VARIABLE GRADE SEWERS
SPECIAL EVALUATION PROJECT
September 1988
INTRODUCTION
The variable grade sewer (VGS), carrying septic tank effluent, is one type
of alternative conveyance system that has seen limited usage in Region V.
Only five VGS projects have been funded by the USEPA's Construction Grants
Program in the Region, with all five located in the State of Ohio. Because
of the small number of VGS systems being constructed and operated, there has
been little published information available on this subject. This special
evaluation project attempts to alleviate the lack of knowledge about VGS
systems through a presentation of facts and observations gained from project
grant files, visits to the five VGS sites, and discussions with consultants,
municipal officials, and system operators.
The five VGS systems are at various stages of development. Three of them
are currently operating. These are in the communities of Maysville,
Roseville (just started operating recently), and Zanesville. The other two
systems were under construction when visited. The Crooksville system was
20% complete and the Midvale/Barnhil1 project was 90% complete.
BACKGROUND
The VGS system consists of small diameter sewer pipes laid at a constant
depth. This results in variable grades, depending on the contour of the
land. As long as there is a net decrease in elevation from the start to the
end of each line, the wastewater will reach the lower end despite any nega-
tive grade in the system. The concept is similar to that of an inverted
siphon. The portions of the sewer system that are below the hydraulic grade
line will constantly have water in them. This water will be displaced by
flow through the sewers so that once the depressed sections are filled, any
quantity of water put into the system should result in an equal amount leav-
ing the lower end.
A danger with small diameter sewers and especially with negative grades is
the possibility of plugging. This is taken care of with the VGS system in
that only septic tank effluent is transported. The septic tanks eliminate
larger solids and grease that could plug the sewers. Occasional cleaning
should prevent the build up of smaller solids in the sewer pipes. Thus,
the VGS system is essentially a septic tank drainage system with appropriate
wastewater characteristics (low solids, reduced BODs values and anaerobic
conditions).
This system has been looked at for use by communfties because of its cost
savings over other conveyance systems. For instance, the construction of the
VGS at a constant depth allows for the use of a trencher to lay the pipe
which results in a significantly lower cost than conventional sewer systems
which have to be installed with a backhoe. There are also cost savings which
result from the purchase of smaller diameter pipe. The VGS is also potentially
more economical than alternative conveyance systems like the Septic Tank
Effluent Pump (STEP) system because it has none of the expenses which go along
with installing and operating mechanical equipment.
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Despite the cost savings of the VGS system, a public information program
to describe to the residents its advantages may be necessary to gain accept-
ance. In Zanesville, the alternative conveyance system was planned to sewer
older, low-income, unsewered sections of the City. Much of the opposition to
the project came from people who wanted "real sewers", not a small sewer that
will have water flowing uphill or constantly standing in it. The City mini-
mized opposition by informing the residents that they are getting a real sewer
system. The City took the people to another part of the City where they were
shown that small diameter sewers were successfully being used. This pacified
most of the remaining opposition. Even with this education process, approxi-
mately 9% of the customers had to be legally required through the courts to
provide easements.
Early design work on the VGS system has been done by the Rural Housing Re-
search Unit of the U.S. Department of Agriculture - Agriculture Research
Service (USDA) and the Farmers Home Administration (FmHA). The two agencies
worked together on a project in Mt. Andrew, Alabama to develop and demon-
strate the VGS system. This project involved a subdivision of 31 homes.
Each of the homes used a modified septic tank with two compartments. The
first compartment provided settling of larger solids from the wastewater.
The second compartment provided storage for the liquid wastewater. Effluent
from these tanks was conveyed to a lagoon by VGS lines without manholes or
cleanouts. Several sections of negative grade were included. Operation of
this system for several years had shown that it had performed well with
little maintenance required. The modified septic tanks were found to operate
adequately, although they were found to accumulate sludge from the settling
process quickly. This was attributed to abnormal loadings from large fami-
lies and also to the small sludge storage volume available in the first com-
partment of the tank. This necessitated the pumping out of the tanks sooner
than anticipated. With the heavy loading, the modified tanks were found to
produce effluent quality less than what was expected with the two compartment
tank but it was similar to that from a conventional septic tank. The proj-
ect showed that even with septic tank quality effluent, the VGS system was
not adversely affected. Several of the VGS lines were dug up and were shown
to have no heavy solids accumulation.
VGS DESIGN
From the Mt. Andrew project, John Simmons and Jerry Newman of the USDA wrote
"Design Workbook for Small-Diameter, Variable-Grade, Gravity Sewers." This
workbook includes information to aid in designing VGS systems, with an em-
phasis on carefully estimating the wastewater flow rates from each connection
to the system. The sewers must be adequately sized for the required users but
overestimating the flows can result in over-design and higher construction
costs. The workbook indicates that while flows are commonly estimated to be
50-100 gallons/capita/day, studies by the FmHA have shown that, in rural
areas, the average water usage is less than 50 gallons/capita/day.
The workbook recommends basic steps to be used as a foundation in a VGS de-
sign procedure. An elevation profile of the proposed sewer is plotted on a
graph, along with the expected discharge elevation of the septic tanks.
The flow rate at various points in the sewer system is then estimated. The
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workbook recommends using 0.4 gallons per minute (gpm) per residential con-
nection (with additional flow for 10 houses added at the upstream end for
future expansion) for a VGS system with onsite surge storage, and 0.6 gpm
per residential connection (with an extra 10 gpm added on to the total
flow) for a VGS system without onsite surge storage. For systems which
combine VGS lines and STEP units (for effluent from septic tanks that must
be pumped up to the sewer), a careful calculation of the expected flow must
be made.
Next, the pipe sizes for mainlines and service laterals are estimated.
These pipe sizes are used with the flow rate and elevation data along with
the Hazen - Williams formula to calculate the friction head at the design
flow. The friction loss for each section of pipe is calculated and is
added to the elevations of the proposed sewer section to get the elevations
of hydraulic gradient. These initial elevations of hydraulic gradient are
then plotted on the elevation profile. In places where it is necessary to
adjust the hydraulic gradient, such as in situations where septic tank
outlets are near or below the hydraulic gradient and may be subject to
excessive backflow, the pipe sizes and/or the elevation of sewer may be
changed in a trial and error process. Finally, the workbook suggests that
decisions need to be made on the necessity of special equipment, like check
valves, pumps (STEP), air release valves, manholes, and cleanouts.
Important design recommendations made by the workbook include: using on-
site surge storage; installing air vents to prevent air locks; and, mini-
mizing the use of manholes which are potential places for infiltration and
entry of grit.
In three of the five VGS projects in Region V, there was very little nega-
tive grade in the sewer lines. In some cases, the topography and the
shortness of the lines were such that even at a constant depth, the sewers
had positive grades from one end to the other. In other cases, the VGS
systems were intentionally designed to minimize the sections with negative
grade.
In estimating a design flow for sizing the VGS system, the designers used
either 0.5 or 1.0 gpm per residence with an allowance for future expansion.
The use of the larger flow rate per residence includes an allowance for
infiltration in some cases. The design flow rate should be carefully esti-
mated so as not to over-design the system. In some instances, infiltration
is a definite possibility, especially when existing septic tanks or man-
holes are used in the design. The manholes are not only a source of infil-
tration but are more seriously a potential source of debris and grit which
could enter the VGS lines with the water and settle out. Any solids enter-
ing the system with the excess flows at the septic tanks or house connections
should be removed in the septic tank before reaching the VGS lines. Another
significant potential source of infiltration that must be addressed is the
house connections.
Minimum pipe diameters were specified at either 2 or 4 inches. Minimum cover
depths ranged from 42 inches to 54 inches. The cover depths are to ensure
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the VGS lines are below the frost depth. However, when cover depths become
too deep, backhoes must be used instead of trenchers to lay the pipe. This
increases the installation costs. In Canada, insulated mainline sewers
have been laid above the frost line with heat tracers on the pipes. But
even without using the external heat, the pipes have been found not to
freeze.
The replacement of the septic tanks varied from project to project. In
three of the five projects, the decision was made to replace all of the
septic tanks so that there would be fewer worries about the integrity of
the system. One of the other two projects, Maysville, utilized as many
of the existing septic tanks as possible and put in surge tanks for on-
site storage capacity. However, since this system has become operational,
it has been subject to an infiltration problem which may be the result of
bad existing house connections to the septic tanks. In an extension of
the Maysville VGS system that is being designed, 100% of the septic tanks
are to be replaced. In the fifth community, Roseville, the existing
septic tanks were uncovered and inspected to see if they could be used in
the VGS project. After inspection, 18 of 20 tanks were abandoned.
Each of the five designs varied slightly from one another. The following
are some of the design criteria used in each project design.
Crooksvilie
Designer: Finkbeiner, Pettis & Strout, Limited
Service: 1200 residences served by VGS
20 residences served by STEP
Major Components: 1100 precast concrete septic tanks
100 polyethylene septic tanks
49,417 feet of 4" VGS sewers
52,700 feet of 4" service laterals
9,369 feet of 6" VGS sewers
2,744 feet of 8" VGS sewers
11,946 feet of 1-1/2", 2", 6", 10" force main
5,454 feet of 8", 12" conventional sewers
168 manholes
154+ cleanouts
5 air release valves
The Crooksville design of the VGS system utilized the Manning equation to
size the sewer pipes and to calculate the slopes of the lines. The sewers
were designed to minimize the amount of negative grade in the system. A
total of 100 feet of sewer had negative grade. The design flow rates were
estimated by allowing 1.0 gpm per residence. A minimum pipe size was
originally set at 4-inch diameter* SDR 35 PVC was specified to be used
for the mainline sewers (SDR 26 PVC when close to waterlines). In general,
the sewer lines were to have a 4 foot cover depth.
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Manholes were specified to be spaced at a maximum of 750 feet apart to
accommodate sewer cleaning equipment. Cleanouts were to be used every 375
feet.
In the design of the septic tanks, all of the existing tanks were to be
replaced. Residential homes were to receive 1000 gallon, concrete septic
tanks and non-residential users were to have their tanks sized based on
two times the average daily water consumption. While concrete vault type
septic tanks were specified, polyethylene tanks would have been considered.
All tanks 2000 gallons or greater were specified to have two compartments
or have two tanks in series. Also, all septic tanks were designed to have
built-in air traps using "tee" pipes.
Maysvilie
Designer: Design Enterprise, Limited
Service: 767 residences served by VGS
343 residences served by conventional gravity sewers
Major Components: 763 VGS surge tanks
6,172 feet of 1-1/2" VGS service laterals
71,061 feet of 2" VGS pipe
14,512 feet of 3" VGS pipe
2,615 feet of 4" VGS pipe
1,560 feet of 6" VGS pipe
113 - 2" cleanouts
The Maysville VGS design utilized the FmHA method described earlier. It is
one of the systems in Region V with an appreciable amount of sewers with
negative grade. A design flow of 0.5 gpm per residence was used with an
allowance for future growth in the sizing of the sewers. The VGS lines
were specified to be PVC SDR 35 and SDR 26. The plans called for 4.5 feet
cover depth for the VGS mainline. The design was intended to utilize as
many of the existing septic tanks as possible. As a safety measure, surge
tanks were to be installed after the septic tanks. Since most of the
existing septic tanks were behind the houses, much of the VGS lines were
also located in back of the homes. This would result in much on-lot con-
struction activity. The design specified cleanouts to be spaced 300 feet
apart due to the measurements of the sewer cleaning equipment, i.e., a
spinning jet nozzle unit. The VGS lines discharge to pumping stations
which lift the wastewater to a conventional gravity sewer.
Midvale/Barnhill
Designer: W. E. Quicksall & Associates, Inc.
Service: 325 residences served'by VGS
3 residences served by STEP
12 residences served by a duplex pump
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Major Components: Septic tanks - 350 - 1000 gallons
7-1500 gallons
4 - 2000 gallons
1 - 2500 gallons
4 - 3000 gallons
8 - 5000 gallons
26,102 feet of 4" service laterals
18,550 feet of 4" house connections
25,973 feet of 4" VGS sewer
5,782 feet of 6" VGS sewer
3,611 feet of 15" VGS sewer
9,175 feet of 8", 10", 12" sewer pipe
The Midvale/Barnhil 1 VGS system was designed based on the FmHA design ap-
proach. The designer made a concerted effort to minimize the amount of nega-
tive grade. As a result of this, only 200 feet of VGS line, under two river
crossings, had negative slopes. A design flow of 1.0 gpm was used for resi-
dential connections which includes an allowance for infiltration. Flow from
commercial and industrial users was based on water usage. The design used 325
connections plus 10 additional connections for all lines where future expan-
sion is possible. The system was designed for both PVC pipe and vitrified
clay pipe to allow an option of materials in the bidding of the project.
This resulted in different materials quantities, as the friction factors are
different for the two pipe materials. The design criteria specified a minimum
pipe diameter of 4 inches. A minimum ground cover of 4 feet was also required.
Manholes and cleanouts were strategically placed throughout the system for
maintenance purposes. They were provided at major intersections and at inter-
sections where inverts were greater than 2.5 feet. Later in the project, the
contractor asked for and received permission to substitute manholes for the
cleanouts. The design specified the use of 1000 gallon precast concrete sep-
tic tanks as a minimum size. The 4 inch gravity house connections were
specified to have a minimum slope of 1.20%. For some houses, the system had
to be designed for the wastewater to be pumped through the septic tank to a
surge tank with a 70 gallon capacity, which then flows by gravity to the VGS
mainline. Backwater valves were used on service connections where the hydrau-
lic gradient exceeds the top of sewer line and is less than 1 foot below the
elevation of the septic tank outlet.
Roseville
Designer: Design Enterprise, Limited
Service: 20 residences served by 2 small VGS subsystems
Major components: 20 - 1000 gallon septic tanks
2 - 1250 gallon septic tanks
2 - existing septic tank upgrades
2 - surge tanks
1,710 feet of service lateral
851 feet of 4n VGS main
1,320 feet of 6" VGS main
400 feet of 2-1/2" force main
2 - 4" cleanouts
3 - 6" cleanouts
5 - 8" manholes
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The Roseville VGS design utilized the FmHA approach. The estimated design
flow was calculated by allowing 0.5 gpm per residence plus 10 gpm for future
growth. The design criteria required a minimum velocity of 2.5 - 3.5 feet
per second in the pipes when flowing full. Also initially required was a
minimum pipe diameter of 2 inches. Because of plugging problems in the
smaller lines in Maysville, where the same consulting engineering firm was
used, this criteria was modified to require a minimum pipe diameter of 4
inches throughout the system, including service laterals. The mainlines
were specified at a minimum strength equivalent to SDR 26 PVC for pipe
6 inches or less nominal diameter and SDR 21 for larger pipes. A cover
depth of 54 inches was specified for the mainlines. Roseville is the
other system in Region V with a large amount of VGS lines with negative
grade. The design called for septic tanks with a minimum capacity of 1000
gallons. The existing septic tanks would be exposed for inspection by the
homeowner's representatives, who would determine the structural integrity
of tanks. If the septic tank was found to be acceptable for use, it would
be renovated and provided with the necessary appurtenances. A surge tank
would be installed after the existing septic tank. If the tank was not
acceptable, it would be abandoned and a new reinforced concrete, two com-
partment tank would be installed.
Zanesville
Designer: URS Dalton
Service: 308 residences served by VGS
368 residences served by grinder pump
Major Components: 308 high density polyethylene septic tanks
368 grinder pumps
35,115 feet of 2" PVC sewer
21,858 feet of 3" PVC sewer
3,030 feet of 4" PVC sewer
6 - 3" inline cleanouts
2 - 4" inline cleanouts
67 - 2" end of line cleanouts
7 - 3" end of line cleanouts
27 - air release valves
20 - drop connections to existing manholes
3 - new manholes
The Zanesville project is a hybrid system of VGS and grinder pumps. The
service area has a very hilly topography, which, along with the shortness
of the lines (the longest line is 2000 feet) and the location of the
interceptors in the lower elevations, results in^no negative grade. The
design flow rate used 0.5 gpm per residence plus 15 gpm to the lines where
future expansion is possible. Using the FmHA approach, the Zanesville
design utilized, the Hazen-Williams formula to size the mainline sewers.
A 2 inch minimum diameter was specified for the mainline sewer pipes. A
minimum depth of 42 inches was required for the schedule 40 PVC mainline
sewers. The designers compared the hydraulic grade line to the liquid
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level in the septic tanks and adjusted the pipe sizes to maintain a minimum
1 foot difference between these two elevations. If a house could not be
served, even after upsizing the line, a grinder pump was used instead.
Check valves were designed on all service connections to prevent backflows.
Cleanouts were used at the upstream ends of the sewer lines, at changes
in pipe size and at locations where additional flushing was thought to be
necessary. The VGS lines were to tie in to existing or new manholes on
existing collection sewer lines. Odor controls were designed in through
the use of drop pipes in the manholes. Other odor controls included soil
absorption fields at each septic tank and automatic air release valve.
Most of these latter controls were deleted from the project when they were
determined not to be allowable for grant participation. The design of the
system included a minimum 1000 gallon high-density polyethylene septic tank
with a 3/8" minimum wall thickness. Eventually, 1000 gallon, spherical
single-compartment tanks were chosen by the City. These were separately
bid and put into the construction specifications.
CONSTRUCTION
The construction of a VGS system is similar to that of a STEP system which
has been done for a number of years. Both involve the installation of a
septic tank with small diameter plastic pipe laid independent of grade.
The major difference between the two systems is that with the VGS, there is
no installation of a pump and wet well. Thus, the construction techniques
of a VGS system are not completely new.
Before construction starts, the communities must get easements from the resi-
dents for access to their property. In many of the Region V projects, dual
easements were acquired: a construction easement and a perpetual mainte-
nance easement. Zanesville was one of the communities that did this. The
City's easement covered an area 5 feet on either side of the service lateral.
The compensation for the easements varied from project to project. In some
instances, the residents were compensated monetarily. In Crooksville, an
accountant summary report stated that the VGS project would raise property
value substantially. Based on this report, the Village provided no other
compensation to the residents.
A notable observation about the construction of the Region V VGS systems
is that because of the depth that the sewer lines were buried, backhoes had
to be used in most of the projects. Only in Zanesville was a trencher
utilized to install the VGS mainline. The use of a backhoe instead of a
trencher results in higher installation costs. Evidence of this can be
found in the complete in place bid prices for the VGS pipes. For the three
pipe sizes installed in the Zanesville project, the bid prices were 7%-35%
lower than those in any of the other projects. PVC pipe was installed in
all of the projects. The pipe classifications used included mostly sche-
dule 40 and SDR - 35, with some SDR - 26 and SDR - 21.
It is necessary to address potential corrosion problems in the VGS system.
For instance, manholes which VGS lines discharge into are subject to corrosion.
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If existing manholes are used, the concrete and metal appurtenances such as
steps and manhole covers must be regularly inspected for corrosion. For
new manholes, the materials utilized must be carefully chosen. The concrete
can be coated to prevent it from pitting. Stainless steel hardware can be
used instead of galvanized steel, as was done in the RoseviVle project.
There has been no major trouble with the installation of most of the septic
tanks, as four of the five projects used conventional concrete tanks. In
Zanesville, spherical, high - density, polyethylene septic tanks were
installed. Initially, the City installed 300 pound tanks. However, during
installation, two of the tanks collapsed; one was buried deeper than the 5
feet limit and the hydrostatic pressure was too great and the other was
pierced by a sharp rock in the backfill. These were replaced by 500 pound
septic tanks of similar construction which will also be used for future
additions to the system.
The installation of the septic tanks varied widely in the VGS projects.
Some of the projects put the tanks in as close to the houses as possible,
which resulted in minimized homeowners' hook-up costs and maximized grant
participation. In Zanesville, the house connections were paid for by the
City because they wanted to ensure the integrity of the system and because
the project is in a low-income section of the City. Midvale/Barnhill also
is funding hook-ups to avoid homeowner fundability problems and to address
integrity concerns. One of the disadvantages with installing the septic
tank near the home is that it will be difficult for the community to pump
out the tank. As is the case in Zanesville, many lengths of hose are
required to reach the septic tanks and with the way the easements are set
up, with a limited access area around the tank and service laterals, the
pumper truck can not get close enough to the tank in many cases without
driving over people's lawns. At the other end of the septic tank installa-
tion spectrum is Maysville, which installed the tanks as close to the
property line as possible. It is the homeowner's responsibility to extend
the house service down to the tank. In this case, access to the
tanks is easier but a larger financial burden is put on the residents.
A common problem found in the construction of the VGS system is site re-
storation. Even though the communities have reduced the number of claims
by video taping on-lot conditions prior to construction, poor/inexperienced
construction inspection has resulted in unacceptable restoration. There
are also complaints about sites not being fully restored for long periods
of time. The Zanesville project started construction in the summer. When
winter arrived, some of the sites could not be fully restored until the
next year. In Midvale/Barnhill, an unusually dry summer has prevented com-
plete restoration as the contractor could not reseed the on-lot construc-
tion site nor the trenching lines.
At the Zanesville project, it has been found that the on-lot ditch lines
have a tendency to settle or the seed will not take hold. Compaction of
the ditch line backfill may have solved this problem.
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Another problem encountered during construction was the construction-re-
lated inconveniences like dust and street closings. In Crooksville, the
dry weather has elevated the dust problems associated with the construction.
Village officials had threatened to stop the project if something was not
done to control the dust. Water was sprayed on the roads and a street-
sweeper was used to collect the dirt and dust to prevent them from blowing
around further.
As can be seen in Appendix 1, "Bid Prices for VGS Projects," the high unit
cost items are the septic tanks and the surge tanks, where they are in-
stalled. The concrete septic tanks range from $930 - $1650 for a capacity
of 1000 gallons. The high-density polyethylene septic tank with the same
capacity used at Zanesville cost $946. The prices for the surge tanks
range from $590 - $1339 for varying capacities. Other high cost items are
the special appurtenances for the VGS system, such as cleanouts, air release
valves, and backwater valves. An item that may not be thought of right
away when considering costs is the demolition/abandonment of the old septic
tanks. A fairly substantial amount is charged per tank, $200 - $330.
When compared to the engineers' estimates, the bid prices are found to be
higher in some projects, close to the estimate in some, and lower in others.
It should be re-emphasized that there is a significant difference in pipe
price depending on whether the pipe is installed with a trencher or a back-
hoe. This lineal foot cost difference is even more substantial when
multiplied by the thousands of feet of piping required in the projects.
Looking at the bids for the four projects that installed the VGS pipes with
a backhoe reveals a wide range of unit prices for the 4 and 6 inch pipe
sizes which were common to all projects. The 4 inch VGS mainline pipes
varied from $8.17/lineal foot (LF) to $30.10/LF. The 6 inch VGS pipe ranged
from $10/LF to $38.05/LF. An interesting observation of the bid prices is
that for those projects with the higher mainline pipe prices, the prices for
same size pipe when used as service laterals was much cheaper. For example,
in the Roseville project, 4 inch VGS mainline pipe was $27.50/LF, while
4 inch PVC service laterals were $14.05/LF. Also, in Crooksville, the bid
price for 4 inch VGS mainline pipe was $26.25/LF (in Section A of the proj-
ect) and $30.10/LF (in Section B). The price for 4 inch service laterals
was $10.00/LF in Section A and $11.00/LF in Section B. It is unclear how
much of this extra cost is due to installation methods (using a backhoe)
and how much is due to the fact that the VGS mainline pipe bids include an
allowance for working under paved areas, as the bid prices are complete in
place.
OPERATION
The operation of the VGS systems in Region V has"been fairly good. There
have been no major problems with the systems. The minor problems that have
occurred are not specifically related to the variable grade nature of the
system, but are more generic to sjnall diameter conveyance systems.
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A few minor problems have occurred after some of the VGS systems have
started up. The most common problem is one of odors. Because of the na-
ture of the septic tank effluent, any mixing with the air releases gases
with offensive odors; e.g., hydrogen sulfide. In many instances, odor
problems are the result of improper plumbing in houses. Ve'nts are some-
times undersized or non-existant. In other cases, the odors come from
various places in the system where gases can escape, like septic tanks,
surge tanks, manholes, and pump stations. In Zanesville, odor control
devices were designed into the project but were removed when they were
determined to be unallowable for grant participation. As a result, the
odors, had to be dealt with after they became a nuisance to residents as
in the other VGS communities. Solutions to these odor problems have
included: sealing septic and surge tank covers with neoprene, using
downpipes in manholes and pump stations to discharge the effluent below
the water level to prevent air stripping of the sewer gases, using solid
manholes covers instead of vented covers, filtering air that is released
from the system with carbon canisters, and installing traps on service
laterals to prevent odors from backing up from the VGS mainlines.
Another problem is one of solids deposition. Solids have been found in the
VGS mainlines and in the service laterals. It is suspected that the solids
in the mainlines may be construction debris that wound up in the sewers.
In Zanesville, the City has experienced service line plugging 10 times in
1987. City officials indicated that if it could be done over, they would
use 4 inch laterals rather than the 1-1/4 or 2 inch pipes that were used.
In the operations at Maysville, it has been seen that there is some surge
capacity in the septic tanks to equalize flows to a certain extent. Thus,
the use of the surge tanks is not as critical in order for the VGS system
to operate properly. In fact, the surge tanks are quite troublesome. They
are sources of infiltration/inflow, odors, and are susceptible to plugging.
Officials at Maysville indicate that while measures have been taken to seal
the surge tanks to mitigate the aforementioned problems, if they continue
to be a source of trouble, the surge tanks will be bypassed altogether.
Without the safety factor that the surge tanks afford, the estimating of
flows and the sizing of the septic tanks and VGS lines will be that much
more critical. However, the septic tank itself will dampen the surge flows.
Once the systems are operating and the start up problems have been worked
out, a limited amount of maintenance has been needed for the VGS system.
Preventative maintenance generally consists of frequent tank inspections
of those homes with high water usage and those known to dump undesirable
things into the system, despite warnings from the communities. The regular
schedule for pumping out the septic tanks in most of the VGS communities
will be determined after inspections of the tanks. These inspections will
range from semiannually to once every 5 years, ^ost communities anticipate
that pumping will be necessary after 3-5 years of operation. The pumping of
the tanks will be done by the communities themselves, as many have their
own sludge trucks. The Village of Roseville will use the Village of Crooks-
vine's truck at a cost of $40.00/load.
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The regional treatment plant for Roseville and Crooksville will accept
septage in a small aerated lagoon specifically built for septic tank sludge
treatment. The Zanesville plant accepts the septage from both Zanesville
and Maysville at its grit chamber.
Another part of maintaining the system is the cleaning of the VGS lines.
This is done by flushing the sewers with high pressure hoses. A few con-
cerns were expressed by the Zanesville personnel over cleaning service
laterals. Because of the "tee" outlet pipes in the septic tanks, it is
difficult for the hose to make the sharp bend. Sometimes this causes the
pipe connections to be forced apart by the pressure of the cleaning water.
Another concern was that when the hose was able to be inserted that if
pushed in too far, it could become caught on a check valve.
The Zanesville personnel have also indicated that repairing breaks in the
PVC lines can be a problem. It involves a lot of digging to find the
break, as the leak can usually only be located as being somewhere between
two cleanouts. Once the break is found, repairing the wet PVC pipe is
also difficult. The maintenance crew suggests that cleanouts should be
placed closer together to better isolate any portion of the system where
work needs to be done. Ball valves would also aid in isolating parts of
the system.
Other things that should be helpful to the maintenance staffs are metallic
tape-pipe detectors and accurate as-built drawings. The metal tape, which
has been installed in a few of the Region V projects, should make locating
the pipes much easier. This will not only help when pipes need repairing
but it should prevent accidental breakages from other construction work.
The as-built drawings are essential for figuring out what is buried where.
This was especially true in the Roseville project. The operation and main-
tenance crew did not have much involvement in the design or construction of
the system. In other projects, the personnel responsible for operating and.
maintaining the system may not be hired until the project is well under way.
SUMMARY
All five of the VGS systems were funded as an innovative technology under
the Innovative/ Alternative (I/A) Program, which was established to improve
wastewater treatment technology. An innovative technology is one that is
not fully proven for its proposed application and offers a significant
advancement over the state-of-the-art. Some of the Region V projects are
mainly positive, variable grade sewers which could be more aptly named small
diameter gravity sewers (except for the fact that- the latter sewers have a
specified minimum grade) because of the lack of negative slope. As such,
the use of the constant depth sewers without much negative grade does not
represent a significant advancement over the state-of-the-art. On the whole,
these systems do not adequately demonstrate a variable grade sewer with
significant amounts of positive and negative grades as the risk associated
with standing water and water flowing uphill were eliminated.
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It is evident from the examination of the VGS projects that these systems
were at a disadvantage in that there was lack of experience with the VGS.
Operation of these systems has led to solutions to problems encountered and
information to be used to improve future systems. Key items- that need to
be addressed are in the areas of project development, design, construction,
and operation.
Project development - The community's residents must be informed early on
in the planning stage. They must be informed that the VGS system is a
"real sewer" despite the fact that it uses small diameter plastic pipes and
has standing water and water flowing uphill. Resident support for the VGS
project will make it easier to acquire easements and could possibly head
off some unreasonable complaints about the system from uninformed people.
Design - (1) Surge tanks are costly and a potential source of problems,
i.e., odors and infiltration. With the proper sizing of the septic tanks
and VGS lines (a critical item), the surge tanks are not necessary for
successful operation. (2) In the sizing of the VGS lines, the cost savings
from the reduction in pipe sizes must be carefully balanced with the in-
creased risk of plugging of the lines. Four inch diameter pipe for service
lines and mains should be the minimum size specifed. (3) Odor controls
must be considered in the design. All potential sources and problem areas
must be looked at, e.g., house vents, septic tank covers, manholes, and
pump stations. (4) The burial depth of the VGS lines must be examined
carefully. Shallower depths would allow for easier, less costly installa-
tion and may justify insulating the sewers. (5) The corrosive nature of
septic tank effluent must be kept in mind when specifying materials for the
entire conveyance system, like the metal hardware in pump stations and the
possibility of coating manhole walls.
Construction - (1) Site restoration problems can be minimized by video
taping on-lot conditions prior to and after construction. The contractors
should be required to restore sites as soon as possible. (2) Rigorous
testing of building connections should be made prior to hookup, to ensure
the integrity of the system. In projects where septic tanks are re-
placed, new house connections should also be considered. Manholes, which
are sources for infiltration/inflow, should be replaced by cleanouts.
(3) The location of the parts of the system needs to be clearly identified
for the benefit of the operation and maintenance personnel. For example,
the septic tanks should be located for easy access by the maintenance crew
and pump truck and should be easily found. The installation of metallic
pipe detection tape should be included as part of the project and accurate
as-built drawings must be obtained from the consulting engineer.
Operations - A regular maintenance program needs^-to be developed and imple-
mented. It must include a strategy/schedule for pumping out septic tanks
and cleaning sewer lines and other appurtenances.
Three of the five VGS projects in'Region V only had minimal amounts of nega-
tive grade. The surging that results from the negative grades in a variable
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grade sewer system has not had an appreciable test. This is probably
the main factor that distinguishes the VGS from other small diameter grav-
ity sewers. Only one of the two projects with substantial amounts of
negative grade, Maysville, has been operating for any length" of time.
There do not appear to be any problems resulting from the negative
grades. Also, the lack of scouring velocity, which has been a concern in
other sewer system designs, has not been a problem in the VGS system. The
septic tanks do a good enough job of settling solids that when combined
with regular sewer flushing, solids deposition in the mainlines is mini-
mal in the positive grade sections of the system.
This report was prepared by
Russell Martin, Thomas Poy and Charles Pycha
Environmental Engineers
Technical Support Section
Municipal Facilities Branch
U.S. Environmental Protection Agency
230 S. Dearborn Street - 5WFT-TUB-9
Chicago, IL 60604
(312) 353-2144
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APPENDIX 1 - Bid Prices for VGS Projects
Crooksville
Contractors: Winze!er Excavating Company
Motion Electric
4" service connection
4" sewer
6" sewer
8" sewer
septic tank-1000 gal
2000 gal
3000 gal
4000 gal
cleanouts
$
Engineer's
Estimate
16.90/LF
19.50/LF
23.40/LF
60/LF
00 ea
1290.00 ea
1990.00 ea
2680.00 ea
75.00/LF
28.
715.
Bid Prices
Section A Section B
$
10.00/LF
26.65/LF
33.90/LF
33.40/LF
1267.00 ea
2215.00 ea
2567.00 ea
3691.00 ea
76.00 ea
$
11.00/LF
30.10/LF
38.05/LF
32.75/LF
1257.00 ea
2215.00 ea
2567.00 ea
3750.00 ea
76.00/LF
Maysville
Contractors: Best Way Mechanical Contracting Co.
Parsons
2" VGS pipe
3" VGS pipe
4" VGS pipe
6" VGS pipe
2"
surge tank -
Engineer's
Estimate
$
1-1/2 service lateral
6.00/LF
8.00/LF
9.00/LF
11.00/LF
125.00 ea
475.00 ea
900.00 ea
5.00/LF
Bid Prices
Division Bl Division Cl
$ 5.00/LF
8.16/LF
8.67/LF
10.00/LF
200.00 ea
590.00 ea
1339.00 ea
6.50/LF
$
5.00/LF
7.66/LF
8.17/LF
200.00 ea
590.00 ea
1339.00 ea
6.00/LF
Division C2
$ 6.00/LF
8.66/LF
200.00 ea
590.00 ea
1339.00 ea
7.00/LF
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Midvale/Barnhill
Contractor: Willard Improvements Co.
4" service lateral
4" house lateral
4" sewer
6" sewer
8" sewer
10" sewer
12" sewer
15" sewer
septic tank - 1000 gal
1500 gal
2000 gal
2500 gal
3000 gal
5000 gal
Manhole 0-6 feet deep
6 feet - 10 feet deep
greater than 10 feet deep
cleanouts
surge tank
air release valve
backwater valve
abandon old septic tank
all sizes
Bid Prices
$
12.00/LF
12.00/LF
15.00/LF
17.00/LF
20.00/LF
23.00/LF
33.00/LF
32.00/LF
1650.00 ea
1800.00 ea
3100.00 ea
4100.00 ea
4100.00 ea
6100.00 ea
800.00 ea
1100.00 ea
1600.00 ea
950.00 ea
800.00 ea
1500.00 ea
700.00 ea
200.00 ea
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Roseville
Contractor: Best Way Mechanical Contracting Co.
Bid Prices
4" service lateral $
4" VGS main
6" VGS main
4" cleanout
6" cleanout
8" cleanout
septic tank - 1000 gal
1250 gal
surge tank
clean existing septic tank
abandon old septic tank
Zanesville
Contractor: Best Way Mechanical Contracting Co.
septic tank CIP
2" PVC UP
2" PVC CIP
3" PVC UP
3" PVC CIP
4" ABS house lateral
4" PVC UP
4" PVC CIP
1-1/4 service lateral UP
1-1/4 service lateral CIP
2" PVC service lateral UP
2" PVC service lateral CIP
cleanouts - inline 3"
4"
end of line 2"
3"
automatic air release valve
septic tank demolition
less than 250 gal
250 - 750 gal
greater than 750 gal
Engineer's
Estimate
$1067.22 ea
15.45/LF
8.70/LF
16.30/LF
9.50/LF
11.10/LF
16.80/LF
10.25/LF
13.60/LF
7.20/LF
13.25/LF
6.60/LF
226.00 ea
264.80 ea
192.95 ea
226.00 ea
1030.85 ea
110.25 ea
137.80 ea
165.40 ea
14.50/LF
27.50/LF
29.00/LF
162.00 ea
203.00 ea
1200.00 ea
930.00 ea
1000.00 ea
700.00 ea
140.00 ea
400.00 ea
Bid Prices
946.00 ea
11.00/LF
4.66/LF
11.33/LF
4.99/LF
16.00/LF
11.76/LF
5.42/LF
11.00/LF
4.78/LF
22.00/LF
4.16/LF
224.50 ea
230.00 ea
175.00 ea
158.75 ea
922.00 ea
233.00 ea
260.00 ea
330.00 ea
UP - under pavement
CIP - complete in place
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