EPA Approved Test Procedures for Pollutant Analysis

Every NPDES permit requires the permit holder to monitor their discharge and report the results. But which laboratory method do you use to measure "total suspended solids" or "chemical oxygen demand"? 40 CFR Part 136 answers that question — it is the master list of EPA-approved analytical test procedures for measuring pollutants in water, wastewater, and stormwater for NPDES compliance purposes. Labs that run samples for NPDES compliance must use Part 136 methods; results obtained by other methods generally are not acceptable for permit compliance unless EPA or the state has specifically approved an alternate method.

Legal Authority

• 33 U.S.C. § 1251 et seq. — Clean Water Act: the general authority for EPA's water quality regulations; NPDES permitting and monitoring requirements depend on standardized analytical methods to have legal meaning
• 40 CFR Part 136 — EPA regulations establishing approved test procedures (analytical methods) for measuring pollutants in water and wastewater for NPDES compliance; lists approved methods by analyte category and specifies laboratory quality control requirements

Key Mechanics

Part 136 is a reference regulation: it does not establish pollutant limits itself, but makes water quality monitoring legally meaningful by specifying which measurement methods are acceptable for compliance reporting. When an NPDES permit requires a facility to measure total phosphorus or ammonia nitrogen in its effluent, the measurement must use a Part 136-approved method or a state/EPA-approved alternative. The regulation lists approved methods by pollutant category (conventional pollutants, toxic metals, organic compounds, biological parameters) with references to specific Standard Methods, ASTM standards, and EPA methods. Laboratories conducting compliance analyses must follow method-specific quality control requirements; samples with missing or failed QC cannot be used for compliance determinations.

Current Rule (2026)

What This Rule Does

40 CFR Part 136 approves specific analytical methods — EPA methods, standard methods published by APHA/AWWA/WEF, ASTM methods, and USGS methods — for measuring pollutants in wastewater samples. The methods are organized into eight tables covering different pollutant categories:

• Table IA — Physical and aggregate chemical parameters (BOD5, COD, TSS, total dissolved solids, pH, turbidity, temperature, conductivity, color, oil and grease)
• Table IB — Inorganic parameters (metals, anions, nutrients: arsenic, cadmium, chromium, copper, lead, mercury, nitrogen species, phosphorus, etc.)
• Table IC — Nonpesticide organic compounds (volatile organics, semi-volatile organics — benzene, toluene, PCBs, phthalates, phenols)
• Table ID — Pesticide and herbicide parameters (organochlorine pesticides, organophosphate pesticides, herbicides including glyphosate)
• Table IE — Whole effluent toxicity (WET) tests — bioassays using indicator organisms (fathead minnow, Ceriodaphnia, green algae) to measure the acute and chronic toxicity of effluent as a whole
• Table IF — Radiological parameters
• Table IG — Microbiological parameters (total coliform, fecal coliform, E. coli, Cryptosporidium, Giardia)
• Table IH — Miscellaneous parameters

Key Provisions

• § 136.1 — Applicability: the prescribed procedures must be used for measurements required by NPDES permits, applications, reports, and other CWA data submissions; exceptions are permitted under §§ 136.4, 136.5, and 136.6 (alternate and equivalent methods)
• § 136.2 — Definitions: the Act means the Clean Water Act of 1977; Director means EPA Regional Administrator or authorized state director; "performance-based measurement system" (PBMS) allows labs to modify approved methods if they can demonstrate equivalent or superior performance for the specific matrix
• § 136.3 — Identification of test procedures: the operative section listing approved methods in Tables IA through IH; each entry identifies the pollutant, the approved method designations (e.g., "EPA Method 200.8" for metals by ICP-MS), and applicable notes on matrix-specific requirements; methods are incorporated by reference; EPA updates the tables through rulemaking as new methods are validated
• § 136.4 — Application for and approval of alternate test procedures for nationwide use: manufacturers, labs, and others can petition EPA to approve a new method for nationwide NPDES use; the application must demonstrate that the proposed method is equivalent to or better than existing approved methods for accuracy, precision, and detection limits; EPA publishes approved alternate methods in the Federal Register
• § 136.5 — Approval of alternate test procedures for limited use: any person may request the Regional Administrator to approve a method for use in a specific region; when the NPDES program is state-administered, the request first goes to the state; approval is granted for the specific matrix and use — not nationally
• § 136.6 — Method modifications and the performance-based measurement system: EPA has adopted a policy allowing laboratories to modify Parts 136 methods to fit specific matrix conditions, provided equivalent performance is demonstrated through quality assurance procedures; this flexibility accommodates the wide variety of industrial wastewater matrices encountered in NPDES compliance monitoring
• § 136.7 — Quality assurance requirements: NPDES laboratories must implement quality systems including method blanks, matrix spikes, duplicates, and laboratory control samples; data quality objectives must be documented; EPA's "Guidance on the Documentation and Evaluation of Trace Metals Data" and similar guidance documents define acceptable QA performance

How It Affects You

Industrial dischargers and municipalities with NPDES permits must ensure that their compliance monitoring laboratory uses only Part 136-approved methods (or approved alternates) for the pollutants regulated in their permit. Using a non-approved method — even if technically accurate — can result in the data being rejected and the facility being cited for a monitoring violation.

Environmental labs doing NPDES compliance work must maintain documentation of method compliance, run required quality controls, and participate in performance evaluation (PE) studies to maintain state certification. Most states require NPDES compliance labs to hold state certification under a program that verifies Part 136 compliance.

Permit writers — when drafting NPDES permit effluent limits, they must specify appropriate monitoring methods and detection limits that align with Part 136 approved methods and the limits being enforced.

Statutory Authority

This rule implements:

• 33 U.S.C. § 1251 — Clean Water Act; data submitted to EPA or states for CWA compliance must use methods that EPA has determined produce reliable, accurate, and comparable results

Recent Rulemakings

• 82 FR 40846 (Aug. 28, 2017) — final rule updating approved methods in Tables IA–IH; added new EPA methods for volatile organics, metals, and microbiological parameters; updated APHA Standard Methods references
• 86 FR 27260 (May 19, 2021) — minor corrections and method updates

Pending Action

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