The simple rule is "keep the water clean."
The Spill Prevention, Control, and Countermeasure (SPCC) Rule is part of the Oil Pollution Prevention regulation - 40 CFR part 112. It does not apply to dry gas, but does apply to liquid condensate. This rule may be applicable to the fracking process. It requires that certain facilities put together and implement a site specific SPCC plan prepared in accordance with good engineering practices.
The plan does not need to be submitted to the EPA for approval, but must be kept onsite in certain circumstances for inspection. The goal is to: contain oil and prevent discharges; proactively control discharges to keep away from navigable waters and adjoining shorelines; and, be ready with countermeasures to clean up a discharge.
The regulations apply to owners and operators of facilities involved in the production process. They do not apply to transportation related facilities (i.e., pipeline in, pipeline out), which are subject to DOT or Coast Guard oversight. However, be careful in setting the boundaries of your facility because if it is overly broad you may unintentionally include transportation facilities and subject them to EPA requirements.
An SPCC plan is required for facilities storing >1,320 gallons above-ground, including all used, non-permanently closed 55+ gallon containers at the facility, or 42,000 gallons buried, and there is a reasonable expectation of discharge to waterway or shoreline.
The fact that you are exploring for gas rather than oil does not matter. This threshold can be met by the oil required to operate shale gas drilling rigs. Diesel storage for turbine units can also bring facilities under the rule. Don't forget generator sets (Gen Sets), frack pumps and transformers.
Examples of oil include petroleum and non-petroleum based oils, crude oil, refined products, animal fats, and vegetable oil. Some examples that may be at your site include lubrication oils, natural gasoline, hydraulic oils, liquid condensate and distillate. Dry gas is not an oil and is not subject to SPCC regulation.
Produced Water Containers are storage of water after initial oil/water separation for future use or disposal. This water is not 100% clean, so it contains residual oil. On overfill, the first thing to come out is probably. . . oil.
Flow back water is that water that flows out of the well after fracking. This water contains the initial additives as well as contaminants from the reservoir. If it contains recoverable amounts of oil, consider an SPCC plan. Regulation of flow back water is coming!
Secondary containment should be used for onshore facilities. It should address the typical failure mode and the most likely quantity of oil that would discharged. Passive secondary containment is always ready for a discharge. Examples of secondary containment measures include dikes, berms, drip pans, retention ponds, and booms.