HomeMy WebLinkAboutNC0023337_Inspection_20220610DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHARD E. ROGERS, JR.
Director
Eddie Braxton
Town of Scotland Neck
P.O. Box 537
Scotland Neck, NC 27874-0537
Dear Mr. Braxton:
NORTH CAROLINA
Environmental Quality
June 10, 2022
Subject: Compliance Evaluation Inspection
Scotland Neck WWTP
NPDES Permit No. NC0023337
Halifax County
On May 5, 2022, Alys Hannum of the Raleigh Regional Office (RRO) conducted a compliance
evaluation inspection of the treatment facilities located at the Scotland Neck Wastewater
Treatment Plant (WWTP). The purpose of this inspection was to ensure compliance with the
subject National Pollutant Discharge Elimination System (NPDES) permit. The presence and
cooperation of Claude Parks Boyd, Operator in Responsible Charge (ORC), during the
inspection was helpful and appreciated.
The Scotland Neck WWTP is located off NC Hwy 258 South in Scotland Neck, North Carolina.
The closest address is 7232 NC Hwy 258 South. The facility is a class WW-3 wastewater
treatment plant that treats domestic wastewater.
This NPDES compliance evaluation inspection consisted of the following:
• Review of the NPDES permit;
• Review of the owner/facility information;
• Review of the previous 12 months compliance history;
• Comparison of eDMR data against lab documents;
• On -site review of log books, calibration, and inspection logs;
• On -site inspection of the wastewater treatment units; and
• On -site inspection of the discharge outfall.
Findings during the pre -inspection file review were as follows:
1. Through NPDES permit NC0023337, the Town of Scotland Neck (Town) is authorized
to discharge treated wastewater from the Scotland Neck WWTP to receiving waters
designated as Canal Creek in the Tar -Pamlico River Basin. The NPDES permit was
issued effective July 1, 2021 and expires October 31, 2024.
NORTH CAROLINA
Department of Environmental Quality
North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh, North Carolina 27609
919.791.4200
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Compliance Evaluation Inspection
Scotland Neck WWTP
NPDES Permit. No. NC0023337
Page 2 of 3
2. As listed in the subject permit, the treatment components include: a mechanical and
manual bar screen, a grit auger, an oxidation ditch, an anoxic section in the outer ring of a
former oxidation ditch, two (2) clarifiers, two (2) tertiary filters, a chlorine contact
chamber and de -chlorination chamber, an aerobic sludge digester, and post aeration.
3. For the review period May 2021 — April 2022, the Town reported: one violation of the
NPDES permit's effluent limits for Weekly Average Nitrogen Ammonia which resulted
in a Notice of Deficiency (NOD); one failure of the aquatic toxicity permit limits which
resulted in a Notice of Violation (NOV), and two monitoring violations which resulted in
an NOD and NOV.
4. From May 2017 to April 2022, six penalty assessments have been issued. There are no
outstanding penalties.
Findings during the inspection were as follows:
1. The operator's log and supporting analytical documentation were consistent and up to
date.
2. The inspector compared the February, April, and August 2021 DMR data against lab
bench data. No discrepancies were noted.
3. The inspector noted the following observations of the treatment components:
a. Primary Treatment: The facility's bar screen was bent at the time of the
inspection and was not operating correctly. The grit chamber has been
inoperable and bypassed since approximately 2017, according to facility staff
and previous inspection reports.
b. Oxidation Ditch: One of two aerators was inoperable. This issue was noted on
the 2020 inspection report as well. Facility staff provided a copy of the proposal
to replace this rotor aerator, approved April 14th, 2022.
c. Secondary Clarifiers: One of the two clarifiers was operational at the time of the
inspection. Little to no pin floc was observed within the unit. The depth of the
first secondary clarifier is 10 feet, and the depth of the sludge at the time of
inspection was 0.1 feet.
The other secondary clarifier is currently used for sludge storage and thickening.
According to plant staff, a grant has been approved to add a new clarifier to the
plant which would operate as intended.
d. BNR Anoxic Section: The plant currently uses a portion of their former oxidation
ditch as an anoxic zone. There was visible vegetation growing on the water's
surface.
e. Filtration: The tertiary sand filters were inoperable.
f. Disinfection. The facility disinfects the treated wastewater prior to discharge
using sodium hypochlorite, followed by a chlorine contact chamber and then
chemical de -chlorination.
NORTH CAROLINAD_E
Department of Environmental Quality
North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh, North Carolina 27609
919.791.4200
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Compliance Evaluation Inspection
Scotland Neck WWTP
NPDES Permit. No. NC0023337
Page 3 of 3
All the above issues were also noted on an internal "Plant Evaluation" report which
facility staff provided to the inspector, and which is attached for reference. Within sixty
(60) days of receipt of this letter, please provide this office with a written report
detailing what actions have been or will be taken to resolve the bolded issues above.
4. Flow measurement is measured instantaneously with a flow meter. The permitted flow
limit is 0.675 MGD. The flow meter was last calibrated in June, 2021. No issues were
observed.
5. Chemicals are stored safely and with the appropriate hazard notifications and signage.
6. The effluent discharge via the outfall pipe was observed to be clear with no observable
solids or foam. No detrimental impacts to the receiving tributary were observed.
Within sixty (60) days of receipt of this letter, please provide this office with a written report
detailing what actions have been or will be taken to resolve the issues noted above.
If you have questions or comments about the inspection, this report, or the requirements to take
corrective action, please contact Alys Hannum at alys.hannum@ncdenr.gov, or by phone at 919-
791-4255.
Sincerely,
DocuSigned by:
t/alt,t,SSa f. 1144tAAAAd,
`— B2916E6AB32144F...
Vanessa E. Manuel, Assistant Regional Supervisor
Water Quality Regional Operations Section
Raleigh Regional Office
Division of Water Resources, NCDEQ
Attachments: EPA Water Compliance Inspection Report
"Plant Evaluation" — March 4, 2020
cc: RRO Files // Laserfiche
John Poteat, ORC (poteat2@aol.com)
GD_E
NORTH CofEn NA
Deparbnent iR of Environmental Quality
North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh, North Carolina 27609
919.791.4200
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
United States Environmental Protection Agency
EPA Washington, D.C. 20460
Water Compliance Inspection Report
Form Approved.
OMB No. 2040-0057
Approval expires 8-31-98
Section A: National Data System Coding (i.e., PCS)
Transaction
1
21I
Inspection
671
Code
IN I 2 IL I
I I I I I
NPDES yr/mo/day Inspection
3 I NC0023337 111 121 22/04/05 117
Type
1810I
I I I I I
Inspector Fac Type
19I S I 2011
I I I I I I I I I I I I I I I I I I I I I I I
I I I
I I I 1 I P6
Work Days Facility Self -Monitoring Evaluation Rating B1 QA Reserved
I 70I2 I 711 1 72 I N I 73I 1 74 71
I I
1 1 1 1 1 1 180
Section B: Facility Data
Name and Location of Facility Inspected (For Industrial Users discharging to POTW, also include
POTW name and NPDES oermit Number)
Scotland Neck WWTP
NC Hwy 258 S
Scotland Neck NC 27874
Entry Time/Date
01:OOPM 22/04/05
Permit Effective Date
21/07/01
Exit Time/Date
03:OOPM 22/04/05
Permit Expiration Date
24/10/31
Name(s) of Onsite Representative(s)/Titles(s)/Phone and Fax Number(s)
///
Claude Parks Boyd/ORC/252-826-3152/
Other Facility Data
Name, Address of Responsible Official/Title/Phone and Fax Number
Contacted
Eddie Braxton,PO Box 537 Scotland Neck NC 278740537/Mayor/252-826-3152/
No
Section C: Areas Evaluated During Inspection (Check only those areas evaluated)
Permit Flow Measurement Operations & Maintenar Records/Reports
Self -Monitoring Progran Sludge Handling DispoFacility Site Review Effluent/Receiving Wate
Laboratory
Section D: Summary of Finding/Comments (Attach additional sheets of narrative and checklists as necessary)
(See attachment summary)
Name(s) and Signature(s)
Alys K Hannum
of Inspector(s) Agency/Office/Phone and Fax Numbers Date
Docusignedby: DWR/RRO WQ/919-791-4255/ 6/9/2022
wa..
4C22170C5AA04F3...
Signature
of Management Q A Reviewer Agency/Office/Phone and Fax Numbers Date
DocuSigned by:
I Um/I t.SS& f. hatn ltiti, 6/9/2022
EPA orem 6-6U-jj-ev 9-94) Previous editions are obsolete.
Page# 1
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
NPDES yr/mo/day
31 NC0023337 111 121 22/04/05
I17
Inspection Type
18LI
1
Section D: Summary of Finding/Comments (Attach additional sheets of narrative and checklists as necessary)
Page# 2
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Permit: NC0023337
Inspection Date: 04/05/2022
Owner - Facility: Scotland Neck WWTP
Inspection Type: Compliance Evaluation
Permit Yes No NA NE
(If the present permit expires in 6 months or less). Has the permittee submitted a new El El ❑
application?
Is the facility as described in the permit? • El El El
# Are there any special conditions for the permit? El • El El
Is access to the plant site restricted to the general public? • ❑ ❑ ❑
Is the inspector granted access to all areas for inspection? • El El El
Comment:
Operations & Maintenance Yes No NA NE
Is the plant generally clean with acceptable housekeeping? • El El El
Does the facility analyze process control parameters, for ex: MLSS, MCRT, Settleable MODE
Solids, pH, DO, Sludge Judge, and other that are applicable?
Comment:
Bar Screens
Type of bar screen
a.Manual
b.Mechanical
Are the bars adequately screening debris?
Is the screen free of excessive debris?
Is disposal of screening in compliance?
Is the unit in good condition?
Comment: Bar Screen is bent in the middle.
Yes No NA NE
•
•
❑ • ❑ ❑
• ❑ ❑ ❑
Grit Removal Yes No NA NE
Type of grit removal
a.Manual •
b.Mechanical •
Is the grit free of excessive organic matter? El • El El
Is the grit free of excessive odor? El El • El
# Is disposal of grit in compliance? ❑ El • El
Comment: Grit chamber has been out of commission since at least the previous inspection,
according to facility staff.
Page# 3
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Permit: NC0023337
Inspection Date: 04/05/2022
Owner - Facility: Scotland Neck WWTP
Inspection Type: Compliance Evaluation
Secondary Clarifier
Is the clarifier free of black and odorous wastewater?
Is the site free of excessive buildup of solids in center well of circular clarifier?
Are weirs level?
Is the site free of weir blockage?
Is the site free of evidence of short-circuiting?
Is scum removal adequate?
Is the site free of excessive floating sludge?
Is the drive unit operational?
Is the return rate acceptable (low turbulence)?
Is the overflow clear of excessive solids/pin floc?
Is the sludge blanket level acceptable? (Approximately'/4 of the sidewall depth)
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
MI ❑ ❑ ❑
Comment: Clarifier #1: 10 feet deep, 0.1 feet sludge // Clarifier #2: 10 feet deep (smaller
circumference), 3 feet sludge. Smaller clarifier is used more for sludge thickening and
storage rather than a fully functional clarifier.
Oxidation Ditches Yes No NA NE
Are the aerators operational? ❑ • ❑ ❑
Are the aerators free of excessive solids build up? • ❑ ❑ ❑
# Is the foam the proper color for the treatment process? • ❑ ❑ ❑
Does the foam cover less than 25% of the basin's surface? • ❑ ❑ ❑
Is the DO level acceptable? ❑ ❑ ❑ •
Are settleometer results acceptable (> 30 minutes)? ❑ ❑ ❑ •
Is the DO level acceptable?(1.0 to 3.0 mg/I) ❑ ❑ El •
Are settelometer results acceptable?(400 to 800 ml/I in 30 minutes) ❑ ❑ El •
Comment: Only one of the two brush aerators is functional.
Nutrient Removal Yes No NA NE
# Is total nitrogen removal required? ❑ ❑ ❑ ❑
# Is total phosphorous removal required? ❑ ❑ ❑ ❑
Type Biological
# Is chemical feed required to sustain process? ❑ ❑ ❑ ❑
Is nutrient removal process operating properly? El ❑ El El
Comment: Note; Facility has a BNR anoxic section in the outer ring of their former oxidation ditch.
Ditch does not mix well; some vegetation growing on the surface.
Page# 4
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Permit: NC0023337
Inspection Date: 04/05/2022
Owner - Facility: Scotland Neck WWTP
Inspection Type: Compliance Evaluation
Chemical Feed
Is containment adequate?
Is storage adequate?
Are backup pumps available?
Is the site free of excessive leaking?
Comment:
Aerobic Digester
Is the capacity adequate?
Is the mixing adequate?
Is the site free of excessive foaming in the tank?
# Is the odor acceptable?
# Is tankage available for properly waste sludge?
Comment:
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
▪ ❑ ❑ ❑
• ❑ ❑ ❑
Filtration (High Rate Tertiary) Yes No NA NE
Type of operation:
Is the filter media present? • ❑ ❑ ❑
Is the filter surface free of clogging? • ❑ ❑ ❑
Is the filter free of growth? • ❑ ❑ ❑
Is the air scour operational? • ❑ ❑ ❑
Is the scouring acceptable? ❑ ❑ ❑ •
Is the clear well free of excessive solids and filter media? • ❑ ❑ ❑
Comment:
Disinfection -Liquid
Is there adequate reserve supply of disinfectant?
(Sodium Hypochlorite) Is pump feed system operational?
Is bulk storage tank containment area adequate? (free of leaks/open drains)
Is the level of chlorine residual acceptable?
Is the contact chamber free of growth, or sludge buildup?
Is there chlorine residual prior to de -chlorination?
Comment:
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
Page# 5
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Permit: NC0023337
Inspection Date: 04/05/2022
Owner - Facility: Scotland Neck WWTP
Inspection Type: Compliance Evaluation
De -chlorination Yes No NA NE
Type of system ? Liquid
Is the feed ratio proportional to chlorine amount (1 to 1)? • ❑ El El
Is storage appropriate for cylinders? • ❑ ❑ ❑
# Is de -chlorination substance stored away from chlorine containers? • ❑ ❑ ❑
Comment:
Are the tablets the proper size and type? ❑ El • El
Are tablet de -chlorinators operational? ❑ ❑ • ❑
Number of tubes in use? 0
Comment:
Effluent Pipe
Is right of way to the outfall properly maintained?
Are the receiving water free of foam other than trace amounts and other debris?
If effluent (diffuser pipes are required) are they operating properly?
Comment:
Laboratory
Are field parameters performed by certified personnel or laboratory?
Are all other parameters(excluding field parameters) performed by a certified lab?
# Is the facility using a contract lab?
# Is proper temperature set for sample storage (kept at less than or equal to 6.0
degrees Celsius)?
Incubator (Fecal Coliform) set to 44.5 degrees Celsius+/- 0.2 degrees?
Incubator (BOD) set to 20.0 degrees Celsius +/- 1.0 degrees?
Comment:
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
Yes No NA NE
• ❑ ❑ ❑
• ❑ ❑ ❑
• ❑ ❑ ❑
❑ ❑ • ❑
Page# 6
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
Town of Scotland Neck
NPDES NC0023337
Plant Evaluation
March 4, 2020
On February 1, 2020, the Town of Scotland Neck resumed operation of the Wastewater Treatment Plant
(WWTP). The Town's staff encountered several challenges with the operation of the facility along with
permit non-compliance issues. The Town requested assistance from NC Rural Water Association in
evaluating the facilities. A cursory review of the WWTP was done on March 2"d and 3`d. The following
comments and observations are a result of this review:
Preliminary Treatment
Bar Screen
One of the bars at the bottom of the screen is broken and pulled out of the water flow. Several of the
other bars are pushed to the side. This creates a hole in the screen that will allow a significant amount
of debris to pass by the screen and enter the flow channel and impact downstream processes. The bars
should be repaired.
The drainpipe for the screenings auger is disconnected. This allows wastewater to flow on the ground.
Grit Removal
The grit removal system consists of two grit pumps and a grit classifier. All these units are out of service.
Grit is removed from the wastewater to prevent accumulation in downstream basins and to prevent
excessive wear on pumps. To accomplish grit removal, the flow needs to slowed to approximately 1 fps
to allow heavier grit to settle out. It appears that the existing grit removal system will not effectively
remove grit even if all components were operational. The grit system is the old original grit chamber
that had a flight and chain to move settled grit to a sump. The flight and chain were removed, the
chamber was cut in to just downstream of the grit sump to install a line to the newer influent pump
station. The suction for the two grit pumps are in this sump. It is not expected that significant grit
removal will be accomplished by gravity settling of grit into this sump.
Influent Pump Station
There are three influent pumps in the influent pump station. One of the pumps is out -of -service at this
time. Operational controls of the pumps were not evaluated.
Chemical Feed System
A caustic feed system is set up inside the influent pump station to provide pH adjustment as needed.
There is one chemical feed pump which sets on top of the control panel for the influent pumps. If this
pump or the tubing going to/from the pump fails, caustic could enter the control panel (door does not
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
seal properly) and cause electrical failure of the influent pumps. Additionally, placement of the pump is
a safety hazard.
The storage tank for the 25% caustic is inside the influent pump station building. It appears that
fumes/spills from this tank has caused deterioration of the building and could possibly cause premature
failure of electrical components.
Biological Treatment Process
Oxidation Ditch
The oxidation ditch has two brush aerators to provide mixing and dissolved oxygen (DO) to the biological
system. The operation of the aerators is essential to the successful operation of the biological
treatment system. One of the aerators is out -of -service and will have negative impacts on plant
operations. During the evaluation period, the DO levels in the oxidation ditch were significantly less
than the recommended DO levels for proper treatment.
The oxidation ditch is approximately four feet deep with sloped sides. Information was not readily
available to determine the volume or dimensions of the oxidation ditch. The ditch was probed from
each side in an effort to determine the amount of grit/sludge accumulation in the bottom of the
oxidation ditch. Two locations had a "sludge bank" in which the debris was nearly to the top of the
water level and extended for 6+ feet. Several locations had accumulations of 2 -3 feet.
When the debris was probed, a significant release of hydrogen sulfide gas was released. The production
and release of hydrogen sulfide in the ditch can cause a drop in pH. The debris accumulation in the ditch
also reduces the amount of detention time for biological treatment and could negatively affect
compliance.
Secondary Clarifiers
There are two secondary clarifiers: Clarifier #1— the larger peripheral feed clarifier, and; Clarifier #2 —
the smaller center feed clarifier. The purpose of the clarifiers is to allow the biological floc to settle to
the bottom and a clarified effluent to flow over the top into the weirs and then to filtration. The settled
sludge is returned to the oxidation ditch.
Clarifier #2 was not in service during the evaluation because the Return Activated Sludge (RAS) pump
was inoperable. The clarifier was cut on briefly and it does appear to be operational. The caulking at
weirs is coming out and the concrete is showing signs of erosion.
Clarifier #1 was in operation during the evaluation. The clarifier appears to have been modified by
installing a small pump in the scum pit for return sludge pumping. This may have been necessitated by
the failure of the RAS pumps in the Return Sludge Pump Station. The purpose of the RAS pump is to
remove the settled sludge/bacteria from the clarifier and return to the oxidation ditch. Insufficient RAS
pumping can cause a high sludge blanket to develop in the clarifier and possible overflow of the blanket
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
to the following treatment processes. During the evaluation, the pump was insufficient to maintain a
low sludge blanket in the clarifier. The aerator in the oxidation ditch was having to be cut off to reduce
the solids going to the clarifier and allow the return pump to catch up.
Excessive debris has accumulated between the outside wall and the influent baffle on Clarifier #1. The
baffle wall is somewhat deflected at this area, possibly due to this buildup.
Return Sludge Pump Station
This pump station not only serves as the RAS pump station but also directs different flows (wastewater
and sludge) to different locations around the plant site. The pumps in the pump station were
inoperable. Clarifier #2 can not properly operate with this station out -of -service which increases the
hydraulic and sludge loading on Clarifier #1. The loss of this station impacts wasting of excess sludge
and other areas of wastewater operation.
Filter Pump Station
This pump station takes effluent flow from the clarifiers and pumps it to the sand filters. A failure of this
system could cause a spill. There are two pumps in this station. Pump #1 is out -of -service. The door
closure to the pump control panel is broken and will not latch. This will allow insects to enter and
possibly cause problems. There is also a strong hydrogen sulfide odor in the pump station. This gas is
corrosive and could damage electrical and mechanical components.
Advanced Treatment
Sand Filters
Sand filters provide enhanced treatment by both physical and biological process. There are two sand
filters. #2 sand filter is out -of -service and #1 sand filter can only me operated in manual mode.
Necessary repairs and programming should be made to place the filters in automatic operation. The
operation of the sand filters is also hampered by the lack of room in the digestor for storage of the filter
backwash.
Disinfection
Chlorination/Dechlorination
Chlorination is accomplished by adding sodium hypochlorite to the wastewater flow prior to the
chlorine contact chamber. The dosage is dependent on several factors, including: quality of
wastewater, temperature, pH, detention time, etc. The chlorine contact chambers had an accumulation
of sludge in the bottom of the basin of 12+ inches. This accumulation can impact disinfection. The state
generally wants the chlorine contact chamber when the sludge accumulation reaches six inches. The
chamber was dye tested to determine actual detention time. The chamber is designed for a detention
DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
time of 30 minutes at design flow. The detention time was approximately 20 minutes at one-half the
design flow.
Disinfection is a critical process and it is recommended that there be spare pumps and parts for both the
chlorination and dichiorination pumps.
Sampling
Sampler
The permit requires effluent sampling to be flow proportional. This requirement is not enforced equally
among the seven NC DWR Regional Offices and has not been enforced at this facility. The samples are
time composited.
Each discrete sample taken is required to be a minimum of 100 ml. Sample volume and number of
samples taken in a 24-hour period should be adjusted to achieve the 100 ml sample volume and the
minimum amount of composite sample volume needed for testing.
Sludge Handling
Digestor
The sludge digestor was completely filled at the time of the evaluation. Plant staff had cut off the
aeration system to allow the sludge to settle and to decant clear water from the top, but the sludge was
too thick.
Every biological wastewater treatment plant creates new sludge/bacteria at all times. A successful
operation requires the excess sludge to wasted out of the system on a regular basis. With the full
digester, the staff can not remove the extra sludge and the failure to do so is having negative impacts on
plant operation and compliance.
Operations
Major Issues
At the time of the evaluation, there were several operational issues occurring that were detrimental to
proper operations and compliance. The major contributory factor is the inability to waste excessive
sludge from the system. This failure affects the oxidation ditch, clarifiers, filters and disinfection. Some
(but not all) of the issues are:
• High MLSS — normal range for MLSS concentration is 2,500 — 3,500 mg/L. Lab data from January
2020 shows the MLSS concentration to have been in the 8,000 — 9,000 mg/L range. Most
recently, due to minimum wasting, the MLSS was approximately 6,000 mg/L.
• DO in Oxidation Ditch — bacteria growing in the oxidation ditch require minimum DO levels for
respiration. The normally accepted DO level for proper operation is approximately 2.0 mg/L.
- DocuSign Envelope ID: 69359C81-C4AF-47D6-8B70-1C68556D7CBB
The DO in the ditch has been in the 0.4 mg/L range. This low number affects bacterial health,
thereby affecting BODE, Ammonia Nitrogen, TSS and TP reduction.
The minimum DO level is not being achieved because: The aerators can not be run
continuously due to the high MLSS concentrations overwhelming the clarifiers and
because one of the aerators in inoperable.
• Return Sludge Pump Station —The failure of this station prevents #2 clarifier from being put in
service, which puts a strain on the #1 clarifier.
• #1 Clarifier Return Pump — a combination of high MISS and the low pumping capacity of the
return sludge pump causes the sludge blanket in the clarifier to rise and to get excessively thick.
Reducing the MLSS, increasing the capacity of this pump and/or returning the RAS Pump Station
to service are needed.
• Digestor— immediate sludge removal from the digestor is needed. The sludge can be land
applied as a liquid or a dewatering box or other aewatering device can be used to remove the
sludge from the facility.
Anoxic Zone
The anoxic zone at the digestor does not appear to have been used recently. The anoxic zone is
designed to reduce the total nitrogen content of the wastewater. If the facility is not meeting their Total
Nitrogen limits as required by the Tar -Pamlico River Association, then this process should be placed in
service.
Process Control
To properly operate the WWTP and maintain the optimal operating environment, staff needs to
evaluate and document plant activities.
• MISS meter
• Microscope
• Computer
■ Various process test modules for the spectrophotometer
Miscellaneous
This evaluation reviewed the most serious of the mechanical and operational issues that were apparent
during a quick review of the facilities. During the evaluation, several safety deficiencies and possible
OSHA violations were observed. In addition to the major mechanical and equipment failures, there
were a number of minor maintenance issues that have not been addressed that could result in larger
problems if not addressed.