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i <br /> The petroleum and vegetable base oils used in formulating hydraulic <br /> fluids are less dense than water They are also relatively insoluble in <br /> water If leaks of such hydraulic fluids reach ground water, they <br /> would be expected to float above the aquifer, and little of these oils <br /> would dissolve in ground water <br /> The base ods are neither water reactive nor explosive They are also <br /> non-flammable, non-corrosive, and non-conductive. <br /> Benzene is the constituent of petroleum products, including hydraulic <br /> fluid, that is of most concern in terms of toxicity and environmental <br /> fate. Benzene is a known carcinogen and is relatively mobile in the <br /> subsurface environment Unlike gasoline, het fuel, and Stoddard <br /> solvent, most hydraulic lubricating oils have a benzene content that is <br /> Rept purposely low to improve the efficiency of the operating HLT <br /> I systems. One environmental benefit of this low benzene content is <br /> F that carcinogenic polynuclear aromatic compounds will not form when <br /> the fluid is heated as part of the HLT operation. <br /> f III Additives are usually important in improving the performance of the <br /> hydraulic fluids and increasing their useful life. An additive can be <br /> defined as a substance that reinforces some desirable property already <br /> possessed to some degree by the oil, or imparts a new and desirable <br /> I property not originally present. Some additives have more than one <br /> function. Additive formulations are usually patented, and their <br /> formulas are protected as proprietary <br /> The following are three of the most widely used additives <br /> (1) zinc dialkyl dithiophosphate <br /> (2) 2, 6-d i-t-butyl-4-m ethyl phenol ("BHT") <br /> J <br /> (3) lead napthenate <br /> I <br /> These additives are usually present at very low levels (parts per <br /> I million) in hydraulic fluid. Due to these small concentrations, neither <br /> toxicity nor environmental fate data on them are included in this <br /> report. <br /> B. ENVIRONMENTAL FATE <br /> There is evidence that vegetable base oils used in hydraulic fluid <br /> SII formulations biodegrade if released into sod or surface water. <br /> Petroleum base oils, which are often composed of hundreds of <br /> jl <br /> t <br /> - 6 - <br />