[Federal Register Volume 68, Number 48 (Wednesday, March 12, 2003)]
[Proposed Rules]
[Pages 11770-11790]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-5712]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 136

[FRL-7463-1]
RIN 2040-AD53


Guidelines Establishing Test Procedures for the Analysis of 
Pollutants; Procedures for Detection and Quantitation

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: This action proposes revisions to the procedures for 
determining the sensitivity of analytical (test) methods under EPA's 
Clean Water Act (CWA). EPA's method detection limit (MDL) and minimum 
level of quantitation (ML) are used to define test sensitivity under 
the CWA. The MDL is used to determine the lowest concentration at which 
a substance is detected or is ``present'' in a sample. The ML appears 
in many EPA methods and has been used to describe the lowest 
concentration of a substance that gives a recognizable signal, or as a 
quantitation limit. The proposed revisions include clarifications and 
improvements that are based on a recent EPA assessment of the MDL and 
the ML and of alternative approaches for defining test sensitivity, 
peer review of the Agency's assessment, and earlier stakeholder 
comments on the existing MDL procedure. This proposal also revises the 
definition of the MDL to reflect the proposed revisions to the 
procedure. The Agency's assessment of existing EPA procedures for 
determining test sensitivity and alternative approaches is also made 
available for public comment in a separate notice in today's Federal 
Register (see Notice of Document Availability and Public Comment Period 
on the Technical Support Document for the Assessment of Detection and 
Quantitation Concepts).

DATES: Comments must be postmarked, delivered by hand, or 
electronically mailed on or before July 10, 2003. Comments provided 
electronically will be considered timely if they are submitted 
electronically by 11:59 p.m. Eastern Time on July 10, 2003.

ADDRESSES: Comments may be submitted by mail to Water Docket, U.S. 
Environmental Protection Agency (4101T), 1200 Pennsylvania Avenue NW., 
Washington DC 20460, or electronically through EPA Dockets at

[[Page 11771]]

http://www.epa.gov/edocket/, Attention Docket ID No. OW-2003-0002. See 
Unit C of the SUPPLEMENTARY INFORMATION section for additional ways to 
submit comments and more detailed instructions.

FOR FURTHER INFORMATION CONTACT: William Telliard; Engineering and 
Analysis Division (4303T); Office of Science and Technology; Office of 
Water; U.S. Environmental Protection Agency; Ariel Rios Building; 1200 
Pennsylvania Avenue, NW.; Washington, DC 20460, or call (202) 566-1061 
or E-mail at [email protected].

SUPPLEMENTARY INFORMATION:

A. Potentially Regulated Entities

    EPA Regions, as well as States, Territories and Tribes authorized 
to implement the National Pollutant Discharge Elimination System 
(NPDES) program, issue permits that comply with the technology-based 
and water quality-based requirements of the Clean Water Act (CWA). In 
doing so, NPDES permitting authorities, including States, Territories, 
and Tribes, make several discretionary choices when they write the 
permit. These choices include the selection of pollutants to be 
measured and, in many cases, limited in permits. If EPA has 
``approved'' (i.e., promulgated through rulemaking) standardized 
testing procedures under 40 CFR part 136 for the analysis of a given 
pollutant, the NPDES permit must include one of the approved testing 
procedures or an approved alternate test procedure. The testing 
procedures can include a specification for detection and quantitation 
levels that must be met. Therefore, entities with NPDES permits could 
potentially be regulated by the proposed revisions to the detection and 
quantitation procedures in this rulemaking. In addition, when an 
authorized State, Territory, or Tribe certifies Federal licenses under 
CWA section 401, they must use the standardized testing procedures and 
meet the associated detection and quantitation levels. Categories and 
entities that could potentially be regulated include:

------------------------------------------------------------------------
                                      Examples of potentially regulated
             Category                             entities
------------------------------------------------------------------------
State, Territorial, and Indian      States, Territories, and Tribes
 Tribal Governments.                 authorized to administer the NPDES
                                     permitting program; States,
                                     Territories, and Tribes providing
                                     certification under Clean Water Act
                                     section 401
Industry..........................  Facilities that must conduct
                                     monitoring to comply with NPDES
                                     permits
Municipalities....................  POTWs that must conduct monitoring
                                     to comply with NPDES permits
------------------------------------------------------------------------

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be regulated by this 
action. This table lists the types of entities that EPA is now aware 
could potentially be regulated by this action. Other types of entities 
not listed in the table could also be regulated. If you have questions 
regarding the applicability of this action to a particular entity, 
consult the person listed in the preceding FOR FURTHER INFORMATION 
CONTACT section.

B. How Can I Get Copies of This Document and Other Related Information?

    1. Docket. EPA has established an official public docket for this 
action under Docket ID No. OW-2003-0002. The official public docket 
consists of the documents specifically referenced in this action, any 
public comments received, and other information related to this action. 
Although a part of the official docket, the public docket does not 
include Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. The official public docket 
is the collection of materials that is available for public viewing at 
the Water Docket in the EPA Docket Center, EPA West Building, Room 
B102, 1301 Constitution Avenue NW., Washington, DC. The EPA Docket 
Center Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday 
through Friday, excluding legal holidays. The telephone number for the 
Public Reading Room is (202) 566-1744, and the telephone number for the 
Water Docket is (202) 566-2426.
    2. Electronic Access. You may access this Federal Register document 
electronically through the EPA Internet under the ``Federal Register'' 
listings athttp://www.epa.gov/fedrgstr/. An electronic version of the 
public docket is available through EPA's electronic public docket and 
comment system, EPA Dockets. You may use EPA Dockets at http://www.epa.gov/edocket/ to submit or view public comments, to access the 
index listing of the contents of the official public docket, and to 
access those documents in the public docket that are available 
electronically. Once in the system, select ``search,'' then key in the 
appropriate docket identification number.
    Certain types of information will not be placed in the EPA Dockets. 
Information claimed as CBI and other information whose disclosure is 
restricted by statute, which is not included in the official public 
docket, will not be available for public viewing in EPA's electronic 
public docket. EPA's policy is that copyrighted material will not be 
placed in EPA's electronic public docket but will be available only in 
printed, paper form in the official public docket. Although not all 
docket materials may be available electronically, you may still access 
any of the publicly available docket materials through the docket 
facility identified in B.1.
    For public commenters, it is important to note that EPA's policy is 
that public comments, whether submitted electronically or in paper, 
will be made available for public viewing in EPA's electronic public 
docket as EPA receives them and without change, unless the comment 
contains copyrighted material, CBI, or other information whose 
disclosure is restricted by statute. When EPA identifies a comment 
containing copyrighted material, EPA will provide a reference to that 
material in the version of the comment that is placed in EPA's 
electronic public docket. The entire printed comment, including the 
copyrighted material, will be available in the public docket.
    Public comments submitted on computer disks that are mailed or 
delivered to the docket will be transferred to EPA's electronic public 
docket. Public comments that are mailed or delivered to the Docket will 
be scanned and placed in EPA's electronic public docket. Where 
practical, physical objects will be photographed, and the photograph 
will be placed in EPA's electronic public docket along with a brief 
description written by the docket staff.

C. How and to Whom Do I Submit Comments?

    You may submit comments electronically, by mail, or through hand 
delivery/courier. To ensure proper receipt by EPA, identify the 
appropriate docket identification number in the subject line on the 
first page of your comment. Please ensure that your

[[Page 11772]]

comments are submitted within the specified comment period. Comments 
received after the close of the comment period will be marked ``late.'' 
EPA is not required to consider these late comments. However, late 
comments may be considered if time permits.
    1. Electronically. If you submit an electronic comment as 
prescribed below, EPA recommends that you include your name, mailing 
address, and an e-mail address or other contact information in the body 
of your comment. Also include this contact information on the outside 
of any disk or CD ROM you submit, and in any cover letter accompanying 
the disk or CD ROM. This ensures that you can be identified as the 
submitter of the comment and allows EPA to contact you in case EPA 
cannot read your comment due to technical difficulties or needs further 
information on the substance of your comment. EPA's policy is that EPA 
will not edit your comment, and any identifying or contact information 
provided in the body of a comment will be included as part of the 
comment that is placed in the official public docket, and made 
available in EPA's electronic public docket. If EPA cannot read your 
comment due to technical difficulties and cannot contact you for 
clarification, EPA may not be able to consider your comment.
    i. EPA Dockets. Your use of EPA's electronic public docket to 
submit comments to EPA electronically is EPA's preferred method for 
receiving comments. Go directly to EPA Dockets at http://www.epa.gov/edocket, and follow the online instructions for submitting comments. 
Once in the system, select ``search,'' and then key in Docket ID No. 
OW-2003-0002. The system is an ``anonymous access'' system, which means 
EPA will not know your identity, e-mail address, or other contact 
information unless you provide it in the body of your comment.
    ii. E-mail. Comments may be sent by electronic mail (e-mail) to: 
[email protected], Attention Docket ID No. OW-2003-0002. In 
contrast to EPA's electronic public docket, EPA's e-mail system is not 
an ``anonymous access'' system. If you send an e-mail comment directly 
to the Docket without going through EPA's electronic public docket, 
EPA's e-mail system automatically captures your e-mail address. E-mail 
addresses that are automatically captured by EPA's e-mail system are 
included as part of the comment that is placed in the official public 
docket, and made available in EPA's electronic public docket.
    iii. Disk or CD ROM. You may submit comments on a disk or CD ROM 
that you mail to the mailing address identified in Unit C.2. These 
electronic submissions will be accepted in WordPerfect or ASCII file 
format. Avoid the use of special characters and any form of encryption.
    2. By Mail. Send an original and three copies of your comments to 
Water Docket, U.S. Environmental Protection Agency (4101T), 1200 
Pennsylvania Avenue NW., Washington, DC 20460, Attention Docket ID No. 
OW-2003-0002.
    3. By Hand Delivery or Courier. Deliver your comments to the Water 
Docket Center, EPA West Building, Room B102, 1301 Constitution Avenue 
NW., Washington, DC, Attention Docket ID No. OW-2003-0002. Such 
deliveries are only accepted during the Docket's normal hours of 
operation as identified in Unit B.1.

C. How Should I Submit CBI to the Agency?

    Do not submit information that you consider to be CBI 
electronically through EPA's electronic public docket or by e-mail. You 
may claim information that you submit to EPA as CBI by marking any part 
or all of that information as CBI (if you submit CBI on disk or CD ROM, 
mark the outside of the disk or CD ROM as CBI and then identify 
electronically within the disk or CD ROM the specific information that 
is CBI). Information so marked will not be disclosed except in 
accordance with procedures set forth in 40 CFR part 2.
    In addition to one complete version of the comment that includes 
any information claimed as CBI, a copy of the comment that does not 
contain the information claimed as CBI must be submitted for inclusion 
in the public docket and EPA's electronic public docket. If you submit 
the copy that does not contain CBI on disk or CD ROM, mark the outside 
of the disk or CD ROM clearly that it does not contain CBI. Information 
not marked as CBI will be included in the public docket and EPA's 
electronic public docket without prior notice. If you have any 
questions about CBI or the procedures for claiming CBI, please consult 
the person identified in the FOR FURTHER INFORMATION CONTACT section.

D. What Should I Consider as I Prepare My Comments for EPA ?

    You may find the following suggestions helpful for preparing your 
comments:
    1. Explain your views as clearly as possible.
    2. Describe any assumptions that you used.
    3. Provide any technical information and/or data you used that 
support your views.
    4. If you estimate potential burden or costs, explain how you 
arrived at your estimate.
    5. Provide specific examples to illustrate your concerns.
    6. Offer alternatives.
    7. Make sure to submit your comments by the comment period 
deadline.
    8. Ensure proper receipt by EPA by identifying the appropriate 
docket identification number in the subject line on the first page of 
your response. It would also be helpful if you provided the name, date, 
and Federal Register citation related to your comments.

Outline of Document

I. Statutory Authority
II. Purpose of This Action
III. Background
    A. Analytical (Test) Methods Used for CWA Programs
    B. Settlement Agreement
    C. Detection, Quantitation, and Current Controversy
    D. Historical Use of Detection and Quantitation Limits under the 
Clean Water Act
IV. EPA's Assessment of Detection and Quantitation Concepts
    A. Study Plan
    B. Information and Data Used in the Assessment
    C. Concepts and Procedures Included in the Assessment
    D. Issues Considered during the Assessment
    E. Evaluation Criteria
V. EPA's Findings and Conclusions
VI. Peer Review of EPA's Assessment
VII. Proposed Revisions to the MDL and ML
    A. Definition of the Detection Limit
    B. Technical Revisions to the MDL Procedure
    C. Editorial Changes to the MDL Procedure
    D. Definition and Procedure for Determining the Minimum Level of 
Quantitation
    E. Acceptance of Test Methods Employing Alternative Detection 
and Quantitation Procedures
VIII. Industry Proposal
IX. Solicitation of Comments
X. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination with 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children from 
Environmental Health & Safety Risks
    H. Executive Order 13211: Actions that Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act

[[Page 11773]]

XI. References
Appendix A: Definitions, Acronyms, and Abbreviations Used in This 
Document

I. Statutory Authority

    This action is being proposed pursuant to the authority of sections 
301(a), 304(h), and 501(a) of the Clean Water Act (``CWA'' or the 
``Act''), 33 U.S.C. 1311(a), 1314(h), 1361(a). Section 301(a) of the 
Act prohibits the discharge of any pollutant into navigable waters 
unless the discharge complies with a National Pollutant Discharge 
Elimination System (NPDES) permit issued under section 402 of the Act. 
Section 304(h) of the Act requires the Administrator of the EPA to 
``promulgate guidelines establishing test procedures for the analysis 
of pollutants that shall include the factors which must be provided in 
any certification pursuant to [section 401 of this Act] or permit 
application pursuant to [section 402 of this Act].'' Section 501(a) of 
the Act authorizes the Administrator to ``prescribe such regulations as 
are necessary to carry out this function under [the Act].'' EPA 
publishes analytical test method regulations for use in CWA programs at 
40 CFR part 136. The Administrator has made these test methods 
applicable to monitoring and reporting of NPDES permits (40 CFR 122.21, 
122.41, 122.44, and 123.25), and implementation of the pretreatment 
standards issued under section 307 of the Act (40 CFR 403.10 and 
403.12).

II. Purpose of This Action

    EPA recently completed an assessment of procedures for determining 
the sensitivity of analytical test methods (i.e., procedures for 
determining detection and quantitation) and their application to Clean 
Water Act Programs. That assessment was conducted pursuant to a 
settlement agreement with the Alliance of Automobile Manufacturers, et 
al. (See III.B. below for details.) The assessment is contained in a 
document entitled, Technical Support Document for the Assessment of 
Detection and Quantitation Concepts or ``Assessment Document'' (EPA 
821-R-03-005, February, 2003). A draft of the Assessment Document was 
peer-reviewed in August 2002 in accordance with EPA peer review 
guidelines. Following peer review, EPA incorporated peer review 
comments into the Assessment Document. EPA is providing an opportunity 
for public review and comment on the assessment and the Assessment 
Document through this notice and also in a separate notice in this 
Federal Register (see Notice of Document Availability and Public 
Comment Period on the Technical Support Document for the Assessment of 
Detection and Quantitation Concepts).
    Based on findings from the assessment, EPA is proposing revisions 
to the method detection limit procedure codified at 40 CFR part 136, 
Appendix B and is seeking comment on the revisions proposed in this 
notice. EPA also is proposing to revise the definition of ``Detection 
limit'' at 40 CFR 136.2 and to add a definition of the ``Minimum level 
of quantitation (ML)'' for consistency with the proposed revisions to 
Appendix B.

III. Background

A. Analytical (Test) Methods Used for CWA Programs

    Section 304(h) of the Clean Water Act requires that the EPA 
Administrator ``promulgate guidelines establishing test procedures for 
the analysis of pollutants'' to be monitored and regulated under the 
National Pollutant Discharge Elimination System (NPDES). EPA proposes 
and promulgates test methods at 40 CFR part 136 in accordance with 
section 304(h). The approved test methods have been drawn from a 
variety of sources, including methods developed by commercial vendors, 
EPA and other government agencies, as well as methods from voluntary 
consensus standards bodies (VCSBs), such as the American Public Health 
Association (APHA), the Water Environment Federation (WEF), and the 
American Water Works Association (AWWA), which jointly publish Standard 
Methods for the Examination of Water and Wastewater; the Association of 
Official Analytical Chemists (AOAC-International); and the American 
Society for Testing and Materials (ASTM International).
    Among considerations for approval of a test method at 40 CFR part 
136 are the demonstrated performance characteristics of precision, 
bias, and sensitivity (i.e., detection and quantitation). EPA generally 
evaluates each of these characteristics to determine if the test method 
will yield results at concentrations of concern that are reliable 
enough to meet EPA needs for permitting and compliance monitoring under 
the CWA. Detection and quantitation limits have been among the most 
controversial of these characteristics, particularly among members of 
the regulated community.

B. Settlement Agreement

    On June 8, 1999, EPA published a final rule adding EPA Method 1631, 
Revision B: Mercury in Water by Oxidation, Purge and Trap, and Cold 
Vapor Atomic Fluorescence Spectrometry (Method 1631B) to the 
``Guidelines Establishing Test Procedures for the Analysis of 
Pollutants'' under section 304(h) of the Clean Water Act. This method 
was developed specifically to measure concentrations of mercury at low 
(i.e., ambient water quality criteria) levels. Following promulgation, 
the Alliance of Automobile Manufacturers, the Chemical Manufacturers 
Association, and the Utility Water Act Group (``Petitioners'') and the 
American Forest and Paper Association (``Intervenor'') filed a lawsuit 
challenging the method. (Alliance of Automobile Manufacturers, et al. 
v. EPA, No. 99-1420 (D.C. Cir.)). The challenge addressed specific 
aspects of EPA Method 1631 as well as the general procedures used to 
establish the method detection limit (MDL) and the minimum level of 
quantitation (ML) specified in the method. On October 19, 2000, EPA 
entered into a settlement agreement with the Petitioners and Intervenor 
(the ``settlement agreement''). The settlement agreement included six 
clauses. EPA has already satisfied the requirements of clauses 1 
through 5, which addressed clarification and revision of specific 
method procedures and requirements. This proposal partially fulfills 
the requirements of clause 6 of the settlement agreement, which 
addresses procedures for determining the sensitivity of analytical test 
methods.
    Clause 6 provides for EPA to assess existing Agency and alternative 
procedures for determining detection and quantitation limits under the 
Clean Water Act and to sign a notice for publication in the Federal 
Register on or before February 28, 2003, inviting public comment on the 
assessment. The assessment is to include, at a minimum, evaluation of 
the ``Definition and Procedure for Determination of the Method 
Detection Limit'' published at 40 CFR part 136, Appendix B and used in 
Method 1631, and evaluation of the corresponding ``minimum level'' of 
quantitation procedures.
    Clause 6 further provides for EPA to submit its assessment to 
formal peer review by experts in the field of analytical chemistry and 
in the statistical aspects of analytical data interpretation. EPA 
conducted peer review of its assessment in August 2002. A summary of 
the results of the peer review is provided in section VI of this 
proposal; the peer reviewers' comments and EPA's responses are included 
in the docket for this proposal. As stipulated in the settlement 
agreement, EPA

[[Page 11774]]

provided the draft Assessment Document to the Petitioners and 
Intervenor for concurrent review and comment in August 2002. Their 
comments are also included in the docket for this proposal.
    Finally, EPA agreed to invite public comment on the assessment for 
a period of no less than 120 days and to sign a notice taking final 
action on the assessment on or before September 30, 2004. Elsewhere in 
today's Federal Register, EPA is publishing a notice of availability of 
the Assessment Document, titled ``Technical Support Document for the 
Assessment of Detection and Quantitation Concepts,'' and announcing a 
120-day comment period on it.

C. Detection, Quantitation, and Current Controversy

    Generally speaking, a detection limit is the lowest concentration 
or amount of a substance that allows for differentiation between a 
sample that contains the substance and one that does not. A 
quantitation limit is the lowest concentration or amount of a substance 
that can be measured with some stated level of confidence. Establishing 
such detection and quantitation limits generally involves the 
application of statistics and chemistry expertise and judgement. The 
fact that scientific judgement is involved in the detection and 
quantitation decision is evidenced by the continuing debate on this 
subject; the number of different terms currently in use by different 
organizations; the number of concepts and procedures that have been 
advanced by different organizations to define or determine the 
detection and quantitation capabilities of analytical test methods; and 
the fact that there is no general consensus among various government 
agencies, method developers, or scientific organizations on a single 
detection and quantitation approach. EPA estimates that more than 50 
different terms have been used in published analytical test methods to 
describe detection and quantitation capabilities of test methods and, 
in many instances, the same term is used by different organizations to 
mean different things.
    Nearly all of the approaches advanced to date fall into one of two 
main categories: (1) Those that assume measurement error is constant or 
effectively constant in the low concentration range and are, therefore, 
based on the error observed in replicate measurements made at a single 
low concentration, and (2) those that assume measurement error varies 
as a function of concentration and are, therefore, based on the error 
observed in replicate measurements gathered in the region of detection 
and quantitation. Examples of the first category (referred to as the 
``single concentration approach'' or ``constant error model'') include 
those first advanced by Lloyd Currie (1968) and later adopted in 
various forms by the American Chemical Society (ACS), the International 
Organization for Standardization (also known as ``ISO''), the 
International Union of Pure and Applied Chemistry (IUPAC), and EPA. 
Examples of the latter category (the ``variable error model'') were 
adopted in various forms by the U.S. Army Toxic and Hazardous Materials 
Agency (USATHAMA, now the U.S. Army Environmental Center, or USAEC) and 
ASTM International. The two categories represent two somewhat different 
conceptual approaches to the problem of assessing detection and 
quantitation capabilities. Both approaches require estimates of 
measurement variability in the low concentration range, but the 
philosophy behind the first category is based on direct measurement of 
variability at a fixed concentration in the concentration region most 
relevant to the problem. The philosophy behind the second category is 
based on the concept that measurement variability throughout the low 
end of the measurement range is relevant to the problem of setting 
detection and quantitation limits. The methodology used in implementing 
procedures in the second category involves statistical estimation 
methods that allow data collected throughout the low end of the range 
to contribute to estimation of measurement variability in detection and 
quantitation region.
    There are also differences in the experimental procedures used to 
determine detection and quantitation limits. Again, these tend to fall 
into two categories. The first category of single-laboratory detection 
limits uses data from an experiment in a single laboratory to estimate 
detection limits. The second category of multi-laboratory detection 
limits uses data from experiments from multiple laboratories to 
estimate detection limits. The rationale for the latter proposal is 
that actual measurement sensitivity varies among laboratories, 
regardless of the approach used to estimate the sensitivity of a given 
method. The Interlaboratory Detection Estimate (IDE) and the 
Interlaboratory Quantitation Estimate (IQE) adopted by ASTM 
International is an example of such an approach. Although EPA's MDL 
procedure does not incorporate specific procedures to account for 
multiple laboratory variability, EPA nonetheless has accounted for this 
variability during method validation as described in Section D.1 below.

D. Historical Use of Detection and Quantitation Limits Under the Clean 
Water Act

    The procedure for estimating the MDL was originally published in 
1981 by staff at EPA's environmental research laboratory in Cincinnati, 
Ohio (Glaser, et al., 1981). The MDL is based on the constant error 
model described by Currie (1968). EPA promulgated the procedure for 
determining the MDL for use in CWA programs on October 26, 1984 (49 FR 
43234).
    The ML was originally proposed on December 5, 1979 (44 FR 69463), 
in footnotes to Table 2 of EPA Method 624 and to Tables 4 and 5 of EPA 
Method 625. Between 1980 and 1984, EPA developed Methods 1624 and 1625 
and included the ML in similar tables in those two methods. When these 
four methods were promulgated for use in CWA programs on October 26, 
1984 (49 FR 43234), EPA replaced the MLs in Methods 624 and 625 with 
MDLs, and retained the MLs in Methods 1624 and 1625. Unlike the MDL, 
there have been changes to the definition of the ML over the years. For 
example, the term ``recognizable signal'' has been used instead of 
``recognizable mass spectra'' for non-GC/MS methods.
    Since 1984, the MDL and ML have been used in a variety of ways by 
analytical laboratories, permitting authorities, and regulatory 
communities. The three most significant uses of the MDL are described 
below, along with some concerns with those uses.
1. Method Development
    The primary purpose of the MDL and ML is to characterize the 
sensitivity of a particular test method for a particular pollutant. 
Information about method sensitivity is critical when deciding which 
method is needed to accomplish a specific measurement objective.
    The MDLs published in some EPA methods have been criticized because 
they are based on the performance of a single laboratory that may not 
reflect the capabilities of the laboratory community. EPA has responded 
to this criticism in recent years by gathering MDL information from 
multiple laboratories. During development of several analytical 
methods, EPA's Office of Science and Technology addressed the issue by 
using single laboratory studies to develop an initial estimate of the 
MDL for each analyte and then verified these MDLs in interlaboratory

[[Page 11775]]

studies or in additional single-laboratory studies at other facilities. 
For example, when EPA initially drafted Method 1631 for measurement of 
mercury, EPA estimated the MDL to be 0.05 ng/L, based on results 
produced by a contract research laboratory. Additional single-
laboratory studies suggested that the MDL should be raised to 0.2 ng/L 
to better reflect existing capabilities of the laboratory community. 
During EPA's interlaboratory study for Method 1631, twelve participant 
laboratories were asked to conduct MDL studies. Each laboratory 
obtained an MDL less than 0.2 ng/L, the value published in the 
promulgated version of Method 1631.
    The ML has been used in the 1600-series of EPA chemical methods 
promulgated for use under the CWA since 1984 as an additional means to 
characterize method sensitivity, establish the lower end of the 
calibration range, and serve as a quantitation limit in those methods. 
Although its use has thus far been limited to the 1600-series methods, 
the ML concept is applicable to any analytical procedure to which the 
MDL can be applied under the CWA.
2. Demonstrating Laboratory Performance
    The MDL also has been used as a means of demonstrating laboratory 
capability or performance. For example, a laboratory often publishes 
results of an MDL study to advertise its ability to detect a pollutant 
at a low level. Similarly, a laboratory client or a certification 
program may require that a laboratory demonstrate its ability to 
achieve a specified MDL using a particular method.
    EPA also has used MDLs in approved EPA CWA methods (i.e., 
promulgated at 40 CFR part 136) to provide a standard for allowing 
increased flexibility and encouraging advances in technology. Under 
EPA's CWA Alternate Test Procedures (ATP) program and in EPA's 
performance-based methods, a laboratory is permitted to modify certain 
aspects of approved method procedures provided that it is able to 
achieve an MDL that is less than or equal to one-third the regulatory 
compliance limit or less than or equal to the MDL specified in the 
approved method, whichever is greater (see section 9.0 of EPA Method 
1631, for example).
3. Use of the MDL and ML in Clean Water Act Programs
    Both the MDL and ML have been used as reporting limits for a 
variety of studies and monitoring efforts under the CWA. For example, 
EPA often uses the MDL as a reporting threshold in surveys designed to 
determine levels of human exposure from consumption of water or fish 
under the CWA in order to characterize health risks from a variety of 
pollutants. In recent years, EPA has used the ML as the reporting limit 
in setting numeric limits for effluent guidelines limitations. EPA 
recommended in a 1994 draft guidance document that the ML be included 
in a National Pollutant Discharge Elimination System (NPDES) permit as 
a footnote to the water quality-based effluent limit (WQBEL) when the 
WQBEL is below either the MDL or ML of the most sensitive method. (See 
U.S. EPA Draft National Guidance for the Permitting, Monitoring, and 
Enforcement of Water Quality-based Effluent Limitations Set Below 
Analytical Detection/Quantitation Levels, 1994.) This 1994 draft 
guidance document was very controversial and was never finalized. 
Because individual States are responsible for implementation and 
enforcement of NPDES permits, use of the MDL and ML in the NPDES 
program varies among the States.
4. Concerns Regarding Use of the MDL
    Over the years, a number of concerns have been raised about the MDL 
procedure. Some of these concerns are technical in nature (e.g., 
selection of appropriate spiking levels and treatment of outliers), 
while others focus on implementation (e.g., use of the MDL as a 
regulatory compliance limit). As part of EPA's assessment of detection 
and quantitation limits, the Agency identified and investigated a 
number of issues, including concerns that had been presented to the 
Agency by a variety of sources (e.g., commercial laboratories, 
permittees, State laboratory and permitting authorities, EPA and other 
Federal laboratories, and others). Section IV.D of this proposal 
highlights the most significant issues addressed during the recent 
assessment. A comprehensive discussion of these issues is provided in 
the Assessment Document that is available in the docket supporting 
today's proposed rule and noticed elsewhere in today's Federal Register 
for public comment.

IV. EPA's Assessment of Detection and Quantitation Concepts

    EPA first began a comprehensive assessment of detection and 
quantitation limits in the mid-1990s as concerns about the increased 
use of water quality-based permitting began to push permit limits for 
many pollutants below the measurement capabilities of some laboratories 
for a number of environmental chemistry methods. One of the key areas 
of concern centered on the nature of measurement error in the region of 
detection and quantitation. Because EPA was not aware of studies that 
included replicate testing across or within the vicinity of this 
region, EPA focused its early efforts on developing such data, first 
with a single-laboratory study of measurement error using inductively 
coupled plasma-mass spectrometry (ICP-MS) techniques, and later with a 
similar single-laboratory study of measurement error using 10 different 
analytical techniques commonly used in Clean Water Act monitoring 
programs.
    The October 2000 settlement agreement described in section III.B. 
of this preamble committed EPA to a fixed timetable and established 
specific milestones for completing its assessment. The general approach 
used in the Agency's assessment of detection and quantitation concepts 
and procedures is summarized below. Additional details concerning the 
assessment are presented in the Assessment Document that is available 
in the public docket supporting this proposed rule. EPA is also 
providing an opportunity for public review and comment on this 
assessment and the Assessment Document in a separate notice in today's 
Federal Register (see Notice of Document Availability and Public 
Comment Period on the Technical Support Document for the Assessment of 
Detection and Quantitation Concepts).

A. Study Plan

    In December of 2001, EPA produced a draft Plan for the Assessment 
of Detection and Quantitation Limits Under Section 304(h) of the Clean 
Water Act. The December 2001 plan described roles and responsibilities 
for implementing the plan, provided a background discussion of 
detection and quantitation limit concepts, and outlined a series of 
events necessary to support EPA's assessment of detection and 
quantitation concepts and procedures as required to comply with the 
terms and schedules set forth in Clause 6 of the settlement agreement.
    The draft plan was circulated for review by EPA staff, the 
Petitioners and Intervenor, and external peer reviewers. The external 
peer review was performed in accordance with EPA's Science Policy 
Council Handbook--Peer Review, 2nd Edition (EPA 100-B-00-001, December 
2001; the ``Peer-review Handbook''). EPA evaluated the comments and 
recommendations provided by reviewers and, where appropriate, 
integrated these comments

[[Page 11776]]

into a revised version of the Plan for the Assessment of Detection and 
Quantitation Limits Under Section 304(h) of the Clean Water Act (EPA 
821-R-02-010, April, 2002; the ``study plan''). The study plan is 
included in the docket for this proposal, along with the peer review 
comments and the Agency's response to them..

B. Information and Data used in the Assessment

    In 1997 and 1998, EPA searched the published literature to identify 
documents that discussed detection and quantitation concepts and 
procedures. EPA conducted a follow-up search in 2001. The principal 
goal of these efforts was to identify concepts, procedures, and issues 
that should be considered by EPA during its assessment. EPA identified 
more than 100 documents describing detection and quantitation concepts 
and issues and has included a list of these documents in the docket 
supporting this proposed rule. Additional information concerning the 
literature search is presented and discussed in the Assessment 
Document.
    EPA initially hoped to identify a large body of data containing a 
sufficient number of results that were generated at, below, and above 
the region of interest (i.e., at concentration levels targeting limits 
of detection and quantitation). EPA determined, however, that few such 
data sets exist. EPA identified six useful data sets for fully 
evaluating measurement variability in the range of analytical detection 
and quantitation. These included three data sets generated by EPA 
expressly for the purpose of characterizing measurement variability in 
the region of interest and three data sets suggested by the Petitioners 
and Intervenor. Although the Petitioners and Intervenor suggested other 
data sets, EPA found that these data sets either did not include a 
sufficient number of data results that were at, below, and above the 
region of detection and quantitation to yield information for the 
assessment or that the data included in the data sets were of 
questionable validity. These data, and EPA's decisions regarding the 
data, are discussed in the Assessment Document.
    As noted above, three of these studies were conducted by EPA for 
the purpose of evaluating the relationship between measurement 
variation and concentration. In these studies, replicate measurements 
from each combination of analyte and measurement technique (i.e., 
analytical method) were produced by a single laboratory over a wide 
range and large number of concentrations. A fourth data set was 
developed as part of a study conducted by the American Automobile 
Manufacturers Association (AAMA) for the purpose of estimating a 
quantitation value based on a concept called the alternative minimum 
level that had been described in the literature (Gibbons et al., 1997). 
In that study, replicate samples were measured at a limited number of 
concentrations by multiple laboratories. The final two data sets were 
jointly gathered by EPA and the Electric Power Research Institute 
(EPRI) to support interlaboratory validation of EPA Methods 1631 and 
1638.
    Additional details concerning each of these studies are provided in 
the Assessment Document available in the docket supporting this 
proposed rule. Data from these studies also are available in the 
docket.

C. Concepts and Procedures Included in the Assessment

    As mentioned earlier in this document, EPA identified numerous 
terms that have been used to describe the sensitivity of a particular 
method or instrument. Examples of these terms are analytical detection 
limit, lower limit of detection, limit of sensitivity, minimum 
detectable quantity, system detection limit, and approximate detection 
limit. For its assessment, EPA considered detection and quantitation 
terms, concepts, or procedures advanced in the published literature and 
by various EPA offices, the American Chemical Society (ACS), the 
International Union of Pure and Applied Chemistry (IUPAC), the 
International Organization for Standardization (ISO), ASTM 
International, industry groups, and others. EPA found that most of the 
terms or concepts considered have no corresponding definition or 
procedure for calculating a value, and it may be that these terms 
reflect the method developer's estimate of the lowest concentration of 
a substance that a test method is capable of measuring. EPA did not 
evaluate any such terms in the assessment. EPA also did not consider 
terms that do not reflect the entire measurement process (such as the 
``Instrument Detection Limit''), concepts that are uniquely designed 
for a single program (such as the ``Contract Required Detection Limit'' 
used in the Superfund Contract Laboratory Program), or concepts no 
longer advanced by the originating organization (such as the 
``Compliance Monitoring Detection Limit'' and the ``Alternative Minimum 
Level'').
    After eliminating terms and concepts for the reasons described 
above, EPA focused its assessment on four sets of concepts that are 
widely referenced and generally reflect the diversity of concepts 
advanced to date. These include (1) The EPA MDL and ML used under CWA 
programs, (2) the Interlaboratory Detection Estimate (IDE) and 
Interlaboratory Quantitation Estimate (IQE) adopted by ASTM 
International, (3) the Limit of Detection (LOD) and Limit of 
Quantitation (LOQ) adopted by the American Chemical Society (ACS), and 
(4) the Critical Value (CRV), Minimum Detectable Value (MDV) and Limit 
of Quantification (LOQ) adopted by the International Union of Pure and 
Applied Chemistry (IUPAC) and the International Organization for 
Standardization (ISO). Although the ACS, IUPAC and ISO concepts are 
functionally similar to EPA's MDL and ML, these organizations have not 
developed detailed procedures for calculating detection and 
quantitation values. Only the EPA and ASTM concepts are supported by 
detailed procedures for calculating detection and quantitation values. 
Without such procedural details, the ACS, IUPAC and ISO concepts are 
unlikely to be useful for establishing detection and quantitation 
limits in analytical methods for use in CWA programs. Therefore, the 
discussion below addresses the EPA and ASTM concepts only. Results of 
EPA's evaluation of the additional concepts are discussed in detail in 
the Assessment Document included in the docket supporting this proposed 
rule.
1. Method Detection Limit (MDL) and Minimum Level (ML) of Quantitation
    As discussed in section III.D of this document, the MDL is based on 
the constant error model proposed by Currie in 1968 and was initially 
promulgated in 1984 for use in CWA programs. The MDL and ML are 
supported by a procedure that involves the analysis of at least seven 
replicate samples containing the target analyte(s) at an estimate of 
the detection limit. Determination of the MDL is based on 
multiplication of the standard deviation among the replicate 
measurements by the 99th percentile of a t-distribution with n-1 
degrees of freedom. The ML is also based on the constant error model 
proposed by Currie in 1968. The ML is derived by multiplying the 
standard deviation of the replicate measurements by 10. The primary 
differences between the MDL, ML, and detection and quantitation limit 
concepts first proposed by Currie are that (1) The MDL and ML are 
supported by detailed procedures for implementing the concepts, and (2) 
the EPA CWA procedures extend Currie's proposed replicate measurements 
of a blank with replicate measurements of reagent water

[[Page 11777]]

(or other reference matrix) to which a small amount of the analyte is 
added. This latter difference results from the fact that the concepts 
developed by Currie assume that measurements on blank samples will 
produce a signal that can be used to estimate measurement variability. 
This is the case with radiochemistry analyses, where there is usually 
some background radiation that produces a response in the analysis of a 
blank sample. For many other types of environmental analyses, the 
analysis of a blank sample produces no instrumental response. Thus, the 
EPA CWA MDL procedure involves adding the analyte to a reference matrix 
(e.g., a blank sample) at low concentrations to ensure that a response 
is produced.
2. Interlaboratory Detection Estimate (IDE) and Interlaboratory 
Quantitation Estimate (IQE)
    The IDE was approved by ASTM International's Committee D 19 for 
Water in 1997, as ASTM Designation 6091-97: Standard Practice for 99%/
95% Interlabortory Detection Estimate (IDE) for Analytical Methods with 
Negligible Calibration Error. Subsequently, members of ASTM Committee D 
19 developed the interlaboratory quantitation estimate (IQE) that was 
approved in 2000 as ASTM Designation D 6512-00: Standard Practice for 
Interlaboratory Quantitation Estimate. The IDE and IQE concepts are 
based on the variable error model and include procedures that require 
that data gathered in a formal study of a method be used to select from 
one of four possible models of the interlaboratory error and 
concentration. The possible models include: the ``constant model,'' 
applicable to both the IDE and IQE, in which the interlaboratory 
standard deviation does not change with concentration; the ``straight-
line model,'' applicable to both the IDE and IQE, in which the 
interlaboratory standard deviation is a linear function of 
concentration; the ``exponential model'' applicable to the IDE, in 
which the interlaboratory standard deviation is an exponential function 
of concentration; and the ``hybrid model'' applicable to the IQE, in 
which the interlaboratory standard deviation has both additive 
(constant) and multiplicative (linear) components that follow the model 
of Rocke and Lorenzato (1995). Such studies involve samples 
representing at least five different concentration levels and analyzed 
in a minimum of six (required) to ten (recommended) laboratories. The 
ASTM procedures are also designed to take into account all possible 
sources of variability, including interlaboratory variability, when 
estimating detection and quantitation limits. As a result, the IDE and 
IQE generally produce higher limits than are produced using other 
procedures.

D. Issues Considered During the Assessment

    In performing the assessment, EPA identified a number of 
statistical and analytical chemistry issues that should be considered 
when evaluating detection and quantitation limit concepts and 
procedures in general, and in the specific context of Clean Water Act 
applications. The issues considered include six specific issues raised 
by the Petitioners and Intervenor, as well as issues identified by EPA 
staff, peer reviewers, and others. The six issues raised by the 
Petitioners are: Criteria for selection and appropriate use of 
statistical models; methodology for parameter estimation; statistical 
tolerance and prediction; criteria for design of detection and 
quantification studies, including selection of concentration levels 
(``spiking levels''); interlaboratory variability; and incorporation of 
elements of probability design.
    Some of the significant additional issues considered by EPA in its 
assessment include: Matrix effects; minimization of false positives and 
false negatives; cost and ease of implementation; and how well 
detection and quantitation limits published in methods reflect 
individual laboratory capability. These and other issues considered by 
EPA are identified and discussed in Chapter 3 of the Assessment 
Document.

E. Evaluation Criteria

    After identifying and considering the issues, EPA developed six 
evaluation criteria that reflect EPA's views concerning the issues. 
These six criteria formed the primary basis for evaluating the ability 
of each detection and quantitation limit approach identified in section 
III.C. above to meet EPA needs under the Clean Water Act. A complete 
discussion of these criteria and EPA's assessment of each approach 
against these criteria is provided in the Assessment Document that is 
available in the docket supporting this proposed rule. The six criteria 
are summarized below.
    Criterion 1: The detection and quantitation limit approaches should 
be scientifically valid. In evaluating this criterion, EPA considered 
the following factors: (1) Whether the concept can be (and has been) 
tested; (2) whether the concept has been subjected to peer review and 
publication; (3) whether the error rate associated with the concept or 
methodology is either known or can be estimated; (4) whether standards 
exist and can be maintained to control the concept's operation (i.e., 
it is supported by well-defined procedures for use); and (5) whether 
the concept has attracted (i.e., achieved) widespread acceptance within 
a relevant scientific community.
    EPA believes that these considerations are helpful for 
demonstrating the scientific validity of a detection or quantitation 
concept.
    Criterion 2: The approach should address demonstrated expectations 
of laboratory and method performance, including routine variability. 
EPA believes that the detection and quantitation limit procedures 
should be capable of providing a realistic expectation of laboratory 
performance. In evaluating different approaches against this criterion, 
EPA considered the sources of variability captured by the procedure and 
the degree to which the statistics that underlie the procedure 
realistically reflect these sources.
    Criterion 3: The approach should be supported by a practical and 
affordable procedure that a single laboratory can use to evaluate 
method performance. Ideally, any required procedure for calculating 
analytical method sensitivity should be simple, complete, and cost-
effective to implement. The laboratories that can be expected to use 
detection and quantitation procedures will range from large 
laboratories and laboratory chains with a wide range of technical 
capability to small laboratories operated by one or a few people with a 
limited set of statistical or analytical skills. If a procedure is 
complicated, it will be, generally, more error prone in its use. 
Similarly, if a procedure requires investment of extensive resources 
that cannot be billed to a client, laboratories will have a 
disincentive to use the procedure. Therefore, if EPA wishes to 
encourage the development and use of innovative techniques that improve 
measurement performance or lower measurement cost, the Agency should 
consider practicality and affordability as significant, if not co-
equal, considerations to scientific validity.
    Criterion 4: The detection level approach should identify the 
signal or estimated concentration at which there is 99% confidence that 
the substance is actually present when the analytical method is 
performed by experienced staff in a well-operated laboratory. Any 
approach to developing detection limits should be capable of providing 
regulators, the regulated community, and data users with confidence 
that a pollutant reported as being present really is present. 
Historically, nearly

[[Page 11778]]

every detection limit approach has set the criterion for detection at 
99 percent confidence (i.e., the lowest level at which a pollutant will 
be detected with a probability of 99 percent). This criterion results 
in the probability of a false positive; i.e., that a pollutant will be 
stated as being present when it is not really present (a Type I error), 
of one percent.
    Criterion 5: The quantitation limit approach should identify the 
concentration that gives a recognizable signal that is consistent with 
the capabilities of the method when a method is performed by 
experienced staff in well-operated laboratories. Measurement 
capabilities among laboratories vary depending on a number of factors, 
including, but not limited to, instrumentation, training, and 
experience. Similarly, measurement capabilities among different 
analytical methods vary depending on a number of factors, including the 
techniques and instrumentation employed and the clarity of the method 
itself. Historical approaches to recognizing laboratory capabilities in 
establishing detection and quantitation limits have varied between two 
extremes of establishing the limit in a state-of-the-art research 
laboratory to reflect the lowest possible limit that can be achieved, 
and establishing the limit based on statistical prediction intervals 
calculated from a large number of laboratories with varying levels of 
experience, instrumentation and competence. Generally, use of the 
former has been employed to serve as a goal or performance standard to 
be met by other laboratories, whereas use of the latter treats the 
limit, not as a performance standard that needs to be met by each 
laboratory, but rather as a characterization of the future performance 
of the entire universe of laboratory capabilities at the time of method 
development. Rather than using one of these two extremes, EPA prefers 
to establish a quantitation limit at a concentration that is achievable 
with a defined level of confidence in well-operated laboratories.
    Criterion 6: Detection and quantitation approach should be 
applicable to the variety of decisions made under the Clean Water Act, 
and should support State and local obligations to implement measurement 
requirements that are at least as stringent as those set by the Federal 
Government. The Clean Water Act requires EPA to conduct, implement, and 
oversee a variety of data gathering programs. These programs include, 
but are not limited to, surveys to monitor changes in ambient water 
quality, screening studies to identify pollutants of concern, data 
gathering to support effluent guidelines, environmental assessments to 
establish water quality standards, and studies to evaluate human health 
and environmental risks under the Clean Water Act. In addition, EPA 
should be able to apply detection and quantitation limits to 
permitting, quality control in analytical laboratories, method 
promulgation, and other uses of the 40 CFR part 136 methods.

V. EPA's Findings and Conclusions

    As noted previously, EPA considered four sets of detection and 
quantitation limit approaches advanced by EPA, ASTM International, ACS, 
and both ISO and IUPAC. Each approach was assessed against the suite of 
criteria described above for use under the Clean Water Act. The EPA 
approaches (i.e., the MDL and ML) and the ASTM International approaches 
(i.e., the IDE and IQE) are supported by clearly defined procedures for 
implementing the concepts. Neither the ACS nor the ISO/IUPAC approaches 
are supported by detailed procedures for implementation; this lack of 
supporting procedures was reflected in the outcome of EPA's overall 
assessment. Briefly, EPA found that (1) no single pair of detection and 
quantitation limit concepts perfectly meets EPA's criteria for use 
under the Clean Water Act, (2) the MDL and ML most closely meet EPA's 
criteria, and (3) minor revisions and clarifications to the MDL and ML 
would allow both concepts to fully meet the Agency's needs under the 
CWA. Details of these revisions and clarifications are described in 
section VII of this proposed rule. EPA also found that, although the 
IDE and IQE procedures may be acceptable for establishing detection and 
quantitation values derived from interlaboratory validation studies, 
the complexity and subjectivity of the procedures, along with their 
inability to address individual laboratory performance, make them 
unsuitable as the primary means of establishing sensitivity under the 
Clean Water Act. However, EPA believes that the IDE and IQE can be used 
to establish sensitivity under certain conditions. EPA would be willing 
to consider and approve under 40 CFR part 136, new test methods that 
include the IDE and IQE. Details of EPA's findings are provided in the 
Assessment Document that is available in the docket supporting this 
proposed rule.

VI. Peer Review of EPA's Assessment

    In August 2002, EPA conducted a peer review of its assessment as 
presented in a draft Technical Support Document (draft Assessment 
Document). The peer review was performed in accordance with EPA's peer 
review policies, which are described in the Science Policy Council 
Handbook (EPA 100-B-00-001), and performed by two experts in the field 
of analytical chemistry and two experts in the statistical aspects of 
analytical data interpretation. Reviewers were provided with a draft 
copy of EPA's Assessment Document, copies of all data evaluated in the 
assessment, statistical programs used to analyze the data, and copies 
of the detection and quantitation approaches evaluated.
    In the charge to the peer reviewers, EPA requested a written 
evaluation of whether the assessment approach described by EPA is valid 
and of the conceptual soundness of the assessment. Reviewers also were 
asked to consider and address eight specific questions pertaining to 
the adequacy of the concepts and procedures, the issues considered, the 
evaluation criteria developed by EPA, EPA's assessment and conclusions, 
the data used to perform the assessment, suggested improvements to the 
procedures discussed, and EPA's consideration of interlaboratory vs. 
intralaboratory issues. A copy of all materials associated with the 
peer review, including the peer review charge, the materials provided 
to the peer reviewers for review, complete copies of the peer 
reviewers' comments, and detailed EPA responses to each of the comments 
is provided in the docket supporting this proposed rule.
    The comments from the peer reviewers were generally supportive of 
EPA's assessment and its presentation of the assessment in the draft 
Assessment Document. The peer reviewers stated that EPA's assessment of 
detection and quantitation concepts appears valid based on the 
evaluation criteria and is consistent with the Data Quality Act and 
EPA's Quality System. The peer reviewers stated further that the 
detection and quantitation concepts and procedures considered, the 
issues addressed, and the evaluation criteria developed based on those 
issues are sufficiently complete and adequate. Although two of the four 
peer reviewers believe that the use of interlaboratory measurements is 
important for a general understanding of the laboratory communities' 
capabilities, they also believe that the MDL and ML are more 
appropriate to address the issues that

[[Page 11779]]

EPA must consider in support of a permittee's CWA requirements. These 
commenters concluded that EPA's approach between inter- and intra-
laboratory studies is balanced and reasonable. Overall, the peer 
reviewers supported the continued use of the MDL and ML procedures, 
almost to the exclusion of the other approaches. The most notable 
exception was a suggestion that EPA consider abandoning the 
``traditional'' concept of a quantitation limit, such as the ML, and 
instead consider that any measured result reported with an associated 
estimate of measurement precision is a quantifiable value. Reviewers 
stated, however, that use of the ML is practical if EPA desires to 
establish a quantitation limit.
    Although the peer reviewers were generally supportive of the 
assessment and EPA's current approach to detection and quantitation 
under the CWA, they had some recommendations for improvement to the 
Agency's assessment and to the MDL procedure. The reviewers suggested 
that EPA consider the following: (1) Providing additional references; 
(2) expanding the discussion of outliers; (3) establishing a repository 
of reference materials that demonstrate the ability to handle 
interferences and low level detection; (4) making minor modifications 
to Evaluation Criterion 4 (i.e., edit to reflect equivalence to an 
implementation of Currie's critical level); (5) clarifying the MDL 
confidence interval calculations discussed in Chapter 5 of the 
Assessment Document; and (6) enhancing the focus on the impact of 
operational procedures (quality control) in method performance. The 
Assessment Document available in the docket supporting today proposed 
rule addresses each of these suggestions.
    The peer reviewers also suggested the following improvements to the 
MDL procedure: (1) Provide clarification to indicate that blank samples 
can be used to estimate the MDL if those blanks generate a signal; (2) 
revise the language in Step 1 of the MDL procedure to address certain 
common misunderstandings (e.g., strengthen the discussion of the 
selection of the spiking level used for the MDL study); and (3) specify 
that the spike level used to establish the MDL should not be more than 
a factor of three times greater than the calculated MDL. The first two 
suggestions from the peer reviewers regarding improvements to the MDL 
procedure, have been included in the proposed revision to the MDL 
procedure. Although EPA agrees with the theoretical arguments related 
to the last suggestion regarding the spike level, EPA already tested 
this suggestion in one of its studies of detection and quantitation 
concepts and found that it could create laboratory burdens that far 
exceed the benefits. Specifically, EPA required a spike-to-MDL ratio of 
three in its multi-technique variability studies (the ``Episode 6000 
studies''), which are described in the Assessment Document supporting 
this rule. Two laboratories reported that a large number of iterations 
would be required (particularly in multiple-analyte methods) in order 
to achieved a spike-to-MDL ratio of three, and would result in 
increased laboratory burden and cost. Therefore, this suggestion is not 
incorporated into the revised MDL procedure in this proposed rule.
    Based on peer review comments and comments received over the years 
from the laboratory community, the Petitioners, and other stakeholders, 
EPA is proposing revisions to the MDL procedure (see section VII 
below).

VII. Proposed Revisions to the MDL and ML

    This proposal would revise the definition of detection limit for 
use under the CWA. It also would revise certain aspects of the existing 
procedure for determining the Method Detection Limit (MDL) in 40 CFR 
part 136, Appendix B (Definition and Procedure for the Determination of 
the Method Detection Limit) and modify the discussion to clarify 
implementation of the procedure. It also requests comment on whether to 
add a stand-alone definition of quantitation limit and procedure for 
determining the Minimum Level of Quantitation (ML) in Appendix B.
    This proposal incorporates the results of EPA's recent assessment 
of detection and quantitation concepts and procedures discussed 
throughout this preamble and in the Assessment Document, and address 
various stakeholder comments received by EPA since the 1984 
promulgation of the MDL (49 FR 43234, October 26, 1984).
    The following discussion is divided into five sections: (1) 
Revisions to the definition of the detection limit are discussed in 
section VII.A; (2) technical revisions to the MDL procedure are 
discussed in section VII.B; (3) clarifications and other minor 
editorial changes to the MDL procedure are discussed in section VII.C; 
(4) the addition of a definition of quantitation limit and the addition 
of a procedure to calculate the ML are discussed in section VII.D; (5) 
section VII.E discusses EPA's continued acceptance of analytical 
methods from organizations that do not necessarily use EPA's MDL and ML 
procedures.

A. Definition of the Detection Limit

    Section 136.2(f) currently defines the term ``detection limit'' to 
mean ``the minimum concentration of an analyte (substance) that can be 
measured and reported with a 99% confidence that the analyte 
concentration is greater than zero as determined by the procedure set 
forth at appendix B of this part.'' EPA is proposing to revise Sec.  
136.2(f) to explicitly equate the term ``detection limit'' with the 
``method detection limit'' and to reflect the proposed revisions to the 
MDL procedure at Appendix B as follows: ``Detection limit means the 
method detection limit (MDL), as determined by the procedure set forth 
at Appendix B of this part. The MDL is an estimate of the measured 
concentration at which there is 99% confidence that a given analyte is 
present in a given sample matrix.'' EPA also is proposing to revise the 
definition of the Method Detection Limit included in Appendix B as 
follows: ``The MDL is an estimate of the measured concentration at 
which there is 99% confidence that a given analyte is present in a 
given sample matrix.'' The MDL is the concentration at which a decision 
is made regarding whether an analyte is detected by a given analytical 
method. The MDL is calculated from replicate analyses of a matrix 
containing the analyte and is functionally analogous to the ``critical 
value'' described by Currie (1968, 1995) and the Limit of Detection 
described by the American Chemical Society (Keith et al., 1980, 
McDougal et al., 1983).
    EPA also is requesting comment on an alternative approach in which 
the term limit of detection would be defined at Sec.  136.2 as ``the 
critical value, which is the concentration at which there is 99% 
confidence that a given analyte is present in a given sample matrix,'' 
and the method detection limit would be defined as ``the procedure set 
forth in Appendix B of this part, which can be used to estimate the 
limit of detection (i.e., critical value).''

B. Technical Revisions to the MDL Procedure

    This notice proposes several technical revisions to the MDL 
procedure at 40 CFR part 136, Appendix B. These revisions are based on 
EPA's recent assessment of detection and quantitation concepts 
described in the Assessment Document, as well as comments received from 
stakeholders, the Petitioners, and the peer reviewers of the 
assessment. Specifically, the proposed revisions would:

[[Page 11780]]

    1. Revise the definition of the MDL to replace the term ``minimum 
concentration'' with the term ``estimate of the measured 
concentration'' and replace the phrase ``greater than zero'' with the 
phrase ``present in a given sample matrix.'' The revised definition 
would note the functional analogy of the MDL with the ``critical 
value'' described by Currie (1968 and 1995) and the ``limit of 
detection'' (LOD) described by the American Chemical Society in 1980 
and 1983. The revised definition also would note that the MDL 
represents the concentration at which the detection decision is made. 
These proposed revisions are intended to make the definition of the MDL 
more consistent with the MDL procedure. The proposed revisions reflect 
peer review comments on EPA's recent assessment of detection and 
quantitation concepts and procedures.
    2. Expand the Scope and Application discussion to recognize that 
there are a variety of purposes and analytical methods for which the 
MDL procedure may be employed. The revised text provides examples of 
four common uses of the MDL procedure (i.e., demonstrating laboratory 
capability with a particular method; monitoring trends in laboratory 
performance; characterizing method sensitivity in a particular matrix; 
and establishing an MDL for a new or revised method for nationwide 
use). The revised text also clarifies that the procedure may not be 
applicable to certain test methods such as those used to measure pH or 
temperature, for example. These revisions are based on questions from 
stakeholders about the scope and applicability of the MDL procedure.
    3. Revise three of the four considerations for estimating the 
detection limit (see Step 1 of the current MDL procedure and section 
4.3 of the proposed revisions), and suggest that the method-specified 
MDL can be used as the initial estimate when performing an MDL study to 
verify laboratory performance or to demonstrate that the MDL can be 
achieved in a specific matrix. The proposed revisions to the original 
considerations include: (1) Clarifying that, if analysis of blank 
samples yields an instrument response, the detection limit can be 
estimated as approximately equal to three times the standard deviation 
of replicate measurements of the analyte in the blank; (2) replacing 
``that region of the standard curve where there is a significant change 
in sensitivity (i.e., a break in the slope of the standard curve)'' 
with ``a concentration in the region of constant or effectively-
constant standard deviation at low concentrations;'' and (3) replacing 
``instrumental limitations'' with ``the lowest concentration that can 
be detected by analyzing samples containing successively lower 
concentrations of the analyte.''
    4. Revise the specifications for establishing the test 
concentration range according to the intended application of the MDL as 
follows: (1) If verifying a published MDL, the test concentration 
should be no more than five times the published MDL; (2) if verifying 
an MDL to support a regulatory objective or the objective of a study or 
program, the test concentration should be no more than one third the 
compliance or target limit; (3) if determining an MDL for a new or 
revised method, the test concentration should be no more than five 
times the estimated detection limit; and (4) if performing an 
iteration, the test concentration should be no more than five times the 
MDL determined in the most recent iteration. (See Step 3.1 of the 
current procedure and section 4.3.1 of the proposed revisions.)
    5. Delete the calculation of a 95% confidence interval estimate for 
the MDL. EPA has determined that these calculations are neither 
routinely performed by laboratories, nor are the results employed by 
regulatory agencies, including EPA.
    6. Revise the discussion of the iterative procedure to require that 
the iterative procedure be used to verify the reasonableness of the MDL 
when developing an MDL for a new or revised method or when developing a 
matrix-specific MDL, but that it remain optional when determining an 
MDL to verify a method-, matrix-, program-, or study-specific MDL. This 
change recognizes that the iterative procedure is rarely used to verify 
laboratory performance, but is considered important during method 
development. The discussion, as revised, also would provide specific 
instructions on how to assess the reasonableness of an MDL used to 
verify laboratory performance. (See Step 7 of the current procedure and 
section 4.8 of the proposed revision.)
    7. Add a new section (section 4.9) to the MDL procedure to address 
the treatment of suspected outliers. EPA is proposing to add this 
section in response to frequent questions from stakeholders with regard 
to outliers in the absence of any affirmative statements in the current 
MDL procedure. The discussion in this proposed section specifies that 
suspected outliers be examined for spurious errors that may occur as a 
result of human error or instrument malfunction, recommends that 
correctable errors be corrected before calculation of the MDL, and 
requires that any corrective actions be documented. The proposed 
section specifically would provide for invalidation of results from 
noncorrectable errors and preclude their use in calculating the MDL. 
The proposed section also describes the use of the Grubbs test for 
outlying values as a means to screen the results of the replicate 
samples for possible outliers, and provides an example application of 
the Grubbs test. Finally, the proposed section would reiterate the 
requirement that any results generated from more than seven replicates 
must be used to calculate the MDL unless they are determined to be 
outliers by the use of an appropriate outlier test. This proposed 
change addresses the possibility that some laboratories could prepare 
more than the requisite seven samples and then select only the seven 
results that yield the most desirable MDL value. Laboratory auditors 
from various agencies have identified this practice as a problem that 
can distort the MDL, but it is not specifically prohibited or addressed 
in the current procedure.
    8. Delete the discussion of analysis and use of blanks included in 
section 4(a) of the current procedure. The current discussion applies 
to methods in which a blank measurement is required to calculate the 
measured level of an analyte; it requires separate measurements of 
blank samples for each MDL sample aliquot analyzed and subtraction of 
the average result of the blank samples from each respective MDL sample 
measurement. The proposed deletion of this discussion is in recognition 
that subtraction of a single (or average) blank sample result from the 
result for each MDL sample would not change the standard deviation and 
thus, would have no effect on the resulting MDL. Although EPA believes 
laboratories would be prudent to analyze blanks for assessing potential 
contamination, EPA also believes that requiring analysis of blanks or 
subtraction of blank results during MDL determinations is unnecessarily 
burdensome.
    9. Revise the optional pre-test described in section 4(b) of the 
current procedure. The current procedure suggests analyzing two 
aliquots to evaluate the estimated detection limit before proceeding 
with the full seven-replicate test. Results from these analyses are 
evaluated to determine if the sample is in the ``desirable range for 
determining the MDL,'' but no criteria are provided for establishing 
this desirable range. The proposed revisions

[[Page 11781]]

to the pre-test procedure are intended to address this issue. These 
revisions now appear in section 4.1 of the proposed procedure. 
Specifically, the pre-test has been modified to suggest analysis of 
three aliquots. Results from these analyses are evaluated by 
calculating a preliminary MDL based on the standard deviation of the 
analyses, and then determining if this preliminary MDL is within 0.2 to 
1.0 times the concentration spiked in the sample. This revision is 
consistent with the current procedure's recommendation that samples 
used to determine an MDL contain the analyte at a concentration that is 
``between 1 and 5 times the estimated method detection limit.''

C. Editorial Changes to the MDL Procedure

    This notice proposes editorial changes to the MDL procedure at 40 
CFR part 136, Appendix B that are designed to clarify the existing 
procedure and improve readability. These editorial changes include 
changes to the numbering scheme, the addition of clearer titles to some 
of the procedural steps, and minor clarifications. Specifically, the 
proposed changes would:
    1. Add a summary section to provide an overview of the various 
steps included in the MDL procedure. The summary section is consistent 
with the current format for analytical methods and should be 
particularly helpful to non-laboratory readers.
    2. Clarify in the Scope and Application discussion that the MDL 
procedure is intended for use in EPA's Clean Water Act programs, and 
that alternative procedures may be used to establish test method 
sensitivity provided the resulting detection value meets the 
sensitivity needs for a specific application.
    3. Clarify throughout the procedure that not all of the steps are 
required for every application. This clarification provides consistency 
with the proposed revisions in the Scope and Application section of the 
procedure.
    4. Expand the discussion of matrix selection to address use of an 
MDL in either a reference matrix or an alternate matrix. (See Step 2 of 
the current procedure and section 4.2 of the proposed revisions.) Use 
of matrices other than reagent water are not discussed until Step 3b of 
the current procedure. The expanded discussion is intended to provide 
additional clarity and consistency with the description of the four 
applications added to the MDL Scope and Application section (see 
section VII.B.2 above).
    5. Expand the discussion of establishing the test concentration 
range to more clearly describe the steps required and prepare the test 
samples. (See Step 3 of the current procedure and section 4.3 of the 
proposed revisions.) These proposed changes are editorial and describe 
the process that may be used for determining a matrix-specific MDL as 
well as determining an MDL in a reference matrix such as reagent water. 
Additional clarifications include recognition that some analytes may 
require that seven aliquots be prepared individually, as opposed to 
preparing a bulk sample of sufficient volume to be split into seven 
aliquots. EPA is proposing this clarification in response to questions 
from laboratories regarding the appropriate means for preparing the MDL 
aliquots.
    6. Expand the discussion of performing the analyses to include a 
brief introduction clarifying that the samples used for MDL analyses 
must be processed using the sample handling, processing, and result 
calculations specified in the analytical method. (See Step 4 of the 
current procedure and section 4.4 of the proposed revisions.) This 
proposed change includes moving this statement from the Reporting 
section of the current procedure to the more appropriate location in 
section 4 of the revised procedure. This proposed change also would 
clarify that blank-correction or recovery-correction procedures are 
applied to the MDL analyses only when those procedures are employed for 
routine sample analyses, and precludes their use if they are not 
specified in the test method. EPA is proposing these changes in 
response to questions raised by laboratories, the Petitioners, and as a 
result of the recent assessment.
    7. Reorganize the procedural steps contained in Step 4 of the 
current procedure, such that the optional pre-test of the MDL is 
discussed before the procedure for performing the full seven-replicate 
test. (See section 4.4 of the proposed revisions.) EPA is proposing 
this change strictly to improve ease of use.
    8. Expand and reorganize the description of the seven-replicate 
version of the MDL described in Step 4(a) of the current procedure. The 
revised version would appear in section 4.5 and reflects comments from 
stakeholders that the discussion in the current procedure is not 
sufficiently clear. The revised procedure also would state explicitly 
that all analytical results must be positive numbers, and that the 
results from all aliquots analyzed must be used in the calculations, 
except those identified as outliers using the procedures described in 
section 4.9 of the revised procedure (see the discussion regarding 
outliers in VII.B above). These proposed changes would clarify 
stakeholder concerns regarding those analytical methods (e.g., for 
metals) that may produce negative numbers at very low concentrations 
and would emphasize the revision made in response to concerns regarding 
inappropriate screening of results used for MDL determinations.
    9. Simplify the calculations of standard deviation of replicate 
measurements in Step 5 of the current procedure. (See section 4.6 of 
the proposed revisions.) For example, the current procedure details the 
calculation of the sample variance (s2), and then details 
the calculation of the sample standard deviation (s) in a separate 
equation. Given that the variance term does not factor into the MDL 
calculation directly, the proposed revision would require only 
calculation of the standard deviation. The proposed revision also would 
include a caution warning the reader to calculate the sample standard 
deviation (s), not the population standard deviation (sigma), when 
using automated programs such as spreadsheets. This error was not as 
likely to occur in 1984, prior to the ready availability of personal 
computers and laboratory data systems, but is commonly seen today.
    10. Move the table of Student's t-values from its current location 
following the text in Step 7 to section 4.7, where the t-value is 
employed. EPA is proposing this change to improve ease of use and 
increase readability.
    11. Add a table of F-statistic values to the iterative procedure 
described in section 4.8. EPA is proposing this change to improve ease 
of use and address those instances in which an iterative MDL might be 
determined from other than seven replicates per data set.
    12. Delete the ``Reporting'' section of the MDL procedure. The 
existing procedure includes a section listing the information that must 
be provided with the MDL for each analyte. EPA is proposing to delete 
this section because it is not relevant to the procedure and it is 
generally duplicative of reporting and recordkeeping requirements that 
States, other regulatory entities, or laboratory certification 
officials already require.

D. Definition and Procedure for Determining the Minimum Level of 
Quantitation

    Although ML values for analytes were published in 1984 in EPA 
Methods 1624 and 1625 (49 FR 43234, October 26, 1984), the definition 
of the ML was

[[Page 11782]]

provided in a footnote to the tables within those methods. The original 
definition was intended to define a minimum level of quantitation for 
these isotope dilution GC/MS methods. However, as described in the 
Assessment Document, EPA has changed the definition of the ML over the 
years and has expanded its applicability to other 40 CFR part 136 
methods. This proposal requests comment on whether to add the following 
definition of the ML to Appendix B of 40 CFR part 136: `` the lowest 
level at which the entire analytical system gives a recognizable signal 
and acceptable calibration point for the analyte, as determined by the 
procedure set forth at Appendix B of this part. The ML represents the 
lowest concentration at which an analyte can be measured with a known 
level of confidence.'' In addition to the definition, EPA requests 
comment on whether Appendix B should contain an explicit explanation of 
the calculation of the ML from an MDL value determined using the 
revised MDL procedure, including a table of multiplier values that may 
be used when the MDL value is calculated from other than seven 
replicate analyses.
    An alternative is to not incorporate a definition in Sec.  136.2 
but to continue to specify the ML on a method-by-method basis. In this 
case, the ML may continue to be determined and supported with data 
gathered during method validation studies. This approach would allow 
maximum flexibility to design studies that are appropriate for the 
intended use of the method.
    A second alternative is to incorporate into Sec.  136.2 the 
definition of limit of quantitation as ``The lowest concentration of an 
analyte that can be measured with a defined level of confidence'' and 
to incorporate the definition of ML (minimum level) as ``The procedure 
set forth in Appendix B of this part of the same name, which can be 
used to estimate the limit of quantitation.''
    In this proposal, EPA is also requesting comment on whether it 
should encourage or require that laboratories periodically demonstrate 
target analyte recovery at the ML by preparing and analyzing a 
reference matrix sample spiked at the ML using all sample handling and 
processing steps described in the method. EPA recognizes that existing 
methods do not provide acceptance criteria for such ``ML standards.'' 
Therefore, EPA suggests that, if the method does not provide acceptance 
criteria for an ML standard, acceptance criteria for other spiked 
reference matrix samples (e.g., laboratory control samples, laboratory 
fortified blanks, ongoing precision and recovery samples, etc.) may be 
used to evaluate analyte recovery at the ML. EPA is soliciting comment 
on whether this recommendation should be made into a mandatory 
requirement, retained as a recommendation, or replaced by an 
alternative recommendation for demonstrating recovery at the ML.

E. Acceptance of Test Methods Employing Alternative Detection and 
Quantitation Procedures

    This proposed rule would allow use of alternative detection and 
quantitation procedures to establish detection and quantitation limits 
in an analytical method, provided that the resulting detection and 
quantitation limits meet the sensitivity needs for the specific 
application. The use of detection and quantitation approaches from 
voluntary consensus standards bodies (VCSBs) and other organizations is 
encouraged under the National Technology Transfer and Advancement Act 
(NTTAA), because it facilitates the approval of analytical methods from 
these organizations at 40 CFR part 136 without requiring that these 
organizations specifically employ EPA's MDL and ML procedures to 
establish method sensitivity. This allowance would result in greater 
flexibility to establish or improve the sensitivity of methods for use 
under the Clean Water Act. It also would facilitate approval of 
analytical methods from VCSBs and other organizations. In selecting an 
appropriate test method for a specific purpose, the laboratory must 
always consider the sensitivity of the approved test methods. Only 
those test methods with the desired sensitivity should be used to meet 
the objective of the CWA ``to restore and maintain the chemical, 
physical, and biological integrity of the Nation's waters.''
    EPA recognizes that there are alternative detection and 
quantitation approaches that may be used for determining test method 
sensitivity. EPA has included test methods at 40 CFR part 136 that 
employ alternative approaches, although some of these approaches have 
not been rigorously defined. In its recent assessment of detection and 
quantitation approaches, EPA evaluated the interlaboratory detection 
estimate (IDE) and the interlaboratory quantitation estimate (IQE) 
procedures published by ASTM International. However, EPA is not aware 
at this time of any published test methods from any source that include 
specific values for the IDE and the IQE, including test methods 
published by ASTM International. EPA will consider test methods that 
include these procedures for use in CWA programs when such methods are 
available. If ASTM International is successful in developing single-
laboratory adaptations of the IDE and IQE that may be used to verify 
the ability of a given laboratory to achieve the IDE and IQE, then EPA 
also may consider those single-laboratory approaches in evaluating both 
method and laboratory performance.

VIII. Industry Proposal

    On December 27, 2002, the Inter-Industry Analytical Group (IIAG) 
submitted a proposal that recommends (1) a sensitivity test intended to 
``replace the MDL as a test of whether an individual laboratory is 
performing adequately,'' and (2) an interlaboratory validation study 
design intended to characterize precision and accuracy of methods used 
for regulatory compliance. EPA did not have the opportunity to evaluate 
IIAG's proposal against the criteria discussed in Section IV of this 
preamble, but intends to do so prior to publication of a final rule. 
EPA is providing a summary of the recommendations contained in the 
``Inter-Industry Analytical Group Proposal for Sensitivity Test and 
Full-Range Interlaboratory Validation Study'' here. The complete text 
of the recommendations has been placed in the docket supporting this 
proposed rule. EPA is soliciting comment on the industry 
recommendations.
    IIAG is proposing a sensitivity test in place of the MDL for 
determining laboratory performance capability. The proposed sensitivity 
test includes the provision that EPA first determine the lowest 
calibration point of a method, prescribe a dilution of that calibration 
point as the spike level (e.g., at one-half or two-thirds the lowest 
calibration point), specify a required number of replicates, and set a 
quality control acceptance criterion. IIAG asserts that an advantage of 
such a test is that it would provide all laboratories with a single 
spike level and an ``unambiguous pass or no-pass test.'' EPA is 
soliciting comment on approaches that might be considered appropriate 
for such determinations (i.e., the lowest calibration point of a 
method, an appropriate dilution, a number of replicates, and an 
acceptance criterion for standard deviation between measurements of the 
replicates). EPA also is soliciting comment on how IIAG's recommended 
sensitivity test would be either more appropriate or less appropriate 
than either the current MDL and ML procedures or the MDL and ML

[[Page 11783]]

procedures if revised according to this proposed rule.
    IIAG's proposed ``full range'' validation study is intended to 
determine precision and bias across the entire working range of an 
analytical method (i.e., from a blank to the upper end of the working 
range) and would account for variability between laboratories. IIAG 
recommends that, unlike the MDL and IIAG's proposed sensitivity test, 
the ``full-range'' validation study could be used to characterize bias 
and precision across the entire working range of the method and results 
of such a study could be used to establish an interlaboratory method 
detection level. EPA is requesting comment on the use of data generated 
through a ``full range'' validation study to determine a quantitation 
level, detection level, and corresponding bias and precision criteria 
that are applicable throughout the entire working range of the method. 
EPA also is soliciting comment on how IIAG's recommended ``full range'' 
validation study would be either more appropriate or less appropriate 
than EPA's use of interlaboratory validation studies, which are 
designed in accordance with ASTM Standard D 2777, or other appropriate 
standards. For example, EPA used the ASTM standard to validate EPA 
Method 1631 (see Interlaboratory Validation Study of EPA Method 1631).

IX. Solicitation of Comments

    EPA is hereby requesting public comment on the proposed revisions 
discussed in section VII of this preamble and on the industry proposal 
discussed in section VIII. Specifically, EPA is requesting comment on 
the proposed revisions to the Definition and Procedure for the 
Determination of the Method Detection Limit at 40 CFR part 136 
(Appendix B), to the proposed revision to the definition of ``Detection 
Limit,'' on whether EPA should add definition of ``Minimum Level'' at 
40 CFR 136.2, and on whether and how the sensitivity test described in 
the industry proposal could be used in CWA programs. EPA is also 
requesting public comment on the Assessment Document supporting the 
proposed revisions discussed in this notice elsewhere in today's 
Federal Register (see Notice of Document Availability and Public 
Comment Period for the Technical Support Document for the Assessment of 
Detection and Quantitation Concepts).
    Commenters are encouraged to support their views with data or 
information that would assist EPA in making a final decision on 
detection and quantitation procedures for EPA's CWA applications. To 
ensure that EPA can properly respond to comments, commenters should 
cite, where possible, the paragraph(s) or section(s) in this proposal 
to which each comment refers. For further details on submission of 
comments, please see the DATES; ADDRESSES; and ``How to Submit 
Comments'' sections at the beginning of this preamble.
    EPA is particularly requesting comment on the following:
    1. EPA is requesting comment on whether to include a definition and 
procedure for the ML in Appendix B of 40 CFR part 136 (see section 
VII.D of this preamble). EPA is soliciting comment on whether the 
proposed addition of an ML definition and procedure in Appendix B is 
appropriate, or whether either of the alternatives discussed in section 
VII.D are more appropriate to maintain flexibility in the application 
of different quantitation approaches.
    2. EPA is proposing a recommendation that laboratories periodically 
demonstrate target analyte recovery at the ML by preparing and 
analyzing a reference matrix sample spiked at the ML (see section VII.D 
of this preamble). Specifically, EPA is soliciting comment on whether 
this recommendation should be made into a mandatory requirement, 
retained as a recommendation, or replaced by an alternative 
recommendation for demonstrating recovery at the ML. EPA also is 
soliciting comments and recommendations regarding procedures for 
establishing acceptance criteria for ML recovery, and when application 
of the criteria would be appropriate (e.g., development of new methods, 
validation of data), if such a requirement were mandatory.
    3. EPA is proposing to add a new Step 8 to the MDL procedure to 
address the identification and treatment of suspected outliers (see 
Section VII.B.7 of this preamble). This proposed step includes 
provision for invalidation of results from noncorrectable errors and 
precludes their use in calculating the MDL. The proposed step also 
states: ``Given the small number of replicates typically used to 
determine the MDL, it is inappropriate to use a data set that contains 
more than one statistical outlier.'' EPA requests comment on (1) the 
procedures for identifying outliers, (2) the specification that only 
one outlier may be removed from a data set that is used for MDL 
determination, and (3) the appropriateness of allowing use of a data 
set containing six results if an outlier is identified and removed from 
a data set containing results from the required minimum of seven 
replicate samples.
    4. EPA is proposing to revise the specifications for establishing 
the test concentration (spike level) that will be used in the 
determining the MDL according to the intended application of the MDL 
(see Section VII.A.4 of this preamble). EPA is soliciting comment on 
these levels and on the appropriateness of applying these levels 
according to the intended use of the MDL.
    5. EPA is soliciting comment on the sensitivity test and ``full-
range'' validation study described by IIAG and included in the public 
docket supporting this proposed rule (see Section VII of this 
preamble). EPA is specifically soliciting comment on those aspects of 
IIAG's proposed study that relate to detection and quantitation issues.
    6. EPA is proposing to delete the Reporting section of the existing 
MDL procedure. EPA is soliciting comments on whether this change is 
appropriate.

X. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735 (October 4, 1993)), the 
Agency must determine whether the regulatory action is ``significant'' 
and therefore subject to Office of Management and Budget (OMB) review 
and the requirements of the Executive Order. The Executive Order 
defines ``significant regulatory action'' as one that is likely to 
result in a rule that may:
    (1) Have an annual effect on the economy of $100 million or more, 
or adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or Tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations of recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    It has been determined that this rule is not a ``significant 
regulatory action'' under the terms of Executive Order 12866 and is 
therefore not subject to OMB review.

[[Page 11784]]

B. Paperwork Reduction Act

    This action does not impose an information collection burden under 
the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. 
This action imposes no information collection, reporting or 
recordkeeping requirements. Burden means the total time, effort, or 
financial resources expended by persons to generate, maintain, retain, 
or disclose or provide information to or for a Federal agency. This 
includes the time needed to review instructions; develop, acquire, 
install, and utilize technology and systems for the purposes of 
collecting, validating, and verifying information, processing and 
maintaining information, and disclosing and providing information; 
adjust the existing ways to comply with any previously applicable 
instructions and requirements; train personnel to be able to respond to 
a collection of information; search data sources; complete and review 
the collection of information; and transmit or otherwise disclose the 
information.
    An Agency may not conduct or sponsor, and a person is not required 
to respond to a collection of information, unless it displays a 
currently valid OMB control number. The OMB control numbers for EPA's 
regulations are listed in 40 CFR part 9 and 48 CFR chapter 15.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedure Act or any other statute unless the agency certifies that the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this rule on small 
entities, small entity is defined as: (1) A small business as defined 
by the U.S. Small Business Administration definitions at 13 CFR 
121.201; (2) a small governmental jurisdiction that is a government of 
a city, county, town, school district or special district with a 
population of less than 50,000; and (3) a small organization that is 
any not-for-profit enterprise which is independently owned and operated 
and is not dominant in its field.
    After considering the economic impacts of this proposed rule on 
small entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. This rule 
proposes to modify existing procedures in 40 CFR part 136, appendix B 
for determination of detection and quantitation in analytical methods. 
This modification would clarify and improve existing procedures.
    Overall, the costs of this modification are minimal. Many 
laboratories using analytical test methods are already implementing 
aspects of the modification, further minimizing any potential cost 
increases. Therefore, EPA believes that this rule will not have a 
significant economic impact on a substantial number of small entities. 
We continue to be interested in the potential impacts of the proposed 
rule on small entities and welcome comments on issues related to such 
impacts.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, Tribal, and local 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State, Tribal, and local governments, in 
the aggregate, or to the private sector, of $100 million or more in any 
one year. Before promulgating an EPA rule for which a written statement 
is needed, section 205 of the UMRA generally requires EPA to identify 
and consider a reasonable number of regulatory alternatives and adopt 
the least costly, most cost-effective or least burdensome alternative 
that achieves the objectives of the rule. The provisions of section 205 
do not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective or least burdensome alternative if the 
Administrator publishes with the final rule an explanation of why that 
alternative was not adopted.
    Before EPA establishes any regulatory requirements that may 
significantly or uniquely affect small governments, including Tribal 
governments, it must have developed under section 203 of the UMRA a 
small government agency plan. The plan must provide for the 
notification of potentially affected small governments, enabling 
officials of affected small governments to have meaningful and timely 
input in the development of EPA regulatory proposals with significant 
Federal intergovernmental mandates, and informing, educating, and 
advising small governments on compliance with the regulatory 
requirements.
    This proposed rule contains no Federal mandate (under the 
regulatory provisions of Title II of the UMRA) for State, Tribal, and 
local governments or the private sector in any one year. This rule 
imposes no enforceable duty on any State, local, or Tribal governments 
or the private sector. This rule proposes to modify existing procedures 
in 40 CFR part 136, appendix B for determination of detection and 
quantitation in analytical methods. This modification would clarify and 
improve current procedures. Overall, the costs of this modification are 
minimal. Thus, this rule is not subject to sections 202 and 205 of the 
UMRA. For the same reasons, EPA has also determined that this rule 
contains no regulatory requirements that might significantly or 
uniquely affect small governments. Thus, this rule also is not subject 
to the requirements of section 203 of the UMRA.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 
10, 1999), requires EPA to develop an accountable process to ensure 
``meaningful and timely input by State and local officials in the 
development of regulatory policies that have federalism implications.'' 
``Policies that have federalism implications'' is defined in the 
Executive Order to include regulations that have ``substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    This proposed rule does not have federalism implications. It will 
not have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in Executive Order 13132. This rule proposes to modify 
existing procedures in 40 CFR part 136, Appendix B for determination of 
detection and quantitation in analytical methods. This modification 
would clarify and improve existing procedures. The costs of this rule 
for State and local governments are minimal. Thus, Executive Order 
13132 does not apply to this rule. In the spirit of Executive Order 
13132, and consistent with EPA policy to promote communications between 
EPA and State and local governments, EPA specifically solicits comments 
on this proposed rule from State and local officials.

[[Page 11785]]

F. Executive Order 13175: Consultation and Coordination with Indian 
Tribal Governments

    Executive Order 13175, titled ``Consultation and Coordination With 
Indian Tribal Governments'' (65 FR 67249, November 9, 2000), requires 
EPA to develop an accountable process to ensure ``meaningful and timely 
input by Tribal officials in the development of regulatory policies 
that have Tribal implications.'' ``Policies that have Tribal 
implications'' is defined in the Executive Order to include regulations 
that have ``substantial direct effects on one or more Indian Tribes, on 
the relationship between the Federal government and the Indian Tribes, 
or on the distribution of power and responsibilities between the 
Federal government and Indian Tribes.''
    This proposed rule does not have Tribal implications. It will not 
have substantial direct effects on Tribal governments, on the 
relationship between the Federal government and Indian Tribes, or on 
the distribution of power and responsibilities between the Federal 
government and Indian Tribes, as specified in Executive Order 13175. 
This rule proposes to modify existing procedures in 40 CFR part 136, 
Appendix B for determination of detection and quantitation in 
analytical methods. This modification would clarify and improve 
existing procedures. The costs of this rule for Tribal governments are 
minimal. Thus, Executive Order 13175 does not apply to this rule. In 
the spirit of Executive Order 13175, and consistent with EPA policy to 
promote communications between EPA and Tribal governments, EPA 
specifically solicits comments on this proposed rule from Tribal 
officials.

G. Executive Order 13045: Protection of Children From Environmental 
Health & Safety Risks

    Executive Order 13045 (62 FR 19885, April 23, 1997) applies to any 
rule that: (1) Is determined to be ``economically significant'' as 
defined under Executive Order 12866, and (2) concerns an environmental 
health or safety risk that EPA has reason to believe may have a 
disproportionate effect on children. If the regulatory action meets 
both criteria, the Agency must evaluate the environmental health or 
safety effects of the planned rule on children, and explain why the 
planned regulation is preferable to other potentially effective and 
reasonably feasible alternatives considered by the Agency. This 
proposed rule is not subject to Executive Order 13045 because it is not 
``economically significant'' as defined in Executive Order 12866. 
Furthermore, it does not concern an environmental health or safety risk 
that EPA has reason to believe may have a disproportionate effect on 
children.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This rule is not subject to Executive Order 13211, ``Actions 
Concerning Regulations That Significantly Affect Energy Supply, 
Distribution, or Use'' (66 FR 28355 (May 22, 2001)) because it is not a 
significant regulatory action under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995, (``NTTAA''), Public Law 104-113, section 12(d) (15 U.S.C. 
272 note), directs EPA to use voluntary consensus standards in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., material specifications, test methods, 
sampling procedures, business practices) that are developed or adopted 
by voluntary consensus standard bodies. The NTTAA directs EPA to 
provide Congress, through the Office of Management and Budget (OMB), 
explanations when the Agency decides not to use available and 
applicable voluntary consensus standards.
    This proposed rulemaking involves technical standards. Therefore, 
the Agency identified and evaluated potential voluntary consensus 
standards. Specifically, EPA identified and evaluated potential 
detection and quantitation concepts and procedures published by the 
American Society for Testing and Materials (ASTM International), from 
the International Organization for Standardization (ISO), the 
International Union of Pure and Applied Chemistry (IUPAC), and the 
American Chemical Society (ACS). EPA determined that, although ISO, 
IUPAC, and ACS have published terms and definitions for detection and 
quantitation, these organizations have not published an applicable 
standard (i.e., a step-by-step protocol to make a detection or 
quantitation determination). EPA did identify applicable standards from 
ASTM International (the IDE and IQE). This proposed rulemaking would 
allow the use of these procedures for methods development purposes and 
would allow the use of any analytical methods with an IDE and IQE, 
provided these test methods meet the analytical sensitivity 
requirements for a specific data use. There is currently no applicable 
voluntary consensus standard for detection and quantitation for 
laboratory quality control purposes. EPA welcomes comments on this 
aspect of the proposed rulemaking and, specifically, invites the public 
to identify potentially applicable voluntary consensus standards and to 
explain why such standards should be used in this regulation.

XI. References

    American Chemical Society, 1980: Analytical Chemistry 1980, 52, 
2242-2249.
    American Chemical Society, 1983: Analytical Chemistry 1983, 55, 
2210-2218.
    Budde, William L., Environmental Science and Technology 1981 15, 
1426-1435.
    Currie, 1968: Currie, Lloyd A. Anal. Chem. 1968 40, 586-593.
    Currie, 1999: Currie, Lloyd A. Anal. Chim. Acta 1999 391, 127-
134.
    Gibbons, 1997: Gibbons, Robert D.; Coleman, David E.; Maddalone, 
Raymond F. Env. Sci. Technol. 1997, 31, 2071-2077).
    Glaser, 1981: Glaser, John A., Foerst, Denis L., McKee, Gerald 
D., Quave, Stephan A., and Budde, William L. (1981), Environ. Sci. 
Technol., 15:1426.
    Kahn, 1998: Kahn, Henry D.; Telliard, William A.; White, Charles 
E. Env. Sci. Technol. 1998 32, 2346-2348.
    Kahn, 1998: Kahn, Henry D.; Telliard, William A.; White, Charles 
E. Env. Sci. Technol. 1999 33, 1315.
    Maddalone, 1993: Maddalone, Raymond F.; Rice, James K.; 
Edmondson, Ben C.; Nott, Babu R.; Scott, Judith W. Water Environment 
and Technology 1993, 5, 1-4.
    Rocke and Lorenzato, 1995: Rocke, D. M. and Lorenzato, S. 
Technometrics 1995, 37, 176-184.

Appendix A: Definitions, Acronyms, and Abbreviations Used in This 
Document

AAMA--American Automobile Manufacturers Association
ACS--American Chemical Society
AOAC--Association of Official Analytical Chemists (now AOAC-
International)
APHA--American Public Health Association
ASTM--American Society for Testing and Materials (now ASTM 
International)
ATP--Alternate Test Procedure
AWWA--American Water Works Association
CBI--confidential business information
CFR--Code of Federal Regulations
CRV--critical value
CWA--Clean Water Act--Federal Water Pollution Control Act Amendments 
(33 U.S.C. 1251 et seq.)
EPA--Environmental Protection Agency
EPRI--Electric Power Research Institute
FR--Federal Register

[[Page 11786]]

IDE--interlaboratory detection estimate
IIAG--Inter-Industry Analytical Group
IQE--interlaboratory quantitation estimate
ISO--International Organization for Standardization
IUPAC--International Union of Pure and Applied Chemistry
LOD--limit of detection
LOQ--limit of quantitation
MDL--method detection limit
MDV--minimum detectable value
ML--minimum level of quantitation
NBS--National Bureau of Standards (now NIST)
NIST--National Institute of Standards and Technology (formerly NBS)
NPDES--National pollutant discharge elimination system
NTTAA--National Technology Transfer and Advancement Act
OMB--Office of Management and Budget
POTW--Publicly-owned treatment works
RFA--Regulatory Flexibility Act
SBREFA--Small Business Regulatory Enforcement Fairness Act
SCC--Sample Control Center
TSD--technical support document
UMRA--Unfunded Mandates Reform Act
USATHAMA--U.S. Army Toxic and Hazardous Materials Agency (now the U.S. 
Army Environmental Center [USAEC])
U.S.C.--United States Code
WQBEL--water-quality-based effluent limit
WEF--Water Environment Federation

List of Subjects at 40 CFR Part 136

    Environmental protection, Reporting and recordkeeping requirements, 
Water pollution control.

    Dated: February 28, 2003.
Christine Todd Whitman,
Administrator.

    For the reasons set out in the preamble, title 40, chapter I of the 
Code of Federal Regulations, is proposed to be amended as follows:

PART 136--GUIDELINES ESTABLISHING TEST PROCEDURES FOR THE ANALYSIS 
OF POLLUTANTS

    1. The authority citation for part 136 continues to read as 
follows:

    Authority: Secs. 301, 304(h), 307, and 501(a), Pub. L. 95-217, 
91 Stat. 1566, et seq. (33 U.S.C. 1251, et seq.) (The Federal Water 
Pollution Control Act Amendments of 1972 as amended by the Clean 
Water Act of 1977).

    2. Section 136.2 is amended by revising paragraph (f) and adding 
paragraph (g) to read as follows:


Sec.  136.2  Definitions.

* * * * *
    (f) Detection limit means the method detection limit (MDL), as 
determined by the procedure set forth at Appendix B of this part. The 
MDL is an estimate of the measured concentration at which there is 99% 
confidence that a given analyte is present in a given sample matrix.
    (g) Minimum level of quantitation (ML) means the lowest level at 
which the entire analytical system gives a recognizable signal and 
acceptable calibration point for the analyte, as determined by the 
procedure set forth at Appendix B of this part. The ML represents the 
lowest concentration at which an analyte can be measured with a known 
level of confidence.
    3. Appendix B of part 136 is revised to read as follows:

Appendix B to Part 136

A. Definition and Procedure for the Determination of the Method 
Detection Limit--Revision 2

1.0 Definition

    The method detection limit (MDL) is an estimate of the measured 
concentration at which there is 99% confidence that a given analyte 
is present in a given sample matrix. The MDL is the concentration at 
which a decision is made regarding whether an analyte is detected by 
a given analytical method. The MDL is calculated from replicate 
analyses of a matrix containing the analyte and is functionally 
analogous to the ``critical value'' described by Currie (1968, 1995) 
and the Limit of Detection (LOD) described by the American Chemical 
Society (Keith et al., 1980, McDougal et al., 1983).

2.0 Scope and Application

    2.1 This procedure is for the determination of an MDL for a 
given analyte (parameter) in a given matrix (the component or 
substrate that contains the analyte) using a given test procedure 
(analytical method). It is applicable to a wide variety of analytes, 
matrices, and instruments, and to a broad variety of physical and 
chemical analytical methods, with some exceptions (e.g., pH, 
temperature). This procedure is intended for use in EPA's Clean 
Water Act (CWA) programs. An alternative procedure may be used 
(e.g., from a voluntary consensus standards body) to establish the 
sensitivity of an analytical method, provided the resulting 
detection limit meets the sensitivity needs for the specific 
application.
    2.2 This procedure requires a complete, specific, and well-
defined analytical method. It is essential that all sample 
processing steps of the analytical method that are applied to 
routine analyses be included in determination of an MDL.
    2.3 This procedure may be used for a variety of applications, 
including, but not limited to:
    2.3.1 Demonstrating laboratory capability with a particular 
method. A laboratory using this procedure to demonstrate capability 
with a particular method is not required to perform the iterative 
verification of the MDL (section 4.8) if the laboratory-determined 
MDL is less than or equal to either the MDL in the method, the MDL 
required to support a regulation, or the objectives of a study (see 
section 4.8.5).
    2.3.2 Monitoring trends in laboratory performance. When used in 
this manner, the MDL for a given analyte measured using a given 
analytical method may vary as a function of laboratory experience 
and the matrix tested.
    2.3.3 Characterizing method sensitivity in a particular matrix. 
An MDL is typically determined in a reference matrix. However, it 
also may be determined in a real-world matrix to verify that the 
target MDL can be achieved in that matrix.
    2.3.3.1 If the MDL required for a specific application can be 
achieved in a real-world matrix, that MDL may be used in lieu of a 
reference-matrix MDL, and iteration (section 4.8) is not necessary.
    2.3.3.2 If the MDL needed for a specific application cannot be 
achieved in the real-world matrix (i.e., if the purpose of the MDL 
study is to demonstrate the effects of matrix interferences in a 
real world sample), the laboratory must (1) perform an MDL study in 
a reference matrix to demonstrate the laboratory's ability to apply 
the method in the absence of interferences, and (2) verify the 
matrix-specific MDL through the iterative procedure given in section 
4.8.
    2.3.3.3 Refer to section 4.2 for additional information 
concerning the selection of test matrices.
    2.3.4 Establishing an MDL for a new or revised method for 
nationwide use. When the procedure is used to establish an MDL for a 
new or revised method, the MDL should be derived from data obtained 
from multiple laboratories. Organizations developing or revising 
methods must document and make available the data and procedures 
used to establish an MDL to obtain approval for use under Clean 
Water Act programs.

3.0 Summary of the Procedure

    3.1 The procedural steps required for determining an MDL vary 
with the intended application of the MDL. However, regardless of the 
intended application, all MDL determinations must include the 
following steps:
    (a) Estimating the detection limit of the method as practiced,
    (b) Selecting the appropriate matrix to be used in the 
determination,
    (c) Selecting the appropriate test concentration,
    (d) Preparing and analyzing a minimum of seven replicate 
aliquots of a blank or spiked matrix,
    (e) Calculating the mean concentration of the analyte, the 
standard deviation of that mean, and the MDL, using the formula 
provided in this procedure,
    (f) Comparing the calculated MDL to a method-specified MDL, 
relevant regulatory requirements, or project-specific objectives, as 
appropriate.
    3.2 When developing MDLs for new or revised methods, or 
developing matrix-specific MDLs for nationwide use, the procedure 
also may include:
    (a) Conducting an optional pre-test using fewer replicates to 
verify that an appropriate

[[Page 11787]]

concentration was selected to perform the MDL test,
    (b) Conducting an iterative procedure involving analyses of 
additional replicates to verify the reasonableness of the MDL 
(required for method development),
    (c) Determining the MDL in additional relevant matrices or in 
multiple laboratories.

4.0 Procedure

    4.1 Estimate the detection limit of the method
    If the purpose of determining the MDL is to verify laboratory 
performance using a specific method or to determine the MDL in a 
specific matrix, the laboratory should use the MDL published in the 
method as the initial estimate. If the MDL is being determined for 
other reasons (e.g., method development), the experience of the 
laboratory is important to properly estimate the detection limit. 
The laboratory must include at least one of the following 
considerations in producing this initial estimate:
    4.1.1 The concentration of analyte that produces an instrument 
signal/noise in the range of 2.5 to 5 for those instances in which 
an instrument is used for the determination.
    4.1.2 The concentration approximately equal to three times the 
standard deviation of replicate measurements of the analyte in a 
blank. If analysis of the blank produces no response (zero), use the 
concentration approximately equal to three times the standard 
deviation of replicate measurements at the lowest concentration that 
always produces a response.
    4.1.3 A concentration in the region of constant or effectively 
constant standard deviation at low concentrations. This assumes that 
the model of Glaser et al. (1981), which includes a low 
concentration region where the standard deviation of the measurement 
error is constant or effectively constant, is suitable to describe 
the measurement process for the analytical method under 
consideration.
    4.1.4 The lowest concentration that can be detected by analyzing 
samples containing successively lower concentrations of the analyte.
    4.2 Select the matrix to be used to develop the MDL. The MDL is 
typically determined in a reference matrix. However, it may be 
determined in a real-world matrix to verify that the MDL required 
for a specific application can be achieved in that matrix.
    4.2.1 Reference Matrix
    The most common reference matrix is reagent water. Reagent water 
is defined as water in which the analyte and interferences are not 
detected at the MDL or, if this is the initial estimate, detected at 
the detection limit estimated in section 4.1. An interference is 
defined as a systematic error in the measured analytical signal 
caused by the presence of a substance other than the analyte. Other 
common reference matrices are sand as a reference matrix for soils, 
sediments, and other solid samples; and corn oil as a reference 
matrix for tissue samples. After selecting the reference matrix to 
be tested, proceed to section 4.3.
    4.2.2 Matrices other than a reference matrix
    4.2.2.1 If the MDL determined in a matrix other than a reference 
matrix is sufficient to meet requirements of the specific 
application (e.g., the laboratory is able to meet the MDL required 
for compliance monitoring or published in the method), it is not 
necessary to determine the MDL in a reference matrix.
    4.2.2.2 If the purpose of a matrix-specific MDL is to determine 
the effects of matrix interferences in a real-world sample, the 
laboratory also must determine the MDL in a reference matrix to 
demonstrate the laboratory's ability to apply the method in the 
absence of interferences.

    Note to Section 4.2.2.2: A laboratory seeking to develop a 
matrix-specific MDL for a specific method must use the same cleanup 
steps that will be used for analysis of samples.

    4.3 Establish the test concentration range and prepare test 
samples Establish the test concentration range per section 4.3.1. 
Prepare the test samples from a reference matrix per section 4.3.2, 
or from an alternative matrix per section 4.3.3. Prepare a 
sufficient quantity of the matrix to provide samples for a minimum 
of seven analyses.

    Note to Section 4.3: For analytes for which a single-volume 
(bulk) sample or spiked single-volume sample would result in non-
homogenous replicates (e.g., for determination of ``oil and 
grease''), or for which preparation of a spiked single-volume sample 
is impractical, a minimum of seven individual aliquots should be 
prepared at the test concentration.

    4.3.1 Establish the test concentration range as follows.
    4.3.1.1 If verifying an MDL that is published in an analytical 
method, the test concentration should be no more than five times the 
published MDL.
    4.3.1.2 If verifying an MDL required to support a regulatory 
objective or the objective of a specific study or program, the test 
concentration should be no more than one third the compliance or 
target limit.
    4.3.1.3 If performing an MDL study for a new or revised method, 
the test concentration should be no more than five times the 
detection limit estimated in section 4.1.
    4.3.1.4 If performing an iteration (see section 4.8), the test 
concentration should be no more than five times the MDL determined 
in the most recent iteration.
    4.3.2 Preparing test samples from a reference matrix
    If a blank sample produces an acceptable signal (see section 
4.3.2), spiking is not required; otherwise, spike the reference 
matrix at the concentration established in section 4.3.1. Proceed to 
section 4.4.

    Note to Section 4.3.2: The laboratory must ensure that the 
levels in blanks are not too high. Otherwise, the resulting MDL 
produced may be artificially biased. For a spiked sample, the 
concentration of the contaminant in the blank should not be a 
significant portion of the total concentration since this also could 
result in an artificial bias for the MDL. It is important to spike 
the analyte at the proper concentration (section 4.3) to ensure the 
MDL is determined accurately.

    4.3.3 Preparing test samples from a matrix other than a 
reference matrix
    Analyze three aliquots of the sample matrix to characterize the 
concentration of the target analyte(s) present in the matrix.
    4.3.3.1 If the average measured concentration of the analyte in 
the matrix is less than five times the concentration established in 
section 4.3.1, proceed to section 4.4.
    4.3.3.2 If the average measured concentration of the analyte in 
the matrix is less than the concentration range established in 
section 4.3.1, spike the matrix to bring the concentration of the 
analyte to the established concentration range and proceed to 
section 4.4.
    4.3.3.3 If the average measured concentration of the analyte in 
the matrix is greater than the concentration range established in 
section 4.3.1, reduce the concentration of the analyte to the 
established concentration range, using one of the following 
techniques before proceeding to section 4.4:
    4.3.3.3.1 Selectively remove the analyte from the matrix.
    4.3.3.3.2 Obtain another matrix with a lower concentration of 
the analyte.
    4.3.3.3.3 Dilute a sample of the matrix with the appropriate 
reference matrix. For example, if the matrix is aqueous, dilute the 
sample with reagent water.

    Note to Section 4.3.3.3.3: Dilution should be used only if the 
analyte cannot be selectively removed (3.3.3.1) or if another matrix 
with a lower analyte concentration cannot be obtained (3.3.3.2) 
because dilution of the sample has the potential to dilute any 
interferences present.

    4.4 Perform the analyses
    4.4.1 The analyses in section 4.4.3 (optional pre-test of 
estimated detection limit) and 4.2 (MDL analyses) must be performed 
using all of the routinely employed calibration, sample handling, 
processing, and result calculations specified in the analytical 
method. For example, many methods contain multiple sample cleanup 
options; any and all cleanup options routinely used to analyze a 
sample must be used when analyzing the replicate samples prepared in 
section 4.3.
    4.4.2 Similarly, if the analytical method employs recovery-
correction or blank-correction procedures for calculating results, 
those procedures must be used when calculating results of an 
analysis of each aliquot. If a recovery- or blank-correction 
procedure is not specified in the test method, such correction must 
not be used.
    4.4.3 Optional pre-test
    It may be economically and technically desirable to evaluate the 
estimate of the detection limit (section 4.1) before proceeding with 
determination of the MDL in section 4.5. This pre-test attempts to 
ensure that the MDL study is being conducted at the correct 
concentration to prevent repeating the entire study; it may be 
particularly useful when the analytical costs are high. To evaluate 
the estimated detection limit, proceed as follows:
    4.4.3.1 Process three aliquots of the test sample prepared in 
section 4.3 through the entire method, per section 4.5.
    4.4.3.2 Calculate the standard deviation of results for the 
three aliquots as follows:

[[Page 11788]]

[GRAPHIC] [TIFF OMITTED] TP12MR03.047

    Where:
Xi = a result in the method reporting units obtained from 
analysis of a sample aliquot, i=1 to 3
X = mean of the three results, and
n = number of sample aliquots (3 in this case)

    4.4.3.3 Calculate a preliminary MDL as follows:

Preliminary MDL = 6.96s

Where:

6.96 = Student's t-value appropriate for a 99% confidence level and 
two degrees of freedom
s = standard deviation of the results of analyses of the three 
replicates from section 4.4.3.2
    4.4.3.4 If the preliminary MDL is in the range of 0.2--1.0 times 
the concentration in the spiked sample (section 4.3), analyze a 
minimum of four additional aliquots and proceed using the procedure 
in section 4.5. Use all seven measurements for calculation of the 
MDL. Otherwise, produce a new bulk sample per section 4.3, with the 
analyte at the concentration of the preliminary MDL and either 
repeat section 4.4.3, or proceed to section 4.5 for determination of 
the MDL.
    4.5 MDL determination
    4.5.1 Process at least seven aliquots of the test sample 
prepared in section 4.4 or section 4.4.3 through the entire 
analytical method.
    4.5.2 Make all computations as specified in the method, with 
final results in the method-specified reporting units.
    4.5.3 To obtain a valid MDL, all of the analytical results must 
be positive numbers. If any of the results are negative or zero, 
increase the test concentration (per section 4.3) and repeat the MDL 
procedure.
    4.5.4 If more than seven aliquots are prepared and analyzed, the 
results from all the aliquots must be used to calculate the MDL, 
except as described in section 4.9.
    4.6 Calculate the standard deviation, s, as follows:
    [GRAPHIC] [TIFF OMITTED] TP12MR03.048
    
    Where:
Xi = a result, in the method reporting units, obtained 
from analysis of a sample aliquot, i=1 to n
X = mean of the results, and
n = number of sample aliquots

    Note to Section 4.6: When using a program such as a spreadsheet 
to calculate the standard deviation (s), make certain that the 
sample standard deviation, which uses (n-1) in the denominator, is 
calculated, rather than the population standard deviation ([sigma]), 
which uses n in the denominator.

    4.7 Calculate the MDL
    [GRAPHIC] [TIFF OMITTED] TP12MR03.049
    
    Where:
s = standard deviation of the results calculated in section 4.6
t(n-1, 1-[alpha]=0.99) = Students' 
t-value appropriate for a 99% confidence level and (n-1) 
degrees of freedom, from the table below.

         Table of Student's t-Values at the 99% Confidence Level
------------------------------------------------------------------------
          Number of replicates for
---------------------------------------------  Degrees of
                                  Iterative     freedom      t(n-1, 1-
    Singles MDL  (df = n-1)       MDL  (df =      (df)     [alpha]=0.99)
                                     n-2)
------------------------------------------------------------------------
7..............................          N/A            6         3.143
8..............................          N/A            7         2.998
9..............................          N/A            8         2.896
10.............................          N/A            9         2.821
11.............................          N/A           10         2.764
12.............................          N/A           11         2.718
13.............................           14           12         2.681
14.............................           15           13         2.650
15.............................           16           14         2.624
16.............................           17           15         2.602
17.............................           18           16         2.583
18.............................           19           17         2.567
19.............................           20           18         2.552
------------------------------------------------------------------------


    Note to Section 4.7: Degrees of freedom = (n-1) if a single MDL 
study is performed. If an iterative MDL study is performed, degrees 
of freedom = (nh + n1-2), as described in 
section 4.8; N/A indicates that the number of degrees of freedom in 
this row does not apply to an iterative MDL study.

    4.8 Iterate and verify the reasonableness of the MDL
    When developing an MDL for a new or revised method, or when 
developing a matrix-specific MDL, the MDL procedure must be iterated 
and the reasonableness of the MDL determined using an F-test, as 
described in sections 4.8.1 through 4.8.4. When verifying a method-, 
matrix-, program-, or study-specific MDL, the MDL is determined as 
described in section 4.8.5 and iteration may not be necessary.
    4.8.1 Iteration
    When developing an MDL for a new or revised method, the spiking, 
analysis, and calculation steps (sections 4.3 to 4.6) must be 
repeated using a spike at no more than five times the MDL determined 
initially or in the most recent iteration, to confirm the 
reasonableness of the MDL.
    4.8.2 Once the iteration is complete (i.e., two successive MDL 
estimates have been produced), calculate the F-ratio (F) as:
[GRAPHIC] [TIFF OMITTED] TP12MR03.050

    Where:
sh\2\ = variance estimate from the higher spike 
concentration
sl\2\ = variance estimate from the lower spike 
concentration
nh = number of observations at the higher concentration
nl = number of observations at the lower concentration
    4.8.3 For seven replicates at each concentration, the 90th 
percentile of the distribution of the F-statistic is 3.055.
    4.8.3.1 If seven replicates were analyzed at each spike 
concentration and F 3.055, the two variances are 
different and the MDL determined at the higher spike concentration 
is not a reasonable estimate. In this case, return to section 4.3 
and produce another sample at a test concentration below the higher 
of the two previous iterations, analyze a minimum of seven aliquots, 
calculate the MDL, and repeat the F-test in section 4.8.2.
    4.8.3.2 If F <= 3.055 for seven replicates at each 
concentration, the two variances are not different. Proceed to 
section 4.8.4.

    Note to Section 4.8.3.2: If more than seven replicates are used, 
the appropriate F-statistic is determined from the table below.


[[Page 11789]]



                                           Table of F-Statistic Values
----------------------------------------------------------------------------------------------------------------
                                                                                  F-statistic
                                                             ---------------------------------------------------
                                                                   6            7            8            9
----------------------------------------------------------------------------------------------------------------
6...........................................................        3.055        3.014        2.983        2.958
7...........................................................        2.827        2.785        2.752        2.725
8...........................................................        2.668        2.624        2.589        2.561
9...........................................................        2.551        2.505        2.469        2.440
----------------------------------------------------------------------------------------------------------------

    4.8.4 When the process has been iterated and the results pass 
the F-test in section 4.8.3, the final MDL is calculated by pooling 
the results from the two iterations that passed the F-test. The 
pooled standard deviation is calculated as:
[GRAPHIC] [TIFF OMITTED] TP12MR03.051

    Where:
(sh)\2\ = variance estimate from the higher spike 
concentration
(sl)\2\ = variance estimate from the lower spike 
concentration
nh = number of sample aliquots used for the higher spike 
concentration
nl = number of sample aliquots used for the lower spike 
concentration
    4.8.5 The pooled MDL is calculated using the pooled standard 
deviation and the Student's t-value for (nh + 
nl-2) degrees of freedom (e.g., 12 degrees of freedom for 
two iterations with seven aliquots each).
[GRAPHIC] [TIFF OMITTED] TP12MR03.052

    Where:
Spooled = pooled standard deviation of the results
t(nh + n1-2, 1-[alpha] = 0.99) = 
Student's t-value appropriate for a 99% confidence level and 
(nh+nl) aliquots
    For 12 degrees of freedom, the t-value is 2.681. If more than 
seven replicates were used for either iteration, the appropriate t-
value must be determined from the table given in section 4.7.
    4.8.5 When verifying a method-, matrix-, program-, or study-
specific MDL, the determined MDL is compared to the method-specified 
MDL, the MDL required to support a regulatory objective, or the MDL 
required to support an objective of a specific study or program. If 
the required MDL is not met for the analyte, make sure that all 
instrumentation and technical aspects of the process (reagent 
concentrations, temperature, clean glassware, proper dilutions, 
etc.) are checked and assessed to be working properly before a 
repeat of the analyses. If the second attempt fails, iteration at a 
more appropriate spiking level for that analyte is necessary until 
the requirement is met. If the regulatory, study, or program 
objective is not known, the MDL is verified if the determined MDL is 
less than or equal to the method-specified MDL.
    4.9 Suspected Outliers
    4.9.1 Results associated with a known, spurious error that 
occurred during analysis should be discarded, or where appropriate, 
corrected. Spurious errors include those that arise through human 
error or instrument malfunction, such as transposing digits in a 
number while recording data, arithmetical errors when calculating 
results, double-spiking of an aliquot, or the presence of an air 
bubble lodged in a spectrophotometer flow-through cell. Recording or 
arithmetical errors can and should be corrected, and the corrective 
actions documented prior to use of results. Results associated with 
spurious errors that cannot be corrected will invalidate the 
measurement and should not be incorporated into the MDL 
determination.
    4.9.2 If random or spurious errors are suspected, it may be 
appropriate to apply a statistically accepted analysis of outliers, 
such as Grubbs test described below. Any outlying result should be 
considered with care to identify potential causes. It is generally 
not an accepted practice to reject a value purely on statistical 
grounds. Therefore, EPA recommends that when the cause of a 
potential outlier cannot be attributed to spurious causes, the MDL 
test be repeated for the analyte(s) in which such an outlier occurs.

    Note to Section 4.9.2: If more than seven aliquots are prepared 
and analyzed, results from all aliquots must be used in the MDL 
determination unless they have been determined to be outliers as 
described above. Given the small number of replicates typically used 
to determine the MDL, it is inappropriate to use a data set that 
contains more than one statistical outlier.

    4.9.3 The use of Grubbs test for outliers is described below, 
followed by an example (section 4.9.4).
    4.9.3.1 Rank the n observed data points in the order of 
increasing numerical value: X1 <= X2 
<=...<=Xn
    4.9.3.2 Using the mean, X, and standard deviation, s, from 
section 4.6, calculate:
[GRAPHIC] [TIFF OMITTED] TP12MR03.053

    Where:
X1 = lowest observed value of X
Xn = highest observed value of X
    4.9.3.3 Choose the larger of T1 and Tn.
    4.9.3.4 Compare the larger calculated value of T (e.g., 
T1 or Tn) with the critical value appropriate 
for the number of observations (n) from the table below. If T is 
larger than the critical value in the table, then the smallest (when 
testing T1) or largest (when testing Tn) 
observed data point is considered to be an outlier with 95% 
confidence.

            Table of Critical Values for T in the Grubbs Test
------------------------------------------------------------------------
                                                             Critical
                Number of data points (n)                  values for T
------------------------------------------------------------------------
7.......................................................           2.020
8.......................................................           2.126
9.......................................................           2.215
10......................................................           2.290
11......................................................           2.355
12......................................................           2.412
13......................................................           2.462
14......................................................           2.507
15......................................................           2.549
------------------------------------------------------------------------

    4.9.4 Example application of the outlier test
    4.9.4.1 Consider the following ranked data set with seven 
observations: 0.0449, 0.0458, 0.0462, 0.0469, 0.0471, 0.0475, and 
0.0508.
    4.9.4.2 Its mean, X, is 0.0470, and its standard deviation, s, 
is 0.0019.
    4.9.4.3 Calculate: T1 = (0.0470-0.0449)/0.0019 = 
1.132 and Tn = (0.0508-0.0470)/0.0019 = 2.007
    4.9.4.4 Select the larger value: T = max{1.132, 2.007{time}  = 
2.007
    4.9.4.5 Compare T with the corresponding critical value in the 
second line of the table above, where n=7 and the critical value of 
T = 2.020.
    Since the calculated value of T, 2.007, is not larger than the 
critical value in the table, 2.020, there is insufficient evidence 
to conclude that any of the observed data points is an outlier, and 
the MDL would be calculated from all seven results.

5.0 References

    5.1 Currie, Lloyd A. (1968), Limits for Quantitative Detection 
and Quantitative Determination, Analytical Chemistry 40: 586-593.
    5.2 Currie, Lloyd A. (1995), Nomenclature in Evaluation of 
Analytical Methods including Detection and Quantification 
Capabilities, Pure and Appl. Chem. 67:10, 1699-1722.
    5.3 Glaser, J.A., D.L. Foerst, J.D. McKee, S.A. Quave and W.L. 
Budde (1981), Trace Analyses for Wastewaters, Environ. Sci. 
Technol., 15:1426.
    5.4 Keith, Lawrence H., et al. (1983), Principles of 
Environmental Analysis, Analytical Chemistry 55:14, 2210-2218.
    5.5 McDougal, Daniel, et al. (1980), Guidelines for Data 
Acquisition and Data Quality Evaluation in Environmental Chemistry, 
Analytical Chemistry 52:14, 2242-2249.

[[Page 11790]]

B. Definition and Procedure for the Determination of the Minimum Level 
of Quantitation (ML)

1.0 Definition

    The minimum level of quantitation (ML) is the lowest level at 
which the entire analytical system gives a recognizable signal and 
acceptable calibration point for the analyte. The ML represents the 
lowest concentration at which an analyte can be measured with a 
known level of confidence. It may be equivalent to the concentration 
of the lowest calibration standard, assuming that all method-
specified sample weights, volumes, and cleanup procedures have been 
employed. It is functionally analogous to the ``determination 
limit'' described by Currie (1968) and the Limit of Quantification 
(LOQ) described by the American Chemical Society (Keith et al.,1980, 
McDougal et al., 1983) and Currie (1995).

    Note to Section 1.0: The ML is directed at obtaining a 10% 
relative standard deviation for determination of an analyte in an 
environmental sample. This error may be reduced by making multiple 
determinations of the analyte in the sample.

2.0 Scope and Application

    2.1 The ML is typically established by the organization that 
develops or modifies an analytical test method. A laboratory that 
employs the method would be expected to include calibration 
standards that encompass the ML when it calibrates an analytical 
system, unless a higher quantitation level is acceptable for a 
specific application. If an ML is not specified in a method, a 
laboratory may use the ML procedure to establish the lowest 
calibration point.
    2.2 This procedure is intended for use in EPA's Clean Water Act 
(CWA) programs. An alternative procedure may be used (e.g., from a 
voluntary consensus standards body) to establish the sensitivity of 
an analytical method provided the resulting quantitation limit meets 
the sensitivity needs (i.e., data quality objective) for the 
specific application.
    2.3 Laboratories are encouraged, but not required, to 
periodically demonstrate recovery of the target analyte near the 
published ML or laboratory-established ML by preparing a reference 
matrix sample spiked at the ML and analyzing it using all sample 
handling and processing steps described in the method. If the method 
does not provide acceptance criteria for such an ML standard, the 
laboratory can make an assessment of whether acceptance criteria for 
other spiked reference matrix samples (e.g., laboratory control 
samples, laboratory fortified blanks, ongoing precision and recovery 
samples, etc.) are appropriate to evaluate analyte recovery at the 
ML. Alternatively, the laboratory may develop its own acceptance 
criteria based on data gathered by the laboratory over time.

3.0 Procedure

    3.1 The ML is based on 10 times the standard deviation of the 
results of replicate analyses of a matrix containing the analyte. 
The method detection limit (MDL) is also based on the same standard 
deviation, multiplied by the Student's t-value appropriate for a 99% 
confidence level and corresponding degrees of freedom. Because the 
standard deviation may not be readily available, the ML is often 
calculated as a factor times the MDL.
    3.1.1 Calculating the ML based on MDL study data
    When available, obtain the actual standard deviation value from 
the MDL study and calculate the ML directly, as 10 times the 
standard deviation. If an iterative MDL study is performed, 
calculate the MDL as 10 times the pooled standard deviation.
    3.1.2 Calculating the ML based on the MDL Assuming a single 
iteration of seven replicates is used to determine the MDL, the 
number of degrees of freedom is 6, and the Student's t-value is 
3.143. Therefore, the MDL is:
MDL = 3.143 x s

and the ML is:

[GRAPHIC] [TIFF OMITTED] TP12MR03.054

    3.1.3 If the MDL is calculated from other than seven replicates 
or using the iterative procedure, the factor of 3.18 will change, 
and the table below is used to establish the correct multiplier. For 
example, if an iterative MDL study is performed consisting of 
exactly 7 replicates in each iteration, the resulting pooled MDL 
would incorporate 12 degrees of freedom, and the equation for the ML 
above would be modified accordingly, using a multiplier of 3.73.

                   Table of Student's t-values at the 99% Confidence Level and ML Multipliers
----------------------------------------------------------------------------------------------------------------
                   Number of replicates for
--------------------------------------------------------------  Degrees of                               ML
                                                Iterative MDL  freedom (df)  t(n-1,1-[alpha]=0.99)   multiplier
             Single MDL (df=n-1)                  (df=n-2)
----------------------------------------------------------------------------------------------------------------
7............................................            N/A              6                 3.143           3.18
8............................................            N/A              7                 2.998           3.34
9............................................            N/A              8                 2.896           3.45
10...........................................            N/A              9                 2.821           3.54
11...........................................            N/A             10                 2.764           3.62
12...........................................            N/A             11                 2.718           3.68
13...........................................             14             12                 2.681           3.73
14...........................................             15             13                 2.650           3.77
15...........................................             16             14                 2.624           3.81
16...........................................             17             15                 2.602           3.84
17...........................................             18             16                 2.583           3.87
18...........................................             19             17                 2.567           3.90
19...........................................             20             18                 2.552           3.92
----------------------------------------------------------------------------------------------------------------


    Note to Table: Degrees of freedom = (n-1) if a single iteration 
MDL study is performed and (nh + nl-2) if an 
iterative MDL study is performed; N/A indicates that the number of 
degrees of freedom in this row does not apply to an iterative MDL 
study.

4.0 Rounding

    The ML may be used to establish the lowest calibration point for 
the analyte. Therefore, in order to facilitate the preparation of 
calibration standards containing the analyte without undue 
difficulty, the ML may be rounded to the nearest multiple of 1, 2, 
or 5 x 10 n, where n is an integer.

5.0 References

    5.1 Currie, Lloyd A. (1968), Limits for Quantitative Detection 
and Quantitative Determination, Analytical Chemistry 40: 586-593.
    5.2 Currie, Lloyd A. (1995), Nomenclature in Evaluation of 
Analytical Methods including Detection and Quantification 
Capabilities, Pure and Appl. Chem. 67:10, 1699-1722.
    5.3 Glaser, J.A., D.L. Foerst, J.D. McKee, S.A. Quave and W.L. 
Budde (1981), Trace Analyses for Wastewaters, Environ. Sci. 
Technol., 15:1426.
    5.4 Keith, Lawrence H., et al. (1983), Principles of 
Environmental Analysis, Analytical Chemistry 55:14, 2210-2218.
    5.5 McDougal, Daniel, et al. (1980), Guidelines for Data 
Acquisition and Data Quality Evaluation in Environmental Chemistry, 
Analytical Chemistry 52:14, 2242-2249.

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