Consult NFPA. Containment may take several forms, earthen dykes, concrete walls, etc. The key thing is to provide enough volume outside the tank to contain a leak of that tank plus some. That "some" may be 10%; it may be "freeboard", or wave action; some amount of rainfall; some amount of firewater/foam spray; or, some combination of above.
Normally, berm heights are limited to 10' above surrounding grade. If 2:1 or 3:1 side slopes on earthen berms take up too much room, consider putting the tank bases on a level at least a few feet below grade or consider vertical concrete walls. Then you have to have ramps up to and over for vehicular traffic, and stairs/steps (in several areas) for personnel egress.
I have lots of more info. But, selection and design just requires rational objective thought. For a fee I can advise further.
