United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
EPA/625/8-90/017
March 1990
Technology Transfer
v>EPA Summary Report
Optimizing Water
Treatment Plant
Performance with the
Composite Correction
Program
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EPA/625/8-90/017
March 1990
Summary Report
Optimizing Water Treatment Plant
Performance with the
Composite Correction Program
U.S. Environmental Protection Agency
Office of Research and Development
Center for Environmental Research Information
Cincinnati, OH 45268
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Notice
This document has been reviewed in accordance with the U.S. Environmental Protection
Agency's peer and administrative review policies and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
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Contents
Section
Page
1 INTRODUCTION 1
Purpose 1
Background 1
Content 1
2 THE COMPOSITE CORRECTION PROGRAM 3
The Comprehensive Performance Evaluation 3
The Composite Correction Program 6
3 RESULTS OF CASE STUDIES g
CPE Findings g
CCP Findings '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 12
Overall Factors Limiting Performance 12
4 CASE STUDIES 15
Plant 1 1C;
Plant 2 21
Plant 3 pn
Plant 4 34
piant 5 ;;;;; 40
Plant 6 ?a
Plant 7 53
Plant 8 cq
Plant 9 57
Plant 10 70
Plant 11 a?
Plant 12 o7
13 !:.'.':::::::::::::::::::::: 95
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Acknowledgments
Although many individuals contributed to the preparation and review of this document, the
assistance of the individuals listed below is especially acknowledged. Those who assisted by
participating in the actual field studies described in the document are noted below as "Onsite
Reid Participants."
Major Authors:
Robert C. Renner and Bob A. Hegg, Process Applications, Inc., Ft. Collins, Colorado
Jon H. Bender, EPA Technical Support Division (TSD), Cincinnati, Ohio
Technical Writing and Editing:
Heidi Schultz and Susan Richmond, Eastern Research Group, Inc., Arlington, Massachusetts
Project Managers:
Jon H. Bender, EPA TSD, Cincinnati, Ohio
James E. Smith, EPA Center for Environmental Research Information (CERI),
Cincinnati, Ohio
Reviewers:
Eric Bissonette, EPA TSD, Cincinnati, Ohio
Robert Blanco, EPA Office of Drinking Water (ODW), Washington, D.C.
Peter Cook, EPA ODW, Washington, D.C.
Dan Fraser, Montana Department of Health and Environmental Sciences (DHES),
Helena, Montana
Denis J. Lussier, EPA CERI, Cincinnati, Ohio
James Westrick, EPA TSD, Cincinnati, Ohio
Onsite Reid Participants:
EPA
Jon H. Bender, EPA TSD, Cincinnati, Ohio
Eric Bissonette, EPA TSD, Cincinnati, Ohio
Dean Chaussee, EPA Region VIII, Helena, Montana
Ben W. Lykins, EPA, Office of Research and Development, Cincinnati, Ohio
James E. Smith, EPA CERI, Cincinnati, Ohio
James Westrick, EPA TSD, Cincinnati, Ohio
State of Montana
Dave Aune, Montana DHES, Helena, Montana
Jerry Burns, Montana DHES, Billings, Montana
Dan Fraser, Montana, DHES, Helena, Montana
Donna Howell, Montana DHES, Helena, Montana
Denise Ingman, Montana DHES, Helena, Montana
James Melsted, Montana DHES, Helena, Montana
Kate Miller, Montana DHES, Billings, Montana
Rick Rosa, Montana DHES, Helena, Montana
Mark Smith, Montana DHES, Helena, Montana
Roy Wells, Montana DHES, Helena, Montana
IV
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State of Ohio
Gary Cutler, Ohio EPA, Columbus, Ohio
Steve Severyn, Ohio EPA, Columbus, Ohio
State of Kentucky
Fred Cooper, Kentucky Department of Environmental Protection (DEP), Morehead, Kentucky
George Schureck, Kentucky DEP, Frankfort, Kentucky
Tom Stern, Kentucky DEP, Frankfort, Kentucky
Damon White, Kentucky DEP, Hazard, Kentucky
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SECTION 1
INTRODUCTION
Purpose
This document summarizes the results of an ongoing
project to evaluate the utility of the Composite
Correction Program (CCP) approach to improving the
performance of drinking water treatment facilities. The
CCP approach, which has already proven successful
when applied to wastewater treatment plants, is
described and the results of evaluating it at 13
drinking water plants to date are summarized.
The 13 "case studies" focus on the potential for the
CCP approach to improve the performance of small
drinking water systems in meeting the turbidity
removal requirements of the Surface Water Treatment
Rule (SWTR).
The CCP approach is still under development. The
end product of this project will be a publication that
describes the refined CCP approach and allows it to
be applied by others.
Background
Many communities are now considering either
construction of new facilities or major modifications to
existing ones to meet drinking water regulations. An
approach that allows communities to meet regulatory
requirements by implementing changes in their
operation, maintenance, and administration
procedures instead of major capital improvements has
obvious advantages. By maximizing the operational
efficiency of their facilities, local administrators can
both improve the ability of the facility to meet Safe
Drinking Water Act (SDWA) requirements and
minimize the financial impact to the community
associated with major upgrades to the plant.
Recognizing that the CCP approach had been
successfully developed and applied to small
wastewater treatment plants to accomplish the same
objectives, the State of Montana decided to evaluate
the potential of modifying it for use at small drinking
water plants. Based on the initial success of this
evaluation, U.S. EPA decided to further develop and
demonstrate the approach to ensure its applicability to
other parts of the country.
Since 88 percent of the 60,000 community drinking
water systems in the United States are small systems
serving fewer than 3,300 individuals, the opportunity
for widespread impacts are large. These small
systems account for approximately 92 percent of the
SDWA compliance problems reported each year. In
1987, more than 80 percent of the community drinking
water systems experiencing significant compliance
difficulties were small systems.
Small systems frequently can neither readily identify
and address the factors that cause their compliance
problems nor easily finance the upgrading of their
facilities. The staff may be inadequate in numbers,
experience and training to effectively solve the
problems. Successful application of the CCP
approach can identify cost-effective measures that
can be taken to improve plant performance and
comply with drinking water requirements.
The CCP approach is another tool that federal, state,
or local regulators, technical personnel, and
consultants familiar with the procedure can use to
identify and correct factors that limit a plant's
performance. Results to date suggest that it is both
highly successful and cost effective.
Content
Section 2 of this document details the CCP approach,
including facility review, performance analysis, and
implementation of corrective measures. Section 3
summarizes the results of the case studies,
highlighting specific instances where the CCP
approach revealed problems that were not previously
obvious to drinking water treatment plant operators.
Also highlighted are instances where the CCP
approach saved the facilities money that otherwise
would have been spent in plant modification. Section
4 includes expanded information on the 13 case
studies that have been conducted to date should the
reader desire additional information.
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SECTION 2
THE COMPOSITE CORRECTION PROGRAM APPROACH
The CCP approach consists of a Comprehensive
Performance Evaluation (CPE) and a Composite
Correction Program (CCP). The CPE is a systematic
step-by-step evaluation of an existing treatment plant
resulting in a comprehensive assessment of the unit
treatment process capabilities and the impact of the
operation, maintenance and administrative practices
on performance of the plant.
It is conducted by a team of individuals with
knowledge of drinking water treatment and results in
the identification of a unique combination of factors
limiting plant performance. This team reviews and
analyzes the plant's physical capacity as well as its
operational capability and associated maintenance and
administration. Based on this analysis, the team
projects the capabilities of the major unit processes
within the plant, and identifies and prioritizes those
factors affecting plant performance.
If the CPE indicates that optimization of existing major
unit processes can result in desired finished water
quality, the CCP phase is implemented. The CCP
systematically addresses those factors identified and
prioritized in the CPE phase.
Figure 2-1 graphically illustrates the CPE/CCP
approach. The CPE team usually is composed of two
individuals experienced in the design and operation of
drinking water treatment facilities and in trouble
shooting their operation. Teams composed of up to
seven individuals were employed for each of the 13
case studies described in this document, although it is
anticipated that teams this large will not be required to
apply the finalized CPE/CCP approach. These larger
teams were used to help evaluate and further refine
the procedure as well as familiarize regulatory
personnel with it.
The Comprehensive Performance
Evaluation
The CPE begins with a plant tour and collection of
information from plant records. Data are obtained by
interviewing plant staff and key administrative
personnel (for example, the mayor and other city
administrators), reviewing the plant's physical
capacity, examining the plant's operation and
maintenance records, and reviewing budgets.
Standardized forms are used to collect the data on
.raw and treated water quality, design and operating
conditions for individual plant processes, plant
operator coverage, user fees for water treatment,
maintenance scheduling, and operating budgets.
While the data collection efforts focus on the current
status of the plant, the review also includes past
records to account for factors such as seasonal
variations in raw water quality and peak demand, and
to establish an accurate record of plant performance.
In addition to gathering existing data, the CPE may
involve collecting new data by conducting special
studies. For example, the CPE team usually develops
a turbidity vs. time profile on a plant's filters before
and after backwashing to determine whether the filters
were performing adequately (see Figure 2-2). At
nearly all plants, such a profile revealed that a
significant breakthrough of turbidity occurred after the
backwash. When the CPE team sampled the clearwell
at one end, they discovered turbidity values of 6.3
NTU, which clearly exceeded the regulatory criteria.
Other special studies conducted as part of the CPE
often reveal similar performance problems that may
not be obvious to the plant staff.
Design Components
The CPE team determines a plant's capacity by
reviewing plant drawings and specifications, making
field measurements, and reviewing information
provided by the plant staff. In addition, the team
applies its experience based on evaluations performed
at other plants. The CPE evaluators then determine
the projected capacity at which plant major unit
processes (flocculation, sedimentation, filtration, and
disinfection) can provide acceptable treated water
quality. Projected values are compared with peak
instantaneous operating capacity and current plant
production. The comparison results are summarized
using a performance potential graph (see Figure 2-3),
which illustrates the strengths and weaknesses of the
plant's unit processes.
Operation and Maintenance
Operational factors are assessed by evaluating
procedures that the plant uses for process control
adjustments and by determining if steps the plant
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I
Figure 2-1 CPE/CCP schematic of activities.
Administrators
Recognize Need To
Improve Plant Performance
CPE Evaluation
of
Major Unit Processes
Major Unit Processes
Are
Adequate
Major Unit Processes
Are
Marginal
Implement CCP to
Achieve Desired
Performance
From Existing Facilities
Major Unit Processes
Are
Inadequate
Implement CCP to
Optimize Existing Facilities
Before Initiating
Facility Modifications
Do Not Implement CCP
Evaluate Options For
Facility Modifications
Desired Performance Achieved
Abandon Existing
Facilities and
Design
New Ones
takes to modify operations are based on proper
application of water treatment concepts and methods.
The CPE team discusses process control measures in
detail with plant operators. This enables them to
accurately assess the plant's operation and to avoid
any misunderstandings related to terminology.
Maintenance capabilities are evaluated by reviewing
maintenance schedules and records, observing spare
parts inventories, observing the condition of plant
equipment, and discussing maintenance activities with
plant personnel.
Administration
The CPE evaluators interview plant operators and
administrative personnel (for example, city managers,
town clerks, water board officials, etc.) to consider
administrative factors such as staffing (including
training, motivation, and morale), budgets, and rate
structures.
Evaluating the Factors that Limit Performance
After critically studying the plant design, performance,
maintenance, administration and operation, the CPE
team assesses the performance of the plant and
conducts an in-depth analysis to identify the specific
factors that limit this performance. They use a
checklist containing more than 65 performance-
limiting factors (see Table 2-1) and define each factor
according to its specific cause of poor plant
performance. Once the factors have been identified,
they are prioritized according to the magnitude of their
adverse effects on plant performance. This is the
major output from a CPE: a prioritized list of
performance limiting factors.
Reporting
The CPE team conducts an exit meeting with
administrative and operations personnel to
communicate the results of the CPE directly to all
concerned. This is followed up with a brief written
report. The purpose of the report is to summarize the
results of the CPE and list the prioritized factors
limiting plant performance. A typical CPE report is 8 to
12 pages in length and addresses the following topics:
Facility description
Major unit process evaluation
Performance assessment
Performance-limiting factors
Projected impact of a CCP
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Figure 2-2. Filter effluent turbidity profile.
Turbidity, NTU
40 r-
10 -
Present Requirements
15 20
Minutes
Figure 2-3. Sample performance potential graph.
Unit Process
Flocculation1
HOT, min
Sedimentation2
SOR, gpd/sq ft
Filtration3
HLR, gpm/sq ft
Disinfection4
Contact time, min
0.2
Flow, mgd
0.4 0.6
0.8
1.0
113 57 38 28
150 302 452 603
0.4 0.7 1.1 1.5
180 90 60
23
1.8 2.2 2.5 2.! I
Peak Instantaneous Operating Flow
Rate, One Pump = 300 gpm
1 Rated at 20 min - assumes variable speed drive would be added.
2 Rated at 750 gpd/sq ft - 12.5-ft depth discourages higher rating.
3 Rated at 3 gpm/sq ft - control system considered limiting.
4 Rated at CT = 127 with 2.4 mg/L CI2 dose, which requires a 53-min HOT; CT based on 4 log required reduction - 2.5 log in plant; 1.5
log disinfection, pH = 8, temperature = 5ฐC. Assumes 10% of usable clearwell volume for contact time..
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Table 2-1. Performance-Limiting Factors
Table 2-1. Performance-Limiting Factors (continued)
ADMINISTRATION
Plant Administrators
- Policies
- Familiarity with plant needs
- Supervision
- Planning
Plant Staff
- Manpower
number
- plant coverage
- work load distribution
- personnel turnover
- Morale
- motivation
-pay
- work environment
- Staff qualifications
- aptitude
- level of education
- certification
- Productivity
Financial
- Insufficient funding
- Unnecessary expenditures
- Bond indebtedness
Water Demand
MAINTENANCE
Preventive
- Lack of program
Spare parts inventory
Corrective
- Procedures
- Critical parts procurement
General
- Housekeeping
- References available
- Staff expertise
Technteal guidance
- Equipment age
A CPE report does not recommend specific actions to
be taken to correct individual performance-limiting
factors, since this could lead to a piecemeal rather
than an integrated approach to corrective actions.
Corrective actions should be undertaken in the next
phase - the CCP - with the help of the CPE team or
similarly experienced individuals.
The Composite Correction Program
The objective of this phase is to improve the
performance of a drinking water treatment plant by
implementing the findings of the CPE when it
indicates that the plant is likely to meet treatment
requirements with the existing major unit processes.
The CCP focuses on systematically addressing the
factors that limit the plant in achieving the desired
finished water quality.
Implementing the Composite Correction Program
To successfully implement the CCP and achieve
improved performance, facilities must utilize the CPE
results and implement a long-term process control
DESIGN
Raw Water
- THM precursors
- Turbidity
- Seasonal variation
- Watershed/Reservoir management
Unit Design Adequacy
- Pretreatment
- intake structure
- pre-sedimentation basin
- pre-chlorination
- Low service pumping
- Flash mix
- Flocculation
- Sedimentation
- Filtration
- Disinfection
- Sludge treatment
- Ultimate sludge disposal
- Fluoridation
Miscellaneous
- Process flexibility
- Process controllability
- Process automation
- Lack of standby units for key equipment
- Flow proportioning units
- Alarm systems
- Alternate power source
- Laboratory space and equipment
- Sample taps
- Plant inoperability due to weather
- Return process streams
OPERATION
Testing
- Performance monitoring
- Process control testing
Process Control Adjustments
- Water treatment understanding
- Application of concepts and testing to process control
- Technical guidance (operations)
- Training
- Insufficient time on job
O&M Manual/Procedure
- Adequacy
-Use
Distribution System
MISCELLANEOUS
program. A factor in any one of the performance-
limiting areas (design, maintenance, administration,
and operation) can contribute to poor performance. It
is unlikely, however, that a single factor limits
performance; rather it is usually a unique combination
of factors that causes poor water quality. Plant
operators and administrators must understand the
relationship among these areas and water treatment
plant product water quality. It is the operation of the
plant that enables a physically capable plant to
produce adequately treated water.
Maintaining Long-Term Involvement
One of the keys, as already noted, to successfully
implementing a CCP program is long-term effort
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(typically involving several months to a year). Long-
term involvement is critical for several reasons:
Repeat training is more effective than one-time only
training. Training should be conducted under a
variety of operating and administrative conditions
(for example, when seasonal water quality or
demand changes) in order for staff to develop
confidence in new techniques or procedures.
Time is required to make the necessary physical
and procedural changes. This is especially true for
any changes that require administrative approval or
funding appropriations.
Necessary changes in staff attitude may mean
personnel changes are needed. If the staff do not
support the CCP approach, the CCP will require
additional effort and perhaps personnel changes to
be successful.
Time is required to identify and eliminate any
additional performance-limiting factors found during
the CCP.
Since the goal of implementing the CCP is to correct
performance-limiting factors until the desired water
quality is achieved, the details of the implementation
often will be site-specific and, therefore, should be left
to the individuals implementing the CCP.
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SECTIONS
RESULTS OF CASE STUDIES
Thirteen CPEs were conducted in 1988 and 1989; 11
at conventional drinking water treatment facilities and
2 at facilities using direct filtration. Of the 13, 9 were
completed in Montana, and 2 each were completed in
Ohio and Kentucky. The plants ranged in size from
3.8 to 202 L/s (86,000-10,000,000 gpd). Table 3-1
summarizes the design capacity and type of plants
evaluated. Conventional plants are defined as using
flash mix, flocculation, sedimentation, filtration, and
disinfection unit processes primarily for turbidity
re.voval and disinfection.
Table 3-1. Summary of Plants Where CPEs Have Been
Conducted
Plant No. Design Capacity Process Type
1
2
3
4
5
6
7
8
g
10
11
12
13
7 mgd
3 mgd
5 mgd
60 gpm
3 mgd
4 mgd
10 mgd
250 gpm
650 gpm
350 gpm
300 gpm
500 gpm
1 .5 mgd
Lime Softening'/Conventional
Conventional
Conventional
Conventional
Direct Filtration
Lime Softening'/Conventional
Conventional
Lime Softening7Conventional
Direct Filtration
Conventional
Conventional
Conventional
Conventional
* Equipped with reactor ciarifiers combining flocculation and
sedimentation in one basin.
CPE Findings
Nearly all 13 case studies revealed significant
information about each plant's condition,
administration, and operation, including findings that
had not been identified in previous inspections.
At Plant 6, the CPE team discovered that plant staff
bypassed the reactor clarifier during winter months
and proceeded to operate using direct filtration
without any chemical coagulant aids. This practice
was discovered by thoroughly examining plant
operating records and conducting followup
interviews with the plant staff. While the operating
records provided only a hint of a problem, the CPE
team was able to pinpoint the problem by posing
directed questions to the staff.
At Plant 3, a direct discharge of backwash water to
a stream was identified. This practice violated the
State's discharge regulations.
At Plant 12, the CPE team learned that the
dilapidated condition of the plant prevented it from
providing acceptable finished water to the
community. While it originally appeared that the
plant would not be able to afford the necessary
repairs, the CPE team's review of the plant's
operating budget and available resources led the
community to believe that sufficient funds were in
fact available to repair the plant and to redirect
priorities.
The case studies also clearly indicate that the
involvement of community administrators is a critical
part of the CPE and, ultimately, to improving a plant's
performance. Administrators frequently had not been
informed of previous inspection results and potential
or existing problems and, therefore, had not
implemented remedial actions. In a CPE, the
administrators are involved from the outset and
informed of the evaluation results during the exit
meeting. Informing administrators of performance
problems during this meeting often led to their
decision to change priorities regarding water treatment
improvements and policies at the plant. Without the
CPE results, existing plant staff frequently were
unable to enlist the support of administrators or to set
priorities for remedial actions.
At Plant 2, the CPE team discovered that the plant
operated at its peak rate 24 hr/day during maximum
demand seasons. When the team reviewed data on
the service population, they learned that per capita
water use was excessive. By lowering peak
demands to more typical rates, the plant could
operate within acceptable loading rates to achieve
compliance with applicable standards. When the
CPE team informed administrators of this fact
during the exit meeting, they decided to change the
water rate structure and penalize high consumption.
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At the same time, administrators initiated a leak
detection survey and identified a major leak into an
old, abandoned oak stave pipeline. Together, these
administrative actions substantially reduced water
demand and enabled the plant to achieve
acceptable treated water quality without major
expenditures.
At Plant 12, the team identified severe finished
water quality problems (very high finished water
turbidity levels) that previously went undetected or
unreported. Mechanical equipment was in a state of
disrepair, thereby adding to the plant's performance
problems. In addition, plant administrators had
scheduled several major extensions to the
distribution system; however, when informed by the
CPE team of the performance problems, the
administrators intended to redirect their resources
from the distribution extensions to upgrading the
water treatment plant facilities.
Town administrators for Plant 13 had signed long-
term agreements to supply water to a new industry
and another water district. Some aspects of the
agreement were considered major concessions to
attract the industry, which would employ 500
people. Rrst, it was estimated that when these
users came on line they would represent one third
of the plant's current capacity, possibly
necessitating facility modifications to provide
additional plant capacity. In addition, the agreement
also required the town to supply the water at a
lower cost than that currently paid by the town's
own drinking water customers. When the CPE team
presented town administrators with this information,
they indicated that they would consider initiating a
rate study and examine the need to renegotiate
these agreements to supply water.
The case studies showed that in all plants but three,
plant performance was much worse than previously
reported data had indicated. In two cases, finished
water quality was so poor that the state threatened to
institute a boil order unless the facilities immediately
made improvements. The CPE teams discovered
these performance problems despite the fact that
monthly operating reports usually showed that finished
water quality met drinking water standards. These
findings indicate that the present requirement to
sample turbidity from the clearwell on a daily basis
does not accurately reflect actual finished water
quality at many plants. The CPE team initiated special
studies that included developing turbidity vs. time
profiles on filtered water.
At Plant 2, 12 months of data previously submitted
to the State revealed no violations. However, when
the CPE team measured turbidity before and after
the filter backwash and plotted the data (see Figure
3-1), they discovered a turbidity breakthrough of
5.8 NTU. Figure 3-1 also reveals that a decision to
delay the backwash resulted in a significant
increase in filtered water turbidity just prior to
initiating the backwash cycle. Similarly, when the
CPE team reviewed operating data for a 1-yr period
at Plant 12, they learned that finished water
turbidities were very consistent and rarely
exceeded 1.0 NTU (see Figure 3-2). However,
when the team measured turbidities during the
CPE, they discovered clearwell turbidities in excess
of 6.0 NTU. The data reported to the State must be
representative of actual operating conditions.
These results indicate that data from daily grab
samples may not reflect true performance and that
data collected over shorter time periods (such as
hours or minutes) is necessary. This suggests that
facilities should perform either in-line continuous
turbidity monitoring and recording on each filter, or
manual monitoring of each filter effluent on an hourly
basis. Less frequent monitoring would likely miss
turbidity spikes.
The case studies indicated that plant operators and
administrators generally did not recognize the serious
public health impacts of short-term digressions in
treated water quality. For example, at Plants 2, 4, and
6, plant operators and administrators did not take
immediate action to correct short-term breakdowns
even when they were aware of performance problems.
A key finding of the studies is that, because most
small water treatment facilities are only operated for 8
or 12 hr/day, they tend to have excess capacity. The
excess capacity results from being able to operate at
a lower flow rate for longer periods of time, enabling
many small plants to address unit process limitations.
For example, Plant 8 operated at its 16-L/s (250-gpm)
capacity for only several hours each day even when
turbidity levels in the surface water exceeded the
plant's treatment capability. The CPE projected that,
by reducing the plant flow to 8 Us (125 gpm) and
operating for up to 12 hr, the plant could treat
turbidities of any anticipated level. Likewise, at Plant
5, reducing the plant flow from 132 L/s (2,100 gpm) to
69 L/s (1,100 gpm) relieved a severe air binding
problem and enabled the plant to operate
successfully. At Plants 8 and 5, water demands were
met even with reduced plant flows; however, this may
not always be the case.
The case studies revealed that proper control of the
filtration process is key to improving plant
performance.
At Plant 2, filter rate controllers malfunctioned
causing the filter effluent valves to open and close
every few seconds. The filter flow rate changed
from 0 to 63 L/s (1,000 gpm). The filter effluent
turbidities also varied, indicating that particles
previously filtered were washed through the filter to
the clearwell. While plant staff knew that the valve
10
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Figure 3-1. Plant 2 turbidity profile.
Turbidity, NTU
6 -r
5 -
4 -
3 -
2 -
1 -
FILTER BACKWASH
-i r
100 200 300
MINUTES AFTER START OF SPECIAL STUDY
400
Figure 3-2. Plant 12 finished water turbidity profile.
1
in
OJ
ru - -
in
Present
Requi rement
Future
Requi rement
i i i i 1 n i i | i i i i 1 i i i i | i i n | i i i i | i i i i | i i i i I i i i i I i i i i I i i i i|
SEP88 OCT NOV DEC JRN89 FEB MflR RPR MRY JUN JUL RUG SEP OCT
11
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"jumped around," they did not realize that it
affected filter performance. The studies clearly
indicate that filter rate controllers must be properly
maintained to allow the filters to operate correctly.
At Plant 2, when plant staff removed one filter for
washing, the entire plant flow was directed to the
remaining filter. This caused severe turbidity
breakthrough.
At Plant 8, filters were "started dirty," causing a
serious detrimental effect on filtered water quality.
At Plant 2, operators changed the flow rate without
adjusting chemical feed rates. This resulted in
improper feed of coagulant chemicals and
subsequent degradation in finished water quality.
The case studies revealed that all 13 plants
implemented only limited process control efforts. Little
testing or data interpretation, both of which are
imperative to making informed operating decisions,
were conducted. As a result, improper operating
practices, such as bumping filters or waiting too long
to backwash filters, were widespread. For example, at
Plant 12, water was allowed to drop from the troughs
onto the filter media, which clearly violates basic
principles of filter operation.
CCP Findings
CCPs were implemented at 2 of the 13 plants. The
objective of the CCP studies was to determine if the
approach could improve plant performance and enable
the plants to comply with the SWTR without major
capital improvements. The specific findings of the
CCPs, which were conducted at Plants 1 and 5, are
also presented in Section 4.
Implementation of these CCPs enabled both plants to
meet the future finished water turbidity requirements
of the SWTR by implementing process control
programs and providing operator training. The
approach demonstrated the potential for drinking water
treatment facilities to meet regulatory requirements
through improved operation, maintenance, and
administration rather than major capital improvements.
At Plant 5, city administrators originally had planned
to spend approximately $1 million to construct
sedimentation basin facilities and related
improvements. They felt the major capital
improvements were necessary to ensure that the
plant could achieve compliance with the
forthcoming SWTR turbidity requirements. After the
CCP was conducted, however, construction of the
improvements was delayed until such time that
water demands required that the plant operate at
higher rates. As a result of the CCP, plant staff
developed increased confidence that, by
implementing process controls, the plant could
produce excellent water quality despite high raw
water turbidities. The CCP also revealed that
accurate coagulant doses could be selected by
using the jar test/filter paper procedure.
At Plant 1, the CCP dramatically improved plant
performance. Turbidity removal in the reactor
clarifiers was improved and stabilized, and chemical
requirements were minimized. The improvement
resulted from a combination of process control and
monitoring, as well as several major process
adjustments.
To achieve the desired results, CCPs should be
implemented over a period of at least 6 months, since
time is necessary to implement process control
programs, purchase equipment, provide training, and
document stable finished water quality for variable raw
water conditions. The case studies demonstrated that
process control programs improved the performance
of individual unit processes at the two plants, thereby
leading to improved finished water quality.
Overall Factors Limiting Performance
A CPE team evaluated 65 performance-limiting factors
at each of the 13 plants; the top 10 performance-
limiting factors are presented in Table 3-2. It is
important to remember that no one factor was
responsible for limiting plant performance, but rather a
unique combination of factors contributed to
performance problems.
Table 3-2.
Rank
Top Ranking Performance-Limiting Factors
Identified at 13 Facilities
Factor
No. Plants Category
Operator Application of
Concepts and Testing to
Process Control
13
Operations
2
3
4
5
6
7
8
g
10
Process Control Testing
Process Controllability/
Flexibility
Disinfection
Sedimentation
Staff Number
Filtration
Policies
Flocculation
Maintenance
11
13
9
10
7
7
7
6
7
Operations
Design
Design
Design
Administration
Design
Administration
Design
Maintenance
The highest ranking performance limiting factors fell
in the operations category, and were related to the
inability of plant staff to respond to water quality
changes with appropriate chemicals in appropriate
doses. In addition, plant staff frequently made
improper operating decisions because they lacked
understanding of unit processes and associated
controls. Compounding these problems was a lack
12
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of process control testing programs at all but two of
the plants.
Design factors represented 5 of the performance
limiting factors in the top 10 list. Process
controllability and flexibility was the highest ranked
design limitation. It was cited most frequently
because of limitations in type and location of
chemical feed options, and in control aspects such
as filter- regulating valves or plant flow control
valves. The CPE team noted that minor
modifications could address these performance
limiting factors at the facilities.
Disinfection facilities were identified as a
performance limiting factor at 9 plants because of
inadequate detention time in clearwells or
transmission lines. The SWTR will require a plant to
provide a certain CT value, which is obtained by
multiplying the disinfectant concentration by the
actual contact time. Most of the plants relied on
unbaffled clearwells to provide most of the required
detention time. These clearwells were projected to
provide inadequate CT because of expected severe
short circuiting. However, modifications to the
clearwells, such as installing baffles, may allow
these plants to meet the CT requirements of the
SWTR. Findings of disinfection inadequacy were
based on the CPE team's estimates of the
allowable contact time at each plant. No thorough
hydraulic analyses, as required by the SWTR,
could be conducted within the scope of this project.
The identification of disinfection inadequacy was
tentative and is meant as a signal that current
operation might not be adequate to meet the
disinfection requirements to be established by each
State.
Sedimentation basin design was identified as a
performance-limiting factor at 10 plants. The impact
was periodic and seasonal during high turbidity or
high- demand episodes. The CPE team projected
that improved operation could minimize the impact
that the marginal basins had on plant performance
(for example, longer run times at lower flow rates or
improved coagulation control).
Filters presented problems at 7 of the facilities. The
CPE team identified this factor because of air
binding (2 plants), backwash limitations (2 plants),
and possible filter underdrain or support gravel
problems (three plants). The team felt that the air)
binding and backwash limitations could be'
minimized or overcome by improved operational
practices, and that the underdrain or support gravel
damage could have been avoided if the operations
personnel had better understood the filtration
process. This damage appeared to be caused by
introduction of air or by excessive instantaneous
hydraulic load at the beginning of a backwash.
Flocculation capability was identified as
performance limiting at 6 plants because of limited
basin volume and lack of staging. The CPE team
concluded that improved operations could minimize
the impact of this factor (for example, lowering
hydraulic loadings, installing baffles, modifying
coagulants).
Administrative factors (including staff number and
administrative policies) also were included in the
top 10 list. An inadequate number of staff to
properly run the facilities was noted at 7 plants.
This deficiency was critical considering the need to
add a process control program and associated
responsibilities at these plants. Frequently,
administrators were unaware of operating
requirements, or had set water rates too low to
maintain adequate treatment or establish a self-
sustaining utility. Few administrative personnel
understood the severity of short-term excursions
from high quality treated water.
Maintenance factors were identified as impacting 7
of the plants. Operators who lacked understanding
of process operations abandoned many of the
automatic and/or manual control systems at the
plants. The CPE team identified several facilities
where maintenance activities were completely
neglected, sometimes due to administrative
indifference. The team concluded that improved
understanding of operations and maintenance,
coupled with an improved administrative attitude,
could lead to improved plant performance.
13
-------
-------
SECTION 4
CASE HISTORIES
The following case histories provide a detailed summary of the results from each of the 13 CPEs on which
this report is based. Each case history consists of a facility description, results of the Major Unit Process
Evaluation and Performance Assessment, and a discussion of the factors found limiting the plant's
performance. The applicability of a CCP is also discussed for each plant as are the results of the CCPs
completed at two plants. These CPEs were completed as part of the project to develop and formalize these
procedures for water treatment plants. Some aspects of the procedures were refined as more CPEs were
completed. As the procedures evolved through these refinements, some of the ways in which the results are
presented have changed. Some inconsistencies between the presentation of the results of the different case
histories, therefore, may be observed.
Plant 1
Facility Description
Constructed in 1974, Plant 1 is owned and operated
by the city and serves approximately 10,000 persons,
with no significant industrial water users. It consists of
a pre-sedimentation basin followed by conventional
treatment and is used as a softening facility during
winter months. Average daily flow for a 12- month
period was 66 L/s (1.5 mgd), with an average daily
flow during the peak month of 131 L/s (3 mgd). The
plant includes the following unit processes (see Figure
4-1):
Three constant-speed, raw water pumps: two 25-
hp, 126-L/s (2,000-gpm) and one 15-hp, 91-L/s
(1,450-gpm)
8.7 million-L (2.3 mil-gal) earthen pre-sedimentation
basin
Three 15-hp, 113-L/s (1,800-gpm) constant-speed,
low-service pumps
Chemical addition (alum, lime, and Dycafloc 587-C)
Two 17.7-m x 17.7-m (58-ft x 58-ft) upflow
clarifiers, 6.4 m (21 ft) and 6.0 m (19.8 ft) deep
Recarbonation with liquid carbon dioxide
Four 7.6-m x 7.6-m (25-ft x 25-ft) dual media filters
1.1 million-L (300,000-gal) clearwell
Disinfection
Fluoridation (sodium silica fluoride)
Sludge removal and thickening
Sludge drying beds
Three high-service pumps: 100, 113, and 157 L/s
(1,600, 1,800 and 2,500 gpm)
The three raw water pumps transfer water from the
nearby river through a 61-cm (24-in) line to the pre-
sedimentation basin. The three low-service pumps lift
the water from the pre-sedimentation basin
approximately -18 cm (7 in), so that it can flow by
gravity through the plant's unit processes.
Powdered activated carbon is added to the water in
the pre-sedimentation basin for taste and odor control
and a cationic polymer is injected following the raw
water pumps. Alum and lime are added in the
flocculation area of the two 22-L/s (500,000-gpd)
solids contact clarifiers.
The clarifiers are square with circular sludge removal
mechanisms. Prior to the clarifiers, water from a 14-
L/s (220- gpm) "soda well" is pumped into the raw"
water stream. Hydraulic conditions cause an uneven
split of this softer water between the two clarifiers.
Water flows through the clarifiers to a recarbonation
basin, where the pH is lowered, and onto four dual
media filters. From the filters, the finished water flows
into the clearwell. Chlorine and fluoride are added to
the water as it; enters the clearwell. The three high-
service pumps deliver finished water to the distribution
system.
15
-------
Figure 4-1. Plant 1 process flow diagram.
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16
-------
Major Unit Process Evaluation
Figure 4-2 illustrates the assessed capacity and
projected performance of each of the plant's major
unit processes in a performance potential graph. The
vertical broken lines indicate the annual average flow
of 70 L/s (1.6 mgd), the peak monthly flow of 131 Us
(3 mgd), and the design capacity of 307 L/s (7 mgd).
As Figure 4-2 shows, the raw water pumps, low-
service pumps, filters, and high- service pumps are
rated at the 307-L/s (7-mgd) plant design flow.
Potential capacities of the pre-sedimentation basin
and the clarifiers are rated at less than design.
The pre-sedimentation basin was derated because of
short circuiting through the basin and no capability to
add coagulant aids. Also, return of backwash water to
the effluent end of the basin results in excessive
turbidity levels in the raw water. The basin was rated
above the peak monthly flow of the plant.
The clarifier/flocculator was rated at 136 L/s (3.1 mgd)
with one unit in service and 272 L/s (6.2 mgd) with
both in service. The corner sweeps on the sludge
mechanisms have failed allowing excessive amounts
of sludge to build up in the basin corners. Sloughing
of the sludge coupled with inconsistent weir elevations
has resulted in periodic solids loss. The clari-
flocculators were derated because of these
conditions.
Performance Assessment
Plant 1 is currently required to produce finished water
with turbidity levels less than 1.0 NTU and with free
chlorine at levels that will ensure less than 0.2 mg/L at
all points in the distribution system. Fluoride is added
to achieve a 0.9-1.1 mg/L residual in the-finished
water. A comparison of plant monitoring data with
state requirements indicated the plant was operating
in compliance with applicable regulations. A review of
operating records, however, indicated numerous
excursions of filter effluent turbidities above
acceptable levels.
The SWTR will require plants to demonstrate by
regular turbidity monitoring or constant recording
turbidimeters, turbidity at less than 0.5 NTU greater
than 95 percent of the time. Additionally, theoretical 3-
log removal and/or inactivation of Giardia cysts and 4-
log removal and/or inactivation of enteric viruses must
be demonstrated.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis are
summarized below in order of priority.
1. Operator Application of Concepts and Testing to
Process Control - Operation: Operation of the
plant is maintenance rather than process control
driven. Priorities need to be established that allow
process control to be integrated into the daily
routine of the plant staff. This involves collecting
additional process control data and interpreting
the data to direct process control that optimizes
plant performance.
2. Process Control Testing - Operation: The lack of
process control testing has resulted in incomplete
data being collected to determine the level of
plant performance. In addition, it is probably
masking periods of production of poor quality
finished water. Items of particular concern are lack
of turbidity testing of raw water and water from the
clarifiers, and continuous monitoring of individual
filter effluent. Plant data indicate that filter effluent
"spikes" were occurring, but it was not possible to
determine their severity or duration.
3. Process Automation - Design: There is a need for
continuous monitoring and recording turbidimeters
on the raw water, each filter, and the clearwell.
The factors identified as having either a minimal effect
on a long-term repetitive basis or a major effect on a
periodic basis were prioritized and are summarized
below.
1. Process Flexibility - Design: More flexibility is
necessary in types of chemicals added and points
of chemical addition. At the time of the evaluation,
alum and lime were added to the flocculation
portion of the clarifier and polymer was added
after the low-service pumps. There was no
process available to feed a filter aid or flocculent
aid. Flexibility to move the alum feed to a point
with greater mixing could reduce the alum feed
rate and may also allow the flocculator speed to
be reduced to better optimize flocculation. The
ability to add a filter aid would improve filter
performance.
2. Lack of Standby Units - Design: There is no
standby backwash pump. If the existing pump
fails, the plant is out of operation until it can be
repaired or replaced.
3. Preliminary Treatment - Design: Obvious problems
exist with the pre-sedimentation basin, including
no chemical feed (except carbon) to the basin,
short circuiting,^ backwash water fouling of the
intake area of the low-service pumps, and
difficulty cleaning the pre-sedimentation basin.
4. Staff Number - Administration: The current major
emphasis is on maintenance; more time must be
spent on process control to improve performance.
In addition, the superintendent is working extra
shifts to keep the plant operating. At least two
additional plant operators are necessary for both
operations and maintenance activities to be
adequately addressed.
17
-------
Figure 4-2. Plant 1 performance potential graph.
Unit Process
Flow, mgd
123456789
10
Raw Water Pumps1
Pro-sedimentation2
Low-service Pumps3
Clari-flocculator"
SOR, gpd/sq ft (1 unit)
SOR, gpd/sq ft (2 units)
Filters*
HLR, gpm/sq ft (1 filters)
HLR, gpm/sq ft (2 filters)
High-service Pumps6
329
154
0.3
0.6
656 9(.
329 4S
0.6 0
1.2 1
i-
32 656 820 984
8 1.1 1.4 1.7 2
5
.0
Annual Avg. Peak Month Design
6/86-6/87 5/86-5/87 Capacity
1 7.8 mgd with individual pumps - assumes design capacity with continued operation.
2 Assumes run 2 filters at 2 gpm/sq ft and backwash 2 filters at end of day.
3 7.8 mgd with individual pumps - assumes design capacity with continued operation.
* Rated at 800 gpd/sq ft for turbidity removal - use 1,000 gpd/sq ft for softening capacity (weir imbalance).
s Rated at 2 gpm/sq ft.
8 2.5 mgd with individual pumps - assumes design capacity with continued operation
5. Sedimentation - Design: The corners of the
clarifiers need to be grouted to prevent buildup of
sludge in the basins and the flow through the
weirs needs to be balanced so that resulting
hydraulic gradients do not impact the quality of
the water from the clarifiers. The combination of
un-level weirs and sludge accumulation in the
basin corners has led to periodic solids loss in the
effluent, which severally degrades plant
performance.
6. Disinfection - Design: Short circuiting of finished
water through the clean/veil results in inadequate
contact time for proper disinfection. This problem
will be amplified with colder water and higher pHs.
7. Return Process Streams: Return of the backwash
water to the pre-sedimentation basin near the low-
service pumps' suction negatively impacts raw
water quality.
In addition to the above major factors limiting
performance, other factors were noted during the
evaluation as having a minor effect on performance.
Action taken to address these factors may not
noticeably improve plant performance, but may
improve the efficiency of plant operation:
The pre-sedimentation basin is not designed to
handle high turbidities caused by runoff and ice
jams.
Flash mixing of chemicals appears inadequate
The ability to sample the sludge return and the
sludge concentration within the clarifiers (top to
bottom) is inadequate.
Projected Impact of a CCP
The CPE indicated that operator training through a
CCP would be beneficial for improving process
stability and finished water.
CCP Results
A CCP was initiated. Monitoring of the two reactor
clarifiers during the CPE phase had revealed problems
18
-------
Figure 4-3. Settled water turbidities from the reactor clarifiers at Plant 1.
Turbidity, NTU
12
11
10
9
8
7
6
5
4
3
2
1
0
14-Mqy-89
28-ttoy-89
Q BASIN #2
09-Jul-89 0$-Aug-89
25-Jun-89 23-Jul-89
' + BASIN #1
with clarifier solids control. Thus, the CCP efforts
began by expanding process control in the clarifiers.
Each clarifier was taken out of service so that several
feet of anaerobic lime sludge that had accumulated in
the basins could be removed.
Figure 4-3 shows the finished water turbidity from the
two clarifiers from the time the cleaning operation was
completed in May until the CCP was concluded in
August. The basins' settled water turbidities gradually
improved and stabilized at 1 to 2 NTU; both basins
exhibited equal performance. Activities that
contributed to this consistent performance included
controlled flow splitting, equalized chemical doses to
each basin, and shutting off of a well that was
contributing a disproportionate amount of flow to basin
2. The reactor clarifiers achieved this performance
despite variable influent turbidities to the basins from
the pre-sedimentation pond, as shown in Figure 4-4.
Most importantly, the improved reactor clarifier
performance "carried over" to improve the
consistency of turbidity removal by the filters. Figure
4-5 shows the overall plant finished water turbidity,
which stabilized at less than 0.2 NTU since the end of
June 1989, coinciding with stable performance from
the contact clarifiers. The improved performance was
achieved despite an increase in treated water volume
and a gradual increase in turbidities from the pre-
sedimentation basin during the last month of the CCP.
The CCP resulted in dramatic improvement of plant
performance without major capital improvements.
Process control and monitoring activities, coupled with
several major process adjustments, improved and
stabilized turbidity removal in the reactor clarifiers.
19
-------
Figure 4-4. Effluent turbidity from the presedimentation pond for Plant 1.
Turbidity,
100
NTU
14-!
Mqy-8911-Jun-89I 09-Jul-89T 06-Aug-S9
28-Hay-89 25-Jun-89 23-Jul-89
Figure 4-5. Finished water turbidity profile from Plant 1.
Turbidity, NTU
.8
.7
.6
.5
.4
.3
.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Future Requirement
14-May-89 11-Jun-89 09-Jul-89 | 06-Aug-89
28-May-89 25-Jun-89 23-Jul-89
20
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Plant 2
Facility Description
Plant 2, constructed in 1931 and expanded and
upgraded in 1976, has approximately 1,000 service
connections and no significant industrial water users.
It consists of a conventional treatment process
including flash mix, flocculation, sedimentation, and
filtration, and no pre-sedimentation. Source water is
provided by the nearby river.
Plant records for a 12-month period show daily water
production to be 1.1-6.1 million L (0.3-1.6 mil gal).
Flow records are obtained from the plant finished
water meter and do not include water used for filter
backwash. During the CPE, water was produced over
an 8-hr day at an effluent flow rate of about 89 L/s (2
mgd); peak effluent flow was 131 L/s (3 mgd). Plant
influent flow is not measured because the raw water
meter is inoperable. Plant 2 includes the following unit
processes (see Figure 4-6):
Two vertical turbine raw water pumps rated at 76
and 69 L/s (1,200 and 1,100 gpm), and one 28-L/s
(450-gpm) engine driven raw water pump
Chemical addition of alum, polymer, and lime with
in-line mechanical flash mix for the alum
Two 206,430-L (54,540-gal) parallel flocculation
basins with two variable speed turbine mixtures in
parallel
Two 666,160-L (176,000-gal) sedimentation basins
with tube settlers over half their surface area
Three 3.4-m x 4.9-m (11-ft x 16-ft) mixed media
filters with Leopold underdrains
Gas chlorination system
204,390-L (50,400-gal) clearwell
Two centrifugal high-service pumps rated at 72 and
94 L/s (1,150 and 1,500 gpm), and one standby
natural gas driven vertical turbine pump rated at 27
L/s (425 gpm)
Water flows by gravity to a wet well through either a
shallow culvert near the bank of the river or through a
second pipe extending toward the center of the river
at an unknown distance and depth. The vertical
turbine pumps deliver water to the plant from the wet
well. The turbine pump supplies water from the
surface intake. A float control in the clearwell initiates
the raw water pumps.
Alum is added to the raw water prior to an in-line
mechanical rapid mixer; lime and polymer are added
downstream of the mixer prior to the flocculation
basins. Chemical addition is not flow paced, although
the influent flow varies because raw water pumps are
initiated and terminated several times a day. After
chemical addition, the water flows to two parallel
flocculation basins with two parallel- operating variable
speed turbine flocculators. Subsequently, water flows
to two sedimentation basins equipped with tube
settlers. During the evaluation, flow did not appear
evenly split between the two
flocculation/sedimentation treatment trains, and the
clarifier weirs were uneven.
Sludge is manually removed from the sedimentation
basins approximately once a year.Following
sedimentation, the water flows through a weir to three
mixed media filters with Leopold underdrains.
Powdered activated carbon is added once a day to
the water prior to filtration. Filtration rates are
automatically adjusted by filter water level floats that
control the filter effluent valves. At the time of the
evaluation, one filter was out of service because of an
inoperable effluent control valve. Another filter effluent
control valve was malfunctioning and was observed to
readjust the flow rate by over 69 L/s (1,100 gpm)
repeatedly within a few minutes.
The filters are normally backwashed once a day; the
process is initiated manually but at automatically timed
intervals and includes surface washing. The backwash
rate can be set as high as 189 Us (3,000 gpm).
Filtered water is disinfected with chlorine and is stored
in the clearwell. The three high-service pumps deliver
the water to the distribution system.
Spent filter backwash water flows by gravity to a
sedimentation basin, which overflows to the raw water
wet well. Each backwash sedimentation basin has the
capacity for one backwash before excessive solids
overflow the effluent weirs and return to the raw water
wet well. The backwash sedimentation basins are
normally cleaned once a year.
Sludge from the flocculation, sedimentation basins,
and backwash water sedimentation basins are
pumped to two sand drying beds. The dried sludge is
disposed of at the landfill.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
7. The flows listed across the top of the graph are the
maximum at which the plant can operate while
remaining in compliance with applicable regulations.
Neither the raw water pumps nor the high-service
pumps were rated because the condition of the
impellers and the actual pump output were not known.
The flash mix was rated at 131 L/s (3 mgd), where it
can produce a G value of approximately 3,000 sec-1.
The in-line mechanical mixer would probably be
limited by water velocity in the pipeline rather than
mixing capability.
21
-------
Figure 4-6. Plant 2 process flow diagram.
-ซ 6
.llrf
22
-------
Figure 4-7. Plant 2 performance potential graph.
Unit Process
Flow, mqd
2
Raw-water Pumps
Flash Mix
Flocculation1
Detention time, min
Sedimentation2
SOR, gpd/sq ft
Filtration?
HLR, gpm/sq ft
Disinfection
Chlorination
Contact Time4
High-service Pumps
Not Rated
78
1,287
1.3
Not Rated
26
Present Plant
Max. Flow
Design
Flow
1 Rated at 45 min because of single stage.
2 Rated at 2,000 gpd/sq ft - may be able to use process control to increase capacity. Also rated on summer water quality, but may be
able to direct filter in winter.
3 Rated at 4 gpm/sq ft - media and underdrain integrity, need to be verified to justify this rating.
4 Based on 2-hr detention time
The flocculation basins were rated below the plant
design flow at 77 L/s (1.75 mgd) for a detention time
of 45 minutes, because the flocculation basins are
single-stage units. Altering the basins to provide
multiple-stage flocculation would better control floe
formation and justify increasing the basin capacity to
153 L/s (3.5 mgd).
The sedimentation basins were rated at 66 L/s (1.5
mgd), which results in a surface overflow rate of 81
m3/m2/d (2,000 gpd/sq ft) (based on tube settler area).
However, improved flocculation and process control
could increase this rating. Direct filtration might be an
option during winter months, which would decrease
reliance on the sedimentation basins for solids
settling.
The mixed media filters were rated at 131 L/s (3 mgd)
for a loading rate of 234 m3/m2/d (4 gpm/sq ft). With
precise process control, the filters could operate
successfully at up to 293 m3/m2/d (5 gpm/sq ft);
however, the media and underdrain integrity must be
verified to justify either rate. If further evaluation
indicates damage to the filter underdrain or support
gravel, the filters would be a major performance-
limiting factor.
The disinfection system was rated as two processes:
chlorination capacity and contact time. The
Chlorination capacity rating of 131 L/s (3 mgd)
indicates that the capacity of the feed unit is sufficient.
The contact time, however, was rated at only 26 L/s
(0.6 mgd), the maximum flow through the plant that
would provide the recommended 2-hr detention time.
The limited detention time provided at normal plant
flows compounds the importance of effective
performance of the other treatment processes for the
removal of pathogens.
23
-------
In summary, the performance potential graph indicates
the plant should be operated at less than 66 Us (1.5
mgd) during periods of high raw water turbidity. Flow
rates above 66 Us (1.5 mgd) may be possible without
adversely affecting finished water quality; however,
filter run times will probably be significantly reduced
because of excessive solids loading, thereby reducing
total plant capacity to 66 Us (1.5 mgd).
During winter months, if raw water turbidities allow
effective direct or in-line direct filtration, plant capacity
may be able to increase to between 66 and 131 Us
(1.5 and 3.0 mgd), depending on whether or not
flocculation is required for successful operation.
Performance Assessment
A review of the finished water quality monitoring data
indicated the plant has been operating in compliance
with the current turbidity Maximum Contaminant Level
(MCL) of less than 1.0 NTU on a monthly average.
The plant has, however, had periodic excursions
above 1.0 NTU. The monitoring data also indicate the
plant may have difficulty meeting the SWTR turbidity
maximum of 0.5 NTU for 95 percent of the time (as
measured every 4 hr of water production). Figures 4-
8, 4-9, and 4-11 show effluent turbidities obtained
through special studies. Figures 4-10 and 4-12 show
turbidities from plant data.
Investigation of the filter media in the out-of-service
filter bed revealed that the media was clean with no
evidence of mudball formation. However, the
evaluation team discovered numerous depressions of
up to 10 cm (4 in) in the surface of the media, and by
probing the filters found that support gravel had
migrated and mounded. The operators mentioned that
sand, anthracite, and garnet had been removed from
the clean/veil during cleaning. Measurement of the
media pile that had been removed from the clearwell
indicated that approximately 0.2 m3 (7 cu ft) of filter
media had passed through the support gravel. The
migration of the support gravel, depressions in the
surface of the filter bed, and the passing of 0.2 m3 (7
cu ft) of media through the filter all indicate serious
damage to the filter support gravel and media.
Typically, this type of damage occurs when air is
introduced into the backwash water.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis are
summarized below in order of priority.
1. Operator Application of Concepts - Operation:
Process control is needed so that operators
respond directly to raw water quality changes. At
the time of the evaluation, finished water quality
was fluctuating drastically with periods of poor
finished water production. Figures 4-8 through 4-
11 show actual plant data indicating the variability
in water quality and the extremely poor water
produced, evidenced by the filtered water turbidity
of 46 NTU from Filter 3 when Filter 1 was
backwashed (figues 4-8 and 4-9). Plant operations
staff need to vary coagulant and flocculant
dosages and to change plant water flow rates
when backwashing filters in response to raw water
of variable quality.
2. Process Control Testing - Operation: Testing to
monitor the treatment process is inadequate to
detect problem areas and indicate necessary
adjustments. This lack of testing allows periods of
extremely poor water to go undetected and
unconnected as shown in Figure 4-12. At a
minimum, additional jar testing and turbidity
measurements of the raw water, sedimentation
basin effluent, and filter effluent will be required to
indicate appropriate plant chemical dosages and
flow rate adjustments.
3. Maintenance: Preventive maintenance is lacking at
the plant. The plant equipment is maintained on a
crisis basis and plant performance is directly
compromised. Major treatment components were
out of service during the evaluation and have
evidently not been repaired for up to several
years. Examples of equipment in need of repair or
out of service include the raw water meter, filter
effluent control valves, raw water pump, and alum
feeder flocculator paddles.
4. Staff Number - Administration: The present
staffing level does not allow the water plant to be
adequately operated or maintained. A minimum of
two additional staff members are needed to
sufficiently cover the utility needs. With adequate
staff, one operator could focus on plant process
control and other utility employees could
specialize in either water or wastewater treatment.
5. Familiarity with Plant Needs - Administration: Plant
administration needs to become more familiar with
the requirements of the plant. Better
understanding of the plant's requirements would
help garner the administrative support necessary
to operate and maintain the plant properly.
6. Filtration - Design: A limited evaluation of the
filters revealed potentially serious problems in the
support gravel. Depending on the outcome of a
subsequent detailed evaluation of filter integrity,
the filters may be found adequate to 131 Us (3
mgd). However, if the filters are found deficient,
they would probably have to be repaired before
the plant could produce consistent high quality
finished water on a continuous basis.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
are summarized below.
1. Pay - Administration: The extremely low pay scale
and lack of employee incentives will make it
24
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Figure 4-8. Filter 3 turbidity profile, June 8,1988 - Plant 2.
Turbidity, MTU
6 -
5 -
3 -
2 -
46.0
Noon
1:00
2:00
3:00
Time of Day
4:00
Filter #1
Backwash
Clearwell
Current Regulatory Maximum - 1.0 NTU
Proposed Regulatory Maximum - 0.5 NTU
6:00
Figure 4-9. Filter 1 turbidity profile, June 8,1988 - Plant 2.
Turbidity, NTU
6 i-
Current Regulatory Maximum -1.0 NTU
Proposed Regulatory Maximum - 0.5 NTU
Filter #1
Backwash
Desired Operating - 0.1 NTU
Clearwell
11:00
12:00
1:00
2:00 3:00
Time of Day
4:00
500
6:00
25
-------
Figure 4-10. Plant 2 performance.
Turbidity, NTU
1.2 r-
1.0
0.8
0.6
0.4
0.2
Future Regulatory Maximum = 0.5 NTU
I
I
10
15 20
Days
2.0
Desired Operating = 0.1 NTU
I I I
25
30
35
Figure 4-11. Filter effluent turbidities profile, June 8,1988 - Plant 2.
Turbidity,
0.5
0.4
0.3
0.2
0.1
NTU
Future Regulatory Maximum = 0.5 NTU
Filter #3 ~
Desired Operating = 0.1 NTU
I
I
4 6
Minutes
10
26
-------
Figure 4-12. Plant 2 performance - May 1988.
Turbidity, NTU
1.2 i-
1.0
0.8
0.6
0.4
0.2
1.6 1.6
Future Regulatory Maximum = 0.5 NT
Desired Operating = 0.1 NTU
10
15
Days
20
25
30
difficult to retain present employees and to attract
additional qualified help.
2. Turbidity/Pre-sedimentation - Design: Excessive
turbidity levels during portions of the year and
fluctuations during high demand periods have
degraded effluent quality. Pre-sedimentation would
minimize turbidity fluctuations and result in a more
consistent raw water quality. Continuing
operations without a pre-sedimentation basin may
require reducing plant flow rates during high
turbidity periods.
3. Sedimentation - Design: Surface overflow rates at
flows above 66 L/s (1.5 mgd) may not allow
adequate settling of the sludge. Poor settling can
cause excessive solids loading to the filters and
subsequently degrade filter efficiency. Uneven
overflow weirs also cause poor distribution of
water within the sedimentation basin, further
impairing settling. Manual sludge removal twice a
year may be inadequate to prevent solids
carryover from the sedimentation basins. This
practice is also operator intensive.
4. Hydraulic Loading - Design: Fluctuations in plant
flows due to cycling of constant-speed, raw water
pumps during high demand periods require
additional operator attention to maintain finished
water quality. An influent flow control valve would
allow plant flow rates to be adjusted more
gradually and set at various rates.
5. Disinfection - Design: The lack of a standby
chlorinator, mixing, proportional feed capability,
contact time, and automatic switchover could
result in inadequate disinfection on a periodic
basis.
6. Process Automation - Design: Effluent
turbidimeters with recorders on each filter effluent
would be beneficial to monitor water quality.
Without such continuous monitoring, an operator
would have to take frequent measurements (i.e.,
hourly) to monitor plant performance.
7. Chemical Feed - Design: The carbon feeder
should be returned to service to replace manual
addition. The capability to add two polymers would
be desirable, with additional flexibility in chemical
feed points. A backup alum feeder is also needed.
8. Flocculation Basins - Design: The single-stage
flocculation basin makes control of proper floe
formation difficult. The retention time is adequate
and minor modifications may allow two-stage
operation with variable energy input in each stage.
9. Process Controllability - Design: Chemical feeders
should be flow paced or manually adjusted to
27
-------
complement and control raw water quality
changes.
10. Standby Units - Design: No standby units are
available for critical process components,
including backwash pump, alum feeder, and
chlorinator.
11. Working Conditions - Administration: Conditions at
the water plant discourage staff from spending
time at the plant and encourage neglect. Provision
of a comfortable climate controlled working area
would improve operator morale.
In addition to the above major factors limiting
performance, other factors were noted during the
evaluation as having a minor effect. Action taken to
address these factors may not noticeably improve
plant performance, but may improve efficiency in plant
operation:
Preliminary treatment: Grit in the raw water wet well
and the lack of screens on the intake piping
produce operational problems because of silt and
debris accumulation.
Flow proportioning to units: Raw water flow to the
sedimentation basins was not evenly proportioned.
Operators can control the distribution of flow to the
units by frequently adjusting valves located in the
sedimentation basin influent piping.
Projected Impact of a CCP
Results of the CPE indicate performance to be
severely limited by a number of administrative, design,
maintenance, and operations factors. Every major unit
process was identified as a performance-limiting
factor. The evaluation team reached a consensus that
significant improvements in water quality could likely
be achieved with a CCP, but that major capital
expenditures may also be required for the plant to
meet the proposed finished water quality criteria.
Many of the unit process limitations described in the
performance potential graph could be eliminated if the
plant were to be operated at a lower capacity than the
present summer water demand, which appears
excessive. Water conservation measures and lowered
water demands together with a CCP were
recommended.
28
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Plant 3
Facility Description
Plant 3 is owned and operated by the city.
Constructed in 1950 and expanded and upgraded in
1975 and 1976, it currently serves approximately
5,000 people with no significant industrial water users.
The plant uses a conventional treatment process
consisting of flash mix, flocculation, sedimentation,
and filtration.
Plant records for a 12-month period indicate that the
average amount of water treated daily was 41 L/s
(0.94 mgd), with a minimum of 22 L/s (0.5 mgd) and a
maximum of 114 Us (2.6 mgd). These daily flows
were pumped through the plant in less than 24 hr and
therefore do not indicate the operational capacity of
the plant. It is typically operated at three standard
rates - 69, 101, or 202 L/s (1,100, 1,600, or 3,200
gpm) - for less than 24 hr. Plant 3 includes the
following unit processes (see Figure 4-13):
Three vertical turbine raw water pumps: two 25-hp,
110-L/s (1,750-gpm) and one 15-hp, 63-L/s (1,000-
gpm)
Chemical addition (alum and polymer) with an in-
line mixer
302,800-L (80,000-gal) flocculation basin with a
variable speed vertical mixing unit
Two sedimentation basins (each 4.1 m x 18.3 m,
3.7-m deep [13.5 ft x 60 ft, 12-ft deep])
Three mixed media rapid sand filters with Leopold
underdrains
Gas chlorination system
246,000-L (65,000-gal) clearwell
Four vertical turbine finished-water pumps: two
200-hp, 94-L/s (1,500-gpm), one 100-hp, 38-L/s
(600-gpm), and one 50-hp, 22-L/s (350 gpm)
Raw water flows by gravity through three 46-cm (18-
in) diameter perforated pipes located beneath the
source creek into a raw water wet well. The three raw
water pumps deliver water from the wet well to the
flocculation basin.
Alum and polymer are added to the flow prior to the
flash mix. The plant's in-line mechanical flash mixer
was not in use at the time of the site visit because of
maintenance problems; therefore, the only chemical
mixing was caused by turbulence in the line at nearby
elbows.
After chemical addition, the water flows into the
single-stage flocculation basin with a variable speed
vertical mixing unit that supplies up to a G value of 70
sec-1. Following flocculation, the water flows by
gravity into two parallel sedimentation basins equipped
with tube settlers. During the evaluation, the flow was
not evenly split between the two sedimentation basins.
Following sedimentation, the water flows to three
mixed media filters with Leopold underdrains. The
filters appeared to be in good con.dition, but some
chemical residue had accumulated on the anthracite.
These filters are typically washed at about 189 L/s
(3,800 gpm), which corresponds to 972 m3/m2/d (16.6
gpm/sq ft). Washing typically occurs at the end of the
day so that the filters start clean the following
morning.
The filtered water is disinfected with chlorine, then
flows into the clearwell, where the four high-service
pumps are available.
Sludge from the sedimentation basins and backwash
water from the filters are directed to two earthen
sludge settling ponds. At the time of the evaluation,
the plant was discharging overflow from the ponds to
the creek without a National Pollutant Discharge
Elimination System (NPDES) permit.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
14. As Figure 4-14 shows, the potential capacities of
the raw water pumps, high-service pumps, and filters
were rated at the 219-L/s (5-mgd) plant design flow.
The flocculation basin, sedimentation basins, and the
disinfection system were rated at less than plant
design flow. The single-stage flocculation basin was
derated because control of floe formation is more
difficult with a single-stage than with a multiple-stage
flocculation system. The sedimentation basins are
limited by a high surface overflow rate, which can
allow solids to be carried over to the filters. The
disinfection system was not considered adequate at
flow rates above 166 L/s (3.8 mgd), because the
clearwell and transmission lines provide inadequate
detention times at these rates.
The sludge settling ponds were not rated but were
determined inadequate at current flows, unless the
plant obtains an NPDES permit to allow discharge to
the creek. Without operational changes such as more
frequent cleaning of the ponds, the effluent quality in
the ponds may not meet typical permit requirements
(i.e., 30 mg/L total suspended solids and 1.0 mg/L
total dissolved aluminum).
Figure 4-14 indicates that the plant should be
operated at less than 101 L/s (2.3 mgd), if possible.
Short periods of increased flow may be possible
without adversely affecting finished water quality;
however, filter run times will probably be reduced
because of excessive solids loading. The plant may
be operated more hours at the 101 L/s (1,600 gpm)
29
-------
Figure 4-13. Process flow diagram of Plant 3.
Flash Mix Unit (Not in Service)
^
*
^v
s^~~ ^
\ 3 Mixed Media Filters
Clearwell
-o
4 High Service Pumps
3 Raw Water Pumps
-o
Sludge
Settling
Ponds
30
-------
Figure 4-14. Plant 3 performance potential graph.
Unit Process
Flow, mad
2 3
Raw-water Pumps1
Flash Mix2
Flocculation3
Detention time, min
Sedimentation4
SOR, gpd/sq ft
Filiations
HLR, gpm/sq ft
Disinfections
Contact time, min
High-service Pumps
Sludge Settling Ponds
1 5
926
Not Rated
58
1,852
72
36
- Inadequate at present flow
24
Current Annual
Avg. Flow
Present Daily7
Max. Flow
Design
Flow
1 Peak flow that plant can treat at worst water quality.
2 Out of service.
3 Based on detention time of 45 min and single stage.
4 Based on 2,000 gpd/sq ft.
5 Based on 5 gpm/sq ft.
6 Based on allowing 2 min of contact time in clwarwell and 18 min of contact time in 2,500 ft Of 18-in transmissin line.
7 Not based on 24 hr/day, so actual flows are higher
rate to overcome the limitation of the
flocculation/sedimentation basins. Also, when raw
water turbidities are low the plant may be operated in
a direct filtration mode, which eliminates the need for
sedimentation.
Performance Assessment
The city is currently required to produce finished
water with turbidity levels less than 1.0 NTU on a
monthly average and with free chlorine at levels that
will ensure a chlorine residual in excess of 0.2 mg/L at
all points in the distribution system. A review of
monitoring data indicated that the plant was operating
in compliance with the applicable regulations.
In the SWTR, the minimum requirements for finished
water turbidity are much more stringent. Plants need
to produce finished water with a turbidity less than 0.5
NTU more than 95 percent of the time, as measured
by regular daily monitoring or constant recording
turbidimeters. Additionally, the plant needs to
demonstrate theoretical 3-log removal and/or
inactivation of Giardia cysts and 4-log removal and/or
inactivation of enteric viruses. In order to meet these
regulations, surface water treatment plants need to
optimize process controls to minimize or eliminate
"spikes" of turbidity in the finished water at critical
times, such as immediately after backwash.
Performance-Limiting Factors
The following factor was identified as having a major
effect on performance on a long-term repetitive basis.
1. Sludge Treatment - Unit Design Adequacy: The
sludge holding ponds are currently discharging to
the creek, but the plant has no permit to allow this
31
-------
discharge. A letter from the Permits Section of the
Water Quality Bureau states that the plant must
apply for a permit, which will require certain
effluent limitations. Permit limitations may require
major modifications to the plant. Failure to obtain a
permit and to meet permit limitations could result
in sizeable fines being levied against the town.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
were prioritized and are summarized below.
1. Sedimentation - Unit Design Adequacy: The
surface overflow rate and weirs limit the
performance of the sedimentation basin. If the
plant were operated at a rate in excess of 101 Us
(2.3 mgd), the resulting high surface overflow rate
would not allow for adequate settling. Excessive
solids would be carried over to the filters, thereby
degrading filtration performance.
2. Flocculation - Unit Design Adequacy: The single-
stage flocculation basin makes control of proper
floe formation difficult. Controlling plant flows at
rates below 101 Us (1,600 gpm) may allow
additional detention time to compensate for the
lack of a multiple-stage unit.
3. Lack of Standby Units- Unit Design Adequacy:
There are no standby units for adding chlorine or
alum. Failure of either of these chemical feeders
would result in unacceptable finished water
quality, which may require the plant to shut down.
In addition, there is no spare backwash pump,
although, in an emergency, the distribution system
could provide limited backwash.
4. Application of Concepts and Testing to Process
Control - Operation: The plant performance could
be improved during periods of variable raw water
quality by application of a thorough process
control program. For example, more frequent jar
testing would provide data on which to base
chemical feed points. By monitoring turbidity from
the sedimentation basins several times each day,
chemical doses could be adjusted to optimize
sedimentation basin performance.
It would also be good practice to monitor the
turbidity of water from each of the filters. At the
present time, a daily turbidity value is being
recorded for water from the clearwell. This
measurement may mask higher turbidities coming
out of the filters. Significant breakthrough may be
occurring that would not be detected by the
present monitoring practice. With continuous
monitoring and recording of the turbidity of each
filter effluent, the increase in turbidity following
backwash could be observed along with the length
of time the elevated turbidity occurs. This would
indicate whether or not chemical addition has
been optimized.
The use of the flash mix unit, especially during the
times of the year when direct filtration can be
utilized, would probably reduce chemical usage.
Also, additional experimentation with polymer
products could result in the selection of more
effective coagulant/flocculent aids.
5. Policies - Administration: Administrative policy
limits the frequency with which the raw water
intake can be backwashed. As a result, the intake
pipes can accumulate a significant amount of silt
before backwashing, thus reducing the plant's
intake capability. More frequent backwashing
would eliminate these periodic limitations in raw
water supply.
6. Chemical Feed Facilities - Unit Design Adequacy.
Inability to feed a filter aid and/or flocculant aid
could result in poor plant performance during
periods of variable raw water quality.
7. Alternate Power - Unit Design Adequacy: There is
no standby power capability at the plant.
Therefore, water would not be supplied to the
distribution system during a power outage.
8. Hydraulic - Unit Design Adequacy: Low stream
flows and upstream water use have resulted in
periods when no raw water is available to be
pumped into the plant. Studies are presently
underway to incorporate in-stream or off- stream
storage to alleviate this problem.
In addition to the major factors limiting performance
discussed above, other minor performance-limiting
factors were noted during the evaluation. Action taken
to address these factors may not noticeably improve
plant performance, but may improve efficiency in plant
operation:
The lack of adequate disinfection could be a
problem when operating the plant above 166 Us
(3.8 mgd) because of the potential for short
circuiting of the clearwell and the limited detention
time provided in the transmission mains.
The lack of automatic continuous turbidity
monitoring and recording on the raw and finished
water from each filter requires the operations staff
to obtain this information manually on a periodic
basis. Not only does this require an additional time
commitment from the operators, but periodic
information is not as effective as a continuous
record.
The pay of the chief operator/superintendent is
approximately the same as the shift operators.
32
-------
This pay differential does not recognize the chief
operator's additional responsibility.
It is very difficult to sample the sludge discharge
lines from the sedimentation basins.
Additional process control testing should be done
to provide more of a basis for process control
decisions. Examples of further testing would
include more frequent analysis of raw water
turbidity and alkalinity, along with measurements
of turbidities of the water leaving each
sedimentation basin and filter.
Projected Impact of a CCP
Results of the CPE indicated that plant performance,
based on daily measurements of turbidity from the
clean/veil and a filter turbidity profile conducted during
the evaluation, was in compliance with applicable
drinking water regulations. The plant monitoring data
also showed very consistent plant performance for the
12-month period evaluated. As a result, a CCP was
not recommended at Plant 3.
33
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Plant 4
Facility Description
Plant 4 is owned and operated by the county water
and sewer district. It was constructed in 1970 and
serves approximately 81 connections, including the
school. It is a packaged, conventional plant and its
processes include pre-sedimentation, flocculation,
sedimentation, and filtration.
A stream fed largely by return flows from the local
irrigation district, supplies the plant. Historically, the
creek flowed only intermittently, but the importation of
irrigation water with subsequent water losses to creek
drainage have significantly increased stream flows.
These artificially increased stream flows, coupled with
naturally erosive soils, have caused a severe
sedimentation and turbidity problem in the creek.
Plant flow records indicate an average daily water
production of 0.4 Us {10,000 gpd) in the winter and
2.6 Us (60,000 gpd) in the summer. Flow records,
obtained from the plant effluent meter, do not include
water used for filter backwash.
The CPE did not determine the accuracy of the
effluent flow meter, but the inconsistency of readings
taken over the day indicated a problem exists. The
influent flow rate is measured by a rectangular weir
located just prior to the flocculation basin.
At the time of the site visit, the influent flow rate was
3.8 Us (60 gpm). The plant operates at this rate for
various hours per day depending on demand. Plant 4
(see Figure 4-15) includes the following unit
processes:
Manually-operated, 2-hp centrifugal raw water pump
22.7 million-L (6 mil gal) earthen pre-sedimentation
basin
1.5-hp, 3.8-L/s (60-gpm) turbine-type settled water
pump
Chemical addition of alum and polymer without
flash mixing; both alum and polymer are mixed in
batches in 189-L and 114-L (50-gal and 30-gal)
tanks, respectively
1.2-m x 1.2-m (3.8-ft x 4-ft), 2,290-L (605-gal)
flocculation chamber with a constant-speed, vertical
paddle wheel
0.9-m x 1.6-m (3-ft x 5.4-ft), 2,290-L (605-gal)
sedimentation chamber with 6-degree tube settlers
0.9-m x 1.2-m (3.1-ft x 4.1-ft) mixed media filter
with perforated pipe underdrain system
1.5-hp, 3.8-L/s (60-gpm)filtered water pump (to
clearwell)
5-hp, 14-L/s (220-gpm) centrifugal backwash pump
Chlorination system consisting of a calcium
hypochlorinator; solutions are made as needed in
189-L (50-gal) batches
45,420-L (12,000-gal) clearwell
Two high-service centrifugal pumps: one 7.5-hp, 5-
L/s (80-gpm), and one 3-hp, capacity unknown,
backup
Raw water is pumped through a 10-cm (4-in) line from
the creek to the pre- sedimentation basin. The 1.5-hp
turbine pump delivers water from the pre-
sedimentation basin through a 5-cm (2-in) line to the
plant. This pump is started automatically by a float
control in the clearwell and the flow rate is regulated
by a float-controlled valve in the chemical mix
chamber.
Alum and polymer are added in line to the raw water
prior to the chemical mix chamber. The manufacturer
originally designed this basin for the addition of calcite
to stabilize the raw water. Some mixing, but no flash
mixing, is provided both in the line and through the
chamber. After chemical addition, the water flows over
a rectangular weir and into a single-stage flocculation
basin with a detention time of 10 minutes at both
design and operating flows. The flocculator is a
constant-speed (12 rpm), vertical paddle wheel type.
Following flocculation, the water flows into the settling
chamber equipped with 6-degree horizontal tube
settlers. Settled water flows over a weir onto a mixed
media filter equipped with a perforated pipe
underdrain. The filter operates on a constant
rate/variable head basis; a float-controlled effluent
valve regulates flow rate. Design filtration rate is 293
m3/m2/d (5 gpm/sq ft); the operating filtration rate was
determined to be 281 m3/m2/d (4.8 gpm/sq ft). Water
is pumped out of the filter to the clearwell.
Backwash is initiated manually or automatically by
headloss across the filter; the filter is not equipped
with a surface wash. The backwash flow rate of 13.9
Us (220 gpm) corresponds to a wash rate of 978
m3/m2/d (16.7 gpm/sq ft). Filter backwash water flows
by gravity to an earthen storage pond located
northwest of the plant, adjacent to the stream. Sludge
from the tube settlers is removed with the backwash
cycle.
Filtered water is disinfected with a calcium
hypochlorite solution within the clearwell and pumped
approximately 2.6 km (1.6 mi) to the town reservoir
34
-------
Figure 4-15. Plant 4 process flow diagram.
35
-------
Figure 4-16. Plant 4 performance potential graph.
Unit Process
20
Flow, gpm
40 60
80
100
Raw-water Pumps
Flash
Flocculatlon1
Detention time, min
Sedimentation2
SOR. gpm/sq ft
Filtration
HLR, gpm/sq ft
Disinfection
Contact time, min
High-service Pumps
Not Rated
None
21 i
1.4
1.7
3.3
600
300
200
150
i 45-m!n HOT for sweep floe; 22.5-min HOT for direct filtration.
2 Based on SOR = 2 gpm/sq ft
Operating and
Design Flow
(capacity of 50,000 gal [189,250 L) through a 10-cm
(4-in) line.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
16. The slashed vertical line on the graph represents
both the design and operating flow rate of 3.8 L/s (60
gpm).
As seen in Figure 4-16, the raw water pumps were not
rated because actual pump output was not known.
The high-service pumps were rated at 4.4 L/s (70
gprn), slightly above the design flow. The flocculation
basin was rated at 0.8 Us (13 gpm) when operated in
the sweep mode of coagulation and at 1.6 L/s (26
gpm) when operated in the direct filtration mode. The
rated flow was doubled for direct filtration because
shorter flocculation times are acceptable in this
operational mode. The flocculation basin was derated
because it is a single-stage unit and only provides 10
minutes of detention time at a 3.8 L/s (60 gpm) flow
rate. Single-stage flocculation and short detention
times make formation of an adequate floe more
difficult.
The sedimentation basin was rated at 1.8 L/s (28
gpm) or 117 m.3/m2/d (2.0 gpm/sq ft) surface overflow
rate (SOR) based on the capability of the tube settler
to produce a clear water with the existing raw water
conditions. The design surface overflow rate of 251
m3/m2/d (4.28 gpm/sq ft) is too high given the raw
water conditions and has resulted in excessive
carryover of solids to the filter.
The mixed media filter was rated at the design flow of
3.8 L/s (60 gpm), which corresponds to a loading rate
of 293 m3/m2/d (5 gpm/sq ft). The backwash rate was
also rated at design, for up to 1,171 m.3/m.2/d (20
gpm/sq ft). The condition of the media must be
restored (mudballs eliminated) and the support gravel
and underdrain integrity must be verified to justify this
rating. The backwash cycle must be extended and
surface wash facilities should be added or the filter
will again become a major limiting factor at this plant.
Disinfection contact time was rated at 2.0 hr at flows
of up to 6.2 L/s (98 gpm). This rating was justified
because of the long transmission line to town and the
189,250-L (50,000-gal) storage reservoir.
36
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The performance potential graph indicates that the
plant capacity is limited by the flocculation and
sedimentation unit processes. To achieve acceptable
finished water quality, the plant capacity may have to
be limited to about 1.9 Us (30 gpm) and operated for
longer periods of time to produce the daily amount
required.
Performance Assessment
A review of the finished water quality monitoring data
submitted to the State indicate that the plant is
operating at the current MCL for turbidity, 1.0 NTU, on
a monthly average. However, much of this data was
collected from the storage reservoir located in town,
2.6 km (1.6 mi) from the plant. Sampling at this point
violates the regulations and intent of the law.
Unreported records of turbidity data taken directly
from the filter reveal that numerous excursions above
the 1.0 NTU occurred on a regular basis for several
months. These data indicate the plant will have
difficulty meeting the SWTR turbidity MCL of 0.5 NTU
for 95 percent of the time. Figures 4-17, 4-18 and 4-
20 depict turbidity data from plant records, while
Figurs 4-19 shows turbidity data generated from
special CPE studies.
Inspection of the filter revealed a heavy layer of
chemical floe on the media surface and numerous
mudballs within the anthracite. The depths of media
were found to be adequate; however, probing of the
media indicated the support gravel varied by as much
as a couple of inches in some areas of the filter. In
the past 18 years of operation, the filter media has
"solidified" to a concrete-like state twice, the last time
about 5 years ago.
Media removal necessitated the use of a jackhammer.
Recently, the clearwell and in-town reservoir were
both cleaned for the first time. Four 189-L (50-gal)
barrels of media and sediment were removed from the
clearwell and a considerable amount of sediment was
removed from the finished water storage reservoir in
town.
Inspection of the automatic backwash cycle indicated
that the backwash time was inadequate to clean the
filter media. This, coupled with the lack of a surface
wash, has allowed the filter to accumulate mudballs.
The inadequate backwash not only results in costly
replacement of the media, but also makes production
of an acceptable finished water quality impossible.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis are
summarized below in order of priority:
1. Water Treatment Understanding - Operation: The
operator is newly hired and, while enthusiastic and
willing to learn, has had no training or background
in the science of water treatment.
2. Process Control Testing - Operation: Testing to
monitor the effectiveness of the treatment process
is inadequate. The available data clearly
substantiates turbidity MCL violations. (See
Figures 4-17 through 4-20.) During certain times,
unacceptable water is supplied to the public,
exposing users to an unacceptable risk of
contracting waterborne diseases. At a minimum,
turbidities should be monitored in the plant
influent, sedimentation basin effluent, and filter
effluent several times each day. Jar testing should
be done daily or at least when raw water
conditions change, to fine-tune chemical dosages.
Continuous-recording, in-line turbidimeters would
be very beneficial in providing information for
optimizing process control.
3. Plant Coverage - Administration: The operator
makes one brief visit to the plant each day, which
is not adequate to perform proper process control
testing, experimentation, and adjustments.
Addition of continuous-recording turbidimeters and
appropriate alarms could reduce the time spent at
the plant, but a minimum of 2 hr each day will still
be required for process control testing.
4. Flocculation - Design: The plant design only
allows for single-stage flocculation and the
detention time is too short to allow optimum floe
formation before water flows to the sedimentation
chamber. The effect of flocculation may be
reduced if the plant could be run in the direct
filtration mode. However, the plant flow rate may
need to be reduced to overcome flocculation
deficiency.
Factors identified as having either a minimal effect on
a routine basis or a major effect on a periodic basis
were prioritized and are summarized below.
1. Laboratory Space and Equipment - Design: The
operator has no equipment other than a
turbidimeter to perform the necessary tests to
determine raw and finished water quality. The
accuracy of the meter cannot even be verified,
because of a lack of equipment. There is no jar
testing or other equipment and supplies for
process control testing.
2. Operator Pay - Administration: The operator pay is
too low to compensate the operator for the
number of hours necessary to run the plant
properly. This pay does not offer an incentive for
keeping qualified operational personnel or for
providing adequate plant coverage.
3. Alarm Systems - Design: Because of a lack of an
alarm system, particularly on the finished water
turbidity, unacceptable water has been pumped
into the distribution system on many occasions.
Without alarm systems and with minimal plant
37
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Figure 4-17. Plant 4 turbidity profile.
Turbidity, NTU
3.0
2.5
2.0
1.5
1.0
A
Unreported
Maximum
A
^*
1 ' '
/ ' '
. \ 1
t-r
V
Regulatory Maximum
^--*^
= 1.0 NTU
v
\
Desired Operating = 0.1 NTU
6/87
8/87
10/87
12/8
Date
2/88
4/88
6/88
Figure 4-18. Plant 4 turbidity profile, August 1987.
Turbidity, NTU
3.0
Reported
2.0
1.0
Regulatory Maximum = 1.0 NTU
Figure 4-19. Plant 4 turbidity profile before and immediately
following backwash.
Turbidity, NTU
1.0 i-
0.8
0.6
0.4
0.2
(DesiredOperating 0.1 NTU
""""" j | i f | i
17 20 24
Day of Month
28 31
Immediately Following Backwash
Prior to Backwash
I I
I
10 20 30
Minutes After Backwash
40
38
-------
Figure 4-20. Plant 4 turbidity profile , January, 1988.
Turbidity, NTU 20 + 20 +
20 +
20 +
20
15
10
Unreported
Maximum
Reported
I
Regulatory Maximum = 1.0 NTU
I
I
10
15 20
Day of Month
25
30
coverage, the operator is not aware of the water
quality being supplied to the town.
4. Staff Number - Administration: The district needs
to have a backup operator, so that the plant
manager can leave town for business or personal
reasons without leaving the plant unmanned.
5. Flash Mix - Design: Lack of a flash mix unit will
limit coagulation effectiveness and increase the
chemical requirement, particularly if the plant is
run in the direct filtration mode.
6. Sedimentation - Design: The surface loading rate
within the sedimentation chamber is too high to
allow floe to settle prior to flowing to the filter.
Better settling would improve or lengthen filter
runs. Operation in the direct filtration mode would
eliminate the sedimentation basin as a potential
problem since the floe that is produced is
filterable, but not settleable.
In addition to the above major factors limiting
performance, other factors identified as having a
minor effect were noted during the evaluation. Action
taken to address these factors may not noticeably
improve plant performance, but may improve the
efficiency of plant operation:
Lack of a preventive maintenance program may
result in excessive equipment downtime, which
could be significant since there are no backup
systems.
Lack of filter surface wash may be contributing to
the inefficient washing of the filter.
Lack of standby units for key equipment could
cause periods of plant downtime.
Projected Impact of a CCP
Results of the CPE indicated performance was limited
by a number of factors in operation, administration,
and design. The evaluation team judged that a CCP
could help the plant make significant improvements in
finished water quality. However, design limitations may
require the plant to operate at a reduced rate to
produce an acceptable finished water quality. In
addition, since many of the limiting factors are in the
areas of administration and design, some minor capital
improvements must be made and greater
administrative support to the plant (i.e., higher
operator salary) must be provided to significantly
improve plant performance.
39
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Plant 5
Facility Description
Plant 5 is a direct filtration plant that was installed in
1978 to replace an older pressure filter. At the time of
the CPE, the system had a total of 1,122 connections.
Water for the plant is supplied from the southeast end
of a multiple use lake located about 29 km (18 mi) to
the northwest.
The plant's water treatment processes include
coagulant chemical feed (alum and polymer),
flocculation in a reaction basin, optional pre-
chlorination and non- ionic polymer filter aid feed,
filtration through four dual media filters, post-
chlorination, and gravity flow from the plant to storage
and distribution. The plant was designed for a flow
rate of 131 L/s (3 mgd). Plant flow records for a 12-
month period indicated an average daily flow of 26 Us
(0.6 mgd). Average monthly flows during the same
period were 12-50 L/s (0.28 and 1.16 mgd). Plant 5
(see Figure 4-21) includes the following unit
processes:
Two 100-hp, 125-L/s (1,980-gpm), vertical turbine
raw water pumps
36-cm (14-in) propeller influent flow meter at the
plant
Chemical addition of alum and cationic polymer
without flash mixing
Three-compartment "reaction" basin that allows
mixing and detention time for flocculation, 6.1 m
(20 ft) in diameter, with a water depth of 2.3 m (7.6
ft)
Four dual media filters, each 3.5 m (11.5 ft) square
and 2.4 m (7.75 ft) deep, with heater/lateral-type
underdrains
Two 60-hp, 167-L/s (2,650-gpm) vertical turbine
backwash pumps
10-hp, 7-L/s (112-gpm) vertical turbine surface
wash pump
Two 378,500-L (100,000-gal) hypalon-lined
backwash water storage basins
Two submersible backwash water recycle pumps
Gas chlorination system
Two 3.8 million-L (1 mil-gal), steel ground level
reservoirs
Water is pumped to the plant through a pair of 30-cm
(12-in) transmission mains. One pump is used at a
time and the pumps automatically alternate each time
one of them stops. The pumping rate through the
plant was measured at approximately 136 L/s (3.1
mgd), at the time of the visit. This is the "normal"
plant flow rate and remains constant.
The influent flow meter was found to measure almost
13 percent less flow than was calculated to be
entering the clearwell. Meters typically measure less
flow with age, so the meter may need to be
recalibrated.
A valve controls the flow to the plant during startup of
the raw water pumps. An orifice plate is located
downstream of the valve to regulate pressure for
optimum operation.
Alum and a cationic coagulant polymer are added to
the influent after the orifice plate. Typical feed rates
were 5-10 mg/L for alum and 0.1 jng/L for the cationic
polymer. No flash mixing is provided; however,
moving the chemical feed points to the orifice plate
would probably result in a hydraulic flash mix. At low
alum feed rates in a direct filtration plant, some type
of flash mixer must be provided.
The three compartment reaction basin allows some
flocculation to occur before filtration. Flow of the water
through the baffled compartments provides hydraulic
"agitation" of the water to promote floe formation. No
outside energy is input to the water. The reaction
basis has apparently been designed to decrease
turbulence as flow proceeds through the
compartments. Approximately 8 minutes of detention
time are provided in the reaction basin at the normal
flow rate.
Chlorine and a non-ionic polymer can be added just
ahead of the filters, but chlorine normally is added
only after filtration. The non-ionic polymer, Serapan, is
added ahead of the filters during some periods of the
year, for example, in winter when turbidities are low.
Water then enters an open influent channel where it is
distributed to the dual media filters. Flow through the
filters is regulated by effluent valves. As the headloss
across the filter builds up, the effluent valve gradually
opens to. counteract this increase. Since the influent
flow to each filter cannot be equally split, the flow rate
through each filter is unknown. 61 cm (24 in) of 0.90-
mm effective size anthracite and 15 cm (6 in) of 0.45-
to 0.55-mm effective size silica sand lie above the 53
cm (21 in) of layered support gravel. A header/lateral
piping underdrain system is located at the bottoms of
the aluminum filter boxes. The filtration rate under
normal plant flow conditions is 234 m3/m2/d (4 gpm/sq
ft).
One interesting feature of the filters is the design of
the discharge header. The header profile rises in
elevation just before the water is discharged into the
clearwell. This discharge pipe then terminates just
40
-------
Figure 4-21. Plant s process flow diagram.
a|
5 flS
a cซ
(3 2
ฃ
-o
-o
I
me
41
-------
above the floor of the clearwell, creating a negative
head in the discharge header from the filters. The
intensity of the negative head depends on the amount
of headless across the filters, the plant flow rate, and
the depth of water in the clearwell. A plug can be
removed from the top of the tee fitting, thus
eliminating the negative head condition. It is not
known what effect this negative head condition has on
the filter operation, but its effects should be evaluated.
Backwash is initiated by adjustable headloss controls.
The two 60-hp pumps each provide 167 L/s (2,650
gprn) of backwash water from the clearwell at 21 m
(70 ft) of head. A rotating arm surface wash system
helps break up sediment at the surface of the filters
during backwash. The 10-hp surface washwater pump
can provide 7 L/s (112 gpm) at 79 m (260 ft) of head.
The spent plant backwash water is stored in the two
hypalon-lined basins adjacent to the plant. After
settling overnight, the decant water is recycled back
into the plant by two submersible pumps. The valve
described previously holds the flow rate through the
plant constant during recycle of the backwash water.
The production of the backwash pumps was restricted
by a butterfly valve to about 118 L/s (1,870 gpm) each
to prevent excessive media loss and disruption during
backwash. This represents a backwash rate of only
about 820 m3/m2/d (14 gpm/sq ft); the backwash
pumps are capable of pumping as much as 167 L/s
(2,650 gpm), or 1,171 m3/m2/d (20 gpm/sq ft). Dual
media filters are typically backwashed at 878-1 171
m3/m2/d (15-20 gpm/sq ft).
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
22. The raw water pumps appear to be capable of
pumping at the plant design capacity of 131 L/s (3
mgd). During the plant evaluation, the plant flow rate
was measured by drawing down the clearwell and
measuring the average rate at which it filled with time.
This rate was measured at 136 L/s (3.1 mgd)).
The reaction basin was not a typical design and,
therefore, was rated in terms of detention time
provided. A detention time in flocculation basins of at
least 20 minutes normally is desirable to permit
adequate floe formation in cold water conditions. (The
reaction rates of the coagulants are slowed
considerably in cold water.) To provide a 20-minute
detention time, the plant flow rate would have to be
decreased to 57 L/s (1.3 mgd). Achievement of this
rate would require the raw water pumps to be
restricted in their output during the winter months.
During warm water conditions, the flow rate
theoretically can be increased because reaction rates
of the coagulant chemicals are higher. The typical
minimum flocculation time for warm water, which
appears in the design standards, is 10 minutes. To
provide 10 minutes, the plant flow rate would have to
be reduced to 114 L/s (2.6 mgd). Further evaluation
would be required to determine the actual detention
times necessary for successful flocculation.
The filters are the weakest major process. The most
significant factor affecting filter performance is air
binding. Air binding (accumulations of air within the
filters) has been a problem since the plant was
constructed. It is believed that the air coming into the
plant from the lake is very high in dissolved gases. As
water flows into the plant from the transmission pipe,
the pressure on the water is relieved, allowing the
dissolved gases to escape. The air accumulations are
so serious that the filters have to be allowed to "rest"
for several minutes prior to backwashing to allow the
gases to escape, so that they will not disrupt the
support gravel and filter media during backwash.
Based upon the uneven surface of the top of the
media in one filter, it is possible that accumulations
have disrupted the support gravel in the past. If
disruption of the support gravel has occurred, it would
need to be removed from the filter(s) and replaced.
Further investigation is needed to evaluate this
potential problem before taking such drastic action.
During air binding, the effective filtration rate through
the filters is increased because the water must flow
around the air bubbles. The net area of the filters is
therefore reduced, resulting in an increase in effective
filtration rate. The only way to reduce the filtration rate
is to either eliminate the air binding problem, or to
reduce the plant flow rate. The plant is now operating
at, or slightly above, the design filtration rate of 234
m3/m2/d (4 gpm/sq ft) or 136 L/s (3.09 mgd). Because
about 20 percent of the finished water must be used
for backwash water, the effective filtration rate is
reduced to 187 m3/m2/d (3.2 gpm/sq ft) or 107 L/s
(2.44 mgd). After observing the amount of air released
from the filters, the evaluation team estimated that the
effective filtration rate of the filters may have to be
reduced to about 117 m3/m2/d (2 gpm/sq ft) or 67 L/s
(1.52 mgd).
The automatic filter backwash cycles (headloss
initiated) did not appear to be long enough to properly
clean the filters. The water was still dirty as the
backwash cycle ended. Improper cleaning of the filters
can lead to poor treatment and short filter runs.
Performance Assessment
Finished water quality data from the past year
indicated that the plant was operating within the 1.0-
NTU standard for finished water turbidity, although
incoming turbidities are extremely variable. Winter
turbidities are often less than 5 NTU, and usually less
than 10 NTU, while spring and summer turbidities can
vary widely, even within a given day. Prevailing
westerly winds often stir up sediment in the relatively
shallow lake, resulting in raw water turbidities of 50-
280 NTU. Monthly average turbidities are reported
42
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Figure 4-22. Plant 5 performance potential graph.
Unit Process
Flow, mpd
Raw-water Pumps
Reaction Tank
HOT, min
Filters^
HLR, gpm/sq ft
Chlorination
Cobntact time, min
Winter - 20 min
(1.3 mgd)
Summer - 10 min
(2.6 mgd)
26
13
(1.5 mgd)
(2.4 mgd)
360
180
12'
Design
Capacity
Flow reduced to 2.44 mgd to account for 20 percent of the production being used for backwash water.
The flow may have to be reduced even further (to approximately 1.5 mgd) because of air binding.
typically at 0.5 NTU or less, but turbidities of 0.5-0.6
NTU range were reported for a few months.
Finished water quality data is taken from the plant
potable water system, which pumps water from the
clearwell. Readings are typically taken at about 9 a.m.
after the plant has been shut down overnight. Figure
4-23 shows, under current operating conditions, the
number of days each month that Plant 5 would be in
violation of the SWTR effluent turbidity standard,
which will require that finished water turbidity be 0.5
NTU or less at least 95 percent of the time.
Inspection of Filter 2 after dewatering did not detect
the presence of any mudballs; there was, however,
deep penetration of the floe into the anthracite. This in
itself is not necessarily indicative of a problem, but a
variation of about 5 cm (2 in) in the elevation of the
top of the anthracite media indicates a potentially
serious problem with the condition of the support
gravel.
The presence of filter sand and anthracite in the
clearwell also indicates a potential problem. This
material was cleaned out of the clearwell previously
but has since accumulated. If the support gravel were
in proper condition, the filter sand and anthracite
layers would not break through to the underdrains.
Readings taken after backwash of Filter 2 during the
site visit indicated that the filter effluent turbidity
exceeded 1.0 NTU. This is of concern both for the
present standard of 1.0 NTU and the proposed 0.5-
NTU standard. These data are presented in a graph in
Figure 4-24.
Over the past several years, the State has completed
microscopic particulate examinations (MPEs) of the
finished water to determine the effectiveness of the
filtration process. These have shown that the finished
water contains a large amount of particles (algae,
insect eggs, etc.), which indicates that, at times, the
filters are not operating well.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis are
summarized below in order of priority:
1. Operator Application of Concepts - Operation:
Varying raw water quality requires changes in
chemical feed rates and plant flow rates to
maintain acceptable finished water quality. The
plant had no organized process control program to
provide information to base operational decisions
upon. Although the operators had a good
understanding of water treatment, they were not
applying that knowledge fully.
2. Process Control Testing - Operation: Proper
operation of a direct filtration plant requires regular
process control testing so that chemical doses
can be optimized. Jar teb^ig, followed by filtration
through Whatman #40 paper filters, is a
reasonable simulation of the direct filtration
process. This regular testing was not being done
at the plant.
3. Filtration - Design: Turbidity measurements taken
.at the time of the evaluation and MPE testing
43
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Figure 4-23. Plant 5 potential for SWTR compliance.
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
Days Allowed
Above 0.5 NTU
done by the State demonstrate that the filters do
have a performance problem. The presence of
filter media in the clean/veil indicates that the
support gravel may have been damaged in the
past. If the support gravel is in fact damaged,
replacement to the media will be necessary. Filter
capacity and finished water quality is being
affected by severe air binding. Periods of high
turbidity also require frequent backwashing, which
further reduces plant capacity. If the support
gravel is in good condition, then the filters could
be rated as a lower priority factor and the filtration
rate decreased because of the air binding problem
and backwash water requirements.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
were prioritized and are summarized below.
1. Turbidity - Design: The turbidity of the raw water
often exceeds that normally recommended for the
direct filtration treatment mode. During periods of
high turbidity, it may be necessary to reduce plant
flow rates to produce an acceptable finished
water. Nearly constant backwashing may also be
necessary because of the solids load to the filter,
which will reduce the effective plant capacity.
2. Plant Coverage - Administration: The plant is not
attended on weekends and the operators are
often away from the plant during weekdays
performing other duties. As a result, periods of
poor finished water quality could go undetected.
3. Lack of Standby Units - Design: There are no
standby alum and polymer feed units. Failure of
one of the units would severely affect plant
performance.
4. Automated Process Monitoring - Design: A lack of
continuous monitoring turbidimeters on the raw
water quality at the lake pumping station and on
the effluent line from each filter makes plant
operation more difficult. Turbidity monitoring on
the raw water would allow increases in raw water
turbidity to be anticipated, so that treatment could
- likely be improved. Monitoring of the filter effluent
quality would provide information necessary to
44
-------
Figure 4-24. Finished water turbidity profile after backwash of filter 2 - Plant 5.
Backwash
Recycle
Pump On
Minutes
adjust chemical feed rates and, therefore,
optimize filter performance.
5. Reactor Basin - Design: The reactor basin may
provide inadequate detention time to allow
chemicals to react and flocculate during cold
water conditions. As a result, the plant flow may
have to be reduced substantially during the winter.
6. Inoperability Due to Weather - Design: As
discovered during the summer of 1985, drought
can severely impact the availability of water from
the lake. The raw water intake is located in a
shallow corner of the lake and considerable
attention has been given to relocating the intake
to a deeper portion of the lake. An engineering
study has been completed that evaluates the
alternatives for another intake location.
In addition to the above major factors limiting
performance, other minor factors were noted during
the evaluation. Action taken to address these factors
may not noticeably improve plant performance, but
may improve the efficiency of plant operation:
Funding the operation of the wastewater system
through water revenues is not a good practice.
Each utility should be self sufficient.
Better communication of priorities to the plant staff
and better teamwork among staff members could
improve plant performance.
Return of spent backwash water to the influent can
result in increased raw water turbidities and a
change in raw water chemical characteristics.
The alum and cationic polymer feed points provide
no flash mix of the chemicals. Movement of the
chemical feed points to just prior to the orifice plate
would provide better mixing.
Projected Impact of a CCP
It was projected that a CCP would help Plant 5
achieve better performance. Results of the CPE
indicated that the plant was limited by a number of
factors, primarily in operation and design. Because of
the design limitations, the plant would need to reduce
its operating rate to produce an acceptable finished
water quality. Some capital investment could be
necessary, depending upon the condition of the filters.
It was recommended that the city continue its efforts
to construct a new water intake on the lake. The new
intake would appear to improve the quality of the raw
water, as well as the reliability of the water source.
45
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CCP Results
A CCP was initiated, at which time the plant flow rate
was reduced so that design-related limitations could
be addressed. During the initial site visit, the CCP
team developed a daily data sheet and implemented a
procedure describing process control testing. In
addition, procedures were developed for calibrating
chemical feeders and calculating chemical dosages so
that chemical feed rates could be accurately applied.
Special studies were implemented to determine the
effect of operating the plant at a reduced flow rate and
operating the filters without a negative pressure.
At the conclusion of the first visit, the plant was
operated at 69 Us (1,100 gpm) rather than at 132 L/s
(2,100 gpm) and a plug was removed from the filter
effluent header to release the negative pressure from
the filter. Chemical feed rates were not changed. The
CCP team developed an action list and assigned tasks
to the operating staff and administrators with due
dates to ensure activity continued until the next site
visit.
During an additional two site visits and weekly phone
consultation sessions, the CCP team explained the
conduct and interpretation of the jar test/filter paper
procedure to the operating staff. This, coupled with
activities from the first site visit, launched full
implementation of the process control program,
including evaluating raw water quality and making a
determination of the correct coagulant and filter aid
feed rates.
The only physical change to the plant was the
relocation of the feed points for alum and cationic
polymer addition to take advantage of a hydraulic flash
mix at an orifice plate located in the influent piping.
City administrators were also convinced to allow time
for the operating staff to remain at the plant so that
they could conduct process control testing and make
plant adjustments.
Figure 4-25 shows the significant improvement in
plant performance achieved by Plant 5 during the
conduct of the CCP. Plant operation improved after
reducing the plant flow rate and eliminating the
negative pressure on the filter bottoms in April, but
performance remained erratic until process control,
including chemical adjustments, was implemented in
July. After July, plant finished water turbidities
remained very consistent at about 0.1 to 0.2 NTU
through the duration of the project, even though raw
water turbidities varied widely (Figure 4-26). Plant
finished water quality remained below 0.3 NTU even
when the raw water turbidities reached 70 NTU,
because the operating staff consistently monitored
varying raw water quality and responded by changing
chemical feed rates.
Plant performance was especially impressive since
influent turbidities frequently exceeded values thought
to be treatable with direct filtration (e.g., less than 50
NTU). Another indication of improved performance
was that filter effluent turbidity following a backwash
did not exceed 0.3 NTU and returned to 0.15 NTU
within minutes after the wash.
The CCP proved that the plant could achieve
compliance with SWTR turbidity requirements without
major capital improvements. City administrators had
planned on spending an estimated $1,000,000 on
construction of sedimentation basin facilities and
related improvements. After the CCP, they decided to
delay any construction until water demands required
the plant to be operated at higher rates. The plant
staff developed increased confidence that excellent
quality water could be produced despite high raw
water turbidities, and they developed a level of pride
that did not allow them to accept marginal finished
water quality. In addition, the jar test/filter paper
procedure proved to be a valuable process control
tool that allowed accurate selection of coagulant
doses.
46
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Figure 4-25. Finished water turbidities during CCP for Plant 5.
-89 12-Moy-89 21-Jun-89 31-Jul-89 09-Sep-89 19-Oct-89 28-Nov-89
Figure 4-26. Raw water turbidities during CCP for Plant 5.
80
70 -
60 -
50 -
40 -
30 -
20 -
10 -
T
no
0 -
02-Apr 12-May 21-Jun 31-Jul 09-Sep 19-Oct 28-Nov
47
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Plant 6
Facility Description
Plant 6 was built in 1916, and underwent major
modifications in 1923 and 1960. To date the plant
serves approximately 5,000 people, with no significant
industrial users. The plant's water source is the
nearby river. The plant is a 175-L/s (4-mgd) lime
softening facility with pre-sedimentation, rapid mix and
flpcculation (in a solids contact unit), filtration, and
disinfection. The maximum quantity of water produced
over a 12-month period was 1,182 L/s (4.15 mgd) and
the lowest was 17 L/s (0.39 mgd). Plant flow is
measured by a raw water meter ahead of the solids
contact unit, and by a master 'meter following the
high-service pumps.
The city is currently under a compliance schedule
from the State to curtail the discharge of untreated
sludge into the river. The city has applied for funds for
the construction of sludge handling facilities and for
other plant modifications. Plant 6 consists of the
following unit processes (see Figure 4- 27):
Four split-case centrifugal raw water pumps: two 69
L/s (1,800 gpm) and two 50 L/s (800 gpm)
Pre-sedimentation basin divided into five sections,
total volume of about 3.8 million L (1 mil gal)
Three non-clog centrifugal pumps (one 63-L/s
[1,000-gpm] and two 94-L/s [1,500-gpm]) as
intermediate pumps for transferring water from the
pre-sedimentation basin to the solids contact unit
Chemical addition of liquid cationic coagulant, alum,
filter aid, pplyphosphate, lime, soda water, carbon
dioxide, activated carbpn, and gaseous chlorine
Solids contact unit with a total surface area of 144
nr>2 (1,555 sq ft) and a 3.1-m (10-ft) depth. A
mechanical 10-hp rapid mix unit is located in the
solids contact unit.
Recarbonation chamber to reduce pH after
softening
Seven single media sand filters with a total surface
area of 167 m2 (1,800 sq ft): three in the plant
addition with surface area of 33 m2 (360 sq ft)
each, and four in the old plant with surface area of
17m2(l80sqft)
- Two chlorinators
487,130-L (128,700-gal) clearwell
Four vertical turbine high-service pumps: three 88-
L/s (1,400 gpm) and one 63-L/s (1,000 gpm)
Raw water is pumped from the river to the pre-
sedimentation basin. Two of the raw water pumps are
located in the basement of the plant and two are
located in a pumping station north of the plant. A
hand-cleaned basket strainer provides preliminary
screening for the two raw water pumps located in the
plant basement. The five separate chambers in the
pre-sedimentation basin are normally run in series, but
may be run in series, parallel, or any combination.
Sludge is removed from the basin manually, and when
the pre-sedimentation basin is cleaned the sludge is
discharged directly to the river. From the pre-
sedimentation basin, water is pumped by the three
intermediate pumps to the solids contact unit. Chlorine
may be added ahead of the solids contact unit, if
necessary.
In the solids contact unit, alum, polymer, lime, soda
water, and activated carbon are added for softening,
turbidity removal, and taste and odor control.
Flocculation and rapid mixing both take place in the
contact unit. From the solids contact unit, water flows
by gravity to the recarbonation chamber, where
carbon dioxide generated onsite by burning natural
gas is added to reduce pH after softening.
Polyphosphates are added prior to filtration.
The design filtration rate is 117 m3/m2/d (2 gpm/sq ft).
Filtration rates are controlled by an effluent regulator
on the basis of flow and headloss. The filters are
backwashed with finished water from the clearwell
pumped by one 189-L/s (3,000-gpm) backwash pump.
Backwash water flow is measured by a Venturi meter
and totalized at the main instrument control panel.
Filtered water is disinfected with chlorine dosed at a
feed rate of 1-2 ppm. Disinfected water then flows to
the clearwell. The clearwell detention time is 46
minutes at a plant flow of 175 L/s (4 mgd).
The three high-service pumps deliver the water to the
distribution system.
There are no facilities available for the disposal of
sludge. 'Sludge generated from cleaning the pre-
sedimentation basins, solids contact unit, and the
spent filter backwash water is piped untreated to the
river.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
28. The raw water pumps were rated at 208 L/s (4.75
mgd), based on information from a previous
engineering study. The pre-sedimentation basin was
rated at 175 L/s (4 mgd) assuming that a coagulant
aid could be added prior to the basin. At 175 L/s (4
mgd), the basin has a detention time greater than the
3-hr minimum recommended by the Ten State
Standards.
48
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Figure 4-27. Plant 6 process flow diagram.
-------
Figure 4-28. Plant 6 performance potential graph.
Unit Process
Flow, mqd
12345
Raw-water Pumps1
Pre-sodlmontatlon Ponds2
HOT, min
Intermediate Pumps2
Contact Units
SOR. gpd/sq ft
Filtration4
Loading, gpm/sq ft
Disinfection5
Contact time, min
High-service Pumps
Sludge Handling
643
1,286
Inadequate
Rated Design
Capacity
i Based on previous master plan study.
2 Based on addition of coagulant aids - detention greater than 3 hr minimum in Ten State Standards.
3 Based on 1,440 gpd/sq ft.
4 Based on 2 gpm/sq ft and assumes filter aid with labor-intensive backwash.
s Based on 120-min contact time and total clearwell volume.
The intermediate pumps were rated at 167 Us (3.8
mgd), slightly less than the 175-L/s (4-mgd) design
capacity, based on a previous study. Based on a
surface overflow rate of 58 m3/m2/d (1 gpm/sq ft), the
solids contact unit was rated at 96 L/s (2.2 mgd), well
below the plant design capacity.
The filters were rated at 228 Us (5.2 mgd) based on a
filtration rate of 117 m3/m2/d (2 gpm/sq ft). This rating
assumes successful use of a filter aid and hand-raking
of the filters during backwash.
Because the clearwell has such a small volume in
relation to total plant production, the disinfection
contact time was rated at only 8.8 L/s (0.2 mgd).
Current design standards require a minimum
disinfection contact time of 2 hr, but the clearwell
provides only 46 minutes at 175 L/s (4 mgd). When
the plant produces water with a turbidity greater than
1.0 NTU, the chlorine contact time must be adequate
to ensure disinfection of any pathogenic organisms
that may have passed through the plant's previous
treatment steps.
The high-service pumps are rated at 241 L/s (5.5
mgd).ln summary, the solids contact unit limits plant
capacity to 96 L/s (2.2 mgd) during periods of high
turbidity. An operational rate greater than 96 L/s (2.2
mgd) may result in increased solids carryover from
the solids contact unit to the filters, with a subsequent
decrease in filter performance and overall plant
performance. Also, if bypass of the solids contact unit
becomes necessary, provisions must be made to add
coagulants prior to filtration.
Performance Assessment
Finished water quality monitoring data indicated that
the plant had been operating in compliance with the
50
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current turbidity MCL of less than 1.0 NTU on a
monthly average. However, the MCL had been
exceeded on days within certain months. The highest
finished water turbidities were noted at a time when
the solids contact unit was being bypassed for
cleaning. Plant records indicated that no coagulant
aids were added at times when the solids contact unit
was bypassed, an unacceptable practice.
Figures 4-29 through 4-31 show selected plant
operating data. The data shown in these figures
suggest that the plant will experience difficulty in
complying with the SWTR, which establishes a MCL
for turbidity of 0.5 NTU for 95 percent of the time.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis are
summarized below and listed in order of priority.
1- Operator Applications of Concepts and Testing to
Process Contro! - Operation: The operators had a
good understanding of water treatment but were
not applying that knowledge fully. For example,
direct filtration without chemical pretreatment can
result in a significant health risk to the consumers.
The Filter 6 effluent turbidity plot presented in
Figure 4- 30 is from a special CPE study and
indicates that the coagulation process has not
been optimized.
2. Disinfection - Design: The limited volume of the
clearwell results in inadequate chlorine contact
time, which in turn limits the time the chlorine has
to act on pathogenic organisms that may have
passed through the previous treatment process.
There was also an inadequate free chlorine
residual in the finished water leaving the plant.
3. Sludge Disposal - Design: No sludge disposal
facilities exist to treat the sludge generated in the
water treatment process. The city is in violation of
the State Clean Water Act because of the
discharge of sludge to the river and has hired a
consultant to evaluate the problem and design a
remedy.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
were prioritized and are summarized below.
1. Process Flexibility - Design: There are no
provisions for chemical feed to the pre-
sedimentation basin or to the filter influent.
Addition of these chemical feed points would allow
operators to better control finished water quality.
2. Process Control Testing - Operation: The absence
of or the wrong type of process control testing
results in improper operational control decisions.
The solids contact unit should be monitored more
Figure 4-29. Plant 6 direct filtration results, February 1988.
Finished Water Turbidity, NTU
2.5 i-
2.0
1.5
1.0
0.5
Proposed Finished Water MCL
J I
5 10 15
Day of Month
Figure 4-30. Plant 6 effluent turbidity after backwash,
September 21,1988.
Turbidity, NTU ,
Proposed Finished Water MCL
0.4 -
0.2
I
J I
I I
I I
20
40 60
Time, min
90
51
-------
Figure 4-31. Plant 6 turbidity.
95% Compliance
with 0.5 NTU
Jul Aug Sep Oct Nov Dec Jan Fed Mar Apr May Jun Jul
87 87 87 87 87 87 88 88 88 88 88 88 88
Date
thoroughly and more frequently. Sample taps and
continuous monitoring turbidimeters should be
installed on each filter effluent so that discrete
changes in filter performance may be observed
before substandard quality water is produced.
Process control activities should be integrated into
the daily routine of operation.
3. Solids Contact Unit - Design: The solids contact
unit severely limits flow during peak periods when
the surface overflow rate becomes excessive, and
results in a high solids loading to the filters.
4. Planning and Guidance - Administration: More
emphasis should be placed on ongoing capital
improvement and replacement of equipment.
Long-term reliability of the plant has been
jeopardized by a reluctance to make necessary
expenditures. Administration should develop an
integrated approach to setting goals, not only for
maintenance and process control, but also for
meeting minimum finished water quality goals and
sludge discharge limitations.
In addition to the above major factors limiting
performance, other factors identified as having a
minor effect were noted during the evaluation. Overall,
there is a heavy focus on maintenance at the expense
of adequate process control. Action taken to address
these factors may not noticeably improve plant
performance, but may improve the efficiency of plant
operation:
The screens on the raw water pumps plug with
moss at certain times of the year. Cleaning the
screens is very labor intensive. Frequent plugging
of the screens affects water quantity more than
finished water quality.
If filter aids are used to improve filter performance,
it may be necessary to agitate the filters by hand
during backwash to facilitate cleaning. This practice
will be rather labor intensive.
Projected Impact of a CCP
The evaluation team believed that a CCP that
addressed factors related to plant operation, such as
operator application of concepts, process control
testing, and flexibility could improve plant performance
for the majority of the year. However, continuous
compliance with proposed regulations for finished
water turbidity and disinfection, and with existing
NPDES permit limitations on sludge discharge to the
river, would require design modifications as well.
52
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Plant 7
Facility Description
Plant 7 is a conventional plant that treats water from a
river for industrial and domestic use by the city. The
peak day demand for a 12-month period was 202 Us
(4.6 mgd) based on plant records. Plant 7 includes the
following unit processes (see Figure 4-32).
Concrete river intake structure that houses
manually cleaned bar screens, 1.9-cm (3/4-in)
spacing.
Three manually operated raw water pumps: one
turbine - 126 Us (2,000 gpm), and two centrifugal -
126 Us (2,000 gpm) and 88 Us (1,400 gpm)
Three turbine pumps used to pump raw water
directly to a large refinery; one 76 Us (1,200 gpm)
and two 126 Us (2,000 gpm)
46-cm (18-in) Parshall flume used to monitor raw
water influent flow
Liquid alum feed pump with a backup dry alum feed
system
ซ Polymer feed pump
Fluoride feed system for sodium silica fluoride
Six manually-cleaned, uncovered "hydraulic"
flocculation basins ("mud basins"), each with a
volume of approximately 81,400 L (21,500 gal)
Two manually cleaned sedimentation basins, one
covered and one uncovered. Each basin has a
volume of approximately 2.8 million L (750,000 gal).
Basin effluent is transferred to the filters through a
61-cm (24-in) pipe
Two 8.5-m x 7.6-m (28-ft x 25-ft) mixed media
filters
Gas chlorination system
Two filtered water "transfer" pumps controlled by
an altitude valve that "transfer" filtered water to a
standpipe or to the high-service pumps
o On-site standpipe with a capacity of approximately
94,625 L (25,000 gal)
Five high-service centrifugal pumps: two 157 Us
(2,500 gpm), one 126 Us (2,000 gpm), one 63 Us
(1,000 gpm), and 38 Us (600 gpm)
* Sludge holding lagoon of approximately 3.4 million
L (900,000 gal) capacity
On-site storage of sludge from the holding lagoon
River water is drawn from the concrete intake
structure located in the middle of the river through
41-, 36-, and 51-cm (16-, 14-, and 20-in) lines. The
intake structure is modified during winter months to
include a perforated culvert intake, which lessens the
impact of pack ice. A portion of the raw water from
the intake structure is pumped directly to a local
refinery.
Raw water pumps located in a pump station adjacent
to the plant deliver the desired volume of water for
treatment. The operators indicated that the turbine
pump is unable to achieve rated capacity output. The
pumps discharge to a Parshall flume. At the time of
the CPE, sodium silica fluoride and liquid alum were
being added just upstream of the throat of the Parshall
flume. The superintendent had only recently switched
from dry to liquid alum. Historically, polymer had also
been added at the flume location.
After the flume, the water flows to the "mud basins,"
a series of six tanks used for flocculation. The basins
appeared to be functioning well even though the only
energy impact was that generated hydraulically. The
operators indicated that observing the floe formation in
these basins was critical in adjusting the chemical
dosages to the raw water. These basins are not used
in the winter because of icing problems. The basins
have noticeably deteriorating concrete, and a
consultant had been retained to evaluate their
structural integrity.
From the mud basins, water flows in series through
two manually cleaned sedimentation basins. The first
basin is uncovered and is used only during warm
weather months. During winter operation, the covered
basin is used for both flocculation and sedimentation.
The basins are cleaned manually approximately six
times each year, and the sludge is pumped to the
earth sludge holding pond; 3-6 hr are required to
clean the basins, and no routine sampling is done on
them.
Effluent from the covered sedimentation basin is
collected in a 61-cm (24-in) pipe and delivered to the
mixed-media filters. The filtration rate is controlled by
a transfer pump located at the discharge from each
filter. The transfer pump discharges filtered water to
the distribution headers of the high-service pumps and
to an on-site standpipe. The transfer pumping rate is
controlled by demand and by an altitude valve which
receives a signal from a pressure sensor on the on-
site standpipe. This filter control has been set to
respond relatively slowly so as to minimize rapid
fluctuations in filtration rate.
Backwash consists of a surface wash and gravity
backwash using the water stored in the standpipe. At
the time of the CPE, filter runs were approximately 10-
20 days, and a dirty filter was started and stopped on
a daily basis. Backwashing was intended to be
53
-------
Figure 4-32. Plant 7 process flow diagram.
Flocculntion
Basins
Sludge Holding
Lagoon
Filter
Sedimentation
Basin
(uncovered)
Sedimentation
Basin
(covered)
Filter
Transfer
Pumps
C12
To Distribution System I
Standpipe
a
a
High
Service
Pumps
River
54
-------
initiated when the headless exceeded 2.4-2.7 m (8-9
ft) or the effluent turbidity exceeded 0.5 NTU.
Backwash water was directed to the sludge holding
pond.
After filtration, the plant effluent is chlorinated and
pumped by the high- service pumps to the distribution
system. The plant does not have a clearwell to allow
contact time of the chlorine with the treated water,
and the first consumer is located approximately 275 m
(300 yd) from the plant site. The target chlorine
residual is 0.7-0.8 mg/L
Operators attempt to match water demand with high-
service pumping. However, caution is used in turning
on high-service pumps so as to avoid high pressure in
the distribution system. Excessive system pressures
have resulted in broken lines because of the existence
of old pipes in the system. The 38-L/s (600-gpm)
high-service pump was out of service at the time of
the CPE.
Sludge from the sedimentation basins and the filter
backwashes is stored in the unlined sludge storage
lagoon from which it is dredged approximately every 2
years and stored in a ditch adjacent to the lagoon.
Supernatant from the lagoons is pumped back to the
head of the plant.
Dried sludge is removed from the ditch and stockpiled
on the plant side. Present stockpile volumes have
practically filled the available space, and alternative
disposal options will be necessary in the foreseeable
future.
Operation is almost totally manual. Pump settings,
chemical dosage rates, and filter backwashing are all
initiated manually by the plant operators. The plant is
staffed 24 hr every day with four operators rotating
shifts every 28 days. A relief operator is available.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
33. The flocculation basins were rated based on a
detention time of 40 minutes, which resulted in a
capacity rating of approximately 206 Us (4.7 mgd).
The 40-minute detention time rating is relatively
conservative but is justified because mechanical
mixing is not provided. This rating is slightly higher
than the current peak demand; therefore, the unit
process is deemed satisfactory.
The sedimentation basins were rated on a hydraulic
loading rate of 12 m3/m2/d (300 gpd/sq ft ) and a
detention time of 5.4 hr because of the relatively poor
outlet structure (e.g., a 61-cm [24-in] pipe) and the
absence of mechanical sludge removal. Polymer
addition was assumed in establishing this rating.
Based on these criteria, the capability of the
sedimentation basins was assessed as 263 Us (6
mgd).
The mixed media filters were assessed based on a
filtration rate of 293 m3/m2/d (5 gpm/sq ft). At this
rate, a potential capacity of 438 L/s (10 mgd) was
projected for the existing filters.
Disinfection capability was severely limited based on
current state criteria of a 2-hr detention time after
chlorination. A capacity of 11 L/s (0.25 mgd) was
projected based on the 2-hr standard and the
approximation that there are 274 m (300 yd) of 36-cm
and 41-cm (14- and 16-in) pipes prior to the first
system user. Despite revisions of existing regulations
that may allow lower detention times, the absence of
any clearwell or contact basin will remain a unit
process limitation.
Except for the noted limitation in the disinfection
process, unit processes were assessed adequate to
meet the current peak demand of 202 L/s (4.6 mgd).
Performance Assessment
In general, the CPE indicated that a high quality water
(e.g., turbidities less than 0.15 NTU) was produced.
However, some difficulty with performance was
indicated during winter operation. Figure 4-34, which
shows a plot of filter turbidity and headloss vs. time,
indicates an excessively long recovery time after
backwash of Filter 1 (e.g., 36 hr until effluent turbidity
stabilized). Ideally, performance stability would be
achieved in less than 10 minutes. Also shown is a
period of approximately 12 hr in which the turbidity
exceeded the current state criteria of 1 NTU. Cold,
low turbidity, low alkalinity water and use of only the
covered sedimentation basin may have contributed in
part to the noted difficulties. Greater operational
control and perhaps additional chemical conditioning
may be required to improve performance.
Another problem indicated on Figure 4-34 is the time
of deteriorated performance before a filter backwash
was implemented. Turbidities increased from the 0.1
NTU range to the 0.35 NTU range, and approximately
1 full day passed before the operators initiated
backwash. Failure to backwash when turbidity begins
to increase can allow significant breakthrough of
particles, causing a potential health risk for the
community. Figure 4-35 shows March 1989 turbidity
data for Filter 2 with results similar to those in Figure
4-34. The performance problem indicated on Figure 4-
35, however, is much more severe. Initial turbidities,
after filter startup, exceeded the state requirements
(1.0 NTU) for over a day. Additionally, backwashing
was delayed for approximately 3.5 days from the time
indicated by plant data. Proper chemical conditioning
and closer attention to the need to backwash would
have lessened the potential for health risk
demonstrated by these data analyses.
55
-------
Figure 4-33. Plant 7 performance potential graph.
Unit Process
Flow, mgd
4 6
10
12
Flooculatlon1
Detention time, min
Sedimentation2
SOR, gpd/sq ft
HOT, hr
Filtration
HLR, gpm/sq ft
Disinfection3
Contact time, min
93
46
100
200
16.2
8.1
3(
Actual Max. Day
5/88 - 4/89
1 Ftocculation basin rated at 40-min HOT because there is no mechanical mixing.
2 Rated at 300 gpd/sq ft and 5.4 hr because there is a poor outlet and no sludge collection equipment. Assumes polymer use..
3 Based on current State standard of 2-hr HOT. Assumed 300 yd of 14- and 16-in pipe to first user. Standards are being revised and
lower detention times may be allowed for existing plants.
During the CPE, a special study on filter startup was
conducted under spring runoff water conditions.
During the study, Filter 1 was removed from service
for backwashing and Filter 2 was placed in service.
The results of this analysis showed that turbidities
never exceeded 0.15 NTU during and after startup of
Rlter 2. The stability of the filter's performance was
also demonstrated when the flow was increased
dramatically over a short period of time and no
increase in turbidity occurred. An additional
evaluation of the surface of Filter 1 after backwash
revealed no mudballs, indicating that the backwash
procedure was adequate.
Performance-Limiting Factors
The following factor was identified as having a major
adverse effect on performance on a long-term
repetitive basis.
1. Disinfection - Design: A detention time of 2 hr is
not available at the plant to ensure effective
disinfection of the treated water prior to use. The
new regulations that will be promulgated as a
result of the SWTR and/or current state criteria
may necessitate capital improvements in order to
provide adequate disinfection capability. This
factor was asterisked because the final rule and
direction could not be established until the latter
part of 1989.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
were prioritized and are summarized below:
1. Supervision/Staff Morale - Administrative:
Communication between administrative personnel
and the plant staff, and communication among the
staff is limited and strained. As a result of the
limited communication; data interpretation,
initiative, maintenance efforts, proper process
adjustments, understanding of standard operating
procedures, and "cross training" of personnel are
limited. The operators seem to function
independently on each shift. This limited
interaction is believed to be a major contributing
factor to the poor operational decisions that
resulted in the deteriorated filter performance
documented in Figures 4-34 and 4-35.
Administrative skills and operator attitude will have
to be addressed to eliminate the impact of this
factor.
2. Application of Concepts - Operation: Inability to
apply proper concepts to optimize unit process
performance was identified for several reasons.
First the supervision/staff morale problem limits
the capability of current personnel to learn from
each other and, therefore, limits their capability to
properly and consistently apply basic concepts to
operational decisions. Also, the practice of
56
-------
Figure 4-34. Turbidity and headloss profiles for filter 1 - Plant 7.
_g
a
CD
I
as
&
jg
n
Headloss
Turbidity
February 1989
Figure 4-35. Turbidity profile for filter 2 - Plant 7.
ZD
>;
.*=!
o
e
1 .5 ซ_
1.4--
1.3 -
1.2 -
1.1 -
0.9 -1
o.a -
0.7 -
0.6 -
0.5 -
0.4--
0.3 -
0.2 -
0.1 -
0 -
I
] Current Standard
I Recommend f
I initiate 5 f-
41 Rfirkwash a J Wi
\ \ 1 jf^V
\A / W
fijTS U* J%i ~"
1 FWI T r
Wy^^^E^ js^ _ jiT ^TB
anrtr>- cyry . _
. ' i " 1 1 ' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
11 12 1314- 15 16 17 18 19 20
March 1989
57
-------
routinely starting up a dirty filter and of occasion-
ally "bumping" the filters with large changes in
flow rate can and has resulted in turbidity spikes
and the associated breakthrough of particles.
Particle breakthrough represents a high potential
health risk.
3. Policies - Administration: The implementation of
very tight fiscal policies limits the expenditure of
funds for necessary items. The lack of in-line
turbidimeters for the two filters, an additional
polymer feed pump, and use of polymer was
assessed to be impacting plant performance. The
CPE did not identify where these policies were
originating. It was felt that improved
communication would greatly assist in addressing
this factor.
Chemical feed capability was identified as having a
minor impact on performance. Moving the
alum/coagulant feed point from its present location to
the throat of the Parshall flume would allow a better
rapid mix to occur and may result in lower chemical
use. As a side benefit, the raw water sample could be
taken in the chemical feed room, although the sample
would contain fluoride.
Projected Impact of a CCP
Generally, the plant was producing a high quality
treated water. As such, a CCP would not dramatically
improve water quality. However, intangibles such as
communication, operational concepts, and a "tight"
fiscal policy represent deep-seated problems that may
be difficult to address using past practices. From this
point of view, an external facilitator may be necessary
to impact the current situation.
In lieu of a CCP, it was recommended that the
community pursue a correction effort to address the
factors identified as limiting plant performance,
recognizing that they will be difficult and time
consuming to eliminate.
58
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Plant 8
Facility Description
Plant 8, operated by the county sewer and water
district, treats water from a nearby river for domestic
use by the town and a local rural water system. The
plant, which began operation in 1981, utilizes a solids
contact clarification/filtration process. Extreme
variations in turbidity exist in the river. During the
winter, turbidity is generally below 30 NTU and can be
as low as 10 NTU; however, during spring and
summer, turbidity ranges from 40 NTU to as high as
several thousand NTU as the result of storm events.
Plant 8 includes the following unit processes (see
Figure 4-36).
1.2-m (4-ft) diameter corrugated steel intake which
extends below the river bottom. The steel intake
pipe is perforated and packed with gravel in the
area below the river bottom
Wet well with two 16-L/s (250-gpm) submersible
raw water pumps. The pumps are automatically
operated from a level signal in the plant clearwell.
15-cm (6-in) diameter propeller meter for measuring
the raw water flow rate
110-4,375 kg (240-9,645 lb)/d dry alum feeder
3-15 L (0.1-0.5 cu ft)/hr lime feeder
3-15 L (0.1-0.5 cu ft)/hr soda ash feeder
Polymer feed system with a 170-L (45-gal) dilution
tank and a 3.7-20.8 L (1- 5.5 gal)/hr feed pump
Steel, 5.5-m (18-ft) diameter, 3.2-m (10.5-ft) deep
solids contact unit with 45ฐ tube settlers
1.3-6.8 L (0.34-1.8 gal)/hr polyphosphate feeder
11 -kg (24-lb)/d carbon dioxide feed system and an
associated in-line static mixer
Steel 3.2-m (10.5-ft) diameter dual-media filter
9-kg (20 lb)/d gas chlorination system
56,000-L (14,800-gal) clearwell with baffled
compartments
Two 16-L/s (250-gpm) vertical turbine pumps which
pump treated water to the distribution system and a
storage tank
Two sludge holding lagoons with a total capacity of
approximately 658,200 L (173,900 gal)
Spent backwash storage lagoon of approximately
2.1 million-L (556,170-gal) capacity
River water flows to the raw water pump wet well
through a pipe that is located inside the corrugated
steel intake structure. The original intake configuration
consisted of an infiltration gallery located in the river;
however, due to plugging of the gallery with sediment,
the system was replaced in 1986 with the current
intake pipe. The operator and board members
indicated that the original infiltration gallery provided
water of much lower turbidity than the current intake
structure. However, as the gallery became plugged
with sediment, raw water capacity was reduced to the
extent that the board decided to replace the infiltration
gallery with the present system.
The two raw water pumps, located in a wet well
adjacent to the river, each deliver the rated plant
capacity. Pump operation is based on a level signal
from the plant clearwell, and operation is alternated to
maintain even run times on both units. The plant
operator reported that a pump is typically operated at
full capacity; however, a butterfly valve located in the
plant can be used to reduce pump capacity. In an
attempt to maintain a sludge blanket in the solids
contact unit, the operator had throttled pump capacity
to reduce flow to the unit. The operator felt that this
experiment did not stabilize the process, and since
that time the plant has operated at 16 L's (250 gpm).
The raw water flow rate is indicated and totalized
through a propeller meter located in the raw water line
inside the plant building. Following the flow meter, raw
water is directed into the solids contact unit.
Components of this unit include an upflow mixing
column with a turbine mixer, a downflow flocculation
cone, and an upflow clarifier with tube settlers
throughout the settling area.
Water treatment chemicals including alum, lime, soda
ash, and polymer can be added into the mixing area.
During the winter, when water hardness increases in
the river, the operator can add lime and soda ash to
the solids contact unit for softening. During the
remainder of the year, alum and a polymer are
typically used for turbidity removal. The operator
reported that the plant was not operated in the
softening mode last winter and that alum and a
cationic polymer were used for coagulation during this
period. At the time of the site visit, the operator
indicated that 80 mg/L of alum and 2 mg/L of cationic
polymer were being fed to the mixing tube.
A variable speed turbine mixer located on top of the
mixing tube directs the incoming raw water upward
through the tube and out into the flocculation cone.
The mixing tube is open at the bottom, thus allowing
the recirculation of flocculated water with the incoming
raw water. The amount of recirculation depends on
the speed of the turbine mixer. According to the
operator, the turbine mixer speed has been operated
throughout the entire range, without changing the
performance characteristics of the solids contact unit
59
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Figure 4-36. Plant 8 process flow diagram.
River
Raw
Water
Pumps
Flow
Meter
Backwash
Supply
Line
Solids
Contact Unit
Sludge Beds
Alum, Lime,
Soda Ash,
Polymer
Backwash
Control
Valve.
Clearwell
Filter Rate
Control Valve
High
Service
Pumps
To
Distribution
System
60
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except at high speed. At high speeds, turbulent
conditions in the unit degraded clarifier performance.
The current practice is to operate the turbine at low to
medium speed, and the turbine and sludge scraper
continuously, even when the plant is not treating
water.
Following the mixing tube, the conditioned water
enters an inverted cone where flocculation occurs. At
the bottom of the flocculation cone, water moves
outward into the clarifier and, theoretically, through a
developed sludge blanket. Water then flows upward
through 45-degree tube settlers before overflowing a
peripheral weir. The operator reported that he has had
a difficult time controlling the sludge blanket in the
solids contact unit. It appeared that sludge solids
generated in the process are typically lost over the
weir and deposited on the filter.
Excess sludge generated in the process can be
directed to two sludge lagoons by opening a sludge
blow-off valve. The operator indicated that sludge has
never been removed from the two sludge lagoons
since startup of the plant. Effluent from the solids
contact unit flows onto a dual-media filter. If the plant
is operating in the softening mode, carbon dioxide can
be added for pH adjustment after the solids contact
unit. Mixing is accomplished by an in-line static mixer.
Polyphosphate can also be added at this location to
control calcium carbonate buildup in the filter. Even
though the plant was not operating in the softening
mode during the site visit, polyphosphate was still fed
to the solids contact unit effluent.
Water level in the filter is controlled by a modulating
flow control valve. According to the operator and
several board members, this control valve has never
provided a constant-rate operating condition as
intended by the original design. Until just recently,
water level in the filter would fluctuate dramatically
during a filter run, causing sudden, high magnitude
flow rate changes through the filter. This condition has
improved significantly since the plant operator and a
board member fabricated an adjustment mechanism to
control the travel distance of the valve seat.
Backwashing of the filter can be initiated by either
filter headloss or filter effluent turbidity. The backwash
supply water is provided by the pressurized
distribution system including an elevated storage tank,
and the backwash rate is controlled by a pressure
reducing valve. Spent backwash water is directed to a
storage lagoon located adjacent to the plant. The
operator reported that spent backwash water seeps
into the ground water and has never accumulated in
the lagoon.
Treated water from the filter is chlorinated and
directed to a baffled clearwell. The two vertical turbine
pumps deliver treated water to the distribution system.
Pump operation is based on a water level signal from
the elevated storage tank. When operated in
automatic mode, the plant may start and stop more
than once daily with each start on a "dirty" filter.
According to the operator, the clearwell is taken out of
service once each year to remove accumulated
sediment in the tank bottom.
Operation is usually by the automatic mode (i.e.,
storage tank elevation). During peak water usage
periods in the summer months, the plant operates 12-
14 hr each day at the design rate 16 Us (250 gpm).
Less operating time is required during the winter. The
plant is staffed about 2-3 hr each day by one operator.
Board members assist with plant maintenance and
repair on an as-needed basis. The plant operator is
also responsible for a booster pump station and
distribution system serving the rural water members of
the district. The operator and board members reported
that maintaining this part of the system can be very
time consuming because of frequent leaks that occur
in areas of the rural distribution system.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
37. Mixing, flocculation, and sedimentation processes
all occur in the solids contact unit. Although
flocculation is typically evaluated on the performance
potential graph, it was not included here because the
process occurs within the solids contact unit.
Flocculation in solids contact units is enhanced by the
recirculation of flocculated water through the mixing
tube with the incoming raw water. The sedimentation
component of the solids contact unit was rated at a
surface overflow rate of 58 m3/m2/d (1,421 gpd/sq ft),
which is slightly less than the design rate. This rating
is also based on incoming raw water turbidity levels of
less than 500 NTU, which is typical for most of the
year, and a relatively shallow depth of 3 m (10 ft). For
occasions when turbidity is greater than 500 NTU, the
sedimentation component was rated at a surface
overflow rate of 32 m3/m2/d (790 gpd/sq ft) or 8 L/s
(125 gpm). At this turbidity level, control of the sludge
blanket might be difficult and solids loss from the unit
would begin to affect filter performance. The plant
could overcome this limitation by operating at the
lower flow rate of 8 L/s (125 gpm) over a longer
period of the day.
The dual media filter was assessed based on a
filtration rate of 176 m3/m2/d (3 gpm'/sq ft). At this
rate, a potential capacity of 16 L/s (250 gpm) was
projected for the existing filter. In some cases, dual-
media filters have been rated over 176 m3/m2/d (3
gpm/sq ft); however, because of the complex
operations associated with the solids contact unit, a
conservative filtration rate was selected. This rating
also assumes that the existing effluent control valve
limits extreme variations in water flow rate through the
filter. Although the modifications made to the control
valve appear to have significantly improved filter
operation, adequate time was not available during the
61
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Figure 4-37. Plant 8 performance potential graph.
Unit Process
50
Flow, gpm
100 150 200 250
300
Solids Contact Unit1
SOR, gpd/sq ft
Filtration*
HLR, gpm/sq ft
Disinfection
Contact time, hr
316 632 947 1,263
0.6 1.2 1.7 2.3 2
4.9 2.5 1.6 1.2 1
9
0
Design
Flow
1 Capacity reduced to approximately 125 gpm when turbidity >500 NTU. Shallow, 10-ft deep clarifier limits capacity to <250 gpm
when turbidity >500 NTU.
2 Assumes adequate filter effluent control valve.
site visit to thoroughly evaluate the valve's
effectiveness.
The chlorine contact basin was rated at 16 Us (250
gpm) based on a hydraulic residence time of 1 hr.
Disinfection capability is typically based on current
State criterfa of a 2-hr residence time after
chlorination. The 1-hr residence time was allowed in
this case because of the efficient baffling that exists in
the contact basin.
At the present time, the plant operates at the 16 Us
(250 gpm) rate for about 12-14 hr/day during the peak
demand period. The performance potential graph
indicates that this peak demand can be met when raw
turbidity is less than 500 NTU without significant
changes in hours of operation. To meet the peak
demand when turbidity is greater than 500 NTU, the
plant would have to operate at a reduced rate of
approximately 8 Us (125 gpm) over a 24-hr period.
Performance Assessment
This plant has historically had operational problems
associated with the operation of the solids contact
unit. During the CPE site visit, the plant operator
reported that maintaining a sludge blanket in the solids
contact unit has been a problem since startup. Other
operations-related information obtained during the site
visit indicated that performance problems have been
more common than indicated by plant monitoring
reports. Rgure 4-38 shows the number of days that
treated water turbidity exceeded 0.5 NTU (the SWTR
turbidity standard for treated surface water) for each
month over the past year. This analysis indicated that
performance problems have occurred on a frequent
basis over the past year, and have been more severe
during the winter months when low turbidity, cold
water was treated by the plant.
During the CPE, a special study on filter startup under
two different conditions was conducted. The first
condition consisted of starting a dirty filter (i.e., a
condition in which a backwash had not occurred
before filter startup) and monitoring effluent turbidity.
The operator indicated that this condition occurs
routinely at the plant because of the automatic mode
of operation. A graph of filter performance under this
condition is shown in Figure 4-39. As shown, following
filter startup effluent turbidity immediately increased to
over 5 NTU and then gradually decreased to about
1.5 NTU after 20 minutes. Results of this test indicate
that starting a dirty filter results in turbidity levels
above the 0.5-NTU limit for an extended period of
time and presents a significant danger of passing
pathogenic organisms through the filter.
The second condition of the special study involved
backwashing the filter and monitoring the effluent
turbidity after it was placed in operation. As shown in
Figure 4-40, turbidity after backwash increased
immediately to a peak value of 13.5 NTU. About 25
minutes after the filter startup, the effluent turbidity
decreased to the 0.5-NTU level. This condition also
indicates the potential for pathogenic organisms to
pass through the filter. Properly conditioned filters
typically experience a turbidity spike of less than 0.2
NTU for less than 15 minutes.
Several problems associated with the backwash
contributed to the subsequent poor performance of
62
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Figure 4-38. Plant 8 performance.
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
the filter. When the backwash sequence was initiated,
the surface wash valve did not open. According to the
operator, the surface wash normally operates the
entire length of the backwash period. The filter was
washed for over 23 minutes, a much longer than
normal duration for this function, without getting clean.
Because of the dirty condition of the filter, the
backwash rate was manually increased by adjusting
the control valve, but never succeeded in cleaning the
filter. Measurements of the rise rate in the filter at the
beginning of the backwash indicated a backwash rate
of approximately 645 m3/m2/d (11 gpm/sq ft), less
than the minimum recommended value of 878
m3/m2/d (15 gpm/sq ft). Proper adjustment of the
backwash control valve would allow an adequate
backwash flow rate.
An additional factor that could have contributed to the
plant's poor performance during the CPE site visit
relates to the alum feed rate to the solids contact unit.
The operator indicated that the alum feed 'rate to this
unit was approximately 80 mg/L. Upon checking the
alum feeder by weighing a sample of dry alum
collected over a selected time period, it was
determined that the actual alum feed rate was about
177 mg/L. Since the raw water turbidity was about 80
NTU at the time of the site visit, alum was probably
being overfed at this dosage rate. Following further
investigation into this problem, it was determined that
the operator had exchanged the alum feeder with the
lime feeder. This change was implemented so that the
feeder with a vibrator could be used for lime addition.
The operator was not aware that the new alum feeder
had a 3.8-cm (1.5-in) feed screw instead of a 1.9-cm
(3/4-in) feed screw, thus causing a higher-than-
expected alum dosage.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis were
prioritized and are summarized below:
1- Water Treatment Understanding - Operation: Lack
of operator understanding of water treatment has
been a major cause of the performance problems
experienced at the plant. The plant operator never
received any formal training on operation of the
plant. This situation is compounded by the fact
that the solids contact process is complex and
requires a high level of process control to achieve
good performance. Examples of this lack of
understanding include incorrect calculations of
63
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Figure 4-39. Turbidity profile - dirty filter startup - Plant 8.
Effluent Turbidity, NTU
6 r-
0
1
5
1
10
Time, min
I
15
I
20
jure 4-40. Turbidity profile - filter startup after backwash
Plant 8.
{fluent Turbidity, NTU
14
4 ~
2 -
5 10 15
Time, min
20
25
alum and polymer feed dosages, startup of dirty
filters, inadequate process control testing, and an
inadequate filter backwashing procedure.
2. Process Control Testing - Operation: The current
process control testing in effect at the plant is
inadequate. The only process control testing
currently done is periodic jar testing to determine
chemical dosages. Jar testing should be
completed whenever raw water quality changes
significantly. Control of the solids contact unit
requires daily monitoring of influent and effluent
turbidity, sludge blanket concentration and
location, and blowoff sludge volume and
concentration. The plant does not have adequate
testing equipment to perform many of these tests.
Although a jar testing apparatus is available at the
plant, it does not accurately simulate the
flocculation and coagulation processes. Equipment
necessary to monitor the solids contact unit
includes a blanket finder and a centrifuge.
3. Plant Coverage - Administration: Paid coverage at
the plant is presently 2- 3 hr/day, 7 days/week. If
unanticipated problems develop at the plant or
distribution system that require time beyond the
routine amount, the operator and board members
volunteer time to correct the situation. The
operator's son currently acts as a backup
operator; however, he has not received any formal
training and is not certified in water treatment.
Given the complex nature of the plant and the
potential for extreme variations in raw water
quality, coverage at the plant needs to be
extended. Ideally, whenever the plant is in
operation, an operator should be at the plant
monitoring its performance. A minimum of 4 hr
each day probably would be required to perform
routine process control testing, data analysis,
reporting, and preventive maintenance activities.
Realistically, it would probably be difficult to staff
the plant at all times that it is in operation because
of the small size of the district. A possible
compromise could include increasing plant
coverage to a minimum of 4 hr/day, not including
the distribution system, and adding an alarm/dialer
system at the plant.
4. Insufficient Funding/Bonded Indebtedness -
Administration: The district received a 40-year
loan from the Farmer's Home Administration to
fund the construction of the plant in 1981.
Repayment of this loan requires approximately 50
percent of the district's revenues at the present
time. Because of the small size of the district,
approximately 46 town customers and 62 rural
customers, and the large indebtedness, water
rates are moderately high relative to other similar
systems. Rates were recently increased to assist
in rebuilding a reserve fund that was depleted
when the new intake structure was installed. Even
64
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with these moderately high rates, revenues are
marginal to cover the cost of additional plant
coverage and minor capital improvements.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
were prioritized and are summarized below.
1. Plant Staff. Number - Administration: The plant is
staffed by one operator at the present time, and
he provides coverage 7 days/week. Occasionally,
the operator's son performs as a backup operator
when the operator is not available. A trained,
backup operator is needed at the plant to routinely
relieve the regular operator. Several of the board
members recognized this problem and expressed
their concern with locating a person who would be
willing to work on a part-time basis at the pay rate
they could afford. The operator's son has
expressed some interest in becoming certified in
water treatment. Given his work experience at the
plant, this option may be worth pursing by the
district. Another option could involve utilizing an
interested board member as the backup operator.
Once trained and certified, the backup operator
could provide plant coverage on alternating
weekends and during vacations.
2. Alarm System - Design: An alarm and automatic
plant shutdown capability are available when high
turbidity is recorded from the filter. As is the case
with any type of automation, this function has
failed on occasion and high turbidity water was
directed to the clearwell. This alarm function
provides a necessary safeguard against
contaminated water entering the distribution
system and should be routinely checked and
maintained. Because of the high degree of
variability in the raw water source, it would be
advantageous to have a similar high turbidity
alarm and automatic plant shutdown capability for
this source. This capability could warn the
operator about a change in raw water turbidity and
allow time to adjust chemical feed dosages.
3. Chemical Feed Facilities - Design: Because of the
exchange made between the lime and alum
feeders, the present alum feeder does not appear
to have a satisfactory range to feed low dosages
under certain water quality conditions. Since
overfeeding alum can detrimentally affect plant
performance, this problem will have to be
corrected. The operator may want to investigate
changing the feeders back to their original
functions. If lime is to be fed in the future, a new
shaker may be required.
4. Process Controllability - Design: Since startup of
the plant, the filter effluent control valve has
caused erratic control of the water level in the
filter. This rapid change in filter water level causes
particles to pass through the filter, thus affecting
treated water quality. Recently, a throttling
mechanism fabricated by the operator and a board
member has limited these fluctuations in water
level. With this modification completed, this factor
moved to a lower priority; however, replacement
of the valve should still be considered when
funding is available.
5. Performance Monitoring - Operation: During the
CPE site visit, performance monitoring records
were reviewed, and some performance problems
were occasionally noted. However, interviews and
special studies conducted during the CPE
revealed serious performance problems at the
plant. Since records did not accurately reflect
actual plant performance, regulatory agency
reviews were not able to establish that a
performance problem existed. Accurate reporting
would probably have resulted in pressure from the
regulatory agency and correction of some of the
factors noted in this report.
6. Raw Water Turbidity - Design: As noted by the
performance potential graph, raw water turbidity
above 500 NTU is projected to limit plant capacity.
High turbidity water typically occurs during the
spring through fall, and only occasionally during
this period as the result of runoff from storm
events. The high turbidity problem can most
realistically be handled through operational
changes and minor expenditures for testing
equipment and an alarm system. If the current
peak demand remains the same, the plant may be
able to treat high turbidity water by reducing the
flow rate through the plant and operating for more
hours during the day. If operational measures are
not successful, there should be added flexibility to
direct the raw water through a pre-sedimentation
basin with chemical addition capability. A pre-
sedimentation pond could be used as a backup
water supply during short runoff events or used to
lower raw water turbidity during longer storm
events.
7. Sedimentation/Solids Contact Unit - Design: The
solids contact unit's capability to treat water under
a variety of conditions may be limited by its
relatively shallow 3-m (10-ft) depth and high
surface overflow rate. Under these conditions,
maintaining a sludge blanket in the unit can be
accomplished; however, considerable process
control testing and possible adjustments to the
plant flow rate are required. The short hydraulic
residence time in the unit may limit the plant's
capability to treat cold, low-turbidity water. Under
cold water conditions, chemical reactions are
slower and longer residence times are required.
Longer residence times can be achieved by
operating the plant at a lower rate for long periods
of time.
65
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A factor identified as having a minor effect on plant
performance is the existing chemical feed
arrangement, which limits the injection of alum,
polymer, lime, and soda ash to the mixing tube in the
solids contact unit. Under cold, low turbidity water
conditions, it would be advantageous to add the
coagulation chemicals ahead of the flow meter. This
injection location would allow more intense mixing and
slightly more detention time when treating cold, low
turbidity water.
Projected Impact of a CCP
As indicated by the performance potential graph and
factors limiting performance, this plant does have
some design deficiencies. However, operational
changes at the plant and administrative support could
be used to overcome most of these deficiencies. As
such, implementation of a CCP could demonstrate
dramatic improvement in treated water quality. Before
a CCP could be implemented, however, the district
would have to commit to providing the additional
staffing and coverage required to operate the plant
and the expenditures necessary to purchase the
necessary testing equipment.
66
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Plant 9
Facility Description
Water is supplied to the city from four sources: a
direct filtration plant and three ground-water wells that
augment the water supply during summer months.
The CPE was limited to the direct filtration plant,
which treats water from an infiltration system for
domestic and commercial use by the city. The peak
day demand for a 12-month period was estimated at
74 Us (1.7 mgd). Plant 9 includes the following unit
processes (see Figure 4-41):
Infiltration system consisting of perforated
subsurface laterals that are connected to shallow
caissons
8,330-L (2,200-gal) basin that serves as a sand trap
In-line static mixer with two elements
30-m2 (324-sq ft) monomedia (sand) travelling
bridge automatic backwash filter
Two polymer feed pumps: one for feeding neat
polymer and one for feeding diluted polymer
Gas chlorination system with two chlorinators, each
23-kg (50-lb)/d capacity
On-site treated water reservoir, 33.5 m (110 ft) in
diameter and 2-m (6.5-ft) deep (1.7 million L
[462,000 gal])
Propeller meter on the discharge line from the
treated water reservoir
On-site 12-m x 12-m x 2-m deep (40-ft x 40-ft x
6.5-ft) concrete backwash holding basin, which
r4ie*r*fa?3mc\o +r\ on iKKir^Qtinri Hity-*h
discharges to an irrigation ditch
Water from one of two creeks is diverted onto a hay
field adjacent to the plant where the water percolates
through several feet of soil to perforated laterals
buried under the field. Water flows through the laterals
to concrete caissons, which are fitted with metal
covers. A line then carries the composite flow from
the caissons to the direct filtration plant. Microscopic
particulate examination of the infiltration system water
has shown that it is directly impacted by the surface
water and, therefore, should be considered a surface
water source.
Raw water flows by gravity from the infiltration system
to a sand trap basin in the plant. Cationic polymer is
fed at the end of the basin after which the water flows
through a control valve that regulates the amount of
water treated in the plant. Any excess water from the
infiltration system flows over a weir at the influent end
of the sand trap basin to an irrigation return ditch. The
control valve can operate automatically to shut down
or start the plant, based on the water level in the
finished water reservoir. At the time of the evaluation,
the valve was being operated manually to maximize
the depth of treated water in the finished water
reservoir.
After passing the control valve, the water flows by
gravity through an in-line static mixer and onto the
automatic backwash filter. The filter was designed to
operate at a filtration rate of 117 m3/m2/d (2 gpm/sq
ft), but was being operated at approximately 211
m3/m2/d (3.6 gpm/sq ft) at the time of the CPE. The
filter has approximately 28 cm (11 in) of sand media in
54 20-cm (8-in) sections.
The filter sections are separated by fiberglass
dividers, which were warped at the top. Because of
the warping, some sections were only 2.5-5 cm (1-2
in) wide at the top, while other sections were over 20
cm (8 in) wide at the top. This variation was caused
by migration of the sand media from one section to
another during backwash.
The filter can be backwashed automatically by
headloss or by timer. During the evaluation, the filter
was being washed automatically based on headloss,
with little consideration given to filter effluent turbidity.
When the filter is backwashed, a travelling bridge
passes across the filter and washes each section.
One pump on the bridge pumps water back up
through the filter section and another pulls the spent
backwash water from the top of each section through
a shroud to a discharge channel adjacent to the filter.
The backwash water flows by gravity to the backwash
storage basin. Following filtration, the water is
chlorinated prior to the filter level control weir and
flows into the treated water reservoir. Effluent from the
reservoir flows by gravity 8 krn (5 miles) to town
through parallel 20-cm (8-in) and 25-cm (10-in)
transmission lines.
Sludge from filter backwashes is stored in the
concrete backwash storage basin. Supernatant from
the basin is discharged over a weir to an irrigation
ditch. According to the operator, sludge is removed
from the basin every 3-4 years by wheelbarrow and
front-end loader and is spread on adjacent fields.
Operation is primarily manual except for filter
backwashing. Plant operation, flow rates, and
chemical dosage rates are all initiated manually by the
plant operators. The two plant operators spend
approximately 0.5-1 hr each day at the plant checking
the operation of the plant. During that time, the plant
is inspected to ensure equipment is operating
properly; no significant process control activities are
conducted. The operators are also responsible for the
wastewater treatment plant, wastewater collection
system, water distribution system, streets, parks,
airport, swimming pool, and grave digging at the
cemetery.
67
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Figure 4-41. Plant 9 process flow diagram.
Infiltration
Laterals
Sand trap.
Overflow
Bypass Line
Automatic
Backwash Filter
Overflow
To Town
68
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Figure 4-42. Plant 9 performance potential graph.
Unit Process
0.5
Flow, mgd
1.0 1.5
2.0
Filtration1
gpm/sq ft
Disinfection
Contact time2, hr
Contact time3, hr
1.1
2.9
6.3
3.2
2.1
Estimated Max.
= 1.7 mgd
1 Rated at 2 gpm/sq ft because there is only 11 in of sand medium.
2 Based on current State standard of 2-hr HOT to first tap. Assumed 10 percent volume of clearwell and 0.75 mi of 8- and 10-in pipe to
first user. HOT refers to time it takes water to travel from the plant to the first tap.
2 Based on current State standard of 2-hr HOT to first tap. Assumed 10 percent volume of clearwell and 2.5 mi of 8- and 10-in pipe to
first user in town.
During the evaluation, peak water use in the city was
approximately five times greater than typical water use
for a community with no large industrial users. This
extensive use required the city to augment the surface
water supply with three ground-water wells.
Determining the cause of the excessive water use and
taking measures to lower it to normal levels would
allow the plant to operate at lower flow rates.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
42. Peak day demand for the plant was estimated by
measuring the depth of flow over the filter effluent
weir and applying that flow on a 24-hr basis. This flow
was then compared to projected plant capabilities. As
Figure 4-42 shows, the monomedia sand filter was
assessed at a potential capacity of 39 Us (0.9 mgd)
based on a filtration rate of 117 m3/m2/d (2 gpm/sq ft).
The filter capability was limited because a direct filter
using 28 cm (11 in) of sand cannot be expected to
provide consistent performance at rates higher than
117 m3/m.2/d (2 gpm/sq ft).
Disinfection capability was rated based on current
state criteria of a 2-hr detention time after chlorination.
As Figure 4-42 shows, two conditions were rated:
detention time to the first tap downstream from the
plant and to town. Disinfection detention time was
adequate to town at flow rates up to 77 L/s (1.75
mgd). However, detention time to the first tap only
resulted in a plant capacity of 33 L/s (0.75 mgd).
Standards are being revised and different criteria may
be used to allow lower minimum detention times for
existing plants, which would likely rely on effective
filtration.
Because of the limitation in the filtration process, the
plant was assessed as inadequate to meet the
projected peak demand. However, water use on a per
capita basis was noted to be extremely high. Normal
water use would result in daily water production of
about 39 L/s (0.9 mgd), which the plant should be
able to handle on a continuous basis.
Performance Assessment
A review of the operating records indicated that the
raw water was of very good quality with peak
turbidities of 0.7 NTU. Treated water was also of good
quality with turbidities normally about 0.2 NTU and
with a peak of 0.45 NTU. However, turbidity of very
clear waters, such as the water from the infiltration
system, is often not a good indication of
bacteriological quality. In fact, previous state
particulate tests revealed that the filter was not
removing a significant number of particles from the
raw water. The operating data revealed that only
about 50 percent of the raw water turbidity was being
removed. Plant data taken during periods of no
chemical feed and some chemical feed indicated little
difference between raw and treated water turbidity
between the two.
During the CPE, a special study was conducted to
determine the effect of backwashing the filter on
treated water quality. The filter was backwashed and
samples were collected as near as possible to the
filter cell being washed and at the filter effluent weir.
Figures 4-43 and 4-44 present the results of the
study. As shown, at both sample points effluent
turbidity increased significantly (to 5 and 7- NTU)
during backwash and remained above the 0.5 NTU
69
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Figure 4-43. Turbidity profile during and after backwash at filter effluent weir - Plant 9.
Turbidity, NTU
5 i-
4 -
3 -
2 -
1 -
Completed 1 st Pass
Completed Wash
Figure 4-44. Turbidity profile during and after backwash at cell effluent - Plant 9.
Turbidity, NTU
8 i-
7 -
6 -
5 -
4 -
O
o -
1
0
24
70
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limit for over 60 minutes. The study results indicate
that a significant amount of the material removed by
the filter was allowed to pass through the filter into the
treated water reservoir. The significant increase in
turbidity is especially indicative of poor performance,
since the raw water turbidity was only about 0.6 NTU
during the special study.
The special study results, State microscopic
evaluations, and plant daily records indicate that the
plant is not effectively removing particles found in the
raw water. Should a significant number of parasitic
organisms such as Giardia cysts or Cryptosporidium
oocysts occur in the raw water (for example, as a
result of cattle feeding on the grass above the
infiltration system), they would likely enter the plant
and pass through the filter. Since some cysts are
resistant to disinfection by chlorine, they could pose a
significant health hazard to the community.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis were
prioritized and are summarized below:
1. Water Treatment Understanding - Operations: The
plant superintendent/utilities director is a very
motivated operator; however, he has not received
any formal training in water treatment practices.
This is compounded by the complexity of
operating a direct filtration plant treating cold, low
alkalinity, low turbidity water. Lack of water
treatment understanding was identified as the top
ranking factor because it has led to poor operating
decisions, such as little or no change in chemical
feed rates, filter backwashing based on headloss
rather than filtered water quality, and bypass of
untreated raw water to the treated water storage
reservoir. Operation of the plant will require a
process control program and an understanding of
coagulation chemistry including chemical feed
calculations.
2. Process Control Testing - Operations: There was
no process control program in place at the plant.
Operation of a surface water plant requires that
testing be conducted and results recorded in a
systematic manner so that data is available to
make process control decisions. Control of the
direct filtration plant will require daily monitoring of
influent turbidity, continuous monitoring of filter
effluent turbidity, and jar testing to select
appropriate coagulant aids and to determine
optimum chemical doses.
3. Process Automation - Design: The plant is not
equipped with a continuous reading and recording
turbidimeter, which is necessary to adequately
monitor plant performance since the staffing levels
do not allow turbidity tests to be conducted more
than once each day. A continuous reading
turbidimeter would allow filter performance to be
monitored following a backwash so that chemical
feed could be optimized to reduce the increase in
turbidity (turbidity spike) that occurs after a
backwash.
4. Disinfection - Design: A detention time of 2 hr is
needed to ensure effective disinfection of the
treated water prior to the first user. The new
regulations that will be promulgated as a result of
the SWTR and/or current state criteria may
necessitate capital improvements before the water
system has adequate disinfection capability. An
example of a capital improvement would be the
installation of baffle walls in the clearwell to keep
the water in the basin longer for disinfection rather
than taking a direct route through the basin from
the influent to the effluent pipe. This factor was
asterisked because the final rule will not be
effective until June 29, 1993, following
development of State criteria in 1990.
5. Filtration - Design: The filter is presently being
operated at too high a rate to expect adequate
performance on a continuous basis. In addition,
warping of the filter section dividers and the
potential inability of the travelling backwash
mechanism to properly wash the filter could
impact filter performance. This factor was
asterisked because it may be possible for the
plant to operate at a flow rate consistent with its
capability, if water use is reduced to normal
levels. Under this condition, the filter dividers and
backwash may prove not to significantly impact
performance.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
are summarized below in order of priority.
1. Process Controllability - Design: The effluent flow
meter does not adequately measure the plant flow
rate because it is located downstream of the
finished water storage reservoir. The flow rate out
of the reservoir is not indicative of the plant flow
rate. Since accurate flow measurement is the
basis for chemical feed calculations and filter
hydraulic loading rates, actual plant flow needs to
be accurately measured.
2. Laboratory Space and Equipment - Design: The
plant is not equipped with a jar test apparatus.
Because of the raw water quality characteristics
(low turbidity, alkalinity, and temperature), special
studies with various coagulant and flocculant aids
will likely be required to optimize plant
performance. A jar test apparatus will be
necessary to conduct the special studies as well
as to optimize plant chemical feeds.'
3. Alarm System - Design: There were no alarm
systems in the plant to warn the operator of
71
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problems, such as chemical feeder shutdown or
raw water quality changes. Since the plant is only
checked once each day for about 1 hr, it is
essential that alarms be provided to warn the
operator of a change in conditions. If alarms are
not provided, the plant should be staffed any time
it is in operation.
4. Watershed Management - Design: Allowing cattle
to graze on top of the infiltration system provides
an unnecessary public health risk. Cattle are
known carriers of Cryptosporidium, a parasitic
cyst that is extremely resistant to chlorine
disinfection and small enough to easily pass
through a poorly operated filter. A direct filtration
plant provides a limited number of barriers to
pathogenic organisms and limited response time
for the operator to react to a change in raw water
quality.
No factors in the administration or maintenance areas
were identified as impacting performance.
Projected Impact of a CCP
Plant 9 produces water that poses a significant health
risk to consumers. Conducting a CCP could result in
an improvement in finished water quality, especially
during and after filter backwashing. However, because
peak water demands exceed the rated capacity of the
filter and disinfection system, the plant would have to
be operated at a lower flow rate. In addition, design
aspects of the filter such as backwashing
effectiveness and uneven filter dividers, could limit
filter performance to the extent that the plant could not
meet regulatory requirements on a continuous basis.
The CCP might discover that limitations in the filtration
system require major capital improvements to ensure
continuous compliance with applicable regulations.
72
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Plant 10
Facility Description
Plant 10 is a conventional water treatment plant
supplied from a nearby river that provides water for
domestic use. The peak operating flow for the plant
was established at 22 Us (0.5 mgd) based on a
review of flow records for the previous year. The plant
is normally operated for approximately 8 hr/day;
however, on several days the plant is operated for
longer than 8 hr to meet demands of peak water use.
On these days, the treatment processes are still
operated only at the 22-L/s (0.5-mgd) flow rate. Plant
10 consists of the following unit processes, shown
schematically in Figure 4-45:
Intake structure located on the bank of the river,
consisting of a manhole intake structure and a wet
well from which raw-water pumps deliver the water
to the plant. A bar screen is provided between the
manhole intake structure and the wet well
Three manually operated vertical turbine raw water
pumps; two 22 Us (350 gpm) and one 16 Us (250
gpm)
Raw water flow measurement consisting of an 20-
cm (8-in) orifice meter with a chart recorder. Also,
a manual rate-of-flow controller
Volumetric feeder each for alum, lime, and
powdered activated carbon
Two 9.1-m (30-ft) diameter sedimentation basins,
each with a surface area of 66 m2 (707 sq ft) and a
volume of 307,000 L (81,100 gal)
Two 19,300-L (5,100-gal) recarbonation basins
Four 2.6-m x 3.0-m (8.7-ft x 10-ft) filters with 61 cm
(24 in) of sand media
94-L/s (1,500-gpm) backwash pump
Gas chlorination system
Two clearwells: one with a capacity of 567,750 L
(150,000 gal) and the second with a capacity of
56,775-L(15,000-gal)
Two 47-L/s (750-gpm) vertical turbine high-service
pumps
Venturi-type flow meter, totalizer, and chart
recorder
Water from the river is pooled behind a low head dam
across the river downstream of the intake structure.
Several pipes extend out into the river from the
manhole intake structure allowing water to be taken
from different locations. The water then flows to the
wet well where it is picked up by the raw water
pumps.
Raw water pumps located on top of the wet well move
the raw water from the intake structure to the plant.
Only one of the 22-L/s (350-gpm) pumps is used.
Though the plant was originally designed for 44 Us
(700 gpm), the plant staff feels that 22 Us (350 gpm)
is the maximum flow that can be handled because of
limitations with the sedimentation basins. Since the
plant is operated at a constant rate of 22 Us (350
gpm), variations in water demand are met by varying
the length of time the plant is operated. Raw water
flows entering the plant are measured and recorded. A
manual rate-of-flow controller is available though not
normally used.
Volumetric feeders discharge dry chemicals into tanks
below the feeders, where water is added and mixed to
make a slurry. As the raw water flows to the
sedimentation basins, alum and lime are added as
slurries into the pipe. Chemical feed rates can be
adjusted by varying the amount of chemical added to
the slurry tanks. These adjustments are made based
on observations of floe formation in raw water
samples that have been placed on a magnetic stirring
apparatus after chemical feed. No mechanical or static
flash mixing is provided. Chemical feed rates are not
routinely adjusted.
After chemical addition, raw water flows to the two
sedimentation basins. These units were originally
designed as a type of upflow solids contact clarifier,
eliminating the need for separate flash mix and
flocculation processes, but they are no longer
operated as designed. Flow enters through a 20-cm
(8-in) pipe at the bottom of the unit and strikes a small
baffle redirecting the flow in the basin. Basin effluent
discharges through peripherally mounted submerged
orifice weirs. Each basin originally had a rotating arm
located near the bottom powered by pressurized basin
effluent. Basin effluent was to be withdrawn and
pumped back through nozzles in the arm causing it to
rotate and promote flocculation. The rotating arm has
been removed from one of the units and is not
operational in the second. Sludge is manually
removed from the basins twice a year. The plant
discharges this sludge to the sanitary sewer or back
to the river.
Settled water flows by gravity from the sedimentation
basins to the four sand filters and is controlled by float
valves in the recarbonation basins. These valves shut
off sedimentation basin effluent flow if the level in the
filters exceeds the maximum. Operators visually
monitor the filter water levels and adjust the flow using
rate-of-flow controllers. Flow meters are available for
each filter, but are not used for filter flow adjustment.
During the CPE, the standard practice for filter
backwashing was to wash two of the filters each day
73
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Figure 4-45. Plant 10 process flow diagram.
74
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using backwash water from Clearwell 2. Headless or
turbidity measurements were not typically used to
initiate backwashing. The backwash pump discharges
through a rate-of-flow controller, but there are no
valves that can easily be operated to slowly start and
stop the backwash flow to the filters. The surface of
the sand is manually raked during the backwashing.
The plant discharges backwash water to the sanitary
sewer or to the river. During the CPE, the backwash
water was being discharged to the river.
Water from all four filters is discharged to Clearwell 1,
immediately following injection of chlorine gas into the
pipe. Chlorine doses are controlled to provide a
residual of 2.5-3.0 mg/L Finished water normally flows
from Clearwell 1 to Clearwell 2; piping is provided to
allow bypassing of Clearwell 1. Clearwell 2 also
serves as the suction pipe for the high-service and
backwash pumps.
Two high-service pumps supply finished water to the
two in-ground storage tanks that feed the village water
distribution system. These pumps are operated
manually based on water levels in the storage
reservoirs.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
46. Flocculation is a key major unit treatment process.
As originally designed, the sedimentation basins were
to provide both flocculation and sedimentation;
however, the flocculation aspect of these units has
been removed or is inoperable. The CPE team doubts
that the units were ever capable of providing
acceptable flocculation even if operated as designed.
As such, the flocculation process was given a peak
instantaneous rated capacity of 0 L/d. This rating
implies that the plant cannot be expected to
consistently produce the desired water quality of less
than 0.5 NTU without adding flocculation process
capabilities.
The sedimentation basins were rated at 12 L/s (0.28
mgd) based on a surface overflow rate of 8.1 m3/m2/d
(200 gpd/sq ft). The surface overflow rate is
significantly lower than that for other types of circular
sedimentation basins with the same depth as Plant
10. The projected peak instantaneous operating
capacity of the sedimentation basins was lowered
because of the extremely poor inlet conditions. With
the inlet structure located in the bottom of the
sedimentation basins, the influent flow disrupts the
settled solids and tends to carry them upwards
towards the effluent. Properly designed sedimentation
basins introduce the influent water near the surface
through an inlet structure that directs the flow into the
basin, promoting the separation of solids from the
clarified liquid over the entire surface area. This allows
the separated solids to move by gravity to the bottom
of the basin and the clarified effluent to move to the
sgrface where it is removed.
The filters were rated at 22 Us (0.50 mgd) based on a
filter loading rate of 58 m3/m2/d (1 gpm/sq ft). This
loading rate is lower than typical values because of
the air binding observed by the CPE team during filter
backwashing. Air binding results in air pockets in the
filter media, which prevents water from passing
through that portion of the filter, effectively lowering
the surface area available for filtration. The filter
loading rate, therefore, was lowered in the
assessment to compensate for the loss of filter area
due to the observed air binding.
The disinfection system was rated at 24 L/s (0.54
mgd). Future drinking water regulations for disinfection
will be based on CT values found to be needed for
various removals of Giardia cysts and inactivation of
viruses. CT is the disinfectant concentration multiplied
by the actual time the finished water is in contact with
the disinfectant. To establish the CT required, it was
assumed that the plant's disinfection system would
have to provide 2 logs (99 percent) of cyst removal
with 2 logs of removal credited for the other treatment
processes. The total of 4 logs of cyst removal
required for the plant was based on the CPE team's
estimate of the quality of the raw water.
To achieve the 2 logs of cyst removal, the CPE team
estimated that the disinfection system would have to
provide a CT of 133. This CT value is for chlorine at a
2.0 mg/L dose, pH 7.5, and temperature of 5C. The
contact time was based on the chlorine being added
ahead of Clearwell 1 and the flow passing through
both clean/veils. Only 15 percent of the theoretical
detention time in the clearwells was used because the
clearwells are not baffled and because they are
subjected to fill and draw operation. The actual levels
of disinfection required for the plant in the future will
be determined by the State. The CPE estimates of the
required total number of log reductions and the
allowances for actual contact times in the clearwells
may change when the final state regulations are
developed.
The performance potential graph shows that the lack
of flocculation severely limits the capabilities of the
treatment processes. Without adequate flocculation,
the CPE team estimates that there is essentially no
flow where the required performance can be obtained.
The sedimentation basins also severely limit the
capacity of the plant, even if adequate flocculation
was provided. These processes prevent the plant from
achieving desired performance at the current peak
instantaneous operating flow rate of 22 L/s (350 gpm).
The filters and disinfection system were projected to
be adequate to treat this flow.
Performance Assessment
Turbidity data from the plant records for the raw
water, settled water from the sedimentation basins,
and finished water over a 1-yr period are plotted in
Figures 4-47, 4-48, and 4-49, respectively.
75
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Figure 4-46. Plant 10 performance potential graph,
Unit Process
0.1
0.2
Flow, mgd ,
0.3
0.4
0.5
0.6
Sedimentation1
SOR. gpd/sq ft
Filtration2
HLR, gpm/sq ft
Disinfection?
Contact time, min
70
141
0.2
0.4
0.6
0.8
356
178
119
89
71
Peak Instantaneous Operating
Flow (1 Pump) = 350 gpm
1 Rated at 200 gpd/sq ft because of poor inlet conditions, turbulence at the basin bottom, and poor durface area development.
2 Rated at 1 gpm/sq ft because of observed air binding.
3 Rated at CT - 133 with 2 mg/L chlorine dose, which requires a 67-min HOT; allowed 15 percent of available volume dfor contact
time, temperature s 5ฐC, pH = 7.5, 4-log required reduction, 2 allowed for plant.
Figure 4-47 shows the fluctuation of raw water
turbidity over the year. Well-designed and operated
treatment processes are expected to produce a water
with consistent turbidity levels even with wide
variations in raw water turbidity. As shown in Figure 4-
48, the sedimentation basins produced a settled water
that also had significant variations in turbidity. The
filters reduced the levels of turbidity, as shown in
Rgure 4-49, but still experience variations as raw
water turbidity changes. These results indicate design
and/or operational problems. Figure 4-50 shows the
finished water turbidity during a 6-month period when
the plant was treating a highly variable turbidity raw
water. The applicable regulation for turbidity is
currently 1.0 NTU. Future regulations will require the
plant to meet a 0.5-NTU finished water turbidity 95
percent of the time. Figure 4-50 shows that the plant
generally complies with the 1.0-NTU regulation, but is
consistently above the 0.5 NTU required by the future
regulations. A probability plot of this same data is
shown in Figure 4-51, which indicates that under
present conditions the plant would only meet the 0.5-
NTU standard approximately 50 percent of the time.
During the CPE, a special study was completed to
assess the filter performance after backwashing. With
adequate facilities and operation of preceding unit
processes, a properly operated filter should produce a
finished water turbidity of approximately 0.1 NTU and
only experience a 0.2-NTU rise in turbidity in the
finished water for approximately 10 minutes after
restart following backwashing. Filters 3 and 4 were
sampled for a 30-minute period after restart following
backwashing. The results of this special study are
shown in Figures 4-52 and 4-53. Both filters
experienced an approximately 0.3-NTU rise in turbidity
that did not drop back to the original value even after
30 minutes. These results could indicate a problem
with the filters or that the water being applied to the
filter has not been properly treated and conditioned in
the preceding unit processes.
An evaluation of the filter media was also performed
during the CPE. The evaluation team determined that
the filters were being adequately backwashed, since
no significant mudballs were found. They did find
some buildup of chemicals on the surface of the
media, but these were not considered to affect
performance. Air binding was also observed during the
special studies.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis were
prioritized and are summarized below:
1. Flash Mix and Flocculation - Design: The plant
has no flash mix or flocculation treatment
processes, facilities which are required to properly
condition the raw water with chemicals prior to the
sedimentation and filtration treatment processes.
Without these capabilities the plant will have
significant problems removing enough turbidity to
consistently meet future regulations.
2. Sedimentation Basins - Design: Adequate
sedimentation basins are required to remove the
coagulated turbidity from the raw water. The
sedimentation basins have basic limitations related
to the lack of a proper inlet structure. At current
76
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Figure 4-47. Raw water turbidity profile - Plant 10.
GO
^ Q
t- CO ~"
13
lo
OJ
0 ฉ
O
RUG88 OCT DEC FEB89 RPR JUN RUG OCT
Figure 4-48. Settled water turbidity profile - Plant 10.
RUG88 OCT DEC FEB89 RPR JUN RUG
OCT
77
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Figure 4-49. Finished water turbidity profile - Plant 10.
in
en
co --
in
i cO +
S ~i
-------
Figure 4-51. Probability plot of finished water turbidity - Plant 10.
en
. 1
10 50
Probability
99 99.9
Figure 4-52. Fiulter 3 effluent turbidity profile after backwash
- Plant 10.
Turbidity, NTU
0.8 r-
0.6
0.4
0.2
I
J
10 15 20
Minutes
25 30
Figure 4-53. Filter 4 effluent turbidity profile after backwash
Plant 10.
Turbidity, NTU
0.8 r-
0.6
0.4
0.2
I
I
10
15 20
Minutes
25 30
79
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loadings (e.g., 22 L/s [350 gpm]), the basin
limitations allow high turbidity water to pass to the
filters, thus degrading their performance.
3. Number of Plant Staff - Administration: Currently a
staff of three persons have responsibility for the
operation and maintenance of the water plant,
wastewater plant, distribution system, and
collection system. CPE interviews with the Board
of Public Affairs revealed that a fourth person may
be hired after construction of the new wastewater
treatment plant is completed. To respond to the
variations in raw water turbidity, increased
coverage of the water plant to make process
changes will be needed. Given this requirement
plus other observed responsibilities, even a staff
of four may be inadequate.
4. Application of Concepts and Testing to Process
Control - Operation: The plant staff appeared to
have proper training, understood 'the basic
concepts of process control, and were very
motivated. However, the chemical doses were not
changed based on changes in raw water
characteristics, the alum dose measured during
the CPE was excessively high, and the filters
were operated without adequate consideration of
the turbidity levels in the filter effluent.
Additionally, dirty filters were regularly started
without any assessment of the impact of this
practice on filter effluent turbidity levels. Because
of these practices, the CPE team assessed that
the planf staff was not consistently applying
proper water treatment concepts and process
control testing to optimize the plant's
performance.
Factors identified as having either a minimal effect on
a routine basis or a major effect on a periodic basis
are summarized below in order of priority.
1. Filtration - Design: The configuration of the
filtration system allows conditions that create air
binding in the filters. The air binding is caused by
negative pressures being created in the filter
media as solids are removed and headloss
increases. This causes the dissolved air in the
water to come out of solution and be retained in
the filter media. Water cannot pass through the
portions of the media where the air is retained,
which effectively reduces the surface area
available for filtration. This condition reduces the
plant's capacity and can significantly affect filter
performance.
2. Lack of Preventive Maintenance Program -
Maintenance: The plant has no formalized
preventive maintenance program. Equipment is
repaired as it breaks down. A lack of maintenance
of a number of key pieces of equipment was
considered to have a minimal, but continuous
impact on performance. This key equipment
included the alum feeder, filter flow measurement
devices and control valves, chlorinator controls,
clarifier equipment including the weirs, and the
raw water pumps. Plant staffing levels appeared to
impact the level of preventive maintenance, but
even with adequate staff a formalized program
would be needed to assure availability of key
equipment.
3. Chemical Feed Facilities - Design: The plant
needs additional chemical feed facilities to
consistently meet required performance. A
polymer feed system is projected as a
requirement to optimize filter performance,
especially during cold weather operation. A
backup alum feeder would also be required to
assure a consistent source of chemical feed.
4. Alarm Systems - Design: The plant is operated for
significant periods of time without any operations
staff present to make process adjustments in
response to variations in raw water characteristics
or correct problems with key processes
equipment. During periods of unattended
operation process performance could degrade to
a point where it poses a potential health risk to
the village. A turbidity monitoring system tied to
raw and finished water could be used to alert the
plant staff to process problems before finished
water quality reached undesirable levels.
The age of some of the equipment was identified as a
minor factor limiting performance. Though not a
performance-limiting factor, the current practice of
disposing of sludge and backwash water into the river
is in violation of State regulations.
Projected Impact of a CCP
The CPE identified numerous design problems related
to the key unit treatment processes, which must be
corrected before any process optimization through
use of a CCP could be successful. A CCP, therefore,
was not recommended.
80
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Plant 11
Facility Description
Plant 11 is a conventional water treatment plant that
treats water from a nearby river for domestic use by
the village. Based on a review of flow records for the
previous year, the peak operating flow for the plant
was established at 19 Us (0.43 mgd). Plant 11
consists of the following unit processes shown
schematically in Figure 4-54.
Intake structure
49 million-L (13 mil-gal) reservoir
Three vertical turbine raw water pumps: two 19 Us
(300 gpm) and one 38 L/s (600 gpm)
19-L/s (300-gpm) submersible raw water pump
Metering pump to feed a ferric chloride solution
Two volumetric feeders, one for lime and another
for alum addition
Rapid mix basin with a surface area of 0.46 m2 (5.0
sq ft); and a depth of 0.6 m (2 ft)
Solids contact clarifier 9.1 m (30 ft) in diameter and
3.8-4.1 m (12.5-13.6 ft) deep; flocculator volume,
29,800 L (7,875 gal); clarifier effective surface area,
61.6 m2 (663 sq ft), and volume, 205,330 L (54,250
gal)
Three dual media filters, two 2.4 m x 2.5 m (8 ft x 8
ft), and one 2.1 m x 2.7 m (7 ft x 9 ft) that contain
46-51 cm (18-20 in) of sand and 20-25 cm (8- 10
in) of anthracite media
Vacuum-controlled solution feed chlorination
system fed from 68 kg (150-lb) cylinders
151,400-L (40,000-gal) clean/veil
321,725-L (85,000-gal) clearwell
Two 24-L/s (375 gpm) vertical turbine high-service
pumps
15-cm (6-in) orifice plate with a totalizer-indicator-
recorder
Water from the river is pooled behind a low dam
across the river downstream of the intake structure.
River water is normally pumped to the reservoir by the
submersible pump. Water from the reservoir flows by
gravity to the wet well beneath the intake structure,
where it is pumped to the plant by the vertical turbine
raw water pumps. These pumps can also pump river
water directly to the plant, bypassing the reservoir.
Raw water flows to the rapid mix basin where ferric
chloride solution is added via a diaphragm metering
pump. A hydrated lime slurry is also fed into the rapid
mix basin via a volumetric feeder. A volumetric feeder
is in place to feed alum, although it is currently not is
use. Flash mixing was not performed during the CPE
due to a bearing problem with the mixer. However, the
CPE team calculated the G value for the rapid mix
basin to be adequate at 1,418 sec-1 if the mixer were
operating. Chemical feed rates can be adjusted
manually by the amount of chemical added to the
slurry tanks, or by adjusting the stroke on the
metering pump, but they were not routinely changed.
Raw water flows to the center flocculation cone of the
solids contact clarifier. After flocculation, water enters
the outer clarifier portion of the unit and is removed
through peripheral v-notched weir troughs. Sludge is
periodically removed automatically from the clarifier,
through use of a timed blow-down, and discharged to
a sanitary sewer for disposal at the wastewater
treatment plant.
Settled water flows by gravity from the reactor
clarifiers to a basin (originally designed as a
recarbonation basin), where the flow is split to the
three filters. Rate of flow through the filters is
controlled by float-activated butterfly valves that open
or close to maintain a constant water level above the
filter media.
Filter runs are normally 24-27 hr, with the plant
operating a total of 8-9 hr/day. One filter is
backwashed each day, so that filters operate 3 days
before backwashing. No individual filter headloss or
turbidity monitoring equipment exists, although the
village intends to install headloss gauges. Backwash
water is supplied by distribution system pressure from
operation of the high-service pumps. The backwash
rate was determined during the CPE to be
approximately 1,110 m3/m2/d (19 gpm/sq ft). The
surface of the media is manually raked during
backwashing. Backwash water is discharged to the
sanitary sewer.
Water from each filter flows through separate pipes
into Clearwell 1, where a chlorine solution is injected
to maintain residuals between 2.3 and 2.5 mg/L.
Finished water normally flows from Clearwell 1 to
Clearwell 2. The high-service pumps take suction from
Clearwell 1.
Two high-service pumps supply finished water to the
two elevated storage tanks that feed the water
distribution system. These pumps are operated
automatically based on water levels in the elevated
storage tanks. The plant comes on and off line usually
two to three times during the day based on water
levels in the clearwell. Typically, the plant operates 8-
9 hr/day at a constant rate of 24 Us (375 gpm).
81
-------
Figure 4-54. Plant 11 process flow diagram.
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82
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Variations in demand are met by varying the length of
time the plant is operated.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
55. The instantaneous peak operating flow of 19 Us
(0.43 mgd) assumes that only one of the small raw
water pumps will supply the plant.
The flocculation capabilities of the reactor clarifier
were rated at 25 L/s (0.57 mgd) based on achieving a
hydraulic detention time of 20 minutes. This rating
depends on retrofitting the basin with the variable
speed drive for the mixers, which was included in the
plant's original design.
The sedimentation capabilities of the reactor clarifier
were rated at 22 L/s (0.50 mgd) based on a surface
overflow rate of 30 m3/m2/d (750 gpd/sq ft). The
projected capacity of the basins was lowered due to
the constraints of the 3.8- m (12.6-ft) basin depth.
The filters were rated at 36 L/s (0.82 mgd) based on a
filter loading rate of 176 m3/m2/d (3 gpm/sq ft). This
loading rate was decreased from more typical values
for dual media filters because of the rate control
system.
The disinfection system was rated at 15 L/s (0.34
mgd). Future drinking water regulations for disinfection
will be based on CT values found to be needed for
removal of Giardia cysts and inactivation of viruses.
This evaluation used a CT of 127, which is for
chlorine at a 2.4 mg/L dose, pH 8.0, and temperature
of 5ฐC. It was assumed that the disinfection system
would have to provide 1.5 logs of cyst removal with
2.5 logs of removal credited for the other.treatment
processes. The 4 logs of total cyst removal required
for the plant was based on the CPE team's estimate
of the potential for contamination of the raw water.
The contact time was based on the chlorine being
added ahead of Clearwell 1 and the flow passing
through both clearwells. Only 10 percent of the
nominal detention time in the clearwells was used
because (1) the clearwells are not baffled, (2) the
piping arrangement does not assure that all of the flow
passes through both clearwells, and (3) the clearwells
are subject to fill and draw operation. In the future, the
actual levels of disinfection required for the plant will
be determined by the State. The estimates of the
required total number of log reductions and the
allowances for actual contact times in the clearwells
may change after the final State regulations are
developed.
As shown in the performance potential graph, the
major unit processes, with the exception of the
disinfection process, have a rated capacity close to or
exceeding the instantaneous peak operating flow. The
flocculation and sedimentation process, although
borderline, were projected adequate to treat the
operating flow rate of 19 L/s (0.43 mgd). The filtration
system, rated at 36 L/s (0.82 mgd), was rated
considerably more than adequate to treat this flow.
Lack of baffling in the clearwells and the piping
arrangement between the two clean/veils limited the
projected capacity of the disinfection process.
Performance Assessment
Figure 4-56 shows turbidity data from the plant
records. The current applicable regulation for turbidity
is 1.0 NTU. The plant normally produces water with
turbidities less than 1.0 NTU, but is frequently above
the 0.5 NTU level, which will be required by the
SWTR, as shown in Figure 4-56. A probability plot of
this same data, shown in Figure 4-57, indicates that
the plant would only meet the 0.5-NTU requirement
approximately 30 percent of the time.
During the CPE, a special study was conducted to
assess filter performance after backwashing. With
adequate facilities and operation of preceding unit
processes, a properly operated filter should
experience a 0.2-NTU rise in turbidity in the finished
water for approximately 10 minutes after restart
following backwashing. Figure 4-58 shows the results
of a study that sampled Filter 3 for a 40-minute period
after restart following backwashing. The filter
experienced an approximate 1.0-NTU rise in turbidity
that did not drop back to the original value even after
40 minutes. This delay may be attributed to a problem
in the filter, or to improper treatment and conditioning
of the water prior to filtering.
After backwash, Filter 3 was drained and 2.5- to 3.8-
cm (1- to 1.5-in) mudballs were observed in the
media. As mudballs increase in size, they can settle to
the bottom of the media and limit the flow through
these portions of the filter. The filter flow is then
forced through the remaining media at higher rates,
which can impact filter capacity and performance.
Proper backwashing procedures, such as adequate
length of backwash, gradual increase in backwash
flow rates, and sufficient agitation of the media, can
minimize the occurrence of mudballs.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis were
prioritized and are summarized below:
1. Application of Concepts and Testing Process
Control - Operation: Several operational practices
performed by the plant staff, including applying
ferric chloride and lime at the same point,
regularly started dirty filters, and an unawareness
of the condition of the filter media, impaired plant
performance. Lime raises the raw water pH above
the range necessary to achieve optimum
coagulation and flocculation using ferric chloride.
Starting dirty filters without monitoring the impact
on finished water turbidity may represent a
0-83
-------
Figure 4-55. Plant 11 performance potential graph.
Unit Process
0.2
0.4
Flow, mgd
0.6
0.8
1.0
Flocculatlon1
HOT, min
Sedimentation2
SOR, gpd/sq ft
Filtration*
HLR, gpm/sq ft
Disinfection4
Contact time, min
57
28
302
603
0.7
1.5
90
2.2
2.9
Peak Instantaneous Operating
Flow (1 Pump) = 350 gpm
1 Rated at 20 -min HOT - assumes variable speed drive would be added.
2 Rated at 750 gpd/sq ft - 12.5-ft depth discourages higher rating.
3 Rated at 3 gpm/sq ft. Rate control system considered limiting.
* Rated at CT - 127 with 2.4 mg/L chlorine dose, which requires a 53-min HOT; allowed 10 percent of available volume for contact
time, temperature = 5ฐC, pH = 8, 4-log required reduction, 2.5 log in plant, 1.5 log disinfection.
Figure 4-56. Raw water turbidity profile - Plant 11.
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Present
Requirement
Future
Requirement
MRR88
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JRN83
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84
-------
Figure 4-57. Probability plot of finished water turbidity - Plant 10.
ru
-------
The State's interpretation of this rule may lead to
different results than indicated by this
evaluation.Factors identified as having either a
minimal effect on a routine basis or a major effect
on a periodic basis are summarized below in order
of priority.
1. Supervision - Administration: There is no clear
definition or delegation of responsibilities between
the superintendent and other members of the
staff. To maintain continuity in plant operations,
specific tasks should be assigned to each staff
member. This would alleviate incidents of poor
communication between the plant staff (e.g., staff
members arbitrarily resetting chemical feed rates
after they have been adjusted by other staff
members). Once plant personnel have clear
definition of duties, daily planning and priority
setting, which is presently minimal, can be
optimized to increase plant performance.
2. Process Accessibility for Sampling - Design: The
lack of sampling locations to evaluate various
plant unit processes limits implementation of an
acceptable process control program. At minimum,
the plant should have taps to determine influent
and effluent turbidity levels for the reservoir (and
river, if pumping directly to the plant), solids
contact clarifier, each of the three filters, and both
clean/veils.
3. Alarm Systems - Design: The plant is operated for
significant periods of time without any operations
staff present to make process adjustments in
response to variations in raw water characteristics
or correct problems with key processes
equipment. As such, finished water quality could
degrade and pose a potential health risk to the
village. A turbidity monitoring system tied to the
clean/veil effluent could be used to alert the plant
staff to process problems before finished water
quality reaches undesirable levels.
4. Number of Plant Staff - Administration: Presently,
a staff of four persons have responsibility for the
operation and maintenance of the water plant,
wastewater plant, distribution system, collection
system, and street maintenance. To properly
respond to the variations in raw water turbidity,
implement a process control program, provide
sample taps, etc., increased coverage of the plant
will be needed. Given these responsibilities and
requirements, a staff of four is inadequate.
5. Plant Staff Morale Pay - Administration: The
current pay structure for the staff may discourage
more highly qualified people from applying for
operator positions. The village does not currently
offer a pay scale competitive with other facilities.
6. Chemical Feed Facilities - Design: The plant lacks
the capability to feed chemicals to various points
in the treatment process. The option to apply
chemicals (e.g., lime) will enable optimal use of
chemicals and chemical dosages. Additional
chemical feed facilities were projected to be
required. A polymer feed system could be used to
optimize filter performance especially during cold
weather operation.
The CPE team identified additional factors that had a
minor effect on plant performance. Specifically, the
lack of a preventive maintenance program, the lack of
variable speed mixing capabilities during flocculation,
and the minimal depth of the sedimentation basin.
Headloss gauges should also be installed on each of
the filters to enable optimization of filter runs based on
headloss and/or effluent turbidity levels. The inability
to control flow distribution to the filters and control the
rate of flow at each filter will also adversely impact
filter operation.
Projected Impact of a CCP
Alleviating the identified factors would appreciably
improve the performance of Plant 11. As such,
implementation of a CCP, if accepted by the village
personnel, represented a viable option for the plant.
86
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Plant 12
Propeller-type finished water flow meter
Facility Description
Plant 12 is a conventional plant that treats water from
a nearby river to provide water for domestic use by
the city. It consists of two separate sets of treatment
process trains that operate in parallel. One of these,
designated the "old" plant, consists of the solids
contact clarifier and the two circular dual media filters.
These were the original treatment processes before
the plant was expanded in 1977. The second set,
designated the "new" plant, consists of two package
plants. Based on a review of plant records, the peak
operating flow for the entire plant was 32 Us (0.72
mgd). Plant 12 consists of two separate sets of unit
processes shown schematically in Figure 4-59.
Raw water intake structure containing two
submersible pumps: one 25 Us (400 gpm) and the
other 31 L/s (500 gpm)
Propeller-type raw water flow meter
Seven volumetric chemical feeders: two for alum,
three for lime, one for fluoride, and one for
KMnO4/PAC
Two 3.4-m (11-ft) diameter flocculation basins, 2.7
m (8.8 ft) deep, each equipped with vertical paddle
flocculators and variable speed drives. Each unit is
divided into two sections by a mid-depth horizontal
perforated baffle
Two package plants each with sedimentation and
filtration. The sedimentation section has a surface
area of 4.8 m2 (51.8 sq ft) and contains a 1.7-m
(5.7- ft) high module of 7.5-degree tube settlers.
Each filter has 10.2 m2 (110 sq ft) of surface area
and 76 cm (30 in) of mixed media
6.4-m (21-ft) diameter, 3.0-m (10-ft) deep upflow
solids contact clarifier. Center flocculation cone has
a volume of 8,515 L (2,250 gal) with a vertical
paddle mixer
Two 2.7-m (9-ft) diameter dual media filters
containing 69 cm (27 in) of media
Two clearwells: one "old", with 246,782-L (65,200-
gal) capacity and the other "new", with 199,470-L
(52,700-gal) capacity
Two backwash pumps: one "new" 63 Us (1,000
gpm), and the other "old", est. at 31 L/s (500 gpm)
Vacuum-controlled solution feed chlorination
system fed from 68-kg (150-lb) cylinders
Three high-service pumps: two "old", estimated at
16 L/s (250 gpm) and 38 L/s (600 gpm) and the
third "new" 31 L/s (500 gpm)
333,080-L (88,000-gal) backwash water and sludge
holding basin
Water is taken from the middle of the river through an
intake pipe. Either of two submersible pumps is used
to supply raw water to the plant. The plant is operated
usually 6-8 hr/day and meets higher demands by
operating for longer periods.
The raw water is split between the "old" and "new"
plant by separate valves at the flow split. Capabilities
exist to pre-chlorinate the raw water. The raw water
flow meter for the "old" plant had been removed for
repair and had never been replaced. For the "new"
plant, raw water flows can be measured and
controlled. During the CPE, the flow meter was
operational, but had not been calibrated and, thus,
was not used by the plant staff. The rate-of-flow
controller was out of service. Neither the flow meter or
controller had been used for a long time.
Alum and lime are added to both of the plants using
volumetric dry chemical feeders. On the "new" plant,
alum and lime slurries were prepared by adding water
to the dry chemicals in mixing tanks beneath the
feeders. These slurries were conveyed by gravity to
the pipe carrying the raw water to the flocculators. No
mechanical or static flash mixing was provided.
Chemical feed rates for both plants were adjusted with
changes in raw water turbidity based on the operator's
experience. A jar testing apparatus was available at
the plant, but not used. Feed rates were not routinely
adjusted.
The two flocculators on the "new" plant had been
modified by removing the horizontal, perforated
baffles. These baffles, intended to separate each of
these units into two stages, would have provided
improved flocculation. The mechanical mixers on
these basins were also not operational.
From the flocculation basins, flow to the "new" plant
enters a tank that has a sedimentation and filtration
section. Flow is directed to the bottom of the
sedimentation section and then flows up through a
module of 7.5 degree-tube settlers. Settled water
discharges into a trough that conveys it to the filtration
section. After passing through the mixed media filter,
the finished water flows to the clearwells.
The filtration units were designed for automatic
operation with electrically actuated valves controlling
the filter flow rate based on level measurements.
Backwashing was also designed to use automatic
electrically actuated valves. Continuous turbidimeters
for the raw and finished water were provided. During
the CPE, however, none of the automatic valves or
turbidimeters were operational. Instead, the plants
were operated manually, but the plant staff could not
87
-------
Figure 4-59. Plant 12 process flow diagram.
88
-------
adequately control the flow through the filters. Settled
water was observed cascading onto the surface of the
filter media. When a filter is properly operated, the
surface of the filter media is flooded, but under the
observed conditions, flow was passing through only a
portion of the media. Both the filters and the tube
settlers were backwashed at the same time using
water pumped from the clearwells. Backwash water
was discharged to the holding basin.
In the "old" plant, a volumetric feeder adds dry alum
directly into the center flocculation zone and lime is
prepared as a slurry and piped to the flocculation
zone. A mechanical mixer provides mixing in the
zone.
The upflow solids contact clarifier on the "old" plant
consists of two sections that provide for both
flocculation and sedimentation. Flocculation occurs in
a mechanically mixed cone-shaped center section,
while sedimentation occurs in the outer portion. Raw
water enters the flocculation section and then flows
downward before proceeding through the bottom of
this section into the upflow sedimentation section. The
mechanical mixer promotes flocculation and settled
water discharges over peripheral weirs. Proper
operation of solids contact clarifiers relies on the
measurement and control of the solids maintained in
the unit. At the plant, solids levels and concentrations
were not measured or controlled.
The "old" plant filters were circular steel tanks that
showed significant signs of corrosion. Two troughs
above the media distributed the settled water to the
filters and collected the backwash water. Filter flow
rates were controlled by float-actuated valves that
were intended to maintain a constant water level
above the filter. During the CPE, these valves were
not operational. Settled water was observed cascading
onto the media surface instead of flooding the filter
media. These filters are backwashed with water
pumped from the clearwells. Backwash water is then
discharged to the holding basin.
Finished water from both plants combines ahead of
the "new" clearwell where chlorine, fluoride, and lime
are added. Chlorine doses are adjusted to maintain a
residual of 2.0 mg/L in the finished water leaving the
clearwell. Both pre- and post-chlorination are used.
The staff attempts to maintain a 50/50 split between
the two addition points, but no provisions are available
to measure this split.
All finished water enters the "new" clearwell, but both
clearwells are interconnected so that the flow is
distributed between them. Separate high- service
pumps draw from each clearwell, an arrangement that
prevents the two clearwells from operating in series,
and thereby optimizing the contact time with the
chlorine. During the CPE, one of the "old" high-
service pumps had been removed for service. High-
service pumps are operated manually to supply the
four storage tanks in the distribution system.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
60. Three sets of bars are presented for each unit
process representing the "old" plant, the "new" plant,
and the total for both plants combined. Disinfection
was only evaluated for the combined plants because
the units are interconnected. The shortest bar
represents the treatment process that limits plant
capacity to achieve the desired performance of less
than 0.5 NTU.
The instantaneous peak operating flow for the plant
was established at 16 Us (0.36 mgd) for each of the
two plants, or 32 Us (0.72 mgd) for the total plant.
This flow is based on a review of flow records for the
previous year and the practice of only operating one
of the raw water pumps. On days the plant operates
for longer than 8 hr, the treatment processes are still
operated at a maximum flow rate of 32 Us (0.36
mgd).
The flocculation basins were rated at 48 Us (1.1) mgd
for the total plant. Most of the flocculation capabilities,
however, are provided by the "new" plant. The two
flocculators were rated at 39 Us (0.90 mgd), under
the assumption that the horizontal perforated baffles
would be replaced and the mechanical mixers made
operational. The flocculation portion of the "old"
plant's solids contact clarifier was rated at 8.3 L/s
(0.19 mgd).
For sedimentation, the solids contact clarifier was
rated at 14 L/s (0.32 mgd) and the combined package
plants at 17 L/s (0.38 mgd) for a total plant capacity of
31 L/s (0.7 mgd). The shallow depth and configuration
of the solids contact clarifier were judged to limit its
capacity. Higher surface overflow rates were applied
to the package plants because of the tube settlers.
Total filtration capacity for the plant was rated at 53
L/s (1.2 mgd). A filter loading rate of 117 m3/m2/d (2
gpm/sq ft) was used for the "old" plant, which
resulted in a rated capacity of 16 L/s (0.36 mgd). The
filters on the "new" plant were rated at 35 L/s (0.79
mgd) based on a loading rate of 293 m3/m2/d (5
gpm/sq ft). These ratings assume the rate control
valves on both plants will be operational.
The disinfection system was rated at 18 L/s (0.42
mgd). Future drinking water regulations for disinfection
will be based on CT values needed for various
removals of Giardia cysts and inactivation of viruses.
To establish the CT required, it was assumed the
plant's disinfection system would have to provide 1.5
logs of cyst removal with 2.5 logs of removal credited
for the other treatment processes. The total of 4 logs
of cyst removal required was based on the CPE
team's estimate of the quality of the raw water.
89
-------
Figure 4-60. Plant 12 performance potential graph.
Unit Process
0.2
0.4
Flow, mgd
0.6
0.8
1.0
1.2
Flooculatfon'
Ok) Plant HOT, min
New Plant HOT, min
Total
Sedimentation2^
Old Plant SOR, gpm/sq ft
New Plant SOR. gpm/sq ft
Tola)
FIItrationซ.s
Old Plant HLR, gpm/sq ft
New Plant HLR, gpm/sq ft
Total
Disinfection6
HOT, min
90
0.43
1.3
1.1
1.3
85
45
30
2.5
3.8
42
23
Peak Instantaneous Operating
Flow = 250 gpm
Peak Instantaneous Operating
Flow = 500 gpm
1 Rated at 20-min HOT - assumes baffles reinstalled and functional micers in new floe basin.
2 Old plant rated at 0.7 gpm/sq ft - shallow depth and configuration considered limiting.
3 Now plant rated at 2.5 gpm/sq ft - tube settlers allow higher rates.
* Old plant rated at 2 gpm/sq ft - integrity of tanks was assumed to be adequate.
5 New plant rated at 5 gpm/sq ft - assumes rate control valves are operational.
8 Rated at CT = 100 with 2.5 mg/L chlorine dose, which requires a 40-min HOT; allowed 10 percent of available volume for contact
time, temperature s 5ฐC, pH = 7.5, 4-log required reduction, 2.5 log allowed for plant if operated well.
To achieve the 1.5 logs of cyst removal, the CPE
team estimated that the disinfection system would
have to provide a CT of 100. This CT value is for
chlorine at a 2.5 mg/L dose, pH 7.5, and temperature
of SO. The contact time was based on the chlorine
being added ahead of the "new" clearwell and the
flow passing through both clean/veils. Only 10 percent
of the theoretical detention time in the clearwells was
used because the clearwells are not baffled and
because they are subjected to fill and draw operation.
The piping arrangement, which does not assure that a
flow passes through both clearwells, also contributed
to this rating. The actual levels of disinfection required
for the plant in the future will be determined by the
State. The estimates in this CPE of the required total
number of log reductions and the allowances for
actual contact times in the clearwells may change
when final regulations are developed.
The performance potential graph shows that, on a
total plant basis, the major unit processes have a
rated capacity close to or exceeding the peak
instantaneous operating flow of 32 Us (0.72 mgd),
with the exception of the disinfection process.
Flocculation is adequate up to 48 Us (1.1 mgd) if the
flocculators on the "new" plant are returned to their
original condition. The sedimentation processes are
projected adequate to treat a flow of 31 Us (0.70
mgd), which is borderline. The filtration system, rated
at 53 Us (1.2 mgd), was rated considerably more than
adequate to treat the peak instantaneous operating
flow. Lack of baffling in the clearwells and the piping
arrangement between the two clearwells limited the
projected capacity of the disinfection process.
On an individual plant basis, the performance potential
graph shows that both plants do not have equal
capabilities. For the total plant to have a rating of 32
Us (0.72 mgd), more than half of the flow will have to
be treated in the "new" plant. The solids contact
clarifier on the "old" plant limits the flow it can
adequately treat to 8.3 Us (0.19 mgd).
90
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Performance Assessment
Figure 4-61 shows the finished water turbidity as
reported by the plant staff for a 12-month period. The
current State regulation for turbidity is 1.0 NTU. The
federal SWTR will require the plant to meet a 0.5-NTU
finished water turbidity 95 percent of the time. The
plant generally complies with the 1.0-NTU regulation,
but is consistently above the 0.5-NTU required by the
SWTR. A probability plot of this same data, shown in
Figure 4-62, indicates that under present conditions
this plant would only meet 0.5 NTU less than 10
percent of the time.
During the CPE, special studies were conducted to
assess the performance of both the "old" and "new"
filters after backwashing. With adequate facilities and
operation of proceeding unit processes, a properly
operated filter should produce a finished water
turbidity of approximately 0.1 NTU and only
experience a 0.2-NTU rise in turbidity in the finished
water for approximately 10 minutes after being
restarted following backwashing. For this special
study, both filters were sampled for a 30-minute
period after being restarted following backwashing.
Figure 4-63 shows the results for the "old" filter. Prior
to backwashing, this filter was producing 0.22-NTU
water. After backwashing, however.the water quality
peaked at 38 NTU after 1 minute and did not drop
back to the original value even after 30 minutes. A
turbidity of 1.0 NTU was not achieved for almost 20
minutes. Figure 4-64 shows the results after
backwashing one of the "new" filters. Prior to
backwashing, the filter was producing a 12.5-NTU
water, significantly above the 1.0-NTU regulation.
After backwashing, the water quality improved, but
had not achieved adequate performance even after 20
minutes.
These results indicate a significant performance
problem that may be attributed to the filters or to the
fact that the water being applied to the filter has not
been properly treated and conditioned in the
preceding unit processes. During the backwash of the
"new" filter, large amounts of air were observed
bubbling up through the media.
During the two special studies, the team also
collected samples of the finished water from the
clearwells. These results, shown in Figure 4-65,
indicated that significantly high levels of turbidity were
passing into the city water systems; well above the
levels allowed by the State. Such high levels of
turbidity pose a significant health risk to the
community.
Performance-Limiting Factors
The factors identified as having a major effect on
performance on a long-term repetitive basis were
prioritized and are summarized below:
1. Performance Monitoring - Operation: The practice
of sampling at optimum times, though allowed by
current regulations, has resulted in an inaccurate
assessment of the plant's true performance.
Accurate monitoring would have alerted the plant
staff to the serious performance problems at the
plant and likely would have resulted in regulatory
pressure to correct them. Improperly operating
laboratory instruments used for monitoring also
led to an improper interpretation of performance.
2. Plant Administrator's Policies - Administration:
Current and historical actions by the mayor and/or
city council were inadequate in recognizing the
significance of poor water quality and
inappropriate in that they did not aggressively
address the causes of the situation. The existing
new plant, constructed in 1977, had been allowed
to deteriorate. Repairs and maintenance to protect
system integrity had been largely ignored. Staff
with expertise in water treatment were performing
numerous other city functions away from the
water plant, and staff with virtually no training in
water treatment were manning the plant for only
portions of the time it was operating. "Muddy"
water was accepted as a way of life. Agreements
to provide water to other communities were
negotiated and perpetuated despite the increased
demand that was placed on a marginally
functioning system. A significant change in past
policies and in emphasis on the water plant will be
necessary to reduce the health risk associated
with current water plant performance.
3. Maintenance: Years of neglect of all plant
equipment have degraded a potentially well-
equipped plant to essentially a nonfunctional state.
Considerable expenditures will be required to
make this equipment operational and to keep it
maintained.
4. Water Treatment Understanding - Operation: The
plant staff demonstrated a significant lack of
understanding of even basic concepts of water
treatment, allowing the water to cascade onto the
filter media, starting dirty filters, performing no
process control testing, and essentially providing
no adjustment of chemical feed rates. There was
also a lack of urgency to repair and/or replace
improperly functioning equipment essential to
providing water treatment.
5. Process Control Testing - Operation: A process
control testing program to optimize unit process
performance did not exist at the plant. Process
control testing is essential for water plants served
by surface sources because of the frequent and
rapid changes in raw water quality. Basic
equipment was available to conduct this testing,
but was not used.
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Figure 4-61. Finished water turbidity profile - Plant 12.
i i i i | i i i i | i i i i | i i i i | i i i i | i i
ID
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ซc m
Present
Requirement
Future
Requirement
i i i i I i i I i [ i I i i | i i i i [ i i i i | i i i i | i i i i [ i i i i I i i i i | i i i i | i i i i | i i i i | i i i i
SEP88 OCT NOV DEC JRN89 FEE MRR RPR MRY JUN JUL RUG SEP OCT
Figure 4-62. Probability plot of finished water turbidity - Plant 10.
in
ป
ru
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in
(S)
1 1
10 50
Probability
90
99 99.9
92
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Figure 4-63. Old plant north filter effluent turbidity profile
after backwash - Plant 12.
Turbidity, NTU
40 r-
Present Requirements
15 20
Minutes
Figure 4-65. Clearwell turbidity profile after filter backwash
Plant 12.
Turbidity, NTU
8 r-
Present Requirements
J I I
10 20 30 40 50 60
Minutes
J
70
Figure 4-64. New plant north filter effluent turbidity profile
after backwash - Plant 12.
Turbidity, NTU
12f
Present Requirements
I
10
Minutes
15
20
6. Filtration - Design*: This factor has an asterisk
because of the air observed above the filters
during backwash. Air entering the filters during
backwash may have disturbed the filter media to
the point that it will have to be replaced. The
condition of the filter media was not verified during
the CPE. The filter tanks on the "old" plant are
severely corroded to the point that they could fail
entirely.
7. Disinfection - Design*: This factor has an asterisk
because it was assessed based on the initial
disinfection requirements of the new regulations.
These requirements may change when final
regulations are developed by the State. On this
basis, however, inadequate contact time is
provided because of a lack of baffling in the two
clearwells and a lack of piping to allow them to
operate in series.
Factors identified as having either a minimal effect on
a routine basis, or a major effect on a periodic basis
are summarized below in order of priority.
1. Staff Number - Administration: Additional staff are
required to provide adequate coverage of the
plant, to perform the necessary process control,
and to complete maintenance functions.
2. Staff Qualification - Administration: All of the plant
staff must have high levels of education to make
93
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proper operation and maintenance decisions; all
staff should also be certified.
3. Process Flexibility - Design: The capability is
needed to feed polymers and filter aids at different
locations in the plant to optimize performance.
This will be especially critical if the plant is to
consistently meet a required finished water quality
of 0.5 NTU.
4. Alarm Systems - Design: The plant experiences
rapid variations in raw water quality and has a
limited number of operations staff present to make
necessary adjustments in response to these
variations (e.g., adjust chemical or chlorine doses,
or correct problems with key process equipment).
On these occasions, process performance could
degrade to a point where it poses a potential
health risk to the city. A turbidity monitoring
system tied to raw and finished water and a
chlorine residual monitoring system could be used
to alert the plant staff to process problems before
finished water quality reached undesirable levels.
5. Flow Proportioning to Units - Design: Flow
measurement and flow control devices are
needed to accurately split flow to ensure that each
plant receives the proper flow rate. This is
especially critical because the flow to the "old"
plant must be limited to achieve desired
performance.
6. Flocculation - Design: In the "new" plant, the
flocculator's original horizontal perforated baffles
will have to be replaced and the mechanical
mixers made operational. The flow to the "old"
plant must be limited because of the size of the
flocculation section of the solids contact clarifier.
7. Sedimentation - Design: The sedimentation
capabilities of the plant are marginal because of
the shallow depth of the solids contact clarifier
and the limited surface area of the sedimentation
sections of the package plants.
The amount of bond indebtedness of the city was
considered a minor factor, because it could limit the
ability to properly fund operation and maintenance or
needed repairs to the plant. Practices used for
disposal of plant sludges were not considered
environmentally sound, but had no impact on plant
performance. A lack of simple taps on all of the filters
prevented proper monitoring of filter performance.
Projected Impact of CCP
Data collected during the CPE indicated severe
performance problems. Correcting the identified
factors would appreciably improve the plant's
performance and allow it to meet both current and
future regulations. As such, implementation of a CCP
represented a viable option for the plant.
94
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Plant 13
Facility Description
Plant 13 is a conventional water treatment plant that
supplies water to the city for domestic use. Its source
is a nearby river. Based on a review of plant records
for the year, the peak flow was 66 Us (1.5 mgd). The
plant includes the following unit processes and is
shown schematically in Figure 4-66:
Raw water intake structure and two vertical turbine
60-hp, 65-L/s (1,040-gpm) pumps
ซ Orifice plate with a totalizer-recorder to measure
raw water flows
Five volumetric chemical feeders: one each for
alum, lime, soda ash, potassium permanganate,
and powdered activated carbon
Mechanical 3-hp flash mixer
Two dual-stage flocculation basins. Each stage is
4.9-m (16-ft) square and 3.7-m (12.2-ft) deep. Each
stage contains a vertical paddle flocculator
operated from a central 1 -hp variable speed drive
Two sedimentation basins 11 m (36 ft) long and
6.1 m (20 ft) wide, containing 60ฐ tube settlers 11
m x 4.5 m (36 ft x 14.7 ft) and 3.7-m (12.2-ft) deep.
Each basin has a weir length of 43.9 m (144 ft)
Two mixed media filters 3.4 m x 3.8 m (11 ft x 12.3
ft) fitted with rotary surface wash, and containing 84
cm (33 in) of media
Backwash water and settling basin sludge decant
basin
Four sludge drying beds
Diaphragm metering pump to feed hydrofluosilicic
acid
Vacuum-controlled solution feed pre-/post-
chlorination system fed from 68-kg (150-lb)
cylinders
Two 575,300-L (152,000-gal) clearwells
189-L/s (3,000-gpm) vertical turbine backwash
pump
Two vertical turbine high-service pumps with a
capacity of 66 L/s (1,050 gpm)
6,340-L (1,675-gal) wet well for the backwash and
high-service pumps
Water is taken from the river through any of three
intake pipes located at different depths. The intake
pipes supply water to a wet well. Either of two vertical
turbine pumps is used to supply raw water from the
wet well to the plant. The plant is usually operated 17-
20 hr/day. Higher demands are met by operating the
plant for longer periods.
An orifice plate measures raw water flow rates just
prior to chemical addition. Flow rates are charted on a
totalizer-recorder located on a panel with the reservoir
level alarm system.
Chlorine is injected prior to lime and alum addition at
concentrations high enough to maintain a 1.5-mg/L
residual on top of the filters - 45 kg (100 lb)/d. The
rate is changed only when "muddy" waters are
observed at the plant influent.
Alum and lime are added using dry volumetric
feeders. Alum and lime slurries are prepared by
adding dry chemicals to mixing tanks beneath the
feeders and conveyed by gravity to a trough carrying
raw water to the rapid mixer. Volumetric feeders are
also in place to feed potassium permanganate,
powdered activated carbon, and soda ash slurries to
meet seasonal variations in raw water quality.
Alum feed rates are adjusted based on visual
inspection of the floe particles in the flocculation
basins. A jar testing apparatus is in place, but is used
infrequently (10-15 times/yr). The lime feeder is
currently operating at maximum output, and is not
adjusted.
The chemical slurries and raw water enter a 0.9-m
square (3-ft square) and 2.4- m (7.8-ft) deep basin
containing a mechanical flash mixer. The basin has a
hydraulic detention time of 30 seconds. The CPE
team calculated the G value for the mixer to be
adequate at 894 sec-"1.
After exiting the rapid mix basin the water splits
hydraulically and flows through a parallel train of
identical flocculation, sedimentation, and filter basins,
prior to entering the two clearwells.
The coagulation/flocculation process is performed in a
dual stage system; each stage is fitted with horizontal
paddles. A pair of variable speed motors, one for each
stage, drives a central shaft which in turn drives the
paddles for each stage of the parallel trains. Each
basin has a detention time of 45 minutes and a peak
G of 77 sec-"".
Flocculation basin effluent is directed to the bottom of
the two pairs of sedimentation basins and flows up
through a set of 60-degree tube settlers. Each of the
two basins has a detention time of 2.1 hr. The basins
have a combined surface overflow rate of 58 m3/m2/d
(1,420 gpd/sq ft). Sludge is manually removed
approximately every 2 months and washed to a
decant basin. Originally, decant from the basin was
95
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Figure 4-66. Plant 13 process flow diagram.
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recycled to the head of the plant, but the recycle
pump is out of service so the decant is discharged to
the river. Sludge from the decant basin is washed to
the drying beds for ultimate discharge to a sanitary
landfill.
Settled water then enters a pair of mixed media filters
through metal troughs above 12.6 m2 (136 sq ft) of
media. Filter flow rates are controlled by raw water
pumping rates, which in turn actuate pneumatic
valves, maintaining an approximate loading rate of 222
m3/m2/d (3.8 gpm/sq ft).
Backwash frequency is determined by measuring
headless across the filters or by observing a rise of
clearwell turbidity. Filter runs are routinely 40-45 hr.
Backwashing routinely consists of 6-7 minutes of
surface wash at a rate of 26 m3/m2/d (0.45 gpm/sq ft).
The media beds are then washed at a rate of 1,055
m3/m2/d (18 gpm/sq ft) for an indiscriminate duration.
The influent troughs are then used to discharge
backwash water to the decant basin. The filters are
capable of filter-to-waste operation, although this is
not commonly practiced.
Chlorine (23 kg [50 lb]/d), hydrofluosilicic acid (91 L
[24 gal]/d), and, occasionally, soda ash are then
added to filtered water prior to entering the two
clearwells. Each clearwell has a hydraulic detention
time of 4.9 hr. Current piping configurations do not
permit operating the clearwells in series.
Finished water then flows into the wet well which
supplies water for the two high-service pumps, as well
as the backwash pump.
Major Unit Process Evaluation
The performance potential graph is shown in Figure 4-
67. The shortest bar represents the treatment process
limiting the plant's capacity to achieve the desired
performance of less than 0.5 NTU.
The instantaneous peak operating flow was
established 66 L/s (1,050 gpm). This is based on a
review of flow records for the previous year and the
practice of only operating one of the raw water
pumps. The plant is normally operated approximately
17-20 hr/day. To meet events of peak water use
during the summer, the plant is operated 24 hr/day.
On those days the treatment processes are still
operated at a maximum flow rate of 66 L/s (1,050
gpm).
The flocculation basins were rated at 149 L/s (3.4
mgd) based on a 20-minute hydraulic detention time
and two-stage flocculation with a variable speed input.
Due to the use of tube settlers, the sedimentation
basins were rated at 101 L/s (2.3 mgd) based on a
surface overflow rate of 88 m3/m2/d (1.5 gpm/sq ft).
Filtration capacity for the plant was rated at 85 L/s
(1.95 mgd) based on the state maximum allowable
loading rate of 293 m3/m2/d (5 gpm/sq ft).
The disinfection system was rated at 26 L/s (0.6
mgd). Future drinking water regulations for disinfection
will be based on CT values needed for various
removals of Giardia cysts and inactivation of viruses.
To establish the CT required, it was assumed that the
plant's disinfection system would have to provide 1.5
logs of cyst removal with 2.5 logs of removal credited
for the other treatment processes. The total of 4 logs
(99.99 percent) of cyst removal required for Plant 13
was based on the CPE team's estimate of the quality
of the raw water.
To achieve the 1.5 logs of cyst removal the CPE team
estimates that the disinfection system would have to
provide a CT of 183. This CT value is for chlorine at a
2.5 mg/L dose, pH 8.0, and temperature of 5ฐC. The
contact time was based exclusively on the post-
chlorine dose. Only 10 percent of the theoretical
detention time in the clearwells was used because the
clearwells are not baffled and thus are subject to
hydraulic short circuiting. The actual levels of
disinfection required for the plant in the future will be
determined by the State. The estimates in this CPE of
the required number of log reductions of Giardia cysts
and viruses and the allowances for actual contact
times in the clearwells may change when final
disinfection regulations are developed.
Raw and finished water pumping capacity was rated at
66 L/s (1.5 mgd). This rating was based on use of a
single raw/finished water pump with one pump out of
service.
As shown in the performance potential graph, the
major unit processes have a rating capacity exceeding
the instantaneous peak operating flow, with the
exception of the disinfection process. Again, the lack
of baffling in the clearwells limited the projected
capacity of the disinfection process.
Performance Assessment
Figure 4-68 shows the settled water turbidity
measured by the plant staff over the previous 12-
month period. Settled water turbidities were generally
less than 2.0 NTUs, although there were also several
periods of higher turbidity. These appeared to be
related to periods of high raw water turbidity,
indicating that chemical feed rates were not properly
adjusted to compensate for the changes in raw water
turbidity.
Figure 4-69 shows the finished water turbidity reported
over the previous 12 months. Current regulations for
finished water turbidity are 1.0 NTU. Future
regulations will require the plant to meet a 0.5-NTU
finished water turbidity 95 percent of the time. Except
for several days in the first 3 months, the plant met
97
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Figure 4-67. Plant 13 performance potential graph.
Unit Process
1.0
Flow, mgd
2.0 3.0
4.0
Flocculatlon1
HOT, min
Sedimentation2
SOR, gpm/sq ft
Filtration*
HLR, gpm/sq ft
Disinfection4
Contact time, min
Raw/Finished PumpingS
68
0.66
2.6
694
34
23
1.3
Peak Instantaneous Operating
Flow (1 Pump) = 1,050 gpm
' Rated at 20 -min HOT - based on 2-stage with variable energy input.
2 Rated at 1.5 gpm/sq ft - based on tube settlers with annual sludge removal.
3 Rated at 5 gpm/sq ft - based on State maximum allowable loading.
4 Rated at CT * 183 with 2.5 mg/L chlorine dose, which requires a 73-min HOT; allowed 10 percent of available volume for contact
time, temperature * 5ฐC, pH = 8, 4-log required reduction, 2.5 log in plant, 1.5 log disinfection.
5 Assumes firm capacity at 1.5 mgd with one pump out of service.
the 1.0-NTU turbidity requirements and was regularly
below the 0.5-NTU required by the SWTR. Figure 4-
70 presents a probability plot of this data and shows
that the plant produces a finished water turbidity of
less than 0.5 NTU approximately 70 percent of the
time. Comparing Figures 4-68 and 4-69 reveals that
higher finished water turbidity occurred during the
same periods that the settled water turbidity was
above 2.0 NTUs, providing further evidence that
chemical feed rates were not properly adjusted when
raw water turbidities changed.
During the CPE, a special study was conducted to
assess the performance of the filters after
backwashing. With adequate facilities and operation of
preceding unit processes, a properly operated filter
should produce a finished water turbidity of
approximately 0.1 NTU and experience only a 0.2-
NTU rise in turbidity in the finished water for
approximately 10 minutes after being restarted
following backwashing. For this special study, finished
water from Filter 1 was sampled for a 40-minute
period after being restarted following backwashing.
Figure 4-71 shows the results of this special study.
Prior to backwashing, the filter was producing 1.0-
NTU water. After backwashing, the turbidity levels
increased to 3.6 NTU and did not stabilize at the 0.1-
NTU level for 30 minutes. The special study also
found a problem with an inadequate amount of
backwash water flow at the beginning of the backwash
cycle. A period of essentially no flow was followed by
a violent eruption of the filter media as the backwash
water finally started entering the filter. Further
investigation of the problem revealed that the valve
that controls the backwash water flow was sticking in
a closed position and would finally snap fully open.
These results indicate that a finished water that meets
current and future regulations is usually produced.
During periods of high raw water turbidity, it appears
that the plant staff is not adequately adjusting process
control to allow the plant to produce a consistently
good quality finished water. Turbidity levels following
backwashing also indicate that better process control
could be practiced to limit the passage of high
turbidity water into the distribution system following
filter backwash.
98
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Figure 4-68. Settled water turbidity profile - Plant 13.
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DEC JRN89 FEE MRR RPR MRY JUN JUL RUG SEP OCT NOV DEC JHN90
Figure 4-69. Finished water turbidity profile - Plant 13.
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Present
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Future
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DEC JRN89 FEB MRR RPR MRY JUN JUL RUG SEP OCT NOV DEC JRN90
99
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Figure 4-70. Probability plot of finished water turbidity - Plant 13.
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Figure 4-71. Filter effluent turbidity profile after backwash
Plant 13.
TurbKiity, NTU
4 i-
0
10
20
Minutes
30
40
Performance-Limiting Factors
The following factor was identified as having a major
effect on a long-term repetitive basis:
1. Disinfection - Design*: This factor has an asterisk
because it was assessed based on the initial
disinfection requirements of new regulations.
These requirements may change when final
regulations are developed by the State. Using this
basis, however, inadequate contact time is
provided because of a lack of baffling in the two
clearwells and a lack of piping to allow them to
operate in series.
Factors identified as having a minimal effect on a
routine basis, or a major effect on a periodic basis
were prioritized and are summarized below:
1. Supervision - Administration: The plant has 24-hr
coverage, which requires a large staff. This large
staff works without any formal organizational
structure, no lines of authority, no chief operator,
and a total lack of leadership. With this absence
of supervision, essentially no communication
occurs between the staff on the different shifts.
There are no regular meetings, no operating log,
and no shift overlaps where essential information
on the status of the plant can be discussed.
Without this essential supervision, the productivity
of the plant staff is poor, which encourages poor
100
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performance. For example, the alum feeder that
needed repair at the end of the first shift was not
repaired during either of the next two shifts. Lack
of supervision and communication were made
worse by a total lack of standard operating
procedures.
2. Application of Concepts and Testing to Process
Control - Operation: While the plant staff is
certified and has a knowledge of water treatment,
they are not able to apply their knowledge to
properly control the treatment processes to
optimize performance. Filter-to-waste capabilities
at the plant are not used to minimize the passage
of high turbidity water to the clearwells after filter
backwash. The plant was also operated for a
month without a turbidimeter. Iron and manganese
levels were high in the finished water on several
occasions, but no process changes were initiated
by the plant staff. Lime is fed at the same point as
the alum even though the lime raises the pH out
of the optimum range for alum coagulation.
3. Process Control Testing - Operation: A process
control testing program to optimize unit process
performance did not exist. Process control testing
is essential for water plants served by surface
sources because of the frequent and rapid
changes in raw water quality. Basic equipment
was available to conduct this testing, but was not
used.
4. Preventive Maintenance - Maintenance: The lack
of a maintenance program has resulted in many
key pieces of equipment needed for optimal
operation not operating or near failure. Filter
controls, the influent control valve, the finished
water flow meter, and backwash water reclaim
pumps are not operating. New alum and lime
feeders were not installed to replace the marginal
units still in operation. Backwash control valves
were malfunctioning and the drives on the
flocculators were making excessive noises with no
indication of repairs being planned.
5. Water Demand - Administration*: This factor has
an asterisk because it is projected that in the
spring of 1990 the water demands of the new
industry and development in the city will exceed
the raw water pumping capacity of the plant. Plant
administrators committed the plant to supply this
water with little regard to its impact on the
capacity or performance of the plant.
Several of the administration's policies are considered
to have a minor impact on the performance of the
plant. Current rate structures do not allow the plant to
be self-sustaining and cover all needed operation and
maintenance costs. There is a total lack of long-range
planning to allow for growth within the community so
as to minimize impact on plant's capacity and
performance. Funding for the plant is also kept low,
preventing repair of key equipment. Other factors
thought to have a minor impact on performance are
the low pay of the plant staff as compared to other
plants in the State and the lack of process flexibility.
Projected Impact of a CCP
Data collected during the CPE indicated that this plant
usually performs satisfactorily, with some problems
responding to changes in raw water turbidity.
Correcting the identified factors would appreciably
improve the consistency of the plant's performance
and allow it to meet both current and future
regulations. As such, implementation of a CCP
represented a viable option for this plant.
101 *U.S.GOVERNMENT PRINTING OFF ICEI 1 990-74 8-159/004 I 2
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