Enforcement
Division
Office of
Water Enforcement
Washington DC
Water
&EPA
NPDES
Compliance Sampling
Inspection Manual
MCD - 51
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NOTES
To order this publication, MCD-51, "NPDES Compliance Sampling
Inspection Manual", write to:
General Services Administration (8FFS)
Centralized Mailing Lists Services
Building 41, Denver Federal Center
Denver, Colorado 80225
Please indicate the MCD number and title of publication.
Multiple copies maybe purchased from:
National Technical Information Service
Springfield, Virginia 22151
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NPDES COMPLIANCE SAMPLING MANUAL
U.S. ENVIRONMENTAL PROTECTION AGENCY
ENFORCEMENT DIVISION
OFFICE OF WATER ENFORCEMENT
COMPLIANCE BRANCH
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DISCLAIMER
This manual has been reviewed by the Office of Water
Enforcement, U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or
commercial products does not constitute endorsement or
recommendation for use.
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ACKNOWLEDGEMENT
The Work Group wishes to express their appreciation to
the secretarial staff of the Compliance Branch, Enforcement
Division, Office of Water Enforcement, for the assistance
provided in the preparation of this Manual, especially
Mrs. Bennie M. Yeargin, Mr. Kenneth B. Goggin and Ms.
Jacqueline A. Price.
111
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NPDES COMPLIANCE SAMPLING MANUAL
TABLE OF CONTENTS
Paqe No,
DISCLAIMER ii
ACKNOWLEDGEMENT iii
TABLE OF CONTENTS iv
LIST OF ILLUSTRATIONS xi
LIST OF TABLES xiii
I. SUMMARY AND CONCLUSIONS 1
A. Wastewater Sampling Objectives 1
B. Obtaining Representative Data 1
C. Accomplishment of Compliance
Sampling Objectives 2
D. Error Minimization 3
II. INTRODUCTION
A. Background 6
B. Enforcement Management System 7
C. Work Group Membership 8
III. NPDES PERMIT SAMPLING REOUIREMENTS
A. Introduction 11
B. Self-Monitoring Data 11
1. Permit Specifications 11
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2. Use of Self-Monitoring Data 12
C. Compliance Monitoring 13
1. General 13
2. Definitions 13
3. Objective of Compliance Evaluation
Inspections 13
4. Compliance Evaluation Inspection
Tasks 14
5. Objectives of Compliance Sampling
Inspection 15
6. Compliance Sampling Inspection
Tasks 15
D. Adequacy of Data 16
E. Determining Compliance with Effluent
Limitations 16
1. Instantaneous Conditions 17
2. Daily Maximum Conditions 17
3. 7-day Average Conditions 18
4. 30-day Average Conditions 18
P. Sample Collection and Handling 19
IV. SAMPLE COLLECTION 20
A. Introduction 20
B. Sampling Considerations 21
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1. General 21
2. Sample Location 23
(a) General 23
(b) Influent 24
(c) Effluent 24
(d) Pond & Lagoon Sampling 24
3. Sample Volume 25
4. Selection and Preparation of Sample
Container 25
C. Sampling Techniques 25
1. Grab Samples 25
2. Composite Samples 26
(a) Selection of Sample Type 27
(b) Compositing Method 27
D. Sample Preservation 29
1. General 29
2. Compliance Considerations 30
E. Analytical Methods 32
1. General 32
2. Alternative Test Procedure 32
F. Sample Identification 33
G. Safety Considerations 34
VI
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V. AUTOMATIC SAMPLERS 37
A. Introduction 37
B. Automatic Sampler Subsystem Components 38
1. Sample Intake Subsystem 38
2. Sample Gathering Subsystem 39
(a) Mechanical 39
(b) Forced Flow 40
(c) Suction Lift 40
3. Sample Transport Subsystem 41
4. Sample Storage Subsystem 42
5. Controls and Power Subsystem 42
6. Sampler Reliability 42
C. Installation and Operation of Automatic
Sampling Equipment 43
1. Site Selection 43
2. Equipment Security 44
3. Power Source 44
4. Waste Characteristics 45
5. Sample Preservation During Compositing
Period 45
6. Winter Operations 45
D. Desirable Automatic Sampler Characteristics 46
VI. WASTEWATER FLOW MEASUREMENT 50
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A. Introduction 50
B. Wastewater Flow Measurement Systems 51
C. Field Verification of Flow Measurement
Systems 55
D. Wastewater Flow Measurement Methods 58
1. Volumetric Techniques 58
(a) Vessel Volume 58
(b) Pump Sumps, 61
(c) Bucket and Stopwatch 62
(d) Orifice Bucket 63
2. Dilution Methods 63
3. Open Channel Flow Measurements 67
(a) Velocity-Area Method 69
i Introduction 69
ii Current Meters 70
iii Field Practice 74
iv Area and Flow Calculations 76
(b) Weirs 77
i Broad Crested 79
ii Sharp Crested 81
(c) Flumes 89
i Parshall Flumes 89
ii Palmer Bowlus Flumes 94
iii Other Flumes 96
Vlll
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(d) Open Channel Flow Nozzles 96
(e) Slope-Area Method 97
(f) Measurement by Floats 99
4. Closed Conduit Flow Measurements 100
(a) Venturi Meter 101
(b) Orifice Meters 102
(c) Flow Nozzles 104
(d) Electromagnetic Flowmeter 106
(e) Acoustic Flowmeter 106
(f) Trajectory Methods 108
(g) Pump Curves 111
(h) Use of Water Meters 111
VII. QUALITY ASSURANCE 114
A. Purpose 114
B. Policy and Objectives 114
C. Elements of a Quality Assurance Plan 106
D. Quality Assurance in Sample Collection 116
1. Duplicate Samples 116
2. Split Samples 117
3. Spiked Samples 117
4. Sample Preservative Blanks 117
5. Precision, Accuracy and Control
Charts 118
E. Quality Assurance Procedures for Field
Analysis and Equipment 118
IX
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1. Calibration and Documentation Plan 118
F. Parameter Requiring Special Precautions 124
1. Organics 124
2. Acidity - Alkalinity 125
3. Miscellaneous Parameters 125
(a) Dissolved Parameters 126
(b) Mercury, Total 126
(c) Phenolics and Cyanides 126
(d) Sulfide and Sulfite 126
VIII. CHAIN OF CUSTODY PROCEDURES 128
A. Introduction 128
B. Survey Planning and Preparation 128
C. Sample Collection, Handling & Identification 129
D. Transfer of Custody and Shipment 132
E. Laboratory Custody Procedures 135
F. Evidentiary Considerations 137
APPENDIX
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LIST OF ILLUSTRATIONS
Figure Page
IV-1 Method For Determining Composite Aliquot Size 31
VI-1 Components Of Flow Measuring System 53
VI-2 Equations For Container Volumes 59
VI-3 Constant Rate And Slug Injection Methods 68
VI-4 Ott Type Horizontal Axis Current Meter 71
VI-5 Assembly Drawing Of Price Type AA Current Meter....72
VI-6 Current Meter Notes And Computations For Midsection
Method 78
VI-7 Broad Crested Weir Profiles 80
VI-8 Sharp Crested Weir Profiles 83
VI-9 Three Common Types Of Sharp-Crested Weirs And
Their Equations 85
VI-10 Sharp-Crested Weir Nomenclature 87
VI-11 Configuration And Standard Nomenclature For
Parshall Flume 92
VI-12 Various Cross-Sectional Shapes Of Palmer-Bowlus
Flumes 95
VI-13 Open Channel Flow Nozzle Profiles 98
VI-14 Venturi Meter 103
VI-15 Flow Nozzle In Pipe 105
XI
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VI-16 Electromagnetic Flowmeter 107
VI-17 Trajectory Methods 109
VIII-1 Sample Identification Tag Examples 131
VIII-2 Recommended Chain of Custody Record Format. 134
XII
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LIST OF TABLES
Table Page
IV-1 Compositing Methods 28
IV-2 Manual Compositing Method 30
VI-1 Standard Conditions For Sharp-Crested Weirs..86
VI-2 Sharp Crested Rectangular Weirs - Velocity
Of Approach Correction 90
VII-1 Quality Assurance Procedures For Field
Analysis And Equipment 119
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SECTION I - SUMMARY AND CONCLUSIONS
A. Wastewater Sampling Objectives
Wastewater sampling is being conducted on an extensive
scale by regulatory agencies to verify compliance with
NPDES permit requirements. Specific objectives in col-
lecting this data may vary, but generally include the
following:
1. Verification of compliance with effluent
limitations.
2. Verification of self-monitoring data.
3. Verification that parameters specified in
the NPDES permit are consistent with
wastewater characteristics.
4. Support of enforcement action.
5. Support of permit reissuance and/or revision.
B. Obtaining Representative Data
In order to accomplish these objectives, it is im-
perative that data collection activities be of high
quality. In performing these activities, consideration
should be given to the following:
1. Variation of flow rates and pollutant
concentrations.
2. Unique properties of materials discharged.
3. Selection of proper sampling equipment.
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4. Installation of appropriate flow monitoring
devices or accuracy verification of on-site
devices.
5. Collection of representative samples.
6. Proper sample collection, handling and
preservation.
7. Performance of prescribed analytical techniques
within allowable sample holding times.
8. Proper maintenance and calibration of automatic
sampling equipment and analytical devices.
C. Accomplishment of Compliance Sampling Objectives
Obtaining representative data can be accomplished by
adhering to the following general guidelines:
1. Sample collection and flow monitoring site
selections require on-site supervision by
experienced professionals with backgrounds in
hydraulics, chemistry, plant processes and
wastewater sampling techniques.
2. Sampling equipment selection and installation
must be tailored to the hydraulic characteristics
and physical and chemical constituents of the
wastewater.
3. Sampling programs must include a minimum of a 24
hour or operating day composite supplemented by two
or more grab samples. When extenuating circumstances
exist such as product line changes, variable production
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schedules or enforcement action, a more extensive
program may be necessary.
4. Sample handling must include an adequate chain of
custody procedure.
5. Quality assurance programs in the field and the
laboratory must be instituted to insure the pro-
duction of accurate, precise and defensible data.
D. Error Minimization
By adhering to these recommended guidelines, errors can be
greatly minimized. Although most errors defy exact quantifica-
tion, the state of the art affords the following conclusions.
Using currently existing primary devices and recorders, flows
can be accurately measured to within +_ 10%. Furthermore,
judicious selection of automatic sampling equipment assures
consistent sample collection. However, due to the difficulty
in obtaining a representative sample of the entire wastewater
stream, especially for suspended solids, careful attention
must be given to the location of the sampling probe. Limited
data indicate that despite properly locating the sampling
probe at 0.4 to 0.6 of the stream depth in the area of maximum
turbulence and sampling at a rate equal to or greater than
the wastewater velocity, inherent bed loads at the monitoring
site can cause suspended solids results to be approximately
30% low (1). Conversely, if the probe is located on the bot-
tom of the channel, within the bed load, results can be con-
siderably higher than actual. To minimize analytical
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error and to provide national uniformity of analytical
techniques, only those approved test procedures listed in
Table I, 40 CFR Part 136, (as last amended on December 1,
1976), or alternative test procedures approved by the
Regional Administrator for the area where the discharge
occurs, may be used for reporting discharge parameter
values.
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REFERENCES - SECTION I
Reed, G.D., "Evaluation Of The Standard Sampling Technique
For Suspended Solids," U.S. Environmental Protection Agency
Region VII, S&A Division, Technical Support Branch,
EPA-907/9-77-OOK1977).
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SECTION II -INTRODUCTION
A. Background
The Federal Water Pollution Control Act Amendments
(FWPCA) of 1972, the Act, established the objective of
restoring and maintaining the chemical, physical, and
biological integrity of the Nation's waters. To achieve
including the goal of eliminating the discharge of pol-
lutants into navigable waters by 1985. The principle
mechanism for reducing the discharge of pollutants is
through implementation of the National Pollutant Discharge
Elimination System (NPDES) established by Section 402 of
the Act.
NPDES permits have been issued to approximately 50,000
municipal and industrial point sources. Permits contain
four primary elements: (1) final effluent limitations
reflecting statutorily required treatment levels; (2)
interim effluent limitations governing until the attainment
of final effluent limitations; (3) construction schedules
for the achievement of final effluent limitations; and (4)
reporting requirements relating to compliance with mile-
stones contained in construction schedules and to compliance
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with effluent limitations established for each parameter
limited in the permit for both interim or final effluent
1 imitations.
Compliance with effluent limitations and self-moni-
toring requirements of NPDES permits is assessed by the
regulatory agency through a combined program of self-
monitoring data review and facility inspections.
B. Enforcement Management System
In order to better manage the Agency's resources
committed to gathering and verifying information regarding
permit compliance, a number of important projects are
presently being sponsored by the Office of Water Enforce-
ment. These projects all tie in with the development of an
overall Enforcement Management System (EMS) which will
enable Regions and States to more efficiently handle
compliance information submitted by the permittees (1).
EMS will improve the Agency's response time to violations,
provide a more uniform national enforcement response to
violations, and insure better control of information that
is placed into the EMS system. It is for this last area,
improvement in the quality of information that is gathered
by the field staff, that this manual is designed.
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The NPDES Compliance Evaluation Inspection Manual
(July 1976) describes procedures for conducting non-
sampling inspections that satisfy enforcement needs
(2). The objective of the NPDES Compliance Sampling
Manual is to perform a similar function for sampling
inspections, i.e., to describe procedures that will
provide effluent data that meet enforcement needs.
C. Work Group Membership
The NPDES Compliance Sampling Manual is designed for
use by the inspection staffs in EPA Regions and States.
The manual was developed by a work group consisting of
State and EPA personnel:
Donald M. Olson, Chairman, U.S. EPA, Washington, D.C.
Richard Christensen, Michigan Department of
Natural Resources
Harry Otto, Delaware Department of Natural
Resources & Environmental Control
John Ciancia, U.S. EPA, Region II
Gary Bryant, U.S. EPA, Region III
M.D. Lair, U.S. EPA, Region IV
Michael Birch, U.S. EPA, Region IV (Previously Region V)
William Keffer, U.S. EPA, Region VII
Edward Berg, U.S. EPA, Environmental Monitoring and
Support Laboratory-Cincinnati
Thomas Dahl, U.S. EPA, National Enforcement Investigation
Center-Denver
Teresa Wehner, U.S. EPA, Washington, D.C.
Comments and suggestions were requested from EPA
Regional Offices, States, selected Federal Agencies and
Headquarters personnel. The work group wishes to thank the
reviewers for their guidance and assistance in the pre-
paration of this manual.
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After gaining some experience with the use of the
manual, readers are encouraged to offer constructive
criticism and proposed revisions to the work group chair-
man. The necessary revisions will keep this manual a
useful working tool.
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REFERENCES - SECTION II
1. "Enforcement Management System Guide," U.S. Environmental
Protection Agency, Office of Enforcement, Office of Water
Enforcement (3/77).
2. "NPDES Compliance Evaluation Inspection Manual," U.S.
Environmental Protection Agency, Office of Enforcement,
Office of Water Enforcement (7/76).
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SECTION III - NPDES PERMIT SAMPLING REQUIREMENTS
A. Introduction
National Pollutant Discharge Elimination System
(NPDES) permits contain specific and legally enforceable
effluent limitations and self-monitoring requirements for
flow measurement and sampling. The sampling frequency, the
sample type (grab or composite), the parameters to be
monitored, the parameter limitations, the analytical
methods, and the reporting frequency are determined by the
permitting agency. Self-monitoring requirements must be
such as to enable reasonable assessment of the discharger's
performance relative to permit effluent limitations and the
potential impact on the environment. Such factors as flow
and concentration variability, treatment methodology,
relative amounts of cooling and process wastewater, and
receiving water quality are considered in establishing the
self-monitoring requirements.
B. Se1f-Mon itor ing Data
1. Permit Specifications
The NPDES permit specifies limitations for various
parameters (e.g. pH, biochemical oxygen demand, suspended
solids, etc). The limitations generally are in terms of
parameter weight and/or concentration and are specified for
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a given time frame. Common time frames specified in
NPDES permits are daily average, daily maximum, seven
consecutive day average, and thirty consecutive day
average. Time frames are always defined in the NPDES
permit.
Self-monitoring data are reported by the permittee at
intervals specified in the permit. Generally, the reports
are submitted to the permitting agency monthly, quarterly
or semi-annually.
2. Us_e of Self-Monitor ing Data
Regulatory agencies principally use self-monitoring
data to assess compliance with permit limitations. Self-
monitoring data showing permit violations may also be used
as primary evidence in an enforcement action. In many
cases, however, additional information may be needed to
verify or supplement self-monitoring data. Where inde-
pendent evidence is gathered by the regulatory agency,
self-monitoring data may be used as corroborative evidence
in the enforcement action or vice veras.
C. Compliance Monitoring
1. General
Compliance monitoring is required to document the
accuracy and completeness of self-monitoring and reporting
activities of permittees and to provide sufficient docu-
mentation and verification to justify and support enforce-
ment actions. Aljl compliance inspection activities should
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kg conducted on the premise that rt may lead to enforcement
action^
2. Definitions
The term "compliance monitoring" is a generic term
meant to cover all activities taken by Federal or State
regulatory agencies to ascertain a permittee's compliance
status. As thus defined compliance monitoring is composed
of two elements:
(a) Compliance Review - the review of all written
material relating to the status of compliance of
an NPDES permit, including Compliance Schedule
Reports, Discharge Monitoring Reports, Compliance
Inspection Reports, etc.
(b) Compliance Inspection - all field activities
conducted to determine the status of compliance
with permit requirements including Compliance
Evaluation Inspections (non-sampling), Sampling
Inspections, production facility inspections, and
remote sensing (e.g. aerial photographs).
3. Objectives of Compliance Evaluation Inspection
A compliance evaluation inspection is undertaken
to accomplish one or more of the following objectives:
(a) observe the status of construction required by
the permit;
(b) assess the adequacy of the permittee's self-
monitoring and reporting program;
(c) check on the completeness and accuracy of the
permittee's performance/compliance records;
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(d) evaluate the permittee's operation and main-
tenance activities;
(e) determine that permit requirements are being
met; and
(f) assess the adequacy of the permit.
4. Compliance Evaluation Inspection Tasks
To achieve the objectives of a compliance evaluation
inspection, a review of one or more of the following items
will be necessary:
(a) the permit;
(b) self-monitoring data;
(c) laboratory analytical techniques, methods
and quality assurance procedures;
(d) field handling, sample transport and
preservation procedures;
(e) data handling and records maintenance
procedures;
(f) compliance with implementation schedules; and
(g) location and calibration of required monitoring
devices, e.g., recording pH meter, DO meter,
flow recorder etc.
Detailed procedures for conducting a compliance
evaluation inspection are contained in the Compliance
Evaluation Inspection Manual, EPA, Office of Water En-
forcement, July 1976.
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5. Objectives of Compliance Sampling Inspection
A compliance sampling inspection is conducted to
accomplish one or more of the following objectives:
(a) verify compliance with effluent limitations;
(b) verify self-monitoring data;
(c) verify that parameters specified in the permit
are consistent with wastewater characteristics;
(d) support permit reissuance and revision; and
(e) support enforcement action.
6. Compliance Sampling Inspection Tasks
To achieve the objectives of a compliance sampling
inspection, one or more of the following tasks will be
accomplished:
(a) sampling at the locations and for the
parameters specified in the NPDES permit;
(b) sampling at locations and for parameters
not specified in the NPDES permit as requested
by enforcement personnel;
(c) verifying operation and calibration of monitoring
equipment;
(d) measuring flow by either verifying accuracy
of in plant equipment or actual independent
flow measurement.
The inspection should also verify that:
(a) the permittee's sampling location(s) includes
all the effluent from process and nonprocess
wastewater system(s);
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(b) the sampling location specified in the permit
is adequate for the collection of a represen-
tative sample of the wastewater;
(c) the permittee's sampling technique is adequate
to assure the collection of a representative
sample;
(d) the permit sampling and monitoring requirements
will yield representative samples; and
(e) the parameters specified in the permit are
adequate to cover all pollutants of concern
that may be discharged by the permittee.
D. Adequacy of Data
Samples collected by field personnel must be relevant
to the effluent limitation requirements of the permit.
Consequently, when the permit requires a "24-hour composite
sample" aliquots must be taken in a manner and at a fre-
quency such that the resulting composite sample is repre-
sentative of the actual discharge during the 24-hour
period. Confidence in the reliability of discharge data
will be enhanced by using a minimum of two independent grab
samples in addition to the 24 hour period or operating day
composite.
E. Determining Compliance With Effluent Limitations
The following paragraphs describe sampling and measure-
ment procedures that are related to effluent limitations
defined by the permit. The majority of compliance sampling
inspections deal only with the verification of instantaneous
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and short term (daily maximum) effluent limitations. Thus,
for routine compliance sampling inspections, the procedures
described for instantaneous and daily maximum conditions
should be followed. However, in some cases data will be
needed to verify a permittee's ability to meet effluent
limitations over a more extended time frame, i.e. 7-day
average or 30-day average conditions. For such cases, the
procedures described for 7-day and 30-day conditions should
be employed. It should be remembered that resource require-
ments will preclude the continuous sampling of a source for
a calendar month in all but the most demanding cases.
1. Instantaneous Conditions - Instantaneous conditions
are conditions that occur at any single moment in time.
Permit compliance with such conditions requires that
monitoring be conducted when the installation is in
operation and that sufficient measurements or samples
be taken to protect the data from error. Grab samples are
normal-ly used to characterize "instantaneous conditions."
2. Daily Maximum Conditions - The time frame for the
expression of the daily maximum limitations is a calendar day.
Where the nature of the effluent will allow (absence of
separating, interacting, or unstable components), compliance
with daily maximum conditions is determined by analysis of
a daily composite sample. Procedures for the collection of
composite samples are described in the Sample Collection
Section of this manual.
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In those cases where a daily maximum is required and a
sample cannot be composited, such as for oil and grease or
time dependent determinations, individual grab samples must
be collected within prescribed time intervals (depending on
the sampling situation), analyzed individually, and their
flow weighted average values calculated. In such situa-
tions, minimum and maximum values should also be reported.
On-site instrumental measurements or observations should be
made at the same frequency as the separate grab samples
described above.
3. 7-Day Average Conditions - The time frame for the
expression of limitations is seven consecutive days. The
7-day average is calculated from daily averages, weighted
by time or flow as required by the permit. The 7-day
average limitations generally apply only to publicly owned
treatment works.
4. 30-Day Average Conditions - Case preparation may
require samples to be taken for each operating day during
the calendar month. This could range from 22 days of
sampling for an industry in production 5 days per week to
30 days of sampling for a publicly owned wastewater treat-
ment facility. The 30-day average would then be the
arithmetic average of the daily values. For permits
containing fecal coliform limits, the 30-day average would
be the geometric mean of the daily values.
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F. Sample Collection And Handling
All samples must be collected according to the
procedures described in the Sample Collection Section and
handled according to procedures described in the Quality
Assurance Section. A chain-of-custody procedure is des-
cribed in Section VIII. This, or an equivalent procedure*,
must be adhered to in order to document that the integrity
of the sample was maintained from the time of collection
through transport to the laboratory and subsequent
analyses.
*An "equivalent procedure" is a sample handling procedure
that is approved by the enforcement attorneys of the
regulatory agency.
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SECTION IV - SAMPLE COLLECTION
A. Introduction
Sample collection is an important part of any survey
or other program to assess industrial or municipal waste-
water discharges. Without proper sample collection
techniques the results of a wastewater survey are neither
useful nor valid, even with the most precise or accurate
analytical measurements.
The planning and on-site implementation of an appro-
priate sample collection program requires supervision by
technically qualified personnel with knowledge of the
industrial or municipal wastewater treatment processes.
The characteristics and pollutant levels in the wastewater
are dependent on the relative flows and composition of the
individual sources contributing to the effluent. The flow
and composition of the individual discharge sources can
vary widely over a long time period, over a short time
period, and in some cases, even instantaneously where
batch type operations are carried out at the plant.
Therefore, the first step in any sample collection program
is to evaluate carefully the nature of the processing
operations, the individual waste sources, and the paths of
the wastewaters in the overall sewer system.
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Carrying out an appropriate sample collection program
includes the development of a study plan which contains the
following items:
1. Selection of parameters to be measured.
2. Selection of representative sampling sites.
3. Collection of sufficient volumes of the
wastewater to carry out the required analyses.
4. Selection and proper preparation of sample container
5. Preservation of samples to maintain the samples'
integrity.
6. Identification of each sample by proper labeling
of the containers.
7. Procedures to insure that recommended sample
holding times are not exceeded.
8. Procedures for identifying and handling potentially
hazardous samples.
9. Chain-of-custody procedure.
B. Sampling Considerations
1. General
The wide variety of conditions existing at different
sampling locations always requires that some judgement be
made regarding the methodology and procedure for collection
of representative samples of wastewater. Each sampling
point will warrant attention commensurate with its com-
plexity. There are, however, basic rules and precautions
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generally applicable to sample collection. Some important
considerations for obtaining a representative sample are as
follows:
(a) The sample should be collected where the
wastewater is well mixed. The sample should
be collected near the center of the flow channel,
at 0.4 - 0.6 depth, where the turbulence is at
a maximum and the possibility of solids settling
is minimized. Skimming of the water surface or
dragging the channel bottom should be avoided.
(b) In sampling from wide conduits, cross sectional
sampling should be considered. Dye may be used
as an aid in determining the most representative
sampling point(s).
(c) The sampling of wastewater for immiscible
liquids, such as oil and grease, requires special
attention. Oil and grease may be present in
wastewater as a surface film, an emulsion, in
solution, or as a combination of these forms. As
it is very difficult to collect a representative
oil & grease sample, the inspector must carefully
evaluate the location of the sampling point. The
most desirable sampling location is the point
where greatest mixing is occuring. Quiescent
areas should be avoided, if possible. Because
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losses of oil and grease will occur on sampling
equipment, the collection of a composite sample
is impractical. Individual portions collected
at prescribed time intervals must be analyzed
separately to obtain the average concentrations
over an extended period.
(d) If manual compositing is employed, the individual
sample bottles must be thoroughly mixed before
pouring the individual aliquots into the com-
posite container.
2. Sample Location
(a) General
Samples should be collected at the location
specified in the NPDES permit. In some instances the
sampling location specified in the permit or the location
chosen by the permittee may not be adequate for the
collection of a representative sample. In such instances,
the inspector is not precluded by permit specifications
from collection of a sample at a more representative
location. Where a conflict exists between the permittee
and the regulatory agency regarding the most representative
sampling location, both sites should be sampled and the
reason for the conflict noted in the inspection report.
Recommendation for any change in sampling location should
be given to the appropriate permitting authority.
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(b) Influent
Influent wastewaters are preferably sampled at points
of highly turbulent flow in order to insure good mixing;
however, in many instances the most desirable location is
not accessible. The preferred sampling points for raw waste
are: (1) the upflow siphon following a comminutor (in absence
of grit chamber); (2) the upflow distribution box fol-
lowing pumping from main plant wet well; (3) aerated grit
chamber; (4) flume throat; and (5) pump wet well. In all
cases, samples should be collected upstream from recir-
culated plant supernatant and sludges.
(c) Effluent
Effluent samples should be collected at the site
specified in the permit, or if no site is specified in the
permit, at the most representative site downstream from all
entering waste streams prior to entry into the receiving
waters. If a conflict exists between the permittee and
inspector regarding the location of the most representative
site, follow the procedure outlined in Section 2(a) above.
(d) Pond and Lagoon Sampling
Generally, composite samples should be employed for
the collection of wastewater samples from ponds and lagoons.
Even if the ponds and lagoons have a long detention time,
composite sampling is necessary because of the tendency
of ponds and lagoons to short circuit. However, if
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dye studies or past experience indicate a homogenous dis-
charge, a grab sample may be taken as representative of
the waste stream.
3. Sample Volume
The volume of sample obtained should be sufficient
to perform all the required analyses plus an additional
amount to provide for any quality control needs, split
samples or repeat examinations. Although the volume
of sample required depends on the analyses to be per-
formed, the amount required for a fairly complete
analysis is normally 2 gallons (7.6 liters) for each
laboratory receiving a sample. The laboratory receiving
the sample should be consulted for any specific volume
requirements. Individual portions of a composite sample
should be at least 100 milliliters in order to minimize
sampler solids bias. Refer to EPA's "Methods for Chemical
Analysis of Water and Wastes 1974" for the sample volumes
required for specific types of pollutant measurements.
4. Selection and Preparation of Sample Containers
It is essential that the sample containers be made of
chemically resistant material and do not affect the con-
centrations of the pollutants to be measured. In addition,
sample containers must have a closure which will not
contaminate the sample. See EPA's "Methods for Chemical
Analysis of Water and Wastes 1974" for selecting container
materials for specific types of pollutant measurements.
C. Sampling Techniques
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1. Grab Samples
A grab sample is defined as an individual sample
collected over a period of time not exceeding 15 minutes.
Grab samples represent only the condition that exists at
the time the wastewater is collected. The collection of a
grab sample is appropriate when it is desired to:
(a) Characterize the wastewater stream at a
particular instance in time;
(b) Provide information about minimum and maximum
concentrations;
(c) Allow collection of variable sample volume;
(d) Comply with the^NPTJES^permit monitoring
specifications; or
(e) Corroborate with composite sample.
In addition, there are certain parameters, such as pH,
temperature, residual chlorine, D.O., oil and grease,
coliform bacteria, that must be evaluated in situ or by
using a grab sample because of biological, chemical or
physical interactions which take place after sample col-
lection and affect the results. Special precautions to be
used in the collection and handling of selected parameters
are discussed in the Quality Assurance Section.
2. Composite Samples
A composite sample should contain a minimum of eight
discrete samples taken at equal time intervals over the
compositing period or proportional to the flow rate over
the compositing period. More than the minimum number of
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discrete samples will be required where the wastewater
loading is highly variable. Six acceptable methods for
collecting composite samples are described in Table IV-1.
(a) Selection of Sample Type
For facilities where production and flow rates
vary, composite sampling is necessary to provide a
representative picture of the quality of the waste
stream. Composite samples show the average condition
of the wastewater discharged during a shift, day or
longer production period. If the flow rate does not
vary by more than +15 percent of the average flow
rate, a time-intervaled composite (method 3, Table
IV-1) will provide a representative measurement of the
wastewater characteristics and load discharged over
the sampling period.
(b) Compositing Method
The preparation of a composite sample can be
performed in various ways. Table IV-2 and Figure IV-1
summarize the technique for preparing a manual com-
posite from time constant, volume variable samples
(method 6, Table IV-1). Note that the average daily
flow rate is needed to compute the quantity of pollutants
discharged. The instantaneous flow rate should not be
used to compute daily loadings unless it is known that
the instantaneous and average daily flow rates are
equivalent.
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TABLE IV - 1
COMPOSITING METHODS
Method No.
1.
Sampling Mode Compositing Principle
Continuous Constant sample pumping
rate
2.
Continuous
3.
Periodic
oo
4.
Periodic
5.
Periodic
6.
Periodic
Sample pumping rate
proportional to
stream flow
Constant sample volume,
constant time interval
between samples
Constant sample volume,
time interval between
samples proportional
to stream flow
Constant time interval
between samples, sample
volume proportional to
total stream flow since
last sample
Constant time interval
between samples, sample
volume proportional to
stream flow at time
of sampling
Comments
Practicable but
not widely used
Not widely used
Widely used in
automatic samplers
and widely used
as manual method
Widely used in
automatic sampling
but rarely used in
manual sampling
Not widely used in
automatic samplers
but may be done
manually
Disadvantages
Yields large sample
volume, may lack re-
presentativeness for
highly variable flows
Yields large sample
volume but requires
accurate flow measure-
ment equipment
Not most representative
method for highly vari-
able flow or concen-
tration conditions
Manual compositing
from flow chart
Manual compositing
from flow chart
Used in automatic Manual compositing
samplers and widely from flow chart
used as manual
method
AFTER:
Shelley & Kirkpatrick (2)
-------
When using a volume constant, time proportional
compositing method (method 4, Table IV-1) previous
flow records should be used to determine an appropriate
flow volume increment so that a representative sample
can be obtained without overrunning the capacity of
the sample container.
In any manual compositing method, sample manipu-
lation should be minimized to reduce the possibility
of contamination.
D. Sample Preservation
1. General
In most cases, wastewaters contain one or more un-
stable pollutants that require immediate analyses or
preservation. The rate of change of pollutant concen-
tration is influenced by temperature, pH, bacterial action,
concentration, and intermolecular reactions. Since treat-
ment to fix one constituent may affect another, preser-
vation is sometimes complicated, thus necessitating the
collection of multiple samples or the splitting of a single
sample into multiple parts.
Prompt analysis is the most positive assurance against
error from sample deterioration, but this is not always
possible for composite samples in which portions may be
stored for as long as 24 hours. It is important that
stabilization of the wastewater be provided during com-
positing, where possible, in addition to preservation of
the composited sample before transit to the laboratory.
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TABLE IV - 2
MANUAL COMPOSITING METHOD
(No. 6)
Bottle
No.
Time Aliquot
Collected
Flow
(MGD)
Sample
size (ml)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
0700
0.07
0.09
0.10
0.13
0.16
0.21
0.23
0.26
0.29
0.31
0.31
0.30
0.28
0.22
0.18
0.17
0.28
0.35
0.39
0.45
0.42
0.42
0.42
0.39
40
55
60
80
95
125
135
150
170
180
180
175
165
130
105
100
165
205
230
260
245
245
245
230
6.43
3770
Average daily flow = sum of flows = (6.43) = 0.27 mgd
24 hrs. 24
*Method is for 24-hour composite using 24 discrete samples
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Q)
DI
C
•C
^
-------
Procedures used to preserve samples include refrigeration,
pH adjustment, and chemical treatment. Refrigeration is
the most common method of sample preservation. Temperature
control near 4°C retards bacterial action and suppresses
volatilization of most dissolved gases.
There are a variety of individual preservation
techniques depending on the constituent to be analyzed. A
detailed discussion on the subject is presented in the
section on Quality Assurance.
2. Compliance Considerations
The list of approved test procedures in 40 CFR Part
136(F.R. Vol. 41, No. 232, Dec. 1, 1976), Guidelines
Establishing Test Procedures for Analysis of Pollutants-
Amendements, is the only legally binding reference the
Agency has on establishing test procedures for analysis
of pollutants for the NPDES program. Included in the
referenced test procedures are the analytical method,
preservation method and sample holding times.
E. Analytical Methods
1. General
The discharge parameter values for which reports are
required must be determined by one of the standard analytical
methods cited in Table I, 40 CFR 1(136.3(F.R. Vol. 41, No.
232, Dec. 1, 1976) or by an alternate test procedure approved
by the Regional Administrator upon the recommendation of the
Director of the Environmental Monitoring and Support Laboratory -
Cincinnati.
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2. Alternate Test Procedures
In instances where an effluent contains a pollutant for
which a test procedure is not specified in Table I, 40 CPR
11136.3, or the permittee desires to use an analytical
method other than the prescribed method, an application
for approval of an alternate test procedure must be filed
with the Regional Administrator in the Region where the
discharge occurs. Application should be filed according to
the provisions contained in 40 CFR Part 136.4(c), "Application
for Alternate Test Procedures."
Where approval for an alternative test procedure for
nationwide use is desired, application is not restricted to
NPDES permittees and the application should be directed to
the Director, Environmental Monitoring and Support Laboratory,
Cincinnati, Ohio 45268. Instructions regarding the in-
formation required in support of an application for
approval of an alternative test procedure for nationwide use
is contained in 40 CFR Part 136.4(d).
F. Sample Identification
Each sample must be accurately and completely iden-
tified. It is important that any label used to identify
the sample be moisture-resistant and able to withstand
field conditions. A numbered label associated with a field
data sheet which contains detailed information on the
sample may be preferrable to using only the label for
information.
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The information provided for each sample should
include the following:
1. Designation and location description of
sample site.
2. Name of collector(s).
3. Date and time of collection.
4. Indication of grab or composite sample
with appropriate time and volume information.
5. Indication of parameters to be analyzed.
6. Notation of conditions such as pH, temperature,
chlorine residual and appearance that may change
before the laboratory analysis, including the
identification number of instruments used to
measure parameters in the field.
7. Indication of any unusual condition at the sampling
location and/or in the appearance of the wastewater.
8. Preservative used.
9. Any noteworthy additional information.
For additional information regarding sample iden-
tification techniques, consult the Chain-of-Custody Pro-
cedure described in Section VIII.
G. Safety Considerations
NPDES Compliance Sampling Inspections are to be
conducted in a safe manner consistent with EPA safety
regulations and any special safety regulations associated
with the particular facility being inspected.
Inspection supervisors are responsible for insuring
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that day-to-day work being carried out under their su-
pervision is accomplished in accordance with established
safety rules and policies. Supervisors are responsible for
insuring that employees perform their jobs in a safe manner
and for initiating immediate corrective action as soon as
an unsafe situation or procedure is observed.
The inspector should be familiar with EPA's Occu-
pational Safety and Health rules and policies contained in
the publication "Occupational Safety And Health For The
Federal Employee"(3). Other references dealing with
various aspects of inspection safety are listed at the end
of this section (4&5).
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REFERENCE - SECTION IV
"Methods For Chemical Analysis Of Water And Wastes, 1974,"
U.S. Environmental Protection Agency, Office of Technology
Transfer, Washington, D.C. (1974).
Shelley, P.E., and Kirkpatrick, G.A., "An Assessment of AutomatL
Sewer Flow Samplers," U.S. Environmental Protection Agency,
EPA-600/2-75-065, Washington, D.C. (12/75).
"Occupational Safety And Health For The Federal Employee,"
U.S. Environmental Protection Agency, Office of Planning
and Management, Occupational Health And Safety Office,
Washington, D.C. (12/76).
"NEIC Safety Manual," U.S. Environmental Protection Agency,
Office of Enforcement, National Enforcement Investigation
Center, EPA-330/9-74-002-B, Denver, Colorado (2/77).
"Safety In Wastewater Works," Water Pollution Control
Federation Manual of Practice No. 1, Safety Committee WPCF,
Washington^ D.C. (1969).
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SECTION V
AUTOMATIC SAMPLERS
A. Introduction
The issuance of NPDES permits containing self-
monitoring requirements calling for the collection of
composite samples, the significant labor cost saving, and
the increased data reliability are the main reasons for
the recent increase in use of automated sample collection
devices.
There are currently about 100 manufacturers of port-
able automatic sample collection devices. These devices
have widely varying levels of sophistication, performance,
mechanical reliability, and cost. No individual composite
sampler now on the market can be considered ideal for every
application. Selection of a unit or variety of units for a
field data gathering program should be preceded by a
careful evaluation of such factors as:
(a) The range of intended use.
(b) The skill level required for installation and
operation of the automatic sampler.
(c) The amount of unavoidable error that can be
tolerated in the sample collection system.
The references listed at the end of this section
discuss the theoretical design considerations and actual
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field performance data from a variety of sources and should
be reviewed prior to the purchase of an automatic sampler.
B. Automatic Sampler Subsystem Components
Five inter-related automatic sampler subsystem com-
ponents are discussed briefly below based o material
presented in references 6 & 7.
1. Sample Intake Subsystem
The operational function of a sample intake is to
reliably gather a representative sample from the flow
stream in question. Its reliability is measured in
terms of freedom from plugging or clogging and
vulnerability to physical damage from large objects
in the flow.
The sample intake of many commercially available
automatic samplers is often only the end of a plastic
suction tube. Users are left to their own ingenuity
and devices to convert this tube to an intake which
will collect a representative sample of a highly
stratified, nonhomogeneous liquid waste. Most recent
available information indicates that a single point
intake is not likely to give a representative sample (see
references 2 & 5). Current assessment of the state-
of-the-art suggests that a fixed nozzle type intake
located at 0.4 to 0.6 of the stream depth in the area
of maximum turbulence with an intake velocity equal to
-38-
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or greater than the average wastewater velocity at the
sample point provides the most representative sample. This
technique ignores contribution from bedload or floatable
solids. Improvements can be made through the use of
multiple samplers with intakes at variable depths.
2. Sample Gathering Subsystem
Three basic sample gathering methods, mechanical,
forced flow, and suction lift, are available in commercial
samplers.
(a) Mechanical - Many of the mechanical devices, such
as cups on cables, calibrated scoops, and paddle
wheels with cups, were developed for a single
site utilizing a primary flow device. Mechanical
devices have arisen from one of two basic con-
siderations:
i. Site conditions requiring very high lifts;
or
ii. Desire to collect samples integrated across
the entire flow depth.
Most mechanical units offer significant obstruct-
ion to the flow stream at least during the sampling
episodes. The tendency for exposed mechanisms to foul,
together with the added vulnerability of many moving
parts, means that successful operation will require
periodic inspection, cleaning, and maintenance.
-39-
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(b) Forced Flow - All forced flow methods (pumps
and pneumatic ejection) offer some obstruction to
the flow, but generally less than mechanical
gathering methods. Pumps offer the ability to
sample at great depths and maintain high flow
velocities, but repairs are more expensive
because of poor accessibility. Pneumatic
ejection units are generally low volume samplers,
and the small sample volume generally prevents
collection of the most representative sample.
The use of air or inert gas to force the sample
into the collection container makes pneumatic
ejection units desirable for applications where
an explosion hazard exists.
(c) Suction Lift - Suction lift units without
detachable gathering systems are practically
limited to operation at heads of 25 feet or less
because of atmospheric pressure and internal
friction losses. Devices in this category
include pre-evacuated bottles, suction pumps with
metering chambers, and peristaltic pumps. With
all suction devices, when the pressure on a
liquid which contains dissolved gases is reduced,
the dissolved gases will tend to pass out of
solution. In so doing, the gases will leave the
-40-
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surface and entrain suspended solids enroute.
This phenomenon may result in the surface layer
of the liquid being enhanced in suspended solids.
To avoid this problem, the first flow of any
suction lift sampler should be returned to waste.
Also, metering chambers should be sized to
collect a minimum of 100 ml per sampling event to
minimize the concentration effect. The suction
lift gathering method offers more advantages and
flexibility for many applications than either
mechanical or forced flow sampling systems.
3. Sample Transport Subsystem
The majority of the commercially available composite
samplers have fairly small diameter tubing in the sample
train. This tubing is vulnerable to plugging, due to the
buildup of fats/ etc. Adequate flow rates must be main-
tained throughout the sampling train in order to effectively
transport the suspended solids. Information in the cited
literature and actual field experiences indicate that transport
lines less than 0.64cm (0.25in) ID should not be used.
Sample train velocities should exceed 2 fps and be constant
controllable for general application in municipal and
industrial sampling. Sharp bends, twists, or kinks in the
sampling line should be avoided to minimize problems with
debris clogging the system.
-41-
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To optimize sampler performance and reliability, the
sampler should be capable of rapidly purging the intake
system prior to and immediately after each sample collection.
This feature becomes more important as the sampler design
sophistication approaches isokinetic sampling (rate of
flow into the sampler is equal to the rate of flow in
wastewater stream).
4. Sample Storage Subsystem
Both discrete samples and single bottle collection are
desirable features for certain applications. Discrete
samples are subject to considerably more error introduced
through sample handling, but do provide opportunity for
manual flow compositing and time history characterization
of a waste stream during short period studies. Total sample
volumes collected should be 2 gallons (7.6 liters) at a
minimum. Sample containers should be easily cleaned or
disposable and shaped to facilitate transfer of the solids
laden sample. The requirements for sample preservation are
discussed in the Quality Assurance Section and will not be
repeated here except to note that refrigeration to 4°C is
the best single preservation method and will be required in
all automatic composite samplers.
5. Controls and Power Subsystem
Solid state control units, encapsulated to minimize
the effect of highly-humid and corrosive atmospheres frequently
encountered in the field, have increased the reliability of
sampler control systems.
-42-
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6. Sampler Reliability
Composite samplers are subject to a variety of rough
usage from transportation and handling, inadvertent submergence
during field surveys and inadequate care and forethought
on the part of the users. Optimal performance, 95 percent
success in obtaining the programmed sample, can be obtained
through training of the users, a routine service program
and an effective dialogue with the vendor to modify any
major deficiencies. Performance summaries from EPA Region
VII field group is presented in reference 1.
Statistically, the data in reference 1 is too limited
to recommend or reject any particular sampler; however,
sampling of raw wastewaters produced the majority of com-
positor malfunctions and more reliable operation can be
expected when sampling treated wastewaters.
C. Installation And Operation Of Automatic Sampling
Equipment
1. Site Selection
At locations which have not been previously sampled,
the field staff should have a qualified team leader present
to select the sampling point, to inspect the flow measurement
device and to supervise installation of the sampling equipment.
This practice reduces the risk of sampler malfunction and
missed samples, improves the representativeness of the
data, and results in a more detailed and informative report.
The primary reason for maintaining a variety of samplers
for use by a field staff is the number of sampling requirements
-43-
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waste stream characteristics, and site conditions encountered
in the field. Utilization of certain sampling equipment is
often precluded by the physical characteristics of the
sampling point such as, accessibility, site security, and
power availability.
Raw municipal wastewaters are preferably sampled at
points of highly turbulent flow in order to insure good
mixing; however, in many instances the desired location
is not accessible. Suggested raw wastewater sampling
points are listed in the Section on Sample Collection.
2. Equipment Security
Equipment security is an item of major concern at sites
which are outside of fenced treatment facilities. Manhole
installations, in which battery operated equipment can be
inserted and the cover replaced, will generally provide
sufficient security. In exposed locations which require
composite samples, one must either risk loss and tampering
with equipment or utilize manual sampling procedures. If
manpower limitations require use of unattended equipment,
the sampler should be provided with a lock or seal which
would indicate tampering if broken or removed.
3. Power Source
Samplers capable of both AC and DC operation are
desirable. This feature increases the overall flexibility
of the unit, and also enhances winter operation reliability.
Battery operated units become less reliable at extremely
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low temperatures. Generally, line operated samplers are
more reliable than battery-operated models for the sampling
of raw wastewaters, the incidence of intake to plugging is
reduced due to the high vacuum and purging feature of the
line operated units. In every case, line current should be
used by the sampling team if it is available at the sampling
site.
4. Waste Characteristics
The physical and chemical characteristics of the waste
stream also play a part in determining the type of sampler
to use. Wide fluctuations in pH, concentration, color, and
volume encountered with some industrial wastewaters will
generally require a discrete sample collector in order that
aliquots can be analyzed individually.
5. Sample Preservation During Compositing Period
All samples should be kept near 4°C during the
composite period. A number of commercial samplers contain
integral ice compartments. With other units, samples can
be chilled by placing the sample collection container in an
ice chest along with a bag of ice. The ice chest can be
placed on end with the drain hole on top, and the discharge
tube of the sampler threaded through this hole and into the
sample container.
6. Winter Operations
Winter operation of sampling equipment can be a trying
experience. During particularly cold weather, sampler
malfunctions due to freezing of intake lines may run as
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high as 60 percent. Recently, heated teflon lines have
become available to eliminate this problem, but they are
expensive. This problem may also be handled by placing the
automatic sampler inside an insulated housing containing a
thermostatically controlled 100 watt electric light bulb.
The heat given off by the bulb is normally sufficient to
prevent problems caused by freezing. NOTE: Catalytic type
heaters should not be used because they give off vapors
that can affect sample composition.
The chance of sampler freezing may also be lessened by
locating the sampler below ground in a manhole or wet well.
If installed below ground, the sampler should be secured in
place. In manholes the sampler may be tied to the steps
(fiber glass tape) or suspended from a rope tied securely
to a stake in the ground. When installing samplers in
manholes or wet wells, precautions should be taken to in-
sure that there is adequate ventilation and light. Sites
with a history of submergence and/or surcharging after
precipitation events should be avoided if possible. Care
should also be taken in the placement of the sampler to
avoid suction lifts in excess of head limits. Battery
operated units generally have more restrictive head
limitations than line operated samplers.
D. Desirable Automatic Sampler Characteristics
Listed below are desirable criteria to be used as
a guide in choosing a sampler which best meets the need of
the individual sample collection program:
-46-
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1. Capability for AC/DC operation with adequate dry
battery energy storage for 120-hr operation at
1-hr sampling intervals.
2. Suitability for suspension in a standard manhole
and still be accessible for inspection and sample
removal.
3. Total weight including batteries under 18 kg (40
4. Sample collection interval adjustable from 10
min. to 4 hr.
5. Capability for flow-proportional and time-composite
samples .
6. Capability for collecting a single 9.5 1 (2.5 gal)
sample and/or collecting 400 ml (0.11 gal) discrete
samples in a minimum of 24 containers.
7. Capability for multiplexing repeated aliquots into
discrete bottles.
8. One intake hose with a minimum ID of 0.64 cm (0.25
in. ) .
9. Intake hose liquid velocity adjustable from 0.61
to 3 m/sec (2.0 to 10 fps) with dial setting.
10. Minimum lift of 6.1 m (20 ft.).
11. Explosion proof.
12. Watertight exterior case to protect components
in the event of rain or submersion.
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13. Exterior case capable of being locked, including
lugs for attaching steel cable to prevent tampering
and to provide security.
14. No metal parts in contact with waste source or
samples.
15. An integral sample container compartment capable
of maintaining samples at 4 to 6°C for a period
of 24 hr. at ambient temperatures ranging from
-30 to 50°C.
16. With the exception of the intake hose, capability
of operating in a temperature range from -30 to
50°C.
17. Purge cycle before and after each collection interval
and sensing mechanism to purge in event of plugging
during sample collection and then to collect complete
sample.
18. Field repairability.
19. Interchangeability between glass and plastic bottles,
particularly in discrete samplers is desirable.
20. Sampler exterior surface painted a light color to
reflect sunlight.
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REFERENCES - SECTION V
1. Harris, D.J. and Keffer, W.J., "Wastewater Sampling
Methodologies and Flow Measurement Techniques," US EPA
Region VII, EPA-907/974-005, Kansas City, Missouri,
(6/1974).
2. Interagency Committee on Water Resources, "Determination
of Fluent Sediment Discharge," Report #14 (1963).
3. Lauch, R.P., "Performance of ISCO Model 1391 Water and
Wastewater Sampler," U.S. Environmental Protection Agency,
EPA-670/4-75-003, Cincinnati, Ohio, (4/75).
4. Lauch, R.P., "Application and Procurement of Automatic
Wastewater Samplers," U.S. Environmental Protection
Agency, EPA 670/4-75-003, Cincinnati, Ohio, (4/75).
5. Lauch, R.P., "A Survey of Commercially Available
Automatic Wastewater Samplers," U.S. Environmental
Protection Agency, EPA-600/4-76-051, Cincinnati, Ohio,
(9/76).
6. Shelley, P.E., "Design and Testing of a Prototype Automatic
Sewer Sampling System," prepared for the Office of Research
and Monitoring, U.S. Environmental Protection Agency EPA
600/2-76-006, Washington, D.C. (3/75).
7. Shelley, P.E., and Kirkpatrick, G.A., "An Assessment of
Automatic Sewer Flow Samples," prepared for the Office of
Research and Monitoring, U.S. Environmental Protection
Agency, EPA-600/2-75-065, Washington, D.C. (12/75).
8. Wood, L.B. and Stanbridge, H.H., "Automatic Samplers,"
Water Pollution Control, Vol. 67, No. 5, pp 495-520
(1968).
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SECTION VI
WASTEWATER FLOW MEASUREMENT
A. Introduction
The measurement of flow in conjunction with wastewater
sampling is essential to almost all water pollution control
activities. All activities such as NPDES permit compliance
monitoring, municipal operation and maintenance, planning
and research rely on accurate flow measurement data. The
importance of obtaining accurate flow data cannot be
overemphasized, particularly with respect to NPDES com-
pliance monitoring inspections, since these data should be
usable for enforcement purposes. NPDES permits limit the
quantity (mass loading) of a particular pollutant that may
be discharged. The error involved in determining these
mass loadings is the sum of errors from flow measurement,
sample collection, and laboratory analyses. It should be
obvious that measurement of wastewater flow should be
given as much attention and care in the design of a
sampling program as the collection of samples and their
subsequent laboratory analyses.
The basic objectives of this chapter are:
(1) To discuss basic wastewater flow measurement
systems;
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(2) To outline what is expected of field personnel
with respect to wastewater flow measurement
during NPDES compliance monitoring activities;
and
(3) To present acceptable wastewater flow measurement
techniques commonly used.
A complete discussion of all available flow measurement
techniques and the theory behind them is beyond the scope
of this manual. Most of the common techniques in current
use are covered, however, in rather general terms. A
comprehensive list of references is included at the end of
this chapter for those who desire a more detailed discussion.
B. Wasterwater Flow Measurement Systems
Flow data may be collected on an instantaneous or a
continuous basis. A flow measurement system is required
for the collection of continuous data. A typical contin-
uous system consists of a primary flow device, a flow
sensor, transmitting equipment, a recorder, and possibly, a
totalizer. Instantaneous flow data can be obtained without
using such a system.
The heart of a typical continuous flow measurement
system, as shown in Figure VI-1, is the primary flow
device. This device is constructed such that it has
predictable hydraulic responses which are related to the
flowrate of water or wastewater through it. Examples of
such devices include weirs and flumes which relate water
- 51 -
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Oj
0)
f-i
-P
Primary
Flow
Device
FIGURE VI-1
COMPONENTS OF FLOW MEASURING SYSTEMS
Flow
Sensing
Device
Flow Recorder
signal
(electrical,
mechanical or \
pneumatic)
Flow Totalizer
CO
03
-------
depth (head) to flow, Venturi and orifice type meters which
relate differential pressure to flow, and magnetic
flow meters which relate induced electric voltage to
flow. A standard primary flow device has undergone
detailed testing and experimentation and its accuracy has
been verified.
A flow sensor is required to measure the particular
hydraulic responses of the primary flow device and transmit
them to the recording system. Typically, sensors include
floats, pressure transducers, capacitance probes, differ-
ential pressure cells, electromagnetic cells, etc.
The sensor signal is generally conditioned by using
mechanical, electromechanical, or electronic systems.
These systems convert the signal into units of flow which
are recorded on a chart or put into a data system. Those
systems which utilize a recorder are generally equipped
with a flow totalizer which displays the total flow on a
real time basis.
NPDES permits that necessitate continuous flow
measurement require a complete system. Permits that
require instantaneous flow measurement do not necessarily
dictate the use of any portion of such a system. Tech-
niques are available (described later in this chapter) for
measuring instantaneous flow with portable equipment.
An important consideration during sampling
inspections for NPDES compliance purposes is that the
-53-
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investigator may want to obtain continuous flow data at a
facility where only instantaneous flow data is required by
permit monitoring conditions. If an open channel primary
flow device is utilized for making instantaneous measure-
ments, only the installation of a portable field sensor and
recorder is necessary. If, on the other hand, the facility
being investigated does not utilize a primary flow device,
and a continuous flow record is desired, the investigator's
job becomes more difficult. A portable primary flow device
will have to be installed. Generally, the investigator is
limited to the installation of open channel equipment,
since the installation of closed-conduit flowmeters is
more complex and time-consuming. This chapter does
not cover in detail the installation of primary flow
devices, but many of the references cited treat this area
quite adequately. The USDI Water Measurement Manual (1)
is an excellent reference for details on checking the
installation of primary flow devices.
The accuracy of wastewater measurement systems varies
widely, depending principally upon the primary flow device
used. The total error inherent in a flow measuring system
is, of course, the sum of each component part of the
system. However, any system that can not measure the
wastewater flow within + 10% is considered unacceptable
for NPDES compliance assurance purposes.
- 54 -
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C. Field Verification Of Flow Measurement Systems
The responsibility of the investigator during NPDES
compliance sampling inspections includes the collection of
accurate flow data during the inspection, as well as the
validation of such data collected by the permittee for self-
monitoring purposes.
The investigator must insure that the flow measurement
system or technique being used measures the entire wastewater
discharge as described by the NPDES permit. A careful inspection
should be made to determine if recycled wastewaters or wastewater
diversions are present upstream of the system. The investigator
should note any anomalies on the inspection report form or
in a bound field notebook.
The investigator's second task is to verify that the
system being used is accurate. In cases where the dis-
charger is making instantaneous flow measurements to
satisfy permit requirements, the specific method used
should be evaluated. Any flow device used, should be checked
for conformity with recognized construction and installation
standards. Any deviation from standard conditions should
be well documented. Where there are significant deviations,
accuracy of the flow device should be checked by making an
independent flow measurement.
All components of continuous flow measuring systems
should be verified. The flow device should be
-55-
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checked for conformity with recognized construction and
installation standards (where possible). The flow sensing
and recording devices are usually checked simultaneously.
The procedure most often used is to make an independent
measurement of the head over the primary flow device,
obtaining the flow from an appropriate hydraulic
handbook and comparing this flow with the recorded value.
Since most primary flow devices do not have linear
responses, several checks should be made over as wide
a flow range as is possible. The accuracy of the recorder
timing mechanism may be checked by marking the position
of the recorder indicator and checking this position after
a known elapsed time interval. Flow totalizers are easily
checked by integrating the area under the curve. If the
investigator has the proper equipment and knowledge,
electronic recorders and totalizers may be checked
by inducing known electric current to simulate
flow. The accuracy of closed conduit flow measurement
systems can be verified by making independent flow measure-
ments at several different flowrates or by electrically,
mechanically or hydraulically inducing known flowrates.
Specific techniques for making independent flow measure-
ments are given later in this section.
If the discharger's flow measurement system is
accurate within ;+ 10% the investigator is encouraged to
use the installed system. If the flow sensor or
recorder is found to be inaccurate, determine if it can be
-56-
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corrected in time for use during the inspection. If the
equipment cannot be repaired in a timely manner, the
investigator should install a portable flow sensor and
recorder for the duration of the investigation. The
installation and use of such equipment is preferred over
attempts to correct erroneous flow measurement systems.
The inspector should note the action taken in the inspec-
tion report and inform the permittee that the equipment
should be repaired as soon as possible. If non-standard
primary flow devices are being used, it is the responsi-
bility of the discharger to supply data supporting the
accuracy and precision of the method being employed.
The inspector should evaluate and review calibration
and maintenance programs for the discharger's flow measure-
ment system. The permit normally requires that the cal-
ibration of such systems be checked by the permittee on a
regular basis. The lack of such a program should be noted
in the inspection report.
The compliance inspection report should contain an
evaluation of the discharge flow measurement system.
Inadequacies may be discussed with the permittee during the
inspection and deficiencies noted in the report so that
follow-up activity can be conducted. Any recommendations
to the permittee should be made in such a manner that any
subsequent enforcement will not be jepordized.
-57-
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D. Wasterwater Flow Measurement Methods
This section outlines and familiarizes the field
investigator with the most commonly used methods of
wastewater flow measurement and the primary devices that
will be encountered during NPDES compliance sampling
inspections. Volumetric and dilution techniques are
presented at the beginning of this chapter, since they are
applicable to both open-channel and closed-conduit flow
situations. The remaining methods are grouped under
categories dealing with open-channels and closed conduits.
The general method of checking individual primary flow
devices is given, where applicable. Several estimation
techniques are presented. However, it should be recognized
that flow estimates do not satisfy NPDES permit monitoring
requirements unless the permit specifically states that
this is permissible.
1. Volumetric Techniques
Volumetric flow techniques are among the simplest
and most accurate methods for measuring flow. These
techniques basically involve the measurement of volume
and/or the measurement of time required to fill a
known-sized container.
(a) Vessel Volumes
The measurement of vessel volumes to
obtain flow data is particularly applicable to
-58-
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SPHERE
FIGURE VI-2
EQUATIONS FOR CONTAINER VOLUMES
Total Volume
V = 1/6 irD^ = 0.523S98D
Partial Volume
V = 1/3 *(!* (3/2 D-d)
RIGHT CYLINDER
h
•*— D — *-
c__ x
c^~~ ~~^
C^ Z5
Total Volume
i i
H
1
V = 1/4 -nD^H
Partial Volume
V = 1/4 -nDzh
ANY RECTANGULAR CONTAINER
Total Volume
y
¥
/
^^_
^
s/'
* r *
jf*
*s^~
W'
H V =
HLW
f Partial Volume
v -
hLW
TRIANGULAR CONTAINER
Case 1
Case 2
Partial Volume (case 1)
V = 1/2 hbL
Total Volume
V = 1/2 HBL
Partial Volume (case 2)
V - 1/2 L (HB - hb)
ELLIPTICAL
CONTAINER
H
Total Volume
V = TtBDH
Partial Volume
V = irBDh
~ 59-
-------
FIGURE VI-2 (CONTINUED).
FRUSTUM OF A CONE
Case 1
Case 2
Total Volume
V = TT/12 H (Di2 + D! D2 + D22)
Partial Volume
V = Tr/12 h (D]/ + DI d + d2)
CONE
Case 1
Case 2
Partial Volume (case 1)
V = 1/12 TT dzh
Total Volume
V = 1/12 TT D2H
Partial Volume
V = 1/12 Tv
(case 2)
d2h)
PARABOLIC CONTAINER
Case 1
Case 2
Partial Volume
V = 2/3 hdL
Total Volume
V = 2/3 HDL
Partial Volume
V = 2/3 (HD - hd) L
-60-
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batch wastewater discharges. An accurate measure-
ment of the vessel volume(s) and the frequency
that they are dumped is all that is required. An
accurate engineering tape measure to verify vessel
dimensions and a stop watch are the only required
field equipment. The equations for calculating the
volumes of various containers is given in Figure Vl-2.
(b) Pump Sumps
Pump sumps may be used to make volumetric
wastewater flow measurements. This measurement
is made by observing the sump levels at which the
pump(s) cut on and off and calculating the volume
contained between these levels. This volume, along
with the number of pump cycles, will give a good estimate
of the daily wastewater flow. One source of error in
this measurement is the quantity of wastewater that
flows into the sump during the pumping cycle. This
error may be particularly significant if the sump
is large, the rate of inflow is high, and/or the
pumping cycle is long. This error may be
accounted for if the inflow is fairly constant,
by measuring the time required to fill the sump
and adding this additional flow for each pump
cycle. The number of times that the pump
cycles during a measurement period may be
obtained by using a counter on the pump or
-61-
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using a stage recorder to indicate the number
of pump cycles.
(c) Bucket and Stopwatch
The bucket and stopwatch technique is particularly
suited to the measurement of small wastewater flows.
It is accurate and easy to perform. The only equipment
required to make this measurement are a calibrated
container (bucket, drum, tank, etc.) and a stopwatch.
The container should be calibrated carefully, using
primary standards, or other containers which have been
calibrated using such equipment. Ordinarily, this
measurement is made at the end of a pipe; however,
using some ingenuity, a bucket and stopwatch flow
measurement may be made in ditches and other open
channel locations. Short sections of pipe may be used
to channel or split flows into measurable portions. A
shovel is often needed to dig a hole under a pipe or
in an open channel to get the container under the
wastewater stream that is to be measured. As with all
flow measurement techniques, it is important to insure
that all of the wastewater stream is measured. This
method is limited by the amount of flow that can practi-
cally be measured in a reasonably sized container. A
five gallon bucket filled to capacity, for example,
would weigh 42 pounds. Also, the filling time of the
container should be sufficiently long so that the
calibrated container can be moved in and out of
- 62 -
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the wastestream without spilling the contents or
overflowing the bucket. A minimum filling time
of 10 seconds is recommended. If the container
is hand-held, the practical limit of container
size is what can be comfortably handled, about
five gallons. Therefore, with a 5-gallon con-
tainer, the maximum flow that could practically
be measured would be 30 gpm. At least three
consecutive measurements should be made, and the
results averaged.
(d) Orifice Bucket
The orifice bucket permits the investigator
to measure higher wastewater flows than is possible by
using a bucket and stopwatch. An orifice bucket is a
metal container (bucket) that has been modified by
cutting holes (orifices) in the bottom. The bucket is
calibrated by plugging the orifices with rubber stoppers
and using bucket and stopwatch measurements to calibrate
the bucket. The calibration curve relates the depth
of the water in the bucket, for various combinations
of orifices, to the flowrate. This method is usable
over a flow range of 7 to 100 gpm. Construction of
the orifice bucket and directions for its use is given
by Smoot (3).
2. Dilution Methods
Dilution methods for water and wastewater flow
are based on the color, conductivity, fluorescence, or
-63-
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other quantifiable property of an injected tracer. The
dilution methods require specialized equipment, extreme
attention to detail by the investigator, and are time
consuming. However, these techniques offer the investigator:
A method for making instantaneous flow
measurements where other methods are
inappropriate or impossible to use;
A reference procedure of high accuracy
to check in situ those primary flow
devices and flow measurement systems
that are nonstandard or are improperly
installed; and
A procedure to verify the accuracy of
closed conduit flow measuring systems.
The tracer may be introduced as a slug (instantaneously)
or on a continuous flow basis. The constant rate dilution
method is performed by injecting a tracer at a constant
rate into a wastewater stream at an upstream location and
measuring the resulting tracer concentration at a downstream
location. The method is based on the following continuity
equation:
Q = q(C1-C2)/(C2-C0) (1)
Where: Q = Flowrate of the stream to be measured
q = Constant flowrate of injected tracer
C = Concentration of injected tracer
C = Concentration of tracer in the stream
at downstream sampling location
- 64 -
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C = Background tracer concentration
upstream from the tracer injection
site.
If the flowrate and background concentration
of the injected tracer are negligible when compared to the
total stream characteristics, this equation reduces to:
Q = qCL/C2 (2)
Where Q, q, C and C are as previously defined
for equation (1).
The use of this method requires that the following
conditions be attained:
The injection rate of the tracer (q) must be
precisely controlled and must remain constant
over the measurement period;
The tracer used must not degrade, sorb, or be
changed in basic characteristics by environmental
factors or the wastestream to which it is added;
The location of injection and sampling sites
must be judiciously selected and located such
that the dye is well mixed across the cross-section,
so that a concentration plateau is reached during
the measurement period; and
The tracer used must be capable of being
analyzed precisely.
In practice, many tracers have been used for dilution
flow measurements including sodium chloride, lithium chloride,
and fluorescent dyes. Fluorescent dyes and fluorometric
-65-
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analyses have been widely employed in dilution measurements
and are particularly convenient. The tracer is normally
injected into the wastestream by using a piston type chemical
metering pump. The use of this type of pump is almost
mandatory to maintain a constant injection rate. Automatic
samplers are widely used to collect samples during the
period of measurement. If fluorescent dyes are used, a
submersible pump may be used in conjunction with a flow-
through fluorometer and recorder to provide a continuous
record of the dye concentration at the sampling point.
The flowrate may also be determined by making a slug
(instantaneous) injection of tracer and measuring the
resultant concentration at the downstream location during
the entire time of passage of the tracer. The principle of
the slug injection method is expressed in the following
equation:
Q = Ci x V/ (C2~C0)dt (3)
Where: V = Volume of tracer injected
t = time
Qf <3f CQ' ci' C2 are as previously
defined for equation (1).
The principal advantage of this method is that so-
phisticated equipment is not required to inject the tracer.
The disadvantages of the method are that it may not be used
for unsteady flow situations and the entire tracer pulse
must be sampled. The latter problem is easily solved by
-66-
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using fluorescent dyes and a flow-through fluorometer and
recorder. The denominator of equation (3) may then be
obtained by simply integrating the fluorometer recorder
chart (after allowing for the background concentration, C0)
for the measurement period.
A graphical comparison of the constant rate and slug
injection methods is given in Figure Vl-3. The use of
dilution techniques is covered in detail in the references
(1, 3, 4). The monograph available from the Turner Design
Company (4) is a particularly valuable reference for the
use of fluorescent dyes and fluorometers in dilution flow
measurement work. Experience indicates that accuracies of
+_ 3 percent are achievable utilizing the dilution method
under field conditions.
•*' Open Channel Flow Measurements
The measurement of wastewater flow in open-channels
is the most frequently encountered situation in field investi-
gations. An open-channel is defined as any open-conduit which
has a ditch or flume or any closed conduit such as a pipe,
which is not flowing full. The most commonly encountered
methods and primary flow devices used in measuring open-
channel wastewater flow are described in this section.
Several flow estimation techniques are also presented.
The measurement accuracies quoted in this section apply
only to the specific method or to the primary flow device
being discussed. The total error involved in a continuous
flow measurement system, which is the sum of the errors of
-67-
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t
O
O
TIME
t
Ul
O
O
O
TIME
oo
I
Q =
CONCENTRATION-TIME CURVE FOR
CONSTANT-RATE INJECTION METHOD,
b. CONCENTRATION-TIME CURVE FOR
SLUG-INJECTION METHOD.
v C,
Q =
/o
dt
Q IS FLOW RATE OF STREAM
q IS FLOW RATE OF CHEMICAL
C IS BACKGROUND CONCENTRATION OF
0 STREAM
C, IS CONCENTRATION OF CHEMICAL
1 INJECTED
C0 IS CONCENTRATION OF STREAM PLATEAU
Q IS FLOW RATE OF STREAM
v IS VOLUME OF CHEMICAL INJECTED
C IS BACKGROUND CONCENTRATION OF
0 STREAM
C, IS CONCENTRATION OF CHEMICAL
1 INJECTED
C IS INSTANTANEOUS STREAM
CONCENTRATION
FIGURE VI-3
CONSTANT RATE AND SLUG INJECTION METHODS (10)
-------
each component, is beyond the scope of this discussion.
The reader is referred to the list of references at the
end of this chapter for such a discussion.
(a) Velocity-Area Method
(i) Introduction
The velocity-area method is the established
method of making instantaneous flow measurements
in open-channels. This method is particularly
useful where the flow is too large to permit the
installation of a primary flow device. it is
also useful for checking the accuracy of an
installed primary flow device or other flow
measurement method. The basic principle of
this method is that the flow (Q) in a channel is
equal to the average velocity (V) times the
cross-sectional area of the channel (A) at the
point where the average velocity was measured,
i.e., Q = V x A. The velocity of water or waste-
water is determined with a current meter; the
area of the channel is calculated by using an
approximation technique in conjunction with a
series of velocity measurements.
While the velocity-area method is an instan-
taneous flow measurement method, it can be used
to develop a continuous flow measurement system.
This is accomplished by making a number of
individual measurements at different flow rates
- 69-
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and developing a curve or curves that relate
water depth (head) to discharge (generally
referred to as a rating curve). This curve can
then be utilized along with a stage recorder to
provide a continuous flow record.
This method requires some experience and
good judgement in practice. A complete de-
scription of the equipment needed and the basic
measurement methods are given in the references
(1, 3, 5). Before attempting to use current
meters or the velocity-area method, the neophyte
investigator should accompany an experienced
field professional during the conduct of several
such measurements.
The accuracy of this method is directly
dependent on the experience of the investigator,
the strict adherence to procedures outlined in
the references, and the care and maintenance of
the equipment used. An experienced field in-
vestigator can make flow measurements using
current meters that are accurate within a + 10
percent.
(ii) Current Meters
There are two types of current meters,
rotating element and electromagnetic. Conven-
tional rotating element current meters are of
two general types—the propeller type with the
- 70 -
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FIGURE VI —4
OTT TYPE HORIZONTAL AXIS CURRENT METER
-71-
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ASSEMBLY
LIST OF PARTS
1. CAP FOR CONTACT CHAMBER 12.
2. CONTACT CHAMBER 13.
3. INSULATING BUSHING FOR CONTACT BINDING POST 14.
4. SINGLE-CONTACT BINDING POST 15.
5. PENTA-CONTACT BINDING POST 16.
6. PENTA GEAR 17.
7. SET SCREWS 18.
8. YOKE 19.
9. HOLE FOR HANGER SCREW 20.
10. TAILPIECE 21.
11. BALANCE WEIGHT
SHAFT
BUCKET-WHEEL HUB
BUCKET-WHEEL HUB NUT
RAISING NUT
PIVOT BEARING
PIVOT
PIVOT ADJUSTING NUT
KEEPER SCREW FOR PIVOT ADJUSTING NUT
BEARING LUG
BUCKET WHEEL
FIGURE VI-5
ASSEMBLY DRAWING OF PRYCE TYPE AA CURRENT METER (10)
-------
horizontal axis as in the Neyrpic, Ott, Hoff, and
Haskell meters (Figure VI-4), and the cup-type
instrument with the vertical axis as in the Price
A-A and Pygmy meters (Figure VI-5).
In comparison with horizontal-axis (propeller)
meters, the vertical axis (cup type) meters have
the following advantages:
(1) Their threshold velocities are usually
lower;
(2) The lower pivot bearing operates in an air
pocket, so the likelihood of silt intrusion
is reduced;
(3) The meter, in particular the Price type,
has earned a reputation for sturdiness and
reliability under field use.
On the other hand, the propeller and ducted
meters have the advantages of being less sensitive
than Price meters to velocity components not
parallel to the meter axis, being smaller in
size, and being more suited for mounting in multiple
units.
Current meters are provided with either a
direct readout or a method for counting meter
revolutions and a rating curve or table that
relates meter vane rotation to velocity. Re-
gardless of type, all current meters must receive
the best of care during transportation and use
- 73 -
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to insure accurate velocity measurements. If the
cups or blades on a conventional current meter
become bent or damaged, the results obtained from
the rating curve for the meter will be unreliable.
Meter damage may occur because of improper packing
and careless handling in transportation. Meters
should be transported in substantial wooden or other
rigid cases with properly fitted interior supports
to prevent movement and damage to the delicate parts.
Although all current meters are provided with a rating
curve or table, they should be recalibrated periodically.
If there is any sign of damage to any of the moving
parts of the meter, it should be reconditioned and
recalibrated.
(iii)Field Practice
The two principal methods for determining mean
velocities in a vertical section with a current meter
are the two-point method and the six-tenths-depth
method. The two-point method consists of measuring
the velocity at 0.2 and then at 0.8 of the depth from
the water surface, and using the average of the two
measurements. The accuracy obtainable with this
method is high and its use is recommended. The
method should not be used where the depth is less
than two feet and should always be used at depths
greater than two and one-half feet.
-74-
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The six-tenths-depth method consists of
measuring the velocity at 0.6 of the depth from
the water surface, and is generally used for
shallow flows where the two-point method is
not applicable.
Current meters should be carefully checked
before each measurement. It is good field practice
to periodically check each current meter against one
known to be in calibration. When making a measurement,
the cross-section of the stream or channel should be
divided into vertical sections, such that there
will be no more than 10 percent, and preferably
not more than 5 percent, of the discharge between
any two adjacent vertical segments. This, of
course, is possible only in open conduits. When
making measurements through a manhole, it is rarely
possible to obtain more than one section (at the
center of the channel, normally). This particular
situation can be a significant source of error.
Appropriate velocity measurements are made and
the depth is measured at each vertical in the
cross-section by using a current meter and wading
rod or special sounding line and current meter
assembly. Depths and velocities are recorded for
each section.
(iv) Area and Flow Calculations
The midsection method and Simpson's
-75 -
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parabolic rule are two methods for computing flow
from current meter measurements. Both are based
on the summation of discharges from each section
measured.
If the two-point method of determining
mean velocities is used, the formula for com-
puting the discharge of an elementary area by the
midsection method is:
Vi + V2 (L2 - L^ (L3 - L2) (4)
q = 2 2
Where
L2» and 1,3 = distance in feet from the initial point,
for any three consecutive verticals,
d2 = water depth in feet at vertical L ,
Vj_ and V2 = velocities in feet per second at 0.2
and 0.8 of the water depth, respectively,
at vertical L2, and
q = discharge in cubic feet per second through
section of average depth d .
The formula for computing the discharge for each
pair of elementary areas by Simpson's parabolic rule is:
Where
a,b,and c = The water depths in feet
at three consecutive
verticals,
- 76 -
-------
V , V , and V = The respective mean velocities
in feet per second at these
verticals,
L = The distance in feet between
the consecutive verticals (note -
this distance is not measured
from the initial point as in
equation (4)),
q' = The discharge in cubic feet per
second for the pair of elementary
areas.
Typical current meter notes and computations
for the midsection method are shown in Figure VI-6.
(b) Weirs
A weir is an obstruction built across
an open-channel or in a pipe flowing partially
full over which water flows. The water
usually flows through an opening or notch,
but may flow over the entire weir crest.
The theory of flow measurement utilizing
weirs involves the release of potential
(static) energy to kinetic energy. Equations
can be derived for weirs of specific geometry
which relate static head to water flow
(discharge). Weirs are generally classified
into two general categories: broad crested
- 77 ~
-------
H
00
LJ
FIGURE VI-6
FIELD NOTES FOR THE MID-SECTION METHOD
A .10 .20 JO .40 MM .70 .TS
River M—
•jj
©
Diit.
from
initiil
point
2
3
4
5
6
7
8
Width
0.5
1.0
1.0
1.0
1.0
1.0
1.0
0.5
7. 0
Depth
0
1
2
1.5
1.4
1.3
0.8
0
||
6
2
8
2
8
6
6
6
Rev-
olu-
tion!
_
30
40
30
50
30
30
20
15
-
Time
in
sec-
ond*
_
M
v2
52
55
43
40
60
47
-
VELOCITY
At
point
_
1.4
1.4
1 . 2 (
1.9
1.5
1,6
.74
.71
-
Meui
in ver-
ticil
_
1.4
LI. 3'
3 I.1
I
5 l.(
I . 7-
2 . 7:
-
Adjusted
for hor.
ingle or
5
3
2
2
An*
-
1.0
2.0
1.5
1.4
1.3
0.8
-
DUclwrge
J
1.40
•
2.68 •
.
2.63
.
2.28 '
j
0.96 J
0.57
LI
-
10.32
cfs J
.(
j
.!
.
.
J
JO
.85
-------
and sharp crested.
(i) Broad Crested Weirs
Broad crested weirs are normally
incorporated into hydraulic projects as
overflow structures. However, they can be
used to measure flow. Typical broad crested
weir profiles are shown in Figure VI-7. The
equation for a broad crested weir takes the
following form:
Q = C L H 3/2 (6)
Where
Q = discharge
L = length of weir crest
H = head on weir crest, and
C = coefficient dependent on the
shape of the crest and the head.
Values of the coefficient for various
shapes of broad crested weirs are given in
hydraulic handbooks (6,7). When these
structures are used to measure wastewater
flow, they should be calibrated using indepen-
dent flow measurements (refer to techniques
later in chapter). A discharge table based
on these measurements should be prepared for
each installation.
(ii) Sharp Crested Weirs
A sharp crested weir is one whose top edge
-79-
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FLOW
FLOW
FLOW
CO
o
I
FLOW
FIGURE VI-7
BROAD-CRESTED WEIR PROFILES (10)
-------
(crest) is thin or beveled and presents a sharp
upstream corner to the water flow. The water
flowing over the weir (the weir nappe) does not
contact any portion of the downstream edge of the
weir, but springs past it. Sharp crested weirs
may be constructed in a wide variety of shapes
(Figure VI-8). A great deal of work has been
performed with sharp crested weirs and certain of
these weirs are recognized as primary flow devices.
If such weirs are constructed and installed in
accordance with standard criteria, they can be
used in the field without calibration.
The advantages of sharp crested weirs are
accuracy and relatively low cost of fabrication
and installation. The principal disadvantages
are maintenance problems if the wastewater contains
corrosive materials, trash or floating solids.
These weirs can also cause undesirable settling
of solids behind the weirs in the quiescent
waters of the weir pool. The nominal accuracy of
a standard, properly installed, sharp crested
weirs in good condition, is approximately
+ 5 percent (3,8,9,10).
(1) Standard Sharp Crested Weir Shapes
The most commonly encountered sharp crested weirs
are the V-notch, rectangular, and Cippoletti.
Typically, V-notch weirs are limited to measuring
- 81-
-------
lower flows, while rectangular weirs are used to
measure higher flows. When a rectangular weir is
constructed with sharp crested sides, it is said
to be contracted; when such a weir extends from
one side of the channel to the other, and the
smooth sides of the channel form the weir sides,
the weir is said to be suppressed. Cippoletti
weirs combine the features of both the contracted
rectangular and V-notch weirs and are used to
measure highly variable flows. These weirs and
their equations are shown in Figure VI-9.
Occasionally a proportional or "Sutro" weir
is encountered in field installations. These
weirs are generally used as velocity control
devices for municipal sewage treatment plant grit
chambers. Flow through these weirs is directly
proportional to the head, and the use of so-
phisticated flow recording equipment is not
required. This type of weir is not generally
considered to be a primary flow device. The
design and construction of these weirs is given
in most standard hydraulic handbooks. The
remaining sharp crested shapes shown in Figure
Vl-8 are rarely encountered.
(2) Standard Conditions
The profile of a sharp crested weir is shown on
Figure VI-10, along with the standard sharp crested
- 82-
-------
RECTANGULAR
2a
TRIANGULAR OR V-NOTCH
TRAPEZOIDAL (INCLUDING
CIPOLLETTI)
INVERTED TRAPEZOIDAL
POEBING
APPROXIMATE EXPONENTIAL
APPROXIMATE LINEAR
PROPORTIONAL OR SUTRO
FIGURE VI-8
SHARP CRESTED WEIR PROFILES (10)
83
-------
Q = 3.33 (L-0.2H)H3/2(CONT.)
Q = 3.33 LH3/2 (SUP.)
Q = 3.367 LH3/2
90 - Q = 2.50 H2-50
Q = 2.49 H2-48
60 - Q =1.443 H2-50
45 - Q=l .035 H2-50
22.5 - Q = 0.497 H2-50
Max Level
RECTANGULAR WEIR
4:l slope
X
-»H
I
CIPOLLETTI WEIR
L at least 3Hmax
X at least 2Hmax
X
J_
fT
7 tT*
-t
X
i
FIGURE VI-9
THREE COMMON TYPES OF SHARP CRESTED WEIRS AND THEIR EQUATIONS (15)
-84-
-------
weir nomenclature. Table VI-1 summarizes the standard
conditions used for the construction and installation
of these weirs.
(3) Field Inspection
All weirs installed by the investigatory agency
or those installed by the facility being investigated
should be checked for conformance with the standard
conditions qiven in Table VI-1. It should be noted
that the dimensions for placement of the weir in the
flow channel and the point at which the head is measured
are in terms of the maximum head that can be measured
for a particular weir. In actual practice, the maximum
head expected during the measurement period should be
used. Any deviation from standard conditions should
be noted on the field sheet.
- 85 -
-------
TABLE VI-I
STANDARD CONDITIONS FOR SHARP-CRESTED WEIRS
(See Figure VI-10)
'1. The weir should be installed so that it is perpendicular
to the axis of flow. The weir plate should be level.
The sides of rectangular contracted weirs should be
truly vertical. V-notch weir angles must be cut
precisely.
2. The thickness of the weir crest should be less than
0.1 inch. The downstream edges of the crest or notch
should be relieved by chamfering at a 45° angle (or
greater) if the weir plate is thicker.
3. The distance from the weir crest to the bottom of the
approach channel should not be less than twice the
maximum weir head and never less than one foot. The
distance from the sides of the weir to the sides of
the approach channel should be no less than twice the
maximum head and never less than one foot (except for
the suppressed rectangular weir).
4. The nappe (overflow sheet) should touch only the
upstream edges of the weir crest or notch.
5. Air should circulate freely under, and on both sides
of, the nappe.
6. The measurement of head on the weir should be made at
a point at least four (4) times the maximum head
upstream from the weir crest.
7. The cross-sectional area of the approach channel
should be at least eight times that of the nappe at
the weir crest for a distance of 15-20 times the
maximum head upstream from the weir. The approach
channel should be straight and uniform upstream from
the weir for the same distance.
8. If the criteria in Items 3 and 7 are not met, the
velocity of approach corrections will have to be made.
9. Heads less than 0.2 feet (2.4 inches) should not be
used under ordinary field conditions, because the
nappe may not spring free of the crest.
10. All of the flow must pass through the weir and no
leakage at the weir plate edges or bottom should be
present.
- 86 -
-------
K = APPROX. O.l"
i
CO
-J
I
POINT TO
MEASURE
DEPTH, H
20 H
max
I
STRAIGHT '
INLET RUN
or
SHARP - CRESTED WEIR
max
disch
level
FIGURE VI-10
SHARP CRESTED WEIR NOMENCLATURE (15)
-------
Any trash, slime, or debris should be removed from
the weir crest before proceeding with a flow measurement.
The head on a sharp crested weir can be measured by
knowing the depth of the weir notch from the top of the
weir and measuring the head approximately four times the
maximum head upstream using the top of the weir as a
reference. The head is the difference in these two
measurements. A carpenter's level, straight edge and
framing square are invaluable for making this measurement.
An engineering level and level rod can also be used.
The carpenter's level can also be used to plumb the weir.
A measuring tape is necessary to check the dimensions of
weirs.
A problem frequently encountered when using suppressed
rectangular weirs is the lack of ventilation of the weir
nappe. When the weir nappe is not ventilated it will stutter
or jump erratically. In permanent installations, provisions
should be made for a vent to maintain atmospheric pressure
behind the nappe. In field installations, flexible
plastic tubing can be used for this purpose.
The pool upstream of the weir should be quiescent with
approach velocities much less than one foot per second.
Generally, excessive approach velocities are not a problem
with V-notch weirs. However, if all the standard conditions
outlined in Table VI-I are not met or some other condition
is encountered, it is possible to encounter excessive
approach velocities when using rectangular weirs. When
-88-
-------
approach velocities exceed one foot per second, a correction
should be applied to the observed measurements. One method
of making such a correction is given in Table VI-2.
(4) Use of Weir Tables
The most convenient method for translating weir
head measurements to flow is a set of weir tables. The
use of weir formulas and curves in the field is not
recommended, since this is a cumbersome procedure and
leads to numerous computational errors. Excellent weir
tables are included in the USDI Water Measurement Manual
(1) and the Stevens Water Resources Data Book (11). The
explanatory material accompanying these tables should be
read thoroughly before they are used. In some cases,
flow data are tabulated which are outside the useful
range for a particular weir.
(c) Flumes
Flumes are widely used to measure wastewater
flow in open channels. They are particularly useful
for measuring large flowrates.
(i) Parshall Flumes
The Parshall flume is the most widely used open-
channel, primary flow device for wastewater flow
measurement. Parshall flumes are available in a
wide range of sizes and flow capacities, and are
available to fit almost any open-channel, flow
measuring application. These flumes operate with
relatively low head loss, are insensitive to the
- 89 -
-------
TABLE VI-2
SHARP CRESTED RECTANGULAR WEIRS
VELOCITY OF APPROACH CORRECTION
1. Compute the Velocity of Approach from: V = Q/A
Where: V = Velocity of Approach in feet per second
Q = Discharge in cfs (from weir formula)
A = Cross-sectional area of approach channel
2. Enter the follo'wing table with the velocity of approach (V)
and head (H) and obtain the coefficient (C) from the table:
0
0.4
.5
.fi
.7
.K
.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
0. 0025
.0039
. 0056
. 0076
.0099
.0126
.0155
.0188
.0224
.0263
.0305
.0350
.039S
.1)449
.1)504
.1)561
.0622
.0686
.0752
.0822
.0895
.0972
.1051
.1133
.1219
.1307
.1399
/1s/2
I). 0002 •
.0003
. 0005
.0007
.0010
. 0014
.0019
.0025
.0033
.0041
.0051
.0064
.0079
. 0095
.0111
.0132
.0154
.0179
.0206
.0235
.0268
.0303
.0340
.0381
.0426
.0472
.0521
0.2
1.014
1.027
1.037
1.050
1.064
1.082
1.09S
1.122
1.141
.163
.186
.208
.225
.254
.277
.308
.335
.363
.391
.420
.449
4SO
511
542
573
606
1.637
0.4
1.007
.013
.019
.026
.033
.042
.051
.052
.072
.084
.096
.109
.122
.135
.149
.165
181
.197
213
231
248
266
285
303
322
341
1.361
0.6
1.004
1.009
1. 013
.017
.022
.029
.034
.041
.049
.057
.086
.075
.084
.093
104
115
126
137
149
161
. 1"6
187
200
213
228
242
1.256
(1.8
1.004
.006
.009
.013
.016
.021
.027
.031
.037
.043
.059
.057
.065
.071
.080
.089
.097
106
.118
124
134
145
155
166
178
189
1.199
4.0
1.004
1.006
1.008
I. Oil
1.014
1.018
1.022
1.1126
1.031
1.036
1.041
1.047
1.052
1. 059
1.065
1.072
1.079
1.087
1.094
1.102
1.110
1.119
1.128
1.137
1.146
1.155
1.165
1.5
1.002
1.004
1.005
1.007
1.009
1.012
1.015
1.017
1.021
1.024
1.028
1.032
1.035
1.040
1.045
1.049
1.055
1.060
1.065
1.071
1.077
J.083
1.088
1.095
1.100
1.108
1.115
11
2.0
1.002
.003
.004
.006
.007
.009
.011
.013
.016
.018
.021
.024
.027
.031
034
038
042
046
050
054
059
063
068
073
078
083
1.088
2.5
1.082
1.01)2
1.003
1.004
1.006
1.007
1.009
1.011
1.013
1.015
1.017
1.019
1.022
1.025
1.027
1.030
1.034
1.037
1.039
1.044
1.047
1.051
1.055
1.059
1.063
1.067
1.072
3.0
1.00 1
.002
.003
.01)4
.005
.006
.007
.009
.011
.012
.014
.016
.018
.021
.023
.026
.028
.031
.034
.037
.040
043
046
050
053
1.057
1.061
3.5
1.001
.002
.002
.003
.004
.005
.006
008-
.009
.011
.012
.014
016
.018
020
022
025
027
029
032
034
037
040
043
046
049
1.053
4.0
1.001
.001
.002
.003
.003
.005
.005
.007
.008
.009
.011
.012
.014
.016
.017
.019
.021
.024
.026
.028
.030
.033
.035
.038
.041
.043
1.046
5.0
1.001
.001
.002
.002
.003
.004
.005
.006
.007
.008
.010
.Oil
.012
.014
.016
.017
.019
.021
.023
.025
.027
.029
.032
.034
.036
.039
1.041
3. The correct flow then = CxQ
For example: V = 1 fps, Q = 6.31 cfs, H = 1 ft,
then C = 1.022 and corrected Q = 1.022 x 6.31 = 6.45 cfs
Note: Method and Table from Water Measurement Manual (1)
-90-
-------
velocity of approach, and are self-cleaning in
most applications. The accuracy of a Parshall
flume in a good field installation is recognized
to be approximately + 5 percent (3,8,9,10).
(1) Parshall Flume Structure and Nomenclature
A Parshall flume consists of a converging
section, throat section, and diverging section, as
shown in Figure Vl-ll. The size of the flume is
determined by the width of the throat section. All
dimensions for various Parshall flume sizes are given
in the USDI Water Measurement Manual (1). Tolerances
for Parshall flume dimensions, as given by this manual,
are +_ 1/64 inch for the throat width and +_ 1/32 for
the remaining sections.
The head (Ha) is measured at the point 2/3 of the
length of the converging section (wingwall), upstream
from the throat section. During conditions of free-flow,
this is the only measurement required to determine
flow. Occasionally, back water exists which causes
some flooding of the diverging section of the flume.
In those cases, it is necessary to check the head at
an additional location (Hb) between the throat and
diverging sections as shown in Figure VI-11. The
ratio of the measured heads (Hb/Ha) is known as
the submergence. Flumes can be used to accurately
measure flow without correction until the following
limits are reached for each indicated size of flume:
- 91 -
-------
L
NOTE: 7.6cm (3in) TO 2.4m (8ft) FLUMES HAVE
ROUNDED APPROACH WINGWALLS
STILLING
WELLS
2/34"
CONVERGING SECTION
PLAN
1/8"
ANGLE
LEGEND:
W Size'of flume, in inches or feet.
A Length of side wall of converging section.
2/3A Distance back from end of crest to gage point.
B Axial length of converging section.
C Width of downstream end of flume.
D Width of upstream end of flume.
E Depth of flume.
F Length of throat.
S Length of diverging section.
K Difference in elevation between lower end of flume and crest.
N Depth of depression in throat below crest.
R Radius of curved wing wall.
H Length of approach floor.
P Width between ends of curved wing walls.
X Horizontal distance to H^ gage point from low point in throat.
Y Vertical distance to H^ gage point from low point in throat.
FIGURE VI-11
CONFIGURATION AND STANDARD NOMENCLATURE IFOR PARSHALL FLUME (10)
-92-
-------
Hb/Ha (%) Flume Size
50 1, 2, 3 inches
60 6, 9 inches
70 1-8 feet
80 8-50 feet
When the submergence exceeds 95%, the flume is not
usable for flow measurement purposes. A detailed de-
scription of submergence corrections is given in the
USD! Water Measurement Manual (!).
Although the Parshall flume is relatively insensitive
to approach velocities, influent flow should be evenly
distributed across the channel as it enters the converging
section. These flumes should not be installed immediately
downstream from transition sections in order to assure such
an even distribution. As a practical matter, a uniform
channel should be provided upstream from the flume as far
as is practical. A minimum distance of 15-20 channel
widths or pipe diameters is recommended.
(2) Field Inspection and Flow Measurement
During compliance sampling inspections, flumes should
~\
be inspected to determine if entrance conditions provide a
uniform influent flow distribution, the flume dimensions
conform to those given in the USD! Water Measurement
Manual (1), the flume converging throat section flow is
level, and the throat section walls are vertical. Useful
tools for checking Parshall flumes include a carpenter's
- 93 -
-------
level, framing square and tape. The flume should be closely
examined to determine if it is discharging freely. If
there is any question about free discharge, the downstream
head (Hb) should be measured. A staff gauge is useful for
making head measurements. Any problems observed during the
inspection should be noted on the field sheet.
A set of flume tables is necessary for calculating
flows. Both the USDI Water Measurement Manual (1) and the
Stevens Water Resources Data Book (11) contain a complete
set of tables. The explanatory material accompanying these
tables should be read and understood before they are used.
In many cases, tabulated flow values are given for measured
heads that are not within the usable measurement range.
The most frequently encountered problems with facility
installed flumes include:
0 Poor entrance and exist hydraulics that cause
poor flow distribution or submergence,
0 Improper installation, out of level
throat sidewalls not vertical, improper
throat dimensions, or
0 Improper location of head measuring
points.
(ii) Palmer-Bowlus Plumes
Palmer-Bowlus flumes depend upon existing
conduit slopes and a channel contraction (provided
by the flume) to produce supercritical flow.
Several different shapes of this flume are currently
-94-
-------
Endvnw
Longitudinal mid sections
Vertical
Horizontal
UJ^
(0
Z2Z
(d)
FIGURE VI - 12
VARIOUS CROSS - SECTIONAL SHAPES OF PALMER-
BOWLUS FLUMES (15)
-------
in use and are shown in Figure VI-12. These flumes
are bveing increasingly used as primary flow
devices for measuring flow in circular conduits.
Their principal advantage lies in simplicity of
construction and ease of installation through
manholes. There is a paucity of data on the
accuracy of this flume, although one reference
reports that the performance of these flumes can
be theoretically predicted to within 3 percent
when used in U-shaped channels, so long as the
upstream depth does not exceed 0.9D (where D is
the diameter of the circular conduit leading
into the flume)(3). A complete description of
the theory of these flumes and their use is given
in the references (3,10,12).
(iii) Other Flumes
A number of other flumes have been developed
to solve specific flow measurement problems,
including cutthroat, trapezoidal with buttom
slope, critical depth, H, etc. (1,3,9,10).
These flumes are seldom used for wastewater flow
measurement purposes.
(d) Open-Channel Flow Nozzles
The open-channel flow nozzle is a combination
of flume and sharp crested weir. Unlike sharp
crested weirs, these devices operate well with
wastewaters that contain high concentrations of
-96-
-------
suspended solids; however, they have poor head
recovery characteristics. These devices are
designed to be attached to the end of a conduit,
flowing partially full, and must have a free fall
discharge. Open channel flow nozzles are de-
signed so there is a predetermined relationship
between the depth of liquid within the nozzle and
the flowrate. The Kennison nozzle has a cross-
sectional shape such that the relationship be-
tween the flowrate and head is linear. These
nozzles require a length of straight conduit
immediately upstream from the nozzle, and the
slope of the conduit must be within the limits of
the nozzle calibration specifications. The pro-
file of a parabolic and a Kennison type open flow
nr zle is shown in Figure VI-13.
Open flow nozzles are factory calibrated and
are ordinarily supplied as part of a flow measure-
ment system. Calibration and installation data
for each nozzle should be supplied by/or obtained
from the manufacturer. The accuracy of these
devices is reported to be often better than +
5 percent of the indicated flow(lO).
(e) Slope - Area Method
The slope-area method consists of using the
slope of the water surface, in a uniform reach of
channel, and the average cross-sectional area of
-97-
-------
a. Linear (Kennison) Nozzle Profile (Q « H)
b. Parabolic Nozzle Profile (Q * lr)
FIGURE VI-13
OPEN CHANNEL FLOW NOZZLE PROFILES (10)
-98-
-------
that reach, to estimate the flowrate of an open
channel. The flowrate is estimated from the Manning
formula:
Q
1.486/n AR / s / (7)
Where
Q
A
= discharge in cfs
average area of the wetted channel
cross-section in square feet
R = average hydraulic radius of
the wetted sectional channel
feet. (Average cross-area
divided by the average
wetted perimeter.)
S = slope of the water surface,
and
n = a roughness factor depending
on the character of the channel
linning.
A long straight section of channel should be
used for this estimation technique. Values of n
may be obtained from hydraulic handbook (6,7).
It should be remembered that the slope in the equation
is of the water surface and not the channel invert.
(f) Measurement by Floats
A crude but simple method of estimating flow
in an open channel is by using floats. A straight
-99-
-------
reach of channel with uniform slope is necessary
for this method. Three cross-sections are used.
The purpose of the middle section is to provide
a check on the velocity measurements between
the beginning and end sections. The velocity is
obtained by measuring the length of the reach and
timing the passage of the float with a stopwatch.
The flowrate is obtained by multiplying the
resulting velocity by the average cross-sectional
area of the section of channel used. Since
surface velocities are higher than the average
velocity of the channel, the velocities obtained
by the float method should be corrected using the
empirical factors presented in the USDI Water
Measurement Manual (1).
4. Closed Conduit Flow Measurements
Closed conduit flow measurement systems present a
special challenge to the field investigator. These systems,
once installed, generally cannot be visually inspected,
nor can the hydraulic responses of the systems be as easily
evaluated as is the case with most open-channel systems.
One procedure for verifying the accuracy of closed conduit
flow measurement systems in the field is to make an in-
dependent flow measurement at an acceptable location. The
constant injection dilution technique, or the velocity area
V
method, both of which were described earlier in this
section, would be acceptable for this purpose. Another
-100-
-------
procedure includes inducing known pressures or voltages on
the sensing system and verifying recorder response.
Some of the most commonly used closed conduit primary
flow devices are presented and discussed briefly in this
section. Several flow estimation techniques are also
presented. The measurement accuracies quoted in this
section apply only to the specific method or to the primary
flow device being discussed. The total error involved in
continuous flow measurement systems, which is the sum of
the errors of each component, is beyond the scope of this
discussion. The reader is referred to the list of refer-
ences at the end of this chapter for such a discussion.
(a) Venturi Meter
The Venturi meter is one of the most accurate
primary flow devices for measuring flowrates in pipes.
Basically, the Venturi meter is a pipe segment (Figure
VI-14) consisting of a converging section, a throat
and a diverging section. A portion of the static head
is converted in the throat section to velocity head.
Thus, the static head in the throat of the Venturi is
lower than in the converging section. This head dif-
ferential is proportional to the flowrate. One of the
advantages of the Venturi meter is that it has a low
head loss.
The meter must be installed downstream from a
straight and uniform section of pipe, at least 5-20
pipe diameters, depending upon the pipe diameter to
_ 101 -
-------
throat diameter ratio. The accuracy of the Venturi is
affected by changes in density, temperature, pressure,
viscosity, and by pulsating flow. When used to measure
flow in wastestreams containing high concentration of
suspended solids, special provisions must be made to
insure that the pressure measuring taps are not
plugged. The typical accuracy of Venturi meters is
given at 1 to 2 percent (3,8,10).
There are a number of variations of the Venturi
meter, generally called flow tubes, presently being
used (10). Because their principle of operation is
similar to that of the Venturi, they will not be
discussed further.
(b) Orifice Meters
The Orifice meter is one of the oldest flow
measuring devices. Flow is measured by the difference
in static head caused by the presence of the orifice
plate. The differential pressure is related to the
flowrate. The thin plate orifice is the most common
variety, and consists of a round hole in a thin plate,
which is generally clamped between a pair of flanges
at a point in a pipe. The most common orifice plate
consists of a sharp 90-degree corner on the downstream
edge. Some orifice plates have a rounded edge facing
into the direction of flow, and perhaps a short tube
with the same diameter as the orifice opening facing
downstream. Pressure measuring taps are located
-102-
-------
PIPE
DIAMETER
THROAT
DIAMETER
o
u>
FIGURE VI - 14
VENTURI METER (15)
-------
upstream and downstream of the orifice plate to
facilitate differential pressure measurements. Only
one pressure tap is required if the orifice plate is
located at the end of a pipe discharging at atmospheric
pressure.
Orifice meters are of limited usefulness in
measuring flowrates in wastestreams containing high
suspended solids, since solids tend to accumulate
upstream of the orifice plate. Orifice meters produce
the highest head loss of any of the closed conduit
flow devices, and are quite sensitive to upstream
disturbances. It is not uncommon to need from 40 to
60 pipe diameters of straight pipe upstream of the
installation. They can be quite accurate, 0.5%,
although their usable range is small (5:1) unless
rated in place (10).
(c) Flow Nozzles
A flow nozzle may consist of designs that approach
the Venturi meter in one extreme and the orifice meter
in the other. The basic principle of operation is the
same as that of the Venturi meter. Typically, a flow
nozzle has an entrance section and a throat, but lacks
the diverging section of the Venturi (a typical flow
nozzle is shown in Figure VI-15). A major advantage
of the flow nozzle over the Venturi meter is that the
flow nozzle can be installed between pipe flanges.
They are intermediate in head loss between the Venturi
- 104 -
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HIGH
PRESSURE TAP
LOW PRESSURE TAP
o
Ul
I
ENTRANCE
CONE
THROAT
FIGURE VI-15
FLOW NOZZLE IN PIPE (10)
-------
and orifice meters. Like orifice meters, they are sen-
sitive to upstream disturbances and 20 or more pipe
diameters of straight pipe are required upstream from
the flow nozzle for successful operation. Some flow
nozzles are not recommended for use in measuring
flowrates in high suspended solids wastestreams.
Flow nozzle accuracies can approach those of Venturi
meters (10).
(d) Electromagnetic Flowmeter
The electromagnetic flowmeter operates according
to Faraday's Law of Induction. Namely, the voltage
induced by a conductor moving at right angles through
a magnetic field will be proportional to the velocity
of the conductor through the field. In the electro-
magnetic flowmeter, the conductor is the liquid stream
to be measured and the field is produced by a set of
electromagnetic coils. A typical cross-section of an
electromagnetic flowmeter is shown in Figure VI-16.
The induced voltage is subsequently transmitted to a
converter for signal conditioning.
Electromagnetic flowmeters have many advantages;
they are very accurate (within ;+!% of full scale) ,
have a wide flow measurement range, introduce a negligible
head loss, have no moving parts, and the response time
is rapid (10). However, they are expensive. Buildup
of grease deposits or pitting by abrasive wastewaters
can cause error. Regular checking and cleaning of the
-106-
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INSULATING
LINER
ELECTRODE
ASSEMBLY
STEEL METER
BODY
MAGNET COILS
POTTING COMPOUND
FIGURE VI - 16
ELECTROMAGNETIC FLOW METER (15)
-107-
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electrodes is necessary.
(e) Acoustic Flowmeters
Acoustic flowmeters operate on the basis of
the difference in transit time between upstream and
downstream directed sonic pulses. The difference in
transit time is caused by the velocity of the water
in the conduit. This time lag is proportional to
the velocity, and hense the flowrate. Manufacturers
employ various methods to take advantage of this
principle. Some flowmeters use the acoustic
doppler principle. According to the manufacturers,
accuracies of one percent of full scale are achievable
(3,10) .
(f) Trajectory Methods
A number of methods for estimating the flowrate
from the end of a pipe with a free discharge are avail-
able. All of these methods, whether theoretically or
empirically derived, have in common the measurement of
the issuing stream coordinates (Figure VI-17) in the
vertical and horizontal directions. It should be em-
phasized that all of these methods are estimates,
none of them are accurate enough for NPDES compliance
purposes.
The California pipe method (Figure Vl-17) uses
a straight level section of pipe at least six pipe
diameters in length as the primary flow device. The
pipe must have a free discharge and must be only
partially full. The distance from the crown of the
-108-
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ZERO SLOPE
T
i
•6d OR GREATER
a. CALIFORNIA PIPE METHOD
MID-DEPTH
b. PURDUE METHODS
TO CENTER OF
STREAM
FIGURE VI-17
TRAJECTORY METHODS (10)
-109-
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pipe to the water surface (a) at the end of the pipe
is related to the flowrate by the following equation:
Q = 8.69 (1-a/d) d (8)
Where
Q = 8.69 (1-a/s) 1 88 d (8)
Where
Q = flowrate in cfs
d = diameter of pipe in feet
It is recommended that a/d be restricted to
values greater than 0.5. The experiments from which
the above equation was derived used pipe diameters of
from 3 to 10 inches (1,3,10).
The Purdue method involves the measurement of
the horizontal (x) and the vertical (y) coordinates
of the issuing stream at the end of a pipe, and
the use of a set of curves that empirically relate
these coordinates to the discharge. Curves for pipes
2, 3, 4, 5, and 6 inches are available (1,3).
If the water jet is treated as a freely falling
body with constant horizontal velocity, the following
equation results (3):
Q = A(g/2y) x (9)
Where
Q = flowrate in cfs
A = cross-sectional area of the issuing stream
X & Y = horizontal and vertical trajectory coordinates
measured as shown in Figure VI-17
-110-
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(g) Pump Curves
Pump curves, supplied by pump manufacturers,
have been used extensively to estimate flows in closed
conduits. Where pumps are operated on a cyclic basis,
a timer hooked to a pump gives an estimate of the
total flow. However, there are so many variables
present in pump and piping installations that it is
likely that most pump curves are not accurate enough
for NPDES compliance purposes. When pump curves are
used for NPDES compliance wastewater flow measurements,
these curves should be verified by making an independent
flow measurement.
(h) Use of Water Meters
Municipal and process water meters have been used
to estimate industrial wastewater flows when all other
methods have failed or are not usable. The use of
water meters should be viewed with caution. All con-
sumptive uses of water must be accounted for and subtracted
from the meter readings. Also, water meters are often
poorly maintained and their accuracy is questionable.
When water meters have to be used, the municipality
or utility that has responsibility for the meters
should be consulted as to when the meters were last
serviced or calibrated.
- Ill -
-------
REFERENCES - SECTION VI
1. "Water Measurement Manual," Second Edition, revised,
United States Department of Interior, Bureau of
Reclamation, 1974. Available from the U.S. Government
Printing Office, Washington, D.C. 20402.
2. Smoot, C. W., "Orifice Bucket for Measurement of Small
Discharges from Wells," Water Resources Division Bulletin,
Illinois Water Survey, Champaign, Illinois, November 1963.
3. "A Guide to Methods and Standards for the Measurement of
Water Flow," U.S. Department of Commerce, National Bureau of
Standards, NBS Special Publication 421, May 1975.
4. "Fluorometric Facts, Flow Measurements," Monograph, 1976.
Available from the Turner Designs Company, 2247A Old
Middlefield Way, Mountainview, California 94043.
5. "Discharge Measurements at Gaging Stations," Hydraulic
Measurement and Computation, Book I, Chapter 11, United
States Department of Interior, Geological Survey, 1965.
6. King, H. W., and Brater, E. F., "Handbook of Hydraulics,"
Fifth Edition, McGraw-Hill, New York (1963).
7. Davis, C. V., and Sorenson, K. E., "Handbook of Applied
Hydraulics," Third Edition, McGraw-Hill, New York (1969).
8. American Society of Testing Materials, "1976 Annual Book of
ASTM Standards," Part 31 - Water, American Society of
Testing Materials, 1916 Rose Street, Philadelphia,
Pennsylvania 10103.
9. "Use of Weirs and Flumes in Stream Gaging," Technical Note
No.117, World Meteorological Organization, Technical Note
No.117, United Nations, New York, N.Y. 1971.
10. "Sewer Flow Measurement A State-Of-The-Art Assessment,"
Municipal Environmental Research Laboratory, Office of
Research and Development, U.S. Environmental Protection
Agency, Cincinnati, Ohio 45268.
11. "Stevens Water Resource Data Book," Second Edition, Leopold
Stevens, Inc., P.O. Box 688, Beaverton, Oregon.
12. Wells, E.A. and Gotaas, H.B., "Design of Venturi Flumes in
Circular Conduits," American Society of Civil Engineers, 82,
Proc. Paper 928, April 1956.
- 112 -
-------
13. "Fluid Meters—Their Theory and Application," Sixth Edition,
1971, American Society of Mechanical Engineers, New York,
N.Y.
14. "Field Manual for Research in Agricultural Hydrology,"
Agricultural Handbook No. 224, Soil and Water Conservation
Research Division, Agricultural Research Service, United
States Department of Agriculture, Washington, D.C. 20402.
15. "Handbook for Monitoring Industrial Wastewater," Technology
Transfer Publication, United States Environmental Protection
Agency, 1973.
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SECTION VII - QUALITY ASSURANCE
A. Purpose
The purpose of this section is to provide guidelines
and procedures for establishing a field quality assurance
program. It is intended to serve as a resource document
for the design of quality assurance programs and to provide
detailed operational procedures for certain measurement
processes that can be used directly in implementing the
field quality assurance program.
A quality assurance program for NPDES monitoring
should address all elements from sample collection to data
reporting, and at the same time allow flexibility.
B. Policy and Objectives
Quality assurance is necessary at each organizational
level to insure high quality data. Each organization
should have a written quality assurance policy. This
policy should be distributed so that all organizational
personnel know the policy and scope of coverage.
The objectives of quality assurance are to produce
data that meet user requirements in terms of completeness,
precision, accuracy, representativeness, and comparability.
For compliance sampling inspections, an estimate of the
resources required to support such a quality assurance
program is 15 percent. It should be recognized, however,
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that many of these elements are already an integral part of
the compliance monitoring program, but may not be specificall
identified as quality assurance techniques.
To administer a field quality assurance program, the
objectives must be defined, documented and issued for all
activities that affect the quality of the data. Such
written objectives are needed because they:
1. Unify the thinking of those concerned with quality
assurance.
2. Stimulate effective action.
3. Provide an integrated, planned course of action.
4. Permit comparison of completed performance against
stated objectives.
Precision and accuracy represent measures of data
quality and data must be representative of the condition
being monitored. Data available from numerous agencies and
private organizations should be in consistent units and
should be corrected to the same standard units to allow
comparability of data among groups.
In addition, certain key assignments for carrying out
the various operational aspects of the program should be
made within the unit engaged in NPDES monitoring and
monitoring support activities. The quality assurance plan
should clearly identify the individuals and their respon-
sibilities and document the unit's operating procedures.
C. Elements of a Quality Assurance Plan
Elements of a recommended quality assurance program,
- 115 -
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including necessary training, are contained in Part VI of
the "Model State Water Monitoring Program"(1). Detailed
specifications for laboratory quality assurance procedures
are contained in EPA's "Handbook For Analytical Quality
Control in Water and Wastewater"(2) and in "Quality Assurance
Handbook For Air Pollution Measurement Systems"(3).
D. Quality Assurance In. Sample Collection
Control checks should be performed by the inspector
during the actual sample collection. These checks are used
to determine the performance of the sample collection
system. In general, the most common errors produced in
monitoring are usually caused by improper sampling, poor
preservation, or lack of adequate mixing during compositing
and testing. The following checks will help the inspector
and QA Coordinator to determine when the sample collection
system is out-of-control:
1. Duplicate Samples
At selected stations on a random time frame,
collect duplicate samples using the field equip-
ment installed at the site. If automatic sampling
equipment is not installed at the site, collect
duplicate grab samples. This will provide a pro-
ficiency check for precision.
2. Split Samples
Aliquots of the collected sample may be given to
the permittee, if requested, as a check on the
- 116 -
-------
permittee's laboratory procedures. Differences
between agency and permittee's results can then
be evaluated and the cause of the difference
usually identified. Having the permittee analyze
known permit parameters will aid in identifying
discrepancies in the permittee's analytical tech-
niques and procedures.
Spiked Samples
Known amounts of a particular constituent should
be added to an actual sample or blanks of de-
ionized water at concentrations where the accuracy
of the test method is satisfactory. The amount
added should be coordinated with the laboratory.
This method will provide a proficiency check for
accuracy of the field sampling procedures.
Sample Preservative Blanks
Acid and other chemical preservatives can become
contaminated after a period of use in the field. The
sampler should add the same quantity of preservative
to a sample of distilled water as normally would be
added to the wastewater sample. This preservative
blank is sent to the laboratory for analysis and
the blank is subtracted from the sample value.
Liquid chemical preservatives should be changed
every two weeks or sooner if contamination occurs.
Precision, Accuracy, and Control Charts
A minimum of seven sets each of comparative data
-117-
-------
for duplicates, spikes, split samples and blanks
should be collected to define acceptable estimates
of precision and accuracy criteria for data validation.
See EPA's "Handbook for Analytical Quality Control
in Water and Wastewater," (2) or W.J. Youden's
"Statistical Techniques for Collaborative Tests,"
(4) for discussions of precision, accuracy, and
quality control charts and their calculations.
E. Quality Assurance Procedures for Field Analysis &_ Equipment
1. Calibration and Documentation Plan
A calibration plan should be developed and implemented
for all field analysis test equipment and calibration
standards to include: calibration and maintenance intervals;
listing of required calibration standards; environmental
conditions requiring calibration; and a documentation record
system. Written calibration procedures should be provided
for all measuring and test equipment. A procedure should:
a. Specify where the procedure is applicable, e.g.
free residual chlorine by amperometric titration
at power plant cooling water effluents.
b. Provide a brief description of the calibration
procedure, a copy of the manufacturer's instruc-
tions is usually adequate.
c. List calibration standards, reagents, and
accessory equipment required.
d. Specify the documentation, including an example
of the format used in the field quality assurance
log book.
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TABLE VII - 1
Parameter
QUALITY ASSURANCE PROCEDURES FOR FIELD ANALYSIS AND EQUIPMENT
General Daily Quarterly
1.
Dissolved Oxygen
a) Membrane
Electrode
Enter the make,
model, serial and/
or ID number for
each meter in a
log book.
Report data to
nearest 0.1 mg/1.
b) Winkler-Azide Record data to
method nearest 0.1 mg/1.
2.
pH - Electrode
Method
Enter the make
model, serial and/or
ID number for each
meter in a log book.
i) Calibrate meter using
manufacturer's instruc-
tions or Winkler-Azide
method.
ii) Check membrane
for air bubbles
and holes. Change
membrane and KC1
if necessary.
iii) Check leads, switch
contracts etc. for
corrosion and shorts
if meter pointer re-
mains offscale.
Duplicate analysis
should be run as a
precision check.
Duplicate values
should agree within
+0.2 mg/1.
i) Calibrate the
system against
standard buffer
solutions of known
pH value e.g., 4,7
and 9 at the start
of a sampling run.
Check instrument calibration
and linerarity using a series
of at least three dissolved
oxygen standards.
Take all meters to the
laboratory for maintenance,
calibration and quality
control checks.
-------
TABLE VII - 1
(Continued)
Parameter
2. pH (Continued)
General
o
I
3. Conductivity
Enter the
make, model,
serial and/or
ID number for
each meter in
a log book.
Daily
ii) Periodically check the
buffers during the
sample run and record
the data in the log
sheet or book.
iii) Be on the alert for
erratic meter response
arising from weak batteries,
cracked electrode,fouling,
etc.
iv) Check response and lin-
earity following highly
acidic or alkaline samples.
Allow additional time for
equilibration.
v) Check against the closest
reference solution each
time a violation is found.
vi) Rinse electrodes thoroughly
between samples and after
calibration.
i) Standardize with KC1
standards having similar
specific conductance values
to those anticipated in
the samples. Calculate
the cell constant using two
different standards.
Quarterly
i) Take all
meters to
lab for main-
tenance, cal-
ibration and
quality contn-
trol checks.
-------
TABLE VII - 1
(Continued)
3.
Parameter
Conductivity
(Continued)
General
Daily
Cell Constant=
Standard Value/
Actual Value
Specific Conductance=
Reading X Cell Constant
i
M
to
I-1
I
ii)
Residual Chlorine
Amperometric
Titration
Temperature
a) Manual
Enter the make,
model, ID and/or
serial number of
each titration ap-
paratus in a log
book. Report re-
sults to nearest
0.01 mg/1.
Enter the make,
model, serial
number and/or ID
number and tem-
perature range for
Rinse cell after
sample to prevent carryover.
Refer to instrument manu-
facturer's instructions
for proper operation and
calibration procedures.
i)
Check for air spaces or
bubbles in the column,
cracks, etc. Compare
with a known source
if available.
Quarterly
ii) Check tem-
perature
compensation.
iii) Check date
of last
platinizing
and replat-
inizing if
necessary.
iv) Analyze NBS or
EPA reference
standard and
record actual vs.
observed read-
ings in the log.
Biweekly: Return instru-
ment to lab for
maintenance and
addition of
fresh, standard-
ized reagents.
Biweekly: Check at two tem-
peratures against a
NBS or equivalent
thermometer. Enter
data in log book.
-------
TABLE VII - 1
(Continued)
Parameter
Temperature
(Continued)
to
10
I
b) Thermistors;
Thermographs
etc.
General
each thermometer.
All standardization
shall be against a
NBS or NBS calibrated
thermometer. Readings
shall agree within +1°C
If enforcement action
is anticipated, cal-
ibrate the thermometer
before and after analy-
sis. All data shall
be read to the nearest
1°C. Report data be-
ween 10 - 99°C to two
significant figures.
Daily
Enter the make, model,
serial and/or ID num-
ber of the instrument
in a log book. All
standardization shall
be against a NBS or
NBS calibrated thermo-
meter . Reading should
agree within +1°C. If
enforcement action is
anticipated refer to
the procedure listed
in 5(a) above.
Initially S
Biannually:
Check thermistor
or sensing device
for response and
operation accord-
ing to the manu-
facturer 's instruct-
ions. Record actual
vs. standard tem-
perature in log book.
Initially &
Biannually:
Quarterly
Temperature read-
ings shall agree
within +1°C or
the thermometer
shall be replaced
or recalibrated.
Accuracy shall be
determined thorough-
out the expected
working range 0°
to 50°C. A min-
imum of three tem-
peratures within
the range should be
used to verify acc-
uracy. Preferable
ranges are: 5 - 10°,
15 - 25°, 35 - 45°C.
Accuracy shall be
determined throughout
the expected working
range 0 ° to 50°C. A
minimum of three tem-
peratures within the
range should be used
to verify accuracy.
Preferable ranges
are: 5 - 10°, 15 -
25°, 35 - 45°C.
-------
TABLE VII - 1
(Continued)
Parameter
6. Flow Measurement
7. Automatic Sam-
plers
General
Enter the make, model,
serial and/or ID num-
ber of each flow measure-
ment instrument in a log
book.
Enter the make, model,
serial and/or ID num-
ber of each sampler
in a log book.
Daily
Install the device
in accordance with
the manufacturer's
instuctions and
with the procedures
given in Section VI
of this manual.
to
U)
l
Quarterly
Annually: Affix record of
calibration NBS,
manufacturer or
other, to the
instrument log.
Check intake vel-
ocity vs. head
(minimum of three
samples), and clock
time setting vs.
actual time interval.
-------
calibration date, when calibration expires and when main-
tenance is due.
F. Parameters Requiring Special Precautions
1. Organics
Preservatives, holding times, sampling procedures,
and sample aliquots or volume for specific organic
analysis should be determined prior to each survey
after consultation with appropriate lab personnel.
The survey leader should provide, if possible, the
following information: raw products; chemical pro-
cesses; and types of wastewater treatment. This will
assist the laboratory in making their recommendations
regarding sampling and handling procedures. Normally,
a one to four liter grab sample, collected in a glass
jar with a teflon or cleaned aluminum foil lined screw
cap, will provide a sufficient sample volume. Normally,
if biological activity cannot be stopped by addition of
a preservative, samples should be iced until analysis
and received in the laboratory within 24 hours.
2. Acidity - Alkalinity
Compositing of grab samples for acidity, alkalinity,
and suspended solids analysis should not be done if a
waste discharge varies outside the pH range specified
in NPDES permits. Mixing acid grab samples with neutral
or basic grab samples changes the acidity-alkalinity
relationship and results in a composite sample which
may not be representative of the discharge during the
-124-
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compositing period. The acid-base reaction may also
dissolve a portion of the inorganic solids. Thus, a
discharge which varies outside the pH range specified
in the NPDES permit should be analyzed for acidity,
alkalinity and suspended solids on an individual "grab"
sample basis.
3. Miscellaneous Parameters
Based on present knowledge, the following pa-
rameters should not be collected using automatic
samplers but should be preserved at the time of
sample collection whether the sample is a grab
sample or a composite of grab samples.
(a) Dissolved Parameters
Samples should be membrane filtered at the
time of collection, if at all possible, and
composited if necessary under acidified conditions.
In any case, preservation should not be performed
until after filtration.
(b) Mercury, Total
Samples for mercury analysis must be acidified
at the time of collection. The addition of potassium
dichromate will help stabilize dissolved mercury(5).
(c) Phenolics and Cyanides
Simple phenolic compounds and free cyanide may
be significantly degraded if not preserved at the time
of sample collection. If the sample contains residual
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chlorine, it is also necessary to dechlorinate the
sample prior to preservation. Standard Methods(6)
recommends the use of ferrous sulfate as a dechlorination
agent for phenolics and ascorbic acid for cyanide.
(d) Sulfide and Sulfite
Table 2 of EPA's "Methods For Chemical Analysis
Of Water & Wastes" (7) lists cooling to 4°C as the
preservative for sulfide, though there is no accept-
able preservative listed for sulfite. Therefore,
sulfite samples must be analyzed at the time of collection.
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REFERENCES - SECTION VII
"Model State Water Monitoring Program," U.S. Environmental
Protection Agency, Office of Water and Hazardous Materials,
Monitoring and Data Support Division, Washington, D.C.
EPA-440/9-74-002, (1975).
"Handbook For Analytical Quality Control In Water And
Wastewater Laboratories," U.S. Environmental Protection
Agency, Technology Transfer, Washington, D.C. (6/72).
"Quality Assurance Handbook For Air Pollution Measurement
Systems," Vol. I. Principles, U.S. Environmental Protection
Agency, Office of 'Research and Development, Environmental
Monitoring & Support Lab, Research Triangle Park, N.C.
EPA-600/9-76-005, (3/76).
Youden, W.J. , "Statistical Techniques For Collaborative
Tests," Assn: of Official Analytical Chemists, Washington,
D.C. (1973).
Analytical Chemistry, Vol. 48, No. 1, Jan. 1976. EL-
Awady, AA., R.B. Miller & M.J. Carter, "Automated Method
for the Determination of Total and Inorganic Mercury in
Water and Wastewater Samples," Anal. Chem. , Vol. 48,
No. 1, 110-116, Jan. 1976.
Standard Methods For The Examination Of Water And
Wastewater, 14th Ed., APHA, Washington, D.C. (1976) .
"Methods For Chemical Analysis Of Water And Waste,
1974," U.S. Environmental Protection Agency, Office
of Technology Transfer, Washington, D.C. (1974).
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SECTION VIII - CHAIN OF CUSTODY PROCEDURES
A. Introduction
As in any other activity that may be used to support
litigation, regulatory agencies must be able to provide the
chain of possession and custody of any sample which are
offered for evidence or which form the basis of analytical
test results introduced into evidence in any water pollution
case. It is imperative that written procedures be available
and followed whenever evidence samples are collected, trans-
ferred, stored, analyzed, or destroyed. The primary objective
of these procedures is to create an accurate written record
which can be used to trace the possession and handling of
the sample from the moment of its collection through
analysis and its introduction as evidence.
A sample is in someone's "custody" if:
1. it is in one's actual physical possession;
2. it is in one's view, after being in one's
physical possession;
3. it is in one's physical possession and then
locked up so that no one can tamper with it;
4. it is kept in a secured area, restricted to
authorized personnel only.
B. Survey Planning and Preparation
The evidence gathering portion of a survey should be
characterized by the conditions stipulated in the permit or
-128-
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the minimum number of samples required to give a fair
representation of the wastewater quality. The number
of samples and sampling locations, determined prior to
the survey, must satisfy the requirements for NPDES
monitoring or for establishing a civil or criminal
violation.
A copy of the study plan should be distributed to
all survey participants in advance of the survey date.
A pre-survey briefing is helpful to reappraise survey
participants of the objectives, sampling locations and
chain of custody procedures that will be used.
C. Sampling Collection, Handling and Identification
1. It is important that a minimum number of persons
be involved in sample collection and handling. Guide-
lines established in this manual for sample collection,
preservation and handling should be used. Field
records should be completed at the time the sample
is collected and should be signed or initialed,
including the date and time, by the sample
collector(s). Field records should contain the
following information:
(a) unique sample or log number;
(b) date and time;
(c) source of sample (including name, location
& sample type);
(d) preservative used;
-129-
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(e) analyses required;
(f) name of collector(s);
(g) pertinent field data (pH, DO, Cl,
residual, etc);
(h) serial number on seals and trans-
portation cases.
2. Each sample is identified by affixing a
pressure sensitive gummed label or standardized
tag on the container(s). This label should contain
the sample identification number, date and time of
sample collection, source of sample, preservative
used and the collectors' ) initial(s). Analysis
required should be identified. Where a label is not
available, the same information should be affixed to
the sample container with an indelible, water proof,
marking pen. Examples of sample identification tags
are illustrated in Figure VIII-1.
3. The sample container should then be placed in a
transportation case along with the chain of custody
record form, pertinent field records and analyses
request form as needed. The transportation case should
then be sealed or labeled. All records should be filled
out legibly in pen.
The use of the locked and sealed chests will elimin-
ate the need for close control of individual sample
containers. However, there will undoubtedly be occasions,
when the use of a chest will be inconvenient. On those
-130-
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*
EPA,
•
Station No — i
uate I Time Sequence No.
Station Location
Grab
Comp.
^V ROD _Metals Remarks /Preservative
-^ Solids .Oil and Grease
con Dn
Nutrients .Bart.
Other
Samplers:
v
GENERAL CHEMISTRY
PH AeH
z Official Sample No. Cond Alk
0 ui TS SO,
2 « DS ci
S = SS F
< co • • BOD2 Cr. +6
a- Turb BODS
lu _ Cnlnr
^ Date and Time «•»"•"
Sampler's Signature Office
OTHER PARAMETERS:
MICROBIOLOGY
Tot. Colif.
Z Official Sample No*
S jj
g ^ • Fecal Colif.
ac D
, 0
2 W Fecal Strep.
ui
g Da* "id-Time Salmonella
Sampler's Signature Office
O
0
111
et
i.
ui
t/i
3
PESTICIDES, ORGANICS
Official Sample No.
UJ
u
(X
^
n
00
£)afe and Time
Sampler's Signature Office
Pesticides
PCB's:
Orgonicss
FIGURE VIII-1
SAMPLE IDENTIFICATION TAG EXAMPLES
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occasions, the sampler should place a seal around the
cap of the individual sample container which would
indicate tampering if removed.
4. When samples are composited over a time period,
unsealed samples can be transferred from one crew to the
next crew. A list of samples will be made by the
transferring crew and signed for by a member of the
receiving crew. They will either transfer the samples
to another crew or deliver them to laboratory personnel
who will then acknowledge receipt in a similar manner.
5. Color slides or photographs taken of the sample
outfall location and of any visible pollution are
recommended to facilitate identification and later
recollection by the inspector. A photograph log should
be made at the time the photo is taken so that this
information can be written later on the back of the
photo or the margin of the slide. This should include
the signature of the photographer, time, date, site
location and brief description of the subject of the
photo. Photographs and written records, which may be
used as evidence, should be handled in such a way that
chain of custody can be established.
D. Transfer of Custody and Shipment
1. When transferring the possession of the samples,
the transferee must sign and record the date and time
on the chain of custody record. Custody transfers,
if made to a sample custodian in the field, should
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account for each individual sample, although samples
may be transferred as a group. Every person who
takes custody must fill in the appropriate section
of the Chain of Custody Record. To prevent undue
proliferation of custody records, the number of
custodians in the chain of possession should be
as few as possible.
2. The field custodian or field inspector, if a
custodian has not been assigned, is responsible for
properly packaging and dispatching samples to the
appropriate laboratory for analysis. This respon-
sibility includes filling out, dating, and signing
the appropriate portion of the Chain of Custody
Record. A recommended Chain of Custody format is
illustrated in Figure VII-2.
3. All packages sent to the laboratory should be
accompanied by the Chain of Custody Record and other
pertinent forms. A copy of these forms should be
retained by the originating office (either carbon or
photo copy).
4. Mailed packages can be registered with return
receipt requested. If packages are sent by common
carrier, receipts should be retained as part of the
permanent chain of custody documentation.
5. Samples to be shipped must be so packed as not
to break and the package so sealed or locked that any
evidence of tampering may be readily detected.
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FIGURE VIII-2
CHAIN OF CUSTODY RECORD
SURVEY
STATION
NUMBER
STATION LOCATION
DATE
Relinquished by: (signature)
Relinquished by: (Signature]
Relinquished by: (signature)
Relinquished by: (signature;
Dispatched by: (signature)
Date/
TIME
SAMPLERS: (Signature)
SAMPLE TYPE
Water
Comp.
Grab.
Air
SEQ.
NO.
NO. OF
CONTAINERS
ANALYSIS
REQUIRED
Received by: (Signature]
Received by: (signature)
Received by: (signature)
Received by Mobile Laboratory for field
analysis: (signature)
'Time
Received for Laboratory by:
Method of Shipment:
Date/Time
Date/Time
Date/Time
Date/Time
Date/Time
Distribution: Orig.— Accompany Shipment
1 Copy—Survey Coordinator Field Files
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GPO 831 -464
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E. Laboratory Custody Procedures
Chain of Custody procedures are also necessary in the
laboratory from the time of sample receipt to the time the
sample is discarded. The following procedures are recom-
mended for the laboratory:
1. A specific person shall be designated custodian
and an alternate designated to act as custodian in the
custodian's absence. All incoming samples shall be
received by the custodian, who shall indicate receipt
by signing the accompanying custody forms and who shall
retain the signed forms as permanent records.
2. The sample custodian shall maintain a permanent log
book to record, for each sample, the person delivering
the sample, the person receiving the sample, date and
time received, source of sample, sample identification
or log number, how transmitted to the laboratory and
condition received (sealed, unsealed, broken container,
or other pertinent remarks). A standardized format
should be established for log book entries.
3. A clean, dry, isolated room, building, and/or
refrigerated space that can be securely locked from
the outside shall be designated as a "sample storage
security area."
4. The custodian shall ensure that heat-sensitive,
light-sensitive samples, radioactive, or other sample
materials having unusual physical characteristics, or
requiring special handling, are properly stored and
maintained prior to analysis.
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5. Distribution of samples to the section chiefs who
are responsible for the laboratory performing the anal-
ysis shall be made only by the custodian.
6. The laboratory area shall be maintained as a secured
area, restricted to authorized personnel only.
7. Laboratory personnel are responsible for the care
and custody of the sample once it is received by them
and shall be prepared to testify that the sample was in
their possession and view or secured in the laboratory
at all times from the moment it was received from the
custodian until the time that the analyses are
completed.
8. Once the sample analyses are completed, the unused
portion of the sample, together with all identifying
labels, must be returned to the custodian. The returned
tagged sample should be retained in the custody room
until permission to destroy the sample is received by
the custodian.
9. Samples shall be destroyed only upon the order of
the Laboratory Director, in consultation with pre-
viously designated Enforcement officials, or when it is
certain that the information is no longer required or
the samples have deteriorated. The same procedure is
true for tags and laboratory records.
F. Evidentiary Considerations
Reducing chain of custody procedures as well as the
various promulgated laboratory analytical procedures to
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writing will facilitate the admission of evidence under
rule 803(6) of the Federal Rules of Evidence (PL. 93-575).
Under this statute, written records of regularly conducted
business activities may be introduced into evidence as an
exception to the "Hearsay Rule" without the testimony of
the person(s) who made the record. Although preferable,
it is not always possible to have the individuals who
collected, kept, and analyzed samples testify in court.
In addition, if the opposing party does not intend to
contest the integrity of the sample or testing evidence,
admission under the Rule 803(6) can save a great deal of
trial time. For these reasons, it is important that the
procedures followed in the collection and analyses of
evidentiary samples be standardized and described in an
instruction manual which, if need be, can be offered as
evidence of the "regularly conducted business activity"
followed by the lab or office in generating any given
record.
In criminal cases however, records and reports of
matters observed by police officers and law enforcement
personnel are not included under the business record
exceptions to the "Hearsay Rule" previously cited (see
RuJ/e 803(8), P.L. 93-595). It is arguable that those
portions of the compliance inspection report dealing
with matters other than sampling and analysis results
come within this exception. For this reason, in criminal
actions records and reports of matter observed by field
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investigators may not be admissible and the evidence may
still have to be presented in the form of oral testimony
by the person(s) who made the record or report, even though
the materials come within the definition of business records.
In a criminal proceeding, the opposing counsel may be able
to obtain copies of reports prepared by witnesses, even if
the witness does not refer to the records while testifying,
and if obtained, the records may be used for cross-examination
purposes.
Admission of records is not automatic under either of
these sections. The business records section authorizes
admission "unless the source of information or the method
or circumstances or preparation indicate lack of trust-
worthiness," and the caveat under the public records
exception reads "unless the source of information or other
circumstances indicate lack of trustworthiness".
Thus, whether or not the inspector anticipates that his
or her compliance inspection report will be introduced as
evidence, he or she should make certain that the report is
as accurate and objective as possible.
»D.S. GOTORNMEm PBIHTIKG OFFICE: 1979 — 680-197/480 REGION NO. 8
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