I recommend you employ a reputable design firm that has designed and built tankfarm facilities...they'll know all the ins and outs of the necessary local / state / environmental permitting, geotechnical investigation, cathodic protection, ASCE, ASME B31.3 piping codes and such, API, NFPA, EPA SPCC (containment), NEC electrical area classification and OSHA regulations to metion a few. For API, be sure and review API 2610 (design construciton and operation of terminals and tank facilities) as well as the good old API 650. NFPA 30 will give guidance on tank spacing, drainage, containment, intermediate diking and such.