Preliminary Engineering Report Newport Water Treatment Plant Sedimentation Basin Upgrade Newport Utilities November 2010

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Preliminary Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

Newport Utilities

November

2010




Overview


The New
port Water Treatment Plant

is a conventional

process
water

treatment facility which was originally bu
ilt in 1964 and
upgraded in 1980

and
2000
. The treatment train consists of
chemical addition and rapid mixing, flocculation, sedimentation,
filtration with dual media gravity filte
rs
, and disinfection prior to
discharge
. At a filter loading rate of 4.0 gpm per square foot

the
facility has a rated capacity of 5.76 MGD. Experimentation and
necessity has shown that the filters are capable of sustaining
quality effluent (turbidities b
elow 0.10 NTU) at loading rates of up
to 6.0 gpm per square foot
,

which would allow the plant to be
rated at 8.64 MGD. This would allow the plant to consistently be
able to meet and sustain summer peak
daily
demands
, which
have been recorded as high as 6.
9 MGD.


Aggravating

the normal peaking factors
, the City’s largest

industry
,

Con
-
Agra
,

is a large water user whose water usage can vary
dramatically. As an example their average daily use in 2009 was
approximately 1,250,000

gallons per day while their pea
k day
usage was
over 2,000,000 gallons

during the same period.

These
large swings in demand overtax

system storage very quickly and
can only be made up by sustained water production.

Exacerbating this already taxing demand, the demands usually
take place

over a weekly period meaning the demand stays fairly
constant for up to a week at a time. This does not allow diurnal or
even normal day to day fluctuations to restore system storage.


Additionally, since the facility was first put in
to

service in 1964
,

the
raw water pump station, which takes water from the French Broad
River, has experienced significant problems with sand and grit.
The pump station originally had an eductor pump installed in the
wet well to remove sand and grit but the quantity of
grit

and design
of the wet well
does

not allow for its e
fficient removal. This results

in the build
-
up of grit in the wet well and the transfer of grit to the
raw water pumps and eventually to the water treatment plant. The
Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




2

resultant wear on pumps and equipm
ent has led to expensive
repair costs and the shut
-
down of treatment units for repair and to
remove accumulated grit.


This report will review the current d
esign conditions and operation
of the sedimentation basins
. Alternatives
for upgrading th
i
s unit
p
rocess

to 8.64 MGD

will be developed

and evaluated
.

A
r
ecommended alternative will be identified.

The installation of a
new grit removal system at the raw water pump station will also be
evaluated and recommendations presented.



Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




3

Existing Conditions


The existing
raw water pump station and treatment facilities are of
concrete and brick

construction. The buildings and structures are
in good condition considering their age and have been well
maintained by plant staff. The sedimentation basins
, particul
arly
basin number 1,

exhibit consider
able spalling of concrete. This
spalling is occurring in areas which were patched due to
honeycombing during the original construction of the basins

and is
actually spalling of the repair materials, not the virgin conc
rete
.
Structural investigations have indicated that the spalling is not
affecting the structural integrity of the basins and can be readily
repaired. The latest structu
ral investigation is included in

Appendix A of this report and its recommendations will

be followed
in developing cost estimates.


The current weak link in the treatment train
is

the sedimentation
basins.
The basins are almost 50 years old and the s
ludge
collection mechanisms have required significant repairs
,

with one
unit being completely

out of service at this time.
The two
circular
basins
are 60 feet in diameter with

a combined su
rface area of

5,65
0

square feet. The side water depth is 14.5 feet resulting in a
total effective volume of 613,000 gallons.

The total weir length
provided
is

18
2

feet

per basin
. There are currently
864

square
feet of tub
e settlers in each basin which at a loading rate of 2.5
gpm per square foot results in a design loading rate of 4,320 gpm
or 6.22 MGD.



The raw water pumping station is equipped with three
v
ertical
turbine raw wat
er pumps; one of the pumps is rated at
2,100

gpm
while the o
ther two are rated at 2,400 gpm at approximately 5
5
0
feet of head.

The smaller pump is brand new with its installation
just being completed within the last month.
Raw wate
r is taken
from the river with three wedge wire intake screens and is
conveyed to the raw water pump station via a 42” gravity ductile
iron pipe. The pipe

discharges into a structure that once housed a
traveling screen which was used prior to the installa
tion of the
existing intake screens. It then flows into the wet well and is
pumped via parallel 14 and 18 inch mains to the water treatment
plant.

The pump station’s electrical controls are currently being
upgraded and will soon be in excellent condition
.



Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




4

Alternatives


Do Nothing


The first alternative is
always
the do nothing alternative. While
this alternative makes some

short term

economic sense, it does
not address the basic problem of
not
being able to meet the peak
demand loads on the system.
Con
-
Agra can and does introduce
almost instantaneo
us demands on the system which can quickly
require sustained production rates at or above the existing
capacity of the treatment facility.

This condition cannot be allowed
to continue and therefore the do
nothing alternative is judged to be
inappropriate.


Refurbish the Existing
Basin
s


The second alternative involves the rehabilitation of the existing
basins

and their sludge collection equipment. Also required is the
installation of sufficient tube settle
rs to allow the peak design flow
rate of 6,000 gallons per minute (8.64 MGD). At a loading
rate
of
2.0 gallons per square foot (regulatory maximum is 2.5 gal / sq. ft.)
this would require the installation of 3,000 square feet of tube
settlers or 1,500 squ
are feet in each basin.

New and additional
effluent weirs will also be required to balance the flow in the
basins and to meet regulatory requirements. A total weir length of
600 feet, 300 ft. in each basin, is required.


There are two basic design confi
gurations which are available for
circular clarifiers: center feed and peripheral feed. The existing
clarifier

basins

are the center feed type with 24” supply lines u
nder
the concrete basins. The 24” feed lines are not capable of
carrying the desired flo
ws without exceeding recommended
clarification entrance velocities. Therefore a new 36” feed line will
have to be brought into each clarifier through the side wall to the
center well, if center feed clarifiers are used. This will
reduce the
amount of tube

settlers that can be placed in the basins
,

but not
below the desired 3,000 sq. ft.

The use of peripheral feed technology eliminates the need to bring
a new feed line to the center of the
basin
s. As implied by their
name
,

peripheral feed clarifiers are fed from the outside wall, not
an interior center well.
The existing
basin
s can be converted to
the peripheral feed type
clarifier
quite easily.
This will allow the
new 36” supply lines to be terminated at the outside wall

and will
allow the installation of more tube settlers within the basins.


A minimal amount of site pipework changes outside of the
basins

is also required with both of these technologies. Existing 30” lines
will need to be extended to the clarifiers and
36” influent lines
installed to reduce inlet velocities.
The repair of the exterior
Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




5

concrete will also need to be addressed if the existing clarifiers are
reused.


Table 1
contains the construction cost estimates for each of the
two clarifier technologies
.


Table 1

Newport Water Treatment Plant

Construction Cost Estimate

Existing Basin Upgrade






Center Feed Clarifier Option




Item

Description


Est
imated

Cost


1

Repair of existing Conc. Basins


$ 50,000.00


2

Clarifier Equipment


$
205,000.00


3

Tube Settlers


$ 180,000.00


4

Demolition & Installation


$ 200,000.00


5

Site Pipework


$ 40,000.00


Total Estimated Construction Cost


$ 675,000.00







Peripheral Feed Clarifier Option




Item

Description




1

Repair

of existing Conc. Basins


$ 50,000.00


2

Clarifier Equipment


$ 254,000.00


3

Tube Settlers


$ 210,000.00


4

Demolition & Installation


$ 200,000.00


5

Site Pipework


$ 30,000.00


Total Estimated Construction Cost


$ 744,000.00




New Assisted Settling Clarifiers


The third evaluated alternative involves the abandonment of the
existing
clarifier basins

and the construction of new clarifiers
. Site
space limitations and the fact that the existing clarifiers must
remain in service

during any renovation dictates that conventional
clarifiers would be problematic to site because of their large size.
A more traditional rectangular structu
re would need to be at least
1
4
0

feet by 100 feet
in interior dimension and would have to
match
the height of the existing clarifiers. Two new circular
structures would need to be 9
5

feet in internal diameter each. It is
readily apparent that additional structures of this size on the site
would tax the existing available land.


Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




6

Assisted settling cla
rifiers are available which through various,
generally proprietary, methods allow the separation of the
developed floc from the water
withi
n a much smaller footprint.
Two technologies of this type were considered for use in this
project. The first was th
e Micr
ofloc Trident system which uses a
plastic media along with polymer addition to filter the floc out of
the water flow. The process is more similar to filtration than
traditional gravity settling but the end result is similar. The
footprint for this

system would be less than 50% of that required
for traditional clarifiers but additional site pipework and pumps
would be required to facilitate its installation.


The second technology is the Actiflo system which uses a
ballasted media i
n which the floc
attaches to an

introduced media
and settles much more quickly than an un
-
ballasted floc. This
once again allows the process to take up a much smaller footprint.


Each of these processes can be supplied as a complete package
in steel tankage or as an equi
pment package to be installed in
built
-
in
-
place concrete tankage.
For the purpose of this evaluation
built
-
in
-
place concrete tankage will be assumed for two reasons:
to match existing construction and to eliminate steel corrosion
issues and required maint
enance painting.
Both

processes

will
require significant pipework changes and site development work.


Another

benefit

of using this type of technology is that cold, low
turbidity waters can be more effectively treated than with
traditional gravity settled

systems. This is because cold, low
turbidity waters produce a smaller, harder to settle floc which the
assisted settling process are generally ideally suited for. During
the winter months this is has been an occasional issue at the
Newport facility.


Ta
ble 2 contains construction cost estimates for each of these two
processes.















Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




7

Table 2

Newport Water Treatment Plant

Construction Cost Estimate

Assisted Settling Clarifier Options






Microfloc Trident




Item

Description


Est
imated

Cost


1

Equipment


$ 1,385,000.00


2

Installation


$ 277,000.00


3

Concrete Structures


$ 554,000.00


4

Site Work & Pipe


$ 100,000.00


5

Electrical


$ 50,000.00


Total Estimated Construction Cost


$ 2,366,000.00







Actiflo




Item

Description




1

Equipment


$ 991,500.00


2

Installation


$ 297,450.00


3

Concrete Structures


$ 495,750.00


4

Site Work & Pipe


$ 100,000.00


5

Electrical


$ 50,000.00


Total Estimated Construction Cost


$
1,934,700.00



Raw Water Grit Removal


Grit removal, especially sand dominated gr
it removal is closely
related to flow velocities and particle settlement velocities.
Provide near quiescent, laminar flow conditions and enough
detention time and most, if not all, grit can be removed from the
flow by gravity settling. Generally, flow velocities of 0.5 feet p
er
second
(fps)
or less and detention times of
1

minute

or more are
adequate

for removing sand based grit. For this purpose a
structure 8 feet wide by 4 feet deep provides a velocity of
0.42 fps

at the design flow of 6,000 gpm. A 30 foot long structure w
ould
allow a 72 second detention time at this flow rate.


The floor of the structure should be sloped to a small sump at one
end to allow the placement of a submersible pump to remove the
grit slurry from the sump. The slurry could be pum
p
ed straight
back

to the river
,

if TDEC will allow this discharge
,

or can be
directed to a grit classifier to separate the grit from the
water. The
water
filtrate
could then be discharged into the raw water pump
station or the river and the grit (river sand) could be disp
osed of
separately.

Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




8

A construction cost estimate for the construction of this structure is
given in Table 3.



Table 3

Newport Raw Water Pumping Station

Construction Cost Estimate

Grit Removal System










Item

Description


Est
imated

Cost


1

Equipment


$ 50,000.00


2

Installation


$ 20,000.00


3

Concrete Structure


$ 50,000.00


4

Excavation


$ 50,000.00


5

Site Work


$ 10,000.00


6

Electrical


$ 20,000.00


Total Estimated Construction Cost


$

200,000.00





Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




9

Analysis


As can be seen
,

the most cost effective alternatives are the ones
in which the existing
basin
s are refurbished and re
-
configured to
allow for the additional
needed treatment capacity. While there
are
additional benefits to using assisted settling systems, in this
case, the added benefits don’t equate to the cost differential.


The periods of time in which cold, low turbidity wa
ters are being
treated correspond to periods in which system

demand are

at

the
lowest annual rates.

This is due to two factors: There is generally
no irrigation
al

or recreational water uses during the winter months
and Con
-
Agra’s production is at its lowest level due to the nature
of seasonal fruit and vegetable production.


Th
erefore during
these critical treatment periods in the winter months, facility
production rates can be reduced to allow additional detention time
and lower overflow rates in the clarification basins. This method
has been successfully utilized at the Newpo
rt facility for many
years and there is no reason to believe it will not continue to be a
successful
operational tactic.


Recommendations


It is the recommendation of this report that Newport Utilities
should proceed with a project to renovate the existing

clarifier

basins

and add sufficient tube settlers to allow the development of
the desired and required peak treatment capacity of 8.64 MGD.
It
is also recommended that the design include both center feed and
peripheral feed options to allow

more competition between
manufacturers

and allow the opportunity for the utility to select the
best overall technology including consideration of the amount of
tube settlers which can be accommodated in each design.


The grit removal structure should
also

be built at the earliest
practical time to eliminate wear and tear on pumps and treatment
equipme
nt. It is recommended that this project should be
constructed
at the same time as the clarifier renovation project to
allow larger contractors with the econo
my of scale to bid and
construct the projects simultaneously.


A total project cost estimate containing the recommended
alternatives’ construction costs and other estimated project costs
is
shown in Table 4.







Preliminary
Engineering Report

Newport Water Treatment Plant

Sedimentation Basin Upgrade

November 2010




10

Table 4

Newport Water Treatment Upgrades

Total Estimated Project Costs





Item

Description


Est
imated

Cost







Existing Sedimentation Basin Upgrades




1

Repair of existing Conc. Basins


$ 50,000.00


2

Clarifier Equipment


$ 254,000.00


3

Tube Settlers


$ 210,000.00


4

Demolition & Installation


$ 200,000.00


5

Site Pipework


$ 30,000.00


Estimated Construction Cost


$ 744,000.00







Raw Water PS Grit Removal




6

Equipment


$ 50,000.00


7

Installation


$ 20,000.00


8

Concrete
Structure


$ 50,000.00


9

Excavation


$ 50,000.00


10

Site Work


$ 10,000.00


11

Electrical


$ 20,000.00


Estimated Construction Cost


$ 200,000.00







12

Construction Costs


$ 944,000.00


13

Construction
Conti
n
gency


$ 94,400.00


Total Estimated Construction Cost


$ 1,038,400.00







Design & Administration Costs




14

Field Survey


$ 1,900.00


15

Soil Boring


$ 3,800.00


16

Engineering Design


$ 54,700.00


17

Bidding


$ 4,200.00


18

Construction Administration


$ 20,500.00


19

Resident Inspection


$ 30,000.00


Total Design & Admin. Costs


$ 115,100.00







Total Estimated Project Cost


$ 1,153,500.00