Is there an Extension Office nearby? Or a university/college that has a limnology department or major? Contact them. They might test the water for free (with the permission of the quarry owner, of course, if it's a privately-owned quarry).
When I dive in smaller, shallow quarries, like the limestone quarry in my neighborhood, I avoid diving near, or stirring up, the bottom. And I avoid even swimming in quarries that don't seem to "see" significant "new" water (from groundwater or rain runoff), if they aren't tested regularly.
rx7diver