Q. Some say that Parshas Poroh is miduraisso (Biblical) the same as Parshas Zachor. I’ wondering, where is this mentioned in the Torah?

A. According to the Staipler Gaon zt’l (Bircha Peretz ”“ Chukas, end of Shiurin Shel Torah) it derives fro the posuk (end of Metzora); You should warn from becoming contaminated. The Torah obligates Beis Din to separate the nation from becoming impure.
Meshech Chochmo (Chukas) writes that it derives from the separation required by the Torah to separate the Cohen Gadol before Yom Kippur and the Tamud (beginning of Yuma) equating it to the process of the Parah Aduma.
Artzos Hachaim and Emes LeYaakov (Beshalach 15: 25) mention it is included in the remembrance of the making of the eiggel, (Devarim 9: 7), since the Parah Adumah redeems the sin of the golden calf.
Aruch Hashulchan (685: 7) maintains that it is based on the posuk that Parah Adumah is an eternal law (chukas olam), even when we don’t have access to the ashes, we can still read it.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a.