' ~ - 831R77101
NPDES COMPLIANCE SAMPLING MANUAL
(T.S* ENVIRONMENTAL PROTECTION AGENCY
ENFORCEMENT DIVISION
OFFICE OF MATER 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 endorcement or recommendation for use.
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ACKNOWLEDGEMENT
The work Group wishes to express their appreciation to the
secreterial 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.
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FOREWORD
The NPDES compliance inspection program represents a
significant commitment of resources by the States and EPA to
the verification of permit effluent limitations and assurance
that permit requirements for monitoring, reporting and
compliance schedules are being met and enforced on a
nationally consistent basis. While compliance inspections
make up only one segment of the overall national water
enforcement program, they are highly visible and may be the
only direct contact that the permittee has with regulatory
personnel. Thus, compliance inspections must be performed
in a thorough, professional manner, with nationally con-
sistent coverage of key compliance elements. Reporting of
inspection data must also cover the key compliance elements
so that the data derived from this program can be aggregated
nationally, regionally and by States for purposes such as
program assessment, budget development and reporting to
Congress.
The previously distributed NPDES Compliance Evaluation
Inspection Manual (CEI) described the objectives and procedures
for performing non-sampling inspections. The NPDES Compliance
Sampling Inspection Manual (CSI) describes technically sound
procedures, derived from the first hand experience of EPA
and State personnel directly involved in compliance inspections,
for the collection of representative samples, flow measurement,
sample handling and field quality assurance.
The CEI and CSI Manuals and the revised Compliance
Inspection Report Form, in conjunction with the annual
program guidance and other memoranda dealing with inspection
policy, form the framework for the compliance inspection
program. Following the procedures and policies outlined in
these documents will improve the quality of NPDES compliance
inspections, enhance the value of data derived from these
inspections, and better serve the needs of the overall NPDES
enforcement program.
The manual is made-up in a loose-leaf format so that
revisions or additions can be easily accomodated. Any'
comments or additions you may wish to make should be
directed to the Compliance Inspection Manual Review
Committee, Compliance Branch (EN-338), Enforcement Division,
Office of Water Enforcement, U.S. Environmental Protection
Agency, 401 M Street, S.W., Washington, D.C. 20460.
June 1977 Assistant Administrator
for Enforcement
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NPDES COMPLIANCE SAMPLING MANUAL
TABLE OF CONTENTS
\
Page No,
DISCLAIMER ii
ACKNOWLEDGEMENT iii
FOREWORD iv
TABLE OF CONTENTS v
LIST OF ILLUSTRATIONS xii
LIST OF TABLES xiv
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 6
A. Background 6
B. Enforcement Management System 7
C. Work Group Membership 8
III. NPDES PERMIT SAMPLING REQUIREMENTS 11
A. Introduction 11
B. Self-Monitoring Data 11
1. Permit Specifications 11
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IV.
2. Use of Self-Monitoring Data 12
C. Compliance Monitoring 12
1. General 12
2. Definitions 13
3. Objective of compliance Evaluation
Inspection 13
4. Compliance Evaluation Inspection Tasks 11
5. Objectives of Compliance Sampling
Inspection 15
6. Compliance Sampling Inspection Tasks 15
D. Adequacy of Data IT
E. Determining Compliance with Effluent
Limitations 17
1. Instantaneous Conditions 18
2. Daily Maximum Conditions 18
3. 7-day Average Conditions 19
4. 30-day Average Conditions 19
P. Sample collection and Handling 19
SAMPLE COLLECTION 21
A. Introduction 21
B. Sampling Considerations 22
1. General 22
2. Sample Location 24
(a) General 24
(b) Influent 25
(c) Effluent 25
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(d) Pond & Lagoon Sampling 26
3. Sample Volume 26
4. Selection and Preparation of Sample
Container 27
C. Sampling Techniques 27
1. Grab Samples 27
2. Composite Samples 28
(a) Selection of Sample Type , 28
(b) Compositing Method 30
D. Sample Preservation 33
1. General 33
2. Compliance Considerations 34
E. Analytical Methods '34
1. General 34
2. Alternative Test procedure 34
F. Sample Identification 35
G. Safety Considerations 37
V. AUTOMATIC SAMPLERS 39
A. Introduction 39
B. Automatic Sampler Subsystem Components 40
1. Sample Intake Subsystem 40
2. Sample Gathering Subsystem 41
(a) Mechanical 41
(b) Forced Flow 42
(c) Suction Lift 42
3. Sample Transport Subsystem 43
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4. Sample Storage Subsystem 44
5. Controls and Power Subsystem 44
6. Sampler Reliability 45
C. Installation and operation of Automatic
Sampling Equipment 45
1. Site Selection 45
2. Equipment Security 46
3. Power Source 47
4. Waste Characteristics 47
5. sample Preservation During Compositing
Period 48
6. Winter Operations 48
D. Desirable Automatic Sampler Characteristics 49
VI. WASTEWATER FLOW MEASUREMENT 53
A. Introduction 53
B. Wastewater Plow Measurement Systems 54
C. Field Verification of Flow Measurement Systems 57
D. Wastewater Flow Measurement Methods 60
1. Volumetric Techniques 61
(a) Vessel Volume 61
(b) Pump Sumps 61
(c) Bucket and stopwatch 64
(d) Orifice Bucket 65
2. Dilution Methods 66
3. Open Channel Flow Measurements 69
(a) Velocity-Area Method 71
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(b)
(c)
«*)
(e)
(f)
i Introduction
ii Current Meters
iii Field Practice
iv Area and Flow Calculations
weirs
i Broad Crested
ii Sharp Crested
(1) Standard Sharp crested
weir Shapes
(2) standard Conditions
(3) v Field Inspection
(4) Use of Weir Tables
Flumes
i Parshall Flumes
(1) Parshall Flume structure
and Nomenclature
(2) Field Inspection and
Flow Measurement
ii Palmer Bowl us Flumes
iii Other Flumes
Open Channel Flow Nozzles
Slope-Area Method
Measurement by Floats
Closed Conduit Flow Measurements
(a)
(b)
Venturi Meter
Orifice Meters
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72
76
77
78
80
80
82
85
85
89
89
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93
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96
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100
101
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(c) Plow Nozzles 103
(d) Electromagnetic Flowmeter 105
(e) Acoustic Flowmeter 105
(f) Trajectory Methods 107
(g) Pump Curves 109
(h) Use of Water Meters 110
VII. QUALITY ASSURANCE 113
A. Purpose 113
B. Policy and Objectives 113
C. Elements of a Quality Assurance Plan 115
O. Quality Assurance in Sample Collection 115
1. Duplicate Samples 115
2. Split Samples 116
3. Spiked Samples 116
H. sample Preservative Blanks 116
5. Precision, Accuracy and Control Charts 117
E. Quality Assurance Procedures for Field
Analysis and Equipment 117
1. Calibration and Documentation Plan 117
F. Parameter Requiring Special Precautions 12ft
1. organics 124
2. Acidity - Alkalinity 125
3. Miscellaneous Parameters 125
(a) Dissolved Parameters 125
(b) Mercury, Total 126
(c) Phenolics and Cyanides 126
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(d) Sulfide and Sulfite 126
VIII. CHAIN OF CUSTODY PROCEDURES 128
A. Introduction 128
B. Survey Planning and Preparation 129
C. Sample Collection, Handling & Identification 129
D. Transfer of Custody and Shipment 133
E. Laboratory custody Procedures 135
P. Evidentiary Considerations 137
APPENDIX
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LIST OF ILLUSTFATIONS
Figure Page
IV-1 Method For Determining Composite Aliquot Size 32
VI-1 Components Of Flow Measuring System 55
VI-2 Equations For container Volumes 62
VI-3 Constant Rate And Slug Injection Methods..... 70
VI-4 Ott Type Horizontal Axis Current Meter..... .,73
VI-5 Assembly Drawing Of Price Type AA Current Meter...74
VI-6 Current Meter Notes And Computations For Midsection
Method 79
VI-7 Broad Crested weir Profiles.. 81
VI-8 Sharp Crested Weir. Profiles 83
VI-9 Three Common Types Of Sharp-Crested Weirs And
Their Equations 84
VI-10 Sharp Crested Weir Nomenclature 87
VI-11 Configuration And Standard Nomenclature For
Par shall 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 102
VI-14 Flow Nozzle In Pipe 104
VI-16 Electromagnetic Flowmeter 106
VI-17 Trajectory Methods 108
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VIII-1 Sample Identification Tag Examples 131
VIII-2 Recommended Chain of Custody Record Format 134
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LIST OF TABLES
Table Page
IV-1 Compositing Methods 29
IV-2 Manual Compositing Method 31
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 Obiectives
Wastewater sampling is being conducted on an extensive scale
by regulatory agencies to verify compliance with NPDES permit
requirements. Specific objectives in collecting this data may
varyr but generally include the following:
1. Verify compliance with effluent limitations.
2. Verify self-monitoring data.
3. Verify that parameters specified in the NPDES permit
are consistent with wastewater characteristics.
1. Support enforcement action.
5. Support permit reissuance and/or revision.
B. Obtaining Representative Data
In order to accomplish these objectives, it is imperative
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.
U. Installation of appropriate flow monitoring devices or
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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
schedules or enforcement action, a more extensive
program may be necessary.
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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 production
of accurate, precise and defensible data.
D. Error Minimization
By adhering to these recommended guidelines, errors will be
minimized. Although most of these errors defy exact
quantification, the state of the art affords the following
conclusions, using currently existing primary devices and
recorders, flows can be accurately measured within ,+ 10%.
Furthermore, judicious selection of automatic sampling equipment
assures consistent sample collection. However, due to the
difficulity 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 bottom of the
channel, within the bed load, results can be considerably higher
than actual. To minimize analytical error and to provide
national uniformity of analytical techniques, only those approved
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test procedures listed in Table I, »*0 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
1. Reed, G.D., "Evaluation of The Standard Sampling Technique
For Suspended Solids," U.S. Environmental Protection Agency,
Region VII, S6A Division, Technical Support Branch,
EPA-907/9-77-001(1977) .
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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 this objective, the Act set
forth a series of goals, including the goal of eliminating the
discharge of pollutants 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 milestones contained in construction
schedules and to compliance with effluent limitations established
for each parameter limited in the permit for both interim or
final effluent limitations.
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compliance with effluent limitations and self-monitoring
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 Agencyfs resources committed •
to gathering and verifying information regarding permit
compliancef a number of important projects are presently being
sponsored by the Office of Water Enforcement. 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 in this last area, improvement
in the quality of information that is gathered by the field
staff, that this manual is designed to fill a need.
The previously completed NPDES Compliance Evaluation
Inspection Manual (July 1976) described 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
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procedures that will provide effluent data that meets 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 17 (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
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personnel. The work group wishes to thank the reviewers for
their guidance and assistance in the preparation of this manual,
After gaining some experience with the use of the manual,
readers are encouraged to offer constructive criticism and
proposed revisions to the work group chairman. 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", O.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» Self-Monitoring Data
1. Permit Specifications
The NPDES permit specifies limitations for certain
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 a given time frame.
Common time frames .specified in NPDES permits are daily average,
daily maximum, seven consecutive day average, and thirty
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consecutive day average. Time frames are 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-
annual ly.
2- Use of SeIf-Monitoring 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 independent 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 documentation and
verification to justify and support enforcement actions. All
compliance inspection activity should be conducted on the premise
that it may lead to enforcement action.
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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;
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(c) check on the completeness and accuracy of the
permittee's performance/compliance records;
(d) evaluate the permittee's operation and maintenance
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-monitor ing 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.
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Detailed procedures for conducting a compliance evaluation
inspection are contained in the compliance Evaluation Inspection
Manual, EPA, Office of Water Enforcement, July 1976.
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;
(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;
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(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);
(b) the sampling location specified in the permit is
adequate for the collection of a representative 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.
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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 W2<» hour composite sample" aliquots
must be taken in a manner and at a frequency such that the
resulting composite sample is representative of the actual
discharge during the 21 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 21 hour period
or operating day composite.
E. Determining Compliance With Effluent Limitations
The following paragraphs describe sampling and measurement
procedures that are related to effluent limitations defined by
the permit* The majority of compliance sampling inspections deal
only with the verification of instantaneous 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 permitteefs 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 requirements
will preclude the continuous sampling of a source for a calendar
month in all but the most demanding cases.
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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 normally 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.
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 situations, 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.
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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. 7-day average limitations
generally apply only to publicaly owned treatment works.
4. 30-Day Average Conditions Case preparation may
require samples to be taken for each operating day during the
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 treatment 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.
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 described 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.
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*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 wastewater
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 appropriate
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 containers.
5. Preservation of samples to maintain the samples1
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 complexity. There are.
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however, basic rules and precautions 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 O.U - 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.
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Quiescent areas should be avoided, if possible.
Because 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 composite 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.
-2*4-
-------
(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.
Preferable raw waste sampling points are: (1) the upflow siphon
following a comminutor (in absence of grit chamber); (2) the
upflow distribution box following 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 recirculated 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.
-25-
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(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 dye studies or past
experience indicate a homogenous discharge, 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 performed, 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.
-26-
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U. selection and Preparation of Sample containers
It is essential that the sample containers be made of
chemically resistant material and do not affect the
concentrations 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
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 NPDES permit monitoring
specifications; or
(e) corroborate with composite sample.
-27-
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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 collection 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 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
-28-
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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 composite 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.
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 manipulation should
be minized to reduce the possibility of contamination.
-30-
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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
24 hrs.
(6.43) =0.27 mgd
24
*Method is for 24-hour composite using 24 discrete samples
-31-
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FIGURE IV-1
METHOD FOR DETERMINING COMPOSITE ALIQUOT SIZE
0.5 -,
O
CO
0.4
0.35
0.3 -
0.2
0.1
Capacity of Sample
Container
0.0
I
100
200
I
300
i
400
i
500
SAMPLE SIZE (ml)
NOTE: Maximum flow rate scaled to fit sample container size,
-32-
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D. Sample Preservation
1. General
In most cases, wastewaters contain one or more unstable
pollutants that require immediate analyses or preservation. The
rate of change of pollutant concentration is influenced by
temperature, pH, bacterial action, concentration, and
intermolecular reactions. Since treatment to fix one constituent
may affect another, preservation 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 compositing, where possible, in addition to
preservation of the composited sample before transit to the
laboratory. Procedures used to preserve samples include
refrigeration, pH adjustment, and chemical treatment.
Refrigeration is the most common method of sample preservation.
Temperature control near U°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
-33-
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discussion on the subject is presented in the section on Quality
Assurance.
2. Compliance Considerations
The list of approved test procedures in 40CFR Part 136(F.R.
Vol. HI, No. 232, Dec. 1, 1976), Guidelines Establishing Test
Procedures for Analysis of Pollutants-Amendments, 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 time.
S. 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, 40CFR Part 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.
2. Alternate Test Procedure
In instances where an effluent contains a pollutant for
which a test procedure is not specified in Table I, 40CFR Part
136.3, or the permittee desires to use an analytical method other
than the prescribed method, an application for approval of an
-34-
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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 40CFR Part 136.t»(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 information
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 identified.
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.
The information provided for each sample should include the
following:
-35-
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1. Designation and location description of sample site.
2. Name of collector (s).
3. Date and time of collection.
U. 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 identification
techniques, consult the Chain of Custody Procedure described in
Section VIII.
-36-
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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 that
day-to-day work being carried out under their supervision 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 Occupational
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
-37-
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REFERENCE - SECTION TV
1. "Methods For Chemical Analysis Of Water And Wastes, 1974,"
U.S. Environmental Protection Agency, Office of Technology
Transfer, Washington, D.C. (1974) .
2. Shelley, P.E., and Kirkpatrick, G.A., "An Assessment of Automatic
sewer Flow Samplers," U.S. Environmental Protection Agency,
EPA-600/2-75-065, Washington, D.C. (12/75).
3. "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).
4. "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) .
5. "Safety In Wastewater Works," Water Pollution Control
Federation Manual of Practice No. 1, Safety committee WPCFr
Washington, D.C. (1969).
-38-
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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 portable
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.
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(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 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 components
are discussed briefly below based on 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
-40-
-------
available information indicates that a single point intake is not
likely to be very satisfactory (see references 2 & 5). Current
assessment of the state-of-the-art suggest that a fixed nozzle
type intake located at O.U to 0.6 of the stream depth in the area
of maximum turbulence with an intake velocity equal to 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 considerations:
i. Site conditions requiring very high lifts; or
ii. Desire to collect samples integrated across the
entire flow depth.
-U1-
-------
Most mechanical units offer significant obstruction 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.
(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
-U2-
-------
will tend to pass out of solution. In so doing, the gases will
leave the 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 maintained 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 and 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.
-43-
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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
-44-
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encountered in -the field, have increased the reliability of
sampler control systems.
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 programed 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 are too limited to
recommend or reject any particular sampler; however, sampling of
raw wastewaters produced the major number of compositor
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
-U5-
-------
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,
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
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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 low temperatures.
Generally, line operated samplers are more reliable than battery-
operated models for the sampling of raw wastewaters, 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.
U. 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.
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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 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
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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 insure 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:
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 Ib) .
4. Sample collection interval adjustable from 10 min to 4
hr.
5. Capability for flow-proportional and time-composite
samples.
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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.
13. Exterior case capable of being lockedr 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 temperature range between -30 to 50°C.
16. With the exception of the intake hose, capability of
operating in a temperature range between -30 to 50°C.
17. Purge cycle before and after each collection interval
and sensing mechanism to purge in event of plugging
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during sample collection and then to collect complete
sample. i
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," OSEPA Region
VII, EPA 907/9-74-005, 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 Sampler," 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, pp495-520 (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 compliance 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;
(2) To outline what is expected of field personnel with
respect to wastewater flow measurement during NPDES
compliance monitoring activities; and
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(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 Measurements 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 continuous 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 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.
-54-
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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, differential 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. Techniques 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 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 measurements, 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
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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 measurements at several
different flowrates or by electrically, mechanically or
hydraulically inducing known flowrates. Specific techniques for
making independent flow measurements are given later in this
section.
If the discharger's flow measurement system is accurate
within + 10 percent, 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 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 inspection 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 responsibility of the discharger to supply data
supporting the accuracy and precision of the method being
employed.
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The inspector should evaluate and review calibration and
maintenance programs for the dischargers flow measurement
system. The permit normally requires that the calibration 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.
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
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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 USD!
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 purposes.
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
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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 discharger is making
instantaneous flow measurements to satisfy permit requirements,
the specific method used should be evaluated. If a primary flow
device is used, the device 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 primary
flow device should be checked by making an independent flow
measurement.
All components of continuous flow measuring systems should
be verified. The primary flow device should be 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 flow measurement utilizing
the primary flow device, obtaining the flow rate from an
appropriate hydraulic handbook and comparing this flow rate 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 an known elapsed time
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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 container of known size.
(a) Vessel Volumes
The measurement of vessel volumes to obtain flow data
is particularly applicable to batch wastewater discharges. An
accurate measurement 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
VI-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
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SPHERE
FIGURE VJ-2
EQUATIONS FOR CONTAINER VOLUMES
Total Volume
V = 1/6 irD* = 0.523598D-
Partial Volume
V = 1/3
(3/2 D-d)
RIGHT CYLINDER
H
Total Volume
V = 1/4 irD^H
Partial Volume
V = 1/4
ANY RECTANGULAR CONTAINER
W"
H
Total Volume
V = HLW
Partial Volume
V = hLW
TRIANGULAR CONTAINER
Case 1
Case 2
J
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 = irBDH
Partial Volume
V = irBDh
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FIGURE VI-2 (CONTINUED).
FRUSTUM OF A CONE
Case 1
Case 2
Total Volume
V = 7T/12 H (Dx2 + D! D2 + D22)
Partial Volume
V = n/12 h (Diz + DI d + d2)
CONE
Case 1
Case 2
Partial Volume (case 1)
V = 1/12 ir d^h
Total Volume
V = 1/12 ir DZH
Partial Volume (case 2)
V = 1/12 ir(D^H - 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
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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 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 stop watch. 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
practically be measured in a reasonably sized container. A five
gallon bucket filled to capacity, for example, would weigh 42
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pounds. Also, the filling time of the container should be
sufficiently long so that the calibrated container can be moved
in and out of 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 container, 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).
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2. Dilution Methods
Dilution methods for water and wastewater flow are based on
the color, conductivity, fluorescence, or 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.
t
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
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Ct = Concentration of injected tracer
C2 = Concentration of tracer in the stream
at downstream sampling location
C0 = 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 * qCt/C2 (2)
Where Q, q, Ct and C2 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
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• 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 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 = Ct X V/0/°°(C2-C0) dt (3)
Where: V = Volume of tracer injected
t ~ time
Qr 3* C0r Ct, C2 are as previously defined
for equation (1).
The principal advantage of this method is that sophisticated
equipment is not required to inject the tracer. The
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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 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 VI-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 fiuorometers in dilution flow measurement work. Experience
indicates that accuracies of +3 percent are achievable utilizing
the dilution method under field conditions.
3. Open Channel Flow Measurements
The measurement of wastewater flow in open channels is the
most frequently encountered situation in field investigations.
An open channel is defined as any open conduit such as 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.
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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 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 wastewater 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 instantaneous 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 and developing a
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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 description of the equipment needed and the
basic measurement methods are given in the references (1, 3, 5) .
Before attampting 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
investigator 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. Conventional rotating element current meters
are of two general types—the propeller type with the horizontal
axis as in the Neyrpic, Ott, Hoff, and Haskell meters (Figure VI-
i»), 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:
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FIGURE VI—4
OTT TYPE HORIZONTAL AXIS CURRENT METER
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(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 typer
has earned a reputation for sturdiness and
reliability under field use.
On the other handr 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. Regardless
of type, all current meters must receive the best of care during
transportation and use 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
-75-
-------
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.
•
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 depths 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).
-76-
-------
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 Simpsons 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 computing the discharge of an elementary
area by the midsection method is:
V, + V,
q =
(L2 - Lt) *
-------
The formula for computing the discharge for each pair of
elementary areas by Simpson's parabolic rule is:
Where
V +4V, +V
q' = a b c
a+4b+c
L (5)
3
a,b,and c = The water depths in feet at three consecutive
verticals,
V , V , and V * The respective mean velocities in feet per
a b c
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 and sharp crested.
-78-
-------
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/-„.
-------
(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 independent 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 (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
-80-
-------
O
c*
a.
a
a
11
Q
<
O
si
ca
-81-
-------
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 + five 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 lower flows ,rf 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.
-82-
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RECTANGULAR
2ct
TRIANGULAR OR V-NOTCH
2
-------
Q = a33 (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=
22.5 -Q = 0.497
Max Level
RECTANGULAR WEIR
CIPOLLETTI WEIR
L at least 3Hmax
X at least
max
/ '"'max
X
i
FIGURE VI-9
THREE COMMON TYPES OF SHARP CRESTED WEIRS AND THEIR EQUATIONS (15)
-84-
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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 sophisticated 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
VI-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 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 given 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
-85-
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TABLE VI-I
STANDARD CONDITIONS FOP 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).
H. 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 (2.1 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-
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X
O
o
*
OS
as
u
Cu
as
CO
-87-
-------
during the measurement period should be used. Any deviation from
standard conditions should be noted on the field sheet.
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 checlc 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-1 are not met or some other condition is encountered,
it is possible to encounter excessive approach velocities when
-88-
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using rectangular weirs. When 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 velocity of approach, and
-89-
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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 following table with the velocity of approach (V)
and head (H) and obtain the coefficient (C) from the table:
9
0.4
.5
. 6
.7
.8
.9
1.0
.1
.2
.3
.4
.5
. Q
.7
.8
.9
2.0
2.1
2.2
2.3
is
2.6
2.7
Z8
Z9
10
A
a 0025
.1X139
.0050
.007(1
.0099
.0126
.0155
.0188
.0224
.0263
.0305
.0350
.0398
.0449
.0504
.0561
.0622
.0686
.0752
.0822
.0895
.0972
.1051
.1133
.1219
.1307
.1399
AV»
0.0002
.0003
.0305
.01107
.0010
.0014
.0019
.0025
.0033
.0041
.0031
.0064
.0079
.0095
.0111
.0132
.0154
.0179
.0206
.0235
.0708
.0303
.0340
.0381
.0426
.0472
.0524
0.2
1.014
1.027
1.037
.050
.064
.082
.098
.122
.141
.163
.186
.208
.225
. 254
!277
.308
.335
.363
.391
.420
.449
.480
.511
.542
.573
.606
.637
1
0.4
1.007
1.013
.019
.026
.033
.042
.051
.052
.072
.084
.096
.109
.122
.135
.149
.165
.181
.197
.213
.231
.248
.266
.285
.303
.322
.341
.361
0.6
1.004
.009
.013
.017
.022
.029
.034
.041
.049
.057
.036
.075
.1)84
.093
.104
.115
.126
.137
.149
.161
.176
.187
.200
.213
.228
.242
.256
0.8
1.004
1.006
1.009
1.013
1. 016
.021
1.027
.1)31
.037
.043
.050
1.057
.065
.071
.080
.U89
.097
.106
.118
.124
.134
.145
.155
!l78
.189
.199
1.0
1.004
.006
.OU8
.011
.014
.018
.022
.026
.031
.036
.041
.047
.052
.059
.065
.072
.079
.087
.094
.102
.110
.119
.128
.137
.146
.155
..165
1
1.5
.002
.004
.005
.007
.009
.012
.015
.017
.021
.02*
.028
.032
.035
.040
.045
.049
.055
.060
.065
.071
.077
.083
.088
.095
.100
.108
.115
If
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
.063
.073
.078
.083
.088
2.5
1.002
.002
.003
.004
.006
.007
.009
.011
.013
.015
.017
.019
.022
.025
.027
.030
.034
.037
.039
.044
.047
.051
.0.15
.059
.063
.067
.072
3.0
.001
.002
.003
.004
.005
.006
.007
.009
.011
.012
.014
.016
.018
.021
.023
.026
.028
.031
.034
.037
.040
.043
.046
.050
.053
.057
.061
1
3.5
.001
.002
.002
.003
.004
.005
.000
.008
.009
.011
.012
.014
.OIA
.018
.020
.022
.02$
.027
.029
.032
.034
.037
.040
.043
.048
.049
.053
4.0
1.001
.001
.002
.003
.0113
.005
.005
.007
.008
.009
.011
.012
.014
.016
.017
.019
.02'
.024
.023
.028
.030
.033
.035
.038
.041
.043
.044
1
5.0
1.001
.001
.002
.002
.003
.004
.005
.006
.007
.008
.010
.011
.012
.014
.016
.017
.019
.021
.023
.025
.027
.029
.032
.034
.03fl
.039
.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-
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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
i
section, and diverging section, as shown in Figure VI-11. The
size of the flume is determined by the width of the throat
section. M.1 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 * 1/6U
inch for the throat width and 4- 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-
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NOTE-' 7.6cm (3in) TO 2.4m (8ft) FLUMES HAVE
ROUNDED APPROACH WINGWALUS
L
— M
FLOW
i! !!-
, ii ii
ii ii
,
1 it H LEVEL FLOOR
CREST
^
, SUBMERGED
l| FLOW
** *"^i-| "I eate n ntti
FREE FLOW
ANGLE
SECTION L-L
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.
0 Width of upstream end of flume.
E Depth of flume.
F Length of throat.
6 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.
M Length of approach floor.
P Width between ends of curved wing walls.
X Horizontal distance to Hfa 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 FOR PARSHALL FLUME (10)
-92-
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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 description of
submergence corrections is given in the USDI Water Measurement
Manual (1).
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 (JSDI 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 level, framing square and tape. The flume
-93-
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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 gage 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 Mea surement 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:
• Poor entrance and exit hydraulics that cause poor flow
distribution or submergence,
• Improper installation, out of level, throat sidewalls
not vertical, improper throat dimensions, or
• Improper location of head measuring points.
(ii) Palmer-Bowlus Flumes
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
in use and are shown in Figure VI-12. These flumes are being
increasingly used as primary flow devices for measuring flow in
circular conduits. Their principal advantage lies in simplicity
-94-
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End VMM
Longitudinal mid sections
Vertical
Horizontal
(0
*• ' ~ ~ ' ' "
(d)
FIGURE VI - 12
VARIOUS CROSS - SECTIONAL SHAPES OF PALMER-
BOWLUS FLUMES (15)
-95-
-------
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 bottom 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
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 designed 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 between the
flowrate and head is linear. These nozzles require a length of
-96-
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straight conduit immediately upstream from the nozzle, and the
slope of the conduit must be within the limits of the nozzle
calibration specifications. The profile of a parabolic and a
Kennison type open flow nozzle is shown in Figure VI-13.
Open flow nozzles are factory calibrated and are ordinarily
supplied as part of a flow measurement 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 (10).
(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 that reach, to estimate the flowrate of
an open channel. The flowrate is estimated from the Manning
formula:
Q = 1.486/n AR2/3S1/2 (7)
Where
Q = discharge in cfs
A = average area of the wetted channel
cross-section in square feet
R = average hydraulic radius of the wetted
channel in feet. (Average cross-
sectional area divided by
the average wetted perimeter.)
s = slope of the water surface, and
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H
a. Linear (Kennison) Nozzle Profile (Q * H)
b. Parabolic Nozzle Profile (Q « H2)
FIGURE VI-13
OPEN CHANNEL FLOW NOZZLE PROFILES (10)
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n = a roughness factor depending on
the character of the channel lining.
A long straight section of channel should be used for this
estimation technique. Values of n may be obtained from hydraulic
handbooks (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 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).
**• Closed Conduit Flow Me a sure me nt s
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
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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 independent flow measurement at an
acceptable location. The constant injection dilution technique,
or the velocity area method, both of which were described earlier
in this section, would be acceptable for this purpose. Another
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
references 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 differential is
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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 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 concentrations 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) . "Their
principle of operation is similar to that of the Venturi, and
they will not be discussed.
(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
-101-
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\n
M
si
-102-
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opening facing downstream. Pressure measuring taps are located
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 UO 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 and orifice meters. Like orifice
meters, they are sensitive to upstream disturbances and 20 or
more pipe diameters of straight pipe are required upstream from
-103-
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-104-
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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 electromagnetic 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 +, 1 percent 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 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
-105-
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INSULATING
LINER
ELECTRODE
ASSEMBLY
STEEL METER
BODY
MAGNET COILS
POTTING COMPOUND
FIGURE VI-16
ELECTROMAGNETIC FLOW METER (15)
-106-
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of the water in the conduit. This time lag is proportional to
the velocity, and hence 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 available. All of these
methods, whether theoretically or empirically derived, have in
common the measurement of the issuing stream coordinates (Figure
VT-17) in the vertical and horizontal directions. It should be
emphasized that all of these methods are estimates—none of them
is accurate enough for NPDES compliance purposes.
The California pipe method (Figure VI-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
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) »••« d2.*« (8)
Where
Q = flowrate in cfs
d = diameter of pipe in feet
-107-
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ZERO SLOPE
i
i
-6d OR GREATER
a. CALIFORNIA PIPE METHOD
MID-DEPTH
b. PURDUE METHODS
TO CENTER OF
STREAM
FIGURE VI-17
TRAJECTORY METHODS (10)
-108-
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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)0.s x (9)
Where
Q = flowrate in cfs
A = cross-sectional area of the issuing stream
X 5 Y = horizontal and vertical trajectory coordinates
measured as shown in Figure VI-17
(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.
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(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 consumptive 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.
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REFERENCES - SECTION VI
1. "Water Measurement Manual", second edition, revised. United
States Department of Interior, Bureau of Reclamation, 197U.
Available from the U.S. Government Printing Office,
Washington, D.C. 20102.
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 9U043.
5. "Discharge Measurements at Gaging Stations", Hydraulic
Measurement and Computation, Book I, Chapter 11, United
Stated 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 19103.
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.
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13. "Fluid Meters—Their Theory and Application", Sixth Edition,
1971, American Society of Mechanical Engineers, New York,
N.Y.
11. "Field Manual for Research in Agricultural Hydrology",
Agricultural Handbook No. 22Hr 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
i
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
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should be recognized, however, that many of these elements are
already an integral part of the compliance monitoring program,
but may not be specifically 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 responsibilities and document the
unit's operating procedures.
C. Elements of a Quality Assurance Plan
Elements of a recommended quality assurance program,
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 equipment installed
-115-
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at the site. If automatic sampling equipment is not
installed at the site, collect duplicate grab samples.
This will provide a proficiency check for precision.
2. Split Samples
Aliquots of the collected sample may be given to the
permittee, if requested, as a check on the 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 performance samples will
aid to identify discrepancies in the permittee's
analytical techniques and procedures.
3. Spiked Samples
Known amounts of a particular constituent should be
added to an actual sample or blanks of deionized 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.
4. Sample Preservative Blanks
Acid and other chemical preservatives can become
contaminated after a period of use in the field. The
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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.
5. Precision, Accuracy, and Control charts
A minimum of seven sets each cf comparative data for
duplicates, spikes, split samples and blanks should be
collected to define acceptable estimates of precision
and accuracy criteria for data validation. See EPA1 s
"Handbook for Analytical Quality Control in Water and
Wastewater," (2) or W.J. Youden's "Statistical
Techniques for Collaborative Tests," (U) for
discussions of precision, accuracy, and quality
control charts and their calculations.
E. Quality Assurance Procedures for Field Analysis & Equipment
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.
-117-
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written calibration procedures should be provided for all
measuring and test equipment. A procedure should:
1. Specify where the procedure is applicable, e.g.
free residual chlorine by amperometric titration
at power plant cooling water effluents.
2. Provide a brief description of the calibration
procedure, a copy of the manufacturer's
instructions 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.
Field equipment should be labeled to indicate the
calibration date, when calibration expires and when maintenance
is due.
Table VII-1 summarizes quality assurance procedures for
field analyses generally conducted during ...*_ES compliance
sampling inspections.
-118-
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-123-
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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 processes; 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 aluminium 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 2U hour.
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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 vdth 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 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 parameters
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.
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(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) ^henolics and Cyanides
Simple phenolic compounds and free cyanide may
be significantly degrade if not preserved at the time of
sample collection. If the sample contains residual
chlorine, it is also necessary to dechlorinated the sample
prior to preservation, standard Methods (6) recommends the-
use of ferrous sulfate as a dechlorination agent for
phenolics and ascorbicr acid for cyanide.
(d) Sulfide and Sulfite
Table 2 of EPA*s "Methods For Chemical Analysis Of
Water 8 Wastes" (7) lists cooling to 4°c as the preservative
for sulfide, while there is no acceptable preservative
listed for sulfite and the sample must be analyzed at the
time of collection.
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REFERENCES - SECTION VII
1. "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).
2. "Handbook For Analytical Quality Control In Water And
Wastewater Laboratories", U.S. Environmental Protection
Agency, Technology Transfer, Washington, D.C. (6/72).
3. "Quality Assurance Handbook For Air Pollution Measurement
Systems", Vol. I. Principles, U.S. Environmental Protection
Agency, office of Research and Development, Environmental
Monitoring 5 Support Lab, Research Triangle Park, N.C., EPA-
600/9-76-005, (3/76).
4. Youden, W.J., "Statistical Techniques For Collaborative
Tests", Assn. of official Analytical Chemists, Washington,
D.C. (1973).
5. 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.
6. Standard Methods For The Examination Of Water And
Wastewater, 14th Ed., APHA, Washington, D.C. (1976).
7. "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. Introduct ion
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 samples 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, transferred, 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; or
2. It is in one's view, after being in one's physical
possession, or
3. It is in one's physical possession and then locked up
so that no one can tamper with it; or
4. It is kept in a secured area, restricted to authorized
personnel only.
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B. Survey Planning and Preparation
The evidence gathering portion of a survey should be
characterized by the conditions stipulated in the permit or 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. Guidelines 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;
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(c) source of sample (including name, location
6 sample type) ;
(d) preservative used;
(e) analyses required;
(f) name of collector (s) ;
(g) pertinent field data (pH, DO, Cl residual,
etc.);
(h) serial numbers on seals and transportation
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 collector(s1)
initial (s1). 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 analysis request form as
needed. The transportation case should then be sealed or
labeled. All records should be filled out legibly in pen.
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EPA,
Station No.
Date
Time
Sequence No.
Station Location
Grab
Comp,
.BOD
.Solids
.COD
.Nutrients
.Metals
.Oil and
_D.O.
_Bact.
.Other
Samplers:
GENERAL CHEMISTRY
Official Sample No.
o
ui
ui
ui
3
O.
Dote and Time
Sampler's Signature
OTHER PARAMETERS:
MICROBIOLOGY
Office
Z Official Sample No.
S 01
O U
in ot
at o
4 8
wi Daf« and Time
Sampler's Signature
PESTICIDES, ORGANICS
Office
Official Sample No.
IU
U
O
Date and Time
Sampler's Signature
Office
Remarks / Preservative:
PH Acid
Cond Alk
TS S04
DS CI
SS F
BOD2 Cr. +6
Turb BODj
Color
Tot. Colif.
Fecal Colif.
Fecal Strep.
Salmonella
Pesticides
PCB's:
Organics:
FIGURE VIII-1
SAMPLE IDENTIFICATION TAG EXAMPLES
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y
The use of the locked and sealed chests will eliminate the
need for close control of individual sample containers.
However, there will undoubtedly be occasions when the use of
a chest is inconvenient. On those occasions, the sampler
should place a seal around the cap of the individual sample
container which would indicate tampering if removed.
H. 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.
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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 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 responsibility includes filling out, dating, and signing the
appropriate portion of the Chain of Custody Record. A Chain of
Custody Record format containing the necessary procedural elements
is illustrated in Figure VIII-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
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FIGURE VIII-2
CHAIN Of CUSTODY RECORD
SURVEY
STATION
NUMBER
STATION LOCATION
DATE
Relinquished by: isignaivn)
Relinquished by: (signature)
Relinquished by: fSignoh/.-.j
Relinquished by: (signatun)
Dispatched by: (signotun)
Date,
TIME
SAMPLERS: is^^,.)
SAMPLE TYPE
Wot.r
Comp.
Grab.
Air
SEQ.
NO.
NO. OF
CONTAINERS
ANALYSIS
REQUIRED
Received by: (signoiuni
Received by: (signotvn)
Received by: (signaiun)
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 File
-134-
GPO 83 I -484
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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.
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 recommended 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.
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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.
5. Distribution of samples to the section chiefs who are
responsible for the laboratory performing the analyses 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.
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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 previously 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 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
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followed in the collection and analysis 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 other law enforcement personnel
are not included under the business record exceptions to the
"Hearsay Rule" previously cited (see Rule 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
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
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of preparation indicate lack of trustworthiness," and the caveat
under the public records exception reads "unless the sources of
information or other circumstances indicate lack of
trustworthiness."
Thus, whether or not the inspector aV *-ipates that his or
her compliance inspection report will be introduced
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