 MGD), it is anticipated that the dewatering
system will operate for 62 hours per week (2.6 twenty-four hour days) with two units operating,
but will need to increase to nm 124 hours per week (5.2 twenty-four hour days) with two units
operating to accommodate the design year (12 MGD) loadings. The centrifuge sizing was
generally designed to accommodate "design year' loadings in 5.2 twenty-four hour periods

each week, 50 weeks per year. This provides time for maintenance and repair each week, and
provides time to do more extensive maintenance during a scheduled two week shutdown each
year.
The dewatered sludge cake will be conveyed from the Dewatering Building to the truck loading
station via progressive cavity pumps (one per centrifuge) and two force mains. See Table 4 for a
summary of the design criteria for the centrifuge feed pumps and polymer feed systems, and
Table 5 for the design criteria for the high solids centrifuges and accessories.
0

TABLE4
HIGH SOLIDS CENTRIFUGE FEED PUMPS AND POLYMER FEED SYSTEMS
DESIGN CRITERIA
Biosolids Production m
Tons/Production Week Dry Weight
73
Lbs/Production Week Dry Weight
145,000
Gal/Production Week (WAS)
2,318,5W gal.@0.75%TS
High Solids Centrifuge Sludge Feed Pumps/Grinders
Design Flow Rate (@ 0.75% TS)
156 gpm
Design Flow Operating Range
40 -175 gpm
(® 0.75 - 3% TS)
TDH ®156 gpm thru 4" Discharge Piping
Approximately 112'
Feed Pump Type
Progressive Cavity; Positive Displacement
Number of units
2
Horsepower Requirement/unit
7-1/2
Total Connected HP
15
Control
Variable Frequency Drives
In -line Grinders
2 units (1 per tank suction)
Provide layout for one additional
future feed pump
High Solids Centrifuge Polymer Feed and Storage System
Biosolids Loading Rate/Production Day
14.5 dry tons/d
Active Polymer/Ton Dry Solids
20 lbs/DV)
Polymer Feed System Type
Continuous solution, mix/feed; emulsion type
Emulsion Active Polymer Conc.
40%
Polymer Feed Solution Conc
0.5%
Number of Polymer Feed Units
2 (one per centrifuge)
Polymer Feed Rate/Unit
Design: 3.8 gph; maximum 5.0 gph (w/10:1 turndown)
Provide layout for one additional
future polymer unit
Initial Year Polymer Required/Month
980 gal./month; 3 (300 gal.) totes
Design Year Polymer Required/Month
1,810 gal./month; 6 (300 gal.) totes
Alternate Bulk Storage System
Two 3,000 gal. tanks
High Solids Centnfuges Sludge Feed Flowmeter
Type
Magnetic
Number of Units
2 (1 per feed Pump)
Flow Range
40 -175 gpm
Meter Size
4"
Provide layout for one additional
future flowmeter
(1) Based on operating 50 weeks per yew (production weeks) at 12 MGD.
(2) Andritz centrifuge pilot study for Triangle W WTP recommends Polydyne C6262 polymer.

TABLES
HIGH SOLIDS CENTRIFUGES AND ACCESSORIES
DESIGN CRITERIA
i I-EM DESCRIPTION DESIGN CRITERIA
High Solids Centrifuges
Required Centrifuge Capacity (2 units operating)
# Production Weeks/Year
50
# Production Days/Week
5.2
# Production Hrs/Day
24
Design Throughput (lbs/I-lour)
1,170 (Dry Weight)
Design Throughput (gallons/Hour)
15,720 @ 0.75% TS
Design Cake Production (lbs/Production Hour)
5,494 @ 22% TS
Design Cake Production (CY/Production Week)
412 @ 22% TS
Number of Centrifuge Units
2 duty
Influent Solids Concentration
0.75% - 2.0%
Design Cake Solids Concentration
20% - 22%
Design Solids Capture Efficiency
95%
Provide layout for one additional future centrifuge
High Solids Centr fuge Accessories
Sludge Cake Pumps
Solids produced/wk
145,000lbs/wk, Dry Weight
Wet cake produced/production wk
660,000 lb/wk, @ 22% TS
Wet cake produced/production day
132,000lb/day, @ 22% TS
Wet cake produced/production week
412 CY/wk, @ 22% TS
Pump Type
Progressive Cavity, Positive Displacement
Number of Units
2 (I/Centrifuge)
Horsepower Per Pump
15 HP
Design Capacity
5.5 GPM
Discharge Pressure
200 psi (Max.)
Pump Control
Variable Frequency Drives
Centrifuge -to -Pump Speed Control
Pump Base Load Cells
Pump Discharge Protective Devices
"Run Dry" and High Pressure
Provide layout for one additional future sludge cake pump
10

Truck Loading Station
A truck loading station will be provided for the off-loading of the dewatered sludge. The
loading station will be located adjacent to the Dewatering Building and will be furnished
without truck scales. The dewatered sludge will be conveyed from the centrifuge area via
progressive cavity cake pumps that will discharge to two force mains which will transport the
sludge cake to the truck loading station.
The truck loading station will have two truck bays and will be approximately 30 ft. wide by 52
ft. long. Three motor -operated swing arm assemblies, each with an in -line knife gate valve, will
be installed near the ceiling, and will be capable of swinging to either truck bay to discharge
sludge cake to the trucks.
The truck loading station will have a roof system which will match the Dewatering Building.
The lower level shall be open on all four sides. The truck bay areas shall be designed to contain
spillage, and shall be sloped to a trench drain system that will interconnect with the gravity
drain line to the equalization basin. The truck loading station floor shall be concrete in the truck
bay area.
The County will contract with a local company to provide the truck trailers, cabs and
manpower to haul the dewatered cake sludge from this plant to a permitted composting facility.
Dewatering Buildine
The Dewatering Building contains two primary areas; one for dewatering operations and one
for housing the centrifuge feed pumps to drain the liquid WAS from the storage tanks. The
dewatering area will be a single story, slab on grade building housing the following
components:
• Centrifuge area
• Polymer feed and storage area
• Office/control room
• Test sample/preparation room
• Electrical room
• Single restroom/shower room
The lower wall section shall be brick/block, and depending on the final eave height of the
building, the upper wall section may be metal siding to match the construction of the existing
administration/maintenance building. The roof system shall be standing metal seam with color
to match the existing administration/maintenance building. It is anticipated that the building
area for the dewatering operations will be approximately 4,850 sf (63' x 77).
11

The centrifuge area will be provided with a monorail/hoist system to allow for removal of the
units. The polymer storage area shall be laid out with a recessed floor in lieu of raised curbs for
chemical leakage containment to allow for easier access utilizing a fork lift truck.
A large concrete pad shall be provided on two sides of the building for unloading/loading
equipment and supplies, along with a ramp to allow access for a forklift truck into the
dewatering building.
The office, sample room, restroom and electrical room will be conditioned space. The
remainder of the dewatering area shall be provided with LP gas heaters and ventilation only.
Vent louvers shall be exhausted to the exterior of the building, but no odor control is to be
provided.
A storage area will be located between the dewatering building and the liquid WAS storage
tanks. This area will provide floor space to accommodate chemical totes and other equipment
storage, as well as a covered area to park the forklift truck when not in use. The floor space for
the storage area, including the stairwell to the basement and the covered area, will be
approximately 1,850 sf (24' x 77).
A basement area will be provided beneath the storage area floor to house the in -line grinders
and sludge feed pumps. Two pumps will be provided with floor space to accommodate one
additional future feed pump. A monorail/hoist system will be provided to allow for removal of
the basement equipment through an access hatch in the storage area floor above. Floor space
for the equipment area, not including the stairwell, will be approximately 1,335 sf (23' x 58).
In -Plant Flow Equalization and Pumping Facility
The existing southern clarifier will be converted to an Equalization (EQ) Basin to flow equalize
sidestream/retum flows from the existing effluent filters, the existing chemical containment
area, decant from the liquid WAS holding tanks, and centrate from the dewatering facilities.
The existing dry pit RAS/WAS pump station located adjacent to the clarifier will be abandoned
and filled with sand. A new submersible pump station wetwell will be installed adjacent to the
EQ Basin on the existing 24" influent pipe to the clarifier. Two new submersible pumps with
variable frequency drive units will be provided to pump equalized flow back to the BNR
process influent distribution box.
One (1) submersible mixer and two (2) submersible aerators shall be installed in the converted
equalization basin to provide for mixing to minimize settlement of solids, and for some aeration
to keep the dissolved oxygen at an acceptable level. The basis of design for the aerators is an
oxygen transfer rate (required) of 401bs. Oz/hr (total for both aerators).
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