# ![](media/image1.wmf)5. Individual Filter Self Assessment

## Introduction

Based on individual filter monitoring requirements in the IESWTR, some
systems may be required to conduct an individual filter self assessment.
Specifically, a system must conduct an individual filter self-assessment
for any individual filter that has a measured turbidity level greater
than 1.0 NTU in two consecutive measurements taken 15 minutes apart in
each of three consecutive months. The system must report the filter
number, the turbidity measurement, and the dates on which the
exceedances occurred.

Filters represent the key unit process for the removal of particles in
surface water treatment. Although filters represent only one of the
"barriers" in a treatment process their role is the most critical as the
final physical "barrier" to prevent passage of chlorine resistant
pathogenic microorganisms into distribution systems. Properly designed
filters used in conjunction with coagulation, flocculation and
sedimentation processes (if in use), when in proper physical and
operational condition, are capable of treating raw water sources.

For any situation regarding a single poor performing filter, or a bank
of poor performing filters:

-   Performance limitations observed at the start of a filter run are
    most often attributed to improper chemical conditioning of the
    filter;

-   Limitations observed during the filter run are most often attributed
    to changes in hydraulic loading conditions; and

-   Limitations observed at the end of the filter run are most often
    related to excessive filter runs.

Filter performance issues may only be apparent during excessive
hydraulic loading and care should be taken to not attribute all
turbidity spikes to hydraulic bumping or overloading. In some
circumstances performance "symptoms" for other causes may only be
evident during these hydraulic episodes. Oftentimes disrupted filter
media may cause filter performance problems. The following chapter
describes the process of an individual filter self assessment and is
intended to provide clarity regarding which of these areas are limiting
the performance of a filter.

The following chapter will include each of the following components of
an individual filter assessment:

-   **A general description of the filter** including size,
    configuration, placement of washwater troughs and surface wash type
    (if applicable) and filter media design (e.g., type, depth and
    placement) and if filter-to-waste is present and/or used and if any
    special conditions exist regarding placing a filter back into
    service (i.e., is the filter rested, polymer or coagulant added
    prior to placement into service, etc.). Table 5-1 provides a
    worksheet to assist the evaluator in collecting this information.

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-   **The development of a filter run profile** of continuous turbidity
    measurements or total particle counts versus time for an entire
    filter run from start up to backwash, including assessment of filter
    performance while another filter is being washed. The run length
    during this assessment should be representative of typical plant
    filter runs. The profile should include explanations of the cause of
    performance spikes during the run.

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-   **An assessment of the hydraulic loading conditions of the filter**
    which includes: the determination of the peak instantaneous
    operating flow for the individual filter, an assessment of the
    filter hydraulic loading rate at this peak instantaneous operating
    flow, and an assessment whether plant flow is distributed evenly
    among all the filters.

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-   **An assessment of the actual condition and placement of the media**
    with a comparison to the original design specifications. The filter
    bed should be investigated for surface cracking, proper media depth,
    mudballs and segregation of media in dual media filters. The media
    should be examined (using coring and/or gross excavation techniques
    as appropriate) at several locations to determine the depth of the
    different media layers in dual and multi-media filters.

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-   **A description of backwash practices** including length, duration,
    presence of and type of surface wash or air scour, and method for
    introducing wash water (i.e., via pump, head tank, distribution
    system pressure, etc.) and criteria for initiating the wash (i.e.,
    degraded turbidity or particle counts, head loss, run time, etc.),
    the backwash rate, and bed expansion during the wash.

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-   **An assessment of the condition of the support media/underdrains**
    including a filter grid detailing placement of support media, as
    well as a summary of inspection of the clearwell for the presence of
    filter media and any observances of boils or vortexing during
    backwash.

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-   **An assessment of the filter rate-of-flow controllers and filter
    valving infrastructure adequacy**. The rate-of-flow controllers and
    ancillary valving related to the filter can also have an impact on
    filter performance and should be visually inspected to assure proper
    operation.

[]{#__RefHeading___Toc448537397 .anchor}Table 5-1. Individual Filter
Self Assessment Worksheet

  ------------------ --------------------------------- ------------------
  **Topic**          **Description**                   **Information**

  General Filter     Type (mono, dual, mixed)          
  Information                                          

                     Number of filters                 

                     Filter control (constant,         
                     declining)                        

                     Surface wash type (rotary, fixed, 
                     none)/Air Wash                    

                     Configuration (rectangular,       
                     circular, square)                 

                     Dimensions (length, width,        
                     diameter)                         

                     Filter-to-waste                   
                     (capability/specify if used)      

                     Surface area per filter (ft^2^)   

  Hydraulic Loading  Average operating flow (mgd)      
  Conditions                                           

                     Peak instantaneous operating flow 
                     (mgd)                             

                     Average hydraulic surface loading 
                     rate (gpm/ft^2^)                  

                     Peak hydraulic surface loading    
                     rate (gpm/ft^2^)                  

  Media Design       Depth, type                       
  Conditions                                           

                     Media 1 -- Sand                   

                     Media 2 (if applicable) --        
                     Anthracite                        

                     Media 3 (if applicable) -- Garnet 

  Actual Media       Depth                             
  Conditions                                           

                     Media 1 -- Sand                   

                     Media 2 (if applicable) --        
                     Anthracite                        

                     Media 3 (if applicable) -- Garnet 

                     Presence of mudballs, debris,     
                     excess chemical, cracking, worn   
                     media                             

  Support            Is the support media evenly       
  Media/Underdrain   placed (deviation \<2 inches) in  
  Conditions         the filter bed?                   

                     Evidence of media in the          
                     clearwell or plenum               

                     Evidence of boils/vortexing       
                     during backwash                   
  ------------------ --------------------------------- ------------------

**Table 5-1. Individual Filter Self Assessment Worksheet (continued)**

  ------------------ ------------------------------- --------------------
  **Topic**          **Description**                 **Information**

  Backwash           Backwash initiation (headloss,  
  Conditions         turbidity/particle counts,      
                     time)                           

                     Sequence (surface wash, air     
                     scour, flow ramping,            
                     filter-to-waste)                

                     Duration (minutes)              

                     Introduction of wash water (via 
                     pump, head tank, distribution   
                     system pressure)                

                     Backwash rate (gpm/ft^2^)       

                     Bed expansion (percent)         

                     Coagulant or polymer added to   
                     wash water                      

                     Filter rested prior to return   
                     to service                      

  Other                                              
  Considerations                                     

                                                     

                                                     

                                                     

                                                     

                                                     
  ------------------ ------------------------------- --------------------

## 5.2 Developing A Filter Run Profile

The profile for the filter being evaluated shall include a graphical
summary of filter performance for an entire filter run from start-up to
backwash inclusively. Performance is typically represented by turbidity
although total particle counts may be used in addition to, or in lieu
of, turbidity measurements. Use of particle counting in conjunction with
turbidity monitoring of filter effluents may offer additional insights
to filter performance, however, care should be taken in the
interpretation of particle count results. The interpretation should
focus on the change in count levels as opposed to the discreet particle
count numbers. Plotting the performance data versus time on a continuous
basis is the desirable approach for development of the filter profile.
However, time increments less than a continuous basis may be used with
the understanding that the intent is to identify and minimize "real"
deviations in performance. The filter run should be representative of a
typical run and should encompass the time period when another filter is
being washed. The profile shall include an explanation of the cause of
performance spikes during the run.

#### Example 

A utility has plotted total turbidity data versus time for a filter that
cannot meet requirements for individual filters. The filter run is
typically 24 to 28 hours with a resting period after backwash that
varies from 8 to 10 hours. The generated filter profile is shown below
in Figure 5-1. The review of turbidity data showed an inordinate number
of spikes occurring during the filter run. This data corroborated with
turbidity data that triggered the filter assessment. These spikes
corresponded to changes in hydraulic loading rates made by the staff and
may be indicative of greater problems within the filter itself. The
significant increases in turbidity passing the filters occurred when the
plant staff initiated recycle of treated backwash water to the head of
the plant and when plant loading rates were modified during the evening
to take advantage of off-peak electrical costs (represented by item
B&D). Table 5-2 provides explanations for turbidity spikes.

![](media/image2.wmf){width="5.997222222222222in" height="2.83125in"}

Figure 5-1. Filter Run Profile -- Turbidity (NTU) vs. Time

[]{#__RefHeading___Toc448537399 .anchor}Table 5-2. WTP Performance
Deviation Trigger Events

  ----------- --------------------------------------------------------------
  **Event**   **Performance Deviation Trigger Explanation**

  A           Pump change

  B           Backwash water decant recycle to head of plant initiated

  C           Backwash water decant recycle completed

  D           Pumping rate increased to take advantage of off-peak
              electrical costs

  E           Immediately following backwash of adjoining filter

  F           Filter backwash

  G           Filter taken out of service

  H           Filter placed back in service
  ----------- --------------------------------------------------------------

## Assessing Hydraulic Loading Conditions Of Filter

Filters with properly chemically pretreated influents are most
vulnerable to pass particles (including pathogenic microorganisms) at
peak loading rates in excess of filter design or during sudden changes
in hydraulic loading rates. Table 5-3 presents a summary of acceptable
filter loading rates for various filters. **However, filters may exhibit
capable performance at loading rates in excess of those presented in
Table 5-3; these values are rule-of-thumb and provide a basis for
evaluating excessive filter hydraulic loading.** State requirements may
differ from acceptable industry loading rates and should be considered
during the assessment.

Since the filters are most vulnerable during excessive loading rates, it
is critical to determine the peak flow on an instantaneous basis that
filters are performing under and to minimize incidences when filters are
expected to perform at these higher loading rates. Peak instantaneous
operating flow rate is identified through review of operating records
and observations of operational practices and flow control capability.

A review of plant flow records can be misleading in determining the peak
instantaneous operating flow. For example, peak daily water production
can only be used when those values are generated during a 24-hour
operational day during specific conditions. If values are used that were
generated for a day when the plant only was in operation for 12 hours,
the peak instantaneous operating flow would be  of the true value.
Additionally, if pumps are used in multiple combinations throughout the
operational day, care should be taken to determine the actual peak
loading on the filters during the day. The peak instantaneous operating
flow should be determined based on the flow distributed to the filters
on a maximum daily minute. The peak instantaneous operating flow that
each filter sees is dependent on the minimum number of filters used per
day at the plant's peak instantaneous operating flow.

[]{#__RefHeading___Toc448537400 .anchor}Table 5-3. General Guide to
Acceptable Filter Hydraulic Loading Rates

  ------------------------- ---------------------- ----------------------
  **Filtration Type**       **Air Binding**        **Loading Rate**

  Sand Media                None                   \~2.0 gpm/ft^2^

                            Exists                 \~1.0 - 1.5 gpm/ft^2^

  Dual/Mixed Media          None                   \~4.0 gpm/ft^2^

                            Exists                 \~2.0 - 3.0 gpm/ft^2^

  Deep bed                  None                   \~6.0 gpm/ft^2^

  (anthracite \> 60 in.)    Exists                 \~3.0 - 4.5 gpm/ft^2^
  ------------------------- ---------------------- ----------------------

#### Example 1

A plant which operates 24 hours per day uses three 5-mgd pumps in
various combinations throughout the year to meet system demand. The
pumps are capable of being throttled to reduce individual flow to 80
percent of capacity. The average daily production is 8 mgd while the
peak production day over a previous 2-year period has been 12 mgd. The
plant in the previous two years has never run all three pumps
simultaneously for an entire day. However, for a 2-hour period each
evening, all three pumps are used to fill on-site storage. Two pumps are
used for the first hour with the third pump only used with the other two
pumps for the last 30 minutes of the 2-hour period. During that 30
minute period plant flow increases to 14 mgd. The peak instantaneous
operating flow that go onto the filters is 14 mgd. The plant's six dual
media filters (each 425 ft^2^) would have a loading rate of 3.8
gpm/ft^2^ at this 14 mgd peak flow.

#### Example 2

A plant with 8 dual media filters and a constant high service pumping
rate of 8 mgd operates 24 hours per day and is unable to consistently
meet the filter requirements. Each filter has 175 ft^2^ of surface area
and typically has a flow rate of 1 mgd. However, two filters are
backwashed per day at the same time with no reduction in plant flow.
During backwash the two filters are out of service for 40 minutes.
During that 40 minute period the entire plant flow of 8 mgd is handled
by just six filters. The peak instantaneous operating flow for each
filter becomes 1.33 mgd. The hydraulic loading rate in gpm/ft^2^ for
each 175 ft^2^ filter at this peak flow becomes 5.3 gpm/ft^2^ (1.33 mgd
converted to gpm divided by the filter surface area) which is at the
upper end of the acceptable loading rates for a dual media filter and
may be contributing to the unacceptable performance.

## Assessing Condition & Placement Of Filter Media 

![](media/image3.wmf)

![](media/image4.png)The filter inspection should begin by draining the
filter. The filter should be drained enough to allow for excavation of
the media to assess the depths of each media type, as well as, each
media interface (e.g., just below the anthracite/sand interface in a
dual media filter). Deeper excavation of the filter may be necessary if
evidence suggests disrupted support gravels or an inadequate underdrain
system (see Section 5.6). Care should be taken not to disrupt the
support gravel/media.

Filter media assessments may be conducted using a gross excavation of
media technique or application of a variety of coring devices (typically
a 1 to 2 inch pipe). Coring methods offer the advantage of being able
to apply the Floc Retention Analysis procedure, if conditions warrant
(see to Section 5.5). Evaluators should place small pieces of plywood on
the media prior to getting on the filters to avoid sinking into the
media. The excavation technique may be conducted using a gross
excavation of the media or a plexiglass box shown in Figures 5-2 and
5-3. The box excavation consists of sinking a plexiglass box into the
media and excavating inside the box down to the support media. The box
excavation technique allows for visual observation of the media depths
and interfaces after the excavation is completed.

Whatever media excavation technique is used, the evaluators should note
the depth of each media type, (comparing this to the original
specifications), the general condition of the media interface, the
presence of any mudballs or excess chemical. After the excavation is
completed, the excavation team should make certain that the media is
placed back in the excavations in the same sequence that it was removed.
The filter should be backwashed after completion of the excavation prior
to return to service.

## Assessing Backwash Practices 

Proper maintenance of filters is essential to preserve the integrity of
the filter as constructed. Limitations of poor performing filters
relating to filter media degradation or disruption of support gravel
placement can often be attributed to inadequate backwashing or excessive
backwashing rates. The duration of the backwash, if excessive, may also
be detrimental. Different facilities have had different experiences in
how clean the filters should be after backwashing. Consideration should
be given to site-specific circumstances in the application of any
recommendations regarding filter backwash procedures with the focus
always being on filter effluent water quality. Table 5-4 summarizes
guidelines for acceptable backwashing practices.

[]{#__RefHeading___Toc448537401 .anchor}Table 5-4. Guidelines Regarding
Acceptable Backwashing Practices

  -------------------------------- --------------------------------------
  **Area of Emphasis**             **Guideline**

  Basis for initiating backwash    focus on filter performance
                                   (turbidity, particle counts)
                                   degradation versus headloss or time

  Backwash flow                    slowly ramped to peak rate

  Backwash flow rate               15 - 20 gpm/ft^2^

  Bed expansion during backwash    20 - 25 percent
  -------------------------------- --------------------------------------

The assessment of the filter backwash procedure should include the
following:

-   A collection of general information related to the backwash;

-   Verification of the adequacy of the backwash SOP;

-   A visual inspection of a backwash; and

-   Determination of the backwash rate and expansion of the filter media
    during the wash.

The individual filter assessment worksheet (Table 5-1) can be used to
collect general information regarding the backwash.

An adequate backwash SOP should describe specific steps regarding when
to initiate backwash, how flows are ramped during the wash, when to
start and stop surface wash or air scour, and duration of the wash.

Backwash rates are designed to provide adequate cleaning of the filter
media without washing media into the collection troughs or causing
disruption of the support gravels. Table 5-4 identifies generally
acceptable backwash rates. These values are to be used as a guide when
assessing adequacy of the backwash procedures. Backwash rates in
gpm/ft^2^ may be determined by simple calculation if backwash pump rates
or backwash flows are available and known to be accurate. If these
values are unavailable or suspect, backwash rates can be determined by
performing a rise rate test of the filter. Periodic rise rate tests can
also be used to verify the backwash flow measurement instruments. The
rise rate test entails determining the amount of time it takes backwash
water to rise a known distance in the filter bed. Typically, a metal rod
marked at 1-inch intervals is fixed in the filter to enable measurement
of the distance that water rises during the wash. The rise rate test
should be conducted such that measurements are taken without the
interferences of the wash water troughs in the rise volume calculation.
Extreme care and great attention to safety should be followed while
conducting the rise rate test. Rise rate is used to calculate backwash
rate by dividing the rise volume for a known time period by the filter
area as follows:

![](media/image5.wmf)

![](media/image6.wmf)Example backwash rate calculation: A filter having
a 150 ft^2^ surface area has wash water rise 10.7 inches in 20 seconds
during the rise rate test. The backwash rate would be 20 gpm/ft^2^.

![](media/image7.wmf)In addition to backwash rate, it is also extremely
important to expand the filter media during the wash to maximize the
removal of particles held in the filter or by the media. Bed expansion
is determined by measuring the distance from the top of the unexpanded
media to a reference point (e.g., top of the filter wall) and from the
top of the expanded media to the same reference point. The difference
between these two measurements is bed expansion. A proper backwash rate
should expand the filter 20 to 25 percent (AWWA and ASCE, 1990).
Attention should be given to the influence of seasonal temperature
changes on bed expansion during application of this procedure. Percent
bed expansion is given by dividing the bed expansion by the total depth
of expandable media (i.e., media depth less support gravels) and
multiplied by 100 as follows:

![](media/image8.png){width="2.9in"
height="2.308267716535433in"}![](media/image9.png){width="2.6755905511811022in"
height="2.304724409448819in"}emptied, affixed higher in the filter above
the media and the bed expansion test repeated. The disk unit is used by
placing the disk on the unexpanded media prior to backwash and recording
the length of the metal rod to the reference point. The disk unit is
then removed and backwashing is initiated. After the backwash is allowed
to reach its peak rate the disk is lowered slowly into the backwashing
filter until media is observed on the disk. The measurement of the
expanded media is then recorded and percent bed expansion may then be
determined. Figure 5-5 depicts the disk bed expansion apparatus. The key
attribute of any method is that determination of the top of the expanded
media be accurately characterized.

#### ![](media/image10.png)  {#section .unnumbered}

#### Example bed expansion calculation: 

The backwashing practices for a filter with 30 inches of anthracite and
sand is being evaluated. While at rest, the distance from the top of the
media to the concrete floor surrounding the top of the filter is
measured to be 41 inches. After the backwash has been started and the
maximum backwash rate is achieved, a probe containing a white disk is
slowly lowered into the filter bed until anthracite is observed on the
disk. The distance from the expanded media to the concrete floor is
measured to be 34 inches. The resultant percent bed expansion would be
22 percent.

> *unexpanded measurement =* 41 *inches*
>
> *expanded measurement =* 34.5 *inches*
>
> *bed expansion =* 6.5 *inches*
>
> *bed expansion (percent) = (*6.5 *inches /* 30 *inches) \** 100 *=* 22
> *percent*

Use of the Floc Retention Analysis procedure may be warranted if the
filter is meeting backwash expansion and backwash rate guidelines while
still not achieving turbidity performance criteria. (Kawamura, 1991,
Wolfe & Pizzi, 1998.) The Floc Retention Analysis procedure allows for
an extremely in-depth analysis of backwash practices.

## Assessing Condition Of Support Media/Underdrains

Maintaining the integrity of the support gravels and underdrains is
extremely important to the performance of a rapid granular filter.
Disrupted or unevenly placed support media can lead to rapid
deterioration of the filtered water quality noticeable by quick
turbidity breakthroughs and excessively short filter runs (Peck, Smith).
Should disruption of the support media be significant, the impacted area
of the filter may act as a "short-circuit" allowing particulates and any
microbial pathogens which are present to pass directly into the
clearwell. Filter support gravels can become disrupted by various means
including sudden violent backwash, excessive backwashing flow rates, or
uneven flow distribution during backwash.

The condition of the support gravel is assessed in three steps. The
first step consists of visually inspecting the filter during a backwash
for the presence of excessive air boiling or noticeable vortexing as the
filter is drained. The second step entails determining whether filter
media has ever been found in the clearwell. This should be determined
visually or by reviewing recent clearwell maintenance records. Clearwell
inspections should be only be conducted following appropriate safety
procedures while minimizing negative impacts on necessary plant
operations. Clearwells containing a significant amount of filter media
may indicate a greater problem than just disrupted support gravels. The
problem may be attributed to a severe issue with the filter underdrain
system. An in-depth assessment of the underdrains typically involves
excavation of the entire filter bed. Systems should use best
professional judgement and seek additional guidance if undertaking an
underdrain assessment, as it is outside the scope of "typical" filter
self assessment. The third step is the most common method of assessing
the placement of filter support media. This method involves "mapping" of
the filter using a steel or solid probe. The mapping procedure involves
a systematic probing through the filter media down to the support
gravels of a drained filter at various locations in a grid-like manner.
At each probe location, the depth of penetration into the filter is
measured against a fixed reference point such as the wash water troughs.
The distance from the fixed reference point to the top of the support
gravels should deviate less than 2 inches. **Care should be taken during
the filter probing not to disrupt the support gravel.**

#### Example

Operators, while draining a poor performing filter, observed vortexing
occurring at the far end of the filter. The operators constructed a
support gravel placement grid by probing through the media down to the
support gravel every 2 feet throughout the filter using a 6 feet long
aluminum rod that had been marked at 1-inch intervals. The operator
using the probe measured the depth of probe penetration against the wash
water trough. Examination of the grid (shown in Table 5-5) indicated
that the support gravels were extremely disrupted at the far end of the
filter.

[]{#__RefHeading___Toc448537402 .anchor}Table 5-5. Example Filter
Support Gravel Placement Grid

Depth of Filter Support Gravels (in inches)

Measured from the Wash Water Trough

  ------ ------------ ------------ ------------ ------------ ------------
                                   **Filter                  
                                   Control                   
                                   Panel**                   

         **2 ft**     **4 ft**     **6 ft**     **8 ft**     **10 ft**

  **2    41           40.75        41           41           41
  ft**                                                       

  **4    40.75        40.5         41           41           40.75
  ft**                                                       

  **6    41           41.25        40.75        41           41
  ft**                                                       

  **8    40.75        41           41           40.75        40.75
  ft**                                                       

  **10   41           41           40.5         40.5         40.75
  ft**                                                       

  **12   41           **46**       **46.5**     41           41
  ft**                                                       

  **14   40.75        **46**       **46.25**    39           40.75
  ft**                                                       

  **16   41           39           38.75        37           40.75
  ft**                                                       

  **18   40.75        41.25        40.75        41           41
  ft**                                                       
  ------ ------------ ------------ ------------ ------------ ------------

## Assessing Rate-Of-Flow Controllers & Filter Valve Infrastructure

The rate-of-flow controllers and ancillary valving related to the filter
can also have an impact on filter performance. Hydraulic changes (such
as those caused by filter bumping) cause filters to shed particles.
Maintaining the rate-of-flow controllers is important in minimizing
hydraulic changes in the filter. Figure 5-6 shows on-line turbidity
measurements for two filters in a treatment plant. Each of the two
filters had rate-of-flow controller problems that became more evident as
headloss built up in the filters. Just prior to initiating backwash in
filter 4 the rate-of-flow controllers were opening and closing
constantly "seeking" the correct position. This was first apparent to
the filter evaluation team who observed constant turbidity fluctuations
of the filter effluent during a filter performance review. Improperly
seated valves can also have similar impacts on filter performance.
Backwash valves may leak and allow wash water to compromise filter
effluent coming from the filters remaining in operation. All filter
assessments should include an evaluation of all the rate-of-flow
controllers and filter valving.

![](media/image11.png)

Figure 5-6. On-Line Turbidimeters Showing Performance Problems Due to
Inoperable Rate-of-Flow Controllers

## 5.8 References

1.  AWWA. 1998. "How to Do A Complete Examination of Your Filters
    (Without Incurring the Wrath of the Filter Gods)." Annual Conference
    Workshop Summary.

2.  AWWA and ASCE (American Society of Civil Engineers). 1990. *Water
    Treatment Plant Design*. Second edition. McGraw-Hill, New York.

3.  Bender, J.H., R.C. Renner, B.A. Hegg, E.M. Bissonette, and R.J.
    Lieberman. 1995. "Voluntary Treatment Plant Performance Improvement
    Program Self-Assessment Procedure." Partnership for Safe Water,
    USEPA, AWWA, AWWARF, Association of Metropolitan Water Agencies,
    Association of State Drinking Water Administrators, and National
    Association of Water Companies.

4.  James M. Montgomery Consulting Engineers, Inc. 1985. *Water
    Treatment Principles and Design*. John Wiley & Sons, Inc.

5.  Kawamura, S. 1991. *Integrated Design of Water Treatment
    Facilities*. John Wiley & Sons, Incorporated, New York, NY.

6.  Peck, B., T. Tackman, and G. Crozes. No date specified. *Testing the
    Sands - The Development of a Filter Surveillance Program*.

7.  Smith, J.F., A. Wilczak, and M. Swigert. No date specified.
    *Practical Guide to Filtration Assessments: Tools and Techniques*.

8.  USEPA. 1998. *Handbook: Optimizing Water Treatment Plant Performance
    Using the Composite Correction Program*. EPA/625/6-91/027.

9.  USEPA. 1998. "National Primary Drinking water Regulations: Interim
    Enhanced Surface Water Treatment Rule; Final Rule." 63 *FR* 69477.
    December 16.

10. Wolfe, T.A. and N.G. Pizzi. 1998. "Optimizing Filter Performance."

    THIS PAGE INTENTIONALLY LEFT BLANK

5\. Individual Filter Self Assessment
[1](#individual-filter-self-assessment)

5.1 Introduction [1](#introduction)

5.2 Developing A Filter Run Profile
[4](#developing-a-filter-run-profile)

5.3 Assessing Hydraulic Loading Conditions Of Filter
[6](#assessing-hydraulic-loading-conditions-of-filter)

5.4 Assessing Condition & Placement Of Filter Media
[7](#assessing-condition-placement-of-filter-media)

5.5 Assessing Backwash Practices [8](#assessing-backwash-practices)

5.6 Assessing Condition Of Support Media/Underdrains
[12](#assessing-condition-of-support-mediaunderdrains)

5.7 Assessing Rate-Of-Flow Controllers & Filter Valve Infrastructure
[14](#assessing-rate-of-flow-controllers-filter-valve-infrastructure)

5.8 References [15](#references)

Figure 5-1. Filter Run Profile -- Turbidity (NTU) vs. Time 5-5

Figure 5-2. Box Used for Excavation 5-7

Figure 5-3. Box Excavation Demonstration 5-8

Figure 5-4. Pipe Bed Expansion 5-11

Figure 5-5. Bed Expansion Device 5-11

Figure 5-6. On-Line Turbidimeters Showing Performance Problems Due to
Inoperable\
Rate-of-Flow Controllers 5-[1](#__RefHeading___Toc438000371)4

Table 5-1. Individual Filter Self Assessment Worksheet
[3](#__RefHeading___Toc448537397)

Table 5-2. WTP Performance Deviation Trigger Events
[5](#__RefHeading___Toc448537399)

Table 5-3. General Guide to Acceptable Filter Hydraulic Loading Rates
[6](#__RefHeading___Toc448537400)

Table 5-4. Guidelines Regarding Acceptable Backwashing Practices
[9](#__RefHeading___Toc448537401)

Table 5-5. Example Filter Support Gravel Placement Grid
[13](#__RefHeading___Toc448537402)