Pump Selection

Based on the pump curves provided by Fairbanks Morse’s website, the selection

of pumps will be three16” four 24” sized pumps. The pump curves used is shown below.

The pump selection summary is shown below.

Plan and Profile of the Lift Station

This project can be easily implemented at any location with a full-capacity

sewer line. A lift station is used to raise the elevation of a current sewer line which may

otherwise be too high to construct, such as incoming gravity flow towards headworks at

higher elevation. To ensure that the lift station is able to meet the demands of the present

without compromising the needs of the future, it is recommended to keep track of

population growth pattern. The 2004 case study will provide the client with a need for a lift

station to allow access for maintenance in a full sewer pipe. Routine cleaning and

maintaining of Theme Street is the main emphasis behind the constriction of the lift station.

Since a lift station is above ground, it can be easily maintained and repaired just in case of

any failures which may result. After the lift station goes obsolete, a new one can easily be

constructed in its place, thus aiding with the Theme Street infrastructure over the years.

Team ABBS: Angelyn Accad EIT, Gabriel Barrera, Glenn Blake, Sean Sims EITAdvisors: Dr. Haroon Stephen (UNLV), Dr. Douglas Drury (CCWRD)

Department of Civil and Environmental Engineering and Construction, University of Nevada, Las Vegas, Nevada

Introduction

The 69-inch concrete sewage pipe near CCWRD property on Desert Inn Road and

continuing into Theme Street’s old pipe was constructed in 1980. This pipe runs as a

“reversed-pressure” pipe, where the manhole covers are sealed, limiting the access for

cleaning, monitoring and maintenance, causing corrosion. The pipe was last relined about

two years ago in 2010, when workers found that one-third of the pipe’s sewage was solid

material.

A case study in 2004 was found on Las Vegas Sun’s website about a sewage line that

collapsed near Treasure Island on Las Vegas Boulevard, causing 2 million gallons of raw

sewage to spill near the Las Vegas Strip. Over 500 feet of the 24-inch unlined concrete lines

collapsed due to lack of maintenance and were replaced with a larger 30-inch PVC pipe.

This situation highlights the importance of regular maintenance and the consequences of

doing little to no maintenance on the pipeline in question.

This problem needs to be addressed to prevent corrosion by hydrogen sulfide H2S at

the top of the pipe and the pipe would need to be converted into a “gravity pipe”. This

section runs as a reverse-pressurized pipe, where water is pushed through the pipe at a slight

slope. The idea is to decrease the depth of the water to three-quarters of the pipe’s diameter

and flow at a downward slope. This would prevent later problems and provide ample room

for odors to flow on top of the wastewater that would make it easier for CCWRD to treat

odors on their property.

Site Study

The site below is shown below.

The small pink square is a small parcel of land is located on CCWRD property. It is

especially beneficial considering the incoming pipe from Theme Street makes it way

through towards headworks and the existing odor control facilities: the existing biofiltration

beds and the chemical odor control system. Measuring at approximately 100 feet by 400

feet from edge-to-edge and from the biofiltration beds to the opposite edge, this plot of land

is large enough to include a lift station and additional odor control. The elevation of the plot

from GPS devices is approximately 1,660 feet. The two biofiltration bed areas were found

as 10,176.907 ft2 (left) and 10,416.939 ft2 (right).

Lincoln Lift Station Visit

The Lincoln Lift Station on CCWRD property was assessed in order to get a general

idea of what the components of a lift station were. The design capacity was 11 MGD

(million gallons per day) and consisted of 5 pumps with one being a redundancy pump.

However, this facility was much smaller than the sewage flow from the incoming Theme

line, which is a main pipe for CCWRD. Some issues to consider are an emergency bypass, a

redundancy pump for design, consideration for the motors being placed above-ground,

enough spacing for maintenance of the pipes and cleaning of the dry well, etc.

Objectives

Conclusion

Odor Control

Background

Alternatives

Modern-day society heavily relies on the sewage system to transport waste and harmful

materials from urban areas to the treatment plant. When the sewage system fails, it poses

problems for those involved with handling the system. In Las Vegas, tourists and locals

complain about odors near the Las Vegas Strip around the Spring Mountain Road area.

Locals and tourists complain about presence of the hydrogen sulfide gas, H2S, which is a

colorless noxious odor that smells similar to rotten eggs. The Clark County Water

Reclamation District (CCWRD) is asked to fix this issue and remove the odors. Rather than

decide a solution near the strip, it is possible to treat the odors on-site instead of

constructing an odor-control facility near the Strip.

In conjunction, a 69-inch concrete sewage pipe near CCWRD property on Desert Inn

Road is currently running at full-depth for almost three miles leading to CCWRD’s

treatment plant. This is important since the odors are transported through this pipe.

Economic Analysis

The do nothing alternative will cost around $52 million. Based on the 2004 case study,

it cost $4 million dollars to repair 500 feet of pipe. Given that the Theme Street line runs

6432.33 feet, according to the GIS data, the cost of the do nothing alternative will cost

around $52 million if the sewer lines go down.

It will cost $250 per foot to replace a sewer pipe using traditional methodology

(Trenchless Sewer Repair). In total, the pipe replacement will cost $1.6 million, not

counting the cost of relocating people along Theme Street out of their houses. According to

the Water District’s cost estimating page, it will cost $460,000 to construct a temporary

bypass for sewage during the excavation process. Altogether, the total cost of sewer line

excavation will cost around $2 million, not counting the cost of relocating people out of

their houses.

The cost of concrete per cubic yard is $75, including the material, equipment,

and labor, bringing a total of $314,700 for the concrete (ConcreteNetwork). The five

Fairbanks-Morris pumps will have an estimated cost of $20,000 each, bringing a total cost

of $100,000. The cost of wiring for the entire lift station will be around $100,000. The cost

of the ATEX odor control units will be $5000. The cost of the control panels is assumed to

be $1000. The annual cost of a maintenance worker in Las Vegas, Nevada is $33,000, and

we will be hiring four workers. With a power cost of $0.08 per kilowatt hour, the annual

power cost of the pump station will be approximately $3500 for four pumps. The total cost

of the lift station will be $520,000 for capital costs and $135,000 for annual costs. With an

average lifespan of 20 years, the complete present worth of the lift station will be $3.22

million.

* Not counting the cost of relocating people out of their homes

Due to the nature of the desired flow (3/4 full during peak dry weather flow) at

more than 100 MGD, a pump system would need to remove the incoming odors. This

system has the dual purpose of increasing safety and controlling odors in the pipeline.

The odor control system will consist of a primary biofiltration bed in series with

a secondary activated carbon odor scrubber. The secondary odor-control system was

designed to be bypassable because it will only be necessary during peak holiday flows and

during the hottest weeks of the summer when odors are more apparent and the biofiltration

beds are less effective. Carbon filtration was chosen over conventional chemical scrubbers

due to ease of maintenance.

Alternative Cost

1. “Do-nothing” $52 million

2. Pipe Replacement *$2 million

3. Lift Station $3.22 million

The main objective in executing this project is to pump the sewage faster than it is

flowing in order to decrease the depth to 75% of the pipe’s diameter for peak dry weather

flow. This will in turn prevent H2S corrosion in the Theme Street line, prevent solids

buildup in the line, design an odor control facility, and allow access for maintenance in the

Theme Street line. It is in the best interest to prevent the Theme Street lines from collapsing

because this is a one of the main inflow pipes.

Aerial map of where the 84-inch pipe meets with the 69-inch pipe on Desert Inn Road and Theme Street leading into CCWRD property and into headworks (or bar screens) to

be treated in CCWRD primary treatment.

“Do-Nothing”Alternative

The “do-nothing” approach is similar to existing conditions and ignores the current

problem. The final option is the do-nothing option, which is to let the Theme line continue

to flow at full capacity. Nothing negative has happened so far, but something may happen in

the future. The pipes will be impossible to clean and maintain while flowing at full capacity

with no prediction of flow rate or depth. If the problem persists, the sewer lines could go

down, resulting in public uproar and several repair fees.

Pipe Replacement Alternative

Another option to lower the depth of flow is to excavate the pipes and replace them

with brand-new pipes for Theme Street. The line will be constructed with a larger

population growth in mind as well as better theoretical pipe design. This will also provide

brand-new pipes as opposed to the 1980 layout, which has corroded and deteriorated,

despite being lined in 2010. Due to the nature of the pipe, the new line will need to be

constructed as a berm. The implementation of the berm will require people to leave their

houses, which will bottleneck the current problem even further. We will need to blockade

the streets as well as relocate the residents elsewhere, which will add several problems to an

already existing problem.

Lift Station Alternative

One option to lower the depth of the water to 75% peak dry weather flow is to

construct a lift station on site which will pump the sewage up to head works, resulting in

reduced pipe capacity. The station will also incorporate an odor-control system to remove

noxious odors from the sewer line. The station will provide ease of maintenance access for

the Theme street pipes. We will be able to construct the lift station directly on CCWRD

property, whereas not to interfere with the public access to roads or houses.

Biofiltration Bed Calculations

Surface area of biofiltration bed (based on gasflow):

𝐴 =𝑔𝑎𝑠 𝑓𝑙𝑜𝑤

𝑙𝑜𝑎𝑑 𝑟𝑎𝑡𝑒=

16990𝑚3

𝑕𝑟

90𝑚3

𝑚2𝑕𝑟

= 𝟏𝟖𝟖.𝟖𝒎𝟐

Mass load rate of H2S:

100𝐿3

106𝐿3× 34.1 g per mole

H2S

0.0241𝑚3

𝑚𝑜𝑙

×16990𝑚3

𝑕𝑟×

32𝑔S

34.1𝑔H2S= 𝟐𝟐𝟕𝟐.𝟎 𝐠 𝐒

Required volume of filter (based on amount of Sulphur):

𝑀𝑎𝑠𝑠 𝑙𝑜𝑎𝑑 𝑟𝑎𝑡𝑒

𝐸𝑙𝑖𝑚𝑖𝑛𝑎𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒= 𝟑𝟒.𝟗𝟓𝒎𝟑 < 188𝒎𝟑

Because the area of the existing biofiltration beds far exceeds the required 188.8m2, it was

decided that tapping them for use in the proposed system was acceptable.

Existing biofiltration beds at

CCWRD with secondary system.

Pipe Flow

Using Manning’s formula for flow in full pipe, the capacity of the existing Theme trunk

line could be determined as shown in the table below. This flow is much larger than the

capacity of the Lincoln pump station and shows how much larger the lift station design

should be.

Pipes leading away from pumps in the Lincoln Lift Station wet well (CCWRD)

Alignment and Side-View of Lift Station and pie changes

Pump Station Cross Section

Dry Well Dimensions (Side View)

Drury Lift Station

Manning's equation for full-flow pipe

Q = CfD8/3S1/2

n

Cf = 0.4632 (unit conversion for ft3/sec)

D = 5.75 ft (69" diameter in feet)

S = 0.0011 (pipe slope)

n = 0.013 (Manning's n)

Q = 127 ft3/sec

Q = 56,954 gpm = 82.0 MGD

Model Size Head Flow Speed Power EFFMax

SphereImpelle

r Size

2414 16in 48 ft9,000 gpm

580 125 hp 87% 5.25 in 25.0 in

2414 24 in 48 ft18,500 gpm

390 rpm 250 hp 86% 8.0 in 37.5 in