&EPA
   United States
   Environmental Protection
   Agency
   Solutions to Analytical Chemistry
   Problems with Clean Water Act Methods
   March 2007
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             Solutions to Analytical Chemistry Problems
                   with Clean Water Act Methods
                              Prepared by

                        Analytical Methods Staff
                    Engineering and Analysis Division
                      Office of Science Technology
                            Office of Water
                  U. S. Environmental Protection Agency
                           Washington, DC
                          EPA821-R-07-002
                              March 2007
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                                         Disclaimer
       This technical document recommends ways to document and resolve analytical chemistry
problems encountered in the analysis of wastewater samples. This advice is not a substitute for the Clean
Water Act (CWA) or EPA regulations, nor is this document a regulation. The advice in this document
does not alter any otherwise applicable statutory or regulatory requirements and does not, and may not,
impose legally binding requirements on EPA, States, Tribes, or the regulated community.

       Our advice may not apply to your case-specific circumstances.  EPA, State and other decision
makers retain the discretion to adopt other approaches on a case-by-case basis where appropriate, or when
additional information is available to them. It is recommended that commercial laboratories convey
analytical problems to their customers and permittees communicate problems to their regulatory authority
and regional EPA water program offices.

       Staff of the Engineering and Analytical Support Branch within the Engineering and Analysis
Division of the EPA Office of Water have reviewed this document. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
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                                         Foreword
       "Solutions to Analytical Chemistry Problems with Clean Water Act Methods" is an update of the
document titled "Guidance on Evaluation, Resolution, and Documentation of Analytical Problems
Associated with Compliance Monitoring", which was published in 1993.  The 1993 document has been
referred to as the APumpkin Book@ because of its pumpkin-colored cover. The material and technical
advice in the Pumpkin Book, and this document are based on questions and situations directed to EPA's
Clean Water Act chemists by the EPA regions, state agencies and other users of our methods.  The
questions and situations discussed in this document concern analytical challenges encountered in the
conduct of compliance monitoring under the Clean Water Act (CWA) for chemical pollutants.

       The purpose of this document is to recommend ways to document the existence of a matrix or
analytical problem with  a CWA sample analysis, and mitigate these problems.

       This document is organized as follows:

       Chapter 1   Introduction
       Chapter 2   Sampling Requirements
       Chapter 3   Flexibility to Modify an Analytical Method
       Chapter 4   Data Required to Document Matrix Interference
       Chapter 5   Case Histories of Reports of Matrix Interferences
       Chapter 6   Solutions to Matrix Interference Problems
       Chapter 7   Review of Data from Analysis of Samples
       Chapter 8   When a Matrix Interference Is Demonstrated
       Chapter 9   Sources of Additional Help

       EPA's Engineering and Analysis Division (EAD) is solely responsible for the content of this
document. Comments and suggestions should be directed to:

       CWA Analytical Methods Staff
       Engineering and Analysis Division (4303T)
       Office of Science and Technology
       U.S. Environmental Protection Agency
       1200 Pennsylvania Avenue, N.W.
       Washington, DC 20460
       E-mail:  OSTCWAMethods@epa.gov
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                                 Table of Contents
Disclaimer	iii
Foreword	iv
Chapter 1 Introduction	1
  Pollutants Regulated Under the Clean Water Act	1
  Analytical Methods Approved Under the Clean Water Act	1
  Scope of This Document	2
Chapter 2 Sampling Requirements	4
  Sample Collection	4
    NPDES Sampling Requirements	4
    Pretreatment Program Sampling Requirements	5
    Trace Metals Sampling Guidance	5
    Compositing Samples for Volatiles	5
  Sample Preservation and Holding Times	5
Chapter 3 Flexibility to Modify an Analytical Method                                  7
  Balancing Flexibility and Performance	7
  EPA's Alternate Test Procedure (ATP) Program	7
  Flexibility in the EPA Methods	8
  Demonstrating Equivalency of a Method Modification	9
    Initial Demonstration of Method Performance	9
    Application of a Method Modification to a Sample Matrix	10
    Suggested QC Acceptance Criteria for Criteria Not Stated in Approved Methods	10
  Intractable Samples	10
Chapter 4 How to Document Matrix Interference	11
Chapter 5 Reports of Matrix Interferences	15
  Case Histories	16
Chapter 6 Solutions to Matrix Interferences	20
  Solving Matrix Problems	20
  Solutions Applicable to Nearly All Analytes	20
    Selective Reaction and/or Removal of the Interferent	20
    Method of Standard Additions (MSA)	20
  Solutions Applicable to Classical Pollutants	21
    Oil and Grease	21
    Cyanide	21
  Solutions Applicable to Metals Pollutants	24
    Clean Room	24
    General Matrix Interferences	25
    Chromium VI	25
    Mercury	25
  Solutions Applicable to Organic Pollutants	25
    Volatiles	25
    Semivolatiles	26
  Determination of Phenol as a Specific Example	27
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Chapter 7 Review of Data from Analysis of Samples                                  29
  Standardized Quality Control	29
  Provision of QC Data	30
  Review of Data from the 600- and 1600-Series Methods	30
Chapter 8 When a Matrix Interference Is Demonstrated	41
  Poor Recovery or Precision of the Matrix Spikes	41
  Inability to Meet the Method Detection Limit (MDL)	41
  Allowance for a Matrix Interference	42
Chapter 9 Sources of Additonal Help and Information                                43
  Web Sites	43
  Method Indices	43
  Office of Water CD-ROMs	43
  Water Docket	44
  Federal Register	44
  Code of Federal Regulations	44
  Approval of an Alternate Test Procedure	45
  Sources for Supporting Documents	46
Appendices
          A) Text of October 26, 1984 Preamble,  pp. 7-11
          B) Text of Preamble to March 12, 2007 Methods Update Rule (Note flexibility only
             applies to 40 CFR Part 136 methods)
          C) Recommended Approved Modifications to EPA Method 625
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                                                                                   Chapter 1
Introduction
Pollutants Regulated Under the Clean Water Act

       The Federal Water Pollution Control Act (FWPCA) Amendments of 1972, later amended as the
Clean Water Act (CWA), classifies each pollutant as a "conventional pollutant," "toxic pollutant," or
"non-conventional pollutant." The five "conventional pollutants" are codified at Title 40, Part 401.16 of
the Code of Federal Regulations (40 CFR Part 401.16).  (For information on how to access the CFR, see
Chapter 9 of this document).  The five conventional pollutants are:

$  biological oxygen demand (BOD)
$  total suspended solids (TSS)
$  fecal coliform
$  pH
$  oil and grease

       There are 65 "toxic pollutants" listed at 40 CFR Part 401.15 and this group of pollutants has been
further refined to a list of 126 "priority pollutants" at 40 CFR Part 423, Appendix A.  The priority
pollutants can be subdivided into:

$  cyanide
$  asbestos
$   13 metals pollutants
$  25 pesticide/PCB pollutants
$  86 non-pesticide/non-PCB organic pollutants

       By definition, all pollutants other than "conventional pollutants" or "toxic pollutants" are "non-
conventional pollutants." Examples of non-conventional pollutants are:

$  toxicity (acute or chronic)
$  chemical oxygen demand (COD)
$  metals and organic compounds not on the priority pollutant list
$  radioactivity
$  color

Analytical Methods Approved Under the Clean Water Act

       CWA Section 304(h) requires EPA to publish test procedures (analytical methods) appropriate for
the measurement of pollutants.  These methods are commonly known as the "304(h) methods".

       CWA Section 402 establishes a National  Pollutant Discharge Elimination System (NPDES) to
control the discharge of pollutants to surface waters of the U.S. NPDES is implemented through
regulations at 40 CFR Parts 100 - 135 and the effluent guidelines and pretreatment regulations at 40 CFR
Parts 400 - 500. The CWA prohibits any discharger of a pollutant except in compliance with the Act,
including Section 402.  EPA regulations implementing Section 402 generally require facilities that
discharge wastewater directly to surface waters of the U.S. to obtain an NPDES permit. The regulations
refer to the facility or person that discharges pollutants as "discharger,"  "permittee," or "applicant".


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Facilities that discharge wastewater to a publicly owned treatment works (POTW) are known as indirect
dischargers and subject to pretreatment requirements. EPA's pretreatment program regulations are found
at 40 CFR Part 403.  The term "discharger" will be used in this document to mean a discharger, permittee,
applicant, or other entity regulated under EPA's wastewater regulations.  Under the regulations, each
discharger is required to monitor its effluent for compliance with any and all relevant Federal and State
discharge limitations, and use the 304(h) methods to demonstrate compliance with NPDES and
pretreatment program limitations. Regulatory authorities have accepted primacy for implementing the
Clean Water Act and with that responsibility have  authority to be more restrictive than the federal
regulations.

       The 304(h) methods are published or incorporated by reference at 40 CFR Part 136 or 40 CFR
Parts 405 - 500 and are commonly known as the "Part 136 methods." For many analytes, these methods
include methods published by EPA, by the U.S. Geological Survey (USGS), by voluntary consensus
standards bodies such as ASTM International (formerly known as the American Society for Testing and
Materials International), and by manufacturers of instruments and testing devices.

       The Part 136 methods include methods approved for use in all of EPA's wastewater and ambient
water programs (e.g., methods for general use).  Methods approved for general use  are listed in tables at
40 CFR Part 136.3(a), including:

$   Table IA - List of approved biological methods
$   Table IB - List of approved inorganic test procedures
$   Table 1C - List of approved test procedures for non-pesticide organic compounds
$   Table ID - List of approved test procedures for pesticides
$   Table IE - List of approved radiological test procedures
$   Table IF - List of approved methods for pharmaceutical pollutants
$   Table IG - Test methods  for pesticide active ingredients
$   Table IH - List of approved microbiological methods for ambient water

       Methods approved for use in a single industrial category are published in tables at 40 CFR Part
136 or at 40 CFR Parts 405 -  500. If the methods are not published in tables at 40 CFR Part 136, they are
not approved for general use, and may only be used for discharges from the  industrial category for which
they are approved. These special category methods are for uses when the nature  of the discharge from a
particular industry poses unique analytical challenges, or when the pollutants to be  regulated are specific
to that industry. For example, methods approved for use in the Pharmaceuticals industrial category are
listed in Table IF at 40 CFR  Part 136, while methods approved for use in the Pesticides Manufacturing
industrial category are listed in Table 7 at 40 CFR Part 455.

       At present, there are 75 pollutants  listed in Table IB, including common inorganic anions, metals,
and many of the conventional pollutants named above. To simplify discussions in the remainder of this
document, the term "classical pollutant" will refer  to all the pollutants listed in Table  IB, except the
metals (i.e., the  conventional  pollutants listed in Table IB and all other non-metals in  the table).

Scope of This Document

       We presume that you have knowledge of, and access to the relevant Part 136  analytical methods.
These methods cover a wide range of pollutants and analytical technologies. The method descriptions
range from a few pages for simple tests to lengthy  and detailed documents covering hundreds of analytes.
Many of these methods and accompanying documents are available on various CD-ROM products or at
the Office of Science and Technology (OST) web site at www.epa.gov/waterscience/methods. Methods
from other organizations are often available from those organizations for a fee (see Chapter 9.)
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       Our goal is to address a broad range of analytical problems and sample types. As a result, some
level of detail was sacrificed and some situations have not been addressed in this document. However,
the approaches to resolve matrix interferences that are described in this document may be applied to
issues not specifically addressed in this publication. States and EPA have laboratories with experts to
answer some questions regarding analytical problems.

       This document does not cover analyses of oil and grease, metals requiring the use of "clean"
sampling and analysis techniques,  whole-effluent toxicity (WET), biological (microbiological), or
radiological pollutants. EPA has provided guidance for some of these categories, including:

$  Analytical Method Guidance for EPA Method  1664A Implementation and Use (40 CFR Part 136),
   EPA 821-R-00-003, February  2000, (Oil & Grease)

$  Guidance for Implementation and Use of EPA  Method 163 IB (40 CFR Part 136), EPA 821-R-01-
   023, March 2001, (Mercury)

$  Method 1669:  Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels, EPA
   821-R-96-011, July 1996,

$  Guidance on Establishing Trace Metal Clean Rooms in Existing Facilities, EPA 821-B-95-001,
   January, 1996,

$  Trace Metal Cleanroom, prepared by the Research Triangle Institute, RTI/6302/04/02 F,

$  Evaluating Field Techniques for Collecting Effluent Samples for Trace Metals Analysis, EPA-821 -R-
   98-008, June 1998,

$  Guidance on the Documentation and Evaluation of Trace Metals Data Collected for Clean Water Act
   Compliance Monitoring, EPA  821-B-96-004, July, 1996,

$  Water Quality-Based Permitting for Trace Metals Fact Sheet, April 1996 (no EPA number),

$  Method Guidance and Recommendations for Whole Effluent Toxicity (WET) Testing (40 CFR Part
   136)  (EPA 821-B-00-004, July 2000; the "WET Methods guidance"), and

$  Understanding and Accounting for Method Variability in Whole Effluent Toxicity Applications Under
   the National Pollutant Discharge Elimination System Program (June, 2000).

       Guidance for microbiological methods can be found  in Section 9000 of Standard Methods for
Examination of Water and Wastewater.

       Guidance for radiochemistry measurements can be found in the Multi-Agency Radiological
Laboratory Analytical Protocols Manual (EPA 402-B-04-001A to C (in three volumes); the "MARLAP
Manual") published in Volume 69, page 77228 of the Federal Register (69 FR 77228) on December 27,
2004.

       The documents listed above are available from the sources in Chapter 9.
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                                                                                   Chapter 2
Sampling Requirements

Sample Collection

       The collection of the sample can have significant effects on the overall analytical process. In
addition, to ensure some degree of consistency and representativeness, EPA requires that a sample for
compliance monitoring be collected in a prescribed fashion. Sampling requirements for the NPDES and
pretreatment programs are spelled out in Parts 122 and 403 of Title 40 of the CFR.

       Even when the analyst or other laboratory personnel are not responsible for collecting the sample,
it is important for them to understand EPA's sampling requirements in order to provide acceptable and
cost-effective analytical results (e.g., there may be little point in analyzing an improperly collected sample
if the results may not be used for compliance monitoring).  Ideally, laboratory personnel will have ready
access to the relevant sections of the CFR.  However, recognizing that this is not always practical, a
reasonable level of detail is provided below.

NPDES Sampling Requirements

       The sampling requirements under NPDES are given at 40 CFR Part 122, as part of the
requirements for applying for an NPDES discharge permit.  The requirements are broken out by type of
industry and discharge. For example:

$   40 CFR Part 122.21(g)(7) provides the requirements for sampling existing manufacturing, commercial,
    mining, and silvicultural dischargers,

$   40 CFR Part 122.21(h)(4)(i) provides the requirements for sampling manufacturing, commercial,
    mining and silvicultural facilities that discharge only non-process wastewater.

$   40 CFR Part 122.21(j)(4)(viii) provides the  requirements for sampling new and existing publicly
    owned treatment works (POTWs).

Although many of the other permit application requirements differ among these types of dischargers, they
have in common the requirements for collecting grab samples for certain pollutants and how composite
samples for other pollutants must be collected, namely:

       "Grab  samples must be used for pH, temperature, cyanide, total phenols, residual
       chlorine, oil and grease, fecal coliform, fecal streptococcus, E.  coli, Enterococci, and
       volatile organics, unless specified otherwise at 40 CFR Part 136. For all other pollutants,
       a 24-hour composite sample,  using a minimum of four (4) grab samples, must be used
       unless  specified otherwise at 40 CFR Part 136. "

       Providing acceptable data for NPDES compliance samples requires that the sample be collected in
the required fashion. Therefore, laboratory personnel should recognize that grab samples are required for
the 12 pollutants listed above and 24-hour composite samples are to be used for all other pollutants
monitored under an NPDES permit.
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Pretreatment Program Sampling Requirements

       Sampling requirements for the pretreatment program are found at 40 CFR Part 403, specifically at
40 CFR Part 403.7(b)(2)(iii), 40 CFR Part 403(b)(2)(iv), 40 CFR Part 403.12(b)(5)(iii), and 40 CFR Part
403, Appendix E. Similar to NPDES program requirements, these sections list the pollutants for which
grab sampling is required. Appendix E to Part 403 gives details on the collection of grab and composite
samples for the pretreatment program.

Trace Metals Sampling Guidance

       Sampling for trace metals presents a unique challenge to avoid sample contamination. EPA has
guidelines for sampling ambient water for trace metals (See Chapter 9).

Compositing Samples for Volatiles

       As specified in 40 CR 122.21 and noted above, samples to be analyzed for volatile organics must
be collected as grab samples and not with an automated compositing device. This stands to reason, since
the compositing equipment is at least partially open to the atmosphere and volatile contaminants could be
lost from the equipment during the lengthy sample collection period. While using grab samples for
volatiles preserves the integrity of the individual sample, it raises the overall analytical cost when multiple
samples of the same discharge have to be collected and analyzed.

       EPA has studied the differences between the analysis of individual grab samples, and analysis of a
composite sample prepared at the laboratory from grab samples collected in the field. The study was not
conclusive so the EPA has not recommended VOA compositing procedures.

Sample Preservation and Holding Times

       Sample preservation and holding time requirements are listed by analyte or analyte group in Table
II at 40 CFR Part 136, and are  detailed in the analytical methods. The information listed in Table II is
often generic, as it applies to a large group of analytes, e.g., metals. The information in the methods is
often more specific because  preservation and holding times generally are studied as a part of method
development. However, in some cases, there are footnotes in the table for specific analytes that provide
additional information or requirements that are critical to compliance monitoring.  The footnotes to Table
II at 40 CFR Part 136 often are quite detailed and address, but are not limited to:

•   Sample containers,
•   Sample holding times,
•   Sample preservation, including instances in which the sample must be held for a shorter time than the
       stated holding time if the shorter time is necessary to maintain sample stability,
•   Department of Transportation (DOT) shipping requirements,
•   Interferences specific to certain parameters; e.g., interferences specific to cyanide.

       Because the footnotes  may change with each update to Part 136, the current version of the CFR
should be consulted for the latest information. The order of precedence for the sample preservation and
holding time requirements is:

$   Table II with footnotes,
$   The individual method
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Conflicts between these requirements can arise, particularly if new methods are brought into use and the
generic requirements in Table II are inadvertently not revised. If you discover a potential conflict between
the holding time requirements in Table II and in a method, please notify the Engineering and Analysis
Division at the e-mail address given in  Chapter 9, and your permitting authority or your client.
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                                                                                   Chapter 3
Flexibility to Modify an Analytical Method
Balancing Flexibility and Performance

       EPA provides analysts with the flexibility to deal with interferences, or otherwise improve method
performance.  This flexibility dates back to the inception of EPA's wastewater method approval program.
In December 1979, when EPA proposed the majority of the test methods for organic pollutants, the
Agency requested comments on the relationship between flexibility in methods and the approach to quality
control. After reviewing those comments, EPA decided to allow limited flexibility in both the sample
preparation and analysis portions of its methods. The major flexibility options are discussed in the
preamble of the October 26, 1984 final rule promulgating the organic methods at 40 CFR Part 136. That
discussion, which is reproduced in the appendix of this document, specifically cites the ability to change
chromatographic conditions such as column packings and detectors and  changes to sample concentration
procedures. The  preamble also states that:

       "However, the primary objective underlying this flexibility is to  enhance precision and
       accuracy for each analysis.  Flexibility should not be permitted  if the altered technique
       would be less precise or less accurate than the standard approved analytical method.
       Thus, a corollary of increased flexibility was an increased need for a rigorous and
       unambiguous quality control procedure. "

All of the EPA methods approved at 40 CFR 136 since 1984 have incorporated a rigorous and
standardized approach to quality control. If unsure, the permittee should contact the regulatory authority
with questions and guidance on what constitutes allowable flexibility.

EPA's Alternate Test Procedure (ATP) Program

       In addition to balancing limited flexibility in the methods against a more rigorous quality control
procedure, EPA included a process for obtaining approval of an alternate test procedure (ATP) on a
nationwide basis  or on a site- or discharge-specific basis (40 CFR Parts  136.4 and 136.5).

       The ATP program is intended to encourage  development of new or improved analytical methods
and to give analysts options  for resolving analytical problems that may be unique to specific wastewaters.
If you want to use a method other than those specified at 40 CFR Partl36, you should apply to the
Engineering and  Analysis Division for approval of a nationwide ATP, or to the State or Regional EPA
authority for approval of a limited-use ATP  e.g. an approval for method  changes from those listed in 40
CFR Part 136 which are granted to a specific site/facility as opposed to all permittees.

       As part of the ATP program, EPA developed protocols to assist  applicants seeking EPA approval
of alternate test procedures or new methods  for use in monitoring wastewater, ambient water, and drinking
water.  There are protocols for organic and inorganic contaminants, and  microbiological contaminants. The
changes instituted in 1999 made the process simpler. These protocols are available at
www.epa.gov/waterscience/methods. (EPA 821-B-98-002 Protocol for  EPA Approval of Alternate Test
Procedures for Organic  and Inorganic Analytes in Wastewater and Drinking Water March 1999)
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Flexibility in the EPA Methods

       As noted above, flexibility is permitted in many EPA analytical methods.  For example, the
methods for organic pollutants published at 40 CFR Part 136, Appendix A note that the analyst is
permitted to "improve separations or lower the costs of analyses" provided that the results obtained are as
or more accurate than the results obtained using the unmodified method. Recent EPA methods for other
analytes may also include specific allowances for flexibility.

       The flexibility to make changes in approved methods without prior approval from EPA is
described at 40 CFR Part 136.6. The full text of Part 136.6 is reproduced in the appendix of this
document. It is strongly recommended that analysts consult the full text of 40 CFR Part 136.6 before
undertaking method modifications. Briefly, Part 136.6 (b)(l) describes allowable method modifications,
including:

$   Changes between automated and manual discrete instrumentation,
$   Changes between automated and manual sample preparations such as digestions, distillations, and
    extractions (provided that the temperatures  and/or exposure times are maintain same as manual method
    to achieve same performance),
$   Changes in the calibration range (provided that the modified range covers any relevant regulatory
    limit),
$   Changes in equipment such as using similar equipment from a vendor other than that mentioned in the
    method,
$   Changes in equipment operating parameters such as minor changes in the monitoring wavelength of a
    colorimeter or modifying the temperature program for a specific GC column,
$   Changes to chromatographic columns, including the use of a capillary (open tubular) GC column with
    EPA Methods 601-613, 624, 625, and  1624B, and
$   Increases in purge-and-trap sample volumes,
$   Adjusting sample sizes or changing extraction  solvents to optimize method performance in meeting
    regulatory requirements.

Such changes are only allowed if the modified method produces equivalent performance for the analyte(s)
of interest, and the equivalent performance is documented. Part 136.6 provides detailed requirements for
both the demonstration and documentation of the performance  of a modified method.

Note:  The allowance for modifications does not apply to a method for a method-defined analyte or a
       change that would result in measurement of a different form or species of an analyte (e.g., a
       change to a metals digestion or total cyanide distillation).  It also does not apply to changes in
       sample preservation and/or holding time.

       In addition to the flexibility provided by the ATP program and in the analytical methods, EPA
suggests that regulatory authorities allow flexibility in the spirit of method improvement.  Because it is not
possible to address all matrix interferences in all wastewaters, it may be necessary to tailor a method
modification to a specific matrix interference problem. For example, the solid-phase and continuous
liquid/liquid extraction have been shown to be effective in reducing emulsions formed with separatory
funnel extraction, and microwave and bomb digestions have been shown to be more effective in
solubilizing some metals than mineral acid digestions. The spirit of allowing a method modification is that
the  change results in improved method performance such as accuracy  (e.g. recovery) a lower detection
limits, or better precision.
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Demonstrating Equivalency of a Method Modification

        Your objective in modifying a method should be to make it more specific for a given pollutant,
more sensitive, more accurate, or to improve the method in some other way without compromising the
performance of the method for the intended use.  Such improvements could include reducing the overall
cost of the analysis, or reducing the volumes of wastes produced by the analysis. However, some
laboratories have interpreted the provision to modify a method solely as a means of increasing the speed of
analysis, thus reducing the analysis time, or taking other "shortcuts" to reduce cost. This is not EPA's
approach.

        EPA has addressed this issue by:

        1.   providing limited flexibility within the methods, so that improvements can be made, and
        2.   requiring the analyst to demonstrate that the results produced by a modification will be equal
            or superior to results produced by the unmodified method.

The yardsticks by which this performance is to be measured are precision and recovery, but can be
extended to include detection limit, chromatographic resolution, mass spectral resolution, and other
measures of method performance.  For compliance analyses, clearly note that the method is modified and
communicate the modifications to  the regulatory authority. If in doubt contact your local regulatory
authority.

Initial Demonstration of Method Performance

        To prove the modification is appropriate, the laboratory should first perform an initial precision
and recovery test (IPR) with the unmodified method, and record the results. The initial demonstration
provides validation of the performance of a method by a specific laboratory. The procedure  is described in
detail in Section 8 or 9 of the 600-series and 1600-Series wastewater methods and also is in ASTM
International methods and other methods systems. For some methods systems, the IPR may be termed an
"initial demonstration of method performance" or "initial demonstration of capability" (IDC). A typical
test consists of an analysis of four  or more replicate volumes of reagent water, or other appropriate
reference matrix, spiked with the pollutants of interest at the concentration specified  in the method or at 5-
10 times the detection limit of the method. The final demonstration should be done in the actual
wastewater matrix of concern.

        For each analyte, the precision of analysis of the replicates, as determined by the standard
deviation or relative standard deviation (RSD) of the measurements, should be less than the standard
deviation or RSD specified in quality control (QC) acceptance criteria in the method. Similarly, for each
analyte, the  average percent recovery of the measurements should fall within the range of percent recovery
specified in the method. If either the precision or recovery test is failed, the test is repeated until the
laboratory is able to meet precision and recovery requirements.

        Include a minimum of one blank in the initial demonstration, and the concentration of the
analyte(s) in the blank should be less than the level(s) specified in the method.

        If you modify a method, repeat the initial demonstration with the modification as an integral part
of the method, until the QC acceptance criteria in the method for precision and recovery and for the blank
are met.  Otherwise, the modification is not permitted. Maintain records that document that the  initial
demonstration was performed on the modified method and those requirements for precision and recovery
and the blank were met.
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Application of a Method Modification to a Sample Matrix

        In addition to the initial demonstration in a reference matrix such as reagent water, the method
modification is applied to the specific discharge or sample matrix to which the modified method will be
applied in monitoring. The modified method is tested by spiking the analytes of interest into duplicate
aliquots of the sample matrix at a concentration of 5 - 10 times the background concentration of the
pollutant in the sample, 1-5 times the quantitation limit, or 1 -5 times the regulatory limit, whichever is
greatest. The recoveries of the analytes from these matrix spike/matrix spike duplicate (MS/MSD) tests
are compared to the QC acceptance limits in the original method. Likewise, the relative percent difference
(RPD) of the MS/MSD results is calculated and compared to the QC limits for RPD in the approved
method.  The modification is acceptable if the recovery and RPD meet the respective limits. Methods
from some sources may use terms other than MS/MSD for these QC samples, but the concept and use
remain the same.

Suggested QC Acceptance Criteria for Criteria Not Stated in Approved Methods

        Many of the older methods listed in the tables at 40 CFR Part 136 do not contain standardized QC
or QC acceptance criteria.  To fill this gap, EPA proposed standardized QC tests and analyte-specific QC
acceptance criteria for all 75 contaminants in Table IB at 40 CFR Part 136 in a "Streamlining Initiative" in
1997. The initiative was proposed on March 28, 1997 (62 FR 14975) and a correction was published on
June 26, 1997 (62 FR 34573). The QC acceptance criteria published in the Streamlining Initiative were
developed from interlaboratory data or from single-laboratory data with an allowance for interlaboratory
variability (see Section III.B.2 of the proposal at 62 FR 14983). Although that initiative was not
completed, EPA remains committed to the intent of this initiative.  EPA suggests use of the QC tests and
QC acceptance criteria in the Streamlining Initiative as a starting point for evaluating method
modifications when the approved method is absent of such tests and criteria.

Intractable Samples

        Method flexibility  permits pollutant identities and concentrations to be determined in nearly all
wastewaters, but EPA recognizes that there may be a few intractable sample matrices that do not yield
readily to extensive analytical efforts. Please let EPA or your regulatory authority know about
modifications that you have made that have worked or not worked with difficult matrices. Reporting to the
permitting authority that "the sample couldn't be analyzed" is not sufficient and will not be accepted as
justification for a claim of matrix interference.  See Chapter 4 for the information that will document a
matrix interference and Chapter 8 for possible relief when a matrix interference is shown.
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                                                                                   Chapter 4
How to Document Matrix Interference

       This chapter outlines the analytical data and other information that the EPA recommends be
provided to evaluate a discharger's claim that a complex matrix precludes measurement of a pollutant.
Generally, the data are the same as data gathered by EPA in developing the Agency's regulations.

       Because different analytical techniques provide different data (e.g., gas chromatography/mass
spectrometry (GC/MS) procedures produce plots of mass intensities while colorimetric procedures do not),
the specific form of the data will differ according to the method. The following items describe the
minimum data that should be developed to support a claim of compliance.

1.  The identity of the method used for the measurement.

    In order to support a claim of a matrix interference, the analyst should, of course, use a method that is
    approved for the pollutant of interest for NPDES compliance monitoring. Therefore, the most basic
    information an analyst should submit is the identity of the method used for the measurement e.g.,
    separatory funnel or continuous liquid/liquid extraction.  This information should include the source of
    the method (e.g., EPA, Standard Methods, or ASTM), the method number, complete with any letter
    suffixes or "point" designations (e.g., 1613B or 350.1), and the date of issue of the method (for EPA
    methods) or the edition of the method compilation (e.g., Standard Methods, 18th edition).  The tables
    at 40 CFR Part 136 illustrate the level of detail required to unambiguously identify a particular
    method. The date of an EPA method revision or the edition from which a Standard Method is drawn
    are often critical because not all EPA method revisions are approved at 40 CFR Part 136 and different
    editions of Standard Methods may use different letter suffixes for the same technique as methods are
    added or removed from the manual (e.g., SM 4500-S"2 E in the 18th edition is the iodometric method,
    but in the 19th and 20th editions, the iodometric method is SM 4500-S"2 F).

2.  A detailed narrative discussing the problems with the analysis, corrective actions taken, and the
    changes made to the approved method identified.

    The discharger should describe the reasons for the change to the approved method, the supporting
    logic behind the technical approach to the change, and the result of the change.

    Many compliance monitoring analyses are performed by contract laboratories on behalf of the
    discharger.  However, the responsibility for providing the information to EPA rests with the
    discharger.  The discharger should, therefore, impress upon its contract laboratory the need for detailed
    technical communication of problems experienced and solutions  attempted.  The narrative  should be
    authored by an analyst and written in terms that another analyst can understand.

3.  A summary level report or data reporting forms giving the pollutants for which analyses were
    conducted and the concentrations detected.  For the pollutants that were not detected, the
    detection limits or estimated detection limits should be provided.

    Such results should be provided for each field sample analyzed, including any dilutions and
    reanalyses.  If not specified in the approved method, the means for estimating the detection limit of
    each pollutant should be provided in the narrative. If the laboratory uses "flags" in its data reporting,
    the definition of each flag should be provided with the data.
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4.  A summary of all quality control results required by the approved method.

    These results include, but are not limited to the following:

    •  Instrument tuning, if applicable
    •  Calibration
    •  Calibration verification
    •  Initial precision and recovery test, as described in Chapter 3
    •  Ongoing demonstration of laboratory capability (i.e., ongoing precision and recovery, laboratory
       control sample, laboratory fortified blank)
    •  Matrix spike/matrix spike duplicate (MS/MSD) or equivalent spiked sample matrices
    •  Surrogate recovery, if applicable
    •  Labeled compound recovery (isotope dilution methods)
    •  Blank results

5.  Raw data that will allow an independent reviewer to validate (reconstruct) each determination
    and calculation performed by the laboratory.

    This validation would consist of tracing the instrument output (peak height, area, or other signal
    intensity) to the final result reported. The raw data are method specific and may include any of the
    following:

    •  Sample numbers or other identifiers used by the both the  discharger and the laboratory
    •  Extraction or digestion date
    •  Analysis date and time
    •  Sequence of analyses or run log
    •  Sample volume
    •  Extract volume prior to each cleanup step
    •  Extract volume after each cleanup step
    •  Final extract volume prior to injection
    •  Digestion volume
    •  Titration volume
    •  Percent solids or percent moisture
    •  Dilution  data, differentiating between dilution of a sample and dilution of an extract or digestate
    •  Instrument and operating conditions
    •  GC and/or GC/MS operating conditions, including detailed information on
              -columns used for determination and confirmation (column length and diameter, stationary
              phase, solid support, film thickness, etc.)
              -analysis conditions (temperature program, flow rate, etc.)
              -detector (type, operating conditions, etc.)
    •  Chromatograms, extracted ion current profiles, bar graph spectra, library search results
    •  Quantitation reports, data system outputs, and other data to link the raw data to the results
       reported.  (Where these data are edited manually, explanations of why manual intervention was
       necessary should be included.)
    •  Direct instrument readouts; i.e., strip charts, printer tapes, etc., and other data to support the final
       results
    •  Laboratory bench sheets and copies of all pertinent logbook pages for all sample preparation and
       cleanup steps, and for all other parts of the  determination
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    The raw data required should be provided not only for the analysis of samples, but also for all
    calibrations, calibration verifications, blanks, matrix spikes and duplicates, and other QC analyses
    required by the approved method. Data should be organized so that an analyst can clearly understand
    how the analyses were performed.

6.   Example calculations that will allow the data reviewer to determine how the laboratory used the
    raw data to arrive at the final results.

    Useful examples include both detected compounds and undetected compounds.  If the laboratory or the
    method employs a standardized reporting level for undetected compounds, this should be made clear in
    the example, as should adjustments for sample volume, dry weight reporting (solids only), dilutions,
    etc.

7.   Possible submission of raw data in electronic format.

    For GC/MS and other instruments involving data systems, the discharger should be prepared to submit
    raw data in electronic format or current permanent format upon request by EPA.

8.   The names, titles, addresses, and telephone numbers of the analysts that performed the analyses
    and of the quality control officer that assured and will attest to the results.

    If a contract laboratory collected the data, it is the discharger's responsibility to see that the contract
    laboratory met all of the requirements in the methods and that the pertinent data listed above are
    provided.

9.   Describe attempts to minimize interference.

    It is important that the laboratory describe all attempts to eliminate or minimize the interference, e.g.,
    use of simple dilution or use of a totally different 40 CFR Part 136 method that still allows reliable
    measurements at the permit level.

10. Document modifications.

    The lab should also lists how any modifications made were demonstrated by the supporting data to
    give equivalent performance over the reference method as written.
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                                                                                    Chapter 5
Reports of Matrix Interferences

        Chapter 4 described the kind of information that in the EPA's view should be provided to
demonstrate that a matrix problem precluded measurement of a pollutant regulated under a NPDES permit
limitation.  This chapter provides case histories of selected reports of matrix interference problems
submitted by dischargers regulated under the Organic Chemicals, Plastics, and Synthetic Fibers (OCPSF)
rule. Additional details of matrix interferences reported by dischargers and others, and how to overcome
these interferences, are given in Chapter 6 of this document.

        In the early 1990s, the Engineering and Analysis Division (EAD) of EPA reviewed data provided
by at least 15 dischargers  regulated under the categorical pretreatment standards for the OCPSF industry.
In each instance, the discharger reported that the facility's wastewater could not be monitored for
compliance with the pretreatment standards because of interferences. EAD was asked by either the Region
or State permitting authority to review these reports of matrix interferences. Over the years, dischargers
have reported similar matrix interferences in other industrial categories and many of the documents cited
in this document were developed by EPA to address these reports.

        EAD's review focused on each facility's reported inability to determine the organic analytes in its
wastewater because of interferences. This chapter presents six case histories of EAD's review of data
submitted by dischargers reporting interference problems and provides further detail as to how these
dischargers might resolve matrix interference problems. None of the dischargers nor any of the
laboratories involved are identified in this document.

        Prior to EAD reviewing the data, each of the permitting authorities was provided with:

•   A draft checklist of laboratory data required to support a claim that the discharger was unable to
    measure pollutants due to matrix problems.  That draft checklist resembled the Data Required to
    Document a Matrix Interference in Chapter 4 of this document.

•   Draft guidance for analysts attempting to identify and quantify pollutants in wastewaters discharged
    from plants manufacturing  organic chemicals, plastics, and synthetic fibers.  That draft guidance was
    ultimately incorporated into the 1993 "Pumpkin" book.

•   Draft guidance for permit writers and others reviewing data from the analysis of organic compounds
    determined using the 600- and 1600-Series methods, similar to that found in Chapter 7 of this
    document.

        It was EAD's intention that these draft documents be  provided to the dischargers and in turn to
their laboratories,  as needed.  However, the review revealed that the States and Regions had either not
provided the draft documents or had not followed them. In general, EAD's review of the reports submitted
by the dischargers revealed the following:

•   In nearly all instances where data were submitted, the dischargers and/or their contract laboratories
    used incorrect analytical methods or did not follow the procedures required in 40 CFR Part 136.

•   In other instances, the dischargers and/or their contract laboratories did not submit data necessary to
    document that the methods were followed.
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•   Finally, the dischargers and/or their contract laboratories did not submit documentation regarding the
    nature of interferences and the attempts (if any) to resolve these interferences.

Case Histories

Case #1: This discharger used a contract laboratory for its analytical work. Information submitted by the
          laboratory revealed inconsistencies with the stated analytical methods.

       The discharger allowed the laboratory to either:

       (1) Use methods other than the 40 CFR Part 136 methods, or
       (2) Modify methods 624 and 625.

       At the time the data were evaluated by BAD, alternative methods were allowed under the ATP
program described at 40 CFR Part 136.4 and  136.5, but required prior approval from EPA.  Otherwise,
alternative methods were not allowed.  BAD found no reference to the approval of the laboratory's
modified methods.

       If Methods 624 and 625 were modified under the spirit of the 40 CFR Part 136.6, the laboratory
did not document these modifications and did not demonstrate their equivalence. Modifications that the
laboratory made to Methods 624 and 625 included:

•   Combining acid and base/neutral fractions for samples analyzed by Method 625,
•   Using a fused-silica capillary column for the analysis of acid and base/neutral fractions (since
    approved by EPA Appendix B and C)
•   Using alternative internal standards,
•   Using alternative surrogates,
•   Using higher detection limits,
•   Using fewer matrix spike compounds, and
•   Using matrix spike amounts inconsistent  with regulatory compliance, background, or method-specified
    levels.

       The October 26,  1984 preamble to the 40 CFR Part 136 methods states that a method is considered
to be equivalent, if its performance has been demonstrated to meet or exceed the specifications in the
original method.  None of the submitted data  provided any evidence supporting method equivalence.

       The use of multiple internal standards and a fused-silica capillary column for the base/neutral and
acid fractions represent improvements. EPA  has provided letters recommending approving of these
modifications. 40 CFR Part 136.6 explicitly allows for changes to the chromatographic column and use of
alternative internal standards and surrogates without prior approval from EPA.

       However, at that time EPA did not accept combining fractions, higher detection limits, alternative
matrix spike compounds, and matrix spike amounts inconsistent with background or regulatory
compliance levels represent improvements. It was determined also at that time these changes degrade
method performance and are therefore in violation of both the spirit and letter of the flexibility permitted in
the 600- and 1600-Series 40 CFR Part 136 organic methods.

       The matrix spike compounds and spiking levels used by the laboratory appeared to have been from
Office of Solid Waste (OSW) SW-846 methods or from Superfund Contract Laboratory Program (CLP)
methods. The 600- and 1600-Series wastewater methods require the matrix spike compounds to be the
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compounds regulated in the discharge (e.g., 40 CFR Part 136, Appendix A: Method 624, Section 8.3) and
require that the spike levels be at:

(1) The regulatory compliance level,
(2) 1-5 times the background level of the analyte in the sample, or
(3) The level specified in the method (e.g., Method 624, Section 8.3.1).

The compounds spiked were not those regulated, and the spikes were not at the levels required. Therefore,
the results were not useful in demonstrating performance of the method for the problem analytes.

        The matrix spike was performed on a diluted sample. Had the matrix spike been performed as
specified in Method 624 or 625, the spike would likely have failed the specifications in the method and the
associated sample result could not have been reported for regulatory compliance purposes.  This should
have triggered cleanup procedures, the use of alternative methods, or modification of Method 624 or 625
to improve method performance.

        The QC specifications for matrix spike recovery used by the laboratory were not the specifications
given in Methods 624 and 625. The specifications in the wastewater methods (40 CFR Part 136, Appendix
A: Method 624, Table 5; and Method 625, Table 6) must be used for compliance monitoring.  While
tighter specifications from a documented source may be acceptable if met, use of wider limits without
documentation is not acceptable.

        The detection limits reported for semivolatiles were, for the most part, twice the minimum levels
given in Method 625 and were approximately 10-20 times the method detection limits (MDLs) given in
Method 625. No explanation for the  increased detection limits was given, nor could the limits be derived
from the data provided.

        The laboratory made no attempt to clean up the samples using pH change, gel permeation
chromatography, or the other techniques described in the 600- and 1600-Series methods or in the draft
guidance provided by EPA.

        Even with the increased and explicit allowance for flexibility provided at 40 CFR Part 136.6, the
majority of the modifications made by this laboratory did not improve performance; did not see the
analytes at the regulatory limits, and thus the modifications were not acceptable.


        EAD has since recommended (Appendix C) allowing several acceptable modifications to EPA
Method 625 for environmental permitting and compliance monitoring under the EPA's CWA program.

Case #2:  Information provided with data submitted by this  discharger was insufficient for a detailed
          review.

        Despite the general lack  of data, it appeared the discharger submitted  samples to a contract
laboratory for analyses by a GC/MS method which failed to produce useful results. The discharger and/or
the laboratory attributed the problems to large concentrations of acetone in the discharge, though this
problem could not be confirmed from the information provided. The analytical contractor proposed to the
discharger that Methods 601 and 602 be used for the volatiles analysis in an attempt to overcome the
interference problems. Both of these methods are approved at Part 136 methods and they are more
sensitive and more selective than a GC/MS method. Therefore, the regulated  analytes  should be
measurable in the presence of a large concentration of acetone. The discharger ignored the laboratory's


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proposal and submitted a report of matrix interferences.  EPA reported that the approach proposed by the
laboratory was workable and appropriate, and should have been attempted.

Case #3:  This discharger used several contract laboratories for analyses. The reports from these
          laboratories consisted of summary reporting forms showing detection limits that were 10-50
          times greater than the MDLs in Methods 624 and 625.

        There were no QC results, no details of how the analyses were performed, and no documentation
of interference problems or steps taken to overcome interference problems, and therefore, no
documentation that an interference existed. The laboratory may have chosen to dilute samples for
convenience. The discharger and its laboratory should have provided the data listed in Chapter 4 of this
document, and attempted to solve interference problems using the techniques discussed in Chapter 6 of this
document.

Case #4:  This discharger submitted a report from one contract laboratory that contained insufficient
          information for evaluation; and two letters from a second contract laboratory describing a
          problem with 4,6-dinitro-o-cresol.

        The report provided by the first laboratory indicated no results for spikes of the OCPSF-regulated
analytes into samples, no details of how the analyses were performed, what interference problems were
encountered, or what steps were taken to  overcome interference problems. In addition, it appeared that the
contract laboratory combined acid and base/neutral extracts, thus exacerbating interference effects.

        The letters from the second laboratory describing the problem with 4,6-dinitro-o-cresol asked for
suggestions on how to determine this compound in the presence of interferences. Chapter 6 of this
document provides general suggestions for overcoming matrix interference problems and specific
suggestions for determination of phenol.  The specific suggestions for determination of phenol can be
applied to 4,6-dinitro-o-cresol.

        Other reports by the contract laboratory showed high detection limits for the substituted phenols
because of a huge quantity of phenol in the sample.  The analytical laboratory should have used the
procedures for determination of phenol detailed in the Chapter 6 of this document.

Case #5:  This discharger submitted letters and reports from several contract laboratories.

        Data items that were present and are required for a thorough review were instrument tunes, run
chronologies, chromatograms, calibration data, calibration verification data, results for blanks, quantitation
reports for samples, and matrix spike data run against the QC limits for Methods  624 and 625. The initial
precision and recovery (IPR) data that demonstrate method equivalence were missing.

        The semivolatile matrix spike data were inconsistent. Results of analysis of unspiked samples
indicated that some of the acids and base/neutrals were not detected, yet results for the spiked samples
showed large concentrations of some analytes that were not spiked into the samples.

        The volatiles matrix spike had been diluted by a factor of 200 and spiked after dilution.  Diluting
and spiking will not show matrix interferences, and thus these data are of no  value in evaluating the
undiluted sample results.
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Cases #6: Several dischargers simply submitted summary reports from their laboratories.

       None of the materials contained the information required in Chapter 4 of this document, and none
contained explanations of the nature of the interferences found or descriptions of attempts to overcome
these interferences. These facilities should have followed the guidance in Chapters 4 and 6 of this
document, and reviewed the data produced using the data review guidance provided in Chapter 7 of this
document.
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                                                                                   Chapter 6
Solutions to Matrix Interferences
Solving Matrix Problems

       The inability to measure the concentration of a pollutant in a specific wastewater is often attributed
to a "matrix problem."  Matrix problems are caused by substances in the water that interfere in some way
in the analysis. These substances can be suspended materials, dissolved salts, polymeric materials, and
highly acidic or caustic waters.  Examples of solutions to matrix problems are described below and given
in references in this chapter. The examples are not intended to be exhaustive, but rather representative
enough to help the analyst understand how to overcome typical matrix interference problems.

       In addition to the information below and in the guidance documents referenced in this document,
the means to overcome  matrix interferences can often be found in the technical literature and in sets of
methods and individual methods published by other EPA Offices and by other organizations, most notably
Standard Methods for the Examination of Water and Wastewater (Standard Methods) and methods
published by ASTM International.  Both of these method sets contain extensive means for overcoming
matrix interference problems, and Standard Methods and ASTM methods should be consulted before
contacting EPA for a solution to a matrix interference problem.
Solutions Applicable to Nearly All Analytes

Selective Reaction and/or Removal of the Interferent

       The best solution to a matrix interference problem caused by a particular substance is to first
identify the substance, then selectively remove it from the sample or from the sample extract or digestate.
Selective removal can be accomplished by reaction with another substance that will not interfere or by
physical separation from the analyte of interest by adsorption on an ion exchange or chromatographic
column. The selective reaction/removal technique is described in some of the suggested solutions to
matrix interference problems below, and is described in further detail in Standard Methods and ASTM
methods.

Method of Standard Additions (MSA)

       A common means of resolving matrix interferences that can be applied to nearly all analytes in all
matrices is the "method of standard additions" (MSA).  MSA for metals is described in Methods for
Chemical Analysis of Water and Wastes (MCAWW Revised March 1983, NTIS PB 84-128677). MSA for
organics is described in ASTM Standard D 5788. Also, instrument manufacturers may provide MSA
procedures  in instruction manuals and/or application notes. In MSA, increasing concentrations, typically
at factors of 2, 4, and 8 times the concentration of the analyte in the sample, are added to separate aliquots
of the sample.  The aliquots are analyzed and a regression or plot of response versus concentration is used
to determine the concentration of the analyte in the sample.
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Solutions Applicable to Classical Pollutants

Oil and Grease

       Oil and grease is the pollutant for which the most matrix interferences have been reported to EPA,
and nearly all of the reports have been about the formation of emulsions in the extraction of oil and grease.
EPA has published advice on these problems in Analytical Method Guidance for EPA Method 1664A
Implementation and Use, EPA 821-R-00-003, February 2000 (see Chapter 9).

Cyanide

       Next to oil and grease, cyanide is the pollutant for which the most matrix interferences have been
reported to EPA.  Cyanide chemistry is very complex, and resolving matrix interferences with cyanides
may involve considerable investigation. Fortunately, companies that work with cyanides are usually very
familiar with the cyanide chemistry used in their products/processes and wastewaters, and have addressed
cyanide interference issues. Suggested means for mitigating or overcoming cyanide interferences are
presented in Section 4500-CN" of Standard Methods for the Examination of Water and Wastewater, in
ASTM D2036, Standard Test Methods for Cyanides in Water, and in OIA Method 1677, approved for use
at 40 CFR Part 136. Standard Method 4500-CN" and ASTM D2036 devote large sections to overcoming
cyanide interferences.

       The most common interfering species in the determination of cyanides is sulfur, primarily in the
form of sulfide. Footnotes  to Table II at 40 CFR Part 136.3 address cyanide interferences other than
sulfide, including:

$   sulfur,
$   sulfite,
$   oxidants (including chlorine and hypochlorite),
$   thiocyanate,
$   aldehydes, and
$   carbonate.

The footnotes also address the preservatives that may be used and how to deal with particulate matter in
the sample. The  following text is based on footnotes to Table II at 40 CFR Part 136.3 and input from
ASTM:

"Add a reducing agent only if an oxidant (e.g., chlorine) is present.  Reducing agents shown to be
effective are sodium thiosulfate (^28203), ascorbic acid,  sodium arsenite (NaAsCh), or sodium
borohydride (NaBH4). However, some of these agents have been shown to produce a positive or
negative cyanide bias, depending on other substances in the sample and the analytical method
used.  Therefore, do not add an excess of reducing agent.  Methods recommending ascorbic acid
(e.g., EPA Method 335.4) specify adding ascorbic acid crystals, 0.1  - 0.6 g, until a drop of sample
produces no color on potassium iodide (KI) starch paper, then adding 0.06 g (60 mg) for each liter
of sample volume.  If NaBFLt or NaAsCh is used, 25 mg/L NaBH4 or 100 mg/L NaAsCh will
reduce more than 50 mg/L of chlorine (see method "Kelada-01" and/or Standard Method 4500-
CN" for more information). After  adding reducing agent,  test the sample using KI paper, a test
strip (e.g. for chlorine, SenSafe™ Total Chlorine Water Check 480010) moistened with acetate
buffer solution (see Standard Method 4500-Cl.C.3e), or a  chlorine/oxidant test method (e.g., EPA
Method 330.4 or 330.5),  to make sure all oxidant is removed. If oxidant remains, add more


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reducing agent. Whatever agent is used, it should be tested to assure that cyanide results are not
affected adversely.

6  Sample collection and preservation:  Collect a volume of sample appropriate to the analytical
method in a bottle of the material specified.  If the sample can be analyzed within 48 hours and
sulfide is not present, adjust the pH to >12 with sodium hydroxide solution (e.g., 5 % w/v),
refrigerate as specified, and analyze within 48 hours. Otherwise, to extend the holding time to 14
days and mitigate interferences, treat the sample immediately using any or all of the following
techniques, as necessary, followed by adjustment of the sample pH to >12 and refrigeration as
specified. There may be interferences that are not mitigated by approved procedures.  Any
procedure for removal or suppression of an interference may be employed, provided the
laboratory demonstrates that it more accurately measures cyanide. Particulate cyanide (e.g., ferric
ferrocyanide) or a strong cyanide complex (e.g., cobalt cyanide) are more  accurately measured if
the laboratory holds the sample at room temperature and pH >12 for a minimum of 4 hours prior
to analysis.

          (1) Sulfur:  To remove elemental sulfur (Sg), filter the sample immediately.  If the
              filtration time will exceed  15 minutes, use a larger filter or a method that requires
              a smaller sample volume (e.g., EPA Method 335.4 or Lachat Method 01).  Adjust
              the pH of the filtrate to 12-13 with NaOH, refrigerate the filter and filtrate, and
              ship or transport to the laboratory. In the laboratory, extract the filter with 100 mL
              of 5% NaOH solution for a minimum of 2 hours.  Filter the extract and discard the
              solids.  Combine the 5% NaOH-extracted filtrate with the initial filtrate, lower the
              pH to approximately 12 with concentrated hydrochloric or  sulfuric acid, and
              analyze the combined filtrate. Because the detection limit for cyanide will be
              increased by dilution by  the filtrate from the solids, test the sample with and
              without the solids procedure if a low detection limit for cyanide is necessary.  Do
              not use the  solids procedure if a higher cyanide concentration is obtained without
              it. Alternatively, analyze the filtrates from the sample and  the solids separately,
              add the amounts determined (in Og or mg), and divide by the original sample
              volume to obtain the cyanide concentration.
          (2) Sulfide: If the sample contains sulfide as determined by lead acetate paper, or if
              sulfide is known or suspected to be present,  immediately conduct one of the
              volatilization treatments or the precipitation treatment as follows: Volatilization -
              Headspace expelling. In a fume hood or well-ventilated area, transfer 0.75 liter of
              sample to a 4.4-L collapsible container (e.g., Cubitainer™). Acidify with
              concentrated hydrochloric acid to pH < 2. Cap the container and shake vigorously
              for 30 seconds.  Remove the cap and expel the headspace into the fume hood or
              open area by collapsing the  container without expelling the sample.  Refill the
              headspace by expanding the container. Repeat expelling a total of five headspace
              volumes. Adjust the pH to >12, refrigerate, and ship or transport to the laboratory.
              Scaling to a smaller or larger sample volume must maintain the air to sample
              volume ratio. A larger volume of air will result in too great a loss of cyanide (>
              10%).  Dynamic stripping:  In a fume hood or well-ventilated area, transfer 0.75
              liter of sample to a container of the material specified and acidify with

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              concentrated hydrochloric acid to pH < 2. Using a calibrated air sampling pump
              or flowmeter, purge the acidified sample into the fume hood or open area through
              a fritted glass aerator at a flow rate of 2.25 L/min for 4 minutes. Adjust the pH to
              12 - 13, refrigerate, and ship or transport to the laboratory.  Scaling to a smaller or
              larger sample volume must maintain the air to sample volume ratio. A larger
              volume of air will result in too great a loss of cyanide (> 10%).  Precipitation:  If
              the sample contains particulate matter that would be removed by filtration, filter
              the sample prior to treatment to assure  that cyanide associated with the particulate
              matter is included in the measurement. Ship or transport the filter to the
              laboratory. In the laboratory, extract the filter with 100 mL of 5% NaOH solution
              for a minimum of 2 hours. Filter the extract and discard the solids. Combine the
              5% NaOH-extracted filtrate with the initial filtrate, lower the pH to approximately
              12 with concentrated hydrochloric or sulfuric acid, and analyze the combined
              filtrate. Because the detection limit for cyanide will be increased by dilution by
              the filtrate from the solids, test the sample with and without the solids procedure if
              a low detection limit for cyanide is necessary.  Do not use the solids procedure if a
              higher cyanide concentration is obtained without it. Alternatively, analyze the
              filtrates from the sample and the solids separately,  add the amounts determined (in
              Og or mg), and divide by the original sample volume to obtain the cyanide
              concentration. For removal of sulfide by precipitation, raise the pH of the sample
              to >12 with NaOH solution, then add approximately  1 mg of powdered cadmium
              chloride for each mL of sample. For example, add approximately 500 mg to a
              500-mL sample.  Cap and shake the container to mix. Allow the precipitate to
              settle and test the sample with lead acetate paper.  If necessary, add cadmium
              chloride but avoid adding an excess. Finally, filter through 0.45 micron filter.
              Cool the sample as specified and ship or transport the filtrate and filter to the
              laboratory.  In the laboratory, extract the filter with 100 mL of 5% NaOH solution
              for a minimum of 2 hours. Filter the extract and discard the solids. Combine the
              5% NaOH-extracted filtrate with the initial filtrate, lower the pH to approximately
              12 with concentrated hydrochloric or sulfuric acid, and analyze the combined
              filtrate. Because the detection limit for cyanide will be increased by dilution by
              the filtrate form the solids, test the sample with and without the solids procedure if
              a low detection limit for cyanide is necessary.  Do not use the solids procedure if a
              higher cyanide concentration is obtained without it. Alternatively, analyze the
              filtrates from the sample and the solids separately,  add the amounts determined (in
              Og or mg), and divide by the original sample volume to obtain the cyanide
              concentration. If a ligand-exchange method is used (e.g., ASTM D6888), it may
              be necessary to increase the ligand-exchange reagent to offset any excess of
              cadmium chloride

          (3) Sulfite, thiosulfate, or thiocyanate: If thiocyanate is known or suspected to be
              present, use UV digestion with a glass  coil (Method Kelada-01) or ligand
              exchange (Method OIA-1677) to preclude cyanide loss or positive interference.  If
              sulfite and thiosulfate are present there is no way to accurately determine cyanide
              if heat is applied.  In these situations a  non-distillation method such as D6888-04,
              or method OI-1677 may be used.

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           (4) Aldehyde: If formaldehyde, acetaldehyde, or another water-soluble aldehyde is
           known or suspected to be present, treat the sample with 20 mL of 3.5%
           ethylenediamine solution per liter of sample.

          (5) Carbonate:  Carbonate interference is evidenced by noticeable effervescence upon
          acidification in the distillation flask, a reduction in the pH of the absorber solution, and
          incomplete cyanide spike recovery.  When significant carbonate is present, adjust the
          pH to 312 using calcium hydroxide instead of sodium hydroxide.  Allow the precipitate
          to settle and decant or filter the sample prior to analysis (also see Standard Method
          4500-CN.B.3.d)".
Solutions Applicable to Metals Pollutants

       In environmental testing, samples analyzed for metals are digested with strong mineral acid(s), or
the metal is chelated and extracted, followed by determination of the metals by:

$  flame atomic absorption spectrophotometry (FLAA),
$  graphite furnace atomic absorption spectrophotometry (GFAA),
$  cold-vapor atomic absorption spectrophotometry (CVAA),
$  hydride generation atomic absorption spectrophotometry (HGAA),
$  direct-current plasma atomic absorption spectrophotometry (DCPAA),
$  inductively coupled plasma/optical emission spectrometry or mass spectrometry (ICP/OES and ICP-
   MS),
$  atomic fluorescence spectrophotometry (AF)
$  or colorimetric, titrimetric, voltammetric, or gravimetric techniques.

The full list of techniques approved for metals analysis is listed in Table IB at 40 CFR Part 136.

       The most commonly used of these techniques for determination of metals in wastewater are
GFAA, HGAA, and ICP-MS.  HGAA is only approved at 40 CFR Part 136 for arsenic and selenium.
CVAA is used exclusively for determination of mercury.  The introduction of EPA Method 1631, an
atomic fluorescence method, has caused a shift in technology because of the ability to measure to lower
levels than CVAA, and with fewer interferences.

Clean Room

       Although not strictly a matrix interference problem, contamination of metals samples, particularly
at or near ambient water quality criteria (WQC) levels, can be a significant problem in sampling and in
some laboratories. The problem is particularly common for mercury, which is a volatile metal and,
therefore, can be transported throughout a building through heating, ventilating, and air conditioning
systems.  However, clean room techniques have been successful at eliminating contamination sources for
many other metals, including lead and zinc.

       To mitigate laboratory contamination problems with mercury and other metals, EPA published
Guidance on Establishing Trace Metal Clean Rooms In Existing Facilities, EPA-821-B-96-001, April,
1995 and Trace Metal Cleanroom, RTI/6302/04-02F, Research Triangle Institute, October, 1995. These
guidance documents detail how the laboratory can modify existing facilities to reduce contamination to the
lowest levels and, thereby, prevent contamination from interfering in the analysis.
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General Matrix Interferences

        Matrix interferences in metals determinations by AA, ICP, and other techniques result in a
decrease or increase in the signal (response) from what the signal would be if the interference were not
present. For analysis of environmental samples, the most common forms of matrix interference are caused
by dissolved materials in the sample digestate.  These interferents change the characteristics of the solution
that is injected into the instrument.

        One means of resolving matrix problems with metals is use of MSA, described in the section on
MSA above. Another means of overcoming matrix interferences from dissolved materials is to match the
blank and the matrix containing the standard used for instrument calibration with the characteristics of the
sample or digestate. Matrix matching can involve matching the pH, acid concentration, and dissolved
solids content of the blank and standards. If chelation is used, or if the sample contains significant
concentrations of organic compounds, the standards and blank should be chelated and/or otherwise
matched to contain the organic compounds also.

Chromium VI

        Although chromium VI (also known as "hexavalent chromium," and colloquially known as
"chrome 6") can be considered a metal pollutant, it has historically been treated as a classical pollutant
because it is usually determined using classical wet-chemistry techniques. Interferences in the
determination of chromium VI have been overcome by use of ion chromatography with methods such as
EPA Method 218.6.

Mercury

        The dual amalgam purge-and-trap and fluorescence system in EPA Method 1631 is less
susceptible to matrix interferences, particularly at low levels, than cold vapor atomic absorption and other
mercury analysis techniques.  Therefore, if a matrix interference is encountered in the determination of
mercury, EPA Method 1631 should be used. Generally, use of this method will resolve most matrix
interferences. Recommended approaches for addressing any remaining interferences can be found in
Chapter 3 of EPA's Guidance for Implementation and Use ofEPAMethod 1631B, EPA 821-R-01-023,
March 2001, which specifically addresses matrix interferences in the determination of mercury.  This
guidance is applicable to subsequent versions of the method, e.g. 163 IE.

Solutions Applicable to Organic Pollutants

        Many of these solutions focus on the pollutants regulated under the OCPSF rule, but are applicable
to pollutants in other effluent guidelines as well.

Volatiles - The 304(h) methods for volatiles include Methods 601, 602, 603, 624, and  1624.

1.  Use of Selective GC Detectors

    The effluent limits in the  OCPSF regulation and any other industry regulations involving volatiles are
    all greater than 10 (ig/L (10 ppb).  The selective GC detectors in Methods 601 and 602 cover all
    OCPSF volatile pollutants regulated, and allow detection at levels well below the effluent limits in the
    OCPSF regulation.  The specificity provided by the electrolytic conductivity detector and by the
    photoionization detector allows detection of the halogenated and aromatic  analytes, respectively, in
    complex matrices.


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2.   Micro-extraction and Gas Chromatography with Selective Detectors

    The selective GC detectors in Methods 601 and 602 provide sensitivity that is 10-100 times greater
    than that required to detect the volatile analytes of interest. Some of this sensitivity can be used to
    substitute micro-extraction in place of purge-and-trap.  The advantage of micro-extraction is that the
    pH of the water can be adjusted to attempt to keep the interferences in the water while the analytes of
    interest are extracted.1

3.   Sample Dilution

    Methods 601 and 602 can achieve method detection limits of less than 1  (ig/L (ppb) for all volatile
    analytes in the OCPSF regulation, and of less than 0.1 (ig/L (ppb) for many of these analytes.  The
    added sensitivity of the selective GC detectors can be used to overcome matrix problems by diluting
    the sample by a factor of 10-100.  Even with this dilution, the pollutants can be detected at the levels
    required, and the effects of the interferences will be reduced or eliminated.

4.   Isotope Dilution

    Method 1624 employs stable, isotopically labeled analogs of the pollutants as internal standards in the
    analysis. The use of these labeled compounds frequently permits the pollutant to be determined in the
    presence of interferences because the unique spectrum of the labeled compound can be located in the
    presence of these interferences, and the pollutant can then be located by reference to the labeled
    compound.

Semivolatiles

1.   Use of Selective GC Detectors

    Methods 604 through 612 employ gas chromatography with selective detectors and high-performance
    liquid chromatography with an ultraviolet (UV) or electrochemical detector to detect pollutants in the
    presence of interferences. In addition, Method 604 employs derivatization and a halogen-specific
    detector for the determination of phenols. As with volatiles, the added sensitivity of the selective
    detectors permits the sample to be diluted by a factor of 10-100 while allowing detection of the
    analytes at the  effluent limits specified in the OCPSF regulation.

2.   pH Change

    A very powerful means of separating the pollutants of interest from interferences is to adjust the pH of
    the sample to keep the interferences in solution while allowing the pollutants to be extracted in an
    organic solvent.  For example, neutral pollutants can be extracted at either low or high pH. Therefore,
    if the main interferences are acidic, the pH can be adjusted to >13 and the acidic interferences will
    remain in the water in ionic form while the neutral pollutants are extracted using an organic  solvent.

    Phenol and 2,4-dimethylphenol can be extracted at high pH (11-13) using continuous liquid/liquid
    extractors, as described in Method 1625. This permits phenol and 2,4-dimethylphenol to be extracted
    in the presence of other, stronger acids.2  Continuous liquid-liquid extraction at low pH  is also an
  1 Rhodes, J.W., and Nulton, C.P., J. Env. Sci. and Health, vol. A15, no. 5, (1980).

  2 Jackson, C.B. et. al.,.7. Env. Sci. and Health, vol. A15, no. 5, (1980).

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    effective means of extracting phenols and overcoming poor recovery "matrix interferences" caused by
    separatory funnel extraction.

    In a manner analogous to the pH change described above, the extract from the primary extraction can
    be back-extracted with water of the opposite pH to remove other interferences. To keep the organic
    pollutants in the extract, the water used for back-extraction can be saturated with salt (sodium sulfate
    and/or sodium chloride). Aqueous solutions containing 2% of each of these salts have been shown to
    be effective in keeping the pollutants of interest in the extract.

3.  Gel-permeation (Size-exclusion) Chromatography (GPC)

    This technique is described in Revision C of Method 1625. The same technique is used in the
    Superfund Contract Laboratory Program (CLP) methods and SW-846 method 3640, and has been
    shown to be effective for removing lipids and high-molecular-weight interferences that can degrade
    GC  and mass spectrometer performance.

4.  Solid-phase Extraction (SPE)

    Although SPE has not been fully evaluated as a cleanup technique, SPE may be effective as a cleanup
    for acidic, basic and neutral organic species. It has been shown to be effective in removing
    interferences from extracts containing pesticides3  and in its use for the extraction of pollutants from
    drinking water in EPA Method 525. Method 525 is the drinking water analog to method 625. The
    principle has been extensively used to remove interferences in HPLC by adding a short CIS or other
    appropriate column as a guard column in front of the HPLC analytical column.

5.  Florisil, Alumina, and Silica Gel Chromatography

    These adsorbents are effective in separating neutral species from polar interferences.  For polar
    analytes of interest, the adsorbent should be evaluated to determine if the analyte will be recovered.
    The level of activation of the adsorbent plays a major role in this recovery  process.  Techniques can be
    found in SW-846 methods 3610, 3620 and 3630.

6.  Isotope Dilution

    Method 1625 permits determination of pollutants  in the presence of interferences in semivolatile
    samples in the same way described above for volatiles. In addition, the wide range of recovery of the
    labeled analogs permitted in the method allows good quantitation of the pollutant when interferences
    reduce the efficiency of the extraction.

Determination of Phenol as a Specific Example

    Phenol is a commonly occurring pollutant in OCPSF wastewaters.  The protocols below are suggested
as approaches to the determination of phenol in a complex sample matrix. After a protocol has been found
to be effective, the laboratory must demonstrate that the modification has equivalent performance to the
original method. This demonstration involves the tests described in Chapter 3  of this document. The QC
acceptance  criteria in the approved method must be met before proceeding with analysis of a sample for
compliance monitoring.
 3 Tessari, J.D., 12th Annual EPA Conference on Analysis of Pollutants in the Environment, Norfolk, Virginia, May
 1989.

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1.   Base/neutral extraction, acid back extraction, and isotope dilution GC/MS (based on Method 1625)

    1.1 Measure 1.0 L of well-mixed sample into a graduated cylinder and spike with labeled phenol per
       Section 10 of Method 1625. Stir and equilibrate per this method. Quantitatively transfer the
       sample to a continuous liquid/liquid extractor.  Adjust the pH of the sample to 11-13 and extract
       with methylene chloride as described in the method.

    1.2 Remove the extract from the extractor and place in a 1-2 L separatory funnel. Back-extract the
       extract sequentially three times with 500-mL portions of salt-saturated reagent water (pH <2),
       discarding the reagent water after each back-extraction.

    1.3 Concentrate the extract to 10 mL and clean up using gel-permeation chromatography (GPC) per
       Section 10 of Method 1625.

    1.4 After GPC, concentrate the extract to 0.5 mL and analyze by isotope dilution GC/MS, as described
       in Method 1625.

    1.5 Calculate the recovery of labeled phenol and compare to the performance specifications in Method
       1625.

2.   Dilution, acid extraction, back-extraction with base, derivatization, silica gel cleanup, and gas
    chromatography with an electrolytic conductivity detector  (based on Method 604)

    2.1 Measure two 100-mL aliquots of well-mixed sample into  1000-mL graduated cylinders.  Spike one
       of the aliquots with phenol at the level specified in Section 8 of Method 604. This aliquot serves
       as the matrix spike sample. Dilute both aliquots to 1.0 L with reagent water. Adjust the  pH of
       each aliquot to less than 2 with HC1.

    2.2 Pour each aliquot into a separate 1-2 L separatory funnel and sequentially extract three times with
       methylene chloride per Method 604.  Discard the aqueous phase and return the extract to the
       separatory funnel.  It is recommended that the use of continuous liquid-liquid extraction in place of
       separatory funnel extraction be used. The  recoveries of the analyte of interest are usually better.

    2.3 Back-extract the extract sequentially three times with salt-saturated reagent water, discarding the
       reagent water after each back extraction.

    2.4 Concentrate, derivatize, and clean up the extract per Method 604.

    2.5 Analyze using the electrolytic conductivity detector. This detector is less susceptible to
       interferences than the electron capture detector used in Method 604. Newer models have
       sensitivity nearly equivalent to the electron capture detector.

    2.6 Calculate the recovery of phenol in the matrix spike aliquot and compare this recovery to the
       specifications in Method 604.
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                                                                                   Chapter 7
Review of Data from Analysis of Samples
       This chapter describes how a responsible party should review data submitted for compliance
monitoring under the National Pollutant Discharge Elimination System (NPDES) and data submitted to
EPA and State authorities under the Clean Water Act. This data should be maintained on file in an
organized fashion available for inspection.  The 1993 Pumpkin Book focused on the review of data for
organic compounds regulated under the OCPSF Rule that was collected with the 600-series and 1600-
Series wastewater methods.  Although this revision of the Pumpkin Book now includes references to EPA
documents for review of other data, the data from the 600- and 1600-Series methods has been  described in
this chapter so that the data reviewer can see details of the information reviewed. EPA uses these data
reviews in data gathering to support development of effluent guidelines and standards under Sections 301,
304, 307, 308, 402, and 501 of the Clean Water Act and for other purposes. The principles of data review
described in this Chapter would also be applicable to data from the 500-series drinking water methods, the
SW-846 (RCRA) methods, and any method that contains the standardized quality control elements that are
contained in these methods; e.g., recent ASTM International Committee D19 (Water) methods.

       The following example is technically detailed and is intended for data reviewers familiar with the
EPA methods and similar analytical methods. Reviewers unfamiliar with these methods should review the
methods and the supporting background materials provided in the preamble to the promulgation of the
600- and 1600-Series methods for a full understanding of the philosophy behind these documents.

Standardized Quality Control

       In developing methods for the determination of organic pollutants in wastewater, EPA sought
scientific and technical advice from many sources, including EPA's Science Advisory Board, scientists at
EPA's environmental research laboratories, scientists in industry and academia, and scientists,  managers,
and legal staff. The result of discussions held among these groups was the standardized quality assurance
and quality control (QA/QC) approach that is an integral Part of the  600- and 1600-Series methods. This
QA/QC takes the form of performance specifications for each  method and contains the following  elements:

•   Purity and traceability of reference standards
•   Number of calibration points
•   Linearity of calibration
•   Calibration verification
•   Method detection limit (MDL) and minimum level of quantitation
•   Initial precision and recovery
•   Analysis of blanks
•   Recovery of analytes spiked into the  sample matrix (e.g., an matrix spike or laboratory-fortified matrix
    aliquot) or recovery of labeled compounds spiked into samples
•   Statements of data quality for recovery of spikes of analytes or labeled compounds into samples
•   Ongoing precision and recovery
•   Statements of data quality for the laboratory

       In reviewing data submitted for compliance, the permit writer or other individual or organization
has the authority and responsibility to assure that the test data submitted contain the elements listed above.
Otherwise, the data may be considered unacceptable for compliance monitoring.
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Provision of QC Data

       Dischargers and other organizations submitting test data under CWA or other acts may use their
own laboratories or contract the testing to laboratories that meet the requirements specified in the methods.
The permit writer may require that the supporting QA/QC data described above be submitted with results
or that it be on record at the discharger's facility or at the testing laboratory.

       EPA strongly recommends that the supporting QA/QC data be submitted along with the analytical
results, so that the quality of the data can be evaluated directly, and so that these supporting data are not
lost between the time of submission of the analytical results and the time that the QA/QC data are required.

       In many of its  early analytical programs, EPA relied upon laboratories to maintain records of
QA/QC data. This practice was cumbersome for the laboratories, because many of the QA/QC data were
common to the analytical  results for a variety of clients. Retrieving these data from the laboratory to
resolve questions of permit compliance was time-consuming for the discharger and the permit writer.
More importantly, this practice occasionally resulted in unscrupulous laboratories failing to perform the
necessary QA/QC testing, or performing the QA/QC testing "after the fact" to satisfy an audit or data
submission request.  In particular, many laboratories did not perform the initial precision and recovery test
(the "start-up" test) prior to practice of the method and did not perform a spike of the analytes into the
sample matrix to prove that the method would work on a particular sample.  Therefore, while the data
provided by those laboratories may have been compliant, there was no way to prove the  data was
acceptable for compliance purposes.

       When collecting data for the development of a regulation, EPA  requires that supporting QA/QC
data be provided along with the results for the sample analyses. If an individual or organization submits
analytical results for inclusion into EPA's regulations, EPA similarly requires submission of the QA/QC
data.  Sample results are evaluated relative to the QA/QC specifications in the method, and those results
that pass the QA/QC requirements are included for consideration.  Submission of QA/QC data at the time
of submission of analytical results is  essential to timely and effective evaluation of permit compliance
issues.

Review of Data from  the 600- and 1600-Series Methods

       Details of the data review process depend to a great extent upon the specific analytical methods
being employed for compliance monitoring. Even for data from the same methods, there are probably as
many specific approaches as there are reviewers.  However, given the standardized QA/QC requirements
of the 600- and 1600-Series EPA methods, a number of basic concepts apply.  The following sections
provide the basic details for reviewing data submitted and provide some of EPA's rationale for the QA/QC
tests.

1.  Purity and Traceability of Reference Standards

    The accuracy of any non-absolute empirical measurement is dependent on the reference for that
    measurement. In determining pollutants in water or other sample matrices, the analytical instrument
    and analytical process should be  calibrated with a known reference material. The 600- and 1600-
    Series analytical methods, as well as other EPA methods, require that the standards used for calibration
    and other purposes be of known purity and traceable to a reliable reference source.

    The ultimate source for reference materials is National Institute for  Standards and Technology (NIST).
    Dischargers and their supporting laboratories submitting analytical data should be able to prove
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    traceability of the reference standards used in the analysis to EPA or NIST.  The proof of this
    traceability is a written certification from the supplier of the standard.

    Documentation of the purity and traceability of the standards need not be provided with every sample
    analysis.  Rather, it should be maintained on file at the laboratory and provided on request. When
    analyses are conducted in a contract laboratory, such documentation ought to be provided to the
    discharger the first time that a laboratory is employed for specific analyses and then updated as
    needed.

2.  Number of Calibration Points

    The 600-series methods specify a minimum of three calibration points.  The lowest of these points is
    required to be near the MDL.  The highest is required to be near the upper linear range of the analytical
    system, and the third point is approximately midway between the two. Some methods, such as
    Methods 1624 and 1625, require calibration at five specific concentrations for nearly all analytes, and
    three or four specific concentrations for the remaining analytes for which the methods are not as
    sensitive.

    The lowest calibration point should be below the action level and the high standard should still be
    within the calibration range of the instrument.

    The flexibility in selecting the levels of the calibration points in the 600-series methods has led to a
    wide variety of calibration ranges as each laboratory may determine its own calibration range. Some
    laboratories may establish a relatively narrow calibration range, for instance a five-fold concentration
    range such as 10 to 50 (ig/L (ppb), because it makes it simpler to meet the linearity specifications of
    the 600-series methods.  Other laboratories may  choose wider calibration ranges, e.g., 10 to 200 (ig/L
    (ppb), in order to minimize the number of samples that should be diluted and reanalyzed because the
    concentration of one or more analytes exceeds the calibration range.

    The data reviewer will need to make certain that all measurements are within the calibration range of
    the instrument.  Samples with analyte concentrations above the calibration range  should have been
    diluted and reanalyzed. The diluted sample results need only apply to those analytes that were out of
    the calibration range in the initial analysis.  In other words, it is acceptable to use results for different
    analytes from different levels of dilution within the same sample. Some flexibility may be exercised in
    acceptance of data that are only slightly above (<10%) the calibration range.  Such data are generally
    acceptable as calculated.

    If data from an analysis of the diluted sample are not provided, limited use should be made of the data
    that are above the calibration range (>10%). The response of the analytical instrument to
    concentrations of analytes will eventually level off at concentrations above the calibration range.
    While it is not possible to specify at what concentration this will  occur from the calibration data
    provided, it is generally safe to assume that the reported concentration above the calibrated range is  a
    lower limit of the actual concentration. Therefore, if concentration above the calibration range is also
    above a regulatory limit, it is highly likely that the actual concentration would also be above that limit.
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3.  Linearity of Calibration

    The relationship between the response of an analytical instrument to the concentration or amount of an
    analyte introduced into the instrument is referred to as the "calibration curve."  An analytical
    instrument can be said to be calibrated in any instance in which an instrumental response can be
    related to a single concentration of an analyte.  The response factor (GC/MS methods) or calibration
    factor (GC, HPLC methods) is the ratio of the response of the instrument to the concentration (or
    amount) of analyte introduced into the instrument.  The response factor and calibration factor concepts
    are used in many methods for organic contaminants, while methods for metals  and some other analytes
    may employ different concepts  such as linear regressions.

    While the shape of calibration curves can be modeled by quadratic equations or higher order
    mathematical functions, most analytical methods focus on a calibration range where the response is
    essentially a linear function of the concentration of the analyte. An advantage of linear calibration is
    that the response factor or calibration factor represents the slope of the calibration line and is relatively
    constant, simplifying the calculations and data interpretation. Whichever approach is used, all the 600-
    and 1600-Series methods specify some criterion for determining linearity of calibration. When this
    criterion is met, the calibration is sufficiently linear to permit the laboratory to use an average response
    factor or calibration factor, and it is assumed that the calibration is a straight line that passes through
    the zero/zero calibration point.  Linearity is determined by calculating the relative standard deviation
    (RSD) of the response factor or calibration factor for each analyte and comparing this RSD to the limit
    specified in the method.  If the RSD does not exceed the  specification, linearity is assumed.

    In the 600- and 1600-Series methods, the linearity specification varies from method to method,
    depending on the quantitation technique. The typical limits on the RSD are as  follows:

    $   15% for the gas chromatography (GC) and high-performance liquid chromatography (HPLC)
    methods
    $   20% for analytes determined by the internal standard technique in the gas chromatography/mass
    spectrometry (GC/MS) methods (624, 625,  1624, and 1625)
    $   20% for analytes determined by isotope dilution in Methods 1613, 1624, and 1625
    $   15% for mercury determined by atomic fluorescence in Method 1631

    Metals methods that employ a linear regression specify a criterion for the correlation coefficient, r,
    such as 0.995.

    If the calibration is not linear, as determined by the RSD of the response factor or calibration factor, a
    calibration curve should be used. This means that a regression line or other mathematical function
    should be employed to relate the instrument response to the concentration. However, properly
    maintained and operated lab instrumentation should have no difficulty in meeting linearity
    specifications for 600- and 1600-Series methods. Linear regression emphasizes the importance of
    higher concentration standards and that the  correlation coefficient is little impacted by poor
    performance of calibration standards with low concentrations.

    For determination of nearly all of the organic analytes using the 600- and 1600-Series methods,
    calibration curves are linear over a concentration range of 20-100 times the nominal concentration,
    depending on the detector being employed.  Whatever calibration range is used, the laboratory should
    provide the RSD results by which one can judge linearity, even in instances where the laboratory is
    using a calibration curve. In instances where the laboratory employs a curve rather than an average
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    response or calibration factor, the data reviewer should review each calibration point to assure that the
    response increases as the concentration increases. If it does not, the instrument is not operating
    properly, or the calibration curve is out of the range of that instrument, and data are not considered
    usable.

4.  Calibration Verification

    Calibration verification involves the analysis of a single standard, typically in the middle of the
    calibration range, at the beginning of each analytical shift.  The concentration of each analyte in this
    standard is determined using the initial calibration data and compared to specifications in the method.
    If the results are within the specifications, the laboratory is allowed to proceed with analyses without
    recalibrating and to use the multi-point calibration data to quantify sample results. It is also
    recommended that a calibration verification at the action level is periodically analyzed.
    Specifications for calibration verification are generally given as a range of concentrations, as a
    recovery range, or as a percentage difference from the test concentration. For the 600-series
    semivolatile GC and HPLC methods, the difference must be within 15%. For Method 625, the
    difference must be within 20%. The GC and GC/MS methods for volatiles and the 1600-Series
    methods specify a range of concentrations or recoveries for each analyte. These ranges are based on
    interlaboratory method validation studies.

    If calibration cannot be  verified, the laboratory may either recalibrate the instrument or prepare a fresh
    calibration standard and make a second attempt to verify calibration. If calibration cannot be verified
    with a fresh calibration  standard, the instrument should be recalibrated. If calibration is not verified,
    subsequent data are considered to be invalid until the instrument is recalibrated.

5.  Method Detection Limit or  Minimum Level

    Although this requirement is  not explicitly stated in EPA wastewater methods (e.g., 600 and 1600-
    Series methods) we recommend use of the method detection limit (MDL) concept to establish
    detection capabilities. Detailed procedures for determining the MDL are provided at 40 CFR Part 136,
    Appendix B. Although exact frequencies vary by method, most methods require that, at a minimum,
    laboratories conduct an MDL study as part of their initial demonstration of capability and whenever a
    modification is made to the method that might affect the detection limit and amends thereafter. Data
    reviewers should consult the  methods used for specific requirements, or the requirements  of their
    customers, auditors, etc.

    The Minimum Level (ML) is used as a quantitation level, and is defined in most of the 1600-Series
    methods as the lowest level at which the entire analytical system gives a recognizable signal and
    acceptable calibration point.  Therefore, each 1600-Series method specifies that the calibration range
    for each analyte encompass the method-specified ML.

    Many of the EPA wastewater methods provide specific requirements regarding reporting results that
    are below the ML or the method-specified quantitation limit when these data will be used for
    compliance monitoring.  Since these requirements vary slightly, data reviewers should consult the
    specific method for details.

    If the sample results are above the ML, but are below the facility's regulatory compliance level, then
    the laboratory should report the results to indicate that the pollutant has been detected but is compliant
    with a facility's permit, assuming all QC criteria are met. If sample results are above the regulatory

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    compliance level, the data reviewer may wish to evaluate the laboratory QC sample results to verify
    that the reported concentration is not attributable to analytical bias. In addition, the data reviewer
    should evaluate all blank results to determine if the level of pollutant detected may be attributable to
    contamination.

6.  Initial Precision and Recovery

    Part 136 methods require this Initial Precision Recovery (IPR) test before use of a method. It is
    sometimes termed the "start-up test." The laboratory should demonstrate that it can meet the
    specifications in the method for the recovery of analytes spiked into a reference matrix (reagent water).
    EPA's experience has been that laboratories that have difficulty passing the start-up test have such
    marginal performance that they will have difficulty in the routine practice of the method.

    The start-up test consists of spiking the analytes of interest into reagent water and analyzing four
    aliquots. The mean concentration and the standard deviation of the concentration are calculated for
    each analyte and compared to the specifications in each method. If the mean and standard deviation
    are within the limits, the laboratory may use the method to  analyze field samples. For some methods,
    a repeat test is allowed because of the large number of analytes being tested simultaneously.

    If start-up test data fail to meet the  specifications in the method, none of the data produced by that
    laboratory using that method should be considered usable.  As with the documentation of the purity of
    the standards, the start-up test data need not be submitted with each set of sample results, but should be
    submitted the first time a laboratory is employed for analyses,  and updated as changes to the method
    necessitate (see below) in order to allow the data reviewer to determine the adequacy of the
    laboratory's performance.

    If the laboratory did not perform the start-up tests, the data should not be considered usable, unless all
    other QC criteria have been met and the laboratory has submitted IPR (and associated instrument QC)
    data that were generated after-the-fact on the same instrument.  If these conditions are met, then the
    data reviewer may consider the data to be acceptable for most purposes.

    Note: Discussion of this alternative should not in any way be  construed as EPA approval of the
          practice of performing IPR analyses after the analysis of field samples.  Rather, EPA regards
          the demonstration of laboratory capability prior to sample analysis as an essential QC
          component.  This suggestion provides a tool to permitting authorities when data have already
          been collected without the required IPR samples. Once the missing IPR data has been
          identified as a problem, all responsible parties should implement corrective action necessary to
          ensure that it is not repeated.

    It is important to remember that if a change is made to a method, the start-up test will need to be
    repeated with the change as an integral part of the method.  Such changes may involve alternative
    extraction, concentration, or cleanup processes; alternative  GC columns, GC conditions, or detectors;
    or other steps designed to address a particular matrix problem. If the start-up test is not repeated when
    these steps are modified or added, then laboratory data produced by the modified method should not be
    considered reliable  and thus should not be used. Many laboratories report the configuration of their
    GCs (instrument number, column, detector) as a part of their report header.  If a configuration change
    is made and new IPR data are not supplied, EPA recommends  requesting the new IPR data from the
    laboratory.
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7.   Analysis of Blanks

    Blanks should be analyzed on a routine basis, when any part of the analytical process has been
    changed, and when contamination of the analytical system is suspected. Most recent EPA methods
    require that a blank be prepared and analyzed with each batch (set) of samples. The size of a batch is
    usually limited to a maximum of 20 field samples. In practice, this means that on each day that a
    laboratory prepare samples, they should also prepare  a blank, even if fewer than 20 samples are
    prepared. The purpose of analyzing a blank with each set of samples is to determine the extent of
    possible  contamination of the samples  while in the laboratory. If the blank is handled by the same
    analysts  in the same way as the  samples and the blank shows no contamination, it is likely that the
    samples  will not have been contaminated. Analyzing a blank when the analytical process has been
    changed is consistent with requiring a repeat of the start-up tests, because the change introduces a new
    possibility for contamination of samples through the use of the new materials or procedures.

    Contamination in the laboratory is a common problem,  though there are many opinions on what
    constitutes contamination. In more recent EPA methods, a concentration above the minimum level of
    quantitation of the method is a cause for concern. In  reality, it is not unusual to find low levels of
    common laboratory solvents, phthalates, and other ubiquitous compounds in laboratory blanks.

    Controlling laboratory contamination is an important aspect of each laboratory's quality assurance
    plan. The laboratory should maintain records, typically in the form of control charts, of blank
    contaminants. These records should prompt corrective  action by the laboratory, including reanalysis
    of any affected samples, when concentration of an analyte in a blank rises above  a historical level.  The
    reviewer in evaluating sample results may request control charts; however, they are not required in
    EPA methods and are not routinely submitted with sample data.

    Unfortunately, by the time that results have been found to be contaminated, it is usually too late for
    corrective action.  Therefore, the reviewer has several options in making use of the sample data.  First,
    if a contaminant is present in a blank, but not present in a sample, then there is little need for concern
    about the sample result, though  it may  be useful to occasionally  review the raw data for samples
    without the contaminant to ensure that the laboratory did not edit the results for this compound.

    The second approach deals with instances where the contaminant is also reported in a sample. Some
    general guidance will help determine the degree to which the contaminant is affecting sample results:

    •   If the sample contains the contaminant at levels of at least 10 times that in the blank, then the
       likely contribution to the sample from the contaminant in the laboratory environment is at most
        10%. Since most of the methods in question are no more accurate than that level, the possible
       contamination is negligible.

    •   If the sample contains the contaminant at levels of at least 5  times but less than 10 times the blank
       result, the compound is probably present in the sample, but the numerical result should be
       considered an upper limit of the true concentration.

    •   If the sample contains the contaminant at levels below 5 times the level in the blank, there is no
       adequate means by which to judge whether or not the sample result is attributable to laboratory
       contamination. The results  for that compound in that sample should be considered unacceptable
       for compliance monitoring.
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    There are two difficulties in evaluating sample results relative to blank contamination. First, the
    reviewer should be able to associate the samples with the correct blanks.  For analysis of volatiles by
    purge-and-trap techniques, where no sample extraction is required, the blanks and samples are
    associated by analysis date and time, and specific to the instrument as well. For methods involving the
    extraction of organic compounds from the samples, the blanks and samples are primarily associated by
    the date on which they were extracted, and by the batch of samples and associated lab equipment
    (glassware, reagents, cleanup media).

    The second difficulty involves samples that have been diluted. Dilution of a sample with reagent
    water or dilution of an extract with solvent represents an additional potential source of contamination
    that will not be reflected in the results for the blank unless the blank was similarly diluted. Therefore,
    in applying the 10-times rule, the concentration of the sample is compared to the blank result
    multiplied by the dilution factor of the sample or sample extract.  For instance, if 12 ppb of a
    contaminant are found in the blank, and the associated sample extract was diluted by a factor of 6
    relative to the extract from the blank prior to analysis, then the sample result would have to be greater
    than 12x6x10, or 720 ppb, to be acceptable. Between 360 ppb and 720 ppb, the sample result would
    best be considered an upper limit of the actual concentration.  Below 360 ppb, the sample result is not
    acceptable for compliance monitoring.

    In general, practitioners of analytical methods do not subtract the concentration of the analyte in the
    blank from the concentration of the analyte in the sample to determine the true concentration of the
    analyte in the sample.  Experience indicates that this practice is not reliable. The obvious problem
    occurs when the blank concentration is higher than that in the sample, and subtraction would yield a
    negative concentration. Using the 10-times rule above provides a more appropriate means of
    evaluating the results and does not require that the reviewer alter the results reported by the laboratory.

8.  Ongoing Precision and Recovery

    The 1600-Series methods require that an "ongoing precision and recovery" (OPR) sample be analyzed
    with each sample set, and the results of this OPR sample should meet the acceptance criteria in the
    method prior to the analysis of blanks and samples. Most other methods approved at 40 CFR Part 136
    contain a similar requirement, but may use different terminology, such as a laboratory control sample
    (LCS), laboratory fortified blank (LFB), or QC check sample. For this purposes of this discussion, all
    such samples are referred to as OPR samples.

    The OPR samples  are used to ensure that laboratory performance is in control during analysis of the
    associated batch of field samples. The data reviewer should determine if the OPR sample has been run
    with each sample set and if all criteria have been met. For methods that do not require sample
    digestion or extraction, such as volatile analyses by Method 1624, the OPR analysis is associated with
    the samples on the basis of the analysis date and time and the specific GC/MS system. For other
    analyses,  such as semivolatile analyses by Method 1625, OPR results are associated with samples
    extracted (or digested) at the same time as the OPR. In addition to defining sample batches by date
    and time of extraction or analysis, each method specifies a maximum batch size (generally no more
    than 10 or 20 samples) that can be associated with a single OPR.  The reviewer should verify that OPR
    samples were run at the proper frequency.

    Because of the large  number of compounds being tested simultaneously in the 600- and 1600-Series
    methods, there is a small probability that the OPR analysis will occasionally fail to meet the
    specifications. While the laboratory is supposed to correct any problems and analyze another OPR
    aliquot, it may still be possible to utilize the data associated with an OPR aliquot that does not meet all
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    of the method specifications.  The following guidelines may be useful to data reviewers when
    evaluating the usability of data:

    •   If the concentration of an analyte in the OPR is above the method specifications, but that
       compound is not detected in an associated sample, then it is unlikely that the sample result is
       affected by the failure in the OPR.

    •   If the concentration of the analyte in the OPR is above method specifications and the analyte is
       detected in the sample, then the numerical result may represent an upper limit of the true
       concentration, and data users should be cautioned when using the data for enforcement purposes.

    •   If the concentration in the OPR is below the method specifications, and that analyte is detected in
       an associated sample, then the sample result is likely a lower limit of the true concentration for that
       analyte.

    •   If the concentration of the analyte in the OPR is below method specification and that analyte is not
       detected in the associated sample, then the sample data are  suspect and are not usable for
       regulatory compliance purposes because the analysis does not demonstrate the absence of the
       analyte.

    If the OPR sample was not run, there is no way to verify that the laboratory processes were in control.
    In such cases, a data reviewer may be able to utilize the field sample data by examining labeled
    compound or matrix spike recovery results, the IPR results, OPR results from previous and subsequent
    batches, and any available historical data from both the laboratory and the sample site. If the matrix
    spike or labeled compound results associated with the sample batch do not meet the performance
    criteria in the methods, then the results for that set of samples cannot be considered usable.

    If the laboratory's IPR results and the matrix spike or labeled compound results associated with the
    sample batch in question meet all applicable performance criteria in the methods, then the data
    reviewer may be reasonably confident that laboratory performance was in control during field sample
    analysis. This level of confidence may be further increased if there is a strong history of both
    laboratory performance with the method and method performance with the sample matrix in question,
    as indicated by additional OPR and matrix spike data collected  from the laboratory and samples from
    the same site.

    Note: The preceding discussion of maximizing use of failed OPR data is not an EPA endorsement of
          the practice of proceeding with uncontrolled laboratory analyses. Rather, laboratories failing to
          meet OPR specifications should identify and correct the problem and re-analyze affected
          samples whenever possible. This preceding discussion is provided only to describe a tool for
          permitting authorities when re-analysis is not possible due to sample holding times, insufficient
          sample volumes, or other reasons.

9.  Recovery of Analyte Spiked into the Sample Matrix or Recovery of Labeled Compound Spiked
    into Samples

    The majority of the  600- and 1600-Series methods were developed to analyze effluent samples, and
    may not be appropriate for in-process samples. While many of the methods were tested using effluents
    from a wide variety of industries, samples from some sources may not yield acceptable  results.  It is,
    therefore, important to evaluate method performance in the sample matrix of interest.
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    The non-isotope dilution wastewater methods require a spike of the analytes of interest into a second
    aliquot of the sample for analysis with the sample. The purpose of spiking the sample (often termed a
    "matrix spike (MS)") is to determine if the method is applicable to the sample in question. Most of
    these wastewater methods also require that laboratories prepare and analyze a duplicate aliquot of the
    matrix spike (often called a "matrix spike duplicate (MSB)"), or a duplicate aliquot of an unspiked
    field sample (usually called a "duplicate"). Generally, one matrix spike/matrix spike duplicate
    (MS/MSD) pair or one MS and one duplicate sample is required for every 10 or 20 field samples,
    depending  on the requirements of the specific method being used.

    In evaluating method performance  in the sample matrix, data reviewers should examine both the
    precision and accuracy of the analysis. Precision is evaluated by comparing the relative percent
    difference  (RPD) of results obtained from the MS/MSD pair or from the duplicate and its
    corresponding field sample.  Accuracy is assessed by examining the recovery of compounds in the
    matrix spike sample (and if applicable, the matrix spike duplicate sample). In evaluating matrix spike
    results, the data reviewer should verify that:

    •   The unspiked sample has been  analyzed.
    •   The spiked sample has been analyzed, and that the analytes were spiked at an appropriate
       concentration (generally 5-10 times the background concentration of the analyte in the sample or
        1-5 times the regulatory compliance limit, whichever is greater). If the analytes are spiked too
       high or too low, it is not usually possible to differentiate recovery of the spiked concentration from
       recovery of the analyte in the unspiked sample.
    •   The recovery of the spike is within the range specified.

    If the RPD and recoveries of the MS/MSD or MS and duplicate samples are within the limits specified
    in the method, the  method is judged to be applicable to that sample matrix. If, however, the RPD or
    recoveries  in these samples are not within the range specified, either the method does not work on the
    sample, or the sample preparation process which includes sample collection is out of control.

    If the method is not appropriate for the sample matrix, changes to the method or use of an alternative
    method would be needed.  Matrix spike results are necessary in evaluating a modified method. If the
    analytical process is out of control, the laboratory should take immediate corrective action before any
    more samples are analyzed.

    To separate indications of method performance from those of laboratory performance, the laboratory
    should prepare  and analyze a quality control check standard (laboratory control sample) or an  OPR
    sample, as  described in Items 4 and 8 of this chapter. If the results for either of these analyses are not
    within the  range specified, the analytical system or process should be repaired. After verifying the
    performance of the repaired system and processes through successful analysis of calibration
    verification and OPR samples, the sample and spiked sample analysis should be repeated. If
    recoveries  and RPD of the repeated matrix spike and duplicate analyses are within the ranges
    specified, the analytical process is judged to be  in control.  If, however, the repeated analysis results
    are still outside the specified ranges, then sample results generally are not  useful  for regulatory
    compliance purposes because the matrix spike and duplicate results indicate that the method is not
    applicable  to the sample.

    In rare cases, it may be possible to make use of such data while efforts are being  made to identify a
    method that works on the matrix in question.  The following guidelines may be applicable as a
    temporary  measure in such circumstances:
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    •   If the recovery of the matrix spike and duplicate are above the method specifications, but the
       regulated analyte was not detected in the associated sample or was detected below the regulatory
       compliance limit, it is unlikely that the sample result was affected by the failure in the matrix spike
       because the factors that caused the analysis to over-estimate the concentration in the  spiked sample
       would not likely have resulted in an under-estimate in the unspiked sample. In other words, it is
       likely that the sampled effluent is in compliance with the permit limit in such cases.

    •   If the recovery of the matrix spike and duplicate are below method specifications, but the regulated
       analyte was detected above the regulatory compliance limit in an associated sample, the sample
       result may represent the lower limit of the true concentration for that pollutant and it is likely that
       true concentration in the effluent is in violation of the permit limit.

    •   If the recovery of the matrix spike and duplicate are above the method specifications and the
       regulated pollutant was detected in an associated sample, the sample result may represent the
       upper limit of the true concentration and the data cannot be considered useable for regulatory
       compliance purposes.

    •   If the recovery of the matrix spike and duplicate are below the method specifications and the
       regulated pollutant was either not detected or was detected below the regulatory compliance limit,
       the sample result may represent a lower limit of the true concentration and cannot be considered
       usable for regulatory compliance purposes.

    Note: The preceding discussion of maximizing use of failed matrix spike or duplicate data is not an
   EPA endorsement of the practice of using methods that do not work on the sample matrix. The
   preceding  discussion is provided only to describe a tool for permitting authorities for use in evaluating
   compliance monitoring results pending the permittees' successful identification and use of an alternate
   method or method modifications such as those described in Chapter 6 of this document.

    For isotope dilution analyses, data evaluation is simpler because isotopically labeled analogs of the
    pollutants are spiked into every sample. If recovery of a labeled compound spiked into a sample is not
    within the range specified in the method, and results of analysis of the ongoing precision and recovery
    standard are within the respective limits, sample results would be considered invalid. When labeled-
    compound recoveries are outside of method specifications, the problem may be related to the sample
    matrix. The  isotope dilution methods specify that, in these instances, the sample should be diluted
    with reagent water and reanalyzed. If the labeled compound recoveries meet the method specifications
    after dilution of the sample, the sample results are acceptable, although the sensitivity of the analysis
    will be decreased by the dilution.

    For some sample matrices, even dilution will not resolve the problem, and for other matrices, the loss
    of sensitivity precludes use of the results for determining compliance. In these instances, additional
    steps need to be taken to achieve acceptable results.

    Steps that may be taken when the results of matrix-spike or labeled-compound recoveries are not
    within the limits specified in the methods are described in Chapter 6 of this document. These steps
    include suggestions for more extensive extraction and cleanup procedures, for sample dilution, and for
    other measures to overcome matrix interference problems.
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10. Control limits for Recovery of Spiked Analytes or Labeled Compounds in Samples

    The 600- and 1600-Series methods specify that after the analyses of five spiked samples, control limit
    is constructed for each analyte.  The control limits for each analyte is computed as the mean percent
    recovery plus and minus two times the standard deviation of percent recovery for each analyte. The
    laboratory should then update their control limits after each five to ten subsequent spiked sample
    analyses.

    For non-isotope dilution results, the control limits can be used to estimate the true value of a reported
    result and to construct confidence bounds around the result. For example, if the result reported for
    analysis of phenol is 25  (ig/L (ppb), and the statement of data quality for phenol is 70% +30% (i.e., the
    mean recovery is 70% and the standard deviation of the recovery is 15%), the true value for phenol
    will be in the range of 28-43 (ig/L (ppb), with 95% confidence.  This range is derived as follows:

    Lower limit = [(25 + 0.7)- (25  x 0.3)] = {35.7- 7.5] = 28 ug/L (ppb)

    Upper limit = [(25 + 0.7) + (25 x 0.3)] =  {35.7 + 7.5] = 43 ug/L (ppb)

    Many laboratories do not maintain or provide control limits with sample results, in which case a data
    reviewer should contact the laboratory to determine if the control limits are being maintained for each
    analyte. If necessary, the reviewer can construct a control limits from individual data points if the
    laboratory has records of recoveries for matrix spikes.

    Statements of data quality for isotope dilution methods are based on the recoveries of the labeled
    compounds.  Using an isotope dilution method, the sample result has already been corrected for the
    recovery of the labeled analog of the compound. Therefore, for a reported result for phenol  of 25 (ig/L
    where the standard deviation of the labeled phenol recovery is 15%, the true value for phenol will be in
    the range of 17-32 (ig/L, with 95% confidence, derived as follows:

       Lower limit = [25 - (25 x 0.3)] = 17 pg/L (ppb)

        Upper limit = [25 + (25 x 0.3)] = 32 ug/L (ppb)

    The lack of control limits does not invalidate results, but makes  some compliance decisions more
    difficult. If the laboratory does  not maintain control limits there may be increased concern about both
    specific sample results and the laboratory's overall quality assurance program.

11. Contol limits for the Laboratory (Methods 1624 and 1625)

    In addition to statements of data quality for results of analyses of the labeled compounds spiked into
    the samples, Methods 1624 and 1625 require that control limits be constructed from the initial and
    ongoing precision and recovery data. The purpose of the control limits is to assess laboratory
    performance in the practice of the method, as compared to the assessment of method performance
    made from the labeled compound results for the samples. Ideally, the two limits would be the same.
    Any difference is attributable to either random error or sample matrix effects.

    If the laboratory is practicing isotope dilution methods, the data reviewer should review the control
    chart for the  laboratory. If the laboratory  does not make these statements available for the reviewer,
    they may be  requested.  If the laboratory still does not make them available, it does not necessarily
    invalidate any data, but indicates that the laboratory may not be  following the method as written.
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                                                                                                                       Chapter 8
When a Matrix Interference Is Demonstrated

       The preceding chapters describe how to overcome matrix interference problems and case histories of matrix interference problems that
were mitigated. This chapter describes help that may be available when all attempts at overcoming matrix interference problems have been
exhausted.

Poor Recovery or Precision of Matrix Spikes

       The most common indication of a matrix problem will be recovery or precision of the matrix spike and matrix spike duplicate (MS/MSD)
outside of the QC acceptance criteria in the method or QC acceptance criteria suggested in the Streamlining Initiative (see Chapter 4 of this
document). Once a matrix interference is demonstrated to be the cause of a laboratory's inability to meet the QC acceptance criteria, the laboratory
should document the interference and attempt to overcome it using the procedures suggested in the analytical method, in Chapter 6 of this
document, and other techniques in the test method or technical literature.

       If an allowance for matrix effects is warranted or appropriate without a demonstration that a matrix interference exists and without an
attempt to overcome the matrix interference, such an allowance provides a disincentive for addressing interferences that may be overcome using the
procedures  recommended in this document and in the method. The discharger should be familiar with its wastewater and thus able to find solutions
to matrix interference problems. However, a site-specific or facility-specific allowance may be warranted after all efforts to remove the
interference(s) have been exhausted, and should be handled on a case-by-case basis by the regulatory/control authority.

Inability to Meet the Method Detection Limit  (MDL)

       Another common indication of a matrix interference is that measurements cannot be made at low levels because interferences are  present at
these levels.

       Statements of the performance in EPA methods, including estimates  of MDLs, are estimates based on the Agency's evaluation of  a method
in various performance studies, and the method may not achieve all of the stated performance  characteristics in all possible sample matrices.  The
Scope and Application section of most modern methods approved for use in EPA's wastewater programs states:  "The detection limit and minimum
level of quantitation in this method usually are dependent on the level of interferences rather than instrumental limitations."  Therefore, the MDL
and minimum level of quantitation (ML) should be treated as "presumptive"  performance characteristics. These characteristics may vary
depending on the sample matrix and on the concentration of interest.  The MDL issue has not been resolved and may change.

       The MDL procedure at 40 CFR Part 136, Appendix B allows determination of an MDL in a matrix other than reagent water (see the Scope
and Application section of the MDL procedure). A permit could specify a different detection or quantitation limit when a discharger demonstrates


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that a different limit is appropriate for its effluent based on the presumptive statement at the beginning of most modern EPA methods, and
statements in the MDL procedure. After the discharger demonstrates that the approved test method cannot achieve the presumptive detection or
quantitation limit on an effluent-specific basis, the discharger and regulatory authority should work cooperatively to establish the permit limit using
a procedure such as the procedure given at 40 CFR Part 132, Appendix F, Procedure 8.  This procedure, titled Water Quality-based Effluent
Limitations Below the Quantification Level allows a discharger to establish an effluent-specific ML.

       Although EPA has provided the procedure  above to develop an effluent-specific ML, EPA recommends that the discharger attempt to
achieve the MDL and ML stated in the approved method by using the interference-reducing procedures given in this document and the analytical
method.  Prior to allowing the adjustment of a permit limit because the discharger reports it is unable to achieve the MDL and ML the appropriate
method approved at 40 CFR Part 136, the regulatory authority should review the steps taken by the discharger to reduce interferences to ensure that
all reasonable efforts have been made to achieve the permit limit. It is critical that the permittee be able to measure and accurately report results at
or above their permit limit and the achievement of method specified MDLs or MLs is of less importance.

Allowance for a Matrix Interference

       Because every situation is different, EPA has not adopted a rigid protocol for obtaining data that demonstrate that a matrix interference
exists, nor can a hard-and-fast rule be developed to state the conditions under which an allowance for a matrix interference should be granted.  After
all attempts at resolving the matrix interference are unsuccessful, the most common analytical solution to a matrix interference problem is to dilute
the sample with reagent water until the precision and recovery are within normal levels. No more than the minimum amount of dilution should be
used. The effect of this dilution will be to raise the MDL and ML and may necessitate development of an effluent-specific MDL and ML. Should
this situation arise, EPA suggests that the regulatory/control authority solicit and evaluate the following information to demonstrate that an
allowance for matrix interferences in the form of an effluent-specific MDL and ML may be appropriate:

•   MDL, IPR, and blank data demonstrating that the laboratory can perform the  method;
•   Field, equipment, and reagent blank data demonstrating that the sampling and analysis systems are free from contamination at the levels
    required for reliable determination of the pollutant;
•   MS/MSD data (where applicable) demonstrating that a potential matrix interference exists because the recovery and or precision is not within
    the QC acceptance criteria of the method;
•   Confirmation of the out-of-specification MS/MSD recovery or precision by a second laboratory;
•   Identification of the potential interferent(s);
•   Steps taken to attempt to mitigate the interference (e.g.,  sample, extract, or digestate concentration; sample  dilution; use of a larger sample size;
    use of cleanup  procedures; use of pH change prior to extraction; use of a greater amount of a removal reagent; use of techniques to selectively
    remove the  interferent; etc.); and
•   Calculation of an effluent-specific  MDL using the procedure at 40 CFR Part 136, Appendix B, and calculation of an ML using the procedure
    given at 40  CFR Part 132, Appendix F, Procedure 8;
•   Other methods approved for NPDES compliance which utilize different approaches were tried.
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       Once the regulatory/control authority receives these data, the authority would make a determination that an effluent-specific MDL and ML
are appropriate.
Sources of Additional Help and Information
                                                                                                                     Chapter 9
       Following are several sources of information and EPA contacts related to the issues addressed in this document. Please visit the websites
(listed below), and/or obtain a copy of the EPA CD-ROMs for reference information on analytical methods and topics discussed in this guidance.

Web Sites
EPA's home page
EPA's Office of Science and Technology's
water science analytical methods pages
Effluent Guidelines
http://www.epa.gov
http://www.epa.gov/ost/methods
or
http : //www . epa. gov/waterscience/methods
http://www.epa.gov/ost/guide
Method Indices
EPA Region 1 Library
EPA Information Sources
National Environmental Methods Index
(NEMI)
http : //www .epa. gov/epahome/index/
http://www.epa.gov/epahome/index/kev.htm
http://www.nemi.gov

Office of Water CD-ROMs

       Selected Office of Water Methods and Guidance, Version 5 (EPA 821-C-04-001; September 2004)
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Water Docket

       The Water Docket contains copies of materials that support our rules under the Safe Drinking Water Act (SDWA) and Clean Water Act
(CWA). These materials include Federal Register notices, references cited in these notices; health criteria, analytical methods, treatment
technology, and economic impact and environmental assessment data; development documents, public comments, and other background
information.

       US Environmental Protection Agency
       EPA Docket Center (EPA/DC)
       Public Reading Room
       Room B102, EPA West Building
       1301 Constitution Avenue, NW
       Washington, DC 20460

The Docket is open to the public on all Federal government work days from 8:30 a.m. until 4:30 p.m. A reasonable fee may be charged for
photocopying. On-line Docket searches may be performed at http://www.epa.gov/ow/docket.html.

Federal Register

       The Federal Register page is at http://www.gpoaccess.gov/fr/index.html.  All issues of the Federal Register from 1994 to the present are
online. Federal Register notices prior to 1994 may be found at a library or through a search service.  Search instructions for the Federal Register
are at the Government  Printing Office (GPO) web site at http://www.gpoaccess.gov.

Code of Federal Regulations

       All issues from 1996 to the present are on line. The Code of Federal Regulations (CFR) is at http://www.gpoaccess.gov/cfr/index.html.
CFRs prior to 1996 may be found at a library or through a search service.
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Approval of an Alternate Test Procedure or Questions Specifically Related to this Guidance

       Procedure for nationwide use (see the regulations at 40 CFR Parts 136.4 and 136.5)

          Analytical Methods Staff (4303T)
          U.S. EPA
          Ariel Rios Building
          1200 Pennsylvania Avenue, N.W.
          Washington, DC 20460
          email:  OSTCWAMethods@epa.gov

Procedure for use on a specific discharge (see the regulations at 40 CFR Parts 136.4 and 136.5)
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Sources for Supporting Documents
Note:  These sources are documents referenced in this document. For a more comprehensive list of guidance and other documents, see EPA's
       waterscience, yosemite, and other websites, or perform an online search for the document by title or subject.
Table 9-1 Sources for Supporting Documents
Subject
Methods Update
Rule
Clean spaces
guidance
Cleanroom guidance
Mercury; Method
1631 guidance
Methods, wastewater
and drinking water
Methods, historical
Methods and
guidance
Metals sampling
techniques
evaluation
Title of Guidance
Guidelines Establishing Test Procedures
for the Analysis of Pollutants Under the
Clean Water Act; National Primary
Drinking Water Regulations; and National
Secondary Drinking Water Regulations;
Analysis and Sampling Procedures; Final
Rule
Guidance on Establishing Trace Metal Clean
Rooms in Existing Facilities
Trace Metal Cleanroom, prepared by the
Research Triangle Institute
Method 1631, Revision E: Mercury in Water by
Oxidation, Purge and Trap and Cold Vapor
Atomic Fluorescence Spectrometry
EPA Methods and Guidance for Analysis of
Water
Methods for Chemical Analysis of Water and
Wastes (MCAWW)
Selected Office of Water Methods and Guidance,
Version 5
Evaluating Field Techniques for Collecting
Effluent Samples for Trace Metals Analysis
Document number
EPA821-F-06-005
EPA821B96001
RTI/63 02/04/02 F
EPA821-R-02-019
EPA821-C-99-004
EPA 600/4-79-020
EPA821-C-04-001
EPA-821-R-98-008
Date
March 12, 2007
January 1996
October 1995
August 2002
June 1999
March 1983
September 2004
June 1998
Source
72 FR 11200
http : //www . epa.gov/wat
erscience/methods/upda
te2003/index.html
http://yosemite.epa.gov/
water/owrccatalog .nsf
Research Triangle
Institute
http : //www . epa.gov/wat
erscience/methods/163 1
guid.pdf
NTIS1 PB99-500209
NTIS1 PB84-128677

http://yosemite.epa.gov/
water/owrccatalog .nsf
46
March 2007

-------
Table 9-1 Sources for Supporting Documents
Subject
Metals sampling
video
Metals data
evaluation guidance
Method flexibility
Oil and grease;
Method 1664
guidance
Radiochemistry
method guidance
Sampling guidance
Whole-effluent
toxicity (WET)
testing guidance
Whole-effluent
toxicity (WET)
variability guidance
Title of Guidance
Office of Water Methods and Guidance, Version
2.0- Suite (video and CD-ROM; includes
methods on CD-ROM EPA 821-C-99-004)
Guidance on the Documentation and Evaluation
of Trace Metals Data Collected for Clean Water
Act Compliance Monitoring
Streamlining Initiative - Guide to Method
Flexbility and Approval of EPA Water Methods
Analytical Method Guidance for EPA Method
1 664A Implementation and Use (40 CFR Part
136)
Multi-Agency Radiological Laboratory
Analytical Protocols Manual (MARLAP
Manual)
Method 1669: Sampling Ambient Water for
Trace Metals at EPA Water Quality Criteria
Levels
Method Guidance and Recommendations for
Whole Effluent Toxicity (WET) Testing (40 CFR
Part 136)
Understanding and Accounting for Method
Variability in Whole Effluent Toxicity
Applications Under the National Pollutant
Discharge Elimination System Program
Document number

EPA821-B-96-004
EPA-821-D-96-006
EPA821-R-00-003
(EPA 402-B-04-
00 1 A to C (in three
volumes)
EPA821-R-96-011
EPA821-B-00-004
EPA 833-R-00-003
Date
2002
July 1996
December 1996
February 2000
December 2004
July 1996
July 2000
June 2000
Source
NTIS1 PB2002-500076,
includes video and
methods on CD-ROMs
http://yosemite.epa.gov/
water/owrccatalog .nsf
http://epa.gov/waterscie
nce/methods/guide/flex.
html
http://www.epa.gov/wat
erscience/methods/1664
guide.pdf
69 FR 77228

http://www.epa.gov/wat
erscience/WET
http://www.epa.gov/wat
erscience/WET
1 National Technical Information Service, http://www.ntis.gov




47
March 2007

-------
&EPA
    United States
    Environmental Protection
    Agency
    Solutions to Analytical Chemistry
    Problems with Clean Water Act Methods
    March 2007
    Appendices
     A) Text of October 26, 1984 Preamble, pp. 7-11
     B) Text of Preamble to March 12, 2007 Methods Update Rule (Note flexibility
    only applies to 40 CFR Part 136 methods)
     C) Recommended Approved Modifications to EPA Method 625
                                                  March 2007

-------
       31. The rule approves the use of newer versions of 19 methods published by AOAC-




International. The new versions of these methods are published in Official Methods of Analysis




of AO AC-International, 16th Edition, 1995.




       32. The rale approves the replacement of the mercuric sulfate catalyst with copper sulfate




in methods approved for the determination of total Kjeldahl nitrogen (TKN).




       33. The rule approves the use of styrene divinyl benzene beads and stabilized formazin as




alternatives to the presently approved formazin standard for determination of turbidity.




                           preamble  to me APril 2004 proposed rule (69 FR 18213), EPA is




adopting a new ง136.6 to introduce greater flexibility in the use of approved methods. The




section describes the circumstances in which approved methods may be modified and the




requirements that analysts must meet to use these modified methods in required measurements




without prior EPA approval. The rule also includes language at ง 136.6 (c) to clarify that analysts




need only meet method performance requirements for target analytes (those analytes being




measured for NPDES reporting) when using multi-analyte methods for compliance monitoring




purposes.  The rule also includes the language at ง136.6 (d) to allow explicitly the use of




capillary (open tubular)  GC columns with EPA Methods 601-613, 624, 625, and 1624B as




alternatives to the packed GC columns specified in those methods, provided that analysts




generate new retention time tables with capillary columns to be kept on file with other




information for




       35. The rule withdraws 109 methods contained in EPA's "Methods for the Chemical




Analysis of Water and Wastes" for which approved alternatives published by voluntary




consensus standards bodies (e.g., ASTM and Standard Methods) are available.
                                          16

-------
   ^


10, Section -136,6 is added to Part 136to feadag follows:  '                  ,n P  ,
                                                                       { • i s — t
ง 136.6  Method Modifications and Analytical Requirements.








    (a) Definitions of terms used in this Section.








    ( 1) Analyst means the person or laboratory using a test procedure (analytical method) in this



Part.








    (2) Chemistry of the Method means the reagents and reactions used in a test procedure that



allow determination of the analyte(s) of interest in an environmental sample.








    (3) Determinative Technique means the way in which an analyte is identified and quantified



(e.g., colorimetry, mass spectrometry).








    (4) Equivalent Performance means that the modified method produces results that meet the



QC acceptance criteria of the approved method at this part.








    (5) Method-defined Analyte means an analyte defined solely by the method used to determine



the analyte. Such an analyte may be a physical parameter, a parameter that is not a specific



chemical, or a parameter that may be comprised of a number of substances! Examples of such



analytes include temperature, oil and grease, total suspended solids, total phenolics, turbidity,



chemical oxygen demand, and biochemical oxygen demand.

                                  ' "•'-" " "W**. •**>. fT^^




                                          175

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are met. When changing from a packed column to a capillary column, retention times will




change. Analysts are not required to meet retention time specified in the approved method when




this change is made. Instead, analysts must generate new retention time tables with capillary




columns to be kept on file along with other startup test and ongoing QC data, for review by




auditors.









   (2) Increased sample volume in purge and trap methodology.  Use of increased sample




volumes, up to a maximum of 25 mL, is allowed for an approved method, provided that the height




of the water column in the purge vessel is at least 5 cm.  The analyst should also use one or more




surrogate analytes that are chemically similar to the analytes of interest in order to demonstrate




that the increased sample volume does not adversely affect the*SrjaMialresults.
                    *                          *           '"•'v^''^^h:^^gyaMH!ป>:-"^'*
                                                               - ••<~'*fH,,fV>pt
-------
             Federal Register  /  Vol. 49,  No, 209 /  Friday,  October 26, 1984  / Rules  and Regulations
 regulatory framework for the specific
 limits is being promulgated as final.
   Table ID contains the 67 parameters
 included under the general "pesticides"
 parameter in the 1976 Guidelines.
 Although most pesticides are organic
 compounds, they have been listed
 separately in Table ID rather than with
 the other organic parameters in Table 1C
 because  of the wide association
 between this subset of organic
 compounds and their end use. Sixteen of
 the 67 parameters are priority pollutants.
 Three additional pesticides were
 identified as priority pollutants under
 the consent decree. Table ID therefore
 now identifies 70 specific pesticides, of
 which 13 are priority pollutants.
 Methods 603 and 625, which were
 proposed for the priority organic toxic
 pollutants, were revised to incorporate
 substantive comments. All other
 references in Table ID have been
 updated, but the updated references do
 not require any substantive changes
 from previously approved test
 procedures.
   Table IE now includes the five
 radiological test procedures approved in
 the 1976  Guidelines. All references have
 been updated, and an EPA reference has
 been added. There are no substantive
 textual changes in these updated test
 procedures.



   Analyses for organics depend upon a
 variety of chromatographic techniques.
 See subsection III-B above, EPA
 proposed and is approving two HPLC
 methods (605 and 610), 10 GC methods,
 and three GC/MS methods (613, '624,
 and 625). In addition, EPA has
 responded to critiques of Methods 624
 and 625 by approving two GC/MS/
 isotope dilution variants (1624 and 1625).
 Each method is accompanied by a
 specific set of quality assurance (QA)
 procedures. The QA process relies on
 specific control limits calculated for
 each parameter for which the method
 can be used. The control limits indicate
 the outer range of precision and
 accuracy found in an extensive inter-
 laboratory study. The limits represent
 the minimum threshold of quality
 expected of competent laboratories: 95
 percent confidence level per compound
 for the 600 series and the 99 percent
 confidence level across the set of
 compounds for the 1624 and 1625
 methods. Most analyses should have far
 better precision and accuracy. The
 calculations of specific numerical
 control limits for the calibration and
 quality control sections of the GC,
 HPLC^and GC/MS test procedures is    ..
''interim final'. This mejnsjhat^thev.are	
 legally effective, but that EPA will
 accept comments on their calculation.
 All other parts of these test procedures
 are finally approved for the analysis of
 the parameters which are indicated in
 Tables 1C and ID.
   Each method is approved for specific
 organic compounds. In general, GC
 Methods 601-603 and GC/MS Methods
 624 and 1624 are approved for the
 analyses of the purgeable priority
 pollutants. GC Methods 604 and 606-612
 and GC/MS Methods 625 and 1625 are
 approved for the analysis of the non-
 purgeable, volatile priority pollutants,
 including, for Method 625 only, the
 priority pesticide pollutants. Method 625
 is also approved for screening samples
 for 2,3,7,8-TCDD (2,3,7,8-
 tetrachlorodibenzo-p-dioxin-);-but only •
 GC/MS Method 613 is approved for final
 qualitative confirmation or
 quantification of 2,3,7,8-TCDD in
 samples. HPLC Methods 605 and 610 are
 also approved for the analysis of the
 nonpurgeable volatiles (the benzidines
. and polynuclear aromatic
 hydrocarbons). MeTltSdงaB21ซia:4625
 are
 with the other test procedures which are
 being approved for the analysis of the
 priority toxic organic pollutants. Their
 most significant difference from
 Methods 824 and 625 is  the requirement
 that, where available, stable,
 isotopically-labeled analogs of the
 priority pollutants are to be used as
 method internal standards,jSjH'c^*
 Methods 624 and 625l|lj|teui
 flexibility in the selection offmernal
 calibration standards and surrogate
 standards, Methods ^2ฅฎa-t625jarei *
 in essence,
 permitted by Methods 624 and 625. They
 improve on Methods 624 and 625 and
 are generally preferable. However,
 Methods 624 and 625 are also being
 approved because they are widely
 available, slightly less expensive, and
 they are of use when interference and
 recovery efficiency are not expected to
 be problems.
   In general, both GC/MS and non-MS
 test procedures have been approved for
 each of the priority toxic pollutants.
 Most of the revisions of the proposed
 test procedures were made either for
 clarification or to give the analyst more
 flexibility to practice professional
 judgment. These procedures now
 contain a section on safety, cautioning
 analysts of the potential hazards
 associated with exposure to the
 chemical reagents required by the test
 procedures, or to the toxic chemicals
 being analyzed. Recommended and^w' •
 mandatory quality assurance practices-•
are also given in each of the test
procedures,
  Methods 601-604, 606-609, 611-S13.
624, 625.1624, and 1625 include
specifications for performing the tests. •
These specifications are based on a
required primary GC column and
specified detector. A primary HPLC
column and specified detector are
required for Methods 605 and 610 and
specifications are provided. The primary
column is also used to identify the
pollutant. A secondary column and
detector are also defined, but not
required, for non-MS Methods 601-604
and 606-611. The secondary column and
detector can be use.d for confirmation of
priority pollutants identified by the
primary column for unfamiliar (non-
routine) samples (see sections 1.2 of the
methods). The GC/MS test procedures
are suggested as the confirmatory test
for identifications made by Methods 605
and 612, and may also be used as the
confirmatory test for identifications
made by Methods 6OT-6Q4 and 606-611,
For example, an unfamiliar sample
which would be likely to need
confirmation would be a single sample
taken for an NPDES application. See 40
CFR 122,21. In contrast, routine
monitoring, such as  that for discharge
monitoring reports, would be less likely
to require a secondary column for
confirmation since the sample is more
likely to be familiar to the analyst.
  Methods 606,609,611 and 612 all use
essentially the same procedure for
sampling, sample extraction, and
concentration. Thus a single sample may
be used to measure the parameters
within the scope of these methods.
  Sample container materials,
preservation techniques, and holding
times are critical to  the procedures and
are specifically defined (Methods 601-
613,624, 625,1624 and 1625). The design
and operation  of the purge-and-trap
device in Methods 601-603,624 and
1624, and the sample extraction
procedures of Methods 604-613,625 and
1625 arjyjH||iy|fy defined as well.

                         maae*to •
                      the remaining
parts of Methods 601-613, 624,625,1624
and 1625. In Methods 604-613, after the
sample has been extracted, the analysts
are now free to choose a technique to
concentrate the extract. The same
flexibility is provided for selecting the
GC or HPLC configurations (column
packings, operating conditions, and
detectors). When analysts use
concentration techniques or
chromatographic configurations other
than those described in the test"* -ซ"**:ซ***
proceduresrthefcapproackes'iftffsFlfTgeP^"

-------
 10          Federal  Register / Vol. 49, No.  209 / Friday,  October 26,  1984 / Rules and Regulations
 they were tested, and sample matrices
 which show labeled compound
 recoveries significantly different from
 recoveries of these compounds from
 reagent water are diluted with reagent
 water to bring these recoveries into the
 expected range.
   It is also important to note that the
 studies provide a strong basis for setting
 control limits which represent a range of
 acceptability. The studies show that
 most laboratories will do far better,
 especially on a single-operator, single-
 laboratory basis. Other performance
 studies, completed since the inter- •
 laboratory analyses, incorporate too
 much flexibility to be directly analogous
 to EPA's collaborative test of the
 methods. However, they appear to
 confirm the assumption that most
 laboratories will exceed the minimum
 standards and indicate that method
 variability will be well within the range
 of the control limits.
   The final specifications derived for all
 of the organ ics methods (except 603)
 were the result of a statistical analysis
 of the data from the multi-laboratory
 studies. These specifications adopt
 initial precision and accuracy for all
 methods. For start-up calibration
 verification, they specify  control limits
 for Methods 601, 602,624,1824,625 and
 1625. For on-going accuracy, they
 specify control limits for recovery of
 pollutant spikes for Methods 601-613,
 624,  and 625, and for recovery of labeled
 compound spikes for Methods 1624 and
 1625. The  methods allow  for
 simultaneous testing of all the
 parameters listed in each method.
   In theory, a problem could arise from
 simultaneous tests for numerous
 compounds. The control limits have
 been calculated to allow only a 5%
 likelihood that a result that exceeds the
 limits for each compound is merely a
 statistical fluctuation (rather than actual
 error). However, the chance of
 "statistical error" rises with the number
 of compounds being tested.
   EPA has corrected for this possibility
 in several ways. First, most users will
 not apply  each analysis to all
 parameters simultaneously; thus they
 will have a greater chance of passing all
 test criteria. Second, in order to allow
 for simultaneous testing of all
 parameters in a given method, the
 specifications for accuracy and
 precision have either been broadened,
 or a re-test has been allowed, or both.
 The  technique of using a re-test was
 chosen because a one-test-only
 specification which allowed for
 simultaneous testing of a large number
 of parameter* would be 30 broadjasjo
' have'h'ttle^eariing. The^rovisjpnjorji
^re^test preserved a meaningful—-—~
specification while allowing for
simultaneous testing of all parameters. If
a laboratory fails the re-test as well as
the initial test, the likelihood of
"statistical error" is extremely low (5%
times 5%, i.e., .0025 for a given
compound). Third, when a re-test is
required, it need only be performed on
the particular compounds which failed
the initial test. Finally, the control
criteria for Methods 1624 and 1625—
those most likely to be simultaneously
used on many compounds—were
determined based on the 99% confidence
level.
  As a voluntary guide to laboratories
practicing a given method, the following
Exhibit 1 gives suggested numbers of
first pass, test criteria .failures which are
unlikely  if the laboratory is satisfying
the probability based quality control
specifications. It assumes all parameters
in a given method are tested
simultaneously. The Exhibit indicates
the maximum number of parameters for
which each method can be used
simultaneously. The two right-hand
columns indicate a certain number of
unacceptable results. 'If the analyst finds
that number, or a greater number, of
unacceptable results, he may conclude
that the entire analysis is flawed. If so, it
may be more efficient to repeat the
entire analysis than to re-examine only
the compounds which exceed the
control limits.

EXHIBIT 1.—SUGGESTED MAXIMUM NUMBER OF
  TEST CRITERIA  FAILURES  WHICH JUSTIFY
  REPEATING ENTIRE ANALYSIS
Method
W , , „-
602. ... _ j
603/635 	
804 .____™__™,
60S „ 	 , 	 , 	 	
607 	 J
SO". 4,i,, ,,
•OS ___.__„__ 	
6 10 --,.,,- 	 ™_™_
611 	 	
612 ..,..„. ,,..„„....,.„„„„
613 ________
624 ..r.-.,r.,,,ป.,.'..T..tf,,,trป
625 .„ J,_,,,,,. ,. .„,„,
1824
1625 _____________
Number of
(imulum-
ouป
panro-
eten
29
7
2
11
6
3
25
4
16
S
S
1
31
81
66
151
NUfttoOf Of tfiflt Crit9*~l
Mura*
Start-op '
7
3
2
4
3
2
6
3
5
3
4
2
7
11
12
1
Ongoing'
4
2
2
3
2
2
4
2
3
2
3
1
S
7
7
5
  1 Baaed on twic* Urn number at parameter! bwng tested
line* both Kojracy tnd precision in being evaluated
  * Bttad on the numbar of parameter! being tested.

  Section 8 of each method defines
acceptable analytical performance limits
for the GC, HPLC, and GC/MS test
procedures (Methods 601-613,624,625,
1624. and 1625). These acceptable
performance limits are also specified in
Footnote 7 to Table 1C. "List of
   -i, .<: •,,-- j _ v 'V^*-*1*-*-!* j---••'••"-••ปi * ซ--•_ _ni -v'.' *;r.ic-.-*ป',"ซ'r*
Approved Teat Procedures for Non-   '^
Pe'sticidi 0rgffii^Sonip6unIs?'-anc[—*-
 Footnote 7 to Table ID, "List of
 Approved Test Procedures for
 Pesticides." System performance is
 acceptable only when the average
 recoveries and standard deviations of
 spikes of the pollutants of interest into
 reagent water meet these performance
 standards. Where large numbers of
 parameters are being analyzed (see
 Exhibit 1 above), there is an increased
 chance that at least one parameter will
 fail for either average recovery or
 standard deviation limits based purely
 on chance. Where such failure occurs,
 the spiking and recoveries must be
 repeated, but only for the failed
 parameters. Repeated failure confirms a
 general problem with the analytical
 measurement system. When such failed
 recoveries are experienced the system Is
 judged to be out-of-control for the failed
 parameter. Thus, the results for the
 failed parameters in unspiked samples
 are suspect and cannot be reported to
 show regulatory compliance.
   The acceptance criteria for spikes into
 samples for each parameter were
 calculated to include both an allowance
 for error in prior measurement of the
 background and another allowance for
 error in prior measurement of spike
 concentrations. The calculation
 assumed a spike-to-background ratio of
 5 to 1. Thus such error will be accounted
 for to the extent the analysts' spike-to-
 background ratio approaches 5 to 1. In
 many cases this allows analysts a
 greater margin of error than should
 actually be expected. This is because
 the calculation assumes  that two prior
 errors are cumulative, ignoring the
 degree to which they actually cancel
 each other out.
   Today's final test procedures
 represent an effort to provide the
 maximum uniformity that is practical for
 a wide cross-section of classes of
 chemical compounds. They will be
 continually reevaluated for their general
 applicability to complex wastewater
 matrices.
   The substantive revisions made in the
 GC, HPLC, and GC/MS methods ia
 response to comments are discussed in
 the public participation section of this
 preamble. Three of the most significant
 changes include; (1) Addition of a
 confirmatory column to Method 602; (2)
 deletion (from 613} of the gas
 chromatographic/electron capture (GC/
 EC) test procedure for screening for
 2,3,7,8-TCDD, and (3] revision of
 Methods 613 and 625 to show that
 Method 825 may be used whenever
 screening for 2,3,7,8-TCDD is required.
 The full text of the apjiroved GC, HPLC Vw
jano* GC/MS tesfpf6'ce
-------
Federal Register  /  Vol. 49.  No. 209 / Friday, October  26. 1984  / Rules and Regulations
                                   11
   The GC. HPLC, and GC/MS test
 procedures are now cited in the
 regulations in the new Table 1C, "List of
 Approved Test Procedures for Non-
 Pesticide Organic Compounds," and
 Table ID, "List of Approved Test \
 Procedures for Peso||!|t."      J

 C. ICP Test Procedure

   The ICP test procedure is cited in the
 regulation as an additional analytical
. option for trace metal analysis in the
 new Table IB, "List of Approved
 Inorganic Test Procedures."
   The ICP test procedure. Method 200.7,
 has been changed only slightly from the
 version proposed on December 3,1979.
 EPA proposed that lithium and
 strontium be analyzed using the ICP test
 procedure, since these parameters could.
 be analyzed using this method. Because
 EPA did not propose or develop
 accuracy or precision criteria for these
 parameters, EPA is unable to approve
 the ICP test procedure for them. EPA is
 considering the ICP and other
 alternative test procedures in a separate
mlemaking. In light of additional
 information received in the public
 comments showing good recoveries for
 antimony and adequate recoveries for
 thallium by the proposed test procedure,
 both of these metals have been added to
 the scope of the ICP test procedure. Also
 in response to public comments the
 detection limit for silica has been
doubled and the wavelengths of the
metal are now given to the third
decimal. In section 3 of the ICP test
procedure a  new definition for "Quality
Control Sample" has been provided for
clarification, and a new section on
safety has been added to alert the
analyst to the hazards of the toxic
reagents and pollutants involved. Other
revisions made in response to comments
                           are discussed in the public participation
                           section of this preamble. The full text of
                           the ICP procedure is printed as
                           Appendix C to this regulation.
                           D. CBOrk Test Procedure
                             The final test procedure for CBODs is
                           essentially the same as that proposed.
                           See Section III-D, above. EPA's
                           proposed test procedure was taken from
                           a draft Standard Methods test procedure
                           for CBODs.
                             The final method language is the same
                           as the language now included in the 15th
                           edition of Standard Methods. This has
                           required minor changes from the
                           wording of the proposal, but no
                           substantive changes were required.

                           E. Table II: Required Containers,
                           Preservation Techniques, and Holding,..
                           Times
                             Table II in Section 138,3(eJ now
                           restricts  the materials of which sample
                           containers can be made, and specifies
                           the procedures by which samples are to
                           be preserved. Table II also limits the
                           maximum time for which samples may
                           be held from the the time of sampling
                           until they are analyzed. Table U has
                           been restructured in this final regulation
                           to correlate with the parameters in the
                           new Tables IA, IB, 1C, ID, and IE in
                           Section 136.3(a}. Table II allows cross-
                           reference between the container,
                           preservative, and holding times arid the
                           individual parameters in Tables IA, to
                           IE.
                            In response to comments, several
                           changes were made in Table II of the
                           final regulations for prescribed"
                           container materials, preservation
                           requirements, and holding times of
                           wastewater samples. Where supported
                           by comments, changes were made
                           primarily in holding times. In response
                           to comments, EPA has  adopted the
 requirement that some samples be
 analyzed immediately, to avoid sample
 degradation. This would be as soon as
 the sample is collected and labelled,
 generally within 15 minutes. Longer
 holding times are generally not
 appropriate where the sample may
 quickly degrade. However,  a longer time
 period may be justified under the
 variance procedure,.Exhibits 3 and 4.
 below, show that for organic compounds
 and pesticides, the holding times were
 generally extended from 30 days after
 extraction to 40 days after extraction.
 Changes were also made to enable a
 single sample to be used for analyses of
 extractable  organics and of pesticides.
 This was a step towards the goal of
 uniformity, sought by EPA and by the
 commenters.
   Table II as promulgated also allows a
 variance to holding times under
 ง 136.3{eJ. Analysts may exceed the
 holding times if they have data on  file to
 show that the specific types of samples
 are stable for a longer time and if they
 receive a variance from the  Regional
 Administrator.
   No changes were made for container
 materials, preservation requirements, or
 holding times in final Table  II from the
 proposed requirements for the biological
 parameters listed in Table IA, or the
 radiological parameters listed in Table
 IE. Changes  which were made in Table
 II forlnorganic parameters listed in
 Table IB, organic parameters listed in
 Table 1C, and pesticide parameters
 listed in Table ID are summarized in the
 following Exhibits 2, 3, and 4, of this
 preamble. Proposed and final container
 materials, preservation requirements,
 and holding times in Exhibits in 2, 3, and
4 are given only for the affected
pollutant parameters in Tables IB, 1C
and ID of the regulation.
                  EXHIBJT 2.-CHANGES MADE IN TABU II FOR TASU- IB PARAMETERS

-------
             UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C. 20460
MEMORANDUM
                                                                       OFFICE OF
SUBJECT:   Recommended Approved Modifications to EPA Method 625   WATER
FROM:      Richard Reding, Ghfef
             Engineering & Analytical Support Branch, EAD, OST

TO;          Quality Assurance Managers
             ATP Coordinators
             NPDES Coordinators

DATE:      November 1,2006

       The 304(h) methods branch recommends allowing several modifications to EPA
Method 625 for environmental permitting and compliance monitoring under the EPA's
Clean Water Act (CWA) programs. This memorandum does not address laboratory
certification requirements that states have mandated,

       The text in "Protocol for EPA Approval of Alternate Test Procedures for Organic
and Inorganic Analytes in Wastewatcr and Drinking Water" Section 1.3.2 allows
flexibility in the modification of "front end techniques" of the test method provided all
criteria in this section and all QC in the method are met and documented, This protocol
can be downloaded at
Recommendations on Method Modifications to EPA Method 625 when Capillary
Columns are used:

       1.    Combining sample extracts before analysis

       If the analytes can be reliably identified and quantified in the combined extracts,
       the extracts may be combined. If, however, the identification and quantitaiion of
       any analyte is adversely affected by another analyte, a surrogate, or an interferant.
       the extracts must be analyzed separately. If there is ambiguity, the extracts must
       be analyzed separately.

       2,    Reverse order of pH extraction

       The pH extraction sequence may be reversed to better separate acid and neutral
       components.  Neutral components may be extracted with either acid or base
       components,
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       Previously, neither of these modifications has been used with Method 625
       primarily because of limitations of the resolving power of the packed columns
       used. In 1985, EPA Region 3 Central Regional Lab requested a modification to
       method 625 as an alternate test procedure (ATP).  Although the approval was for
       limit use by EPA's Region 3, Central Regional Laboratory only, this modification
       has come to be used throughout the laboratory community  (sec attached memo).

       Why allow these modifications? Following the base-neutral than acid extraction
sequence of method 625 in some cases demonstrated the decomposition of some analytes
under basic conditions, Orgartochlorine pesticides may dechlorinate; phthalate esters
may exchange; phenols may react to form tannates. These reactions increase with
increasing pH.  Reversing the extraction pH sequence may better separate acid and
neutral waste components,

       Other Recommended Modifications to Method 625 '

       A smaller sample volume may be used to minimize matrix  interferences provided
       matrix interferences are demonstrated and documented.

       Alternate surrogate and internal standard concentrations other than those specified
       in the method are acceptable provided that method performance is not degraded;

       An alternate calibration curve and a calibration check other than those specified in
       the method;

       A different solvent for the calibration standards to match the solvent of the final
       extract.

       Other Method Flexibility News

       We are revising the "Guidance on Evaluation, Resolution, and Documentation of
Analytical Problems Associated with Compliance Monitoring" often referred to as the
"Pumpkin Book".  Many of the recommendations in the revised "Pumpkin Book" cover
ways to mitigate matrix effects.

       More explicit flexibility to make changes in approved methods without prior EPA
approval is now described at 40 CFR Part 136.6.  Such changes are only allowed if the
modified method produces equivalent performance for the analyte(s) of interest, and the
equivalent performance is documented. It is essential to consult the full text at 40 CFR
136.6 before undertaking method modifications.

       Please feel free to forward this information.  If you have any questions regarding
this memorandum, please contact Lemuel Walker of EASB/EAD/OST by email at
walker.|gmuel@:epa.gov.

cc     Lemuel Walker
             ATP Coordinator

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