"Oil and grease" means the total oil and grease measured in a wastewater sample by methods set forth in 40 CFR 136 or its successor. Oil and grease is composed of a mixture of all those polar and nonpolar materials which are soluble in hexane at pH 2 or less, and remain after boiling off the solvent. If an environmental sample is composed of nonpolar material (such as petroleum hydrocarbons), and polar materials (such as animal or vegetable oils and fats), EPA method 1664A will directly quantify all the materials as hexane extractable materials (HEM). The silica gel treated hexane extractable material (SGT-HEM) procedure of the same EPA method will measure the nonpolar material (petroleum hydrocarbons) after the polar material is removed. The difference between the two (2) measurements will give the amount of polar material (animal and vegetable) present. (Ord. 68-11, 2011)