Oil and Grease

Questions and Answers

Determination of oil and grease and total petroleum hydrocarbons (TPH) in wastewater

Withdrawal of approved methods employing CFC-113

Methods that employ CFC-113 as the extraction solvent and that are approved for testing of oil and grease in water at 40 CFR part 136 are EPA Method 413.1 and Standard Method 5520B. EPA proposed to withdraw these methods from approved use in the update rule published on April 6, 2004 (69 FR 18165), and EPA withdrew these methods in the final rule published March 12, 2007; 72 FR 11199. The only method approved for testing oil and grease in wastewater, is EPA Method 1664A. Method 1664A uses n-hexane as the extraction solvent.

Recommended method for testing oil and grease and total petroleum hydrocarbons

Method 1664A has been tested extensively and produces results that are generally comparable to results produced by methods that use CFC-113 as the extraction solvent. EPA promulgated Method 1664A for use in EPA's Clean Water Act (CWA) and Resource Conservation and Recovery Act (RCRA) programs on May 14, 1999 (Volume 64 of the Federal Register, p. 26315). EPA has published a document titled, Analytical Method Guidance for EPA Method 1664A Implementation and Use. For the guidance and more detailed information on analytical methods for oil and grease, please refer to EPA's oil and grease web site.

EPA Method 418.1

Although not approved for use at 40 CFR part 136, EPA has published EPA Method 418.1, Petroleum Hydrocarbons, Total Recoverable for determining total petroleum hydrocarbons (TPH) in water (for a copy see Methods for Chemical Analysis of Water and Wastes (EPA 600/4-79-020, Revised March 1983)). This document is available from the National Technical Information Service as document number PB84-128677.

EPA Method 418.1 uses CFC-113 as the extraction solvent. After extraction, the polar components in the sample are removed by adsorption on silica gel, and the remaining components are measured by infra-red spectrometry (I-R). As with EPA Method 413.1 and Standard Method 5520B, EPA 418.1 may be used for determination of TPH in water until EPA Method 413.1 and Standard Method 5520B are withdrawn (see the section above titled "Withdrawal of approved methods employing CFC-113").

Between 2001 and 2004, EPA worked collaboratively with ASTM International on development of a method to replace EPA Method 418.1 for determination of TPH in water. The method was published in 2004 as ASTM International Method D7066-04 Standard Test Method for dimer/trimer of chlorotrifluoroethylene (S-316) Recoverable Oil and Grease and Nonpolar Material by Infrared Determination. The method uses solvent S-316 for extraction, in place of CFC-113 used in EPA Method 418.1. Although not approved at 40 CFR Part 136, the method is available for instances in which Method 1664A may not be suitable; e.g., instances in which it is desirable to measure n-hexane or other components with a boiling range near or below the boiling point of n-hexane. EPA may propose ASTM Method D7066-04 for inclusion at 40 CFR Part 136 at some point in the future.

Approval of other solvents used (besides n-hexane and CFC-113) for testing water for oil and grease to meet EPA requirements

Any solvent that may be proposed as an alternative to CFC-113 or n-hexane would have to be subjected to extensive study to determine whether it produces results equivalent to results obtained with the approved methods. The use of an alternate solvent is governed by the alternate test procedure regulations at 40 CFR 136.4 and 136.5.

Source for n-hexane for use with EPA Method 1664A

Method 1664A requires use of n-hexane as the extraction solvent. The specification for the n-hexane to be used is "85% minimum purity, 99.0% min. saturated C6 isomers, residue less than 1 mg/L." In 2004, EPA received notice from Conoco Phillips that, effective November 1, 2004; Conoco Phillips would discontinue n-hexane production at its Borger, Texas, facility. This facility was the main supplier of n-hexane that met the Method 1664A specification. Unless another supplier is found, the alternative is to use a higher grade, e.g. 95% minimum purity. If you learn of another supplier for 85%, please send an e-mail to Lemuel Walker (walker.lemuel@epa.gov), so that we can update the list.

Use of Repetitive Amounts of Silica Gel with EPA Method 1664A

Use of repetitive treatments with silica gel is allowed without prior EPA approval under the equivalency provision in Section 9.1.2 of EPA Method 1664A. The provision contains rigorous requirements for a demonstration of equivalency, including tests of initial precision and recovery, blanks, matrix spikes and duplicates (MS/MSD), and other data, with and without the repetitive treatment, as required by EPA Method 1664A. For acceptable repetitive treatment with silica gel, one should test for removal of the polar fraction, particularly if the silica gel is highly activated, as required in EPA Method 1664A. One could test for this removal by demonstrating removal of the stearic acid component of the PAR (Precision and Recovery) standard in the initial precision and recovery test and the matrix spikes and duplicates (MS/MSD) test. If this removal is demonstrated, use of repetitive treatment of extracts of environmental samples with silica gel for determination of total petroleum hydrocarbons (TPH; also "Non-polar Material" (NPM) and "Silica Gel Treated Hexane Extractable Material" (SGT-HEM)) should be allowed because this modification meets the spirit and letter of the modification provisions in EPA Method 1664A.

Where can I get additional information, including copies of Method 1664A?

You may view the full text of EPA Method 1664A or download it from EPA's oil and grease web site.
You may retrieve additional guidance on the application of EPA Method 1664A (PDF) (238 K, 44 pp.)