As defined by 40 CFR Part 112, oil includes all grades of motor oil, hydraulic oil, lube oil, fuel oil, gasoline and diesel, automatic transmission fluid (ATF), waste oil, and transformer mineral oil. The definition of oil also includes non-petroleum oils such as animal or vegetable oils and synthetic oils.
“Petroleum” is defined as crude oil, or any fraction thereof, that is liquid at 60°F at normal atmospheric pressure. This includes petroleum-based substances comprised of a complex blend of hydrocarbons.
Common “petroleum” substances include: motor oil, hydraulic oil, gear oil, automatic transmission fluids (ATF), used oil, machine coolant, water-soluble coolant, gasoline, diesel, jet fuel, residual fuel oils, lubricants, petroleum solvents, and water/oil mixture.
"Petroleum" does not include antifreeze, liquid propane gas (LPG), acetone, and alcohol (i.e., ethanol, methanol, etc.).
Brine is not oil and is not covered by the SPCC regulatios.
Brine has NFPA hazard ratings of : Health 1 Flammability: 0 Reactivity: 0
Methanol has NFPA hazard ratings of : Health 1 Flammability: 3 Reactivity: 0
Sulfuric Acid has NFPA hazard ratings of : Health 3 Flammability: 0 Reactivity: 2
So, it makes sense to have containment for the methanol and sulfuric acid tanks. However, the brine tank does not need containment.
Having said that, you always should do a risk assessment and consider the consequences of a tank failure. If you are located inland and a tank ruptured, what would happen? If you are located in an industrial area, the consequences are minimal. If you were located next to a pristine environment and the ruptured tank will immediately drain to that area, then you have a different risk.
Talk to the manufacturers of salt for further information.