My guess is that they'd have to build a grow facility within a building, and then bring in things like soil like a commercial garden company would. They need a year-round supply, so growing it outside isn't an option, and for a large commercial operation, it's not feasible to use inferior soil like is in that site.

The worst they might get is using water from the site, but if there's concern about quality they probably will install commercial filtration, because they won't want it to jeopardize their final product.