HomeMy WebLinkAbout131217 Trunk Sanitary Sewer Infiltration Study Report - Bolton and MenkTrunk Sanitary Sewer
Infiltration Study Report
City of Edina, Minnesota
December 2013
Project No. T16.106814
Prepared by: Bolton & Menk, Inc. – T16.106814 Certification
Trunk Sanitary Sewer Infiltration Study Report – City of Edina
CERTIFICATION
Preliminary Engineering Report
for
Trunk Sanitary Sewer Infiltration Study Report
City of Edina
Edina, Minnesota
T16.106814
I hereby certify that this plan, specification or report was
prepared by me or under my direct supervision, and that I am
a duly Licensed Professional Engineer under the laws of the
State of Minnesota.
By:
Marcus A. Thomas
License No. 26499
Date: 12/5/2013
Prepared by: Bolton & Menk, Inc. – T16.106814 Table of Contents
Trunk Sanitary Sewer Infiltration Study Report – City of Edina
TABLE OF CONTENTS
I. STUDY BACKGROUND ............................................................................................... 1
II. STUDY PURPOSE ........................................................................................................ 2
III. AVAILABLE STUDY BACKGROUND MATERIAL AND DATA ......................................... 2
IV. ANALYSIS OF AVAILABLE DATA ................................................................................. 4
V. PIPE REHABILITATION METHODS .............................................................................. 7
VI. RECOMMENDED PROJECT LIMITS ............................................................................. 9
APPENDIX
FIGURE 1 .................................................................... SANITARY SERVICE AREA SUMMARY
FIGURE 2 ............................................. ENVIRONMENTAL FEATURES & IMPAIRED WATERS
FIGURE 3 ........................................... DEVELOPMENT & SEWER CONSTRUCTION HISTORY
FIGURE 4 ............................... YEARS OF DEVELOPMENT AND REDEVELOPMENT PROJECTS
FIGURE 5 ................................................................ TRUNK SEWER PIPE DEVEOPMENT AGE
FIGURE 6 ...................................................................... OVERALL INFILTRATION SUMMARY
FIGURE 7 ................................................. OVERALL INFILTRATION PER ACRE SERVICE AREA
FIGURE 8 ................................................................ GROUNDWATER DEPTH ABOVE INVERT
FIGURE 9 .............................................................................. DRY WEATHER PIPE CAPACITY
FIGURE 10 .................................................................................................... PIPE MATERIAL
FIGURE 11 ................................................... SERVICE CONNECTIONS ALONG TRUNK LINES
FIGURE 12 ..............................................................................................................PIPE SIZE
FIGURE 13 ......................................... TRUNK SEWER INFILTRATION ABATEMENT PRIORITY
FIGURE 14 ................................................................... 5-YEAR ROAD IMPROVEMENT PLAN
FIGURE 15 ....................................................................... EXAMPLE OF PROJECT SYNERGIES
FIGURES 16 TO 32 .................................................................................... REHAB PROJECTS
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I. STUDY BACKGROUND
This trunk sanitary sewer infiltration study report was ordered in support of the City of Edina’s
overarching goals of reducing infiltration and inflow into its sanitary sewer system, and renewal of
its aging sanitary conveyance system. The City’s Wastewater and Comprehensive Sewer Plan
defines the “service” the City provides as “effective and efficient removal of sanitary sewage for all
areas of the City of Edina, while also eliminating inflow and infiltration, protecting the health,
safety and welfare of our citizens, and supporting the needs of a dynamic and sustainable
community.”
Identification and reduction of infiltration and inflow (I/I) has been a regional priority of
Metropolitan Council Environmental Services (MCES). Infiltration, which typically contributes a
continuous flow of “clean water” into the system through cracked pipes and manholes, increases
the City’s flows into MCES facilities and directly increases costs to the City for the ongoing
treatment of these excess flows. Inflow typically comes through illicit storm water connections into
the sanitary sewer system (e.g., roof drains, sump pump drains, etc.) or surface openings such as
openings in manhole lids, and deteriorating rings and castings. These flows are less continuous but
typically cause greater flow “spikes” during storm events and can exceed pipe capacity and cause
system backups and consequential damages. A current response by MCES is to assess a surcharge
to those municipalities exhibiting these types of spikes in their systems.
Recent Evaluations and Mitigation Efforts
The City of Edina recognizes both the regional and local implications of I/I and continues to take
action toward eliminating these problems within the City. Past steps taken by the City include
various studies and field evaluations. Large area I/I studies were completed in 1983 (Donohue) and
1997 (TKDA) which quantified volumes of I/I entering the City’s sanitary sewer system, provided
estimated costs for system rehabilitation, and identified neighborhoods with sump pump
connections to the sanitary sewer. Pipe televising and field inspections of sewer manholes have
been completed in advance of neighborhood reconstruction projects to identify necessary sewer
infrastructure improvements; the result being replacement and rehabilitation projects implemented
throughout the City’s system. Local sewer system analyses have been completed in conjunction
with redevelopment projects to determine capacity needs. In 2005/2006, Barr Engineering
collected sewer flow meter readings and completed system wide modeling to estimate general
volumes of infiltration being carried by the trunk sewer system. Most recently, the City has been
televising the trunk sewer system, much of which has never been visually inspected to this degree
in the past.
Special Trunk Sewer Considerations
Sanitary trunk sewers, which are the focus of this study report, are the primary pipes within the City
of Edina’s sanitary sewer system. In addition to their larger diameter, these trunk lines can
generally be identified by their deeper depths and by their alignments along creeks and other low
terrain. The trunk lines are a critical component of the City’s sanitary sewer system, as they
ultimately collect and rout all sewer flows out of the City and into MCES facilities. It is imperative
that the trunk sewers are maintained in a structurally sound condition and are free of excessive
“clear water” flows via groundwater infiltration. Therefore, the rehabilitation priority
recommendations given in this report are in support of both necessary system renewal and
infiltration reduction. The trunk sewer system that is the subject of this study is illustrated in
Figure 1.
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The City of Edina’s trunk lines are relatively aged, and based on previous assessments as described
above, groundwater and storm water infiltration flows into the trunk lines are evident. Specific
attributes of the trunk sewer system that raise concerns of I/I problems include pipe alignments
along creek beds, high groundwater, and flood-prone zones; exposure of deteriorating manholes;
antiquated manhole covers (including those with vent hole openings); and overall age, material type
and diameter of the trunk sewer pipes. These attributes, which are given further consideration in
this report, can be correlated to various levels of potential infiltration within the trunk sewer
system. Finally, it should be noted that while a focus on the City’s trunk sewer system is certainly
warranted, it is also important to recognize the I/I potential of the broader lateral (or neighborhood)
sanitary sewers throughout the City, and that the City of Edina should continue its proactive
practice of lateral system evaluation and maintenance.
II. STUDY PURPOSE
This trunk sewer infiltration study supports the City of Edina’s objectives of reducing infiltration
into its sanitary sewer system, initiating an overall trunk sewer system renewal process and the
establishment of a service-reliable, next-generation trunk sewer system. This report includes
recommendations for prioritizing trunk sewer system segments for rehabilitation, along with a
preliminary identification of individual project areas. A discussion of various rehabilitation
methods is included, with a focus on cured in place pipe (CIPP) lining as a viable trenchless
alternative for many of the trunk sewer segments. Estimated project costs are also provided for
capital improvement planning.
III. AVAILABLE STUDY BACKGROUND MATERIAL AND DATA
Several sources of information were assembled for this study to define the sanitary system and its
proximity to other physical system components. Important relationships between quantitative and
qualitative information were also developed as a method to measure specific system characteristics
and their effect on potential infiltration.
GIS Information
The City of Edina has a comprehensive inventory of its existing sanitary system maintained in a
geographical information management system (GIS). This includes geometric information for
manholes, gravity pipe, force mains, lift stations, service connections, valves, and fittings. Other
GIS data provided by the City includes groundwater depth information and development age. The
available data is further summarized below.
• Sanitary system wide data: The attributed data contained in the City’s sanitary system GIS is
extensive. Manhole information includes elevation data when available; information on the
physical condition and the date of inspection; structure type and material; and a unique
identity number. Pipe information, including gravity and pressure main, includes diameter,
material, length, slope (where available), and additional inspection records. Other system
information incorporated in the GIS includes services, lift stations, supervisory control and
data acquisition (SCADA) sensors, pipe fittings, valves, pipe casings, and clean out
structures.
• Ground water elevation model: A Metropolitan Area Groundwater Flow Model was
developed by Met Council and Barr Engineering, et al, for the Twin Cities area called Metro
Model 2, which further enhanced a model developed by the MPCA in 2000. One product of
Metro Model 2 is the approximate water elevation of the aquifer based on water budget data,
historic climate data, stream elevations, and well information. The data is stored as a digital
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elevation model (DEM); each cell in the DEM raster represents a water table elevation. The
approximate resolution of the data is +/- 20 feet vertically. Therefore the data was considered
preliminary and approximate and used as a relative comparison to structure elevations.
•Citywide development age: Utilizing historic development information, the City assembled a
map showing the principal periods of significant residential construction from 1940 (and
before) to 1970 (and after) in 10 year increments. The map was digitized by Bolton & Menk
in GIS to be used for geospatial analysis, as seen in Figure 3. The City also provided parcel
information including the actual age of development and redevelopment. This data is shown
in Figure 4. While the parcel information was useful in determining when construction
activity took place on the parcel, it does not always correlate to the age of the sanitary system.
Therefore, Figure 3 was used to develop approximate pipe age.
•Flow meter locations: In 2005, several temporary flow meters were installed throughout the
system to collect wet and dry weather flows at key discharge points. The locations of the
flow meters were used to develop the contributing sanitary service area including gravity
main, force main, lateral lines, and services. These areas are illustrated in Figure 1. The flow
meters, in conjunction with approximate infiltration summary data developed by Barr
Engineering, were then used to develop relationships between service area, length of pipe,
age of development, and other system parameters and approximate infiltration.
•Other statewide and regional data: Additional GIS data was collected in the area from state,
county, and local sources including light detection and ranging (LiDAR) mapping, surface
water information, and parcels. While most of the data was utilized for display, some was
used to develop important proximity relationships.
City Wide Sanitary Sewer Model
The City of Edina and Barr Engineering established a hydraulic model of the sanitary sewer system
using XPSWMM in 2005/2006 to develop dry and wet weather system capacities and to identify
areas in the City where I/I was likely originating. In 2008, an effort to update and calibrate the
hydraulic model was performed utilizing Met Council flow monitoring locations at the City’s trunk
outfalls plus several flow meters along the trunk lines at key locations throughout the City. Figure
1 identifies the metering locations and corresponding service areas. The flow monitoring was
performed during drier, winter months to establish a better base flow condition and during the
spring months to capture system flows during a high likelihood of rainfall. The difference between
the modeled base flow and calibrated peak wet weather flow hydrographs correlated the expected
infiltration. The results of this analysis were summarized for each of the meter locations.
2008 Sanitary Sewer Comprehensive Plan
Chapter 8 of the City’s Comprehensive Plan, addresses Water Resources Management, including a
comprehensive plan for wastewater and sanitary sewer. Since the City is fully developed, the
Comprehensive Plan addresses system capacity and required improvements for major areas of
redevelopment, increases in residential and commercial development densities, and anticipated
future land use changes. Based on two development scenarios, increases in the trunk sewer and
resulting increase in flow to MCES interceptors were summarized. The Comprehensive Plan
indicates that two thirds if the City’s sewage flows into MCES meter M-129 and into interceptor 1-
RF-491. This interceptor is critical to the planning of Edina’s future growth since the majority of
planned future flow increases will be directed to this interceptor. As a result, the City has mapped
the potential trunk sewer upgrades in their Comprehensive Plan which is utilized to help the City
prioritize sewer improvements based on future capacity needs and level of current infiltration. See
Figure S-4 in the 2008 Comprehensive Plan.
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Field Observations
On August 8th, 2013, Bolton & Menk staff completed a field analysis of the trunk sewer lines
analyzed in this project. The goals of the field observations were to analyze the trunk system on the
ground, locate critical manholes, determine access points for rehabilitation equipment, identify
areas where open-cut replacement options were viable, and formulate a set of notes to help establish
future project locations.
Sewer Televising
The City of Edina Public Works Department has televised several thousand feet of sewer to collect
critical information regarding the condition of pipes and manholes that indicate sources of
infiltration. The City has also contracted for the televising of other critical pipe segments.
Televising of pipe segments reveals crushed and cracked pipe, separated joints, root intrusion, leaky
services, pipe material where previously unknown, signs of infiltration in manholes, and a wealth of
other information that is otherwise impossible to collect.
Local Knowledge from City Staff
The City’s cumulative knowledge of the trunk system provided specific information that may
otherwise not be evident in the GIS and televising. This includes areas with known issues, lift
station conditions, areas of future bypass or relief lines, areas with regular sewer backup issues,
specific pipe rehab and concrete encasing projects, and other anecdotal and qualitative information
useful in determining the condition of the existing system.
IV. ANALYSIS OF AVAILABLE DATA
The available study materials and background information was organized and populated in a GIS
database to develop geospatial relationships that identify trunk sewer infiltration potential and
prioritize rehabilitation. A system was developed to assign a rating to each level of data acquired
so that the cumulative “score” could be easily compiled.
Quantitate Infiltration Data
Infiltration data provided by Barr Engineering and the location of the flow meters in the system
were used to establish sanitary service areas, which are displayed in Figure 1 with additional system
information summarized further. Flow data collected at the meters during dry and wet weather
periods and the resulting estimates of infiltration based on hydraulic model calibration was used as
a predictor of the degree of infiltration within the service area. It is difficult, however, to directly
correlate infiltration on the trunk line to this data because of the unknown infiltration potential in
the extensive upstream lateral system. For instance, while the meter-shed associated with
temporary meter 4 has the second highest calculated infiltration, it also has nearly 37 miles of trunk
sewer and 2500 service connections.
Figure 6 shows the overall results of the infiltration analysis for each meter-shed associated with
the 2005 temporary meter locations. Another representation of the data is to normalize the data
over the area to better predict the severity of infiltration. Figure 7 shows the result of the
normalization. When comparing Figures 6 and 7, it is observed that the distribution of infiltration
across the city changes when the data is normalized over area. Other techniques were considered,
including normalizing the data based on number of service connections along the trunk line or
length of lateral or trunk line pipe. However, it is still difficult to target the source of infiltration
without additional flow data and modeling in the lateral systems.
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Compiled Qualitative Data
Information regarding known sources of infiltration, historic sewer backups, and previously
determined pipe upgrade recommendations was compiled to help further prioritize future
rehabilitation projects. While this information was not used to enhance or inhibit a pipe segment’s
need for rehabilitation, it was used to check the results of this physical system analysis to verify its
accuracy.
Creation of the Prioritization Database
As described above, several sources of system information were provided to compile a database
that was manipulated to describe the primary sources of infiltration in the system. In all cases, the
study trunk sewer pipe was utilized to create a set of raster, or grid data that describes each of the
prioritization criteria. Using this method, rasters are reclassified to rank the importance of layer in
terms of infiltration potential, and a summation of the relative infiltration risks is utilized to
calculate the cumulative ranking. The final layers used to prioritize rehabilitation projects are
described below. The referenced figures include a color gradation from green to yellow to red
defining low to medium to high (respectively) infiltration potential. This study is focused on the
trunk lines’ contribution to infiltration only. The upstream lateral system is also a critical
component to overall infiltration. The limitations of each analysis layer are also discussed below.
•Age of development: Pipe age was correlated to the development age information provided
by the City (Figure 3). The result of this intersection is shown in Figure 5. The age
categories used were based on the historic development information maintained by the City.
In this case, it is assumed that older pipe has a higher likelihood of infiltration.
•Groundwater depth: Sanitary manhole structure invert (pipe elevation) data was compared to
the Metro Model 2 groundwater elevation model to determine the height of groundwater
above the invert. Manholes along the trunk sewer line were selected and used to intersect
with groundwater elevations. Subtracting the groundwater depth from the invert generates a
depth of groundwater above the invert. In some cases, the manhole invert has two or more
feet of separation from the water table. In others, the depth above the invert was as much as
21 feet. The higher the groundwater depth above the invert, the higher the correlation to
infiltration. Figure 8 shows the resulting raster generated from the manhole intersection
along the trunk sewer line.
•Dry weather pipe capacity: Dry weather pipe capacities were provided by Barr Engineering
from the 2008 hydraulic model to determine the current level of service of the trunk sewer
pipe. While dry weather capacity is not correlated to infiltration, it does provide information
on what trunk lines need to be replaced and upsized. In an open cut rehabilitation, it is
crucial that the City understands the current capacity and installs a pipe that meets future
growth patterns. Figure 9 shows the City’s service level as of 2008. Lower capacity pipes
are given a higher priority of rehabilitation. We understand that the City is currently in
process of updating the 2008 hydraulic system model with current land use and service flows.
This new information, when available, can be reviewed in conjunction with the modeling
results of this study to determine if any the recommendations in this report need updating.
•Pipe material: The City’s sewer system GIS contains information regarding pipe material.
The pipes in Edina consist of vitrified clay pipe (VCP), reinforced concrete pipe (RCP), cast
iron pipe (CIP), and pipe that has already undergone a cured-in-place pipe (CIPP)
rehabilitation. Pipe age, and often condition, can be correlated to pipe material. VCP is the
oldest material in town and has the highest probability of leaking joints or other significant
structural issues. While RCP is strong, it can be susceptible to deterioration by long term
exposure to hydrogen sulfide gases generated by wastewater. This is evident in some recent
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sewer television videos that illustrate spalling (loss of cement) along the crown of some
concrete pipes. This type of deterioration, particularly in the vicinity of individual pipe
joints, can often lead to infiltration. CIP and CIPP are less susceptible to infiltration. Figure
10 shows the locations of pipe material in the City along the trunk lines. This data describes
infiltration susceptibility along the trunk line only. A CIP or CIPP trunk line may include
lateral systems that are all VCP, indicating that the trunk line is not the only culprit
susceptible to infiltration.
•Service connection frequency: Figure 11 shows the number of service connections per 1,000
feet of trunk line. Service connections are a critical point for infiltration. Therefore, a higher
number of service connections can lead to a higher infiltration potential. However, service
connections along lateral lines must also be considered in the overall infiltration potential. A
trunk line with no service connections can still have a large infiltration contribution from a
heavily serviced lateral system.
•Pipe Size: Figure 12 is a summary of the pipe sizes along the trunk lines. In general, pipes
with large diameter have a higher surface area susceptible to infiltration issues. Therefore,
larger pipes should be targeted over smaller ones where high rates of infiltration are known.
Comprehensive Plan Information
The 2008 Comprehensive Plan discusses the impacts of recent significant redevelopment to the
sanitary sewer system, including higher density residential and commercial development. The
Comprehensive Plan indicates that the majority of this development will impact the area draining to
MCES interceptor 1-RF-491, with smaller portions draining to 1-RF-490 and 3-NB-499. With the
hydraulic model developed by Barr, the system was analyzed for two development scenarios under
a range of population growth projections. Figure S-4 in the Comprehensive Plan shows the areas of
the City that may require upgrades as development continues. As growth plans in these areas
become more refined, these trunk upgrade areas should be considered for pipe replacement
projects, if necessary, to account for increases in service flows.
The Comprehensive Plan also addresses future infrastructure improvements based on known I/I
related issues. The City’s CIP also includes a five-year plan for sanitary system improvement
projects. The projects identified in the Comprehensive Plan include manhole rehabilitation, pipe
rehabilitation of low lying sewers near Minnehaha Creek, drainage improvements near 70th and
France, and disconnection of systems contributing runoff to the sanitary system.
Prioritization of Trunk Sewer Rehabilitation
The items listed above are the essential quantitative and qualitative components of the GIS database
used to prioritize pipe rehabilitation projects. The process for determining the prioritization factors
is discussed below.
1. Populate the GIS: For this analysis, all of the GIS layers used were based on the trunk sewer
segments largely delineated by the location of flow metering data. The geometry type
includes lines, broken at each manhole. Therefore, as seen in the figures described above, all
data used for the analysis was first converted to line geometry.
2. Convert to Raster: Each line shapefile was converted to a raster with a cell size of 60’. It
was essential to ensure that each analysis layer had the same cell size as well as identical
alignments. If all of the layers do not overlap exactly, the results of the spatial analysis will
be skewed at the non-overlapping cells.
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3. Reclassify Cells Based on Determined Prioritization Factors: Prioritization factors were
assigned to each unique field in the GIS based on the potential contribution to infiltration.
For instance, older, clay pipe has a higher susceptibility to infiltration that a newly lined CIPP
pipe. Therefore, the clay pipe should have a higher priority for rehabilitation. The
prioritization factors range from 0 to 5 and are summarized for each layer in Table 1 below.
4. Calculate Cumulative Prioritization Ranking: Once the rasters have been reclassified, simple
raster math was performed in ArcGIS to sum the individual factors and generate a cumulative
rehabilitation score. The higher the score, the higher the priority for rehabilitation. The final
trunk sewer infiltration abatement priority is displayed in Figure 13.
Table 1: Summary of trunk sewer infiltration abatement prioritization factors.
Prioritization
Factor Pipe Age
Groundwater
Depth Above
Pipe Invert
Dry
Weather
Capacity
Pipe
Material
Service
Connection
Frequency
(per 1000’) Pipe Size
0 < -2.0 CIPP
1 >1970 -2.0 - 3.0 0-10% CIP 0-3 15" - 16"
2 3.0 - 5.0 11-50% 3-10 18"
3 1960-1969 5.0 - 7.0 51-70% RCP 10-18 20" - 21"
4 1950-1959 7.0 - 10.0 71-100% 18-31 24"
5 1940-1949 >10.0 >100% VCP 31-74 33"
V. PIPE REHABILITATION METHODS
As a sanitary sewer pipeline nears its end of useful life, there are a variety of methods that can be
considered for its rehabilitation or replacement. In general, the pipe can be replaced via traditional
open trench methods, or there exists a few different trenchless methods that can also be employed.
Open Trench Replacement
Open trench pipe replacement basically involves the excavation and removal of the existing pipe
and the laying of a new pipe in its place. This approach is typically most feasible for relatively
shallow sewers where necessary surface restoration is minimal or when coordinated with overlying
road reconstruction projects. It is many times the most feasible way to upsize a pipe’s diameter to
increase flow capacity. Existing service connections are typically reinstated with traditional wye
fittings and couplers connected to the service lines.
Cured In Place Pipe (CIPP)
Cured in place pipe (CIPP) has become a very popular trenchless method of rehabilitating and
effectively replacing existing pipes. The process involves inverting a resin-filled felt tube into the
existing (host) pipe that, when cured, results in a new pipe that fits tightly against the inside of the
existing pipe. When properly designed, the new liner pipe does not rely on the host pipe for any
structural or flow carrying capacity. While the interior of the CIPP liner may have a slightly
smaller diameter than the original host pipe, the increased smoothness of the liner plus the
reduction of infiltration flows typically result in a new pipe with similar flow capacity as the
original pipe.
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The CIPP process can usually be completed via access manholes, with little to no digging required.
Service connections are also typically reinstated, trenchlessly, through the use of robotic cutting
machines navigated within the new pipe. The flexibility of the pre-cured liner also makes it
adaptable to offset pipe joints, sweeps, and low-degree angle bends along the pipe alignment.
Individual runs can typically extend between 750’ to 1,000’. Given its typical cost effective nature
up to around 48” diameter pipes, it is widely used by cities and MCES, alike.
Special consideration should be given to groundwater conditions when implementing a CIPP liner
solution. For design purposes, high groundwater increases external pressures on the pipe, which
can influence the liner’s design thickness. During construction, it may be necessary to lower the
groundwater to below the pipe zone if there is potential for significant infiltration flows to interfere
with the liner’s curing process.
Slip Lining/ Fold-and-Form Liner
Slip lining is the process of inserting a new “rigid” pipe into an existing pipe. Unlike the CIPP
process that constructs and cures a new pipe inside of the old, the slip lining process involves
sliding a smaller diameter pipe (usually HDPE or PVC) inside of the existing host pipe. For larger
diameter pipes (>48” dia.), fiberglass pipe such as Hobas is sometimes used. The annular space
between the inside and outside pipes is typically filled with grout to complete the process. Fold and
form liners are round HDPE pipes that are pre-folded in half lengthwise to make a U-shape, then
pulled through the host pipe and heated to reestablish their original round shape. In both cases, slip
liners and fold and form liners do not rely on the continued integrity of the host pipe, but often time
result in greater pipe diameter reductions than CIPP lining. While the lining processes typically
require little to no excavation (sometimes only at the launching or receiving ends), reinstating
service connections to these liners typically requires a dig at each location. Compared to CIPP
lining, slip lining sanitary sewers typically becomes more cost effective for larger diameter pipes
(>60”).
Pipe Bursting
Pipe bursting is a trenchless process which involves the literal “bursting” of the existing pipe via
the use of a larger diameter expanding head which breaks apart the existing pipe, then pulling a new
pipe through the resulting opening. The result is the placement of a new pipe (typically HDPE,
PVC, or DIP) along the old pipe’s alignment. In addition to the trenchless replacement of similar
size pipes, as CIPP and slip lining provides, pipe bursting also allows for the upsizing of pipes
where additional capacity is required. A disadvantage of pipe bursting is that individual service
connections need to be dug up to be reconnected. Pipe bursting is also generally more expensive
than CIPP and slip lining.
General Trunk Sewer Rehabilitation Recommendations
In consideration of the typical characteristics of the City of Edina’s trunk sewer system, it is
recommended that CIPP lining be considered as the initial approach to rehabilitating the City’s
system. Factors that support this general recommendation include the need for a trenchless
solution, as much of the pipe has very limited access potential, such as along Minnehaha Creek. As
a trenchless solution, CIPP also conforms well to Edina’s trunk sewer pipe sizes of 33” and less,
and there are many lines with service connections which could be reinstated trenchlessly with the
CIPP system. CIPP also continues to be a cost-competitive method amongst the variety of
trenchless rehabilitation methods. Prioritization recommendations and project limit
recommendations (discussed later in this report) are based, to some extent, on project costs. The
costs of CIPP rehabilitation are a basis of these recommendations. In addition to the mainline
lining of a CIPP project, individual projects should be reviewed for necessary manhole and service
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line repairs. For example, manholes within a project area that are found to be deteriorated and
susceptible to infiltration may also be lined using various epoxy or cement based coating
technologies. Mainline pipe televising sometimes reveals service line problems near the connection
point. Short segments of service pipe can also be lined from the mainline in some circumstances.
Under certain circumstances, it may be desirable to replace a trunk sewer segment via open trench
replacement; particularly in concert with future road projects where the ground surface is already
being disturbed. Figure 14 illustrates the trunk sewer system with an overlay of the City’s 5-year
road improvement plans. An example of potential project synergies exists along Minnehaha
Boulevard, between West 52nd and 54th Streets – this area is further detailed in Figure 15.
Consideration could be given to reconstructing this trunk sewer line directly underneath the street,
in conjunction with a street reconstruction project.
In general, alternative alignments and other factors (such as future capacity and pipe size needs)
that could influence pipe improvement project decisions should be considered in conjunction with
any future sewer rehabilitation projects. Full evaluation of those factors is beyond the scope of this
particular study.
Pre-Televising Inspections
General knowledge of an existing pipe’s characteristics and condition is oftentimes all that is
needed to make preliminary recommendations as to what type of trenchless rehabilitation method
may be feasible. It is important that pre-televising inspections be done, however, to confirm the
suitability of the selected method. Sections of collapsed pipe or service connections that
extensively protrude into the pipe, for example, may require “spot dig” repairs in order for a CIPP
liner to be installed. If the City can acquire this televising information early on, this information
can help inform the design phase of a project. In any case, it is standard protocol for lining
contractors to pre-televise, themselves, to confirm existing conditions.
Flow Bypassing During Construction
All pipeline replacement and rehabilitation methods can, to a certain extent, interfere with normal
sewer flows through the pipes. During open trench replacement projects, these flows are typically
diverted during the daytime construction hours using pumps to route flows from manhole to
manhole around the construction zone. Properties with direct connections within the construction
zone are given advance notice to reduce or eliminate sewer discharges during the working hours. It
is typically a minor inconvenience lasting for a couple of days with normal sewer use being granted
during the evenings and overnight.
Trenchless methods can potentially extend the disruption of sewer service to properties for longer,
more continuous lengths of time. In some cases, bypass pumps may need to run 24 hours per day
for several days, depending on the rehabilitation processes used and the unique circumstances of
the project area. For any specific project, these factors can usually be identified ahead of time and
coordinated with affected property owners. Effective communication during the design and
construction phases of these projects can help ensure project success.
VI. RECOMMENDED PROJECT LIMITS
Based on the prioritization maps and estimated project costs, rehabilitation project limits were
delineated. Rehabilitation lengths were divided into 2,000 to 2,500 foot segments based on an
estimated total project cost of $500,000. It is assumed that all rehabilitation projects will be CIPP.
However, it may be more cost effective for the City to consider alternative methods where
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Trunk Sanitary Sewer Infiltration Study Report – City of Edina Page 10
applicable. Project delineations are illustrated in Figures #16 through #32.
Project Cost Estimates
A review of CIPP cost estimates and recent project bid abstracts was performed to calculate an
average project cost per foot of pipe. Several components to the rehabilitation process were
considered, including average cost of CIPP lining for pipes ranging from 15” to 33”; service
connections; temporary bypassing and services; and pre- and post-construction televising. CIPP
rehabilitation projects within the range of Edina’s trunk sewer diameters cost an average of $200 to
$250 per foot. Therefore, based on the City’s annual budget of $500,000, the average project
length is 2,000 to 2,500 feet. If the City wishes to extend the budget to $1M per year, two project
segments could be rehabilitated.
Access Considerations
Manhole access is very important in determining project segments because CIPP lining begins and
ends at a manhole. Based on field investigations performed in August, 2013, manhole access was
reviewed for the entire trunk system. Individual project delineations based on project costs,
manhole access and other field observations are summarized in Figures 16 to 32.
Final Project Prioritization
The prioritization recommendations for future trunk sewer rehabilitation investments are
summarized in Figure 13. This priority map represents a weighted summation of the various sewer
pipe attributes described previously in this report and illustrates the relative potential for infiltration
throughout the trunk sewer system.
The Minnehaha Creek line stands out as the highest priority trunk sewer for future rehabilitation.
Recent televising of this line also confirms our analysis and recommendations, as it revealed active
infiltration at multiple locations along this VCP sewer. It is recommended that the City considers
including the rehabilitation of this line in its upcoming capital improvement planning schedule.
This would include project segments #1 through #5.
The prioritization map illustrates a second priority segment, just east of T.H. 100, extending
through the Lake Edina/ South Cornelia neighborhoods. Projects #8 and #9 encompass most of this
line. This is primarily an RCP line. It is recommended that this line be televised to verify its
infiltration potential. If active infiltration is discovered, similar to the Minnehaha line, it is further
recommended that this line be considered as a part of the City’s upcoming capital improvement
plan. If televising does not reveal immediate and significant concerns, it is recommended that this
line be monitored on a more frequent basis, either through televising or flow metering, in response
to the infiltration potential this line exhibits. It is important to reiterate the redevelopment growth
and resulting flow increases that the Comprehensive Sanitary Sewer plan anticipates in this area.
Future increases in flow may also dictate pipe size increases in conjunction with future
rehabilitation projects.
Initial televising is also recommended for the trunk sewer immediately downstream of meter #6,
which travels through The Heights neighborhood. Projects #12 through #14 encompass this line.
A similar response of CIP planning or more frequent monitoring, depending on the initial televising
results, is also recommended. Because this is a VCP sewer pipe, it could possibly deteriorate more
rapidly than its RCP counterparts, and therefore presents further reason to monitor this line more
frequently if it is not currently exhibiting immediate and significant concerns.
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The City of Edina currently televises its entire sanitary sewer system on a rotation schedule of
approximately thirteen years. It is recommended that the remainder of the trunk sewer lines
evaluated as a part this study be managed within the City’s normal schedule and maintained and
rehabilitated in response to any concerns that are revealed.
Table 2, below, summarizes the priority recommendations. The recommendations are generally as
follows:
Include in CIP: These sewers have been confirmed via televising that pipe deterioration and
resulting infiltration is present and that they are nearing the end of their service life.
Verify Priority: These sewer rank higher in priority for potential infiltration problems and should
be televised for confirmation.
Regular Televising: These sewers rank lower in priority for potential infiltration problems but
should continue to be a part of the City’s regular sewer televising schedule.
Potential open cut segments are also summarized and correlated to the City’s 5-Year Road
Improvement Plan.
Table 2: Summary of Rehabilitation Projects.
Project
#
Rehab
Length
(ft) Recommendation
Potential
Open
Cut?
Potential
Coordination
w/ Upcoming
Street
Project?
Street
Imp.
Year
1 2115 Include in CIP No No
2 2598 Include in CIP No No
3 2373 Include in CIP No No
4 1727 Include in CIP Yes Yes 2015
5 2142 Include in CIP No No
6 3430 Regular Televising Yes No
7 2800 Regular Televising Yes No
8 2180 Verify Priority Yes Yes 2013
9 2250 Verify Priority Yes Yes 2013
10 2405 Regular Televising Yes Yes 2013
11 1865 Regular Televising Yes No
12 2260 Verify Priority No No
13 2400 Verify Priority Yes No
14 2560 Verify Priority Yes No
15 2500 Regular Televising Yes No
16 2540 Regular Televising No No
17 1640 Regular Televising Yes No
18 2570 Regular Televising Yes No
19 2200 Regular Televising Yes No
20 2480 Regular Televising Yes No
21 2330 Regular Televising Yes Yes 2015
22 3040 Regular Televising No No
APPENDIX
FIGURE 1 .................................................................... SANITARY SERVICE AREA SUMMARY
FIGURE 2 ............................................. ENVIRONMENTAL FEATURES & IMPAIRED WATERS
FIGURE 3 ........................................... DEVELOPMENT & SEWER CONSTRUCTION HISTORY
FIGURE 4 ............................... YEARS OF DEVELOPMENT AND REDEVELOPMENT PROJECTS
FIGURE 5 ................................................................ TRUNK SEWER PIPE DEVEOPMENT AGE
FIGURE 6 ...................................................................... OVERALL INFILTRATION SUMMARY
FIGURE 7 ................................................. OVERALL INFILTRATION PER ACRE SERVICE AREA
FIGURE 8 ................................................................ GROUNDWATER DEPTH ABOVE INVERT
FIGURE 9 .............................................................................. DRY WEATHER PIPE CAPACITY
FIGURE 10 .................................................................................................... PIPE MATERIAL
FIGURE 11 ................................................... SERVICE CONNECTIONS ALONG TRUNK LINES
FIGURE 12 ..............................................................................................................PIPE SIZE
FIGURE 13 ......................................... TRUNK SEWER INFILTRATION ABATEMENT PRIORITY
FIGURE 14 ................................................................... 5-YEAR ROAD IMPROVEMENT PLAN
FIGURE 15 ....................................................................... EXAMPLE OF PROJECT SYNERGIES
FIGURES 16 TO 32 .................................................................................... REHAB PROJECTS