I have a friend here in Ohio that kept 20-25 Saanens in milk for her goat creamery 8 months out of the year. She closed her creamery about 9 years ago, so the regs may be more stringent now, but she described her whey disposal system as follows:
She was required to install a leach field system to the creamery for whey disposal only and to tie black water into a separate septic aerated system (for her small business she was allowed to tie the creamery blackwater into her the tank for her residence.).
She was able to install a diverter for the whey so she could feed it to her pigs, but the size of her required leach system was determined by the maximum capacity of her operation as if no whey were diverted.
One comment that she made was that she wished she would have developed the whole facility larger or at least for room for expansion.