Are these clauses independent?

I work as an editor for a technical firm, and I'm struggling with figuring out if this sentence and others like it need a comma:

"Very limited grading is necessary to achieve the proposed grades because the site is essentially level and the proposed finished floor elevations are within 1 to 2 feet of the existing surface and surrounding finished grades."

I want to use a comma after 'level' because it's a longer sentence, and that does divide it into two complete sentences/clauses. However, are the clauses truly independent if both of them ('the site is essentially level' and 'the proposed elevations are') relate back to 'very limited grading is necessary because'? In other words, is independence solely a syntax question, or can it also involve meaning?

Sidenote: As an editor here, I'm generally not at liberty to rewrite unless something is technically wrong.