Embed Size (px)
DESCRIPTION
Sewer redesign
Citation preview
UNIVERSITY OF GUYANA
FACULTY OF TECHNOLOGY
DEPARTMENT OF CIVIL ENGINEERING
CIV 413
Environmental Engineering
Project Title:
Evaluation & Redesign of University of Guyana Sanitary Sewer System
Lecturer: Mr. M. Jackson
Date: December 03, 2010
i
Table of ContentsGroup Members......................................................................................................................................... iv
1.0 Abstract...........................................................................................................................................1
2.0 Introduction.....................................................................................................................................2
3.0 Background......................................................................................................................................4
4.0 Statement of Problem.....................................................................................................................6
5.0 Objectives........................................................................................................................................6
6.0 Scope and Limitations......................................................................................................................7
7.0 Assumptions....................................................................................................................................7
8.0 Literature Review............................................................................................................................8
8.1 Design Period...............................................................................................................................9
8.2 Contributing Area........................................................................................................................9
8.3 Determination of Design Flows....................................................................................................9
8.4 Minimum Velocity.......................................................................................................................9
8.5 Types of Flow.............................................................................................................................10
8.6 Design Criteria...........................................................................................................................10
8.7 Calculation of Pipe Size..............................................................................................................10
8.8 Manning’s Roughness Coefficient "n"........................................................................................11
8.9 Minimum Slope..........................................................................................................................11
9.0 Methodology.................................................................................................................................12
9.1 Investigation Phase....................................................................................................................12
9.2 Design Phase..............................................................................................................................12
10.0 Design Criteria...............................................................................................................................14
11.0 Sanitary Sewer Flow Calculation....................................................................................................15
11.1 Calculation of Pipe Size..............................................................................................................16
11.2 Modelling.....................................................................................................................................17
12.0 Preamble to Bill of Quantity..............................................................................................................18
12.1 General........................................................................................................................................18
12.2 Quantities....................................................................................................................................19
12.3 Materials......................................................................................................................................19
ii
12.4 Prices and Currency.....................................................................................................................19
12.5 Rights of Employer.......................................................................................................................21
12.6 Site Access and Storage...............................................................................................................22
12.7 Site Installation............................................................................................................................22
12.8 Duration.......................................................................................................................................22
13.0 Priced Bill of Quantity........................................................................................................................23
14.0 Recommendations.........................................................................................................................24
15.0 Conclusion.....................................................................................................................................25
16.0 References.....................................................................................................................................26
17.0 Appendices....................................................................................................................................27
iii
Group Members
BACCHUS, Keron 08/0933/1041
BROWN, Oliver 08/0933/1049
GAFOOR, Safiya 08/0933/1050
PEARSON, Carissa 08/0933/1068
PRASHAD, Devi 08/0933/1072
SINGH, Kalvika 08/0933/1084
WALTERS, Sekou 08/0933/1088
iv
1.0 Abstract
This report summarizes the findings for the redesign of the University of Guyana sewer
system using the SEWER AND DRAINAGE FACILITIES DESIGN MANUAL, Council Adoption
September 2006, and Revised June 2007 as well as the Bureau of Engineering Manual - Part
F. This project was executed by Civil Engineering students of CIV 413 (2010) on instruction
by Mr. Maxwell Jackson (H.O.D Civil Engineering: Faculty of Technology).
The objective of this study is to redesign the University of Guyana sanitary sewer system
which serves a land area of eighty (80) acres and an estimated population of six thousand
(6,000) inclusive of staff and students. The existing system comprises of minor four 4”
diameter P.V.C pipes and one 12” inch diameter P.V.C pipe which serves as the main
collector from the wet well to the treatment plant for disposal.
The minor sanitary sewers which are connected to the tributary buildings serve sixty six
(66) manholes which then flow to the major sewer which has a total length of 1,846 feet.
The design will utilize manning’s equation for flow along with a recommended minimum
discharge of 3 ft3/sec for an efficient system.
1
2.0 Introduction
Wastewater is a broad descriptive term for liquids and waterborne solids originating from
domestic, commercial and industrial activities as well water that has been contaminated by
the activities of humans and whose quality have been degraded. Wastewater is usually
discharged to a sewerage system. The term “sewage” has been used to describe wastewater
containing only sanitary waste but it technically denotes any wastewater that passes
through a sewer1.
Sewage or wastewater disposal comprises of several processes for the collection, treatment
and sanitary disposal of wastewater from households and industrial plants. A sanitary
sewer is defined as a conduit, which is designed for wastewater discharges from domestic,
commercial and industrial institutions. A system of sewers is generally called a sewerage
system.
The composition of wastewater is analyzed using several physical, chemical and biological
measurements. The most common analyses include the measurements of solids,
biochemical oxygen demand (BOD), chemical oxygen demand (COD) and pH. The solid
wastes include dissolved and suspended solids. Dissolved solids are the materials that will
pass through filter paper while suspended solids are those that do not. Suspended solids
are further divided into settleable and non settleable solids, depending on the quantity of
solids that will settle out of 1 liter of wastewater in 1 hour. All these classes of solids can be
divided into volatile or fixed solids, volatile solids generally being organic materials and the
fixed solids being inorganic materials or mineral matter.
The concentration of organic matter is measured by the BOD and the COD analyses. The
BOD is the amount of oxygen used over a five day period by microorganisms as they
decompose the organic matter in sewage at a temperature of 20°C. Similarly, the COD is the
1 “Environmental Engineering” Merrit, S. Frederick, Lofting, M. Ken and Ricketts, Jonathan T. Standard Handbook for Civil Engineers, 4th Edition, New York: Mc Graw Hill Book Company,1996
2
amount of oxygen required to oxidize the organic matter by use of dichromate in an acid
solution and to convert it to carbon dioxide and water. The value of COD is always higher
than that of BOD because many organic substances can be oxidized chemically but cannot
oxidize biologically. Commonly, BOD is used to test the strength of treated and untreated
municipal and biodegradable industrial wastewaters. COD is used to test the strength of
wastewater that is either not biodegradable or contains compounds that inhibit activities
of microorganisms.
Sewer systems are classified as:
1. Sanitary Sewer system - is comprised exclusively of sewers which convey liquid
wastes from residences, commercial buildings, industrial plants and institutions;
2. Storm Sewer system - conveys storm water runoff from buildings, streets and other
surfaces but excludes domestic, commercial and industrial wastewater. Storm
water runoff is that portion of precipitation that flows over these types of surfaces
during and after a storm;
3. Combined Sewer system - is comprised of a network of sewers that collect and
convey both sanitary and storm water runoff.
3
3.0 Background
The sewerage system of the University of Guyana was laid down in 1969 shortly before the
campus was opened and consists of approximately 66 manholes within a network of
gravity pipes. Each manhole is approximately 2ft wide × 2ft long × 2ft–9 in. deep. These
manholes are strategically located at points:
1. Where there is a significant change of direction or grade;
2. To allow access to the sewer at strategic locations to facilitate maintenance,
inspection and cleaning.
The population it served in October 1969 was approximately 164 students and staff2.
Today, 41 years later the buildings on the campus increased have to 25 and the students
and staff population increased to over 6000 persons. 3
The existing sewerage system consist of a network of pitch fibre and PVC gravity sewer
pipes draining to Du-O-Jet sewage ejectors. The pitch fibre and PVC pipes are mainly of
4”diameter. The sewage ejectors operate by pneumatically ejecting the collected
wastewater from the university complex a distance of approximately 1846ft via a 12”
diameter discharge PVC pipeline to a model V treatment plant that is no longer functional.4
This plant was previously responsible for treating the sewage by utilizing a process called
the activated sludge process, after which its effluent is discharged into a nearby drainage
trench.
The Smith & Loveless lift station consist of Du-O-Jet ejectors located just north of UG’s
library and consist of three compartments within a cylindrical steel chamber. The top
compartment accessible from ground level houses the ejector, controls and compressor.
The middle section is a combination of air- storage tanks and chamber for the valves and
manifold. The bottom compartment is the sewage receiver. The lift station receives the
2 University of Guyana Website3 Office of the Assistant Registrar4 Smith & Loveless Inc.
4
sewage from the sewer lines through the inlet gate valve, thru the inlet check valve and into
the sewage receiver. When the sewage fills the receiver an electrical circuit is completed
from the electrode, through the liquid to the ground at the receiver walls, energizing the DC
relay which activates the three way air valves, through a hallow electrode air pipe, into the
sewage receiver. The pressure forces the sewage up the inlet pipe, through the discharge
check valve and gate valve into the force main, which discharges the sewage through a
750ft, 12” PVC pipelines to the treatment plant. This pipe is buried at a grade of 1 in 200
and there is 1ft of compacted sand fill under the pipe with a 2inch thick concrete slab above
it. Three liquid level displacement switches in the wet well controls the pumping cycle.
With a rising wet well, the low lever “ON” displacement switch is tilted and the base pump
starts. If the wet well level continue to rise, the high level “ON” displacement switch setting
and the low level “OFF” displacement switch shut off both pumps. Every eight (8) hours the
pumps are alternated so that the standby pump becomes the base pump.
In Guyana there are only two sewage treatment plants utilizing the activated sludge
process; the model V treatment plant being used by the University of Guyana, which was
acquired in the mid- 70’s, at value recorded by the Bursary as twenty three million Guyana
dollars (G$23,000,000). The treatment plant was manufactured by SMITH & LOVELESS,
Inc., based in Lenexa, Kansas. This treatment plant was factory built and utilizes a
rectangular aeration tank with two truncated pyramid shaped clarifiers. The other is the
Tucville Sewage Treatment Plant, which was designed by Loius Berger Inc., in association
with local consultants, Aubrey Barker Associates to treat wastewater by extended aeration,
activated sludge process. However, due to lack of proper maintenance and unavailability of
spares and replacement parts, the works has ceased to function as intended.
5
4.0 Statement of Problem
The University of Guyana sewerage system was designed for a population of approximately
1500 persons in 1969, as only 10 buildings were existent at the time. Today, forty one
years later, the number of buildings on the campus has increased to 25 and the student and
staff population increased to over 6,000 persons. The sewage lines leading from some of
these new buildings were connected to the existing University sewerage system while for
others, there are septic tanks constructed to dispose their sewage. Due to the increase in
population and buildings at the University of Guyana, there is an increased hydraulic load
on the sewers and hence, to cater for this scenario there is a need to evaluate the existing
capacity and design an adequate sewerage system based on the existing population and the
population growth for the next 25 years.
5.0 Objectives
1. To evaluate the adequacy of the current sewer system in providing for the needs of
the current population as well as its ability to serve future increases in population.
2. If it is established that the existing system is inadequate; a redesign of the system
will be undertaken.
6
6.0 Scope and Limitations
1. This project is confined to the University of Guyana Sewer System and focuses on
analyzing the current system and determining its capability to support the current
and future population as well as the redesign of the sewerage pipe works at
University of Guyana.
2. The pumps at the lift station would not be sized.
3. This project does not entail the design and checks for the treatment plant.
4. Design does not include branched sewers for new nodes in the sewerage system.
7.0 Assumptions
1. All exiting pipes are four inches (4”) in diameter.
2. All manholes are fully functioning.
3. For ideal conditions the discharge would be 3ft3/sec.
4. A manning’s “n” of 0.014 (for P.V.C pipes) will be used.
5. No intercepting flows.
7
8.0 Literature Review
Bradford (2005) has outlined the design procedure for sanitary sewer design. The
suggested procedure consists of:
1. Determining the design period;
2. Identifying the contributing area;
3. Estimating the sanitary sewage flow rates;
4. Carrying out the hydraulic design and
5. Calculating the pipe sizes.
The table below explains the activities involved in each stage of the sanitary sewer design.
Table 1 - Design stages for a sanitary sewerage system
Design Stage Activities Involved
Design Period A suitable design period and the population
growth rate must be selected. The water usage
rate must also be determined.
Contributing Area The boundaries of the network must be defined
and the population within the area determined.
The unit water usage must also be determined.
Flow Rates The sanitary sewage flow and peak flow rates
must be determined.
Hydraulic Design The hydraulic constraints must be identified.
These include: pipe roughness, velocities, depths.
Pipe Sizing Sizes, gradients and depth must be determined.
8
8.1 Design PeriodThe design period is that length of time over which the capacity of the sewerage facility is
anticipated to be adequate to service its contributing area. It must be determined before
design of the facility commences. A standard for minimum design periods for various
components of a sewer system is provided by the Bureau of Engineering (n.d.) and states
that for lateral sewers - sewers less than 18-inch in diameter, the minimum design period
is 100 years.
8.2 Tributary AreaThe tributary area of a sewer includes all areas which will contribute flow to the system.
Potential service areas, such as, areas served by septic tanks should also be assessed for
possible inclusion in the contributing area. The area may be limited by natural topography,
natural or human-made barriers, political boundaries or economic factors.
8.3 Determination of Design FlowsThe design of sanitary sewers must consider minimum, average, and peak flows. Normally,
the average flow is determined or selected, and a factor is applied to determine the peak
flow. The Peak flow is the design flow used to select the pipe size. Minimum flows are used
to determine if specified velocities can be maintained to prevent deposition of solids. The
Bureau of Engineering (n.d.) states that the ratio of peak flow to average flow will range
from less than 130% for some large sanitary sewers to more that 260% for smaller sewers.
Additionally, the ratio of the peak flow at the end of the design period to the minimum flow
at the beginning of the design period may range from less than 3:1 to more than 20:1,
depending on the rate of growth of the contributing area served.
8.4 Minimum VelocityAccording to the Bureau of Engineering (n.d.) gravity sewers shall be designed for a
minimum velocity of three (3) fps using the peak flow that exists at the time the pipe is
placed into service. Approval must be obtained when using slower design velocities. This
minimum velocity is necessary to prevent deposition of solids in the sewer pipe.
9
8.5 Types of FlowThe flow of wastewater in sewers may be open channel or pressure flow. When flow fills
the conduit and the Hydraulic Grade Line (HGL) rises above the sewer crown, the flow is
classified as pressure flow. When the conduit is partially full and the HGL is below the
sewer crown and a free water surface develops in the sewer, the flow is classified as an
open channel flow. Open channel flow will be the basis for general hydraulic design of
sanitary sewers.
8.6 Design CriteriaThe criteria for design of sewer pipe includes:
1. Type/size sewer line;
2. Design period;
3. Design depth of flow; and
4. Peak flow.
According to the Bureau of Engineering (n.d.) sewers shall be sized so the depth of the
peak flow, projected for the design period, shall be no more than one half the pipe
diameter: d/D = 0.5
Where: d = depth of flow and D = Pipe diameter
8.7 Calculation of Pipe SizeThe required pipe size may be calculated using Manning's formula:
Q= k nnA R2/3S1 /2
Where:
Q = volume flow (ft3/s, m3/s)
kn = 1.486 for English units and kn = 1.0 for SI units
A = cross sectional area of flow (ft2, m2)
n = Manning coefficient of roughness
R = hydraulic radius (ft, m)
and R = A / P (where: A = cross sectional area of flow (ft2) and P = wetted perimeter (ft))
S = slope of pipe (ft/ft, m/m)
10
8.8 Manning’s Roughness Coefficient "n"A Manning's roughness coefficient of "n" = 0.014 shall be used for sizing gravity sewers.
This Manning's roughness coefficient shall be used regardless of the type of pipe specified.
8.9 Minimum SlopeGravity sewers shall be designed for a minimum velocity of three (3) fps using the peak
flow that exists at the time the pipe is placed into service.
11
9.0 Methodology
This research was conducted in two phases: the investigation phase and the design phase.
Theoretical and practical work was conducted for both phases and the general outline of
the methodology adapted is outlined below:
9.1 Investigation PhaseThe investigation phase covered the analysis of the existing system to determine the
necessity for a new sewerage system and the parameters that are required for the design of
the system. Implementation considerations were also made so as to establish exactly how
and where the system would be installed. The steps were as follows:
1. The need for a new sewerage system at the University of Guyana was reviewed. This
was done by reviewing previous investigations that were done on the sewage
disposal system of the University of Guyana as well as the existing system.
2. The parameters that are required for the analysis and design of the sewage network
were investigated.
3. Plans for the University of Guyana were obtained and site visits were carried out to
examine the general terrain of the area and to make suitable corrections on the
sewage layout plan. Also this visit was used as an opportunity to inspect the existing
system.
4. A site reconnaissance also allowed the location of possible expansion routes for the
sewerage system. Other important features such as the drainage outlets, surface
hydrology and land distribution were also noted.
9.2 Design PhaseThe design phase for the sewer system included the following:
1. The topography of the general area to be served, its slope and terrain was
determined by using previous plans of the University and consulting previous
works.
2. The population size and distribution size for each building was determined.
12
3. Based on past and existing campus population data, the present population growth
was determined.
4. The required flow was determined for each building and was done by establishing
the effluent volume production for each area. The required flow in the sewer is the
maximum flow resulting from the collection of sewage at any point in a system. The
average, peak, and minimum flow must be considered in design. The average flow is
estimated by considering future population, water consumption and the relevant
standards.
5. The design flow of pipes was determined based on the population of each section
and the volume of effluent that is expected to pass through the pipes.
6. Infiltration and extraneous flow also contribute to flow volume. Peak and minimum
flows are determined by applying factors to the average flow. These factors are
generally based on local experience and codes. Peak flow is used to select pipe size
and minimum velocity, taking into consideration peaking factors as well as factor of
safety. A minimum self cleansing velocity of 0.75m/s was considered in the design of
sewers.
7. The hydraulic flow through the sewer system was carried out using the Manning’s
hydraulic flow equations. The equations were used to design sewers to transport
the waste water.
8. From the calculations carried out for the peak flow, and consideration of the
minimum self cleansing velocity and maximum flow of the sewer, the pipe size was
determined, considering also the roughness coefficient and the slope of the pipes.
13
10.0 Design Criteria
The design criteria adopted for the sanitary sewer design are those acceptable to the
relevant standards. These criteria used to estimate the design flows which will in turn be
utilized in the design of the sewer system are:
i. Tributary areas
Estimate of population
Land use
Per capita flow
ii. Institutional
Major point source discharge
Ground water
Infiltration and Inflow
The Tributary area of a sewer shall include all areas that will contribute flow to the sewer
system inclusive of flows from the developed area to the point of connection to main
discharge line.
The Estimate of population shall be for the proposed development and shall be as accurate
as possible. The estimate should be projected to the end of the design life of the sewer
system.
Land use contributes to and defines the density of population and the type of users
contributing to the flow within the tributary area. To verify that the projection is
reasonable, field review may be used.
14
11.0 Sanitary Sewer Flow Calculation
Q=(Qavg ) PF+ IA equation (1.1)
Where:
Q = Sanitary Flow
Qavg. = Average Sanitary Flow = 0.002 cfs/capita
P = Population of Tributary Area based on design density
PF = Peak Factor = 3.5
I = Infiltration allowance = 0.003 cfs/acre
A = Tributary Area
The University of Guyana occupies a total area of 1,450 acres of which only 80 acres will be
considered in the design of the sanitary sewer. The additional 1,370 acres is not being
considered since area is undeveloped and covered with natural vegetation. The current
population of the University of Guyana Campus is approximately 6,000 inclusive of
students and staff.
Applying the conditions outlined above in equation (1.1)
Q= (0.0002cfs/c×6000c )3.5+0.003 cfs/acre×80 acres
Sanitary flow=4.44cfs
Q=0.13cumec
Minimum Velocity to design for is 2ft/sec.
15
11.1 Calculation of Pipe SizeAfter the design criteria have been determined the required pipe size may be calculated
using
Manning's formula.
Q=1.486n
A R2/3S1 /2 equation (1.2)
Where:
Q = Flow, cfs
A = Area of flow, ft2
R = Hydraulic radius (A/P), ft
n = Roughness factor
Rearranging equation 1.2 to solve for diameter of pipe “D”
D = 1.3346 Q 0.375 n 0.375
S 0.1875
Where:
D = Conduit inside diameter, ft
Q = Volumetric flow rate, cfs
n = Manning’s roughness coefficient
S = Friction slope, ft/ft (minimum slope for pipe is approx. 0.0036 ft/ft)
The manning “n” used in this design will be taken as 0.014 (P.V.C) since P.V.C pipes will be
used through this design.
D = 1.3346 x4.44 0.375 x0.014 0.375
0.00360.01875
D = 0.52ft (6 inches) (150mm)
Diameter of pipe = 6 inches.
Maximum depth of flow “d” = 2/3D (for 10 inch and smaller)
d = 4 inches
Current diameter of pipe in operation is four inches. (P.V.C)
16
11.2 Modelling
Modeling of the sewer system is required when proposed development intensifies. The
land use from the existing development on the site to the proposed development requires
the general plan to be amended to cater for the increased usage. The following three
scenarios must be modeled:
1. Existing Condition – to identify existing deficiencies in the system
2. Existing Condition with Proposed Development – to identify additional
deficiencies created by the proposed development
3. General Plan Build Out Condition – to identify the ultimate pipe size for
improvements
17
12.0 Preamble to Bill of Quantity
12.1 General
The nature of this contract is measured unit price contract and the Bill of Quantity (BOQ)
shall reflect this fact.
BOQ shall be read and construed in conjunction with other Contract Documents. General
directions and description of work and material given in the Technical Specification are not
necessarily repeated in the Bill of Quantities. The Technical Specification forms an integral
part of the Bill of Quantities. The Tenderer is obliged to check the number of the pages of
the Bill of Quantity and should any be found missing or duplicated or the figures or writing
indistinct, the Tenderer must notify the Employer/Engineer at once and have the matter
rectified before the Tender is submitted. No liability whatsoever will be accepted in respect
of any claim for errors in the Tenderer’s offer resulting from failure to comply with the
fore-going.
The Tenderer is deemed to have visited the site/s and fully acquainted himself as to the
location of each of the items and works to be carried out and to all conditions which may
affect the performance of the works, including but not limited to:
Access to each of the roads where demolishing and removal process will be carried
out, and Access for the storing dump site and crushing site.
Affected buildings’ conditions.
All safety regulations and employer site safety procedures.
All Guyanese regulations.
The Tenderer is also deemed to have surveyed the actual condition of the site and buildings
and made his own assessment of the type and extent of the works prior to submitting his
offer.
18
12.2 Quantities
Even though that practical care was exercised in preparing the BOQ, but all quantities given
herein shall be deemed to be estimated quantities of the work to be done but they are not
to be taken as actual and correct quantities of the work to be executed and they are not to
absolve the contractor of his obligations under the Contract. They are not to be taken as
guarantee that the actual quantities increase or decrease, and any claim whatsoever
submitted for cost or extra expenses incurred from such increase or decrease will not be
accepted by Employer/Engineer except where else stipulated in the Contract.
12.3 Materials
All materials used are to be of the best new available and subject to the Employer/Engineer
approval, and of durable nature, guaranteed, not liable to any base exchange and
manufactured according to applicable BS or ASTM Standards. Execution also is subject to
approval of Employer/Engineer and shall be the best available common practice in
engineering codes at the time of execution.
Items that contain materials or products of special make with names of manufacturers are
to be taken as samples of what will be required. Subject to the Employer/Engineer
approval, the Contractor may, at his discretion, offer similar products of other make if the
equivalent quality of the specified materials is guaranteed. In this case, the Contractor shall
submit a description and/or drawings showing all technical conditions, characteristics,
make, type and address of Manufacturer, etc., of the materials offered as alternatives.
12.4 Prices and Currency
The prices given, by the Contract, hereunder in the BOQ shall be in Guyana Dollars and
shall not be exchangeable with other foreign currencies. Furthermore inflation and
escalation or changes whatsoever shall not be subject of claim later on.
19
The Unit Prices entered against the various items in the following Bill of Quantities include
all operations for execution, completion and maintenance of the various items of the works
finished completely in every respect till the final acceptance as specified or described in the
Tender Documents, with or without modifications, either by way of additions or
deductions, or alterations as may be offered in writing during the progress of the works,
and include, without being limited to, all matters and things particularly referred to in the
Tender Documents.
The Unit Price shall cover all costs of every kind whatsoever including, without being
limited to, all charges for additional site installations, relocation, supervision, labor,
transportation and supply of materials; the provision, maintenance, use and efficient repair
of all plant, equipment and appliance of every kind, the construction and maintenance of all
temporary works, the performance of all services and the fulfillment of all obligations and
responsibilities herein defined.
The Tenderer shall be deemed to have fully considered all the conditions, obligations, and
requirements of the Tender Documents before entering the respective unit price against
the various items of the Bill of Quantities.
The Unit Prices given hereunder the BOQ shall also include erection, installation, fixing, and
re-fixing of all elements. These prices shall also include taxes, accommodations for the
Contractor’s staff and labors, all required insurance and work permits, guarantees, bonds,
traffic plan requirements, safety procedures, etc. and all requirements necessary to have
the work maintained until its final handing over.
The Unit Prices given hereunder in the Bill of Quantity for this work shall also include
overheads, risks, profit etc. and all other financial matters to have all these civil works
completed.
The works, materials or activities listed in the following shall always be considered as
Supportive works to be included in the Unit Prices bid for any item in the Bill of Quantities:
Any measurement for execution and payment of the works, including the provision
of measuring instruments, gauges, setting out marks, marking paint and relevant
tools, labor, etc., the maintenance and preservation of gauges and setting-out marks
during the execution of the works.
20
Provision of small tackle tools or any other equipment required for the execution of
the works.
Supply of consumable materials for the Contractor’s equipment.
Removal of all contamination (refuse, debris, building rubbish and the like) arising
from or in connection with the Contractor’s work.
Protection of the executed works and of the items made available for execution of
the works from damage, fire, inclement weather, vandalism and theft etc., to the
time of final acceptance.
Transportation of all materials and structural components from the storage places
on site to the points of use and return transportation, if required.
Submitting and transporting any samples required.
Carrying out tests on materials and works, etc., that is required by the Engineer.
Fuel and lubricants for operation of Contractor’s equipment.
All safety precautions and measures for safeguarding labor as well as securing
surrounding areas.
Lighting of the work site.
Maintenance or repair damaged infrastructure resulted by contractor’s activities
12.5 Rights of Employer
The following rights are reserved to the Employer:
To omit individual items mentioned in the Schedule of Prices if not required in the
opinion of the Employer and/or to replace them should it be more advantageous to
execute them in another way.
To order execution of alternative or provisional items as if they were main items.
To order execution of additional works as well as alternatives of works, always in
conformity with the conditions outlined in the Contract. Any order and/or delivery
of material or equipment by the Contractor for performance of the works may only
be based on instructions and/or approved execution drawings by the
Employer/Engineer.
21
All equipment and materials for installation and finishing works to be incorporated
in this contract shall prior to ordering and/or delivery by the Contractor, be
approved by the Employer/Engineer both in respect of quality and type as well as of
quantity.
12.6 Site Access and Storage
The Tenderer shall visit all sites and ascertain the location of required access onto these
sites and the location of allowance for complying with the requirements and for the
reinstatement to original condition of all roads and areas used or disturbed by the
Contractor to the satisfaction of the Engineer.
12.7 Site Installation
All costs of labor, works, provisions, materials and equipment for Site Installations
required by the Contractor and stipulated in the Tender Documents shall be included in the
various unit prices of the Bill of Quantity. No extra payment will be allowed by the
Employer for any of these activities.
12.8 Duration
The total duration of the contract is six calendar months including weekends, holidays
and official holidays.
22
13.0 Priced Bill of Quantity
23
14.0 Recommendations
1. New manholes should be constructed; the new design should cater for
diverting the current sewer lines (which have been sealed and currently
cannot be accessed or serviced) to the new manholes which will flow to the
collector system and then main disposal system. This would also enable the
sewer system to be adequately maintained.
2. Skilled personnel should be hired to examine the mechanical appurtenances
for the jet to reinstate the current system to its initial fully automated state.
3. Due to the increase in flow due and the increase utilization of the sewer
system the sizing of the sewer diameter should be revised.
4. All broken and damaged sewer pipes should be replaced.
24
15.0 Conclusion
The existing sewer system is inadequate to cater for the projected population growth of the
entire campus for the design period. A drawing and design are outlined for the rerouting of
a new sewer system to serve the needs of the University of Guyana, Turkeyen Campus.
The existing system has the following deficiencies:
1. There are a series of non-functioning manholes due to the rapid increase in the
campus population and inability of the university to provide sufficient classroom
and office space for students and staff. This has resulted in manholes that run below
buildings being sealed off to provide the additional space required.
2. The fully automated system of the pumps is not functioning; this resulted in a semi-
automated operation.
3. The current system is inefficient since current student population exceeds the initial
design capacity.
4. Inadequate pipe sizing also hinders the efficiency of the current system since a
recent redesign was not done to offset the exiting discharge.
5. According to the calculations it was also revealed that the optimum sewer diameter
necessary for an efficient flow was 6 inches; however this is for the current
population and thus will become efficient with growth in the student population.
25
16.0 References
1. Bradford, Andrea. (2005). Sanitary Sewer Design Tutorial: Urban Water Design – 437.
Retrieved November 27, 2010, from
http://www.hydrolatinamerica.org/jahia/webdav/site/hydrolatinamerica/shared/
Reference/Sanitary%20Sewer%20Design.pdf
2. Bureau of Engineering (n.d.). Sewer Design Manual - Part F. Retrieved November 27,
2010, from http://eng.lacity.org/techdocs/sewer-ma/index.htm
3. Sanitary Sewer Design Guidelines, Engineering Design & ROW Management Division
November 2004.
26
17.0 Appendices
Photo showing: “The Smith & Loveless lift station consist of Photo showing: the control panel of the Du-O-Jet ejectors.
Du-O-Jet ejectors” (taken by: Kalvika Singh on the 12th -10-2010)
Photo showing: “The interior of the wet well” Photo showing: “The manhole within a building”
(Taken by: Kalvika Singh on the 12th -10-2010)
27
Photo showing: “A existing manhole” (Technology Sport Club) Photo showing: “A sealed manhole within a building”
(Taken by: Kalvika Singh on the 12th -10-2010) (Technology Lab)
28
