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Oil and Grease Measurements - Frequent Questions
Determination of oil and grease and total petroleum hydrocarbons (TPH) in wastewater
- Withdrawal of approved methods employing CFC-113
- Recommended method for testing oil and grease and total petroleum hydrocarbons
- EPA Method 418.1
- Source for n-hexane for use with EPA Method 1664A
- Use of repetitive amounts of silica gel with EPA Method 1664A
- Reports on replacement of Freon with hexane as the extraction solvent
Methods that employ CFC-113 as the extraction solvent and that were approved for testing of oil and grease in water at 40 CFR Part 136 are EPA Method 413.1 and Standard Methods No. 5520B. EPA withdrew these methods in the final rule published March 12, 2007 (72 FR 11199) (PDF).(50 pp, 469 K, About PDF) The only method approved for testing oil and grease in wastewater is EPA Method 1664A. Method 1664A uses n-hexane as the extraction solvent.
Total petroleum hydrocarbons (TPH) are not Part 136 pollutants. However, there may be samples for which Method 1664 may not be suitable; e.g., when it is desirable to measure n-hexane or other components with a boiling range near or below the boiling point of n-hexane. In those situations, analysts in the past may have used EPA Method 418.1 (“Petroleum Hydrocarbons, Total Recoverable”) for determining TPH in water. However, this method uses CFC-113. If you wish to determine TPH, we recommend 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.” S-316 is a chlorofluorocarbon alternative to CFC 113. Neither Method 418.1 nor D7066 are Part 136-approved methods.
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 (email@example.com), so that we can update the list.
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 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.
Preliminary Report of EPA Efforts to Replace Freon for the Determination of Oil and Grease (also known as Phase I) (1993)