Upgrades/Improvements to EPA Methods 624 and 625 

Included in the docket for the 2014 Methods Update Rule proposal is a copy of the following presentation 

on “Upgrades/Improvements to EPA Methods 624 and 625” given by EPA at the 2014 National 

Environmental Monitoring Conference (NEMC) in Washington, DC, in August 2014. The presentation 

provides an overview of revisions made to these methods as a result of several rounds of internal and 

external reviews between 2012 and 2014. 

Reviews were performed by: 

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EPA’s Office of Research and Development (ORD), 

EPA’s Office of Enforcement and Compliance Assurance (OECA), 

EPA’s Office of Solid Waste and Emergency Response (OSWER), 

EPA and state regulatory/control personnel, 

EPA’s Laboratory Technical Information Group (LTIG), 

the Independent Laboratories Institute (ILI) of the American Council of Independent Laboratories 

(ACIL), 

EPA laboratory personnel, 

Commercial laboratory personnel, 

Instrument vendors, 

Independent consultants, 

the Environmental Laboratory Advisory Board (ELAB) including members of industry, and 

Participants at several EPA workshops.

EPA believes that the revisions made as a result of these reviews represent a significant improvement in 

these methods, and form the basis for soliciting comments from stakeholders as part of the promulgation 

process. As part of its proposal, EPA seeks comments on the revised methods.
Office of Water

Upgrades/Improvements to

EPA Methods 624 and 625

Lem Walker

Engineering and Analysis Division

Office of Science and Technology
Office of Water

Method 624 and 625 Revisions 

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Methods 624 and 625 were revised to 624.1 and 625.1 with 

stakeholder input between June 2012 and June 2014.

Interim drafts of each method were circulated for comment in:

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June 2012, with comments accepted through December 2012

June 2013, with comments accepted through August 2013

Methods 624.1 and 625.1 are in near final form at present, and 

stakeholder comments will be solicited shortly.

EPA expects to propose Methods 624.1 and 625.1 in the upcoming 

Methods Update Rule, and public comments on the revised 

methods are expected in response to the proposal 
Office of Water

Methods 624.1 & 625.1 – Analytes of Interest

• Methods 624.1 and 625.1 focus on “analytes of interest”

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Analytes of interest are those required to be determined by a 

regulatory/control authority, in a permit, or for a client

Quality control (QC) tests must be performed, and QC acceptance 

criteria must be met, for the analytes of interest

If analytes of interest are not specified to the laboratory by the 

regulatory/control authority, by a permit, or by a client:

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The analytes in Table 1 of 624.1 must be determined

The analytes in Table 1 (base/neutrals) and Table 2 (acids) of 625.1 must 

be determined

• EPA “priority pollutants” (40 CFR 423, appendix A) are identified in 

the tables
Office of Water

624.1/625.1 – Discharge-specific Spiking

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Moved responsibility for identifying samples to be spiked from lab to the 

discharger. Each specific discharge must be spiked at a frequency no less 

than 5 percent (1 in every 20 samples)

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Requirement negotiated with industry when 600-Series methods were developed

Assures applicability to each specific discharge

Requirement made more explicit in 624.1 and 625.1, including preparation 

of an MS/MSD pair to allow assessment of precision in the sample matrix

Spike concentration should be at:

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Regulatory compliance limit, 

1-5 times the background concentration in the sample, 

Near the mid-point of the calibration range, or 

Concentration in the laboratory control sample, whichever is greater
Office of Water

624.1/625.1 – Miscellaneous Changes

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Require reporting of results for the blank and sample separately.

Allow reporting a blank-subtracted result only if required by a 

regulatory/control authority or in a permit.

Provide procedures for dilution of a sample or sample extract 

when a pollutant concentration exceeds the calibration range

Provide suggestions for analysis of complex samples

Allow reporting of problems with results when QC tests are failed 

repeatedly
Office of Water

624.1/625.1 Reporting Levels

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Methods 624 and 625 were promulgated in 1984 and did not 

specify reporting levels

Methods 624.1 and 625.1 require reporting to the Minimum Level 

of Quantitation (ML)
Office of Water

624.1/625.1 RSD of RF

• Relative standard deviation (RSD) of response factor (RF) is used 

as a breakpoint between the allowed use of an average RF that 

models a straight line through the origin, and the required use of a 

calibration curve (a straight line not through the origin or quadratic)

• Full scan GC/MS methods promulgated in 1984 (624, 625, 1624, 

1625), and other CWA GC/MS methods use <35% as the breakpoint

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<35% is based results of the interlaboratory study of Method 1625

<35% was set based on an overall failure rate of <5% when a large 

number of analytes are tested simultaneously
Office of Water

624.1/625.1 QC Acceptance Criteria

• QC acceptance criteria are listed in Table 7 of 624.1 and 

in Table 6 of 625.1

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Criteria in these tables were developed in the early 

1980s

Stakeholders stated that QC acceptance criteria were 

too broad
Office of Water

624.1/625.1 QC Acceptance Criteria Continued

• For Methods 624.1 and 625.1, EPA will require development of 

“in-house” QC acceptance criteria by each lab

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Separate in-house QC acceptance criteria for the LCS and for the 

MS/MSD, for each analyte and surrogate, must be established as:

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the mean recovery ± 3 standard deviations, and 

the mean RPD + 3 standard deviations

Criteria must be based on analysis of a minimum of 20 samples; 

interim criteria of 60 – 140% recovery and 30% RPD must be used 

until 20 results are obtained.

At least 80% of QC acceptance criteria must be tighter than the 

criteria in the tables in the methods. If an in-house criterion is not 

tighter, the limit in the table must be used.
Office of Water

624.1/625.1 Nationwide Method Modifications

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For Methods 624.1 and 625.1, EPA will allow a discharger and/or 

laboratory to modify a method for nationwide use, provided that:

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all QC tests were run, 

all QC acceptance criteria were met with the modification as an 

integral part of the method,

the modified method is tested by spiking a minimum of nine (9) 

different discharges in duplicate (MS/MSD) and meeting the QC 

acceptance criteria for the MS/MSD

An example of a modification would be the use of solid-phase 

extraction (SPE) in Method 625.1.

Characteristics of the nine discharges are given on the next slide
Office of Water

Characteristics of Discharges Tested when 

Modifying a Method 

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Effluent from a Publicly Owned Treatment Works (POTW)

ASTM D 5905, Standard Specification for Substitute Wastewater

Sewage sludge, if sewage sludge will be in the permit

ASTM D 1141, Standard Specification for Ocean Water, if ocean 

water will be in the permit

A proficiency testing (PT) sample from a recognized provider

Untreated and treated wastewaters from a minimum of 9 matrix 

types, as defined in the alternate test procedure (ATP) protocol
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Characteristics of Discharges Tested when 

Modifying a Method (cont.)

• At least one of the nine matrix types must have at least one of the 

following characteristics:

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TSS >40 mg/L

TDS >100 mg/L

Oil & grease >20 mg/L

NaCl > 120 mg/L

CaCO3 >140 mg/L
Office of Water

Revised ATP and New Method Protocols for 

Chemical Methods for use in Wastewater

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Current protocols were published in 1999:

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Protocol for EPA Approval of Alternate Test Procedures for Organic and 

Inorganic Analytes in Wastewater and Drinking Water, March 1999

Protocol for EPA Approval of New Methods for Organic and Inorganic Analytes 

in Wastewater and Drinking Water, March 1999

These protocols introduced a three-tiered validation system based 

on the intended use of the method

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Tier 1 – Limited use in one or more laboratories, in one or more matrix types 

(approved by Regional ATP Coordinator)

Tier 2 – Nationwide use in all laboratories, in a single matrix type (approved 

through rulemaking)

Tier 3 – Nationwide use in all laboratories, in all matrix types (approved 

through rulemaking)
Office of Water

Revised ATP and New Method Protocols for 

Chemical Methods for use in Wastewater (cont.)

• The protocols have been revised to:

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Focus only on methods intended for use in wastewater compliance monitoring

Include procedures for validation of methods that measure method-defined 

parameters

Provide updated contact information for National and Regional ATP 

Coordinators

Clarify that methods developed by VCSBs do not fall within the scope of the 

alternate test procedure program and have a separate path for review and 

potential approval

Clarify that for limited-use ATPs, the approval may be restricted to use only 

with respect to a specific discharge or facility (and its laboratory) or, at the 

discretion of the Regional ATP Coordinator, to all dischargers or facilities (and 

their associated laboratories) specified in the approval for the Region
Office of Water

Questions or Comments

 Lemuel (Lem) Walker, Jr.

Office of Science and Technology

Engineering and Analysis Division (EAD)

walker.lemuel@epa.gov

http://www.epa.gov/waterscience/methods

Methods Questions? Write to:

OSTCWAMethods@epa.gov