NC0026000_Report_20130104

NPDES DOCUWENT SCANNING: COVER SHEET
NC0026000
Tabor City 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
(tri'
f
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
January 4, 2013
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INFLOW AND INFILTRATION ANALYSIS
UPDATE
FOR THE
TOWN OF TABOR CITY
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PREPARED BY
HOBBS, UPCHURCH & ASSOCIATES, P.A.
300 S.W. Broad Street
Southern Pines, NC
January, 2013

TABLE OF CONTENTS
1.0 INTRODUCTION 2
2.0 DESCRIPTION OF EXISTING SYSTEM 3
2.1 Collection System 3
2.2 Wastewater Treatment Plant 4
3.0 WASTEWATER FLOW EVALUATION 5
3.1 Infiltration Screening 5
3.2 Inflow Screening 6
4.0 COLLECTION SYSTEM EVALUATION 8
4.1 Manhole Inspections 8
4.2 Pump Station Inspections 8
4.3 Smoke Testing 8
4.4 Video Inspections 9
4.5 Soil Characteristics & Seasonal High Groundwater 9
5.0 CONCLUSIONS & RECOMMENDATIONS 11
LIST OF TABLES
Table 1: Collection System Summary 4
Table 2: Infiltration Screening Summary 6
Table 3: Inflow Screening Summary 7
Table 4: Service Area Groundwater Characteristics 10
APPENDICES
APPENDIX A — MAPS
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 1

1.0 INTRODUCTION
The Town of Tabor City has an ongoing problem with extraneous influent flows,
commonly referred to as inflow and infiltration or I/I. Infiltration refers to groundwater
that enters the sanitary sewer system through defective pipes, pipe joints, service
connections or manholes. Groundwater infiltration can be divided into two primary
categories: dry weather infiltration and wet weather infiltration. Dry weather infiltration
is the more inclusive of these terms. It is defined as the function of seasonal variations in
the depth of groundwater tables. Dry weather infiltration typically remains constant and
peaks in late winter and early spring. Wet weather infiltration, also known as rainfall -
induced infiltration, refers to the phenomenon of elevated groundwater tables that result
from isolated rainfall events. It begins during or shortly after the rainfall subsides and can
last for several days. Inflow refers to storm water runoff coming from sources such as
roof gutter drains, cellar drains, drains from springs and swampy areas, manhole covers,
cross connections between storm and sanitary sewers, catch basins and surface runoff, as
well as water from cooling towers and street washing. Inflow and infiltration WI) is the
volume of both inflow and infiltration found in existing sewer systems. Problems caused
by excessive I/I include:
• Utilization of sewer facility capacity that should be reserved for present
wastewater transportation;
• Utilization of sewer facility capacity that should be conserved to enable future
urban growth and economic development;
• The need to construct new, additional sewage treatment facilities prior to their
planned expansion date and thereby prematurely raising sewer rates;
• Overloading the sewer system to the extent that capacity is exceeded and
wastewater backs up and floods streets and basements and damages personal
property;
• Overloading the wastewater plant such that some untreated wastewater flows
directly into the waterways that normally recieve the treated effluent;
• Overloading of the wastewater treatment facility causing excessive wear on
pumping stations and treatment components, leading to higher user rates.
In 2001, Hobbs, Upchurch & Associates, P.A. was retained to evaluate and report on the
condition, of the wastewater collection system and make recommendations for I/I
reduction projects for the Town of Tabor City. Since that evaluation was completed, the
Town of Tabor City has completed multiple I/I repair projects and made improvements to
the Town's wastewater treatment plant to enhance its ability to process high peak flows.
The Town has had some success in reducing I/I flow; however, opportunities for further
flow reduction are available.
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 2

2.0 DESCRIPTION OF EXISTING SYSTEM
The Town of Tabor City owns and operates a wastewater collection system and treatment
facility that provides sewer service to the bulk of the residents and businesses within the
Town. In addition, the Town has a usage agreement with Grand Strand Water and Sewer
Authority to provide treatment for wastewater generated by the NC Department of
Corrections facility located northwest of the collection system service area. Wastewater
from the facility is pumped directly to the Grand Strand collection system and does not
pass through the Tabor City collection system.
2.1 Collection System
The Town of Tabor City's wastewater collection system consists of approximately
119,630 LF (22.66 miles) of sewer pipes ranging in size from 6 to 18 inches in
diameter. The core of the system is predominantly vitrified clay pipe (VC) which can
be more prone to inflow and infiltration. Recent line extensions and replacements
consist of polyvinyl chloride (PVC) pipes. Collection system repairs and
improvements have been completed as funding has been available; but, a large
portion of the older, vitrified clay piping remains in service. Inherently, the most
common weakness of vitrified clay piping has been the methods used to join pipe
segments. In most cases, joints were sealed with cement mortar or "hot -poured"
bituminous materials. Any deflection of the pipe joint would break the "seal" in the
joint allowing groundwater to enter.
As stated above, the current collection system consists of approximately 119,630 If of
sewer lines ranging from 4 to 18 inches diameter, eight pump stations, 513 manholes
and a wastewater treatment facility. The collection system is shown in Map 1 in
Appendix A. The following is a detailed inventory of the collection system piping
network:
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 3

Table 1: Collection System Summary
Diameter
Material
Length (ft.)
Length (mi.)
Inch -miles
4
VC
179
0.03
0.14
6
Unknown
545
0.10
0.62
6
PVC
1,233
0.23
1.40
6
VC
1,906
0.36
2.17
8
Unknown
23,529
4.46
35.65
8
PVC
16,902
3.20
25.61
8
VC
64,674
12.25
97.99
10
PVC
10,577
2.00
20.03
10
VC
1,246
0.24
2.36
12
Unknown
296
0.06
0.67
12
PVC
3,939
0.75
8.95
12
VC
3,501
0.66
7.96
15
Unknown
246
0.05
0.70
15
PVC
8,533
1.62
24.24
15
VC
3,537
0.67
10.05
18
Unknown
82
0.02
0.28
18
PVC
1,273
0.24
4.34
18
VC
241
0.05
0.82
Totals:
142,439
26.98
243.97
The Town has completed three separate UI repair projects between 2004 and 2010
that replaced or rehabilitated approximately 10,500 if of 8-inch through 18-inch sewer
main and approximately 45 manholes. The total cost of all improvements totaled
approximately $870,000.00. A summary of each project is as follows:
• WWTP Outfall Replacement (2004) - Replacement of approximately 1,300 If
of 18-inch gravity sewer.
• Jessie Street Outfall Replacement (2007) - Replacement of approximately
2,100 if of 12-inch gravity sewer.
• Miscellaneous I/I Improvements (2010) - Replacement / rehabilitation of
approximately 7,4001f of 8-inch through 15-inch gravity sewer.
2.2 Wastewater Treatment Plant
The Town of Tabor City operates its own wastewater treatment facility under NPDES
Permit No. NC0026000. The facility currently has a capacity of 1.1 MGD, with
average daily flows of 0.380 MGD. The treated effluent from this plant is discharged
to Town Canal, a tributary to Grissett Swamp, located in the Waccamaw River sub -
basin of the Lumber River. Miscellaneous improvements to the WWTP were
completed recently and included the addition of a flow equalization basin, tertiary
filtration, and UV disinfection. The effluent quality and influences from inflow and
infiltration in the collection system continue to be a concern with regard to the
operation and maintenance of this plant. Additional improvements to the WWTP are
scheduled for 2013 that will include repairs to one of the clarifiers as well as to an
aeration basin. The repairs are intended to improve the ability of the plant to meet
permit limits and operational standards.
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 4

3.0 WASTEWATER FLOW EVALUATION
Ideally, the total volume discharged from the wastewater collection system to the
wastewater treatment plant would be the output of the Tabor City potable water system
minus consumptive losses such as: evaporation, lawn irrigation, and other recreational
activities. However, this ideal situation cannot be realized since the collection system is
never perfect. The network of underground piping and manholes, which comprise the
collection system, always will have voids that allow leakage. These imperfections could
be: open joints, broken pipes, root intrusions, deteriorated manhole structures or failed
service laterals and connections. Other sources of fugitive contributions may be: cross
connections to storm sewers; roof drains inadvertently tied into the system; or inflow
from areas that tend to flood or pond after rain events. Sources of infiltration typically are
harder to find and repair than sources of inflow. However, effective repair of infiltration
sources can have greater benefits in reduction of daily flows. Repair of inflow sources
generally reduces system surcharging as well as overflows if they exist, but have less
effect on daily flows.
3.1 Infiltration Screening
In order to quantify the effects of inflow and infiltration on the collection system,
wastewater flows were compared to water usage and rainfall data as recorded June
2011 through June 2012. The Town of Tabor City provided wastewater flow data and
water usage; rainfall data was provided by the North Carolina State Climate Office.
The expected wastewater flow rates were calculated based on the water billing
records minus a consumptive loss of 10 percent. Water customers not connected to
the sewer system were not included in the analysis. Infiltration is calculated to be the
average daily flow to the treatment facility minus the average daily expected flow.
Since infiltration is relative to the length and diameters of the collection system, it is
generally stated in terms of the collection system's total inch -miles. The inch mile
parameter is the sum total of the line length in miles multiplied by the pipe diameter
in inches. From the data derived from the inspection and mapping of the collection
system, the total system inch -miles were computed to be 243.97.
Historically, I/I greater than 3,000 GPD / inch -mile for the three wettest consecutive
months annually have been considered to be excessive. This benchmark was set to
estimate the effectiveness of collection system rehabilitation or replacement, Systems
with a higher level of infiltration per inch -mile could see greater flow reductions from
repair projects. Conversely, systems with lower infiltration per inch -mile may need to
repair or replace a significant portion of the system to achieve a worthwhile reduction
in infiltration.
The following table summarizes the calculation of inflow and infiltration in the Tabor
City collection system. Sewer billing records were provided by the Town, expected
flow is based on billing records minus a consumptive loss of 10%, and the amount of
sewer treated was taken from WWTP flow records. Rainfall data was provided by the
NC State Climate Office and is based on observed rainfall at the Columbus County
Airport, which at approximately 13 miles from the project area is the closest active
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 5

I
1
1
1
1
M
u
11
11
n
11
observation station. This distance would likely have an effect on the accuracy of daily
rainfall totals, but monthly totals should be reasonably reliable.
Table 2: Infiltration Screening Summary
Month
Sewer
Billed
Expected
Flow
Sewer
Treated
infiltration
Rainfall
GPD
GPD
GPD
GPD
GPD/in.-mi,
in.
Jun-11
205,119
184,607
230,800
46,193
189.34
0.46
Jul-11
157,728
141,956
248,129
106,173
435.19
3.73
Aug-11
169,728
152,756
327,581
174,825
716.58
4.43
Sep-11
117,319
105,587
329,200
223,613
916.56
4.27
Oct-11
148,664
133,798
351,065
217,267
890.55
1.29
Nov-11
181,586
163,427
377,733
214,306
878.41
2.11
Dec-11
129,793
116,814
384,226
267,412
1,096.09
0.26
Jan-12
175,890
158,301
380,742
222,441
911.76
0.95
Feb-12
167,572
150,815
394,414
243,599
998.48
1.46
Mar-12
140,599
126,540
513,774
387,235
1,587.22
2.96
Apr-12
150,453
135,407
373,200
237,793
974.68
2.47
May-12
166,245
149,620
579,290
429,670
1,761.16
5.61
Jun-12
148,719
133,847
459,267
325,419
1,333.85
1.52
Average:
158,417
142,575
380,725
238,150
976
31.52
Infiltration during the three wettest consecutive months of the study period totaled
678 GPD/in-mi. However, the average annual infiltration totaled 977 GPD/in-mi or
238,150 GPD. Although infiltration in the Tabor City collection system is almost 1.7
times the expected flow from sewer customers, it remains well below the benchmark
of 3,000 GPD/in-mi. As such, a sizeable portion of the collection system may need to
be repaired or replaced to make a significant I/I reduction.
3.2 Inflow Screening
Inflow refers to stormwater runoff that flows directly into the collection system from
storm drains, roof drains, or collection system structures in low-lying areas could
flood during rainfall events. Typically, inflow causes short-term flow increases during
or shortly after significant rainfall events. Since daily rainfall totals are not logged in
Town and instantaneous wastewater flow data is not available, it is not possible to
accurately quantify inflow in the collection system.
For the purposes of this report, inflow is estimated based on available rainfall data
and daily flow to the WWTP. Some rainfall events that were observed at the
Columbus County Airport did not result in a significant flow increase at the Tabor
City WWTP. It was assumed that these were more isolated events that did not result
in significant rainfall in the WWTP service area. The following table shows the
impact of rainfall events on flow to the WWTP. The base flow was calculated from
dry weather flow on days immediately preceding the rainfall event.
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 6
11

Table 3: Litlow Screening Summary
Date
Base Flow
Wet Weather
Flow
Inflow
Rainfall
5/9/2012
0.3733
0.63
0.2567
0.72
5/17/2012
0.5095
1.186
0.6765
0.81
5/30/2012
0.415
2.345
1.93
2.89
Based on available data, it appears that inflow in the collection system could be
excessive. Inflow shields recently have been installed in all collection system
manholes to preclude runoff from entering the system through vent holes and other
voids in manhole lids. The effect of the inflow shields is not yet known but
potentially could be significant.
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 7

4.0 COLLECTION SYSTEM EVALUATION
The evaluation of the Tabor City collection system was completed in 2001 as part of the
original I/I study. For the purpose of this report, a desktop review of the data collected
was completed to formulate updated recommendations or confirm previous
recommendations. The collection system evaluation was performed using various
methods of testing and data collection. Manholes and pump stations were visually
inspected, the system was tested for storm sewer interconnections, a small portion of the
piping network was inspected using closed circuit video equipment and flows were
monitored to evaluate the effects of rainfall and seasonal groundwater fluctuations.
4.1 Manhole Inspections
The initial task in the analysis consisted of creating a base map of the Tabor City
sewer collection system. Manhole locations were recorded using sub -meter accuracy
GPS data collection units. The additional information needed to complete the map
was gathered primarily from a visual survey of all the manholes. Each manhole was
inspected to evaluate structural integrity, identify construction material and identify
infiltration or other abnormalities. Pipe diameter also was noted in the survey. All
data collected was integrated into a database and the map was created using GIS
mapping software.
The collection system survey indicates that there are 513 manholes in the Tabor City
collection system. Of those 513, 67 are brick manholes, eight are mixed brick -and -
block manholes, and the remaining 438 manholes are constructed of pre -cast
concrete. The majority of the brick and mixed brick -and -block manholes observed
had defects in the mortar that could allow groundwater to enter the collection system.
A review of the manhole inspection data revealed several manholes with observed
infiltration and others that showed signs of intermittent infiltration.
4.2 Pump Station Inspections
The Tabor City collection system utilizes eight sewer pump stations within the town
limits to convey wastewater to the treatment facility. Based on inspections performed
previously, none of the pumps stations significantly contributed to overall system I/I.
4.3 Smoke Testing
Smoke testing is a quick and effective method of detecting UI sources. It is especially
effective in locating point sources of inflow including cross connections with storm
sewers, roof leaders and area drains. Also, inflow points such as damaged or
abandoned service laterals, and leaks from drainage paths, or areas that tend to pond,
can be pinpointed using this method. The testing was accomplished by forcing non-
toxic smoke through the collection system using a gas -powered air blower. A two -
person crew observed and documented findings. A single setup covered an average
800 If to 1,2001f of sewer main.
Eleven (11) possible sources of inflow were located, the majority of which were
abandoned service connections and broken service cleanouts. There were a couple of
areas where segments of failed or abandoned sewer pipe were located as well as
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 8

several manholes with potential inflow sources. The testing revealed no major
sources of inflow.
4.4 Video Inspections
Based on sewer main age, material, and observations made during the manhole
inspections, several segments of the piping network were selected for internal
inspection. These areas were cleaned and inspected by a local contractor using
closed-circuit television equipment. The segments inspected total approximately
1,900 linear feet of 8-inch pipe along W 71h Street and Fowler Street.
The internal inspections revealed separated joints that could allow groundwater to
enter during seasonal peaks or following rainfall events. Additionally, excessive
quantities of sediment were present that indicated voids in the system piping.
4.5 Soil Characteristics & Seasonal High Groundwater
Characteristics of soils within the collection system service area were obtained from
the USDA Web Soil Survey. Areas with seasonally high groundwater, above normal
depths of the collection system's gravity sewer, were identified and compared with
piping material. Soils that are saturated for longer than one month at a time are
considered to have high seasonal groundwater. Areas where high seasonal
groundwater corresponds to vitrified clay piping and brickfblock manholes will have
a greater potential for infiltration. An analysis of the data obtained from USDA
indicates that practically all of the collection system exists in soils prone to high
seasonal groundwater. Table 4 shown below summarizes the USDA soil data.
Additionally, these areas are shown in Map 2 located in Appendix A. Soils with high
seasonal groundwater shown in the map are separated based on the approximate depth
to groundwater. Soils where the depth to groundwater is within 3.5 feet of the surface
are indicated as "High Groundwater", and Boils with groundwater between 3.5 feet
and 6 feet of the surface are indicated as "Moderate Groundwater".
Inflow and Infiltration Analysis Update
January 201.E
Town of Tabor City, North Carolina
Page 9

Table 4: Service Area Groundwater Characteristics
Soil Map
Unit
Depth to Water
Table (ft)
Approximate
% of Service
Area
AuB
4.0 - 6.0
2.1%
BnB
4.0 - 6.0
0.0%
Co
0.0 - 1.0
5.4%
Fo
2.0 - 3.5
0.9%
GoA
2.0 - 3.0
11.1%
LnB
0.0 - 1.0
0.6%
Ly
0.5 - 1.5
11.6%
Me
0.0 - 1.0
1.8%
Mk
0.0 - 1.0
3.0%
NoA
3.3 - 6.0
4.5%
NoB
3.3 - 6.0
7.7%
NuB
3.3 - 6.0
19.0%
Pa
0.0 - 1.0
2.3%
Ra
0.0 - 1.0
13.0%
Ru
0.0 - 1.0
8.3%
St
1.0 - 2.5
0.3%
To
0.0 - 1.0
1.4%
Ud
>6
0.1%
WaB
5 - 6.7
2.5%
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 10

5.0 CONCLUSIONS & RECOMMENDATIONS
Multiple collection system rehabilitation projects have been completed since 2009 and
have decreased UI to some degree. However, the Tabor City collection system continues
to experience a high volume of inflow and infiltration. It is believed that the older
vitrified clay piping and brick manhole in the system arc the primary contributors to the
infiltration. In particular, the portions of the system in areas with highest seasonal
groundwater are likely the greatest contributors.
The system is particularly susceptible to inflow during significant rainfall events. Smoke
testing indicated that there are no significant cross connections between the sanitary
sewer system and storm drains. However, additional smoke testing could be beneficial to
locate smaller sources that could combine to make a significant impact on total inflow.
The Town recently has taken steps to reduce inflow by installing inflow shields in each
manhole within the collection system. The effectiveness of these inflow shields should be
more formally quantified before making additional expenditures to locate inflow sources.
We recommend that the Town continue to complete the previously recommended inflow
and infiltration repair projects, as funding becomes available. However, it would be
beneficial to collect wastewater flow data from collection system subsystems to compare
flow trends with seasonal groundwater fluctuations and rainfall events. Ideally, twelve
(12) months of data would be collected. The collection system is divided into nine (9)
separate subsystems based on topography. Eight (8) of these subsystems drain to pump
stations and the remaining flows directly to the WWTP. Reasonably accurate flow data
could be collected by monitoring pump station runtime then comparing that data to pump
capacity tests. This information would provide a basis to prioritize recommended
improvements. In addition, the data may identify areas where repair or replacements
would be most beneficial. A list of the recommended projects is given below with
estimated cost. The project areas are shown in Map 2 in Appendix A.
Project Area
701 Bypass
McGougan Street and
Manhole Rehab
Fowler Street
Pine & Sarvis Streets
Lewis Street
2nd, 3rd, and 4th
Streets
Total Estimated Cost:
Estimated Project Cost
$297,000.00
$112,000.00
$133,000.00
$303,000.00
$555,000.00
$387,000.00
$1,787,000.00
Inflow and Infiltration Analysis Update
January 2013
Town of Tabor City, North Carolina
Page 11

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Tabor City Inflow and Infiltration Study
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Manholes
• Brick
• Mixed
• Precast
Gravity Sewer
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it? Subsystems
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701 Bypass
Tabor City Inflow and Infiltration Study
Update - Map 2: Recommended
Ill Repair Projects
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• Pump Stations
Manholes
• Brick
• Mixed
• Precast
Gravity Sewer
vc
/4/ PVC
"/ Unknown
,V Repaired Sewer
s, Forcemain
Subsystems
High Groundwater
Moderate Groundwater
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